Discharge measurement

Carry out the measurement at uniform flow, avoiding locations with varying discharges (e.g. pools).

1. Find an ideal cross-section perpendicular to the flow. If the river width is less than 10m then divide into 10 sub-sections. If the river width is 10 to 20m then spacing should be by 1m.

2. Measure river depth at each dividing line and record.

3. Set the mid-point of each section as the line for discharge measurement. If the depth is less than 75cm then carry out one-point measurement at 60% below water surface (six-tenth-depth method). For the depths more than 75cm, calculate the average between 20% and 80% below water surface measurements (two-point measurement method).Each measurement will be made using Hiroi-electric-current-meter (converts the number of revolutions/min into discharge). When the discharge is very slow, lengthen the measurement time to increase accuracy. If the discharge is variable, repeat the measurement a few times and take their average.

In the lab:

4. Use the conversion formula (written on the current-meter) to calculate velocity.

5. Calculate the area of each sub-section by approximation (e.g. trapezoid/triangle) and find discharge/subsection. Sum the sub-section discharges to get an overall discharge of the cross-section.