Patterns and Implications of Hydrologic Regime Change in Chongwe River, Zambia

Moses Ngongo Chisola,Michal Kuráž

doi:10.5539/jgg.v8n3p1

Abstract

Conflicts regarding water use have emerged in some small irrigation dominated peri-urban catchments in Zambia; Chongwe being one such catchment. Despite these conflicts suggesting a change in hydrologic regime, the nature of the changes and their drivers has not been adequately investigated. The Mann Kendall trend test and Flow Duration Curves were used to investigate changes in hydro-climatic time series data in Chongwe upper catchment for the period 1955-2006. Although the results reviewed a significant upward trend in temperature at 0.05 significance level, there is no significant trend in rainfall. Annual and seasonal runoff at the upstream located Ngwerere weir reviewed significant upward trends at 0.05 significance level. This increased runoff which is attributed to sewer water discharge and increased imperviousness is abstracted for agricultural activities upstream. In this regard, results reviewed no significant trend in runoff at the outlet gauging station (Chongwe 5025). However, analysis of the Flow Duration Curves at this outlet gauging station indicated an increase in wet season flows and a reduction in dry season flows for the 1990-2006 period. These results suggest that human activities in the upstream parts of the catchments could be the major contributing factors to the changes in flow regime, hence the ensuing upstream vs downstream water use conflicts. However, there is still excess runoff in the wet season that could be harvested by downstream water users in order to offset the deficit in downstream dry season flows.

Highlights

Monitoring trends in hydro-climatic data is often times overlooked
The graphs show that rainfall over Chongwe catchment is decreasing while temperature is increasing
The study results suggest that, there is a surplus of water in the rainy and a deficit in the dry season flows (Figure 6b)

Summary

Introduction

Changes in hydro-climatic variables only become of concern in times of drought or when people’s property is damaged by floods and when upstream vs downstream water use conflicts persist. In Zambia, conflicts are prominent in many catchments such as Chongwe, Chalimbana, Lunsemfwa, and Kaleya among others, suggesting that the flow regime of these rivers have been altered. These conflicts have arisen mainly due to climate change or variability, increased water resource developments, and indiscriminate cutting of trees in river basins. It is not surprising that conflicts over water use have persisted in Chongwe catchment especially among the commercial farming community upstream and the villagers downstream since the 1990s (Mucheleng'anga et al, 2002; Chongwe District Council, 2006)

Methods

Results

Conclusion