“Technical Note” AN EMPIRICAL MODEL FOR PREDICTION OF CONVEYANCE EFFICIENCY FOR SMALL EARTH CANALS*

Abstract – Most of the water loss in distribution and conveyance earth canals occurs through seepage. This loss should be considered in irrigation network design through conveyance efficiency (ec). It is a common practice for the value of ec to be measured in existing irrigation systems under different soil types, vegetation covers and canal sizes. However, it is a costly and time consuming practice, therefore, empirical models to indicate the relationship between ec and soil texture, canal capacity and vegetation cover in earth canals may be effective in the estimation of ec at different conditions. This research was conducted to measure the conveyance efficiency in earth canals that are well above groundwater level with different soil textures and water weed densities in the northern and north-western areas of Isfahan province, I.R. of Iran. Conveyance efficiency of a km reach in distributary earth canals with a sandy loam soil was 67.3%, and for a clay loam soil in tributary earth canals 95.8%. The vegetation cover in the earth canal did not affect the ec value significantly. Therefore, it is concluded that traditional earth canals with medium to heavy soils in the study area have high ec and the lining may not be economically justified. Furthermore, for earth canals well above the groundwater level a multiple regression model was presented to estimate the ec value based on flow rates smaller than 404 l s-1 in distributary and tributary canals and sand content in soil