Abstract
A laboratory study was conducted on stepped and unstepped weirs in order to find their efficiency of dissipating flow energy. Thirty six weirs were constructed and tested to compare between stepped and unstepped weirs in flow energy dissipation, twenty seven of them were stepped while the rest were unstepped. Three heights of stepped weirs (P=36,45,54)cm were used with different numbers of steps (n=9,12,15) , and three downstream slopes of stepped face (h/l=1/2,1/3,1/4) were tested, while for unstepped weirs one height of weir (P=54)cm and three downstream slops (α=26.6o,18.4o,14o) were tested. The results showed that increasing height of weir and decreasing both number of steps and downstream slops stepped face of the weir will cause an increase of the ratio of flow energy dissipation, and the stepped weirs are more efficient in flow energy dissipation compared with unstepped weirs. The percentage of flow energy dissipation (E%) is increased by increasing the ratio of height of weir to critical water depth (P/dc), the ratio of length of the step to critical water depth (l/dc) and the ratio of height of step to critical water depth (h/dc) while it decreases by increasing the discharge (Q). Imperical relationships between the ratio of flow energy dissipation and factors affecting it were obtained in stepped weirs.
