Abstract
Ngwerere and Kanakatampa Streams are the main tributaries of the Chongwe River. The Ngwerere stream originates from the city of Lusaka and meanders through Lusaka City and Chongwe Town for an approximate distance of 41 km before joining into the upper part of Chongwe River. The Kanakatampa Stream is a tributary of the Chongwe River. It meanders from the Kanakatampa Area for approximately 52 km before discharging into the middle of the upper part of the Chongwe River. The Chongwe River Catchment which is a sub-catchment of the Zambezi Basin drew the attention of researchers and policymakers when the Chongwe River started drying up in the dry seasons causing a water crisis particularly in the downstream regions of the middle catchment. Therefore, it is important from the water resources management perspective, to assess the contribution of tributaries into the flows of the Chongwe River. Ngwerere and Kanakatampa streams are socially, economically, and environmentally important streams for the city of Lusaka and surrounding area. This study, therefore, concentrated on evaluating the flow contribution of the two streams to the Chongwe River using the Water Evaluation And Planning (WEAP) tool. The streamflow data (1970-2010) recorded at the Chongwe Great East Road Bridge gauging station were used in the WEAP embedded Parameter ESTimation (PEST) auto-calibration tool to calibrate (1970-1999) and validate (2000-2010) the model. The monthly streamflow model calibration and validation results were assessed using the correlation coefficient (CC), Coefficient of determination (R2), Nash-Sutcliffe Coefficient of Efficiency (NSE), and Percent bias (PBIAS). The model performance results achieved were PBIAS of 1.24%, CC = 0.81, R2 = 0.66 and NSE = 0.62 during the calibration period and a positive PBIAS of 2.94%, CC = 0.81, R2 = 0.67 and NSE = 0.62 during the validation period. The median of the flows (Q50) was obtained from the historical flow duration curves (FDCs) generated in averaged intervals of 10-year from 1970 to 2019. The results showed that on average, the Ngwerere and Kanakatampa Streams contribute 52.8% and 29.6% respectively, to the flow of the Chongwe River in the upper and middle Catchment. The results also showed that the contribution of the Ngwerere and Kanakatampa Streams to the Chongwe River discharge has been reducing historically at a rate of 0.65% per decade and 1.35% per decade respectively over a period of 50 years (1970-2019). Suggestions for sustainable management of the tributaries such as the Ngwerere and Kanakatampa Streams were provided in this study.
Highlights
Water is an essential resource that is necessary for life to exist
This study presented a simplified process of assessing the streamflow contribution of the Ngwerere Stream to the streamflow of the Chongwe River as part of the hydrological study of the water-stressed Chongwe River Catchment in Zambia
The study revealed that the contribution of the Ngwerere Stream to the flows of the Chongwe River has been historically reducing at a rate of 0.648% per 10 year period and this is expected to continue reducing with the ever-growing urbanization in the cities of Lusaka and Chongwe
Summary
Water is an essential resource that is necessary for life to exist. Freshwater is needed for farming, industrial, domestic, hydropower, recreational, and environmental activities [1]. It is necessary to apply an integrated approach for the effective management of water resources, which considers the environmental, ecological processes, and human activities in the catchment. This explains the management of the multiple values of water and reflects the impacts of decisions across the environment, politics, science, tradition, engineering, economics, culture, and tradition. The understanding of the tributaries’ contribution to the river basins is vital for the management of water resources. The authors in [5] evaluated the contribution of tributaries in the Mekong river basin in South-East Asia and stated the significance of each tributary to the flows of the Mekong River including highlighting the factor of damming. It is clear that tributaries have a huge impact on the waterways of the river catchments
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