Abstract

From a traditional point of view, irrigation canals are conceptualized only as structures with the function of transport water. However, current knowledge of ecology, water quality and sociology take us to review that conceptualization. For example irrigation canals and its riparian vegetation are habitat for fish, bird and small animals and from the social point of view; many rural communities are organized around the irrigation canals, because people get identified with its water source. Irrigation canal water quality is a critical issue for Chilean agriculture. In the Central Zone of Chile, different pollution sources, transport and mitigation processes had been observed and documented in irrigation canals. Observed pollution sources are wastewater and urban runoff discharges; non point pollution is mainly associated with domestic waste disposal in the canals and runoff from confined poultry and swine production. Pollutant transport processes in irrigation canals are controlled by short residence times and high oxygen levels. Riparian vegetation could produce an important mitigation ofpollutants, but there is a lack of research about it. In some areas of the Chilean Central Valley, irrigation canals are an important hydrologic boundary condition. Irrigation canal seepage recharges groundwater in summer and the canals works as storm-water drainage in winter transporting the water to the river at the lower end of the valley. Four study cases are discussed: i) Effect of irrigation canal on the hydrology of a agricultural valley; ii) Needs of redesign diversion structures to improve on-canal water quality; iii) Use of irrigation canals as urban storm-water drainage and iv) Irrigation canals as a organization pole. As a conclusion, it is becoming necessary the use of a holistic approach for the design, operation and modification of irrigation canals.