Flood Damage Analysis Using HEC- FDA Software (In case of Upper Awash Sebata-Awas Woreda
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Date
2019-06
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Addis Ababa University
Abstract
Flood occurs with high frequency in Sebata-Awas Woreda and cause tremendous damage
to cultivated land inundation and silting, displacing people, life and other properties every
year. The study describes technical approach in flood Damage analysis, with objective of
detail study environmentally feasible flood protection plan and flood damage
management.
Flood frequency for different return period done, by selecting appropriate probability
distribution based on goodness fit test. Statistical analysis i.e. outlier, independent and
stationary and filling missing data performed for flow observed at Awash Belo gauge
station. Contour of 1m interval from (Digital Elevation Model) DEM 30m prepared to
determine depth damage function. Flood inundation mapping in ArcMap and field survey
done to estimate property loss. Triangulated Irregular Network (TIN) prepared from
contour in ArcMap with GeoRAS extension to set layout for both canal and river.
However, the cross section entered from field data. Manning number and Boundary
condition estimated on field. Water surface elevation computed by HEC-RAS model.
Observed data are independent and have no outlier. Flood frequency estimated by Gumbel
(Extreme I) method 42.36 m3 /s, 49.01 m3 /s, 53.41 m3 /s, 58.97 m3 /s, 63.10 m3 /s, 67.20
m3 /s, 72.59 m3 /s and 76.66m3 /s discharges for 2, 5, 10, 25, 50, 100, 250 and 500 year
respectively. These floods used for water surface profile computation. Expected and
Equivalent, annual damage amount reduced for different exceedance probability
estimated. Total economic loss 69423.77 $ damage expected annually without project. By
providing canal we can reduce loss to 5572.80 $ s per annum and reduce ton of sediment.
Canal loss which very low per households. Inland flood protection and dyke integrated to
Canal nullifies (0 $) expected damage per annum. Equivalent annual damage report shows
without project, Canal and Integration of Canal with dyke and Inland flood protection are
69423.77 $, 5572.80 $ and 0 $ respectively through project life 50 years. Expected annual
damage and Equivalent annual damage HEC-FDA model statics shows that flood
protection plan is required.
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Keywords
Sebeta-Awas, Flood Protection Structure, Flood frequency, Expected annual damage, Equivalent annual damage