Hydrology Field Methods

Weirs and Flumes

WEIRS

General Information:
- Weirs are used to measure streamflow with great precision
- The accuracy is degraded by obstructions, leaves, branches, ice, etc.
- Sediment collecting in the weir pool also degrades accuracy
Weir Components:
- Weir Blade: vertical obstruction in stream over which water must fall.
- Weir Basin: upstream of weir blade used to calm water before falling.
- Cutoff Wall: used to prevent water from moving under or around weir blade.
- Stilling Well: used to calm water level even more than in weir basin
- Staff Gage: used to manually measure water level in weir basin or stilling basin
- Water Level Recorder: used to automatically measure water level
Weir Equations:
- Q is discharge
- A is cross-sectional area
- v is water velocity
- g is gravitational constant
- h is water level above lowest point of weir blade
- Q = A v
- v² = 2 g h
- A = function of weir geometry

H-FLUMES

General Information:
- H flumes are primarily designed for measuring flows that vary widely such as seasonal runoff and overflow from dams.
- The recommended approach channel length is five times the height of the flume.
- The width of the channel should equal the width of the entrance to the flume.
- The flume crest should be set level with the approach channel.
- The approach channel slope should not exceed 2%.
- As the flow exits the flume, it must be able to spill clear or flow in a manner equivalent to spilling clear.
- The flumes may be set in concrete or earth or bolted to companion structures.
- When pouring concrete, brace the flume internally with 2" x 4" blocks cut to size to prevent bulging the walls.
- Remove the bracing when the concrete is set.
Flume Dimensions:

Type W/H L/H T/H

H 1.90 1.35 0.10

HS 1.05 1.50 0.05

HL 3.20 1.50 0.20

Flume Capacities:

Type Flume Dimensions (feet)¹ Discharge

Height Width Length Spout Min Max

H W L T (gpm) (gpm) (cfs)

H 0.5 0.95 0.675 0.05 0.180 149 0.33

0.75 1.425 1.0125 0.075 0.269 430 0.96

1 1.9 1.35 0.1 0.314 862 1.92

1.5 2.85 2.025 0.15 0.494 2,392 5.33

2 3.8 2.7 0.2 0.628 4,928 11.0

2.5 4.75 3.375 0.25 0.808 8,618 19.2

3 5.7 4.05 0.3 0.943 13,645 30.4

4.5 8.55 6.075 0.45 1.391 37,704 84

HS 0.4 0.42 0.6 0.02 0.072 36 0.08

0.6 0.63 0.9 0.03 0.103 99 0.22

HL 4 12.8 6 0.8 2.244 52,517 117

Flume Calibration Equations
- x = log10(h)
- y = log10(Q)
- h = stage, feet
- Q = discharge, cfs
- 1-foot flume:
- 2-foot flume:

Flume Rating Curves:

1-Foot H-Type Flume (Stage in feet - Discharge in gpm)

Stage 0.00 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

0.00 0.00 0.04 0.31 0.73 1.24 1.86 2.58 3.41 4.36 5.42

0.10 6.60 7.91 9.34 10.9 12.6 14.4 16.4 18.5 20.7 23.1

0.20 25.6 28.3 31.1 34.1 37.3 40.5 44.0 47.6 51.3 55.3

0.30 59.4 63.6 68.0 72.6 77.4 82.3 87.5 92.8 98.2 104
0.40 110 116 122 128 135 142 149 156 163 171

0.50 179 187 195 203 212 221 230 239 249 258

0.60 268 278 289 300 310 322 333 345 357 369

0.70 381 394 407 420 433 447 461 475 490 505

0.80 520 535 551 567 583 600 617 634 652 669

0.90 688 706 725 744 764 784 804 825 845 867

1.00 888 910 933 956 979 1,002 1,026 1,051 1,075 1,101

1.10 1,126 1,152 1,178 1,205 1,233 1,260 1,288 1,317 1,346 1,376

1.20 1,405 1,436 1,467 1,498 1,530 1,562 1,595 1,629 1,662 1,697

1.30 1,732 1,767 1,803 1,840 1,877 1,914 1,953 1,991 2,031 2,071

1.40 2,111 2,152 2,194 2,236 2,279 2,322 2,367 2,411 2,457 2,503

1.50 2,550 2,597 2,645 2,694 2,744 2,794 2,845 2,896 2,949 3,002

1.60 3,056 3,110 3,166 3,222 3,279 3,336 3,395 3,454 3,514 3,575

1.70 3,637 3,699 3,763 3,827 3,892 3,959 4,026 4,094 4,162 4,232

1.80 4,303 4,374 4,447 4,521 4,595 4,671 4,747 4,825 4,904 4,983

1.90 5,064 5,146 5,229 5,313 5,398 5,484 5,571 5,660 5,749 5,840

Useful information:

Assignment:

Working in teams of three, find additional websites documenting various control structures for measuring streamflow.

Type	W/H	L/H	T/H
H	1.90	1.35	0.10
HS	1.05	1.50	0.05
HL	3.20	1.50	0.20

Type	Flume Dimensions (feet)¹				Discharge
	Height	Width	Length	Spout	Min	Max
	H	W	L	T	(gpm)	(gpm)	(cfs)

H	0.5	0.95	0.675	0.05	0.180	149	0.33
	0.75	1.425	1.0125	0.075	0.269	430	0.96
	1	1.9	1.35	0.1	0.314	862	1.92
	1.5	2.85	2.025	0.15	0.494	2,392	5.33
	2	3.8	2.7	0.2	0.628	4,928	11.0
	2.5	4.75	3.375	0.25	0.808	8,618	19.2
	3	5.7	4.05	0.3	0.943	13,645	30.4
	4.5	8.55	6.075	0.45	1.391	37,704	84

HS	0.4	0.42	0.6	0.02	0.072	36	0.08
HS	0.6	0.63	0.9	0.03	0.103	99	0.22

HL	4	12.8	6	0.8	2.244	52,517	117

Stage	0.00	0.01	0.02	0.03	0.04	0.05	0.06	0.07	0.08	0.09
0.00	0.00	0.04	0.31	0.73	1.24	1.86	2.58	3.41	4.36	5.42
0.10	6.60	7.91	9.34	10.9	12.6	14.4	16.4	18.5	20.7	23.1
0.20	25.6	28.3	31.1	34.1	37.3	40.5	44.0	47.6	51.3	55.3
0.30	59.4	63.6	68.0	72.6	77.4	82.3	87.5	92.8	98.2	104
0.40	110	116	122	128	135	142	149	156	163	171
0.50	179	187	195	203	212	221	230	239	249	258
0.60	268	278	289	300	310	322	333	345	357	369
0.70	381	394	407	420	433	447	461	475	490	505
0.80	520	535	551	567	583	600	617	634	652	669
0.90	688	706	725	744	764	784	804	825	845	867
1.00	888	910	933	956	979	1,002	1,026	1,051	1,075	1,101
1.10	1,126	1,152	1,178	1,205	1,233	1,260	1,288	1,317	1,346	1,376
1.20	1,405	1,436	1,467	1,498	1,530	1,562	1,595	1,629	1,662	1,697
1.30	1,732	1,767	1,803	1,840	1,877	1,914	1,953	1,991	2,031	2,071
1.40	2,111	2,152	2,194	2,236	2,279	2,322	2,367	2,411	2,457	2,503
1.50	2,550	2,597	2,645	2,694	2,744	2,794	2,845	2,896	2,949	3,002
1.60	3,056	3,110	3,166	3,222	3,279	3,336	3,395	3,454	3,514	3,575
1.70	3,637	3,699	3,763	3,827	3,892	3,959	4,026	4,094	4,162	4,232
1.80	4,303	4,374	4,447	4,521	4,595	4,671	4,747	4,825	4,904	4,983
1.90	5,064	5,146	5,229	5,313	5,398	5,484	5,571	5,660	5,749	5,840