We propose a water management framework for bringing together formal and informal water rights and irrigation intake design to apportion water in catchments. This framework is based on setting and modifying seasonally applied volumetric and proportional caps for managing irrigation abstractions and sharing water between upstream irrigators and downstream users in river basins. The volumetric cap, which establishes the upper ceiling of irrigation abstractions in the wet season, relates to formal water rights and maximum intake capacities. The proportional cap, which functions in the dry season beneath the volumetric ceiling, builds on customary water negotiations and on the design and continual adjustment of intakes by users. Both caps should be viewed as being adjustable in response to dialogue between users. The analysis is informed by conditions found in the Great Ruaha river basin, southern Tanzania, where rivers sequentially provide water for irrigation, a wetland, the Ruaha National Park and for electricity generation. Consequences for catchment interventions in the face of climate, population and land use change are explored.
In: Community-Based Water Law and Water Resource Management Reform in Developing Countries, Edited by Barbara Van Koppen, Mark Giordano, and John Butterworth. Comprehensive Assessment of Water Management in Agriculture Series, CABI Publishing. Chapter 14, 228-247. ISBN 9781845933265