Assessment of Needs and Options for Sustaining Ecological Water Supply to Ruaha National Park in Tanzania through Damming Ndembera in Iringa Tanzania

Abstract

Ndembera river is one of the rivers contributing to the Great Ruaha River (GRR) basin in Tanzania. Since 1993, GRR flow started to cease during the dry period due to over-abstraction of water from the river for upstream irrigation activities. Thus, it was essential to evaluate the water resources availability in the catchment and analyze options available to sustain the ecological water supply in the Ruaha National Park (RNP) and to satisfy other water users in the basin. The study used the Water Evaluation and Planning (WEAP) model as Decision Support System (DSS) to simulate current demand and forecast future water availability. This aimed at predicting the possible impacts on the water balance and allocation to various water demand sites. The study used historical data (1990-2018) to simulate water supply and demand in the GRR basin for the period 2019 to 2050. The calibration of the streamflow data for the period 1990 to 2005 was performed, and validation for the period 2006 to 2015 from two gauging stations. The scenarios involved in this study were: population growth of 2.2% and high population growth rate of 2.8%. Other scenarios were; expansion of irrigation farming area by 50% and 100% of the current area; improvement of irrigation systems and water abstraction infrastructures; construction of two dams in the Ndembera river; implementation of environmental flow requirement (EFR), and impoundment of the Ihefu Swamp. The study involved the evaluation of five water demand sites: namely, domestic, agriculture, livestock, bricks making, and EFR. The improvement of irrigation systems was found to reduce the irrigation water demands from 33.2MCM (2018) to 22MCM (2050). High population growth led to an increase in unmet demand from 2024 (580 to 600TCM) to 2050 (20 to 30TCM) under reference and high population scenarios respectively. The construction of Lugoda dam was found to increase irrigation water demand coverage from 80.87% to 98.17%. The introduction of (EFR) for (RNP) was found to compromise the water demand coverage for other sectors in the basin. Thus, the impoundment of Ihefu swamp showed to facilitate the 100% water demand coverage for all demand sites throughout a year. Also, data available regarding the availability of groundwater resource showed a maximum of 5L/s available for domestic tail-enders. Moreover, the study showed that Mwagusi, Itiku, and Mdonya rivers found within RNP are potential for impounding and hence being used for ecological water supply during the dry period. However, for effective management of the river flow, EFR consideration, control of illegal water abstraction, and timely granting of water rights are recommended.