Water management and competition between users in water scarce river basins is a major challenge facing the human race. The inter dependence of users in such basins, necessitates a clear understanding of each user in relation to the location, the water demand, and the duration of water need. An understanding of these factors, together, is very important for the management of the basins without which, it is argued that, the competition and conflict between users become increasingly high. As an example of this, the supposed competition between irrigation and hydropower generation is well documented in Tanzania. Yet, well-founded scientific analyses are a necessary part of this understanding, as they can inform us whether sectors are truly in competition or not. Likewise, such studies can allow us to quantify associated tertiary phenomena and factors that lead us to believe that these sectors are in competition when in fact they may not be.
This paper explores a study conducted in the Usangu basin, Tanzania, since the year 1999 to investigate the partitioning of water needs for irrigation, and what implications this has for downstream users, particularly hydropower (HEP). The paper discusses the problems relating to arrangement and needs of the water users (irrigators, animals, hydropower stations, and environment) in the Usangu basin and it concludes that the commonly held views a) that irrigation is inefficient; b) that rice irrigation is in direct competition to HEP, do not hold up to close scrutiny. This study tell us that wet season flooding is proportionally more important in recharging the reservoirs than visible low flows in the dry season. Looking to the future, this study tells us that inefficiency of irrigation is not a great problem in volumetric terms so much as the increasing area of rice and the total abstractive capacity in Usangu (circa 50 cumecs and rising).
Paper Presented at Ruaha+10 Seminar, 11 & 12 December 2003, Morogoro, Tanzania. 10 pp. (paper) + 4 pp. (powerpoint)