Application of integrated water resources management in computer simulation of River Basin's status - case study of River Rwizi

Abstract

During the last few years, concern has been growing among many stakeholders all over the world about declining levels of surface water bodies accompanied by reduced water availability predominantly due to ever increasing demand and misuse. Furthermore, overexploitation of environmental resources and haphazard dumping of waste has made the little water remaining to be so contaminated that a dedicated rehabilitation/remediation of the environment is the only proactive way forward. River Rwizi Catchment is an environment in the focus of this statement. The overall objective of this research was to plan, restore and rationally allocate the water resources in any river basin with similar attributes to the study area. In this research, Integrated Water Resources Management (IWRM) methodology was applied through Watershed/Basin Simulation Models for general river basins. The model chosen and used after subjection to several criteria was DHI Model, MIKE BASIN 2009 Version. It was then appropriately developed through calibration on data from the study catchment, input data formatting and its adaptation to the catchment characteristics. The methodology involved using spatio-temporal demographic and hydrometeorological data. It was established that the model can be used to predict the impact of projects on the already existing enviro-hydrological system while assigning priority to water users and usage as would be deemed necessary, which is a significant procedure in IWRM-based environmental rehabilitation/remediation. The setback was that the available records from the various offices visited had a lot of data gaps that would affect the degree of accuracy of the output. These gaps were appropriately infilled and gave an overall output that was adequate for inferences made therefrom. Several scenarios tested included; use and abstraction for the present river situation, the effect of wet/dry seasons on the resultant water available for use, and proposed projects being constructed on and along the river. Results indicated that the river had insufficient flow to sustain both the current and proposed water users. It was concluded that irrespective of over exploitation, lack of adequate rainfall was not a reason for the low discharge but rather the loss of rainwater as evaporation, storage in swamps/wetlands, and a considerable amount of water recharging groundwater aquifers. Thus, the proposed remedy is to increase the exploitation of the groundwater resource in the area and reduce the number of direct river water users, improve farming methods and conjunctive use of groundwater and surface water - the latter as a dam on River Rwizi. The advantage of the dam is that the water usage can be controlled as necessary in contrast to unregulated direct abstraction, thus reducing the risk of subsequent over-exploitation.