An electromagnetic induction technique to locate seepage losses in irrigation canals – preliminary results

Reducing the losses from irrigation canals would improve the efficiency of the irrigation systems, but the irrigation canals lining is an expensive procedure sustainable only in the presence of high seepage losses. The two methods most commonly used to locate seepage losses from irrigation canals (inflow-outflow and ponding test) are also quite expensive and time-consuming. EMI (Eletromagnetic Induction) equipments have been used for decades for mapping soil properties: they are easy to use in the field and not excessively expensive. We propose the use of EMI equipment as a fast and low cost technique to locate seepage losses in irrigation canals. We verified the applicability of such technique on two stretches of different canals, where we used EMI equipment to measure the apparent electrical conductivity of the canal banks. The measurements were replicated either with water in the canal and with a dry canal. The volume of water in the canal could alter the electrical conductivity measurements if detected by the EMI equipment. To test the lateral sensitivity of the EMI equipment, we performed electrical conductivity measurements along three transect parallel and progressively closer to a tank of polyethylene containing water. We compared apparent electrical conductivity values with measurements of soil water content and with the discharge measurements performed on the canal banks employing a propeller flowmeter. Preliminary results show that: i) the lateral sensitivity of EMI equipment is very low, so that it cannot detect highly conductive materials located at 0.25 m from the measurement transect; ii) EMI equipment can locate areas with seepage losses because the water flow through the canal banks causes the fluctuation of the values of apparent electrical conductivity of the soil compared to the results obtained with dry canals at comparable soil water content values.