Total discharge would be the summation of discharge for all subsections. A portable weir plate is a useful device for determining discharge when depths are too shallow and velocities too low for a reliable current-meter measurement of discharge. A 90 degrees V-notch weir is particularly suitable because of its sensitivity at low flows. The weir plate is made of galvanized sheet iron. The 90 degrees V-notch that is cut in the plate is not beveled but is left with flat, even edges.
Thin weir plate at low flow.
A staff gage, attached to the upstream side of the weir plate with its zero at the elevation of the bottom of the notch, is used to read the head on the weir. The staff gage should be installed far enough from the notch to be outside the region of drawdown of water going through the notch. To install the weir, the weir plate is pushed into the streambed. A pick or shovel may be necessary to remove stones or rocks that prevent even penetration of the plate. The top of the plate should be horizontal and the face of the plate vertical.