Effect of Traditional Water Allocation Practices on the Environmental Flows In Ntcheu-Malawi: case study of Rivirivi River

Abstract

The headwater catchments of the Rivirivi River basin play a vital role in meeting downstream water resources requirements. In recent years, the Rivirivi River has experienced significant changes in its hydrological regime, including an increased number of zero-flow days. These changes have serious implications on water security and basin management. This study was aimed at investigating the effect of traditional water allocation practices in the catchment on environmental flows. Water quantity indicators were assessed through flow duration analysis of the river flow regime behaviour before and after the introduction of the traditional water allocation practices. Further, desktop reserve model was applied to determine various categories of maintenance of high and low flows. Anthropogenic land use induced change patterns and their potential effect on water resources were investigated by time series analysis satellite imagery. Standard water quality assessment techniques were applied to assess spatial variation in water quality. The results indicate that there was a considerable difference in average annual stream flow between two identified main periods (between 1963 to 1983 and 1984 to 2004) and zero flows increased from 5% to 12%. The high flow index (Q5/Q50) increased by 16% between 1963 to 1983 and 1984 to 2004 whereas there is a dramatic reduction in the low flow index (Q95/Q50), with up to 100% reduction. Median flows (Q50) reduced by 8% in the same period. Further, the ecosystems need approximately the range of 35–40% of the MAR to be maintained at class A (Class A is streamflows with negligible modification from natural conditions and have negligible risk to sensitive species) and the range of 9–13% of MAR for class D (Class D is streamflow with high degree of modification from natural condition and intolerant biota unlikely to be present). In addition, the area experienced a 65% reduction in forest cover from 1992 to 2008 which resulted in increased high flow index by 16%. Furthermore, there was an overall significant spatial variation of chemical and physical water quality parameters in the catchment except for nitrates. However, the variations are within the Malawian standards of surface water quality set by MoIWD. The results suggest that traditional water allocation practices have negatively affected low flow environmental flows requirements by increasing zero flow days in Rivirivi River catchment.