UM-49 : User's manual for estimation of seepage from a canal

Abstract

The seepage from a canal, which is hydraulically connected with an aquifer, is governed by the difference between the hydraulic head at the canal periphery and the hydraulic head in the aquifer in the vicinity of the canal, the hydraulic conductivity and anisotropic characteristics of the porous medium in which the canal runs, canal cross section, and geo-hydrological boundary of the aquifer. Considering the fact that influent seepage from a canal is zero for zero potential difference and a finite quantity for infinite potential difference, the relationship between influent seepage and potential difference has to be non-linear. A non-linear relationship between influent seepage and potential difference has been proposed by Rushton and Redshaw. In this user manual, the two parameters of the non-linear relation for influent seepage have been derived in terms of reach transmissivity constant, hydraulic conductivity, width of the canal at the water surface, and maximum depth of water in the canal. Using this manual unsteady influent seepage from a canal in a homogeneous isotropic aquifer of infinite areal extent can be computed. Some specific result has been presented in nondimensional form. The data required for the computation are: (1) canal cross section, (2) maximum depth of water in the canal, (3)depth to water table, (4) thickness of aquifer, (5) hydraulic conductivity and (6) storage coefficient. The results presented in the manual show that the seepage rate from unit wetted surface area of a canal depends on width of the canal and can not be taken as one unique value as being assumed currently. The seepage rate from unit surface area for canal of small width is higher than that from a canal of larger width, all other parameters remaining same. The other governing factor is the potential difference which needs to be considered during computation of seepage. This manual has been prepared by Dr. G. C.Mishra, Scientist 'F', as a part of the Institute's work programme. Manual for effluent seepage and seepage from canal for other hydro-geological condition will be prepared in future.