A typical circular clarifier

A typical effluent launder

First, we figure how high a weir can be installed in the launder without causing the v-notched weirs to flood during high flows. In this case, a simple 1x6 was used.

Next, if we can accomplish what we want to do with only one weir, we block off the other side of the launder, leaving the top of the blocking at the base of the champher on the concrete.

2x4 kickers are usually sufficient to hold the weirs in place.

A couple of braces will hold the high side.

The completed flow measurement weir set-up.

Water flowing over the 1x6 weir.

Water is now flowing over the one side of the weir.

The head is measured about two feet upstream from the flow measurement weir. In this picture, the measurement is first made from the “4-foot level” to the top of the 1x6 weir. Then the measurement is made from the top of the “4-foot level” to the top of the water surface. The difference is the “head” on the weir.l

If possible, a simple strut is nailed to the concrete to simplify the measurement of the heads. In this installation, there is a single weir plate installed across the opening to the effluent drop box. It’s parallel with the v-notched effluent weirs and the concrete wall.

The “head” is determined by measurements from the strut.