Blackhead Consulting (Pty) Ltd
Tel : 011 958 0054
Email : hiltonsparks@blackhead.co.za
GAUTENG DEPARTMENT OF
HUMAN SETTLEMENTS
DIEPSLOOT EAST EXT 0
ENGINEERING SCHEME REPORT WATER
AND SEWERAGE
TITLE
GAUTENG DEPARTMENT OF HUMAN
SETTLEMENTS
DIEPSLOOT EAST EXT 0
ENGINEERING SCHEME REPORT WATER AND
SEWERAGE
CLIENT
Gauteng Department of Human Settlements
14th Floor
1066 Building
35 Pritchard Street
Johannesburg
Tel: +27 11 630 5000
PREPARED BY :
Blackhead Consulting (Pty) Ltd
9 Willowbrook Office Park
Van der Kloof Street
Ruimsig
1732
DATE
24/02/2014
REFERENCE NUMBER
2014/001
Engineering Scheme Report Water and Sewerage
PROJECT TEAM
H D N Sparks
__________________
PR Eng No 740604
REVISION
DATE
DESCRIPTION
1
9 JANUARY 2014
ORIGINAL
2
24 FEBRUARY 2014
FINAL
TABLE OF CONTENTS
1. INTRODUCTION ............................................................................................................................................ 5
2. DESCRIPTION OF SITE.................................................................................................................................. 6
2.1. EXISTING DEVELOPMENT ON SITE ................................................................................................................... 6
2.2. TOWN PLANNING .............................................................................................................................................. 6
3. INVESTIGATIONS ..........................................................................................ERROR! BOOKMARK NOT DEFINED.
3.1. GEOTECHNICAL INVESTIGATION ........................................................................................................................ 7
3.1.1. SITE GEOLOGY ................................................................................................................................... 8
3.1.2. FOUNDATION SOLUTIONS ................................................................................................................... 8
3.2. FLOODLINES .................................................................................................................................................. 10
4. EXISTING AND PROPOSED SERVICES .......................................................................................................... 11
4.1. WATER RETICULATION ................................................................................................................................... 11
4.1.1. EXISTING WATER SERVICES ............................................................................................................... 11
4.1.2. PROPOSED WATER SERVICES .......................................................................................................... 13
4.2. SEWER RETICULATION.................................................................................................................................... 14
4.2.1. EXISTING SEWER RETICULATION ........................................................................................................ 14
4.2.2. PROPOSED SEWER RETICULATION ................................................................................................... 14
5. COST ESTIMATES ...................................................................................................................................... 16
5.1. WATER RETICULATION ................................................................................................................................... 16
5.2. SEWER RETICULATION.................................................................................................................................... 16
5.3. SUMMARY OF COST ESTIMATES ...................................................................................................................... 17
6. BULK SERVICE CONTRIBUTIONS ................................................................................................................. 18
6.1. WATER ......................................................................................................................................................... 18
6.2. SEWER ......................................................................................................................................................... 18
LIST OF TABLES
Table 1 – Proposed Land Uses ...................................................................................................................7
Table 2 - Design Criteria for Bulk Water Connection ..............................................................................13
Table 3 - Design Criteria for Water Reticulations ....................................................................................14
Table 4 - Design criteria for Sewer Reticulations ....................................................................................15
Table 5 - Cost Estimate Water Reticulation .............................................................................................16
Table 6 - Cost Estimate Sewer Reticulation .............................................................................................16
Table 7 - Summary of Cost Estimates ......................................................................................................17
APPENDIXES
Appendix 1 - Plans ....................................................................................................................................19
1.
INTRODUCTION
Blackhead Consulting (Pty) Ltd was appointed by the Client, Gauteng
Department of Human Settlements, as the Civil Consulting Engineers for the
compilation of an Engineering Scheme Report for Diepsloot East Ext 0. The
purpose of this report is to establish the civil services and material and design
standards for the proposed development as required by the Johannesburg
Water (JW), a utility of the City of Johannesburg (CoJ).
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2.
DESCRIPTION OF SITE
The site is located east of the Diepsloot Township on portion 119 of the farm
Diepsloot 388 JR, as shown below.
FIGURE 1 – LOCALITY PLAN
2.1.
EXISTING DEVELOPMENT ON SITE
There are no existing developments on the site.
2.2.
TOWN PLANNING
Table 1 below shows the proposed land uses for the township.
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TABLE 1 – PROPOSED LAND USES
Land Use
Area (ha)
Special
Institutional
Private Parking
Public Open Space
Roads
Total
No of stands
40,96
10,40
1,00
6,41
2,77
73,24
39
3
4
3
49
Figure 2 below shows the township layout, which has been approved by the
City of Johannesburg
FIGURE 2 – TOWNSHIP LAYOUT
2.3.
GEOTECHNICAL INVESTIGATION
Africa Exposed Consulting Engineering Geologists conducted the geotechnical
investigation for the Diepsloot East Ext 0 proposed development. The objectives
of the geotechnical investigation were to give information and recommendations
on the following issues:

Recommendations on the most suitable foundations for new
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


structures;
Recommendations on the suitability of in situ material for road and
pavement construction, terraces and general earthworks;
Presence of groundwater and the recommendations on how to deal with it
during construction and operation of the development; and,
Comments of any geotechnical features that may influence the construction
and operation of the development.
Refer to the geotechnical report prepared by Africa Exposed Consulting
Engineering Geologists for specific information on the geotechnical
investigation methodology.
2.3.1.
Site Geology
The site geology is underlain by coarse gritty quartzite of the Langlaagte Quartzite
formation, Johannesburg Subgroup, Central Rand Group, Witwatersrand
Supergroup. Large portions of the site are underlain by poor selected fill to a
depth of 2,4 m thick with a loose to very loose consistency and consist of
abundant fragment in a matrix of ash. Natural occurring transported soils were
identified below the fill. This hillwash consists of fine colluvial sands and clayey
silts of alluvial origin that occur to a depth of up to 2,0 m below ground level.
The area on the western side of the site is underlain by a wetland, which has been
altered and modified by development in the vicinity. The transported soils are
underlain by residual silty sandy soils which are derived from the in situ
decomposition of the quartz bedrock. The upper horizons which include the
imported fill and the transported soils, including the pebble marker that occurs
at an average depth of 1,0 m, will be collapsible and compressible and the
underlying residual quartzite that occurs beyond this depth will be marginally
compressible.
2.3.2.
Foundation Solutions
The foundation solution for each of the zones:
2.3.2.1.
Zone S1
The foundation solution for heavy structures in this zone should be founded on
deep pads or strip footings that can be placed on the dense to very dense
residual quartzite or the very soft rock quartzite at an average depth of 1,2 m
below the current ground level. Bearing pressures have to be limited to 150
kPa. The foundation solution for light structures can be placed on modified
normal strip footings. The external and internal walls of the structures must be
founded on reinforced strip footings that can be placed at an average depth of
0,8 m below ground level. The foundations must be reinforced and construction
may proceed with brick force included between each course in the plinth wall for a
minimum of 6 courses. Articulation joints must be included at all external and
internal doors and openings. Particular attention must be placed on drainage
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precautions and ensuring the competence of water bearing services. Bed
preparation must be done by the removal of in situ soils to a depth of 450 mm
and replaced in 150 mm thick layers with the same excavated material,
compacted to 93% of Mod AASHTO. Bearing pressures to be limited to 50 kPa.
Under individual footings the in situ soils have to be removed to a depth 1,5
times the foundation width or to a competent horizon. Excavated material must
be replaced in 150 mm thick layers with the same excavated material which is
compacted to 93% Mod AASHTO. Bearing pressures have to be limited to 80
kPa.
2.3.2.2.
Zone C2
For modified normal strip footings all the external and internal walls are founded
on reinforced strip footings placed at an average depth of 0,8 m below ground
level. The foundations must be reinforced and construction may proceed with
brick force included between each course in the plinth wall for 6 courses. For the
surface bed preparation, the in situ soils must be removed for 450 mm, and
replaced in 150 mm thick layers with inert material, compacted to a minimum
density of 93% of Mod AASHTO. The allowable bearing pressures not to
exceed 50 kPa.
Under individual footings the in situ soils have to be removed to a depth of 1,5
times the foundation width or to a competent horizon. Excavated material must
be replaced in 150 mm thick layers and compacted to 93% Mod AASHTO
density. For the surface bed preparation, the in situ material must be removed
for 450 mm, replaced in 150 mm layers and compacted to 93% Mod AASHTO
density. The allowable bearing pressures not to exceed 80 kPa.
It is imperative that good site drainage is provided around individual structures and
no excess moisture should accumulate adjacent to foundations.
2.3.2.3.
Zone P (marshy)
Shallow groundwater seepage and the presence of hydrophilic plants indicate a
shallow and permanent perched water table. The soils are loose, silty and
clayey sand, rich in organic matter and of lacustrine origin. It is recommended
that no structures are constructed within this zone, but be developed as open
recreational areas.
2.3.2.4.
Zone P (uncontrolled fill)
A large portion of the south-eastern side of the site was previously used as a
disposal area for ash and domestic waste. The ash is very loose to loose with a
thickness in excess of 2,5 m and significant consolidation can occur.
Structures in this zone must be founded on piles.
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2.4.
FLOODLINES
There is a floodline in the south west section of the development.
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3.
EXISTING AND PROPOSED SERVICES
3.1.
WATER RETICULATION
3.1.1.
Existing Water Services
GLS Consulting, the Master Planners appointed by Johannesburg Water,
compiled a water master plan for the Blue Hills and Diepsloot Water SubDistricts (Ref. JWAT-C-1060-01-00-10209) for Johannesburg Water (JW) in
December 2009. This report and the latest hydraulic models (2013-02) formed
the basis of the water impact study undertaken for the proposed development.
The development is also located within the future Diepsloot West sewer basin
for which GLS compiled a Sewer Network Analysis Report in October 2008
(Report No. JWAT-C-0155-00-01-2008) following which JW appointed GLS to
revise the Diepsloot West master plan to incorporate the proposed Diepsloot
East development and changes to the COJ urban development boundary which
then included the Diepsloot Corridor area. The report submitted to JW was
dated 16 March 2009.
GLS Consulting recently updated the above-mentioned models and master
plans with the latest as-built information and water demands which formed the
basis of this investigation, which included:


Consideration of the latest cadastral layout for Diepsloot East and
adjacent future developments as well as future PWV servitudes, ESKOM
servitudes and proposed road layouts;
An update of the water master to include the option for supplying the highlying parts surrounding the proposed Diepsloot Reservoir from a
proposed tower and not directly from the Rand Water R33 pipeline in
order to improve redundancy and meet the RW Water Supply Abstraction
Requirements.
The water demand for the proposed development, assuming a unit demand for
each of the proposed zoning areas mentioned above as per the JW Design
Guidelines, is estimated to be 6 717 kl/d. This demand translates into a peak
demand of 310 l/s assuming a peak factor of 4 to be applicable. This peak
demand was used in the hydraulic analysis undertaken.
Figure TG_W1 and TG_W2 has reference.
Current Scenario:
The proposed development is currently located adjacent to the Diepsloot West
water sub-district which is currently supplied via a 600 mm dia JW bulk pipeline
directly from the Rand Water R33 pipeline which terminates at RW connection
RW5590.
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It should be noted that the Diepsloot Township has experienced major
densification in the past 3 years with typically up to 4 structures per stand. This
has resulted in a significant increase in water demand increasing from 13 100
kl/d for the year ending September 2009 to 20 500 kl/d currently. This has
resulted in the areas on the upper reaches of the valley experiencing low peak
pressures.
The existing Diepsloot Township system cannot currently supply a peak hour
demand of 4 x AADD (as required by the JW Design Guidelines), but only a
peak hour demand of about 2.5 x AADD, which is not unrealistic given the
current nature of the development. However, as the actual peak hour demand
factor is unknown, the actual peak pressures could vary considerably as well as
the actual pipe velocities in the 600 mm dia bulk main supplying Diepsloot.
The proposed Diepsloot East Developments form part of the proposed
Diepsloot Reservoir and the proposed Diepsloot Tower (previously RW33
Direct) water sub-districts as indicated on Figure TG_W2. The construction of
the Diepsloot Reservoir as well as the bulk supply pipes to the future Dainfern
Reservoir is currently in the planning phase in-line with the current master plan.
Therefore, it has been assumed for the Diepsloot East developments that the
proposed Diepsloot Reservoir and Tower will be constructed. However, as an
alternative to the previous master plan, the construction of a Tower is proposed
to supply the high-lying parts of the Diepsloot East and adjacent future
developments.
Therefore, a new 375 mm dia bulk main and 1 600 kl Tower (Project BH12) will
be required to supply the portion of the Diepsloot East development located
north of the greenbelt as well as the future area to the west from Diepsloot
East.
A 315 mm dia connection to the existing 600 mm dia JW pipeline in the vicinity
of point A is proposed to supply the Diepsloot East development located south
of the greenbelt. The existing system analysis (assuming a peak hour factor =
2.5 for the existing Diepsloot Township), including the additional peak demand
for the proposed Diepsloot East development (assuming a peak hour factor =
4), indicates that the peak pressure at point A would then be 50 m with the
minimum pressure in the high-lying parts of the development only 20 m, which
is below the minimum pressure criteria of 25 m as per JW Design Guidelines.
Therefore, a secondary 315 mm dia supply pipe (Item BH13.2) is required,
following route X1-X2-X3 as indicated on Figure TG_W1, to establish a ring
feed between the proposed Dainfern bulk pipeline and the existing 600 mm dia
Diepsloot bulk supply pipeline. The first section of this pipeline must be a 500
mm 0 pipe (Item BH13.1) as indicated. The minimum pressure at the highest
point of the Diepsloot East development will then be 33 m, which is acceptable.
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The above analysis, including the demand of Diepsloot East, indicates that the
velocity in the existing 600 mm dia JW pipeline upstream of point A will then be
1,9 m/s, which is acceptable.
It is proposed to supply the proposed hospital through a 250 mm dia connection
(Item BH24.1) to the 600 mm dia JW pipeline also connecting at point A, which
means it will also form part of the proposed Diepsloot Reservoir supply area
and not the tower zone.
As mentioned previously, low pressures currently occur in the high-lying parts
of the Diepsloot Township. The additional demand from the Diepsloot East at
point A will make matters worse. Therefore, it is proposed to install a 200 mm
dia pipeline (Projects BH23.1 and BH20.2-4) as well as a PRV (Item BH20.1)
and close off three pipes (Items BH20.5-7) to establish the proposed Diepsloot
Reservoir Diepsloot East PRV2 sub-district, which is in-line with the master
plan and will eliminate pressure problems in this area.
Duncan Hulley of Johannesburg Water has indicated that the reservoir sites are
in the process of being expropriated, and construction of the reservoirs should
commence in July 2014.
3.1.2.
3.1.2.1.
Proposed Water Services
Water Connection
As shown on Fig TG_W2, the bulk water supply to the development will be located
at the south eastern corner of the development, and will be 315 mm in diameter.
Based on the layout provided, the bulk water requirement is
TABLE 2 - DESIGN CRITERIA FOR BULK WATER CONNECTION
Item
Value
Total No of Housing Units
AADD per unit
Total AADD = 5 825 * 600
Peak Factor
Max Demand = 4*410400/24/3600
Pipe Velocity (315 mm diameter)
5 825
600 l/d
3 495 000 l/d
4
161,8 l/s
2,08 m/s
This is less than the upper value of the JHB Water standards of 3.5 m/s.
3.1.2.2.
Water Design Criteria
The Johannesburg Water Guidelines, Version 2 dated 5 March 2004 will be used
to design the water reticulation. Table 3 below summarizes the requirements.
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TABLE 3 - DESIGN CRITERIA FOR WATER RETICULATIONS
Design Element
Criteria
Average Annual Daily Demand (AADD) –
Low income up to 300 m2
Daily Peak Factor
Minimum residual head under condition of
peak flow
Maximum linear flow velocity under
condition of peak flow
Pipe type: Larger than 90 mm less than
200 mm
Fire flow at any one hydrant under condition
of domestic peak flows (one hydrant at a
time
Minimum residual head (fire plus domestic
peak flow)
Duration of Fire
Spacing of hydrants
Minimum cover to pipes
Maximum cover to pipes
600 l/unit/day
3.2.
SEWER RETICULATION
3.2.1.
Existing Sewer Reticulation
4
25 m
3,5 m/s
uPVC
8 l/s at 0,7 bar
20 m
1 hour
240 m
800 mm
1 500 mm
There is an existing sewer network in the Diepsloot township to the west of the
proposed development There is no sewer reticulation on the proposed site..
3.2.2.
Proposed Sewer Reticulation
The total estimated peak daily dry weather flow (PDDWF) for the proposed
development is 4 550 kl/d. 4.2 Existing Sewer System Capacity and Connection
Point
Figure TG_S1 has reference. The proposed development is located to the east of
Diepsloot West within a portion of the Diepsloot West Basin which is currently
undeveloped. Therefore, the existing Diepsloot West master plan was updated
using the information provided including the proposed development layout. This
also constitutes an update of the previous impact investigation undertaken for JW
dated 16 March 2009.
Due to the topography of the area it is proposed that the northern portion of the
development connect to the planned 200 mm/315 mm dia outfall
(DSW_TANG2.1 and DSW_TANG2.2) at positions A and B. Furthermore, it is
proposed the southern portion of the development connect to the existing sewer
reticulation system at position C.
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The future system analysis indicates that the existing system does not have
sufficient capacity to accommodate the planned development and as a result the
following upgrades will be required:
a) DSW_TANG2.3: Upgrade existing 250 mm dia outfall to 450 mm dia (820 m);
b) DSW_TANG2.4: Upgrade existing 300 mm dia outfall to 450 mm dia (900 m);
c) DSW_DSW2.1: Upgrade existing 150 mm dia to 200 mm dia (415 m – subject
to survey); and,
d) DSW_DSW2.2: Upgrade existing 150 mm dia to 200 mm dia (272 m).
It should be noted that section DSW_DSW2.1 was modelled at minimum
slope as no as-built information could be obtained. Therefore, this upgrade is
subject to the survey of the pipe section.
It should be noted that there is an existing pump station on the Diepsloot West
outfall located within the Northern WTW site, which needs to accommodate the
additional 15 l/s form the Diepsloot East Development draining through point C.
The detail of this pump station is unknown, which requires further investigation to
confirm if spare capacity is available. JW Operations could not supply the
information to GLS.
Duncan Hulley of Johannesburg Water has indicated that a contractor is due to
be appointed by Johannesburg Water to upgrade the main sewers, and
construction of the sewers should commence shortly.
3.2.2.1.
Sewer Design Criteria
Table 4 below gives the design criteria that will be used for this project
TABLE 4 - DESIGN CRITERIA FOR SEWER RETICULATIONS
Design Element
Average Annual Daily Demand (AADD)
Peak Factor
Maximum Depth of Flow at peak discharge
Infiltration into 150 mm diameter Sewer
Sewer Pipe Type
Minimum gradient 100 mm diameter pipes
Minimum gradient 150 mm diameter pipes
Minimum velocity
Pipe Diameters
Minimum depth of Cover
Criteria
500 l/unit/day
2,3
67%
0,012 l/s/100 m
uPVC CL34 solid wall pipes to
SANS 791
1 : 60
1 : 140
0,7 m/s
160 mm for Reticulation, 100
mm for connections
1,4 m Road Servitudes, 1,0 m
Other Areas
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4.
COST ESTIMATES
4.1.
WATER RETICULATION
Table 5 below gives the cost estimate for the Water Reticulation
TABLE 5 - COST ESTIMATE WATER RETICULATION
WATER RETICULATION ESTIMATED COST
Item
No.
Description
Unit
1
Bulk Connection Line 315 mm
m
1 000
R 2 000.00
R 2 000 000,00
2
Internal Reticulation
m
4 000
R
R 1 400 000,00
3
Other
4
Sub Total
5
P&G
6
Sub Total
7
Contingencies
8
9
Sub Total
Value Added Tax (VAT @
14%)
10
TOTAL
4.2.
Quantity
Rate
350.00
Prov
Amount
R 1 000 000,00
R 4 400 000.00
10.0%
R
440 000.00
R 4 840 000.00
10.0%
R
484 000.00
R 5 324 000.00
14.0%
R
745 360.00
R 6 069 360.00
SEWER RETICULATION
Table 6 below gives the cost estimate for the Water Reticulation
TABLE 6 - COST ESTIMATE SEWER RETICULATION
SEWER RETICULATION ESTIMATED COST
Item
No.
Description
1
Bulk Connection
2
Internal Sewers
3
Other
4
Sub Total
5
P&G
6
Sub Total
7
Contingencies
8
Sub Total
Unit
Quantity
Rate
Prov
Amount
R 2 000 000.00
m
4 000
R 550.00
Prov
R 2 200 000.00
R 2 000 000.00
R 6 200 000.00
10.0%
R
620 000.00
R 6 820 000.00
10.0%
R
682 000.00
R 7 502 000.00
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Value Added Tax (VAT @
14%)
10
TOTAL
4.3.
14.0%
R 1 050 280.00
R 8 552 280.00
SUMMARY OF COST ESTIMATES
Table 7 below gives the Summary of the Cost Estimates
TABLE 7 - SUMMARY OF COST ESTIMATES
SUMMARY OF ESTIMATED COSTS
Item
No.
Description
Unit
Quantity
Rate
Amount
1
Water Reticulation
R 6 069 360,00
2
Sewer Reticulation
R 8 552 280.00
5
TOTAL
R 58 012 740.00
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5.
BULK SERVICE CONTRIBUTIONS
JW would not provide Bulk Service Contributions at this stage. However they did
provide a spreadsheet which is used to calculate the contributions, and this was
utilised. It must be emphasized that these calculations are estimates only, and
are subject to the correct calculation from the utilities.
5.1.
WATER
Contribution
=
Area * 2,7 kl/d per 500 m2 of area * R2 458/kl
=
73 240 m2 * 2,7 kl/d per 500m2 of area*R2 458/kl
=
R 97271296,17
This rate is from 1 January 2006, so should be escalated at 10% pa.
5.2.
SEWER
Contribution
=
Area * 2,295 kl/d per 500 m2 of area * R5 973/kl
=
73 240 m2 * 2,295 kl/d per 500m2 of area*R5 973/kl
=
R 2 007 952,97
This rate is from 1 January 2006, so should be escalated at 10% pa.
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APPENDIX 1 - PLANS
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