Water Flow Estimate Over a Weir

Commercial Trout Production in western North Carolina

Depth (inches)	Dishcharge per Foot of Weir Width		Depth (inches)	Dishcharge per Foot of Weir Width
Depth (inches)	cfs	gpm	Depth (inches)	cfs	gpm
1/2	.03	13	7	1.48	665
3/4	.05	24	7 1/4	1.56	702
1	.08	36	7 1/2	1.65	738
1 1/4	.11	50	7 3/4	1.73	776
1 1/2	.15	66	8	1.81	814
1 3/4	.19	83	8 1/4	1.90	853
2	.23	102	8 1/2	1.98	890
2 1/4	.27	122	8 3/4	2.07	930
2 1/2	.32	142	9	2.16	971
2 3/4	.36	164	9 1/4	2.25	1012
3	.42	187	9 1/2	2.35	1053
3 1/4	.47	211	9 3/4	2.44	1096
3 1/2	.53	236	10	2.53	1136
3 3/4	.58	262	10 1/4	2.63	1179
4	.64	287	10 1/2	2.73	1223
4 1/4	.70	315	10 3/4	2.82	1268
4 1/2	.77	343	11	2.92	1312
4 3/4	.83	372	11 1/4	3.03	1358
5	.90	402	11 1/2	3.12	1401
5 1/4	.97	433	11 3/4	3.23	1448
5 1/2	1.03	463	12	3.33	1495
5 3/4	1.10	495
6	1.18	528
6 1/4	1.25	562
6 1/2	1.33	596
6 3/4	1.41	631

*cfs = cubic feet per second
*gpm = gallons per minute

Use the above table to estimate the water flow over damboards or
similar devices. In a stream without such a device, a wooden board
(1 inch x 6 inches or 1 inch x 8 inches) can be placed on edge in
the stream from bank to bank so that the water flows over the
board. Once the average depth and the width of the water over the
weir is measured with a ruler (Figure 1), use the table to estimate
the flow.

For example:
water depth = 1.5 inches
weir width = 3 feet
flow estimate = 3 x 66 or 198 gallons per minute

from: King's "Handbook of Hydraulics", Fourth Edition, Table
36.

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