This research is about the effects of sediments on discharge coefficient of rectangular, v-notch, ogee

and overflow weirs. Two open channels with 7m and 5m length for low and high flow rates are used in the

experiment. Tests are done for 2°, 4° and 5° slope of 7m open channel and 0.5° slope of 5m open channel

in two states, including water flow and water- sediment flow. Experiments were conducted with flow rates

ranging from 8 lit/s/m to 14.7lit/s/m and 1.8 lit/s/m to 11.8 lit/s/m in the 7m and 5m open channels, respectively.

Sediment particles are thrown into channel according to the flow rate. A calibrated pitot tube is used

for velocity measurement and a point or hook gauge with 0.02m accuracy is used for depth measurement.

Each test is done three or four times and data are recorded. It can be concluded that sediments decrease the

discharge coefficient and this effect is obvious in lower flow rates and smaller slopes and this trend is independent

of weir type. Also, according to the results and data, some equations are suggested by correlation

method which enables calculation of discharge coefficient in water-sediment flow from discharge coefficient

in water flow.