hydraulic charts and tables

Discharge from Rectangular Weir with End Contractions

Figures in Table are in Gallons Per Minute
Head (H) in Inches Length (L) of Weir in Feet Length (L) of Weir in Feet
1 3 5 Additional GPM for Each Ft. Over 5 Ft. Head (H) in Inches 3 5 Additional GPM for Each Ft. Over 5 Ft.
1 35.4 107.5 179.8 36.05 8 2338 3956 814
1 1/4 49.5 150.4 250.4 50.4 8 1/4 2442 4140 850
1 1/2 64.9 197 329.5 66.2 8 1/2 2540 4312 890
1 3/4 81 248 415 83.5 8 3/4 2656 4511 929
2 98.5 302 506 102 9 2765 4699 970
2 1/4 117 361 605 122 9 1/4 2876 4899 1011
2 1/2 136.2 422 706 143 9 1/2 2985 5098 1051
2 3/4 157 485 815 165 9 3/4 3101 5288 1091
3 177.8 552 926 187 10 3216 5490 1136
3 1/4 199.8 624 1047 211 10 1/2 3480 5940 1230
3 1/2 222 695 1167 236 11 3716 6355 1320
3 3/4 245 769 1292 261 11 1/2 3960 6780 1410
4 269 846 1424 288 12 4185 7165 1495
4 1/4 293.6 925 1559 316 12 1/2 4430 7595 1575
4 1/2 318 1006 1696 345 13 4660 8010 1660
4 3/4 344 1091 1835 374 13 1/2 4950 8510 1780
5 370 1175 1985 405 14 5215 8980 1885
5 1/4 395.5 1262 2130 434 14 1/2 5475 9440 1985
5 1/2 421.6 1352 2282 465 15 5740 9920 2090
5 3/4 449 1442 2440 495 15 1/2 6015 10400 2165
6 476.5 1535 2600 528 16 6290 10900 2300
6 1/4 1632 2760 560 16 1/2 6565 11380 2410
6 1/2 1742 2920 596 17 6925 11970 2520
6 3/4 1826 3094 630 17 1/2 7140 12410 2640
7 1928 3260 668 18 7410 12900 2745
7 1/4 2029 3436 701.5 18 1/2 7695 13410 2855
7 1/2 2130 3609 736 19 7980 13940 2970
7 3/4 2238 3785 774 19 1/2 8280 14460 3090

This table is based on Francis formula:

Q= 3.33 ( L-0.2H)H1.5

Which

Q = ft. 3 of water flowing per second
L = length of air opening in feet (should be 4 to 8 times H)
H =head on weir in feet (to be measured at least 6ft. back of weir opening).

Water fall and vanishing edge points

1. Water falls with a drop of over 3 feet and 1/4″ depth at the top of the weir. For every 3′ over the first 3′ drop, you should add an additional 1/4″ in depth at the top of the weir.

2. Rounded or Copping edged weirs require at least 1″ depth of water to break the plane and not rap under the edge.

3. Water surges from swimmers can increase the required extension by as much as one foot.

vanishing edge sump capacities in gallon

Water Feature Surface Area Water Depth at Top of Weir (*Capacity in Gallons)
1/4″ 1/2″ 3/4″ 1″ 1 1/4″ 1 1/2″ 1 3/4″ 2″
100 sq. ft. 486 935 190 1,870 2,356 2,805 3,254 3,740
200 sq. ft. 935 1,870 2,805 3,740 4,675 5,610 6,545 7,479
300 sq. ft. 1,421 2,805 4,188 5,610 7,031 8,414 9,798 11,219
400 sq. ft. 1,870 3,740 5,610 7,479 9,349 11,219 13,089 14,959
500 sq. ft. 2,356 4,675 6,993 9,349 11,705 14,024 16,343 18,699
600 sq. ft. 2,842 5,610 8,377 11,219 14,061 16,829 19,596 22,438
700 sq. ft. 3,291 6,545 9,798 13,089 16,380 19,634 22,887 26,178
800 sq. ft. 3,740 7,479 11,219 14,959 18,699 22,438 26,178 29,918
900 sq. ft. 4,226 8,414 12,603 16,829 21,055 25,243 29,432 33,657
1,000 sq. ft. 4,712 9,349 13,987 18,699 23,411 28,048 32,685 37,397

Notes:

1.Sump should be 6″ to 1′ wider that the weir to catch ” leakage” at both ends of the weir.

2.Main drains should not exceed 50 rpm each to avoid eddy’s and possible entrapment. A minimum of two are required for flower blow 100 gpm.

3. An over flow protection should be installed ti handle “Swimmer Waves” and heavy rains.

4. A low water float switch should be installed no closer than 1 foot from the bottom of the sump to protect the pump(s) in case the water level drops too low.

5. An automatic water fill should be located in the sump to maintain the correct water level.