Design of a water drainage system to control floods on Tochi irrigation scheme.

Abstract

The Tochi irrigation scheme, located in Oyam district, northern Uganda, has been plagued by floods since its establishment in 2016. The floods have resulted in significant damage to crops, disruptions in farming activities, and abandonment of plots by farmers. The main cause of these floods is the overflowing of the Tochi River, which bursts its banks and inundates the area. Additionally, the inadequate water drainage system has further exacerbated the problem, leading to the submergence of a substantial portion of the scheme The objective of this study was to design a water drainage system for Tochi irrigation scheme to control floods. This study aimed to achieve three specific objectives: Ascertaining peak discharge through simulating a rainfall-runoff model: By modeling the rainfall-runoff. The study also performed a hydraulic model to determine the flood depth, water velocity, and water surface elevation which would aid in the design of the channels. Flood frequency analysis was done with Gumbel distribution to generate IDF curves and frequency storms that were used in flood modeling. Flood modelling was performed using HEC-HMS model software 4.11 and discharges of 93.5, 215.1, 256.6, 461, 578.9, 702.9m3/s corresponding to floods of return periods 2, 5, 10, 25, 50 and 100year floods respectively. The model calibration was done using the Nash-Sutcliffe model efficiency (NSE). As a result, the model calibration was found to be very satisfactory with NSE 0.985. Flood analysis was done using HEC-RAS software version 6.3.1, flood inundation maps corresponding to discharges of different return periods were developed and analyzed. A 10-year return period discharge of 256.6m3/s was considered as the design discharge of the drainage channel. Trapezoidal channels were designed with the help of manning’s equation and storm water drainage formula for different 12 plots of the scheme as was divided appropriately.