Flood Mapping Case Study on Bantyeketu River in Addis Ababa

93 Pages·2015·2.26 MB·English

ADDIS ABABA UNIVERSITY
INSTITUTE OF TECHNOLOGY SCHOOL OF GRADUATE STUDIES
DEPARTMENT OF CIVIL ENGINEERING

FLOOD MAPPING
Case study: on Bantyeketu River in Addis Ababa
By
ELIAS ZELEKE

Advisor: Dr. DANEAL F/SILLASSIE
APRIL, 2015
Flood Mapping Case Study on Bantyeketu River in Addis Ababa

CERTIFICATION
I, the undersigned, certify that I read and hereby recommend for the acceptance by the
Addis Ababa University a dissertation entitled: Flood Mapping Case study on
Bantyeketu River in partial fulfillment of a degree of Masters of Science in Hydraulic
Engineering.

_____________________________________________________________________
Dr .Daneal F/Sillassie
(Advisor)

Date:-____________________________
Flood Mapping Case Study on Bantyeketu River in Addis Ababa

FLOOD MAPPING
Case study: on Bantyeketu River in Addis Ababa
By
ELIAS ZELEKE

A thesis submitted to the School of Graduate Studies of Addis Ababa Institute of
Technology in partial fulfillment of the requirements for the degree of Master of Science
in Hydraulics Engineering.

Date of Defense:
Members of Examining Board:
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(Chairman) (Signature)
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(Advisor) (Signature)
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(Internal examiner) (Signature)
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(External examiner) (Signature)
Flood Mapping Case Study on Bantyeketu River in Addis Ababa
ABSTRACT
Floods represent a natural risk with a very high frequency, which yearly produce important
material and human losses. Therefore, developing some detailed maps regarding flood
imposes for the accuracy of representation, these must be done at high scales. This study
assesses the potential impact of flood on extreme hydrological events in Bantyeketu River
in Addis Ababa.
ARC-GIS 10 modeling software is used to delineate catchment for different river system in
Akaki catchment and helps to obtain hydrological and physical parameters and spatial
information of the Akaki catchment. Road Networks, houses and buildings as well as
vegetation cover of Akaki catchment is digitized and corresponding areas is calculated.
A hydrological model, HEC-HMS was utilized to simulate Runoff in Akaki Catchment. The
performance of the model was assessed through calibration process and resulted R2=0.7.
Optimal calibration parameters were developed for Akaki Catchment and these parameters
was used as an input for HEC-HMS for estimation of peak discharge in the study. The peak
discharge for Bantyeketu River for the coming ten years, Twenty five years and fifty years
was found to be 13.1 m3/s, 14.7 m3/s and 16 m3/s respectively.
Bantyeketu river carrying capacity was estimated using river cross section and HEC-RAS
hydrological modeling software. Major problematic areas due to flooding were identified.
The cross section around the distance of 1.2 km, 1.5 km, 2.8 km and 3.5 km from Finfina
Bridge show low carrying capacity less than 13.1 m 3/s or 10 years estimated probable
flood.
50 years return period flood of Bantyeketu River is used for the design of flood protection
structure and river bed improvement work. Different flood protection structures and river
bed improvement works were recommended depending on the flood depth and condition of
river bank. Masonry flood wall and dyke were recommended and designed for areas
around ECA ,Hay hulet , and up stream of Bantyeketu confluence with Kebena River. River
bed improvement works were also recommended for Bambisse Area
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Flood Mapping Case Study on Bantyeketu River in Addis Ababa
ACKNOWLEDGEMENT
First of all I would like to thank the almighty God for giving me the strength to walk all the
long way to reach this point in my life.
I would like to express my sincere gratitude to my Advisor Dr.Daneal F/Sillassie for giving
me valuable guidance and support from the inception of this work to the end.
I am also grateful to the Hydrology Department of MOWE and NMA of Ethiopia for
providing me data free of charge.
At last but not least, I would like to extend my deepest gratitude to my family, for there
encouragement and moral support without your encouragement and care this would not
have happened.

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Flood Mapping Case Study on Bantyeketu River in Addis Ababa
LIST OF TABLE
Contents
ABSTRACT .........................................................................................................................................................I
ACKNOWLEDGEMENT ...................................................................................................................................II
LIST OF FIGURE ............................................................................................................................................ VI
LIST OF TABLE .............................................................................................................................................. VII
ABBREVIATIONS ......................................................................................................................................... VIII
CHAPTER ONE .................................................................................................................................................1
1 INTRODUCTION .......................................................................................................................................1
1.1 Back Ground ......................................................................................................................................1
1.2 Statement of problem .......................................................................................................................2
1.3 General objective ..............................................................................................................................3
1.4 Framework of the study ....................................................................................................................3
1.5 Limitation of the study .......................................................................................................................3
1.6 Study area ..........................................................................................................................................5
1.7 Hydrology............................................................................................................................................6
1.7.1 Bantyeketu River ................................................................................................................ 6
1.7.2 Kechene River .................................................................................................................... 6
1.7.3 Kurtume River ..................................................................................................................... 6
1.8 Vegetation ..........................................................................................................................................7
1.9 Climate ................................................................................................................................................7
1.10 Water Reservoirs ...............................................................................................................................7
CHAPTER TWO ................................................................................................................................................9
2 Review of Literature ..................................................................................................................................9
2.1 Storm Water .......................................................................................................................................9
2.2 Impact of Climate Change on Availability of Water ................................................................... 10
2.3 Flooding ........................................................................................................................................... 10
2.4 Hydrological model ......................................................................................................................... 11
2.5 HEC-GEO RAS (Hydrologic modeling System) ........................................................................ 12
2.6 HEC-RAS (Hydrological modeling System) ............................................................................... 12
2.7 Model selection ............................................................................................................................... 12
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Flood Mapping Case Study on Bantyeketu River in Addis Ababa
CHAPTER THREE ......................................................................................................................................... 15
3 Material and Analysis ............................................................................................................................ 15
3.1 Meteorological Data ....................................................................................................................... 15
3.2 Filling Missing Precipitation .......................................................................................................... 16
3.3 Checking the Consistency of Data .............................................................................................. 16
3.4 Hydrological data availability ........................................................................................................ 19
3.5 Digital elevation model (DEM) ...................................................................................................... 19
3.6 Hydrological Model ......................................................................................................................... 19
CHAPTER FOUR ........................................................................................................................................... 22
4 Methodology............................................................................................................................................ 22
4.1 General ............................................................................................................................................ 22
4.2 River Cross section ........................................................................................................................ 22
4.3 Hydrological modeling ................................................................................................................... 23
4.4 HEC-HMS hydrological model...................................................................................................... 23
4.5 HEC-RAS Hydrological model...................................................................................................... 23
4.5.1 Deficit and Constant ......................................................................................................... 26
4.5.2 Clark unit hydrograph transform .................................................................................... 27
4.5.3 Lag Model .......................................................................................................................... 27
4.6 Modeling base flow with HEC-HMS ............................................................................................ 27
4.7 HEC-HMS model setup ................................................................................................................. 28
4.8 Basin model ..................................................................................................................................... 28
4.9 Meteorological model ..................................................................................................................... 29
4.10 Control specification ....................................................................................................................... 29
4.11 Arc GIS............................................................................................................................................. 29
4.12 Calibration ....................................................................................................................................... 31
4.13 Model Validation ............................................................................................................................. 31
4.14 Model Evaluation ............................................................................................................................ 32
4.15 Frequency of point rainfall ............................................................................................................. 34
CHAPTER FIVE ............................................................................................................................................. 35
5 Result and Discussion ........................................................................................................................... 35
5.1 ARC-GIS model result ................................................................................................................... 35
5.2 HEC-HMS hydrological modeling results ................................................................................... 36
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Flood Mapping Case Study on Bantyeketu River in Addis Ababa
5.2.1 Calibration ......................................................................................................................... 36
5.2.2 Peak Flood ........................................................................................................................ 40
5.3 HEC-RAS hydrological modeling result ...................................................................................... 40
5.3.1 Flooding Areas .................................................................................................................. 43
CHAPTER SIX ................................................................................................................................................ 45
6 Conclusion and Recommendation....................................................................................................... 45
6.1 Design Background ........................................................................................................................ 45
6.2 Other flood Protection Measures ................................................................................................. 45
6.3 Hydraulic Modeling of Bantyeketu River Channel ..................................................................... 46
6.4 Carrying Capacity ........................................................................................................................... 46
6.5 Structural Measures ....................................................................................................................... 47
6.5.1 Masonry Flood wall .......................................................................................................... 47
6.5.2 Masonry dyke .................................................................................................................... 47
6.5.3 River bed excavation ....................................................................................................... 47
References ...................................................................................................................................................... 50
7 Annexes ..................................................................................................................................................... 53

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Flood Mapping Case Study on Bantyeketu River in Addis Ababa

LIST OF FIGURE
Figure 1-1: Frame work of the study ..............................................................................................................4
Figure 1-2: Study Area Location Map ............................................................................................................5
Figure 1-3: Akaki Catchment River System .................................................................................................8
Figure 3-1: Rainfall Data ............................................................................................................................... 15
Figure 3-2: Double mass curve for Addis Ababa Bole Meteorological stations ................................... 17
Figure 3-3: Distribution of Meteorological and gauging station ............................................................... 18
Figure 3-4: Mean monthly flow at Big Akaki for a period of (2003-2007) .............................................. 19
Figure 3-5: HEC-HMS Hydraulic model of Akaki Catchment .................................................................. 21
Figure 5-1: Study Area catchment delineation ........................................................................................ 35
Figure 5-2: Simulated and Observed flow Hydrograph (Calibration) ..................................................... 38
Figure 5-3: Simulated and Observed flow Hydrograph (Validation) ....................................................... 39
Figure 5-4: Bantyeketu river carrying capacity ......................................................................................... 42
Figure 6-2: Lay out map of Bantyeketu River ........................................................................................... 49
Figure 7-1: Water surface Profile 50 years ............................................................................................... 67
Figure 7-2: Water surface Profile 25 years ............................................................................................... 68
Figure 7-3: Water surface Profile 10 years ............................................................................................... 69
Figure 7-4: 3D View of 50 years flood........................................................................................................ 70
Figure 7-5: 3D View of 25 years flood........................................................................................................ 71
Figure 7-6: 3D View of 10 years flood........................................................................................................ 72

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Flood Mapping Case Study on Bantyeketu River in Addis Ababa

LIST OF TABLE

Table 4-1: General Performance ratings for recommended Statics values .......................................... 33
Table 4-2: Rain fall depth for different return periods ............................................................................... 34
Table 5-1: Optimal model calibration parameters ..................................................................................... 37
Table 5-2: Peak flood ..................................................................................................................................... 40
Table 5-3 Bantyeketu River Characteristics .............................................................................................. 40
Table 5-4: Bantyeketu River carrying capacity .......................................................................................... 41
Table 5-5: Flooding area (10 years return period) ................................................................................... 43
Table 5-6: Flooding area (25 years return period) ................................................................................... 43
Table 5-7: Flooding area (50 years return period) ................................................................................... 44
Table 6-1: Design Background for Flood Protection Structures (Flood Wall and Masonry Dyke). .. 46
Table 6-2: Recommended Flood Protection Structures .......................................................................... 47
Table 6-2: Recommended Flood Protection (River bed Excavation ..................................................... 48

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