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Wageningen University (2010)

Role of sediment in the design and management of irrigation canals : Sunsari Morang Irrigation Scheme, Nepal

Paudel Krishna Prasad

Titre : Role of sediment in the design and management of irrigation canals : Sunsari Morang Irrigation Scheme, Nepal

Auteur : Paudel Krishna Prasad

Université de soutenance : Wageningen University

Grade : PhD thesis 2010

The sediment transport aspect is a major factor in irrigation development as it determines to a large extent the sustainability of an irrigation scheme, particularly in case of unlined canals in alluvial soils. Investigations in this respect started since Kennedy published his channel-forming discharge theory in 1895. Subsequently different theories have been developed and are used around the world. All of them assume uniform and steady flow conditions and try to find the canal dimensions that are stable for a given discharge and sediment load. In the past irrigation schemes were designed for protective purposes with very little flow control, hence steady and uniform flow conditions could be realised to some extent. Modern irrigation schemes are increasingly demand based, which means that the water flow in a canal is determined by the crop water requirements. Accordingly the flow in the canal network is not constant as the crop water requirement changes with the climate and the growing stages of the crops. Also the inflow of the sediment is not constant throughout the irrigation season in most schemes. The situation is even worse for run-of-the-river schemes where fluctuations in the river discharge have a direct effect on the inflow of water and sediment. The conventional design methods are not able to predict accurately the sediment transport behaviour in a canal, firstly due to the unsteady and non-uniform water flow conditions and secondly due to the changing nature of the sediment inflow. Hence, the actual behaviour of a canal widely diverges from the design assumptions and in many cases immense maintenance costs have to be met with to tackle the sediment problems. An irrigation scheme should not only be able to deliver water in the required amount, time and level to the crops on the field, but also should recover at least its operation and maintenance cost. Cost recovery is, to some extent, related to the level of service provided by the irrigation organization and the expenditure for operation and maintenance of the scheme. Past experiences in Nepal have shown that modernization of existing irrigation schemes to improve the level of service has also increased the operation and maintenance costs. These costs are, in some cases, high compared to the generally low level of ability of the water users and farmers to pay these costs. The search of making schemes more equitable, reliable and flexible has resulted in the introduction of new flow control systems and water delivery schedules that may, if not carefully designed, adversely affect the sediment transport behaviour of a canal. In quite some schemes unpredicted deposition and/or erosion in canals have not only increased the operation and maintenance costs but also reduced the reliability of the services delivered.

Mots clés : irrigation / irrigation systems / irrigation channels / hydraulic engineering / design / management / sediment / water flow / nepal


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Page publiée le 14 novembre 2011, mise à jour le 30 mai 2022