What methods can I use for estimating groundwater recharge from irrigation canals? Based on the cross section canal width and available water levels of canals.
Recharge has been defined as the process of addition of water to the saturated zone. Because it is almost impossible to measure directly, recharge is usually estimated by indirect means. The accuracy of the indirect estimates is usually difficult to determine, so a common recommendation is that recharge should be estimated by the use of multiple methods and the results compared.
Darcy method, water-table fluctuation method, and recession-curve displacement method.
http://water.usgs.gov/ogw/gwrp/methods/
The amount of seepage flow through the canal bed and boundaries can be estimated through the canal water balance computation and also there many empirical equations for seepage flow through canal reach
Pls refer to the code of water resources and irrigation that developed by MWRI. The methods described in this code can be used for Egyptian irrigation network.
In Piedmont region (NW Italy) a study was recently carried out involving mainly the estimation of canal water balance through various methods. Also shallow geophysical investigations and water table measurements in monitoring micro-wells drilled along the canal banks were combined. In order to understand the differences among various canal types (e.g. cemented or uncovered boundaries), several canal sections with different characteristics were compared. For further details, please refer to M. Lasagna, D.A. De Luca and others' work
The simple way to estimate is difference between in/out disharge -evaporation. Evaporation depends upon projected area of i.e. top width and length.
I agree with Walgak Chuol Bel that the USGS formulation is best. However, I wonder what others on the list think of the following quick back of the envelope method: (1) estimate the amount of water that is in the irrigation canal. Then (2) look to see if the government or some other entity has a calculation for the rate of evaporation in your area, and (3) assume some rate of recharge based on the soil type - again there are tables for recharge rates for different types of soil - and use the following formula - amt. of water in the canal in gallons or liters (minus) the evaporation rate (minus) recharge rate and you should have rough number.
Asaad, Please have a look at this document:
http://cgwb.gov.in/documents/gec97.pdf
http://www.cgwb.gov.in/documents/GEC97-Detailed_Guidelines.pdf
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