This document discusses the development of a uniform trans-boundary methodology for flood risk assessment between Bulgaria and Serbia. It covers terminology, legislation, databases, and types of floods. Methods are described for determining maximum run-off, creating digital terrain models and hydraulic models. Guidelines are provided for creating flood hazard maps and flood risk maps, including showing inundation areas, water depths and velocities, protection measures, and classifying risk. The goal is a common approach for flood risk assessment in the cross-border region.

1. Програма за ТГС по ИПП България – Сърбия
DEVELOPMENT OF A UNIFORM TRANS-BOUDARY METHODOLOGY FOR
FLOOD RISK ASSESSMENT
CONTENTS:
INTRODUCTION
CHAPTER ONE
1. USED TERMINOLOGY
2. EUROPEAN APPROACHES
3. LEGISLATION AND INSTITUTIONAL FRAMEWORK
4. DATABASE
5. TYPES OF FLOODS
CHAPTER TWO
1. COMMON APPROACH
2. HYDROLOGY
2.1. DETERMINATION OF THE MAXIMUM RUN-OFF
2.2. CLIMATE CHANGE
3. GEODESY
3.1. COORDINATE SYSTEMS AND PROJECTIONS
3.2. DIGITAL TERRAIN MODEL
3.3. ADDITIONAL ANALYSIS OF THE DIGITAL TERRAIN MODEL
3.4. GEODESIC SHOOTING
4. HYDRAULIC MODELLING
4.1. CALCULATION METHODS AND PROGRAMMES
4.2. CREATION OF A HYDRAULIC MODEL
CHAPTER THREE
1. FLOOD HAZARD MAPS
1.1. DETERMINATION OF THE INUNDATED AREAS
1.2. КCORRECTION OF THE INUNDATED AREAS
1.3. PROTECTION MEASURES
1.4. FORMATTING OF THE MAPS
2. FLOOD RISK MAPS
1.5. RISK MAPPING APPROACHES
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1.6. SOCIO-ECONOMIC ASPECTS
1.7. RISK CLASSIFICATION
1.8. FORMATTING OF THE MAPS
CHAPTER ONE
EUROPEAN APPROACH
Czech Republic
Orthophotos and topographic maps, scale of 1:10 000, are used as a basis for the
preparation of flood hazard and flood risk maps in Czech Republic. The orthophotos
and topographic maps are provided by the Czech Surveying Office for Mapping and
Cadastre (file ZABAGED).
Figure 1: Orthophoto and topographic map
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Figure 2: Scheme for flood hazard and flood risk maps elaboration for given scenario
(water quantity).
LEGISLATION AND INSTITUTIONAL FRAMEWORK
General obligations of the parties with respect to the management of flood risk and
cross-border cooperation are determined by international legal frameworks such as
the Water Convention of the UNECE and the Floods Directive of the EU.
National legislation should set clearly defined and allocated responsibilities and rights
of all institutions and organizations that are relevant to flood risk management.
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Figure 3. Legislation and institutional framework in flood risk managament
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Figure 4 Current organization of water management in Republic of Serbia
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Figure 5 Scheme Structure of the specialized institutions in flood risk management
DATABASE
Categories of databases:
 Basic data
 Hydrology
 Hydraulics
 Climate
 Damage assessment
TYPES OF FLOODS
The main feature for typifying floods is their source. Depending on it, the following
types of floods can be defined: "sea floods", "river flooding", "rain floods", "
groundwater floodings" and "infrastructure floodings".
CHAPTER TWO
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5. HYDROLOGY
5.1. DETERMINATION OF THE MAXIMUM RUN-OFF
Statistical methods
The statistical methods are applicable for determination of the maximum run-off in
basins with built hydrometric network and an area greater than 1000 km. The
statistical methods are applied in both countries.
Models „rainfall – run-off”
Figure 6 Model „Rainfall – run-off”
Method for regionalization of the maximum run-off
 Eight factors and characteristics of drainage basins and river systems that are
essential for the formation of maximum flow are set out in LUBW, 2007:
 • area of the catchment AEo [km2]
 • urbanized territory S [%]
 • afforestation W [%]
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 • average slope Ig [%]
 • river length L [km] along the main rivers of the watershed to the confluence
 • river length LC [km] from the center of gravity of the catchment to its estuary;
 • average annual rainfall in the catchment hNG [mm]
 • landscape factor LF [-]
GEODESY
DIGITAL TERRAIN MODEL
A variety of sources can be used to create a terrain elevation model: topographic
maps, satellite images, orthophotos, surveys of the river flow, LIDAR. The described
sources are characterized by different accuracy of the topographical information.
Therefore, the combined use of these sources is recommended to obtain a digital
terrain model with sufficient accuracy.
Figure 7 Geodesic measurements /shooting of cross-sections/
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Figure 8 Encoding of the cross section folds based on inverted cross sections of the
plane
Figure 9 Generation of 3D folds of the river bed terrain
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Figure 10 Digital terrain model, developed on the basis of laser scanning data
Figure 11 Digital terrain model of river section, developed with laser scanning data
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Figure 12 conbination of laser scanning data, geometry of the facilities and folds f the
terrain structure
GEODESIC SHOOTINGS
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Figure 13 Method of the profiles
1. HYDRAULIC MODELLING
1.1. CALCULATION METHODS AND PROGRAMMES
Use of 1D model for river section calculation (i.e. HEC-RAS)
In these models, the geometry of the river valley and the river bed is laid depending
on multiple cross sections. The hydraulic impact on equipment and hinders in the
riverbed,on the local expansion or narrowing, of the changes in the slope of the river
bed, etc. can be reproduced by 1D-models of the river flow.
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Figure 14 Determination of cross-sections for hydraulic measurements of the digital
terrain model (based on topographic maprs 1:5000)
Figure 15 Calculated inundated areas from 1D calculations
1.2. CREATION OF A HYDRAULIC MODEL
Use of 2D models of the river sections (i.e. Hydro_AS-2D)
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Figure 16 2D-calculation network of the basis of elevation sports connection of
SRTM-elevation terrain model, (basis: Google Earth)
Figure 17 Calculated inundated area with 2D hydraulic measurements (basis: Google
Earth)
Use of hydrologic model, based on calculation raster network for 2D calculations of
the surface run-off (i.e. GSSHA model)
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Figure 18 Image of the modelled area with run-off model (GSSHA) based on
calculation raster network.
CHAPTER THREE
FLOOD HAZARD MAPS
Flood hazard maps are made for the following scenarios:
 flooding with low security or high repetition period (extreme floods);
 flooding with medium security (≤ 1%), respectively, with an average repetition
periods (≥ 100 years);
 individually, floods with high security or a small repetition period.
In compliance with the flood risk directive, flood hazard maps must contain the
following information:
of flooding;
of flooding and water levels;
individually, flow velocity or the relevant water flow.

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легенда:
заливни дълбочини за висока вълна с
период на повторение 100 години [см]
залети площи
площи със свободен борд < 30 см
степен на застрашеност на сгради:
незастрашени сгради
потенциално застрашени сгради
Figure 19 Borders of inundation and calcualted depths of floods during high wave
with repetition period 100 years, respectively 1% security.
легенда:
застрашени зони при висока вълна с
период на повторение (ПП):
10 години 50 години
20 години 100 години
oпасност от заливане на сгради:
незастрашени
слабо застрашени (ПП > 100 год.)
средно застрашени (ПП 20 -100 год.)
силно застрашени (ПП < 100 год.)
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Figure 20 Borders of inundation for floods with repetition period 10, 20, 50 и 100
years, respectively 10%, 5%, 2% и 1% security.
Figure 21 Determination of the flood hazard in Wallone
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Figure 22 Integration of the determination methods of the repatition and inundation of
the river
Figure 23 Exemplary flood hazard map
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Figure 24 Exemplary flood risk map
PROTECTION MEASURES
If there are protective measures against flooding, it does not necessarily mean that
the location is protected from flooding. Often there are protection measures which do
not functioning normally due to lack of maintenace and no longer correspond to the
modern technologies. Even with perfectly working facilities it must be alwasys
considered that they can not provide absolute protection at a certain risk. Often the
protection degree of the protection measures is not known exactly, so it is difficult to
accurately estimate the effect of the measures, in example for HQ100
FORMATTING OF THE MAPS
According to the Floods Directive, the flood risk assessment should covere the
negative impacts on the following protected categories "human health",
"environment", "cultural heritage" and "business". A prerequisite for achieving this
goal is the definition of clear criteria for assessing the negative effects on each
protected category separately.
CALSSIFICATION OF THE RISK
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Figure 25 Exemplary map of classification of the inundated areas
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