Quantifying Total Water Productivity for Multiple-Use Small Reservoirs in Mzingwane Catchment, Zimbabwe

Abstract

The Government of Zimbabwe embarked on construction of small, medium and large multiple-use dams as a strategy to increase the level of water security in the country. Over 10,000 dams have been constructed in communal and large-scale-commercial farming areas. So far, the socio-economic contributions made by medium-to-large scale dams have been fairly documented, but those by small reservoirs are scantily documented. A study on total water productivity was conducted to determine total water productivity and apply this to value and allocate scarce water resources to uses that optimise societal benefits in semi-arid areas. Water productivity gives the value of a product that can be obtained from using a unit amount of water on alternative functions such as domestic use, livestock watering, crop production, fishery, brick making and related uses so that the resources can be wisely allocated to more productive sectors. Eight small reservoirs surrounding Avoca Business Centre in Mzingwane Catchment, Zimbabwe, were studied. Questionnaires were administered and physical measurements carried out on crops, livestock, thatching grass, bricks and fisheries. The results were that donkeys had the highest monetary water productivity of 145 US$/m3 followed by bricks and cattle(32 US$/m3), tomatoes (24 US$/m3), sheep and goats(11 US$/m3), small vegetables (8 US$/m3), green maize(2 US$/m3), dry beans (0.9 US$/m3), fish (0.7 US$/m3), wheat (0.2 US$/m3), domestic water use (0.03 US$/m3) and grass (0.02 US$/m3). Formulation of an allocative strategy recognised scarcity of water resources in terms of dry season reservoir yield, individual-use water productivities and societal values. Two paths for increasing productivity per unit of utilizable water resources were considered for the strategy; (i) depleting developed primary water supply for beneficial purposes by increasing water savings and (ii) producing more output per unit of depleted water by increasing unit water productivity. By re-allocating water based on water productivities within and across sectors, income levels were increased by about 350% from current uses. The results of the study illustrated that water productivity can be used as a strategy for allocating scarce water resources for attaining optimum societal benefits. The water productivity strategy, however, should be complimented with wide stakeholder consultations to derive the optimum societal benefits.