H.S. Chauhan

Optimal operation scheduling model for a canal system

Abstract An improved method of water allocation to different canals in a canal system has been devised, using a linear programming (LP) technique. The results of the model are compared with the existing, and three alternate operation policies in which optimal allocation takes place at different stages of water distribution. All four operation policies are found superior, and have a 16.68, 16.18, 15.46 and 9.98% higher aggregate net return, over the existing operation policy. The opimal operation policy in which optimal allocation starts right at the branch canal level has the highest return amongst all including the return from the present operation policy.

A Hele‐Shaw Model Study of steady state flow in an unconfined acquifer resting on a sloping bed

Experiments were conducted on a vertical Hele-Shaw model to study the effect of slope of an impermeable layer on flow profiles and flow rates in an unconfined aquifer. Experimental results were compared with the solutions of Pavlovsky (1930) and Childs (1971) for nonuniform seepage on a small sloping impermeable bed. These studies showed that the solution of Pavlovsky may be used for the prediction of the flow profile downslope up to 30% slope and upslope up to 15% slope. Pavlovskys equations also predicted flow rates and normal depths satisfactorily up to 30% slope. Childs’ equations also predicted similar results. None of these equations predicted the flow rate on negative slope satisfactorily.

Transient water table rise with canal seepage and recharge

Abstract An analytical solution to the problem of water table rise in a finite length phreatic aquifer based on appropriate transformations is obtained. The proposed solution is simpler than the available solution and for the selected illustrative numerical example gives fairly close results.

Water table fluctuations due to canal seepage and time varying recharge

Transient water table variation in an unconfined horizontal aquifer, lying between two canals located at different elevations above the impermeable barrier and receiving time varying recharge, is predicted by obtaining an analytical solution to the linearized Boussinesq equation. The proposed solution is for the generalized form of time varying recharge and has been obtained by applying an indigenously devised transformation to the flow governing equation. The solution for constant rate of recharge, a special case of the proposed solution, is compared with the existing analytical solution and almost identical values of water table rise are obtained. The effect of constant recharge, exponentially decreasing recharge and a combination of constant and exponentially decreasing recharge on the water table rise is analyzed with the help of a numerical example.

Modified steady state drainage equations for transient conditions in subsurface drainage

Abstract The steady state drainage solutions of Ernst, Dagan and van Beers were modified to predict the rate of fall (or rise) of water table midway between drain lines by using the integration technique of Bouwer and van Schilfgaarde. The same assumption to account for the non-uniformity of flux per unit area because of the change in the shape of the water table during recession, was followed. The integrated equations of Ernst, Dagan and van Beers were compared with the integrated equation of Hooghoudt and of Toksoz and Kirkham which were developed by Bouwer and van Schilfgaarde and the non-steady equation of van Schilfgaarde, using the field data for falling water table collected from subsurface drainage experiment in the saline soil of Mundlana, India. From the comparison of predicted and actual hydraulic heads it was observed that all the equations showed good agreement. No specific trend for the behaviour of different equations could be found from the analysis of field observations at geographically different experimental locations given by Bouwer and van Schilfgaarde, Nwa and Twocock and El-Mowelhi and Hermsmeier.

Unsteady state drainage in a vertically heterogeneous soil

Abstract An analytical model is presented for prediction of transient water table heights between two parallel drains for a vertically heterogeneous soil. The drains lie on a horizontal impervious layer. The model was applied to field conditions for prediction of water table fluctuations in a clay soil whose hydraulic conductivity decreased exponentially with depth. The predicted results compared reasonably correctly with field observations for a given long-term rainfall input.