FLOW CAPACITY THROUGH WIDE AND SUBMERGED VEGETAL CHANNELS

The presence of vegetation in irrigation canals in Egypt after the Aswan dam was built has become considerable problem in irrigation system. Many irrigation canals were designed by applying the common Manning's equation, but the presence of submerged weeds makes the application of Manning's equation for design of wide channels inadequate, because of the variation of the retardance coefficient over a wide range. Four canals were selected and considerable field data collection was carried out to identify the flow resistance and to modify Manning's equation. The velocity, slope, and discharge were measured in wide channels that had different capacities and that were filled with submerged vegetation (Potamogeton spp.) through the annual life cycle of weed growth. A more general discharge-depth equation that offers advantages for a modified Manning's equation is developed based on the field data. A relationship was found between Manning's roughness coefficient for earth canals and an equivalent Manning's roughness for submerged weeds. The experimental setup is described and the results of the measurements are given.