Cutthroat Flume Accuracy
The Cutthroat Flume was developed to provide accurate flow measurement with a precision of +/-3% under free-flow conditions.
This accuracy holds when the ratio of flow depth (at the point of measurement) to flume length is between 0.1 and 0.4. Above 0.4 and higher approach velocities and rapid changes in the water surface introduce inaccuracies. Most standard Cutthroat Flumes have an overall depth that is 0.33 that of the length and fall within the recommended range.
However, it is important to remember that raising the sidewalls of a Cutthroat Flume beyond the 0.4 limit may impact accuracy. This is important as Cutthroat Flumes are the type of flume most commonly extended.
Cutthroat Flow Equations
For free-flow conditions, the level-to-flow equation for the Cutthroat Flume can be expressed as:
| Q = KW1.025Han = CHan |
|
Q = free flow rate (cfs / m3/s) |
|
K = flume discharge constant (varies by flume length / units) C = Calculated flume discharge constant (varies by flume length / throat width / units) |
| W = throat width (feet / meters) |
| Ha = depth at the point of measurement (feet / meters) |
| n = discharge exponent (depends upon flume size) |
|
Length |
Width |
n |
K (Imperial) |
K (SI) | C (Imperial) |
C (SI) |
|---|---|---|---|---|---|---|
| 18" Length | ||||||
|
18” |
1" |
2.150 |
6.100 |
7.4791 | 0.494 |
0.1802 |
|
18” |
2" |
2.150 |
6.100 |
7.4791 | 0.974 |
0.3553 |
|
18” |
4" |
2.150 |
6.100 |
7.4791 | 1.975 |
0.7205 |
|
18” |
8" |
2.150 |
6.100 |
7.4791 | 4.030 |
1.4701 |
| 36" Length | ||||||
|
36" |
2" |
1.840 |
4.500 |
3.7758 | 0.719 |
0.1811 |
|
36" |
4" |
1.840 |
4.500 |
3.7758 | 1.459 |
0.3675 |
|
36" |
8" |
1.840 |
4.500 |
3.7758 | 2.970 |
0.7503 |
|
36" |
16" |
1.840 |
4.500 |
3.7758 | 6.040 |
1.5213 |
| 54" Length | ||||||
|
54" |
3" |
1.720 |
3.980 |
2.9394 | 0.960 |
0.2103 |
|
54" |
6" |
1.720 |
3.980 |
2.9394 | 1.960 |
0.4293 |
|
54" |
12" |
1.720 |
3.980 |
2.9394 | 3.980 |
0.8718 |
|
54" |
24" |
1.720 |
3.980 |
2.9394 | 8.010 |
1.745 |
| 108" Length | ||||||
|
108" |
12" |
1.560 |
3.500 |
2.1383 | 3.50 |
0.6322 |
|
108" |
24" |
1.560 |
3.500 |
2.1383 | 7.11 |
1.2843 |
|
108" |
48" |
1.560 |
3.500 |
2.1383 | 14.49 |
2.6175 |
|
108" |
72" |
1.560 |
3.500 |
2.1383 | 22.0 |
3.9741 |
Cutthroat Flume Flow Tables
Free-flow discharge tables for Cutthroat Flumes can be found in the Discharge Tables section.
