ASSESSMENT OF DESIGN PRACTICES AND PERFORMANCE OF SMALL SCALE IRRIGATION STRUCTURES IN SOUTH REGION

Abstract

The gravity supply of water to irrigation fields can be achieved by impounding schemes or diversion schemes. Unlike impounding dams, diversion structures for irrigation are usually exposed to the overflow action of water and sediments. Hence, they are liable to exhibit problems & predicting their performance under this condition is very difficult. Accordingly, irrigation structures demand the multi-faceted considerations of hydrologic, structural, sediment and hydraulic analysis, geotechnical & agronomic considerations and if not properly designed, .often end up in consequential problems. Thus, practicing engineer in the field often faces to make sure this problem will not happen in the designs even if there is very limited or no actual data in the field. A case study considering 26 existing small scale irrigation works (1/3 of the total schemes) in the south region is carried out for this research work and attempt is made to understand the causes of the major problems that are related to the design consideration of the different components of the structure and identify the gap in knowledge between the current design practices and performance of the structures. The pre and post construction institutional aspects and water management problems are also given due attention. Some of the many structural problems in the existing irrigation structures are problems of sedimentation at the headwork and main canal, downstream scouring, upstream flooding, damage on impervious and flexible apron, change of river