Problems on Weirs

Problems on Weirs
1. Water flows through a rectangular channel 1m wide and 0.5m deep and then over a sharp trapezoidal weir of crest length of 0.6m. If the water level in the channel is 0.225m above the weir crest, calculate the discharge over the weir. Take .
2. A rectangular notch of crest width 0.4m is used to measure the flow of water in a rectangular channel of 0.6m wide and 0.45m deep. If the water level in the channel is 0.25m above the weir crest, find the discharge in the channel. For the notch, assume .
3. a 5m wide rectangular channel with 1.2m depth of flow, a sharp-crested weir of 2.5m length and 0.6m height is fixed symmetrically across the channel width. If it flows free, determine the discharge.

4. A sharp crested weir of 1m height is fixed across 5m wide channel as shown in the following figure. The depth of flow on the upstream and downstream sides of the weir is 1.5m and 1.2m respectively. Find the discharge over the weir.
A rectangular sharp-crested weir is to be constructed in a testing station with small stream in which the discharge varies from 50 liters/s and 1250 liters/s. Find the suitable length of the weir, if the minimum head to be measured is 50 mm and the maximum head on it does not exceed one-third of its length.
Workings
Given,
? Qmax = 50 liters/s = 0.05 m3 /s
? Qmin = 1250 liters/s = 1.25 m3 /s
? Hmin = 50 mm = 0.05 m
Let, H = Length of weir in meters
Maximum head of water, Hmax = L/3
We know that the minimum discharge over the weir (Qmin)