CRITERIA AND METHODS
FOR RISK DETERMINATION AND CLASSIFICATION AND DETERMINATION
OF AREAS WITH POTENTIAL SIGNIFICANT FLOOD RISK (APSFRs)
Part II of the Methodology under Article 187 (2) i.6 of the Water Act
Approved by the Minister of Environment on 22 January 2013
1. Directive on the assessment and management of flood risks and its transposing into the
Water Act in respect of APSFRs
Directive 2007/60/EC of the European Parliament and of the Council of 23 October 2007 on
the assessment and management of flood risks (Floods Directive – FD) and the Water Act
(WA) provide for drafting of Flood risk management plans (FRMPs) for each basin
management region in the Republic of Bulgaria, as several main stages shall be implemented
within this process.
In the first stage of implementation of the Directive and development of FRMPs, the
provision of information is required as to all areas for which it is considered that there exists a
potential significant flood risk, or a probability of such could be envisaged (APSFRs) Article
5 Chapter II of DF and Article 146 of WA).
The determination of such areas according to the Directive is to be carred out based on the
results from the preliminary flood risk assessment (PFRA), as the relevant requirements are
set forth in Chapter II, Article 4 of the Directive.
There shall be determined areas with potential significant flood risk (APSFRs) for each river
basin management district, and if within the territory of the respective river basins/
management units, there is an international river basin, then the APSFRs’ determination shall
be co-ordinated with the respective neighbouring member-states.
The determination of areas with potential significant flood risk is an integral part of the
Preliminary flood risk assessment (PFRA) and comprises its final phase, as at the same time it
constitutes baseline information for the second phase of implementation of the Directive
determining the areas for which flood hazard maps and flood risk maps are to be prepared
(Article 6 Chapter III).
In Chapter VII, Article 13 of the Directive on Floods it is stated that members-states may
decide not to undertake PFRA, if they already have taken measures for performance of risk
assessment and have come to a conclusion that for certain areas there is a potential significant
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flood risk, or if they have decided to develop maps and management plans in respect thereof.
In this particular case, Bulgaria does not have any detailed mapping of flood risk in the scope
and with the particular details as required under the Directive, and Article 13 does not apply.
Pursuant to Article 146d of the Water Act APSFRs are determined based on the existence of
potential significant flood risk or a probability of potential significant flood risk, without
stating any specific requirements regarding the method of determination thereof. Likewise,
the Directive also allows for freedom of each member-state to determine independently
APSFRs as per a set of criteria specific to its territory.
The correct determination of APSFRs is of great significance since only the territory within
their scope shall be subject to the second stage under the Directive, namely, preparation of
flood hazard maps and detailed flood risk maps (Chapter III), accordingly, Section III of WA.
The maps preparation is the next stage in the development of FRMPs. The final stage of
FRMPs’ development is the setting of measures for decrease of the flood risk. According to
the dates specified in the Directive and WA, FRMP will be elaborated and accepted by the
end of the year 2015. Thereafter is to follow a six-year period of implemention of the first
plan and its update, while providing for the repeated performance of all stages in the FRMPs’
preparation.
Additional supplementation and review of APSFRs is to be performed as at 22 December
2018 within the update of FRMPs and at six-year periods thereafter. This provision of the
Directive is to be borne in mind in determining APSFRs, since the further preparation and
plans is a time-consuming and costly process. Given the lack of detailed analyses of flood
risks in the country, it is appropariate to accept such criteria for significant risk that will
determine only the highly risky regions in order to elaborate the respective plans for decrease
of such flood risk for each basin management region. The inclusion of regions with lower risk
could shift the second period of updating the Directive so that the resources necessary for
decreasing the risk could be ensured.
2. Requirements regarding information about APSFRs according to reporting documents
3
The Directive specifies more detailed requirements on reporting APSFRs in the so-called
reporting documents, or Floods Reporting Database v3.mdb. This is the official document
which will describe in a standardized manner both past and potential future floods, and
APSFRs.
3. Preliminary flood risk assessment (PFRA) in Bulgaria and methodologigal
developments for determination of APSFRs
The approaches used in the elaboration of a methodology for determination of APSFRs reflect
the available condition of information providing in the various member-states, and not every
one of these approaches is suitable for direct application under the conditions in the Republic
of Bulgaria.
At this stage, the documents available in the country in this respect are:

Methodology for preliminary flood risk assessment in the main river basins in the
Republic of Bulgaria – methodology for flood risk assessment under the
requirements of Directive 2007/60/EC;

Results reported to EC under PFRA in respect of significant past and potential
future floods;

Databases used in the preparation of PFRA.
The approach for determination of APSFRs is developed based on an analysis of the existing
approaches and methods related to the available steps for determination of significant past and
potential future floods and APSFRs in these basic documents and available data which are
used, the approach for determination of significant past and potential future floods and the
availability of analyses in respect of determining areas with significant risk in each basin
management region.
4. Determination of APSFRs
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The technological process for determination of APSFRs must rely on and use only data which
are easily accessible and available in PFRA with methodology allowing for fast and
facilitated means for determining APSFRs. Therefore, it is envisaged to use final criteria and
thresholds for determination of the risk degree out of the data about the significant past and
future potential floods, information about which is obtained from PFRA and the
accompanying databases used in drawing up thereof.
The use of the threshold value criteria introduces determination of three degrees of risk: low,
medium and high.
4.1. Rationale of the criteria for determination of APSFRs
The criteria for determining APSFRs can be divided into two parts:

Unified criteria for classification of the risk in three degrees as per flood location;

Criteria for grouping of places with significant risk in APSFRs
The deducing is based on the available documented information from PFRA and possible
options for application and synchronization of various metrics to risk assessment.
In the course of the data analysis as per the relevant indicators used in PFRA, separate peak
values are excluded as non-typical. Based on the maximum value so determined for the
relevant indicator used in PFRA for assessment of the significant floods (for which there are
numerical data available in PFRA), the threshold values are calculated for the respective
indicator.
For risk determination, a unified table is accepted, irrespective whether there will be used any
data from past or potential future floods for each basin management region. The analysis of
the data on past floods and potential future floods is performed in the above described
manner, as after comparing the results one of the risk assessment results is accepted. (In most
of the cases this is the result for past floods, as more reliable data). Where the indicators’
values equal zero, the indicator is ignored.
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The criteria with defined threshold values in 3 degrees: low, medium and high risk are given
in the table below.
Table 1. Unified criteria for classification of the risk for determination of APSFRs
No
Criteria per categories
Human health
1 Affected inhabitants (victims)
2
Affected critical infrastructure elements or
affected buildings of public significance
(hospitals, schools, etc.)
3
Wells and pumping stations for public
drinking water supply
Economic activity
UoM
Low
Medium
High
Pcs.
300
1 500
3 000
Pcs.
1
3
6
Pcs.
4
18
38
4
Motorways, class І and ІІ, railways, bridges,
airports, transmission grids and other linear
infrastructure
Pcs.
1
5
10
5
Motorways, class І and ІІ, railways, bridges,
airports, transmission grids and other linear
infrastructure
Affected agricultural areas
m
1 000
5 000
10 000
Decares
6 000
30 000
65 000
6
7
Summarized economic value of damages (for
past floods)
Environment
BGN
Sewage systems of settlements – discharge of
municipal seweage systems or urban
wastewater treatment plants
9 Affected protected areas: drinking water, areas
under the Protected Areas Act, Natura 2000
10 IPPC and SEVESO enterprises, etc. (PRTR) of
Environment Executive Agency, MoEW, BD
strips
Cultural heritage
Pcs.
1
2
5
Pcs.
1
2
5
Pcs.
0
0
1
11 Cultural and historical monuments of
UNESCO and such of national significance
Pcs.
0
0
1
8
700 000 3 000 000
7 000 000
4.2. Risk determination per indicators
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Assessment is performed of the locations with significant floods included in PFRA, for each
of the indicators for which there are data available in PFRA, by determining a degree of
“low”, “medium”, or “high” risk according to the adopted threshold values for the indicators
under i. 4.1. In the cases when in one location there are several significant floods, for the
purposes of the risk assessment, the data with the highest reported values are used for each
indicator regarding all events for which there are data available.
4.3. Risk determination for each of the categories: human health, economic activity,
environment, cultural and historical heritage
After determination of the risk degree as per each indicator for which there are available data
in PFRA, a risk degree is determined for the relevant category: Human health; Economic
activity; Environment; and Cultural and historical heritage. The degree of risk for each one of
the categories corresponds to the highest risk, determined for the indicators of the relevant
category.
4.4. Assessment and ranking of the risk per location
The location risk is determined as a combination of the risk determined per categories while
observing the following principles:
 If a high risk is determined for each basin management region for any of the
categories, the location remains in high risk;
 If the risk is medium in three of the categories, the location is in high risk;
 If the risk is medium in two of the categories, the location is in medium risk;
 If the risk is medium in two of the categories when these categories are human health
and economic activity, the location is in high risk;
 If the risk is medium in one of the categories, and if the risk in the remaining
categories is low, the location is in low risk, save in the cases where the determined
medium risk as per the human health category.
The final risk degree of a location may not be lower than the determined degree of risk as per
the human health category.
4.5. Determination of APSFRs
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The determination of APSFRs is carried out based on the determined location risk as per
PFRA.
The final determination of the APSFRs’ boundaries is prepared in 2 variants:
1. APSFRs comprising only locations assessed in high risk;
2. APSFRs comprising locations in high and medium risk.
5. Methodology for determination of APSFRs
This section describes the methodology for the second baseline part of determining APSFRs –
unification of sites and areas in significant flood risk within aggregated aeras in view of their
assessment at the second stage of implementation of the Directive on Floods – detailed
mapping of the hazard and detailed mapping of the risk. The main concept of the
methodology is based on the standard definition of risk – a threat and adverse consequences.
Since for the territory of the country there is no evenly distributed information base available
as regards the risk hazard, a main source includes the significant past and potential future
floods as per the results of PFRA already reported to the EC. The proposed method is based
on the visual interpretation of the hazard location and its combination with elements of the
risk classification criteria.
An important consideration, taken into account in the elaboration of the methodology, is also
the obligation to individualize as APSFRs only those places in which the present risk is
significant indeed, and to remove from them the areas in which there have been significant
floods in the past, but within a more stringent assessment they would have been removed. The
mapping and setting of particular measures for protection or diminishment of the impact of
floods in places in relatively low risk would lead to a necessity of implementation of
measures and restrictions in their economic and social development.
Thus, the methodology does not replace the already reported significant past and potential
future floods, but reviews their characteristics in a territorial aspect, in order to individualize
them within areas in which there is an existing potential significant flood risk, or a probability
of a significant potential risk.
The methodology takes into account also the condition of the informational base, which is to
secure its implementation. The first step is certainly the information reported to the EC about
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significant past and potential future floods. For risk assessment in territorial aspect, there shall
also be used the data about the GIS layers, included in the development of PFRA.
In this respect, it is necessary for the available input information about the basin management
regions (BMR) to be structured in a database.
5.1. General scheme of the technological process
The methodology for determination of APSFRs can most generally be divided into 4 stages.
Each one of these is characterized by a certain input information and data development and
analysis, after which the input data are prepared, forming the baseline for the work at the
following stage. A scheme with the proposed main stages of the Methodology with the substeps of each one of them is presented in the figure below:
Approaches in location determination
Databases of locations of significant past and
potential future floods as per PAFR
Determination of PAPSFR
Rules for neighbouring PAPSFRs
Check as per flood characteristics
Database of PAPSFRs
Significant risk criteria for determination of
APSFRs
APSFR determination
List of APSFRs
Approaches in risk determination
Detailing of boundaries
Check of risk elements proximity
Database of APSFRs
Combined approached for boundary determination
Reporting requirements
Determination finalization
Additional identifiers
Final database of APSFRs with their passports and
reporting execution
Descriptive approaches in finalization of the
documentation
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Figure 1. General scheme of the technological process for determination of APSFRs.
5.1. 1. Stage one – determination of PAPSFRs
At the first stage with the use of purely geographical methods are to be determined the
preliminary areas of significant flood risk (PAPSFRs). The initial step is the integration of the
information layers for significant past and potential future floods in a standardized database
with extraction of the necessary information for the subsequent risk analysis. Within the
following analysis, PAPSFRs are outlined in accordance with certain rules for neighbouring
areas described below.
The defining of areas of potential significant risk is based on the presence of centres of
significant flood risk situated close to each other, which may be viewed in a summarized
form, and not individually, and therefore, their assessment does not impose any significant
investments in the collection and processing of risk information. On the other hand, at this
very step of the technological process, some of the places in the larger areas can be divided
based on specific indicators only, without being necessary to perform a risk assessment.
The purpose of this step is focusing of the analyzer on areas in which there is a grouping of
significant floods that have occurred one next to the other, and the arising of which is
probably due to similar reasons. As a result of the performance of this step, a vision is
presented as to what the result after the final step would be and the respective APSFRs would
look like.
The grouping of nearby areas with significant floods cannot be executed on an arbitrary
principle by a simple circling of such close locations. Therefore, the use of the following main
rules for neighbouring areas is suggested:
Rule code
RN_01
RN_02
RN_03
Description
In one PAPSFR there may be included only significant floods within one
river basin
Exclusion of PAPSFRs, for which there are no available data about
significant past and potential future floods determined during PFRA
As regards marine floods, the role of independent PAPSFRs is played by
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coastal sections in which the conditions for flood formation are identical.
As baseline polygon sites playing the role of PAPSFRs in these initial steps of the
methodology, the polygons of layer H_Catchment from the database under project JICA are
used. This layer represents the catchments in the Republic of Bulgaria as a polygon class of
sites.
The reasons for an initial choice of polygon site – catchments, in which the significant floods
are to be examined instead of merely being drawn - are the following:
-
The suggested GIS layer is standardized for all BDs;
-
The catchments surround territories with similar hydrological conditions;
-
The catchments give clear idea of the river system and the catchments area of the
particular polygon;
-
The catchments are presented for all more important feeders within the river systems;
-
the area of the available polygons is appropriate for the initial steps of the
methodology;
-
in employing the metodic by various experts a unified GIS laeyr will be used and any
differences in the initial outlining of the PAPSFRs will be avoided.
Before the initiation of a check for significance criteria, another editing is to be performed as
regards the boundaries of PAPSFRs for the purpose of a more accurate regionalization of the
area with a possible significant flood risk.
For this purpose, the following main rules on a regional principle must be applied:
Rule code
RN_04
RN_05
RN_06
RN_07
Description
Editing the PAPSFRs boundaries according to the information about
related events
Editing the PAPSFRs boundaries as per the scope of the settlements
Editing the PAPSFRs boundaries as per the homogeneity of the subcatchments as regards flow formation factors (e.g., lower, middle river
course, at high altitudes).
Rule for existing complex dams
o RN_04: Rule regarding the connectedness of events:
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Under this rule, it is checked whether in neighbouring PAPSFRs there are locations
which have been the subject of one and the same flood. Data about this are available
in the tables reporting significant past and potential future floods.
o RN_05: Rule regarding the settlement scope:
Under this rule it is checked whether on the boundaries of neighbouring PAPSFRs
there are settlements which are situated in two PAPSFRs. This case is frequent, since
there are rivers in many settlements and hence, different catchment areas have been
formed there. Upon existence of such places, the PAPSFRs boundary is so adjusted
that the settlement can fall within the PAPSFR located upstream. If no PAPSFRs are
located upstream, it is to be unified with the one located downstream.
In the event that the settlement falls within different catchment areas, it is adjoined to
that PAPSFR which is determined for the catchment area with the greatest
significance for occurrence of a flood and while taking into account land forms.
o RN_06: Rule regarding the homogeneity of the sub-catchment areas
Under this rule neighbouring catchment areas characterized by similar flow-formation
characteristics are unified. They are basically divided into high-altitude, middle and
lower river courses. During this analysis it is checked also whether the respective
catchment areas belong to main feeders. The purpose is to decrease the number of
PAPSFRs by unifiying similar catchment areas, but not such belonging to different
major feeders of the main river.
o RN_07: Rule regarding the existence of complex and significant dams:
The period of active dam construction is in the 1960-70s and after 1985 there are
rather few newly constructed hydrotechnical facilities. If a flood has occurred before
the year 1985 and it has not recurred ever since, than the boundary of the polygon is
edited by excluding the respective location from PAPSFRs.
The application of these rules will allow for defining the working PAPSFRs in a clear and
transparent manner and they will be transferred for assessment to the next stage.
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5.1.2. Second stage – application of unified criteria for risk classification in view of
determining APSFRs
At the second stage based on the defined criteria for risk classification in table 1 and the rules
regarding the characteristics of the floods, the scope of PAPSFRs is to be particularized more
precisely, whereupon some of the areas may drop out, while others may have their scope
changed. The final result from this stage is determination of a list with APSFRs.
The criteria application is effected in several manners:
-
For locations with past significant floods the values for each criterion are derived from
the data available in PFRA;
-
For locations with potential future significant floods the values are derived from the
data available in PFRA;
After calculation of the quantitative characteristics for each criterion (presented in Table 1), it
is determined whether they go beyond the threshold values. Initially the passing of the risk
threshold is to be checked for each location. Those locations which are within this threshold
are indicated as eligible participants in APSFRs.
The assessment of the characteristics of the respective locations as per each of the defined
criteria is performed as per the presented coordinated Table 1 with threshold levels in three
degrees.
Those locations having a risk level under the threshold rates for significant level (3rd degree or
equalized to significant medium level – 2nd degree) for all criteria, drop out of PAPSFRs. The
remaining locations form APSFRs, the boundaries of which are transferred for subsequent
processing described in the following chapter of the Methodology. If within the PAPSFRs
there are no locations or other sites with risk values above the threshold under the ctriteria,
such area is removed from the list of APSFRs.
5.1.3. Third stage –detailing of the APSFRs boundaries – determination of the final
APSFRs
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This stage aims at determining in detail the boundaries of APSFRs as per defined rules for
proximity of risk elements. Those APSFRs, which have undergone a considerable change in
the boundaries, may again be subjected to the activities under i. 5.1.2.
In respect of the scope of APSFRs the Directive on floods allows for determination of
boundaries that are considerably wider than those within which a flood may occur.
For detailing the APSFRs boundaries, the application of rules for determining a start and end
point of APSFRs is suggested.
Rules on determining the start and end points of the APSFRs boundaries:
-
In cases in which a settlement is located on the APSFR’s boundary, then the APSFR
shall include the entire settlement with a certain buffer thereof, depending on:
o Type of settlement: for larger settlements where future development is
expected, the buffer shall be larger, whereas for smaller settlements suffering
from depopulation, its size is minimal;
o Type of flood plain: for wide flood plains along the river valley at the point
before it reaches and at the point after it leaves the settlement, the buffer is
bigger, whereas for larger slopes where the speeds are greater and there is no
spillover, this location may be deemed as a point of interruption of the area;
o Type and configuration of the available risk elements:

If beyond the boundaries of the settlement are located existing
pollutants and next to them there are nearby elements under the
environment criteria, then the boundaries are to be expanded so as to
comprise these as well;

If at the point before it reaches and at the point after it leaves the
boundaries there are large enterprises or industrial zones, the buffer is
to encompass them either;

If at the point before it reaches and at the point after it leaves the
boundaries there are agricultural lands with proven intensive
agriculture (greenhouses, etc.), then the buffer is to comprise them as
well - marked in field;
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
If at the point before it reaches and at the point after it leaves the
boundaries there are nearby elements under criteria 2, 3, 4, 5, 8 and 11,
then the buffer is to comprise them as well.
The buffer is determined as per an expert assessment.
After the final detailing of the boundaries of APSFRs, it is proceeded with the establishment
of their linear equivalent, which is the final form of presentation of APSFRs.
5.2. Main requirements as regards data for implementation of the methodology for
determination of APSFRs
For determination of APSFRs, as per the present methodology are used:

Data from the PFRA reported to the EC;

Data used in the process of PFRA for determining the significance of the flood
consequences;

Other data available at BD.
The set of minimally required layers apart from those reported under PFRA to EC includes:
 Regarding “Human health”category:
o Population
number
according
to
the
Unified
Classifier
of
Administrative-Territorial and Territorial Units (EKATTE);
 Regarding”Economic activity” category:
o Republican transport network, including road network, railway network
and airports;
o Industrial and economic infrastructure;
o Urban infrastructure, including wells and pumping stations for public
drinking water supply, treatment plants;
o Data presenting summarized economic value, e.g., BEAM;
o Critical infrastructure, including buildings of public significance, such
as hospitals, schools, etc.
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 Regarding “Environment” category:
o Sewage systems of settlements and urban wastewater treatments plants;
o Protected areas pursuant to the Protected Areas Act;
o Areas as per NATURA 2000;
o Drinking water zones;
o IPPC and SEVESO enterprises (only where generating water pollution);
o Other industrial activities (apart from IPPC and SEVESO) sources of
(water) pollution under the Directive concerning the priority substances
and the Directive concerning the hazardous and harmful substances.
 Regarding “Cultural heritage” category:
o Cultural and historical monuments of global significance, included in
the list of UNESCO; cultural and historical monuments of national
significance pursuant to Article 50 (1) of the Cultural Heritage Act.
The input data and the obtained results upon determining APSFRs are structured in a single
unified format. The attributative information shall conform to the requirements as regards
reporting to EC.
Upon determining of APSFRs coordinate system WGS 84, UTM Zone 35N is used in respect
of the spatial data.
For the purposes of reporting to EC the obtained results in GIS format are transformed in the
ETRS89 coordinate system.
The resulting APSFRs are to be marked with a unique code.
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