A Modelling Approach to Assess Inter-Sectoral Competition for Water Resources in the Kafue Flats, Zambia zyxw M P McCartney, MSc and H A Houghton-Carr, MSc* Abstract zyxwvutsrqpon The Kafue River joins the Zambezi River just below Kariba dam. Upstream from its confluence with the Zambezi, it flows through the primary sugar-cane pro- ducing region of the Kafue Flats and then through Kafue Gorge where there is an important hydro-electric power station. These different activities compete for limited surface-water resources. An evaluation of existing water resources and their ability to cope with future demands and different operating policies is made difficult because of the intricacy of the hydrological system and the limited availability of long-term reliable data series. In this study, complex site-specific models, traditionally regarded as the answer to such problems, were discarded in favour of a standard, relatively simple reservoir-simulation model. The model was successfully used to simulate the present conditions and test a possible future water-use scenario. Key words: Hydro-electricity; inter-sectoral competition; Kafue flats; modelling. Introduction Most of Zambia's mining, industrial and agricultural activities, and approximately half the country's popu- lation, are concentrated within the Kafue basin - making the Kafue River the most significant waterway in Zambia in terms of the national economy('). The Kafue Flats region is Zambia's primary sugar-cane producing area, and there is a major hydro-electric power station at Kafue Gorge dam, downstream from the flats; however, there is potential for these sectoral water requirements to conflict. In the past, emphasis has been on hydro- electricity production but, increasingly, agricultural development is becoming an important component of the Zambian tiovernment's plan to revitalize its economy. However, the associated additional irrigation require- ment would increase abstractions from the Kafue River, with potential implications for generation of hydro- electricity. An assessment of the availability of water resources for these different activities must consider present and estimated future demands. Previous work in the region resulted in the production of complex, site- specific models, e.g. DHV Consulting Engineerd2) developed a semi-distributed water-balance model of the Kafue Flats, requiring many assumptions about the system hydrology, in particular inflows and outflows within the flats, where many watercourses are ungauged. With the past focus on hydro-electricity production, *Hydrologists. Institute of Hydrology, Wallingford, Oxfordshire, UK other complex models have been used to optimize operation of the Kafue Flats system to increase reliability of the energy prod~ction(~). Kafue Basin The Kafue basin lies on the Central African plateau and is a principal sub-catchment of the Zambezi River (Fig. 1). It lies completely within Zambia, with an area of 155 000 km2 making up about 20 O/o of the total land area of the country. The basin can be divided into three zones: the Upper Kafue (extending from the headwaters to Itezhi-tezhi), the Middle Kafue or Kafue Flats (from Itezhi-tezhi to Kafue Gorge), and the Lower Kafue (extending from Kafue Gorge to the Zambezi conflu- ence). The altitude of the basin ranges from 1300 m above sea level in the headwaters, to 1000 mat the head of Kafue Gorge. The broad alluvial plain of the Kafue Flats between Itezhi-tezhi and Kafue Gorge has an area of about 7000 km2 and is characterized by floodplain swamps and marshlands. The flats support local industries such as recession agri~ulture(~), dry-season cattle grazing and traditional fisheried5). The Kafue River flows 450 km through the flats, and it takes about six weeks for water to flow from Itezhi-tezhi to Kafue Gorge. Water is abstracted for a variety of purposes, including municipal supplies, agriculture - primarily sugar-cane growers (the largest is the Zambia Sugar Company (ZSC)), and winter wheat producers. Most of these industries are net consumers of water, which reduce the amount of water reaching Kafue Gorge, where the Zambian Electricity Supply Corporation (ZESCO) need the maximum flow in the river to generate electricity. zyxw Zambian Sugar Industry The entire Zambian sugar industry is situated near Mazabuka, 130 km south-west of Lusaka (Fig. l), where excellent agronomic conditions exist. The climate is generally hot and humid with max. and min. tempera- tures of 32OC and 24°C respectively in October (usually the hottest month) and mean max. and min. tempera- tures of about 20°C and 1O"C, respectively, between April to August (the cool season)(6).However, the dry season (from May to October each year) means that irrigation is essential for cane cultivation. Recently, the Zambian Government increased the emphasis on agricultural development as a means of attaining economic recovery, while ensuring self- sufficiency in food production('). One of the proposals for expansion entails increasing the area under sugar-cane from 132.5 km2 (producing 170000 t of cane) to 174 km2 (producing 230 000 t of cane). However, increased zy 0 J.CIWEM,1998, 12, April 101