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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 (=26.6 o ,18.4 o ,14 o) 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/d c), the ratio of length of the step to critical water depth (l/d c) and the ratio of height of step to critical water depth (h/d c) 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.

The main objective of this investigation is to be obtain the coefficient of discharge for labyrinthine side weir. 24 labyrinthine side weirs were constructed and built in upstream of side channel of a 15 cm width and 30 cm depth and 2 m long with constant horizontal bed. The weir height were varied three times as 9cm, 12 cm, and 15 cm and each height tested for four different angels of the weir crest (). The weirs were used with direction and opposite direction of flow with different discharges. From the analysis of results it was found that the labyrinthine side weir with small height and small angle is more efficient when put in the direction of flow. Two general expressions were obtained to estimate the coefficient of discharge in terms of the hydraulic parameters in direction and opposite direction of flow, also it was found that the rate between length of weir to the depth of flow is the most effective parameter.

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