Sedimentary dynamics for irrigation canal systems based on radio-activable tracers

Most of the time, the managers of irrigation systems have to cope with the problems of sand deposition. Within a program conducted in Pakistan, we were asked to provide to the irrigation managers a new tool to diagnose the functioning of the systems, including the sedimentary problems. Then, the objectives of our work are to develop methodologies to represent and explain the sand deposition phenomena in these systems. Our approach is based on the analysis of hydraulic and sedimentary data sets collected on an actual irrigation system. The first part of our works consists in selecting a minimal set of parameters which allow to represent the observed phenomena, and a method for partitioning the system in homogeneous reaches. So we identify generic laws of behavior of the deposition for the different levels of the system. The coefficients of these laws are calibrated on actual deposition trends in the canals of an irrigation system of the Sindh province (Pakistan), on the basis of observed data during several years and a dedicated measurement campaign using radio-activable tracers. Following this analysis, we suggest a global sedimentary model, which can be assimilated to the result of a systemic approach based on the physics of the fluid mechanics and the sediment transport. (authors)