DAM BREACH MODELLING AND FLOOD INUNDATION MAPPING: (A CASE STUDY OF TABA EMBANKMENT DAM)

DAM BREACH MODELLING AND FLOOD INUNDATION MAPPING: (A CASE STUDY OF TABA EMBANKMENT DAM)

The major goal of the present study was to identify the critical erosion areas of an agricultural Koga watershed and recommend the best management practices using a physical process-based watershed scale model, soil water assessment tool (SWAT). The semi-automated Sequential Uncertainty Fitting (SUFI2) calibration process built in SWAT calibration and uncertainty program (SWAT-CUP) was used to calibrate the model parameters using time series of flow and sediment load data of 1997 to 2006 and validated with the observed data from years 2007 to 2011. The performance of the model was evaluated using graphical methods to assess the capability of the model in simulating the runoff and sediment yield for the study area. The coefficient of determination (R2 ) and Nash Sutcliff efficiency values for the daily flow calibration using SUFI2 are 0.89 and 0.89 respectively for validation and it was 0.89 and 0.88. For daily sediment yield by using SUFI2 calibration technique the model evaluation coefficients R and NSE for calibration was computed as 0.87 and 0.88 respectively, for validation it was 0.86 and 0.86 respectively. The sensitivity analysis runoff and sediment producing parameters was also carried out and discussed. This paper presents sediment yield simulations in the Koga watershed under different Best Management Practice (BMP) scenarios. Scenarios applied in this paper are (i) Base scenario (Jones et al.) Applying terraces (ii) (iii) contouring (iv) introduce strip cropping. The scenario results showed that applying terraces, contouring and introducing Strip cropping reduced sediment yields both at the sub watershed and the watershed outlets. Considering the critical sub watershed for the existing conditions scenario (Base scenario), the model result indicates that simulated annual average sediment yield was 33.45 t/ha/yr. Depend on this from base scenario terraces are saving 18.45 tons/ha/year of soil loss. Contouring was found to reduce soil erosion by 10.54 tons/ha/year. Strip cropping for agricultural fields in the watershed reduces erosion also by 8.75 tons/ha/year. These results indicate that applying BMPs could be effective in reducing sediment transport for sustainable water resources management in the watershed
URI: http://hdl.handle.net/123456789/2043
Date: 2024-01

Abstract:

It is important to accurately predict the flow behavior of a dam breach so that potential mitigation strategies can be investigated for disaster management planning. Flooding resulting from the collapse of a dam is a highly destructive event. This study aims to predict the breach outflow hydrograph, prepare downstream flood inundation maps and develop an emergency action plan for the flood-prone areas around the Taba Dam. Meteorological data, salient features of dams, DEM, land use and land cover and soil data were the data collected and software’s of HEC-HMS 4.11, Autodesk 2018, HEC-RAS 6.4.1, ArcGIS 10.5 and HEC-GeoRAS 10.5 were used for analysis. The dam failure mode was analyzed for overtopping and piping failure cases using five dam failure regression equation methods which are: - MacDonald and Langridge Monopolis (1984), Von Thun and Gillette (1990), Froehlich (1995), Froehlich (2008) and Xu and Zhang (2009) are used for breach parameter estimation. A meteorological station data from 1972 to 2021 is used for hydrological analysis and the probable maximum precipitation of the station is 323.1mm and the probable maximum flow generated from the watershed is 410.82m3 /s. This inflow and the water impound in the dam are the expected outflow when the dam fail and after comparing the result of the five methods outflow hydrograph, the result obtained using the Von Thun and Gillette (1990) equation for the case of overtopping was selected for the downstream inundation map analysis with a side slope of 0.5H:1V, a breach width of 77 m for the lower breach formed, a development time of 0.59 hours for the breach failure and a maximum flooding of 4,857.21 m3 /sec. The flood was also used to identify the most vulnerable area, this flood partly affects village called Dukie, Wajel, Abekesti and Chifer and also fully submerge a bridge found on the road from Addis Ababa to Bahir Dar. This case study presented an integrated emergency action plan to protect population found around the dam and siren alarming method is recommended when there is a sign of failure at the dam and the findings and recommendations were also incorporated.

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