GOVERNMENT OF ROMANIA
MINISTRY OF REGIONAL
DEVELOPMENT AND TOURISM
1. ------IND- 2012 0584 RO- EN- ------ 20121112 --- --- PROJET
ORDER
No ………….of ………...2012
for the approval of technical regulation
"Normative document regarding the design, construction and
operation of water supply and sewage systems in localities. Code NP 133 – 2011”
In accordance with the provisions of Article 10 and Article 38 paragraph (2) of Law No
10/1995 regarding quality in constructions, with its subsequent modifications, the provisions of
Article 2 paragraphs (3) and (4) of the Rules regarding the types of technical regulations and costs
for the regulatory activity in the field of constructions, town planning, landscaping and habitat,
approved by Government Decision No 203/2003, with its subsequent modifications and
supplementation, and the provisions of Government Decision No 1016/2004 regarding measures for
organising and carrying out the exchange of information in the field of technical standards and
regulations, as well as the rules regarding information society services between Romania and the EU
Member States, as well as the European Commission, with its subsequent modifications,
on the grounds of Article 5 (II)(e) and Article 13 (6) of Government Decision No 1631/2009
concerning the organisation and operation of the Ministry of Regional Development and Tourism,
with its subsequent modifications and supplementation,
the Ministry of Regional Development and Tourism hereby issues the following
ORDER:
Article 1 – The technical regulation "Normative document regarding the design, construction and
operation of water supply and sewage systems in localities. Code NP 133 – 2011” is hereby
approved, as follows:
a) "Part I: Water supply systems in localities. Code NP 133/1-2011”, stipulated in Annex No 1;
b) Part II: Sewage systems in localities. Code NP 133/2 - 2011”, stipulated in Annex No 2.
Article 2 – Annexes No 1 and 2 are an integrated part of the present order.
Article 3 - This order1) shall be published in the Official Journal of Romania, Part I and shall
come into force 30 days after its date of publication.
Article 4 – (1) The following technical regulations shall be repealed on the date this order comes
into force:
a) "Normative document for the design of urban wastewater treatment structures and
installations-Part II: Biological step. Code NP 088-2003”, approved by Order No 639/23.10.2003
of the Ministry of Transport, Constructions and Tourism, published in the Official Journal Part I
No 773/04.11.2003 and the Constructions Journal No 4-5/2004, edited by the National Institute for
Research and Development in Constructions and the Economics of Constructions, Bucharest;
b)"Normative document for the design of urban wastewater treatment structures and
installations-Part III: Water treatment plants of low capacity (5<Q, 50 l/s) and very low capacity
(Q, 5 l/s). Code NP 089-2003", approved by Order No 639/23.10.2003 of the Ministry of Transport,
Constructions and Tourism, published in the Official Journal Part I No 773/04.11.2003 and the
Constructions Journal No 4-5/2004, edited by the National Institute for Research and Development
in Constructions and the Economics of Constructions- Bucharest;;
c) "Normative document for the design of urban wastewater treatment structures and
installations - Part IV: advanced wastewater treatment step. Code NP 107-2004”, approved by
Order No 163/15.02.2005 of the Ministry of Transport, Constructions and Tourism, published in the
Official Journal Part I No 337 bis/21.04.2005 and the Constructions Journal No 2/2005, edited by the
National Institute for Research and Development in Constructions and the Economics of
Constructions, Bucharest;
(2) The following technical regulations shall cease to be applicable on the date this order comes
into force:
a) "Technical specifications for the design and construction of structures and installations
related to free-level sand filters to provide operational safety measures. Code ST 021-1997",
approved by Order No23/N/22.05.1997 of the Ministry of Public Works and Territorial
Development, published in the Constructions Journal No 13/2001, edited by the National Institute
for Research and Development in Constructions and the Economics of Constructions- Bucharest, as
well as the Information Journal edited by PROED SA;
b) "Normative document for the design of water harvesting structures. Code NP 028-1998",
approved by Order No78/N/13.10.1998 of the Ministry of Public Works and Territorial
Development, published in the Constructions Journal No 6/2000, edited by the National Institute for
Research and Development in Constructions and the Economics of Constructions- Bucharest;
c) "Normative document for the design of urban wastewater treatment structures and
installations-Part I: Mechanical step. Code NP 032-1999”, approved by Order No 60/N/25.08.1999
of the Ministry of Public Works and Territorial Development, published in the Constructions Journal
No 4-5/2004, edited by the National Institute for Research and Development in Constructions and
the Economics of Constructions- Bucharest.
d) "Normative document for the design and construction of delivery pipes, as well as water
supply and sewage systems in localities. Code I 22-1999”, approved by Order No23/N/07.04.1999
of the Ministry of Public Works and Territorial Development, with its subsequent modifications and
supplementation, published in the Constructions Journal No 13/1999, edited by the National Institute
for Research and Development in Constructions and the Economics of Constructions- Bucharest.
The technical regulation approved by the present order was adopted in accordance with the
notification procedure No RO/......... of ......................, stipulated by Directive 98/34/EC of the European
Parliament and of the Council of 22 June 1998, laying down a procedure for the provision of information in
the field of technical standards and regulations, published in the Official Journal of the European
Communities L 204 of 21 July 1998, amended by Directive 98/48/EC of the European Parliament and of the
Council of 20 July 1998, published in the Official Journal of the European Communities L 217 of 5 August
1998.
MINISTER
Eduard HELLVIG
The Order and its annex shall also be published in the Constructions Journal edited by the “URBANINCERC” National Institute for Research and Development in the field of Constructions, Town Planning, and
Sustainable Territorial Development, which is coordinated by the Ministry of Regional Development and Tourism.
1)
Annex No 2-A
To MDRT Order No ................../ 2012
NORMATIVE DOCUMENT REGARDING THE DESIGN,
CONSTRUCTION AND OPERATION OF WATER SUPPLY
AND SEWAGE SYSTEMS IN LOCALITIES.
Code NP 133 – 2011
Part II: SEWAGE SYSTEMS IN LOCALITIES. Code NP 133/2 – 2011
A – GENERAL PROVISIONS FOR THE DESIGN OF SEWERAGE
NETWORKS
CONTENTS
01. General data
01.1 Aim of the normative document.
01.2 Users
01.3 Field of application
01.4 Components of the sewage system and their role
01.5 Criteria for choosing the sewage system diagram
01.6 Sewage systems and procedures
PART I : DESIGN OF SEWERAGE NETWORKS
1.Objectives and functions of the sewerage network
1.1 Structure of the sewerage network
1.2 Water collected into sewerage networks
1.3 Integration within the rural/urban environment
1.4 Structure of sewerage networks
1.5 Classification of sewerage networks
1.5.1 Ensuring the water flow into the storage basins
1.5.2 Quality of collected water
1.5.3 Network shape
2. Design of the sewerage network
2.1 Separate wastewater network
2.1.1 Sizing flow rates
2.1.2 Elements for hydraulic sizing
2.1.2.1 Degree of filling
2.1.2.2 Minimum/maximum velocities
2.1.2.3 Minimum diameters
2.1.2.4 Minimum and maximum pipe-laying depth
2.1.2.5 Longitudinal slope of the collector
2.1.3 Hydraulic sizing
2.1.3.1 Determination of the design flow rates for each pipe section
2.1.3.2 Choosing the diameters and hydraulic parameters of the design pipe section
2.2 Separate stormwater network
2.2.1 Sizing flow rates
2.2.2 Choosing the diameters and hydraulic parameters
2.2.2.1 Calculation of the flow rates for each pipe section
2.2.2.2 Choosing the diameters and hydraulic parameters of a pipe section
2.2.2.3 Retention basins
2.3 Unitary sewerage network
2.3.1 Determination of the sizing flow rates
2.3.2 Choosing the diameters and hydraulic parameters of a pipe section
3. Siting the sewerage network
3.1 Wastewater network
4. Components of the sewerage network
4.1 Pipes used to construct the pipe sections
4.1.1 Cross-sectional shape
4.1.2 Pipe materials
4.2 Related structures built within the sewerage network
4.2.1 Pipe fittings
4.2.2 Discharge outlets
4.2.3 Manholes
4.2.3.1 Pass-through manholes
4.2.3.2 Junction manholes
4.2.4 Spillways
4.2.4.1 Structure of spillways
4.2.5 Stormwater retention basins
4.2.6 Sewer siphons
4.2.7 Pumping stations
4.2.7.1 Siting of pumping stations
4.2.7.2 Components of pumping stations
5. Vacuum sewerage networks
5.1 Components
5.2 Design requirements
5.2.1 Gravity pipe fittings for collector manholes
5.2.2 Water main connection manholes
5.2.3 Vacuum network
5.2.3.1 Flow rates, diameters, lengths
5.2.3.2 Layout, lifts, slopes
5.3 Vacuum station
5.3.1 Vacuum recipients.
5.3.2 Vacuum pumps
5.3.3 Time required to produce the vacuum
5.3.4 Daily operating time of the vacuum pumps
5.4 Requirements for choosing the design of the vacuum sewerage networks
5.5 Pressure sewerage networks
5.5.1 Components
5.5.2 Design requirements
5.5.3 Recipient chamber
5.5.4 Pressure generating equipment
5.5.5 Pipeline network
5.5.6 Pipes and pipe couplings
5.5.7 Stoppers
5.5.8 Requirements for choosing the design of the pressure sewerage networks
6. Discharge outlets
ANNEXES
Annex 1–IDF curves for zone 8
Annex 2–Diagram for the calculation of plastic and composite pipes
Annex 3–Diagram for the calculation of cast iron, concrete and steel pipes
Annex 4–Curves for the degree of filling
Annex 5–Plotting the IDF curves
Annex 6 - Legislation
01. General data
Definition: The sewage system is an assembly of engineering structures which collect
wastewater, carry it to the water treatment plant where it is cleaned to a degree of purity
established depending on the environmental conditions, and then discharge it into natural
drainage basins which can be: rivers, lakes, seas, permeable soils with suitable facilities or
depressions.
01.1. Scope of the normative document
(1)The scope of this normative document is to design the assembly of engineering
structures defined in § 01., in accordance with the applicable provisions stipulated by the
legislation in force with regard to quality in constructions, in order to comply with the
fundamental requirements applicable to structures throughout the entire lifespan of the respective
structures.
(2) The normative document does not contain provisions for the stability and strength
calculation of the structures, installations, mechanical and automation equipment, as well as
sanitary, thermal and ventilation installations.
(3) The design stage shall focus on adopting solutions which will guarantee the quality of
the works carried out in order to build the sewage system, including by using materials of a
suitable quality.
(4) The normative document fully complies with the provisions of Directive 91/271/EEC
(NTPA 001 and NTPA 002) concerning urban wastewater treatment and supplements the
national legal framework for the implementation of this European Directive in Romania.
01.2. Users
This normative document is to be used by all parties involved in the investment process:
planners, planning assessors, technical experts, contractors, technical managers, investors,
owners, administrators and users, personnel responsible for operating the facilities, operators of
the public water supply and sewage services, as well as local public administration authorities
and inspection bodies.
01.3. Field of application
(1) This normative document contains provisions for the technological design of the
assembly of engineering structures and installations to be used for sewage and the purification of
wastewater produced by urban and/or rural localities, and provides the specialists working in the
field with the knowledge, as well as the theoretical, technological and structural elements they
need to design and construct these installations.
(2) Part II of this normative document includes design requirements for the assembly of
engineering structures and installations to be used for sewage and the purification of wastewater.
(3) Given the low profile, and in many cases the absence, of this industry, the nature of
the wastewater produced by urban and rural agglomerations is household or urban at most.
(4) Household and urban wastewater can be defined as follows:
a) Household wastewater is the waste water resulting from the use of drinking water for
household purposes, in social and public buildings, local industrial facilities as well as watering
of circulation spaces and green spaces;
b) Urban wastewater is the mixture of household wastewater, technological wastewater
produced by the sewage and water supply system and industrial wastewater, as well as
wastewater resulting from agricultural and animal husbandry activities, which has or has not
been pre-treated so that its physical, chemical, biological and bacteriological properties comply
with the values specified in NTPA 002;
(4) In very small, small and medium-size water treatment plants where the biological
treatment is carried out in activated sludge basins, the primary settling tank may be missing, but
at least one wastewater grinding step must be included.
(5) The biological treatment shall take place in specially designed installations and
consist of a set of biochemical phenomena carried out using microorganisms that mineralise the
carbon-based organic compounds present in the wastewater in colloidal or dissolved form,
turning them into living cellular material, or biomass, which is then retained in the form of
biological sludge in the secondary settling tanks.
(6) An advanced biological treatment shall continue the treatment processes carried out
during the mechanical step, contributing to the retention of the colloidal and dissolved organic
compounds present in the wastewater and retaining the phosphorus and nitrogen-based
compounds or substances.
(7) The present normative document covers the design of structures and installations
intended to be used for advanced water treatment and processing the sludge retained in
wastewater treatment plants.
(9) The advanced treatment can be carried out through processes incorporated in the
biological treatment stage, which are designed to eliminate carbon compounds and/or can be
carried out as part of independent processes.
(10) The diagram of the water treatment plant shall be chosen based on the values of the
required degree of purification and the efficiency in retaining the main indicators in accordance
with Chapters 5 § 1 and § 2 of this normative document.
(11) The mechanical and biological treatment of urban wastewater must provide effluents
of a suitable quality which meet the requirements stipulated by the water protection standards
approved by Government Decision No 188/2002, with its subsequent modifications and
supplementation, which transpose, in full, the provisions of Directive No 97/271/EEC (NTPA
001, NTPA 002) concerning urban wastewater treatment.
(12) The monobloc or compact structures, installations and equipment used for
wastewater treatment, which are tendered by specialist suppliers, shall have to hold the required
technical approval issued by the competent authorities.
(13) For the retained substances, including primary and biological sludge, the
installations located along the sludge line shall ensure that the finished products obtained are
hygienic, recoverable and easy to integrate in the natural environment.
(14) The importance class and category of the water treatment structures and installations
shall be determined in accordance with the provisions stipulated in Government Decision No
766/1997 for the approval of regulations regarding quality in constructions, with its subsequent
modifications and supplementation, as well as the applicable normative documents in force with
regard to quality in constructions.
01.4 Components of the sewage system and their role
(1) The following groups of structures are necessary to build a sewage system for a
human agglomeration or industrial facility:
a) sanitary appliances and the interior network;
b) the exterior network;
c) the water treatment plant;
d) discharge facilities.
a) Sanitary appliances
Residential, socio-cultural or administrative buildings are equipped with sanitary
appliances such as sinks, bath tubs and other utilities.
(2) The water is guided from the reservoirs to indoor systems via pipes, and shall be
taken over into the network installed inside the premises, which are called interior networks.
(3) The interior network shall be connected to the exterior network via a connecting
channel and a manhole, which is called a water main connection manhole and shall be used for
inspection and interventions.
b) The exterior network
(1) The exterior network shall consist of underground and above-ground channels,
pumping stations and other auxiliary structures located between the collection points and the
water treatment plant or the discharge outlets to the emissary.
(2) Pumping stations shall be built on the lower points of the region being provided with
a sewage system, when the terrain configuration prevents the gravity flow of sewage water or
when the flow velocity is insufficient.
(3) The auxiliary facilities that need to be built within the network are: discharge outlets
which collect stormwater from the road, manholes, connecting chambers, slope-interrupting
manholes, flushing manholes, spillways, retention basins, desilters, depression underpasses and
communication ways.
c) The water treatment plant
The water treatment plant consists of all structures and installations used to correct the
quality parameters of the influent wastewater so that the characteristics of the purified water
comply with the applicable regulations, depending on the characteristics of the recipient.
d) Discharge structures
Discharge structures must ensure that the water is discharged to recipients under
conditions that are safe both for the sewage system and the recipient.
Figure 1.1 shows the diagram of a sewage system.
1
1
11
1
2
2
2
3
2
8
6
5
9 10
7
4
2
Figure 1.1. Sewage system diagram.
1- service (secondary) channels
2-secondary collectors
3-main collectors
4-inverted siphon
5-junction chamber
6-spillway chamber
7-spillway channel
8-water treatment plant
9-discharge manifold
10-discharge outlet
11-recovery systems
sludge resulting from the water
treatment plant
01.5 Criteria for choosing the sewage system diagram
(1) The sewage system diagram shall be chosen based on the data about the site
configuration and the functional elements of the user. The documentation that is absolutely
necessary in order to draw up the sewage system diagram includes:
a) the General Urban Plan (PUG) and Regional Urban Plan (PUZ) for the urban/rural
locality, highlighting the existing situation and providing a development outlook for
at least 30 years;
b) Topographic, geotechnical, hydro-geological and hydrological surveys of the ground,
surface water and underground water in the area;
c) Studies on variants. Any sewage system must be studied in multiple variants, from
which the planner shall choose to propose the version which:
 ensures that the wastewater is collected in sanitary conditions, without putting
public health at risk;
 has minimum effects on the environment;
 incurs minimum unitary and energy costs, regardless of any variable factors that
may occur over time.
d) Technical and economic criteria for choosing the system:
 unitary/separate collection of water as per wastewater categories; all designs shall
include versions with at least 2 networks (wastewater and stormwater) and 1
network (unitary system) for the entire site or its sections;
 wastewater transportation criteria; gravity flow, pressure or vacuum network
systems shall be analysed;
 elements required by the position of the recipient, recovery of the retained
substances and sludge.
(2) The technical and economic calculations for determining the optimum variation must
include:
a) The total volume of investment;
b) The investment schedule staggered over a period of at least 10 years;
c) The operational costs and facilities for each version;
d) The cost of the treated water (collection, treatment, discharge of the retained
substances) in correlation with the degree of supportability of the system users.
(3) The sewage system diagram must fit at all times with the development of the
populated centre, so that the sewage utility system can meet the needs of the users and the
requirements of technological progress.
01.6 Sewage systems and procedures
(1) A sewage system shall include:
a) the sewerage network;
b) the water treatment plant;
c) purified water discharge structures;
d) discharge systems for the substances retained in the water treatment plant;
(2) The wastewater shall be collected and discharged via one of the following processes:
a) Unitary process;
b) Separation (divider) process;
c) Mixed process.
(3) In the unitary process all sewage water (household, industrial, public, meteoric,
surface and drainage) is collected and transported through the same sewerage network.
The unitary process poses the advantage that it only requires one drainage network and
has lower operating costs, but also has the disadvantage that it incurs high initial investment
costs.
(4) In the separation process the wastewater (household, pre-treated industrial and public
water) and stormwater is collected and transported through a minimum of 2 different networks.
Household water shall flow through enclosed channels. Pre-treated industrial wastewater
shall flow through enclosed networks. Stormwater can be discharged above ground, via street
gutters or open channels (ditches), or via a network of enclosed channels.
(5) A sewerage network that uses the separate process shall be developed by:
a) applying the principle of retaining stormwater at the place where it falls and building
infiltration-storage basins with/without the option of reusing this water;
b) Reducing impermeable surfaces in urban developments;
c) Increasing the maintenance and cleaning requirements for developed urban areas and
increasing the specific surface areas (m2/inhabitant) covered by vegetation.
PART I: DESIGN OF SEWERAGE NETWORKS
1. Objectives and functions of the sewerage network
(1) The sewerage network consists of the technological facilities provided within a
sewage system, which have the role of collecting and discharging wastewater and/or stormwater
outside of the human agglomeration in conditions that are safe for the health of users and the
environment.
(2) The sewerage network ensures the discharge of wastewater produced by domestic
activities, as well as pre-treated industrial wastewater, wastewater produced by public utilities
and rainwater which falls over the area served by the network.
(3) The sewerage network discharges wastewater from a delimited area called a drainage
basin. The drainage basin can differ for each category of wastewater.
1.1 Structure of the sewerage network
The sewerage network is made up of the following:
a) Collector pipes which transport the collected water;
b) Auxiliary structures which ensure the good operation of the network: pipe fittings,
manholes, discharge outlets, spillways, pumping stations, retention basins, water
quality control systems and systems for measuring the volume of water being
transported.
1.2 The water collected by the sewerage network may come from:
a) Indoor installations fitted in dwellings and household wastewater, collected either
directly or via water mains connection manholes;
b) Indoor installations fitted inside public buildings (schools, hospitals, facilities for
public activities, sports grounds);
c) Household wastewater from toilet units in industrial facilities;
d) Industrial wastewater collected either directly or from pre-treatment plants when the
quality requirements are different to the requirements for the water discharged into
the public network;
e) Rainwater entering the sewage system through drain holes (rainwater, water resulting
from the melting of snow and ice);
f) Underground water which infiltrates through damaged areas of the collectors or
auxiliary structures.
(1) Except for water which infiltrates into the sewage system, all other categories of
water are of a good enough quality to be accepted in the public sewerage network. The quality
requirement is specified in NTPA 002.
(2) The same principle: compliance with the provisions stipulated in NTPA 002, shall
also apply to rural sewerage networks used to collect wastewater produced by agricultural and
zootechnical farms, product processing facilities and animal farms.
(3) The collection of any category of wastewater quality into the public network shall be
permitted if the following requirements are met:
a) Ensuring that the public network is operated without causing any damage, affecting
material, posing a threat or limiting its safe operation;
b) Limiting any negative effects on the biological processes carried out in the water
treatment plant;
c) Knowing the volumes of wastewater and quantities of pollutants (suspended matter,
organic substances – BOD5, N and P) at all times.
1.3 Integration within the rural/urban environment
The sewerage network shall be included:
a) In provisions stipulated in the General Urban Plan (PUG) and Regional Urban Plan
(PUZ) drawn up for the areas being developed;
b) In the Management Plan drawn up for the hydrographic basin of the respective human
agglomeration;
c) In the Master Plan for the sewage and water supply systems of the site and the
hydrographic basin.
1.4 Structure of the sewerage network
The configuration of the network shall take into consideration:
a) The current and predicted street network (for at least 25 years), in accordance with
PUG;
b) The topographic conditions on site, which enable gravity flow;
c) The position of the water treatment plant and the position of the collector;
d) Ensuring that the water is discharged along the shortest route;
e) Tackling the critical zones: depressions, counter-slopes, underpasses in a precise way.
f) A staggered development plan that matches the development of the human
agglomeration served by the network;
g) The possibility of installing utility tunnels in areas with a high density of networks,
central areas, areas with intense traffic and areas where it is difficult to lay down
pipes.
h) A reasonable solution to installing the network in floodable areas; the design of the
network shall enable it to continue pumping wastewater (or purified water) in the
event of a flood.
1.5 Classification of sewerage networks
Sewerage networks can be classified as follows:
a) According to the way in which the water flows;
b) According to the quality of the water collected;
c) According to the shape of the network.
1.5.1 Ensuring the water flow through collectors
a) A gravity network which ensures a free-level water flow;
b) The vacuum system shall be used to transport household water; the pressure of the
water flow shall systematically be negative (p ≈ 0.4 – 0.6 at.);
c) Pressure network, in which the water flows under a pressure created by pumping.
1.5.2 Quality of collected water
a) Network with a unitary process; all water collected from the surface of the
agglomeration is discharged via a single network;
b) Network with a separation/division process in which water with similar
characteristics is discharged via the same network; agglomerations can be provided
with two networks (a urban/rural wastewater sewerage network and a stormwater
discharge network);
c) Network with a mixed process, both unitary and separative, in different areas of the
agglomeration;
1.5.3 Shape of the network
(1) The sewerage network is a branching network; if, after taking into account the
operating/repair conditions, it can be reasonably demonstrated that an annular network is the
right choice, this type of system can be implemented; this can be beneficial in certain situations
which require remedy operations to be carried out, or for the discharge of stormwater
(agglomerations where rainwater does not fall on all areas at the same time).
(2) The configuration of the network shall be chosen based on a supporting technicoeconomic calculation, using criteria relating to investment costs and operating costs. The damage
that would be incurred in the event of a malfunction must be taken into account.
(3) The method for ensuring the risk-free operation of the network shall be determined in
accordance with the applicable standards and by means of a decision taken by the local authority.
It is also sensible to estimate the consequences of a potential increase in the level of operational
safety in the future, due to the construction of important underground facilities and the
possibility of building flyovers at some junctions or introducing special means of transport.
2. Design of the sewerage network
2.1 Separate wastewater network
2.1.1 Sizing flow rates
(1) The sizing stage shall take into consideration the maximum hourly wastewater
discharge, for different types of consumption (household, public, business, etc.):
𝑄𝑢𝑧,𝑜𝑟,𝑚𝑎𝑥 = 𝛼 ∙ ∑ 𝑁𝑖 ∙ 𝑞𝑖 ∙ 𝑘𝑧𝑖,𝑖 ∙ 𝑘𝑜𝑟,𝑖 ∙ 10−3 ∙ 24−1 (m3 /h)
where:
(2.1)
α – coefficient of reduction or increase of the flow rate; the reduction shall be given by
water used for sprinkling and washing; the increase shall be induced by economic
activities that use other sources of water; the values can frequently be between 0.9 –
1.05;
Ni– number of users as per consumption category;
qi – the specific demand for drinking water (l/person/day), in accordance with SR 1343–
1:2006;
kzi,i – coefficient of variation for the daily water consumption, in accordance with the
values stipulated in SR 1343 – 1:2006;
kor,i – coefficient of variation for the hourly water consumption, in accordance with SR
1343–1:2006;
10-3, 24-1 – coefficients of transformation;
(2) The compliant flow rate (2.1) is a value used for hydraulic sizing of the sewerage
network and shall not be used for the balance calculation of the daily, monthly or annual
volumes of wastewater being discharged.
The sum ∑ 𝑁𝑖 ∙ 𝑞𝑖 ∙ 𝑘𝑧𝑖,𝑖 ∙ 𝑘𝑜𝑟,𝑖 in relationship (2.1) refers to:
 household wastewater (no. of inhabitants);
 public wastewater (schools, hospitals, public services, etc.);
 household-type wastewater produced by industrial facilities.
(3) Wastewater produced by economic operators - these shall be considered to be pretreated (in accordance with NTPA 002) and shall be estimated by the user and notified by
means of written protocols.
(4)Infiltrated water- shall be calculated with the expression:
𝑄𝐼𝑁𝐹 = 𝑞𝐼𝑁𝐹 ∙ 𝐿 ∙ 𝐷𝑁 ∙ 10−3 (m3 /zi )
(2.2)
where:
qINF – specific volume of infiltrated water, in dm3/m ∙ zi, with values of 25 – 50
dm3/linear metre and diameter metre of the collector/day;
L – length of the collector (m);
DN – diameter of the collector (m);
For a network laid above the groundwater table: qINF = 25 dm3/m/day for DN=1m;
For a network laid below the groundwater table (>1.0m) qINF = 50 dm3/m/day, for
DN=1m;
(4) When the sewerage network is subject to technological updating, special studies shall
be carried out to determine the volumes of infiltrated water.
2.1.2 Elements for hydraulic sizing
2.1.2.1 Degree of filling defined as the ratio between the height of the water
during its maximum discharge through the section and the structural height
of the channel (DN,H):
𝑎=
where:
ℎ
ℎ
;𝑎=
;
𝐷𝑁
𝐻
(2.3)
a – degree of filling;
DN – nominal diameter (m);
H – interior height of the channel, (mm);
h – height of the water inside the channel, (mm);
Table 2.1. Degree of filling as a function of the DN or Hchannel.
Item No
1
2
3
4
DN or H (mm)
< 300
350 – 450
500 – 900
>900
a – degree of filling
≤ 0.6
≤ 0.7
≤ 0.75
≤ 0.8
2.1.2.2 Minimum/maximum velocities
a) The self-cleansing velocity ≥ 0.7 m/s to prevent the settling of deposits in the sewage
collectors;
b) Maximum velocity: ≤ 8 m/s for collectors made of special or metallic pipes;
≤ 5 m/s for other materials;
2.1.2.3 Minimum diameters
(1) The minimum diameter of sewage collectors shall be considered to be:
a) Dn 250 mm for separate (divider) wastewater networks;
b) Dn 300 mm for (separate) stormwater networks and unitary networks.
(2) New networks can be adopted, with DN=200 mm, in the following situations:
a) (separate) wastewater networks, street drains with Lmax ≤ 500 m, no. of pipe fittings
≤ 100;
b) degree of filling a ≤ 0.5;
c) the difference between the diameter of the sewage collector and the diameter of the
pipe fitting must be at least 50 mm;
2.1.2.4 Minimum and maximum pipe-laying depths
(1) The minimum depth above the exterior face of the upper arch of the channel, shall be
equal to the highest of the following values:
a) hmin= 0.80 m;
b) hmin≥ hfreezing to avoid stressing the pipe material during freeze-thaw cycles (in
accordance with STAS 6054-77);
c) special calculations shall be carried out for stresses induced by traffic;
The minimum depth shall also be determined by the water-collection capacity of the pipe
fittings installed at the user end; for buildings without a basement, the depth must be equal to 1.0
m (at the height of the foundation raft), whilst the minimum depth for buildings with a basement
must be – 2.0 m; in structures with several basements, the total quantity of wastewater present in
the basement shall be pumped into the sewerage network via flood-control systems, to prevent
flooding of the basements when the network is pressurised.
(2) Maximum depth; for diameters with DN≤400 mm, the maximum depth shall be
limited to 6.0 m (the difference between the height of the foundation raft and the ground
elevation); this limit is required to enable the possibility of carrying out interventions by
excavation. At depths of more than 2 m, a manhole shall be installed on the collector of the pipe
fittings in buildings.
2.1.2.5Longitudinal slope of the collector
(1) Gravity flow network:
a) the slope shall be equal to the slope of the road, if the direction of the water flow is
the same as the downhill direction of the street, but ≥ 1: DN;
b) the minimum structural slope shall be 1‰ and ≥ 1: DN;
c) the minimum slope required in order to reach the self-cleansing velocity, in
accordance with SR EN752:2008, shall be ≥ 1: DN;
d) the maximum slope that would enable the maximum water velocity to be achieved
through the collector shall be determined for each nominal diameter and type of
material;
(2) Vacuum network:
a) the structural values of the slope shall be determined depending on the position of the
pressurised collector; negative or positive;
b) the piping slope between two consecutive lifts in vacuum networks shall be equal to
0.002;
c) the sewage pipes shall be made of HDPE - high-density polyethylene, PE polyethylene with glass and shall have a diameter between 90 - 200 mm, with
waterproof fitting.
2.1.3 Hydraulic sizing
2.1.3.1 Determination of the design flow rates for each pipe section
(1) A collector pipe section shall be considered to be the length between two junctions or
a pipe section with a maximum length of 250 m in a straight line.
(2) The design flow rate is the flow rate in the downstream section of the pipe section whose
size is being determined. The following shall be adopted in order to determine the design flow
rate:
0→1
𝑄𝑐𝑎𝑙𝑐𝑢𝑙
= 𝑞𝑠𝑝,𝑢𝑧 ∙ 𝐿0→1 (l/s), for any end section (2.4)
𝑖→𝑖+1
𝑖−1→𝑖
𝑖
𝑄𝑐𝑎𝑙𝑐𝑢𝑙
= 𝑄𝑐𝑎𝑙𝑐𝑢𝑙
+ 𝑄𝑙𝑎𝑡
+𝑞𝑠𝑝,𝑢𝑧 ∙ 𝐿𝑖→𝑖+1 (l/s)
(2.4’)
where:
𝑞𝑠𝑝,𝑢𝑧 =
𝑄𝑢𝑧,𝑜𝑟,𝑚𝑎𝑥
(l/s ∙ m )
∑ 𝑙𝑡𝑟
(2.5)
Qi-1,i– flow rate through the pipe section located upstream from the current pipe section,
in accordance with relationship (2.4);
Qlati– the volume of water brought by the side collectors which discharge into the node i.
(3) The calculation shall apply if the following requirements are met:
a) the pipe fittings and the volume of water collected in the sewage system are
uniformly distributed; same type of dwellings, with similar technical and sanitary
equipment;
b) a value for qsp,uz. ,(l/s,m) shall be available and used for each area with similar density
and equipment.
(4)
a)
b)
c)
For situations with:
pipe fittings installed at large distances from each other, with concentrated flows;
different types of equipment provided;
for high flow rates (above 5% or 10% of the volume of water delivered), the junction
pipe section shall be considered a calculation node.
(4) The volumes of water discharged shall be calculated using the concentrated flows,
each pipe section being calculated by adding up the volumes of water transported through the
upstream sections.
2.1.3.2 Choosing the diameters and hydraulic parameters of the design pipe section
(1) The calculation shall be carried out in a tabular manner, taking each pipe section at a time, simultaneously to calculating
the longitudinal profile of the collector with regard to its installation on the ground.
Table 2.2.Calculation for the pipe section j – k.
Ite
m
no.
Tr
Quz
(l/s)
L
(m)
0
1
2
3
Slopes
Groun Foundatio
d iT
n raft iR
4
5
Nominal
diameter
mm
Qpl
(l/s)
Vpl
(m/
s)
α=
Quz/Qpl
β=
vef/vpl
a=h/D
N
h=aDN
(mm)
Vef=βvp
l (m/s)
ΔH=iR
L
(m)
6
7
8
9
10
11
12
13
14
L – pipe section length (m);
Qpl – flow rate through a full section (l/s);
Quz – wastewater flow rate through the upstream
vpl – velocity for a full section (m/s);
pipe section (l/s);
iT – ground slope;
iR – slope of the foundation raft;
vef– effective velocity (m/s);
Δhi-k= iR ∙ L (m)
k
CR =
CRi
– Δhi-k (m)
DN – nominal diameter of the collector (m);
Hs– excavation depth;
h – water height (m);
Heights
Groun
Foundati
d
on raft
(m)
(m)
15
16
Hs
(m)
17
(2) Comments to Table 2.2:
a) If the street slope is downward and has a value ≥ 1/DN, the value iR=iT shall be
adopted;
b) The nominal diameter shall be chosen so that the calculation will lead to: a ≤ amax; v ≥
vmin;
c) Failure to comply with the requirement stipulated in point 2) shall lead to the
calculation having to be repeated by adopting iR> iT and, potentially, another diameter
or shape (ovoid);
d) Columns 1 – 14 describe the pipe section (j – k);
e) Columns 15 – 17 describe the ends of the pipe section;
f) Qpl, vpl, α, β and a shall be determined using diagrams like those given in Annexes 2 4; the diagrams shall be valid for a material determined by k=1/n; (n – relative
roughness) and the shape of the section;
g) The pipe sections located downstream from the section (j – k) must retain a nominal
diameter ≥ DN j – k ;
The elevation levels of the foundation raft in the same section shall be determined by
taking into consideration the connection to the top of the pipes adjacent to the section;
𝐶𝑅2 = 𝐶𝑅1 − (𝐷𝑁𝑘,𝑘+𝑖 − 𝐷𝑁𝑖𝑘 )(m)
(2.6)
DNik
CR1
DNk,k+i
CR2
Figure 2.1. Elevation levels for the foundation raft of the section to be calculated.
Each collector shall be materialised, in accordance with the calculation, by a longitudinal
profile.
h) The final position in which connection to the next collector is made shall be taken
into account;
i) The possibility of by-passing obstacles located along the route (fixed points - other
networks, required heights, etc.) shall be taken into consideration;
2.2 Separate stormwater network
2.2.1 Sizing flow rates
(1) Concept: For small basins (under 10 km2 = 1,000 ha), the quantities of stormwater
shall be determined using the rational method based on the following concept: rainfall with a
rated frequency shall lead to the maximum flow rate through a section of a basin when the
rainfall duration is equal to the maximum flow time from the furthest point to the section being
considered; on this basis, there will be a single rainfall event with rated frequency of the territory
for each calculated section, from which the sizing flow rate shall be obtained.
(2) The calculation shall be based on the relationship:
𝑄𝑚𝑎𝑥,𝑝𝑙𝑜𝑎𝑖𝑒 = 𝑚 ∙ 𝑆 ∙ 𝜙 ∙ 𝑖
(l/s)
(2.7)
where:
S – is the surface area of the drainage basin for the calculated section, (ha);
i – is the average intensity of the design rainfall, l/s/ha ; this shall be determined using the
IDF curves (STAS 9470-73) or on the basis of a specialist study (which is
compulsory for sites with a surface area larger than 1,000 ha), depending on the rated
frequency and the rainfall duration;
m – flow-rate reduction factor; the accumulation effect occurring within the network
shall be taken into consideration, with the following values:
a) m = 0.8 for a rainfall duration < 40 min.
b) m = 0.9 for a rainfall duration > 40 min.
ϕ – drainage coefficient; ratio between the volume of water reaching the sewage system
and the amount of rain which falls over the basin;
(3) Coefficient ϕ shall be variable over time; it shall be higher at the beginning of the
rainfall event and shall decrease as the rainfall duration increases. It shall be determined as the
weighted mean for non-homogeneous surfaces:
𝜙=
∑ 𝜙𝑖 ∙ 𝑆𝑖
∑ 𝑆𝑖
(2.8)
The ϕ values for different types of surfaces can be adopted in accordance with SR1846 –
2:2007.
(4) Rated frequency of the design rainfall : with the notation f; for preliminary
calculations, it shall be determined in accordance with STAS 4273-83 and SR EN 752:2008 or
on the basis of special studies.
For localities with a population ≥ 100,000 inhabitants, the rated frequency of the design
rainfall shall be considered to be f = 1/10.
For urban/rural localities with less than 100,000 inhabitants, the planner shall take into
consideration the following:
a) A decision made by the water management company and the local authorities to
ensure total or partial protection of the respective region; this shall specify the value
of the rated frequency f = 1/1, 1/2, 1/3, 1/5.
b) On the basis of the requirements issued by the local authorities, the planner shall
establish the flow rates and sections of the water collectors for at least 2 design
rainfall frequencies; on this basis, the costs for both options shall be assessed,
together with the damages caused when the rainwater harvesting capacity of the
network is exceeded;
c) The version (option) which has the lowest added costs and takes into account the
minimum social effects relating to the protection of assets and people shall be
adopted.
The design performance criteria and frequencies recommended by SR EN 752:2008 shall
be taken into consideration.
(5)Duration of the design rainfall: tp
a) For the first pipe section of the network:
𝑡𝑝 = 𝑡𝑐𝑠 +
𝐿
(min. )
𝑣𝑎
(2.9)
where:
tcs – surface concentration time:
 tcs = 5 minutes for medium slopes of the basin surface> 5%;
 tcs = 10 minutes for medium slopes of the basin surface, between 1 - 5 %;
 tcs = 15 minutes for medium slopes of the basin surface< 1 %;.
L – length of the pipe section, from the first discharge outlet to the section being calculated (m);
va – velocity estimated for the pipe section being calculated, (m/s);
b) For the following pipe sections:
𝐿𝑖,𝑘
𝑡𝑝 = 𝑡𝑝 𝑖−1 + 𝑖−𝑘 (min. )
(2.10)
𝑣𝑎
where:
tpi-1– rainfall duration corresponding to the section i of the pipe section i – k, (min.);
vai-k– estimated velocity,(m/s);
At the junction between 2 collectors, at the first downstream pipe section, the highest
value of the design rainfall duration shall be taken into consideration for the 2 collectors.
If the flow rate calculated for the downstream pipe section is lower than the flow rate in
the upstream pipe section, then the flow rate with the highest value of the two shall be adopted.
(6)The estimated velocity shall be determined based on the ground slope and the
planner's experience; the value obtained by actual calculation must not differ by more than 20%
from the estimated value. The calculation shall be iterative.
For large basins (> 10 km2), in accordance with the provisions of SR 1846 – 2:2007, the
planner shall use meteorological studies (drawn up by the National Meteorological
Administration-ANM) to determine the design rainfall hydrographs for the characteristic sections
of the collectors.
(7)Design rainfall intensity – This shall be determined based on the rainfall duration (tp)
and using the IDF curves in accordance with the provisions stipulated in STAS 9470-73 or the
updating studies drawn up by ANM; for networks serving a territory > 1,000 ha, the planner shall
contract the National Meteorological Administration to carry out statistical studies for the site;
these shall specify the historic rainfalls of maximum duration and intensity and shall update the
IDF curves corresponding to the region where the site is located.
The IDF curves shall be plotted in accordance with Annex 5.
The design rainfall intensity shall be determined for each zone of the stormwater sewage
sub-system using the adopted rated frequency.
2.2.2 Choosing the diameter and hydraulic parameters
The configuration of the separate stormwater network shall be adopted in correlation
with:
a) The configuration of the site of the user and catchment basin;
b) The permissible discharges and their impact on the recipient environment, by
adopting a dilution coefficient of 4 to 8 times the flow rate during dry weather, on the
basis of the self-cleansing capacity of the catchment basin;
c) Setting up retention (settling) basins in order to reduce the maximum flow rates and
retain the stormwater collected during the first 5-10 minutes of rain.
2.2.2.1 Calculation of the flow rates for each pipe section
The design flow rate is the flow rate in the downstream section of the pipe section.
𝑄𝑚𝑎𝑥.𝑝𝑙𝑜𝑎𝑖𝑒 = 𝑚 ∙ 𝑆 ∙ 𝜙 ∙ 𝑖
(l/s)
(2.11)
where:
S – surface area of the drainage basin, consisting of:
𝑖−𝑘
𝑖−𝑘 (ha)
𝑆 = 𝑆𝑡𝑟
+ 𝑆𝑎𝑚
(2.12)
Stri-k – the surface area of the drainage basin corresponding to the pipe section being
calculated, (ha);
Sami-k – the surface area of the drainage basin located upstream from the pipe section
being calculated, (ha);
𝛟 – average drainage coefficient calculated as the weighted mean for all surfaces
corresponding to the pipe section i – k;
i – intensity of the design rainfall with rated frequency; it shall be considered that the
design rainfall corresponds to the section k of the pipe section i – k;
m – determined in accordance with § 2.2.1.
2.2.2.2 Choosing the diameters and hydraulic parameters of a pipe section
(1) The calculation shall be carried out in a tabular way, when installing the ground
connector in the longitudinal profile.
(2) A table similar to Table 2.3 shall be drawn up.
Table 2.3. Sizing a stormwater discharge system (example); rated frequency f=1/1; t cs =15’.
Tr.
L
(m)
S
(ha)
Va
(m/s)
tp
(min)
m
Φ
i
(l/s/h
a)
Qm
(l/s)
iT
iR
Nomina
l
diamete
r (mm)
Qpl
(l/s)
Vpl
(m/s)
α
β
a
h
(mm)
Vef
(m/s)
Δh
(m)
Ct (m)
Cr
(m)
Hs (m)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
1
7
18
19
20
21
22
23
16.5
0.9
150
236.2
0.015
400
330
2.63
0.7
1
1.07
0.
6
2
3.0
0.01
5
146
5
0.
3
5
148
270
284
2.81
4.05
141,95
2,05
141,85
2,15
i
k
144
L – pipe section length (m);
DN – nominal diameter of the collector
vef– effective velocity (m/s);
S – collection surface area (ha);
(mm);
Δhi-k= iR ∙ L (m)
va– estimated velocity (m/s);
Qpl – flow rate through a full section (l/s);
CRk= CRi – Δhi-k (m)
tp– rainfall period (min);
vpl– velocity through a full section (m/s);
Hs – excavation depth;
m – coefficient of reduction (0.8 – 0.9);
The estimated velocity shall not vary from
Φ – drainage coefficient;
vef (Column 19) by more than 20%.
i – design rainfall intensity (l/s, ha);
Qm– stormwater flow rate (l/s);
iT – ground slope;
h – water height (m);
iR – slope of the foundation raft;
DN(H) – diameter or height of the channel;
(3) Comments on Table 2.3:
a) Columns 1, 2, 3, 4, 7, 10, 11, 21 must be filled in;
b) A value shall be estimated for the water flow velocity through the pipe section
(column 4) and a rainfall duration shall be calculated (column 5);
𝑙𝑖𝑘
(min. )
𝑡𝑝 = 𝑡𝑐𝑠 +
(2.13)
𝑣𝑎
c) The coefficient m (column 6) shall be chosen depending on the rainfall duration;
 tp> 40’for m = 0.9;
 tp< 40’ for m = 0.8;
d) The IDF curves or special studies shall be used to determine the design rainfall
intensity (column 8) for f= rated and the rainfall duration-tp (2.10); Qm shall be
determined using relationship (2.11) (column 9, table 2.3);
e) A diameter shall be chosen for the sewage pipe (column 12), based on the known
flow rate value and the adopted slope of the foundation raft (column 11);
f) The variables given in columns 15, 16, 17 (α,β,a) shall be determined from the
diagrams showing the degree of filling, knowing that α= Qm/ Qpl(see Annex 4);
g) The water height in the sewage pipe (column 18) shall be calculated, together with
the actual water flow velocity (column 19). If the velocity differs by more than 20%
from the estimated velocity (column 4), the calculation shall be repeated by
considering that the estimated velocity is equal to the actual resulting velocity;
h) The elevation levels of the pipe foundation raft (column 22) shall be determined so
that the burial depth is more than 0.8 m (above the arch of the channel) and two
neighbouring pipe sections are connected to the top, therefore maintaining the linear
continuity of the upper arch of the channel.
i) Stormwater drains can operate for a full section.
2.2.2.3 Retention basins
(1) These shall be adopted in accordance with the provisions stipulated in SR 1846 –
2:2007, Chapter 2.4 to retain polluted water, reduce the peak flow when the rainfall duration is
equal to the concentration time but longer than the duration of the design rainfall.
(2) The objectives of the retention basins are:
a) To offset maximum discharge due to rainfall by reducing the downstream flow rates
and ensuring that the water discharges over longer periods of time;
b) To retain the pollutants carried by stormwater during the first part of the water
discharge;
c) To protect the aquatic environment of the drainage basin.
(3) The structure of stormwater retention basins shall be analysed in correlation with the
Regional Urban Plan for the region where the sewage system is installed, to ensure that they fit
within the urban system of the region. It is recommended that the retention basin is given an
additional intended use. These basins shall be cleaned on a regular basis.
2.3 Unitary sewerage network
2.3.1 Determination of the sizing flow rates
The design flow rate for each pipe section shall be obtained by adding up:
a) The design wastewater flow rate, relationship (2.1) § 2.1.3.1.;
b) The maximum rainfall volume for the pipe section, relationship (2.11) § 2.2.21.
2.3.2 Choosing the diameters and hydraulic parameters of a pipe section
(1) Calculations shall be carried out for the similar procedures presented in Table 2.2 for
a wastewater network, and in Table 2.3 for a stormwater network. The following requirements
must be complied with:
𝑄
a) The minimum self-cleansing velocity for dry weather shall be ensured; 𝛼 = 𝑢𝑧 shall
𝑄𝑝𝑙
h
u
also be determined in accordance with the filling diagrams: degree of filling a = DN
and β =
vu
vpl
; these relationships shall be used to calculate vu ≥ 0.7 m/s;
b) To ensure that the sewage collector operates during rainfall, the permissible degree of
filling can be amax = 1.0;
c) The minimum diameter of a unitary sewerage network shall be DN ≥ 300 mm;
d) For diameters DN > 1000 mm or a height H > 1000 mm and low wastewater volumes
(in dry weather), the planner shall implement measures to ensure that the minimum
self-cleansing velocity is reached, by building a gutter at the base of the collector; this
solution must also be analysed when considering a technological update of existing
large-size collectors which operate within a unitary system.
(2) An example of the content of a longitudinal profile is shown in Figure 2.2.
(3) Existing sewerage networks shall undergo technological updating in accordance with
the provisions stipulated in SR EN 752:2008.
*
Receptor
Statia de epurare
Camin de intersectie
Deversor
Camin de intersectie
Camin de intersectie
Camin de intersectie
Nmax
2 CV
la 71,5 m
R
395,08
393,88 394,08 496,00
396,55 396,65 400,00
396,38 396,58 399,80
397,08 397,28 400,60
SE
393,36 393,56 395,00
E Dv
D
399,29 402,25
398,65 398,85
401,05 402,35 404,75
401,25
Cote sapatura
403,65 403,85 405,75
Cote radier
1 CV
la 75 m
C
B
A
Punctul
Cote teren
5 CV
la 62,5 m
6 CV
la 68 m
4 CV
la 65 m
3,36
3,34
2,07
1,68
476
375
150
215
75
vef =0
,47
i=0,0
04
6
1175
800
325
Distante cumulate(m)
Pante si viteze
efective (m/s)
Schema in plan
diametre(mm)
vef =0,7
7
DN=500
i=0,0042
1000/1500
vef =0,9
4
i=0,00
42
1200/1800
i=
ve = 0,00
f 0
,98 42
ve =
f 1
,62
i=0
1615
3,25
325
1540
2,15
Distante partiale(m)
0
Hmed sapatura(m)
i=
,00 ve 0,0
7 f =1 07
,62
1200/1800 DN=500 DN=500
Punctul
Cote teren
Cote radier
Cote sapatura
Hmed sapatura
Point
Ground elevation levels
Foundation raft elevation levels
Excavation elevation levels
Hmed for the excavation
Distante partiale (m)
Distante cumulate (m)
Pante si viteze efective (m/s)
Schema in plan diametre (mm)
Camin de intersectie
Deversor
Statia de epurare
Receptor
Partial distances (m)
Cumulated distances (m)
Slopes and effective velocities (m/s)
Planar diagram, diameters (mm)
Junction manhole
Spillway
Water treatment plant
Catchment basin
Figure 2.2.. Longitudinal profile of the main collector.
*It is permissible to discharge the mixture of wastewater and stormwater into the emissary; spillways shall be
constructed in accordance with Chapter 7 § 7.1 of this normative document.
3. Siting the sewerage network
3.1 Wastewater network
(1) The siting of the network shall essentially depend on the configuration of the street
network:
a) For streets and pavements with a width of less than 10 - 12 m, the wastewater
network shall be located in the axis of the road; the pipe fittings connected at the user
end shall be installed at heights lower than the other networks;
b) For streets and pavements with a width > 16 m, the option of installing the wastewater
drains on each side of the street shall be considered; the presence of a public space
between the pavement and the building front shall be considered as a priority when
siting the sewerage network.
(2) The position of the drains and the manholes thereof shall be chosen by taking into
consideration the position of the other underground networks and the specific conditions that
must be provided to ensure their operation.
These distances shall be determined in accordance with the provisions stipulated in SR
8591:1997.
(3) In special situations, which raise difficulties in ensuring the required minimum
distances between the networks, protocols and agreements shall be concluded with the owners of
these networks and the local authorities to help choose the location of the sewerage network and
modify the distances stipulated in SR 8591:1997.
The generally-accepted design shall take into account the following:
a) The position of the drains must not affect the safety of the other underground
networks and the sanitary safety of users;
b) Rational solutions must be found to enable interventions to the network so that any
necessary repairs/rehabilitation works can be carried out without damaging other
networks;
c) Any intervention to the network must be rational.
4. Components of the sewerage network
4.1 Pipes used to construct the pipe sections
4.1.1 Cross-sectional shape
(1) The nominal diameter (mm) of the cross-section shall be obtained from the
calculation performed for the sewerage network. In general, a circular shape shall be considered
the optimum cross-section from a hydraulic point of view.
(2) In situations determined by: narrow pipe-laying spaces, low minimum water volumes
or large water volumes, an ovoid cross-section shall be used, which will ensure a higher flow
velocity for the same water height.
(3) A bell-shaped cross-section can be used for large drains (flow rates measured in m3/s)
where economising of vertical space is desirable.
4.1.2 Pipe materials
(1) The pipe materials used to build sewerage pipe sections shall be chosen by taking into
consideration the following elements:
a) Physico-mechanical and structural-dimensional characteristics and properties;
b) Structural strength and joining methods;
c) Requirements with regard to installation, maintenance and repairs;
d) Resistance to the aggression of wastewater and soils with/without underground water;
e) Service life and operational safety;
f) Compatibility of the material with the quality of the wastewater being transported
through the pipes;
g) Investment costs.
(2) For networks with a length > 5 km, a preliminary study shall be carried out to
determine the cost/performance ratio that will be used to choose the material for the pipe
sections.
This study must include:
a) The cost of the pipes (including installation and testing thereof);
b) Compatibility factors that would enable the pipes to be adapted to the particular
situation in which they are to be used: soil characteristics, permanent loads and traffic
loads, quality of the wastewater, including their risk behaviour (uncontrolled or
accidental wastewater discharges);
c) Service life guarantee, which cannot be less than 50 years;
d) Solutions for the necessary interventions to the facility carried out during its operation
(repairs to a broken pipe/sleeve joint, leakage, behaviour under seismic loads and
remedying solutions);
The material shall be chosen based on a joint decision agreed between the planner,
operator and the local authority, in its capacity of network owner.
4.2 Related structures built within the sewerage network
4.2.1 Pipe fittings
(1) Pipe fittings collect the household wastewater produced by users and carry it into the
public sewerage network.
(2) A pipe fitting shall include:
a) Water main connection manhole; this shall be located inside the residential building
or the public area of shared dwellings; it shall be waterproof and enable access to the
pipe fitting;
b) Connecting channel; shall be made of circular pipes with a nominal diameter ≥ 150
mm;
c) The connecting channels and the street drain shall be connected by means of special
elements;
d) The pipe fittings shall be installed in accordance with SR EN 295–2:1997 and SR EN
295–2:1997/A1:2002 or inside inspection chambers of the public sewage system;
(3) In localities with macroporous soil and a high number of structures close together,
one or more connecting channels shall be linked to a manhole of the street drain.
(4) When the street drain has high depth, one or more pipe fittings shall be connected to
the drain through a manhole; the pipe fittings shall be connected at hmax=0.8 m from the manhole
bench.
4.2.2 Discharge outlets
(1) Objective. Drainage outlets are used to collect and discharge stormwater into the
sewerage network; these are circular shafts covered with passable grate covers and connected to
the sewerage network by pipes with a nominal diameter of 150 mm.
(2) Classification of discharge outlets:
a) Discharge outlets with a reservoir and siphon; in accordance with the provisions
stipulated in STAS 6701-82, these can be classified into type A - with passable grate
cover and type B - with non-passable grate cover; the role of the siphon shall be to
prevent sewer gases from being released into the air; the provisions stipulated in SR
EN 124:1996 shall be complied with;
b) Discharge outlets without a siphon and reservoir; these shall be used in the division
process, within a stormwater drainage network and only on asphalted roads where the
quantity of suspended matter or other deposits that could be carried into the network
is small (non-existent).
(3) Discharge outlets shall be installed:
a) On the street gutter, upstream from a pedestrian crossing;
b) In large junctions, near the pavement, in spaces with no traffic;
c) On sloping platforms installed in spaces with reduced traffic.
(4) The distance between the discharge outlets shall be determined in a rigorous way on
the basis of the efficient flow rate of the gutter (depending on the street slope and the roughness
coefficient of the gutter) so that the maximum water level in the gutter (for the design rainfall) is
lower than the top of the pavement edge (clearance ≥ 5cm).
Sectiunea A - A
6
1
H
2
4
45°
3
10
50
5
A
Sectiunea A-A
A
Section A-A
Figure 4.1. Discharge outlet with reservoir and siphon.
1-grate cover
4-elbow with DN
(nominal diameter) 150
2- plain concrete pipe, DN 500
5-foundation raft
3-plain concrete element for drainage outlets
6-pavement edge
(5) A recipient should be installed inside the discharge outlet manhole, which can be
removed with machines to make the cleaning of discharge outlets easier.
4.2.3 Manholes
(1) Objective. Manholes are vertical structures which connect the sewage collector to the
road. Manholes shall have a concrete foundation.
(2) Functions. In accordance with standard SR EN 752:2008, manholes shall have the
following functions:
a) to enable the operating personnel to access the collectors;
b) to ensure ventilation of the network;
c) to enable periodic cleansing of the network;
(3) Siting:
a) along the line of the channels;
b) in the sections where the diameters and the vertical and horizontal directions change;
c) in sections where the channels intersect with and connect to other channels;
d) in sections where cleansing of the network is required.
e) at the start of each collector.
4.2.3.1 Pass-through manholes
(1) These shall be designed and installed in accordance with the provisions stipulated in
STAS 2448-82 and SR EN 1917:2003. Figure 4.2 shows an example of how pass-through
manholes are designed.
Sectiune A-A
Sectiune B-B
Scari
acces
Scari
acces
Scari
acces
1,00
12
12
12
variabil
> 1,80
30
30
C
C
1,00
rigola
rigola
Sectiunea C-C
B
A
A
1,0
0
1,50
A
A
80
B
1,50
a)
Sectiunea A-A
Rigola
Scari acces
variabil
b)
c)
Section A-A
Gutter
Access ladders
variable
Figure 4.2. Pass-through manhole.
a) with its own foundation and walls made of prefabricated pipes;
b) with its own foundation and brick or concrete walls; c) built on the collector pipe.
(2) The distances between the manholes shall be:
a) 50 – 60 m for collectors with a nominal diameter ≤ 500 mm;
b) 75 – 100 m for semi-visitable collectors with a nominal diameter ≥ 1,500 mm;
c) 120 – 150 m for visitable collectors with a nominal diameter ≥ 1,800 mm.
(3) Manholes shall include:
a) an open gutter that is hydraulically profiled;
b) a working chamber (above the gutter): minimum ϕ 1.0 m (or the side equal to 1.0 m)
and a minimum height of 1.80 m;
c) shaft (tube) for allowing access from the ground level: minimum ϕ 0.8 m;
d) secured cover: passable or non-passable, depending on the location;
e) steps mounted on the walls, to enable access to the gutter.
4.2.3.2 Junction manholes
(1) These shall be installed at the junction between 2 or more collectors; for large
collectors, they shall be turned into junction chambers.
(2) Where channels with a nominal diameter ≥ 500 mm intersect, a hydraulic connection
must be created so that:
a) the 2 currents can mix without creating hydraulic phenomena that could damage the
structure;
b) the shape of the connection shall avoid any stationary areas where deposits could
occur.
4.2.4 Spillways
(1) Spillways shall be installed within unitary sewerage networks to discharge certain
volumes of water directly into the catchment basin.
(2) The dilution ratio for the wastewater discharged into the catchment basin shall be
determined as follows:
n = 1 + n0(4.1)
n0 = Qmeteoric / Qwaste
(4.2)
where:
n0 – dilution coefficient;
(3) the volume of wastewater mixed with stormwater that can be discharged into the
catchment basin shall be determined as follows:
𝑟𝑒𝑐𝑒𝑝𝑡
𝑄𝑎𝑑𝑚 = 𝑄𝑟𝑒𝑐𝑒𝑝𝑡 ∙
− 𝐶𝐵𝑂5𝑎𝑑𝑚
𝑢𝑧
𝐶𝐵𝑂5 − 𝐶𝐵𝑂5𝑎𝑑𝑚
𝐶𝐵𝑂5
(m3 /s)
(4.3)
where:
Qadm – volume of wastewater and stormwater that is permitted to be discharged into the
catchment basin, (m3/s);
BOD5recept – the 5-day biochemical oxygen demand of the catchment basin before the
spillway, (mg O2/l);
BOD5uz – the 5-day biochemical oxygen demand of wastewater mixed with stormwater,
(mg O2/l);
BOD5adm – the 5-day biochemical oxygen demand of the catchment basin in accordance
with NTPA 001, (mg O2/l).
(4) The dilution ratio shall be chosen in accordance with the provisions stipulated in SR
EN 752:2008.
4.2.4.1 Structure of spillways
(1) Spillways shall be made up of:
a) a discharge chamber;
b) an off-take channel for evacuating the water discharged into the catchment basin;
c) the outlet of the off-take channel.
(2) The most frequently used type of spillway is a lateral spillway; Figure 4.3 shows the
diagram of a lateral spillway.
Figure 4.3.. Basic lateral spillway.
A
Sectiunea A - A
b
D1
H
D3
h
b
L
D2
B
A
(3) The length of a lateral spillway shall be determined as follows:
𝐿=
𝑄
0,66 ∙ 𝜇 ∙ √2𝑔 ∙ ℎ3/2
(m)
(4.4)
where:
μ – discharge coefficient (0.62 – 0.64);
Q – volume discharged, (m3/s);
h – average height of the overflowing nappe, (m);
(4) The compulsory design requirements are:
a) Access to and working inside the spillway chamber shall be enabled; ladders and
gutters shall be installed; the minimum height of the spillway chamber, measured
from the gutter, shall be ≥ 1.80 m;
b) Elements shall be installed to prevent flooding of the spillway chamber when the
water level in the catchment basin is high; the discharge conduit to the catchment
basin shall be closed by a cofferdam; dams with automatic closing system shall be
provided for catchment basins with large variations and high frequencies of the water
level;
c) For spillways located at the entrance to the water treatment plant, the chamber can
have an open design; a sump shall be provided on the foundation raft of the chamber
to retain large matter; this shall be regularly cleaned using a clamp bucket;
d) A bar screen shall be installed on the spillway.
4.2.5 Stormwater retention basins
(1) These basins shall be chosen and calculated in accordance with Chapter 2.4. SR 1846
– 2: 2007.
(2) Stormwater retention basins can be:
a) Implemented within the network to reduce peak flow rates;
b) Installed within a unitary sewerage network and connected to spillway that discharge
the water directly into the catchment basin;
c) Used for pre-treatment of stormwater.
(3) Retention basins located at the entrance to the water treatment plant shall ensure and
adjust the volumes of influent water directed into the plant.
(4) In all situations, retention basins shall have to:
a) Reduce the volumes of water discharged downstream from the basin;
b) Improve the quality of the water by sedimentation.
(5) Retention basins set up in built-up areas shall be enclosed; after the rain, such basin
shall be emptied gravitationally or by pumping into the sewerage network located downstream
from the basin;
(6) The basins shall be built:
a) with a minimum of 2 compartments;
b) to include systems for collecting and discharging deposits (gutters, sludge collection
systems, sludge pumps), as well as cleansing systems;
c) to include equipment for retaining floating suspended matter.
4.2.6 Sewer siphons
(1) Sewer siphons shall be installed when collectors run underneath other structures,
watercourses, roads, railways or depressions.
a
(2) Siphons shall be made up of:
a) inlet and outlet chambers on each side of the underpass;
b) siphon pipes.
b
(3) The diagram of a lower sewer siphon system is shown in Figure 4.4.
N.A.asig. 1‰
A
4,00
1
15,00
A
15,00
16,00
1
3,50
N.A.asig. 1‰
Deversor
Conducta de
ape meteorice
DN 1000
Sectiune A - A
Stavila
Conducta de
ape uzate
DN 500
N.A. asig. 1%0
Deversor
Sectiune A-A
Conducta de apa meteorice DN 1000
Stavila
Conducta de ape uzate DN 500
N.A. ens. 1%0
Spillway
Section A-A
Stormwater pipe with nominal diameter 1000
Dam
Wastewater pipe, nominal diameter 500
Figure 4.4. Siphon.
(4) The sewage system dictates the number of siphon pipes chosen for the same crossing:
a) A separate network design can include only one line for each function (wastewater,
stormwater);
b) A unitary network shall always consist of 2 lines: 1 line shall be used in dry weather,
whilst the second line shall be used when it rains.
(5) Siphon pipes shall be sized as follows:
a) minimum velocity > 0.5 - 0.6 m/s;
b) velocity for the design flow rate shall be 1.25 - 1.5 m/s.
(6) When special requirements regarding operational safety apply, the number of siphon
pipes shall be doubled and each line shall be sized to 0.75 Qcalcul.
(7) The requirements for eliminating any risks during the operation of underpass pipes
shall include:
a) choosing materials that provide increased safety: protected steel pipes, ductile cast
iron, polyester reinforced with fibreglass of a special design;
b) implementing structural measures to stabilise the river bed, absorb the dynamic
stresses induced by traffic and consolidate the ground in the area of the underpass.
(8)The downward and upward sections of the siphons shall have slopes of at least 20 ° to
prevent the settling of deposits at la Quz or min.
(9) If the siphon pipes need to be insulated, sluice gates shall be installed in the
inlet/outlet chambers; the pipe sections inside the inlet chambers shall be fitted with systems for
flushing (cleansing) the siphon pipes and/or draining the sewerage network.
(10) The hydraulic sizing of siphon pipes shall be based on the following equation:
𝛥𝐻 = ∑ ℎ𝑟
(4.5)
where:
ΔH – is the minimum difference between the level in the inlet chamber and the level in
the outlet chamber;
∑ 𝐡𝐫 – the sum of the local load losses and the losses distributed within the hydraulic
circuit, between the inlet chamber and the outlet chamber;
4.2.7 Pumping stations
(1) A sewerage network shall require installation of pumping stations:
a) In sagging areas where the gravity flow cannot be ensured;
b) In different network sections where the pipe-laying depths are high (> 7 – 8 m) due to
the slopes that need to be created in order to achieve the minimum self-cleansing
velocity;
c) On sites where the water treatment plant is built at a higher elevation level than the
main collectors.
(2) The pumping station solution for the sewerage network shall be chosen on the basis of
a technico-economic calculation, which shall take into consideration:
a) The network operating costs (periodic removal of any deposits);
b) The costs for the electricity used in the pumping stations.
4.2.7.1 Siting of pumping stations
The pumping station shall be built in a designated space that shall be incorporated in the
regional and general urban plans by considering:
a) Any negative effects on the environment: potential odours, the discharge of retained
matter onto the bar screens, noise;
b) Allowing a distance of at least 50 m from any residential buildings;
c) Setting up a green area within the pumping station grounds.
4.2.7.2 Components of the pumping station
(1) The catchment basin used to collect and store wastewater, which shall also house the
(submerged) pumps or the inlets thereof.
(2) The volume of the catchment basin shall be determined on the basis of:
a) The hourly variation of the influent water flow rates in the pumping station;
b) The variation of the volumes of pumped water determined by the capacity of the
equipment, the number of pumps and the requirements enforced by the self-cleansing
velocities through the backwater pipes;
c) The requirements issued by the pump manufacturer with regard to how many times
per hour the equipment can be activated/deactivated.
(3) For low-capacity pumping stations (< 5 l/s), the volume of the catchment basin
(prefabricated from plastic material or concrete) shall be determined for times within the interval
catarg de
of 1–3 minutes.
ridicare pompe
dulap de
comanda
palan
imbinare
demontabila
clapet
colector
de intrare
vana
cos-gratar
camin anexa pentru
instalatia hidraulica
electro-pompa
conducta
de refulare
Dulap de comanda
Catarg de ridicare pompe
Palan
Colector de intrare
Imbinare demontabila
clapet
suport
regulator
de nivel
Switch cabinet
Pump lifting mast
Hoist
Inlet collector
Dismantable joint
valve
Figure 4.5. Example of a wastewater pumping station (low flow rates).
(4) When determining the volume of the catchment basin of a pumping station:
a) The accumulation of wastewater for any period of time long enough to lead to the
settling of deposits shall be avoided;
b) Grates (cutters) shall be installed to the water inlet to the basin, to prevent the access
d/cos α
α
of large matter.
α
d/cos α
(5) Figure 4.6 shows the general layout of a pumping station, in 2 versions:
a) With submersible electric pumps installed in a wet chamber;
b) With electric pumps installed in a dry chamber; this solution shall be chosen for large
pumping stations ( Q > 750 – 1,000 m3/h); coarse bar screens and automatic cleansing
shall be installed near the wastewater pumping station.
container
camin
debitmetru
gratar
admisie
apa uzata
conducta
refulare
admisie
apa uzata
Nmax
camera
umeda
Nmax
Nmin
electro-pompa
submersibila
Pompa in
camera uscata
cheson
Nmin
cheson
beton simplu
beton simplu
debitmetru
Admisie apa uzata
cheson
Conducta refulare
Electro-pompa submersibila
gratar
container
Camera umeda
Pompa in camera uscata
Cam in diametru
Beton simplu
debitmetru
Wastewater intake
caisson
Backwater pipe
Submersible electric pump
bar screen
container
Wet chamber
Pump installed in a dry chamber
Chamber diameter
Plain concrete
flow meter
Figure 4.6. Pumping station – (a) wet chamber, (b) dry chamber.
(6) The catchment basin of the pumping station shall be designed in the shape of a
circular or rectangular caisson; the following requirements must be met:
a) The foundation raft shall be constructed so that the sludge is guided into the pumps;
b) Structural measures shall be taken to enable dismantling (removal) of the submersible
pumps;
c) For enclosed catchment basins, measures shall be implemented to ensure that any
gases are released via ventilation systems;
d) For high-capacity stations ( >1,000 m3/h) the compartmentalisation of the basin for
each pumping unit shall be taken into consideration.
(7) The solution recommended for low and medium-capacity pumping stations (Q <
25,000 m3/day) shall include a catchment basin, a scrubber and submersible electric pumps; a
compartment for the hydraulic installations shall be attached to the catchment basin and shall be
accessed independently from the catchment basin; enclosed tunnels fitted with bar screens shall
be provided in the ceiling of the catchment basin to enable extraction of the pumps and bar
screens containing retained matter, as well as natural ventilation.
(8) Measures shall be implemented in high-capacity pumping stations that are equipped
with electric pumps installed in a dry chamber, in order to:
a) Make sure that the dry compartment of the pumps and hydraulic installations is
perfectly sealed;
b) Install a superstructure, lifting systems and systems that enable access to the
equipment and hydraulic installations;
c) Ventilate the dry chamber at a rate of 10 air exchanges/hour;
d) Prevent any access to the dry chamber until the ventilation system has been operating
for at least 30 minutes before access is required.
(9) In the event of a failure of the pumping station, the station must be isolated by
shutting off the water intake to the catchment basin using a valve (sluice gate) (a gate valve shaft
located upstream from the pumping station).
5. Vacuum sewerage networks
(1) Objective: To collect wastewater via a hydraulic system which prevents deposits, and
to lay the pipes at high depths in areas with flat terrain or very low slopes.
(2) Intended use: Separate wastewater sewerage network.
5.1 Components
a)
b)
c)
d)
e)
f)
Gravity pipe fittings connecting to the sources of wastewater;
Collector manholes equipped with vacuum valves;
Pipe networks operating at p < patm;
Vacuum recipients and vacuum pumps;
Wastewater pumping station;
Automation systems.
(1) Figure 5.1 shows the diagram of a vacuum sewage system.
1
2
2
2
2
2
2
3
3
2
3
4
4
5
6
1- producatori apa uzata
2 - camine echipate cu supape
3 - retea vacuumata
4 - recipienti vacuum
5 - pompe vid
6 - statie pompare apa uzata
SE - statie de epurare
camine de vane de izolare
la SE
1.
Producatori apa uzata
1.
Wastewater sources
2.
Camine echipate cu supape
2.
Manholes equipped with valves
3.
Retea vacuumata
3.
Vacuum network
4.
Recipienti vacuum
4.
Vacuum recipients
5.
Pompe vid
5.
Vacuum pumps
6.
Statie pompare apa uzata
6.
Wastewater pumping station
7.
SE – statie de epurare
7.
SE - water treatment plant
8.
Camine devane de izolare
8.
Check valve manholes
Figure 5.1.. Vacuum sewage system.
(2) The operating principle of a vacuum sewage network:
a) Installation of vacuum valves in the collector manholes (Figures 5.2 and 5.3); these
shall open automatically when the maximum level is reached in the collector
manhole, and shall close 3-4 seconds later, when the entire volume of water contained
in the tank has been discharged;
plutitor
plutitor
float
Figure 5.2.. Valve.
Figure 5.3.. Collector manhole.
b) Network with a pressure < patmospheric (max. 0.6-0.7 bar) which collects the wastewater
mixed with air and transports it to the downstream zone at a two-phase air-water
mixture velocity of more than 2 m/s;
c) The configuration of the vacuum network shall be designed in the form of descending
pipe sections equipped with successive lifts, similar to the diagrams shown in Figures
5.4, 5.5 a, b, c.
h
L
Figure 5.4.. Lift configuration.
Teren plat
a)
Teren cu panta coboratoare
b)
Teren in contrapanta
iT
h
Configuratia liftului
Teren plat
Teren cu panta coboratoare
Teren in contrapanta
lT
c)
Lift configuration
Flat terrain
Sloping terrain
Counter-sloping terrain
Figure 5.5.. Positioning of the vacuum pipes in relation to the ground slope.
In diagram c) lT = f (h, iT); hmax ≤ 1.5 m.
d) The operation of the vacuum sewerage network shall depend on the size of the
vacuum losses caused by:




the intake of air during opening of the valves;
hydraulic losses in the pipe system, due to the two-phase mixture;
the air-water ratio required to open the valves;
the total pressure losses as a difference between the pressure in the vacuum tank
and the pressure at the most remote collection point.
(3) The system of lifts used to operate the vacuum network can be: enclosed lift (Figure
5.6) or open lift (Figure 5.7).
p1
d
p2
x
v
h
p
p
d
v
Figure 5.6.. Enclosed lift v > d/cos α.
Figure 5.7. Open lift v ≤ d/cos α.
(4) The vacuum pressure loss for an enclosed lift shall be determined with the following
relationship:
Δpstatic = ρ · g · x · 105(bar)
(5.1)
where:
ρ – wastewater density, (kg/m3);
g – gravitational acceleration, (m/s2);
x – difference between the elevation height of the arch underside in the lower area and
the elevation height of the lift foundation frame in the upper area, ( m ).
5.2 Design requirements
5.2.1 Gravity pipe fittings for collector manholes (Figure 5.8)
(1) The following shall be adopted:
a) Pipe fitting diameter Dn 150 - 200 mm;
b) With/without a collector manhole, depending on the: terrain configuration distances
and siting of the vacuum network.
(2) Figure 5.8 shows a siting diagram.
(3) Gravity pipe fittings shall be built in accordance with § 4.2.1, Chapter 4.
Sistem aerisire
Airing system
Retea vacuumata
Vacuum network
Camin colector
Collector manhole
Figure 5.8.. Diagram of the collector manhole of a vacuum network.
5.2.2 Water main connection manholes
(1) The water main connection manholes shall be made of reinforced concrete or plastic
materials with/without a passable/non-passable concrete slab; D = 1.0 m; H = 1.0 – 1.5 m.
(2) Requirements:
a) installation of an air intake system in the manhole (Ø 20 mm);
b) installation of a tank in the lower area, with a capacity of at least 40 dm 3; the capacity
of the tank shall depend on the type of valve chosen, so that the water is collected in t
< 5 seconds. 4-5 houses/households or 10-15 equivalent inhabitants can be connected
to one water main connection manhole.
5.2.3 Vacuum network
5.2.3.1 Flow rates, diameters, lengths
The nominal diameters shall be chosen in accordance with Table 5.1, depending on the
flow rate and the length of the pipe section.
Table 5.1. Flow rates, diameters and lengths.
Nomina
Measur
Item
Q*max
l
Lmax
ement
No
(l/s)
diamete
(m)
unit
r (mm)
1
<2
dm3/s
110
500
2
>2
dm3/s
110
300
3
=2
dm3/s
110
200
4
5
dm3/s
125
800
5
10
dm3/s
160
120
6
≤ 14
dm3/s
200**
≤ 1900
* The maximum hourly discharge rate of the wastewater shall be considered.
** Diameter of the main collector located upstream from the vacuum station .
5.2.3.2 Layout, lifts, slopes
a) Flat terrain (IT ≈ 0)
Pipe sections with a downward slope shall be chosen IR = 2%.
Distance between 2 consecutive lifts Lmin = 6 m, Lmax=150 m.
Maximum number of lifts: 25; Lmax = 150 x 25 = 3,750 m.
b) Terrain with a downward slope:
1 lift shall be installed for every 300 m.
c) Terrain with an upward slope/counter-slope
Lifts with a downward slope of 2%, the length of which shall be chosen so that the burial
depth of the vacuum network does not exceed 1.5 m; the distance between the lifts shall also
depend on the size of the counter-slope of the ground.
Height of the lifts on the same slope: IR = 2%.
-L = 150 m h = 0.30 m;
-L = 50 m h= 0.1 m.
-Pressure losses on the lift:
-10 cm/lift for a nominal diameter of 200 mm;
-20 cm/lift for a nominal diameter of 90 mm.
- a linear variation and an average loss of 0.15 m/lift shall be permissible.
d) The pipe sections of the network shall be isolated using valves installed on the branch
pipes, so that no more than 20% of the total length of the network needs to be
decommissioned at any one time such that interventions can be carried out.
5.3 Vacuum station
(1) The vacuum station represents the building that will house the following equipment:
a) vacuum recipients;
b) vacuum pumps;
c) pumps that collect wastewater;
d) operating systems;
(2) The dimensions of the building shall be established depending on the distances
between the various pieces of equipment and the distances required in order to enable the access
of operating personnel.
5.3.1 Vacuum recipients
(1) The volume shall be determined as follows:
Vo = 0.06 x Quz x tR (m3)
where:
Quz – wastewater discharge rate (maximum hourly rate), (dm3/s);
tR – the retention time, in minutes, shall be considered to be 15 min.
Vo – usable volume of the catchment basin, (m3).
(2) The chosen volume shall be:
a) VT = 3 x Vo – for small-size systems;
b) VT = 2 x Vo – for large-size systems.
(5.2)
5.3.2 Vacuum pumps
(1) The vacuum pumps shall be chosen on the basis of the ratio R = Qair/Qwater; it is
recommended that R = 6/1 - 12/1.
Qpv = Quz. or. max (m3/h) x R x 1.5 (m3/h)
(5.3)
(2) At least the following shall be chosen: 1+1 vacuum pumps with Qpv and the vacuum
pressure: 0.6 – 0.7 bar.
(3) The air discharged by the vacuum pumps shall pass through an activated carbon filter.
5.3.3 Time required to produce the vacuum
𝑉
𝑡𝑠
𝑇 = 0,7 𝑥 2 𝑥𝑄
≤ 5 𝑚𝑖𝑛
𝑝𝑣
(5.4)
where:
Vts– volume of the vacuum system, (m3);
Qpv – capacity of the vacuum pump, (m3/h).
Vts = Vnetwork + Vrec (m3)
(5.5)
Vnetwork– volume of the vacuum network, (m3);
Vrec– volume of the vacuum recipient, (m3).
5.3.4 Daily operating time of the vacuum pumps
Tp vac = Qavr.us.day x R/Qpv ≤ 5 h/day
(5.6)
where:
Tp vac – operating time of the vacuum pump;
R – air/water ratio.
5.4 Requirements for choosing the design of the vacuum sewerage networks
a) These requirements shall apply to site sections limited to 1,500 –2,000 EI, and a
maximum total length of the network collectors ΣLi ≤ 5 km; the pipe sections for a
vacuum network shall be chosen based on the difficulties that the nature of the terrain
and the presence of underground water may create when building a gravity network,
as well as in light of the subsequent intervention difficulties that may arise due to the
high pipe-laying depths (≈ 5.7 m);
b) The solution shall be chosen, on the basis of a technico-economic analysis of all
options, from among: a gravity network which ensures the required self-cleansing
velocity by creating abrupt slopes and using several pumping stations, and a vacuum
network; the investment costs, energy consumption and operating costs shall be taken
into consideration, together with the set of works that need to be carried out,
including transportation of the wastewater to the water treatment plant;
c) The specific energy consumption (kWh/m3 wastewater) shall be limited to a
maximum of 0.2-0.3 kWh/m3 wastewater;
d) The valve for automatic loading of the vacuum network shall be chosen based on at
least 2 options, taking into account the operating safety and the guaranteed number of
duty cycles (min. 250 x 103 cycles);
e) It is essential to ensure that qualified personnel are used.
5.5.
Pressure sewerage networks
(1) Objective: To collect and transport wastewater through a hydraulic system which prevents
the settling of deposits in areas with flat terrain, very low dips in areas of depression or with
counter-slopes where the other types of sewage systems cannot be implemented.
(2) Intended use: Separate wastewater sewerage network.
5.5.1. Components
a) Gravity pipe fittings connecting to the sources of wastewater;
b) Inlet chambers equipped with cutter pumps (pumping stations);
c) Pipe networks operating at p > patm;
d) Pressure generating equipment - cutter pump, installed in the inlet chamber.
e) Automation panel
(3) A pressure sewerage network is a branched network.
Figure 5.5 shows the diagram of a pressure sewage system.
Figure 5.5 Diagram of a pressure sewerage network (branched network).
1 – Water users
2- Inlet chamber and pressure generating equipment (collector manhole and electric pump);
3 - Check valve (Manhole with check valves);
4 - Pressurised pipe connecting the inlet chamber to the main network;
5 - Gravity pipe fitting connecting to the sources of wastewater;
6 - Main pressure sewerage network
7 - Manhole for discharging the water into a main collector or the water treatment plant
5.5.2. Design requirements:
(4) The operating concept of a pressure sewerage network - branched network.
One or more buildings can be connected to one inlet chamber. The maximum number of
buildings shall be limited depending on the capacity of the pressure generator.
Figure 5.6 Diagram of a pressure sewage system
1.
2.
3.
4.
Gravity sewage pipe fitting
Pressure generating equipment - electric pump
Inlet chamber - manhole
Pressure sewerage network
5.5.2.1.
Pipes
(5) The dimensions of the pipes used within the sewerage network shall be calculated so
that the minimum flow velocity of the water through the pipes corresponds to the values given
in Table 5.2.
Table 5.2. Minimum flow velocities
Item
No
Nominal
diameter
[mm]
Minimum
velocity
[m/s]
1
32-100
0.70
2
150
0.80
3
200
0.90
4
250
0.95
5
300
1.00
6
400
1.10
(6) The minimum permissible diameters shall be equal to 32 mm; these shall be used for
the pipe fittings connecting the pumping stations to the main network.
5.5.2.2.
Calculation of the system
(7) Hypothesis: the minimum velocity through the sewerage pipe network shall be v ≥ 0.7
m/s.
(8) This hypothesis correlated with the minimum diameter shall lead to a minimum
discharge rate of 0.56 dm3/s.
(9) Any inlet manhole which serves a user consisting of at least 2 persons shall have to be
equipped with an electric pump with a minimum capacity of 2.025 m3/h.
a) Determination of the pipe section diameters and pumping height.
b)
(10) The continuity equation shall be used to determine the flow rates for each pipe
section, by adding up the capacities of the pumping stations located at the user end. The
diameters shall be chosen based on the recommended velocities given in Table 5.2.
(11) The pumping height of the electric pumps responsible for pumping the wastewater in
node "i" shall be:
k


H p   C (pk )   h r   h racord   C imin
i


where:
C(pk ) - the piezometric level in the downstream node (k);
k
h
r
- the sum of the distributed and local load losses for the pipe section i-k
i
h
- the sum of the hydraulic load losses along the connecting pipe in the pumping
station which injects into node i
The hydraulic load losses shall be determined as follows:
v 2  L

 h r  2g  D    i 
racord
where:
v – average velocity through the pipe (i-k); [m/s]
 - coefficient of loss of distributed load (shall be determined using the Colebrook- White
formula);
L - length of the pipe section [m];
D - nominal diameter of the pipe section [m];
 i - sum of the local load loss coefficients; valve, elbows, reducing pieces, needle
valves, etc.
(12) If a large number of users are connected to the same manhole (inlet chamber) and if
there is a large number of such manholes installed on one branch of the network, the simultaneity
diagram shown in Figure 5.7 shall be used, obtained on the basis of statistical data recorded
during the operation of the existing pressure sewerage networks.
(13) The prerequisite for the operation of the network shall be that the minimum and
optimum velocities are ensured through the pipe sections of the network.
Figure 5.7 Simultaneity diagram
5.5.3. Inlet chamber:
(14) The usable capacity of the collection chamber shall be determined based on the
number of users connected to the network, the specific
restitution, in accordance with the
3
standards, considering that the usable volume is 30% of Qaver.us.day; it shall be considered that
the pump inside the manhole will not be activated/deactivated more than 8-10 times/day; an
emergency capacity (25% of the usable capacity) shall be added to cover for special situations
2
(power failure).
A
A
(15)
The essential elements of a collection chamber shall be:
• Level gauges installed in the collection space, for the1 automatic control of electric pumps
• Closing elements and non-return valves
4
• Ventilation
All the components must be suitable for use in residual water.
Figure 5.8 shows a diagram of a collection chamber.
5.5.4. Pressure generating equipment (electric pump):
(16) The pressure generating equipment shall be of the electric cutter pump type; this shall start
automatically when a preset maximum level is reached and shall stop automatically after a few
seconds, when the entire quantity of water accumulated in the inlet chamber has been
discharged. The provisions stipulated in Chapter 7.8 of this normative document shall be
complied with.
5.5.5. Pipe network:
(17) The pipes shall be laid in accordance with the provisions stipulated in SR EN 805:2000
The following requirements must be complied with when laying down the pipes of a pressure
sewerage network:
- all routes shall have continuous, upward or downward slopes between the low and high
points;
- man-lock elements shall be installed at all low points (in manholes) to enable
machinery/instruments to access the network in order to inspect/cleanse the adjacent pipe
section;
- all high points shall be fitted with vents or systems for the intake/discharge of air when
the pipes are being filled or drained;
- one-way valves shall be installed in all nodes located upstream from the user junction to
ensure that the wastewater flow in a single direction;
- the pressure pipe system shall be leak tested in accordance with the provisions stipulated
in SR EN 805:2000
1. - Inlet chamber and pumping station
2. - Pipe fitting connecting the inlet chamber
to the network
2.a - Backwater pipe
2.b – Check valve
2.c - Hose assembly
3. - Gravity pipe fitting at the user end
4. - Ventilation
5. - Check valve control lever
6. - Inlet chamber cover
Figure 5.8 Diagram of the inlet chamber
and pressure generating equipment
5.5.6. Pipes and pipe couplings.
(18) Pipe couplings shall have a smooth inner surface without any distortions, to prevent
deposits and clogging.
Negative pressure pipes shall be resistant to:
- interior and exterior chemical and biochemical influences,
- temperatures up to 35 °C,
- mechanical abrasion,
- internal and external pressure.
(19) In addition, special stresses shall also be taken into consideration. All pipes and fittings
on the pressure pipes shall have a rated pressure of at least 10 bar.
5.5.7. Closing elements
(20) Valves (cocks) shall be installed to enable maintenance, locate any leakages and allow
interventions to each pipe section.
(21) The valves (cocks) used in a pressure sewerage network shall be protected against
corrosion or be corrosion resistant, and shall ensure a smooth passage. Threaded rods shall be
made of materials resistant to corrosion
5.5.8. Requirements for choosing the design of the pressure sewerage networks
a)
These requirements shall apply to sites limited to 10,000 EI; the pipe sections for the
chosen pressure sewerage network shall be selected depending on the difficulties that
the configuration of the terrain and the presence of underground water may create
when building a gravity network, as well as in light of the subsequent intervention
difficulties that may arise due to the high pipe-laying depths (5 - 7 m)
b) the solution shall be chosen following a technico-economic analysis of the options,
from among:
- a gravity network which ensures the required self-cleansing velocity (0.7
m/s) by creating abrupt slopes and using several pumping stations;
- a pressure sewerage network
Both options shall take into account:
- the specific energy consumption [kwh/m3 wastewater)
- the annual operating costs, taking into consideration the maintenance
interventions required for a set period of time (10 years);
- investment costs
c)
ensuring that the sewerage network is operated by qualified personnel who will
inspect the condition of the pumping equipment and the components of the pressure
sewerage network
6. Discharge outlets
(1) Discharge outlets are structures used to discharge the purified water into natural
drainage basins.
(2) The shape and dimensions of the discharge outlets shall depend on the size of the
drainage basin, as well as the quantity and quality of the water being discharged.
(3) Drainage outlets shall comply with the following requirements:
a) To ensure hydraulic conditions that would enable mixing with the water inside the
drainage basin;
b) To not be flooded when the water level of the river is high;
c) To not damage the banks and bottom of the drainage basin or affect in any other way
the normal drainage process of the basin;
d) Discharge outlets should be located at a 30–45º angle with the water flow direction of
the drainage basin;
e) The discharge outlets needed to discharge the wastewater collected from the division
sewerage network and the unitary sewerage network, treated either mechanically or
biologically, shall have to ensure the best possible dispersion of the sewage water into
the drainage basin.
(3) The foundation frame of the discharge outlet shall be located at a suitable height from
the bottom of the drainage basin, to prevent clogging of the channel by suspended matter from
the drainage basin.
(4) A concrete wall shall be built in the section where the channel ends, to consolidate the
connection between the channel and the corresponding river bed.
(5) The bottom and banks of the drainage basin shall be reinforced for a distance of at
least 10 m upstream and 30 m downstream from the discharge point.
(6) The structural safety and stability of the entire structure shall be ensured by protection
systems provided for all possible flow rates and levels of the river.
(7) Drainage pipes shall be laid on the bottom of emissaries with large capacities to
discharge the water as close to the thalweg as possible; this shall enable the 2 types of water to
mix completely and rapidly, and prevents the pollution of the emissary near the bank.
3
2
A
A
1
Sectiunea A-A
4
1
5
4
Figure 6.1. Example of a discharge outlet.
1-concrete tubes; 2- drainage basin; 3-revetment;
4-riprap; 5-access chamber.
Annex 1
IDF (Intensity - Duration - Frequency) curves
for zone 8, in accordance with STAS9470-7
Rainfall intensity
(l/s,ha)
Rainfall intensity
(mm/min.)
Rainfall duration
Anexa 2
Q (dm³/s)
1
2
3
4
5 6 7 8 9 10
20
30
200
500 700 900
300 400
600 800 1000
Dn
50
mm
0.6
0.5
0.0004
0.0002
m
0.4
/s
0.004
0.003
0.002
0.001
0.0009
0.0008
0.0007
0.0006
0.0005
0.0004
0.3
1
2
3
4
5 6 7 8 9 10
20
30
40 50 60 7080 100
90
0.0003
18
00
20
00
22
0
24 0
0
26 0
28 00
00
30
00
v=
0.2
0.0003
0.01
0.009
0.008
0.007
0.006
0.005
12
00
0.7
900
10
00
0.8
0.001
0.0009
0.0008
0.0007
0.0006
0.0005
700
400
450
500
300
350
250
0.002
800
200
150
125
0.003
0.02
3.
2.80
2.6
2.4
2.2
2.0
1.9
1.7
1.
1.56
1.
1.34
1.2
1.1
1.0
0.9
600
100
80
0.004
0.0001
0.03
3.5
0.01
0.009
0.008
0.007
0.006
0.005
i
0.04
4.0
65
0.02
0.09
0.08
0.07
0.06
0.05
v=
5m
4.5 /s
0.04
0.03
2000
5000 7000 9000
3000 4000 6000 800010000
14
15 00
16 00
00
0.1
0.09
0.08
0.07
0.06
0.05
Annex 2
90
40 50 60 7080 100
200
300 400
600 800 1000
500 700 900
2000
0.0002
0.0001
3000 4000 6000 800010000
5000 7000 9000
(dm³/s)
Calculation diagram for pipes made of plastic Qand
composite materials, n=0.01 - 0.0111, k=1/n=90 - 100.
Diagrama de calcul pentru conducte din materiale plastice dupa relatia Manning (n=0.01, k=1/n=100)
i
Anexa 3
Annex 3
Calculation diagram for pipes made of cast iron, steel and cement-washed reinforced concrete. K=83
Annex 4
Profil circular
Circular profile
Detaliu pentru curba debitelor
Detailed drawing of the flow rate curve
Profil ovoidal
Ovoid profile
Filling curves: variation
and
as a function of the degree
of filling for circular/ovoid collector sections
Annex 5
PLOTTING OF IDF CURVES
1. General considerations
(1) A punctual rainfall is the rainfall recorded at the station. The probability of
exceedance P% of the maximum rainfall or its intensity at the station is represented as
frequency (1:T) or as the average recurrence interval T.
𝑃=
1
𝑇
or 𝑇 =
1
𝑃
(2) To enable the statistical processing of the rainfall, a partial series containing the
extreme values of the rainfall with the duration D shall be determined using one of the
following methods:
a) By selecting the annual maximum rainfall events with the duration D, which leads to
a number of statistical sequence values equal to the number of years for which data
was recorded.
b) By selecting the annual maximum rainfall events with the duration D, which exceed
a certain threshold (Peaks Over Threshold - POT); this way, 2 or even more
exceptional rainfall events shall be selected, whilst for other years no value will be
selected. The threshold from which the maximum rainfall will be considered shall be
an arbitrary variable, but the number of resulting values should be equal to the
number of years for which measurements are carried out. The partial data series
obtained with the POT method must consist of independent elements, which means
that the selected peak values must be separated by a rain-free period. According to
various authors, its size varies between 1 hour and 1-6 days; as a compromise, a rainfree period of 1 day shall be considered sufficient.
(3) After the statistical processing of the maximum rainfall events for various durations
D, the results shall be represented on a diagram with time on the x-axis and intensity on the yaxis. The IDF curves shall be obtained by joining all the points corresponding to the same
probability of exceedance (frequencies), and each curve shall correspond to a certain frequency
or average recurrence interval.
(4) The IDF curves help calculate the average intensity of the rainfall corresponding to a
frequency given for a range of rainfall durations. These shall be used, for basin surface areas of
less than 10 km2, to determine the size of urban sewerage networks or basins for the temporary
retention of excess rainfall that cannot be discharged by the network during the rain.
(5) If using the maximum rainfall events for various durations D to calculate the IDF
curves, it will be necessary to continuously record the volume of rainfall fallen over a period of
at least 30 years. Stations with less than 20 years of records shall use the POT method, so that
the sequence of maximum rainfall events with a duration D contains at least 30 values. In
stations where data for certain periods are missing, but which hold data for a total period of 20-
30 years, the missing data up to 30 years shall be supplemented by making correlations with the
neighbouring stations or stations in similar regions, or the POT method can also be used. The
POT method can also be used if the number of years for which recorded data are available
exceeds the threshold of 30 years.
(6) The main issue with the POT method is that, if a number of rainfall events is
selected that differs from the number of years, the average sampling interval can have any
duration, shorter or longer than one year, depending on whether the number of rainfall events
being selected is smaller or larger than the number of years. Therefore, the theoretical
probabilities corresponding to a maximum rainfall event for an interval other than one year
must be converted into annual exceedance probabilities. If the annual exceedance probability is
noted with P1% and Pd% is the notation used for the probability of exceedance corresponding to
the rainfall value calculated for the variable d of the average calculation interval, the passing
relationship shall be:
𝑛
𝑃𝑑 =
𝑃
𝑚 1
where:
m is the number of rainfall events taken into consideration, and n is the number of years.
Another relationship used to calculate the probability Pd %, which can be applied both when m<n, as
well as when m>n is the following:
𝑃𝑑=𝑛/𝑚 = 1 − (1 − 𝑃1 )𝑛/𝑚
These additional calculation problems can be resolved, in principle, if the number of rainfall events
selected is equal to the number of years of the design period.
(7) The partial data series used for the statistical analysis must be homogeneous and stationary.
The following significance tests should be used:
 data independence (Wald-Wolfowitz test)
 homogeneity (Mann-Whitney test, Wilcoxon test)
 stationarity (Mann-Kendall test, recommended by WMO).
(8) If the data set is non-homogeneous or displays a trend, it must be divided into homogeneous
sub-sets, or the POT method must be used for the recent data set, with several peaks during certain years,
to ensure that at least 30 values are available.
(9) The Weibull formula should be used to calculate the empirical distribution:
𝑃𝑖𝑒 =
𝑖
𝑛+1
where:
n is the number of years (intervals) in the design period.
(10) The following can be used as theoretical distributions:
a) The type I (Gumbel) General Extreme Values (GEV) distribution for the partial series of
annual maximum rainfall events with the duration D
b) The General Pareto Distribution(GPD) for the partial series of maximum rainfall events with
the duration D over a certain threshold.
(11) In general, the theoretical distribution parameters shall be estimated using the moments
method, the weighted moments method or the maximum likelihood method.
2. Algorithm for plotting the IDF curves using the annual maximum
rainfall events with a duration D
(12) We take ℎ𝑖,𝑗,𝑘 as the cumulative rainfall, expressed in mmHg, at the moment i during the
rainfall event j that took place in year k.
(13) 𝐷𝑙 is considered the notation for the design rainfall duration, considered as a multiple of the
time step ∆𝑡 used to record the rainfall events as such,
, where is a natural number.
a) The height of the layer of water which falls during the rainfall event j that took place in the
year k during the
design rainfall, between moments
and
, shall be
obtained with the following relationship:
where
b) The maximum height of the layer of water which falls for the duration
during the rainfall
event j that took place in the year k shall be obtained by looking for the maximum value
amongst the calculated values:
c) Then, scanning the multitude of rainfall events j that took place in the year k, the annual
maximum height of the layer of water which falls during the interval
shall be
calculated:
d) The resulting values of the maximum rainfall events with the duration
shall be turned into
intensities by dividing them by the rainfall duration, equal to the concentration time :
Intensity is usually expressed in mm/minute or l/s ha.
e) For each duration , the resulting sequence shall be processed statistically and the intensity
of the rainfall events with probabilities of exceedance (expressed in the form of frequencies
or average recurrence intervals) shall be determined.
f) In the end, the values corresponding to the same frequency (average recurrence intervals)
shall be joined by a curve, creating a family of Intensity – Duration – Frequency (IDF) curves
corresponding to the frequencies 1:T (or the average recurrence intervals T) taken into
consideration.
3. Algorithms for plotting the IDF curves by using rainfall events with a
duration D above a given threshold
(1) The notations
(cumulative rainfall at the moment i during the rainfall event j
that took place in the year k) and (design rainfall duration) shall have the same meaning as in
the previous paragraph. Also, the first and last 2 steps shall be the same as in the algorithm that
uses the annual maximum rainfall events with a duration . For simplicity, the entire algorithm
is presented.
a) The height of the layer of water which falls during the rainfall event j that took place
in the year k during the
design rainfall, between moments
and
,
shall be obtained with the following relationship:
where
b) The calculation presented in step 1 shall be repeated for all the rainfall events j that
took place in the year k, , gradually processing all the design years.
c) The resulting aggregate of value shall undergo concatenation, after which it shall be
organised in a descending order.
d) The first n values shall be kept from the resulting aggregate, where n is the number of
design years.
e) The independence of the retained values shall be checked, which means that two
values of the rainfall with a duration
cannot belong to the same rainfall event, as
they must be separated by a rain-free period. If it is found that two rainfall values are
not independent, the lowest value shall be excluded and replaced with the first value
in the sequence remaining after the processing operations described in step 4 and 5,
respectively (if other similar situations occurred during the process described at this
step).
f) The resulting values of the maximum rainfall events with the duration
above a
given threshold shall be turned into intensities by dividing them by the rainfall
duration, equal to the concentration time :
where:
is the value with the rank k in the descending sequence of rainfall events with
a duration
above a given threshold (resulting from the requirement to retain n independent values
of the design rainfall).
In this case, it can be noted that the index
no longer represents the current year,
but the current value of the rainfall above the given threshold.
g) For each duration , the resulting sequence shall be processed statistically and the
intensity of the rainfall events with probabilities of exceedance (expressed in the form
of frequencies or average recurrence intervals) shall be determined.
h) In the end, the values corresponding to the same frequency (average recurrence
intervals) shall be joined by a curve, creating a family of Intensity – Duration –
Frequency (IDF) curves corresponding to the frequencies (average recurrence
intervals) taken into consideration.
4. Determination of the rainfall volumes in points without measurements
(1) For low-capacity basins (less than 10 km2) for which measurements are not
available, a regional analysis shall be employed using data from neighbouring stations located
no further than 25-30 km away. One of the following procedures can be used:
a) inverse square weighting of the distance to the nearest stations;
b) performing an analysis of the regional variability of the statistical parameters;
4.1. Inverse square weighting of the distance to the nearest stations
4.2.1. In an initial phase, the statistical parameters for the chosen distribution shall be
determined for all N stations located in the vicinity of the site for which measurements are not
available.
4.2.2. Then, each statistical parameter at the location for which measurements are not available
shall be estimated as the mean of the values of the same parameter at the neighbouring stations,
weighted by the inverse square value of the distance from these stations:
where:
is the value estimated at station i for parameter
,
- the distance-weighted mean of the values of the same parameter
– distance from station i to the site (identified by 0)
4.2.3. In a more advanced approach, the number
of values recorded at each station shall also
be taken into consideration, the estimated parameter
being:
A weighting relationship by the distance and by the number of values recorded at each station
shall have the following relationship:
where:
is a weighting factor of the two estimators:
and
.
If
, only the distance from the site shall be of significance when estimating the
unknown parameter, and if
only the length of the data sequence recorded at the stations
shall be significant. For intermediate values of , the redundancy of the two estimators shall be
used to obtain a better estimate of the desired parameter.
The value of the weighting parameter shall be obtained by calculating, for different
values of , the parameter
at the stations where its value is known, by only using the values
from the other stations and then comparing the resulting values of the desired parameter with
the known values of the same parameter. This analysis shall serve as the basis for choosing the
best weighting parameter
4.2 Analysis of the regional variability of the statistical parameters
4.2.1. This method shall be used if the spatial correlation between the annual maximum
rainfall values can be ignored. To verify this hypothesis, the correlation coefficients for the
annual maximum values from the neighbouring stations shall be calculated. If the correlation
between the coefficients and the distance between the stations is low, it can be concluded that
there is no spatial correlation between the annual maximum rainfall values. For the POT
method, the degree of association shall have to decrease with the size of the threshold.
4.2.2. Another requirement for applying this method is that the statistical parameters
must be relatively equal within the analysed region.
4.2.3. Taking
as the value of one of the statistical parameters of the distribution
analysed for the station
The equality of the parameters
can be analysed by
calculating the following statistical value:
where:
is the value estimated for parameter
the same parameter with the number of values
, and
is the weighted mean of the values of
measured at station i:
The statistical value
shall be calculated for various durations shorter than the
concentration time of the rain fallen over the studied basin.
If there is no spatial dependency between the maximum rainfall values or this
dependency is low, for the null hypothesis
=.... =
the statistical value
shall have a
distribution with N-1 degrees of freedom.
4.2.3. The equality of the parameters can also be verified by making correlations
between the parameters from the N stations and the average multi-annual rainfall value. The
slope of the regression line for each rainfall duration must be very close to zero (e.g. below the
value corresponding to a 5% significance threshold for the Student test).
4.2.4. If the spatial dependency between the maximum values is low and the distribution
parameters do not display a spatial variation, then the time series of the rainfall values from all
stations in the analysed area can be concatenated and analysed as if they formed a single
sequence. The statistical processing of this sequence shall lead to the precipitation values or the
intensities with the desired exceedance probability (frequency).
5. Statistical distributions used.
5.1 Gumbel distribution (EVI)
5.1.1. The Gumbel or Extreme Value type I (EVI) distribution is widely used to analyse
the annual maximum rainfall events and has the distribution density:
the complementary distribution function (probability of exceedance):
5.1.2. The parameters
and
can be expressed as a function of the mean square
deviation and the mean value of the sequence of maximum rainfall events with a duration
D, using the following relationships:
where:
mean
,
and the selected mean square deviation
It can be noted that parameter is positive. Parameter u represents the distribution method (the
variable value for which the distribution density is maximum).
5.1.3. The complementary distribution function shall be invertible, which means that it enables
determination of the quantile
corresponding to the probability of exceedance P% (frequency 1/T and
the mean recurrence interval T, respectively):
After determining the parameters and using the mean and mean square deviation of the
selected sequence of values, the previous relationship can be used to directly determine the value of the
rainfall or its intensity for frequency 1/T.
5.1.4. Normally, in practice, the calculation shall be simplified by defining the reduced variable:
By replacing the reduced variable in the formula for the probability of exceedance, it results
that:
The following shall be obtained by solving the equation as a ratio of y:
The resulting relationship shall be replaced in the formula of the reduced variable , giving the
quantiles corresponding to the recurrence interval T:
5.1.5. The calculation procedure is the following:
a) The statistical parameters and
shall be calculated (the mean value and the mean square deviation
for selecting the statistical sequence of maximum rainfall events or their corresponding intensities)
b) Then, the parameters and u of the Gumbel distribution shall be determined
c) The value of the reduced variable
shall be calculated as a function of T
d) These elements shall be used to calculate the value of the quantile which corresponds to the mean
recurrence interval T.
5.2. Generalised Extreme Value (GEV) distribution
5.2.1. The Gumbel distribution can be used with good results for relatively short
recurrence intervals (up to 10 years). Instead, it underestimates the quantiles corresponding to
long recurrence periods. In this situation, the alternative is to use the Generalised Extreme
Value (GEV) distribution that best describes the distribution in the high value region due to an
additional parameter. Large datasets are necessary to estimate the shape parameter correctly. It
shall also be possible to use data from several stations in the area, if adopting the hypothesis
that the shape parameter is constant or varies only slightly throughout the area.
5.2.2. The Generalised Extreme Value (GEV) distribution shall have the following
formula of the distribution function:
where:
k, u and
are the parameters that need to be determined.
5.2.3. The GEV distribution combines 3 extreme distributions into a single distribution.
For the value
, the Gumbel or Extreme Value type I (EVI) distribution shall be
obtained. For
, the EVII (Fréchet) distribution shall be obtained, whereas
shall
lead to the EVIII (Weibull) distribution.
5.2.4. Since the function
is invertible, the quantile
representing the variable value
corresponding to the mean recurrence interval T shall be obtained with the following relationship:
where:
is the mean recurrence interval.
5.2.5. The L-moments method should be used to determine the GEV distribution parameters for
the annual maximum values. Initially, the weighted moments shall be calculated, with the probability:
where:
represents the annual maximum values in a descending order.
The L-moments for the selection shall be obtained with the following relationships:
The estimated value
where:
of the shape parameter shall be obtained with the following relationship:
The estimated values for
and u shall be:
where  (.) is the Gamma function.
5.3 Generalised Pareto Distribution (GPD)
5.3.1. The Generalised Pareto Distribution (GPD) shall have the following formula of the
distribution function:
for
for
where:
c is the lower distribution limit, b is the scale parameter, and a is the shape parameter.
5.3.2. The distribution density shall be:
for
for
5.3.3. Since the function
is invertible, the quantile
representing the variable value
corresponding to the mean recurrence interval T shall be obtained with the following relationship:
for
for
and
and
where:
is the mean recurrence interval. Then, the quantile
a, b and c.
shall be calculated using the parameters
5.3.4. The parameters a, b and c can be calculated using the moments method, by equalising the
theoretical moments with the empirical moments:
where:
the mean
the dispersion
the asymmetry G
is the rank 1 moment
is the rank 2 moment
is the rank 3 moment.
Initially, the parameter a shall be obtained by solving the last equation. The other 2 parameters
can then be calculated as a function of a, with the following relationships:
5.3.5. The parameters a, b and c can also be calculated using the weighted moments method,
using the formulas:
where:
is the weighted moment with the rank r (
and has the expression:
5.3.6. Finally, parameters a, b and c can be calculated using the maximum likelihood
method, by solving the system:
5.3.7. For low asymmetry, better results can be obtained with the moments method and
the weighted moments method, whilst the maximum likelihood method should be used for high
asymmetry values.
LEGISLATION
Item Title of the normative document
no.
1.
Water Law No 107/1996, with its subsequent
modifications and supplementation.
2.
Order No 161/2006 for approval of the Normative
document for classifying the quality of surface water in
order to determine the ecological condition of bodies of
water,
3.
Order No 756/1997 of the Ministry of Water, Forests and
Environmental Protection approving the Regulation on
the assessment of environmental pollution, with its
subsequent modifications
4.
Government Emergency Ordinance No 152/2005 on the
prevention and integrated control of pollution, with its
subsequent modifications
5.
Government Emergency Ordinance No 195/2005 on
environmental
protection,
with
its
subsequent
modifications
6.
7.
8.
Government Decision No 188/2002 for the approval of
standards laying down requirements for the discharge of
wastewater into the aquatic environment, with its
subsequent modifications and supplementation
1. Technical standard regarding the collection, treatment
and discharge of urban wastewater, NTPA-011
2. Normative document laying down requirements for the
discharge of wastewater into municipal sewage systems
and directly into water treatment plants, NTPA-002/2002
3. Normative document establishing the pollutant load
limits for industrial and urban wastewater upon its
discharge into natural drainage basins, NTPA-001/2002
Directive 91/271/EEC concerning urban wastewater
treatment, amended and supplemented by Commission
Directive 98/15/EC, transposed by Government Decision
No 188/2002 for the approval of standards laying down
requirements for the discharge of wastewater into the
aquatic environment, with its subsequent modifications
and supplementation
Publication
Official Gazette, Part I, no. 244 of 8
October 1996
Official Gazette, Part I, No. 511 of 13
June 2006
Published in the Official Journal, Part I,
No 303 of 06 November 1997
Published in the Official Journal, Part I,
No 1196 of 30 December 2005
Published in the Official Journal, Part I,
No 1078 of 30 November 2005
Published in the Official Journal, Part I,
No 187 of 20 March 2002
Published in the Official Journal of the
European
Communities
No
L135/30.05.1991 and No L67/29,
07.03.1998
Directive 86/278/EEC on the protection of the Published in the Official Journal of the
environment, and in particular of the soil, when sewage European Communities No L181/6,
sludge is used in agriculture, transposed into the national 12.06.1986
legislation by
Joint Order No 344/708/2004 of the Ministry of the
74
9.
10.
11.
Environment and Water Management and the Ministry of
Agriculture, Forests and Rural Development for the
approval of Technical standards on the protection of the
environment, and in particular of the soil, when sewage
sludge is used in agriculture, with its subsequent
modifications and supplementation
Directive 91/676/EEC concerning the protection of
waters against pollution caused by nitrates from
agricultural sources, transposed by Government Decision
No 964/2000 for approval of the Action plan for the
protection of waters against pollution caused by nitrates
from agricultural sources, with its subsequent
modifications and supplementation
Directive 2000/76/EC on the incineration of waste,
transposed into the national legislation by
Government Decision No 128/2002 on the incineration of
waste, with its subsequent modifications and
supplementation
Published in the Official Journal, Part I,
No. 959/19.04.2004
Published in the Official Journal of the
European Communities No L 375,
31.12.1991
Published in the Official Journal, Part I,
No. 256/25.10.2000
Published in the Official Journal of the
European Communities No L 332,
28.12.2000
Published in the Official Journal, Part I,
No.160/6.03.2002
Published in the Official Journal of the
Directive 2006/12/EC on waste, transposed by European Communities No L 114/16,
Government Emergency Ordinance No 78/2000 approved 27.04.2006
with modifications and additions by Law No 426/2001, Published in the Official Journal, Part I,
with its subsequent modifications and supplementation
No. 28 /22.06/.000
STANDARDS
Item
no.
Code
1.
SR 1343-1:2006
2.
SR 1846-1:2006
3.
SR 1846-2:2007
4.
5.
SR 8591:1997
SR EN 752:2008
6.
SR EN 295-2:1997
7.
SR EN 2952:1997/A1:2002
8.
SR EN 124:1996
9.
SR EN 1917:2003
10.
SR EN 1899-2:2002
Name of standard
Water supply. Part 1: Determination of the quantities of drinking water
necessary for urban and rural localities
Outdoor sewage systems. Design requirements. Part 1: Determination
of wastewater sewage discharges
Outdoor sewage systems. Design requirements. Part 2: Determination
of stormwater discharges
Underground public utility systems. Siting requirements
Outdoor sewerage networks.
Vitrified clay pipes and fittings and pipe joints for drains and sewers.
Part 2: Quality inspection and sampling
Vitrified clay pipes and fittings and pipe joints for drains and sewers.
Part 2: Quality control and sampling
Gully tops and manhole tops for vehicular and pedestrian areas.
Design principles, type model tests, marking, quality inspection
Concrete manholes and inspection chambers, unreinforced, steel fibre
and reinforced
Water quality. Determination of biochemical oxygen demand after n
75
11.
SR ISO 6060:1996
12.
SR EN 25663:2000
14.
SR EN ISO
6878:2005
STAS 9470-73
15.
STAS 6054-77
16.
STAS 4273-83
17.
18.
STAS 6701-82
STAS 2448-82
19.
STAS 6953-81
20.
STAS 12264-91
13.
22.
SR EN 1991-1-4:
2006/NB 2007
STAS 4162/1-89
23.
STAS 3051-91
21.
days (BODn). Part 2: Method for undiluted samples-OUTSIDE
Water quality. Determination of the chemical oxygen demand.
Water quality. Determination of Kjeldahl nitrogen. Method after
mineralisation with selenium.
Water quality. Determination of phosphorus. Ammonium molybdate
spectrometric method
Hydrotechnics. Maximum rainfall. Intensities, durations, frequencies
Foundation ground. Maximum freezing depths. Zoning of the territory
of the Socialist Republic of Romania
Water engineering structures. Classification into categories of
importance
Sewage systems. Discharge openings with siphon and deposit
Sewage systems. Manholes. Design requirements
Surface water and wastewater. Determination of suspended matter,
loss of ignition and calcination residues.
Sewage systems, oil and grease separators for municipal wastewater
treatment plants. General design requirements
Eurocode 1. General actions on structures. Part 1-4: General actions –
Wind actions. National Annex.
Sewage systems. Primary settling tanks. Design requirements
Sewage systems. Channels of external sewage systems. Fundamental
design requirements
Note:
1. the given references were taken into account when drawing up the technical regulation
2. on the date when the technical regulation is used, the latest edition of the applicable standards shall be used as
reference
76