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The final year group project was a research based project soil permeability related to sub-surface drainage system in water logged area. The irrigation network installed decades ago in the Mardan district in Pakistan resulted in the problem of water logging and salinity. WAPDA (Water and Power Development Authority) initiated SCARP (Salinity control and reclamation project) to solve this problem. Subsurface drains were installed in the project area to lower the water table. This system of PVC buried pipes is fairly expensive but effective. The cost of system increases if pipes have to be placed at close spacing. The spacing in turn depends on soil permeability. The spacing is short for clay that has low permeability and is more for sandy soil. The field officers of WAPDA observed that the discharge from the drains increases with lapse of time. Since the spacing of drains is function of permeability so if this observation can be scientifically established then the spacing of drains can be increased in anticipation of high permeability during project life time The project was an effort to compute post project permeability at number of locations in the project area. Extensive field and lab testing was carried out and the data was analyzed to draw firm conclusions and to make further recommendations.
The permeability for Mardan SCARP project collected about 15 years back for designing the spacing was collected from concerned offices. Later field permeability tests were conducted at the same location to determine the present soil permeability. Undisturbed samples of clay were also collected for comparing field and lab values. Disturbed samples were collected for soil classification and determination of index properties. The results were computerized. Analysis on data was performed for comparing old and new permeability. To Asses the impact of present permeability, the spacing of drain was recomputed. Based on this analysis certain conclusions and recommendations were drawn. For an undergraduate level project, the conclusions drawn from the project were outstanding.
It was concluded that allowance may be kept while calculating the spacing of the lateral drains, for example, if the spacing between the drains for a project during design is calculated as 300 ft with some permeability value, then the same results can be achieved with having 23.5% more spacing i.e. 370 ft instead of 300 for the project under consideration. So the material and operation cost can be saved significantly. Since the material and operational cost of field drain is about 80% of the total material and operational cost of the project, so by implementing 23.5% more spacing for 80%, we may save 18.5% of the total project cost.