An assessment of surface water availability in the Pungwe Sub Catchment and development of an appropriate water allocation framework.

Abstract

Pungwe River is a transboundary river which is shared between Zimbabwe (4.7% of land area) and Mozambique (97.3% of land area). The two governments are preparing a Bilateral Agreement on the management of water in the Pungwe River basin to allow part of the total runoff generated in Zimbabwe to flow to Mozambique. This is in line with the SADC and other International protocols governing the use of international Rivers. Zimbabwe needs to have a water allocation system that is equitable and fair to comply with this agreement. Part of the catchment from Zimbabwe is not gauged further constraining the testing of alternative allocation systems that can be adopted by Zimbabwe. The aim of this research is to assess surface water availability in the tributaries of Pungwe River and Honde River and develop a water allocation framework to guide Pungwe sub-catchment council in water allocation. The Pitman model was used to generate surface runoff for the Pungwe River and Honde River catchments. The Pitman model was calibrated and validated using observed runoff for three gauging stations (F14, F22 and F23). A WAFLEX model was set up to evaluate different water allocation systems. The models were run to assess the performance of the different water allocation systems in terms of water shortages for different users within the sub catchment and satisfying proposed international flow obligations. Three water allocation practices were investigated namely proportional, proportional combined with priority and market based water allocation system. The Pitman model was found to be suitable for modelling the Pungwe Sub-catchment area with model results providing a NSE value of 0.7 and R2 value of 0.8 between observed and modelled stream flows. Results from the WAFLEX model showed that international obligations would be 100% satisfied under all the water allocation practices in Pungwe micro-catchment. However shortages were noted in Honde micro-catchment. Proportional combined with priority water allocation practice improved satisfaction with an average 20% agricultural water uses in Pungwe micro-catchment and 10% in Honde micro-catchment. Proportional combined with priority water allocation practice was considered the best practice to be used by the sub catchment. The data generated from this research has to be incorporated in the allocation of permits in the sub catchment and transboundary management of the Pungwe Basin.