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

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 . 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.

Hydrological Modelling and Water Resources Assessment of Chongwe River Catchment using WEAP Model

“…The observed trend for a period of 34 years shows that precipitation is decreasing at a rate of 0.12 Mm 3 /year. This decrease agrees with the findings in the study by Chisola et al [28] in which the decrease was attributed to climate change.…”

“…This is in line with the result that showed there is high runoff in rainy seasons and very low in dry period. The study conducted by Chisola et al [28] on the upper catchment of the Chongwe River also indicated that there is an increase in runoff during wet season flows and a reduction in dry season flows. An analysis of the long-term time series variation of streamflow at the outlet of the catchment for a period of 34 years (Figure 7) indicates that the streamflow is increasing at a rate of about 0.13 Mm 3 per annum.…”

Analysis of River Tributaries’ Streamflow Contribution Using WEAP Model: A Case of the Ngwerere and Kanakatampa Tributaries to the Chongwe River in Zambia

“…The Chongwe River Catchment (shown in Figure 1) largely covers the Chongwe district of Lusaka province in Zambia. The catchment also covers the districts of Lusaka, Chibombo, Kafue, and a small fraction of the Luangwa district [10]. It is a sub-catchment of the Zambezi Catchment and covers a total area of 5150 km 2 .…”

“…Various studies have been conducted by other researchers in this regard. Chisola & Kuraz [10] investigated the patterns and implications of hydrologic regime change in the upper Chongwe River Catchment and reported that human activities in the upstream region of the catchment could be the major contributing factors to the changes in flow regime.…”

“…When the downstream region of the middle part of Chongwe River dries up, one of its main tributaries; the Ngwerere Stream in the upstream region is reported to have flows during such times making it a unique tributary [10]. Furthermore, [11] [12] reported that the Ngwerere stream together with Kanakatampa Stream are socially, economically, and environmentally important stream for the big city of Lusaka where it originates.…”