Design and simulation of an earth embankment dam for water harvesting for increased agricultural production

Abstract

Due to uneven distribution of rainfall throughout the year characterized by heavy rains in a short period of time following prolonged dry spells, it has necessitated the design of water harvesting structures to store water during heavy rains for multipurpose uses including controlling floods and water for irrigation during dry periods. The overall objective for this project was to design and simulate an earth-embankment dam for agricultural production. The specific objectives were; to carryout hydrological data analysis thereby understanding the hydrological conditions of the river and watershed and estimate the crop water demand, locate a suitable dam site by considering primarily the topographical and geological characteristics of the study area, design the dam components and simulating the dam to evaluate its stability conditions. Literature review discusses the dam definition and its history in Uganda, Various dam types, choice of dam type and site, possible failures of embankment dams, foundation conditions for dams, importance of reservoirs/dams, factors considered while selecting an irrigation water source and various dam components. The various methods used in this study include; desk study, oral interviews, consultations and discussions as well as carrying out topographical surveys. All hydrological data was analyzed using Microsoft excel and XLSTAT. River discharge data was found with gaps which were filled using the “Multiple imputations” approach in XLSTAT. The minimum and maximum flows for the selected period of 37 years (1978-2014) were found to be 0.0 and 54.8m3/s in 1995 and 1979 respectively. The average flow and standard deviation were 15.1 and 9.7m3/s respectively. Analysis also shows a general increase in flow from 1997 to 2014. Dependable yields from the river were estimated using the flow-duration curve. Flows were estimated at 85, 90 and 95% of the time to be 8.5, 7.3 and 6.0m3/s respectively. The average annual Volume of water in the river was estimated to be 489.54Mm3. This is the amount of water that would be collected in a year if this river was impounded. This information was helpful to the researcher to know whether the river has adequate flow to meet the demand. For spillway design purposes, flood frequency analysis was carried out and the peak discharge was taken at 100year return period to be 66.25m3/s. Locating a dam site was carried out using the Digital Elevation Model and the ArcHydro tools and 3D analyst tools in ArcGIS 10.4. Reservoir calculations were performed and by plotting the Elevation-Area and Elevation-Capacity curves using the python tool, the height of the dam was established. Simulations were performed using Geostudio 2018 and the minimum factor of safety for slope stability was found to be 1.233. This value is greater than 1 indicating that the structure is safe and should be implemented.