Using EM equipment to verify the presence of seepage losses in irrigation canals

摘要

Climate models predict a general future increase in air temperatures and, therefore, an augmentation of water requirements for agricultural purposes. However, without an appropriate management of the water resource, the competition between agriculture and other sectors risk to worsen the water scarcity crisis. Reducing the losses from irrigation canals will surely improve the efficiency of the irrigation systems, but lining the irrigation channels is an extremely expensive procedure sustainable only in the presence of high losses. Moreover, the two most known methods for determining losses from irrigation canals (inflow-outflow and ponding test) are quite expensive and time-consuming. In this context, the EM (Electromagnetic Induction) system has been used for decades for mapping soil properties: it is a fast and user friendly technique, easy for field applications and not excessively expensive. In this study we verified the usefulness of the EM system to determine the presence of leakage of irrigation canals. To this aim we selected three canals in the Piedmont plain (northwest of Italy) representatives of the most common regional typologies. Electrical conductivity values, collected using an EM device, were combined with data measured with traditional techniques such as inflow-outflow measurements (acoustic Doppler profiler and propeller flow meter), and soil water content measurements (TDR - Time Domain Reflectometer). EM electrical conductivity measurements were performed at different discharges values in permanent flow, hence, at different water level heights. The two replications were necessaries to investigate the variation of electrical conductivity versus the water level height. Results show that EM allows detecting seepage losses. Namely, these lasts cause a lowering of the soil electrical conductivit y values in steady conditions of soil water content.