Abstract:
Spate irrigation is runoff farming where flash floods are diverted by intake
structures to irrigate crops using basin system. The indigenous spate irrigation
practices have been described to be not effective and of low crop productivity
due to many problems (such as the destruction of headwork during large flood
events and deposition of heavy sediment load in canals and irrigated fields).
Spate irrigation system has been largely neglected in the literature and there
are no available technical guidelines that determine its specificities. Yet, it is
different from conventional irrigation in many ways and needs special skills
and approaches of which practitioners are not always aware. The, standard
design approaches cannot appropriately take into account the level of
uncertainty related to floods, the hydraulic challenge of guiding flood flows,
the heavy sediment loads, the exceptional nature of the water rights, or the
management and maintenance models that are specific to spate irrigation. To
improve productivity of spate irrigation it is recommended to select proper
rehabilitation and modernization program. Basic step to reach this end is to
quantitatively diagnose these problems and there by decide on program
activities. Against this background, this study is directed to analyze the
existing performance and mode of operation in El Semeih agricultural
scheme, which is one of the old spate systems in Sudan. Therefore, the overall
objective of this study is to assist planners and practitioners in designing and
managing other spate irrigation projects. The study specific objectives are two
folds: Firstly: to diagnose and evaluate performance of El Semeih Scheme
with respect to water utilization and management, agricultural productivity,
and allocation of seasonal budget. Secondly: to identify the type and
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distribution of sediment load entering in El Semeih agricultural scheme. To
achieve these objectives primary and secondary data is collected for Khor
Abu Habil and El Semeih spate irrigation project during season2010/2011.
The primary data covers measurement of discharge, sediment settling
velocity, concentration, and Particle size distribution, Sediment removal rate,
and land levels along the main canal. While secondary data covers soil,
climate, areas, agricultural data, project budget and past studies. The obtained
results are discussed with reference to the reviewed past studies, theoretical
framework, and current practices. The study employed evaluation procedure
for diagnosis of project performance covers water resource utilization and
sediment monitoring. Water resource utilization is discussed in terms of:
water use efficiency (WUE), hydraulic performance (adequacy, and equity
indicators), agricultural performance (area utilization and crop productivity
indices), and budget utilization. Sediment monitoring is discussed in relation
to determination of sediment sizes, spatial and temporal distribution of
sediment, and sediment removal rate. It is inferred from the results that
indices of irrigation efficiency, crop productivity, area utilization efficiency,
budget allocation, and water use efficiency are low due to poor system of
water management. The equity indicator is low reflecting existence of top-tail
ends problem in the project and adequacy of supply can be described as poor
and function of available rain water. The study also reveals that low sediment
removal rate (high sediment concentration) is found at reaches located at
canal top and more sediment deposition occurred at these reaches (non
uniform head- tail sediment distribution) due to the mode of water
distribution. As conclusion the study recommend to improve the existing
mode of water management and distribution, study alternative schemes to
store water and select the most feasible method for sediment control.
Key words: Spate Irrigation, Sediment monitoring, irrigation performance;
agricultural production; water resources