Abstract
This research deals with the experimental study of the effect of roughened the flood plain of symmetrical compound channel (having 18 cm main channel and 29 cm flood plain width from both sides) on the resistance of flow using different size of gravel roughness (D50=6.8 ,16.8, 24,47) mm, as well as the flood plain is smooth. Five discharges (34,27.8,19.35,12,7.87)L/sec were carried out for each case, The compound channel was divided to 3 sections perpendicular to the direction of flow and each of them divided to 7 sections , 4 in flood plain and 3 in main channel . Pitot static tube used for velocity measurements and point gage for water surfacelevel measurement as well as the temperature of water was measurement, From the measurements it can be concluded that the velocity over the flood plain was reduced clearly up to 40 – 70 % when the flood plain roughened by course roughness compare with that of smooth one , while the velocity in the main channel increased to satisfy the continuity equation . Empirical equations were developed to combine the resistance coefficient n with other variables include the flow and geometry characteristics
