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Appendix D — SOP for Stream Flow Measurement — Hansen Project 7 <br />c <br />3 <br />r <br />m <br />m <br />r <br />Flume Length Coefficients, Kf, Ks <br />W A LA 01 V O iD O :+ k <br />Flow Exponents, nf,ns <br />tll Ql V W CD <br />4 O O O O <br />Transition Submergence, St, in % <br />Figure 1. Coefficients and Exponents for a Cutthroat Flume <br />For accurate discharge measurements, the recommended ratio of flow depth to flume length should be less <br />than or equal to 0.33 and should be no greater than 0.50. If the downstream depth submerges the throat <br />allowing submerged conditions to exist, the equation is modified to: <br />Where: <br />= CS (h, — hd P <br />(_log Sp <br />S = the submergence (height upstream gage / height downstream gage) <br />C, = the submerged flow coefficient; and <br />n, = the submerged flow exponent <br />CS = KsW' 025 <br />Values for K, and n, can be obtained from Figure 1. A simplified calculation for the Baski portable cutthroat <br />flume is provided below: <br />Alternatively, the flow rate can easily be determined from based on the approach depth in a Baski portable <br />cutthroat flume, using the lookup table (Table 2), provided that all assumptions and conditions are met. Note <br />that when the submergence approaches 90 percent, it is difficult to make sufficiently accurate gauge readings in <br />the field and alternative flow measurement methods may be required. <br />4153A.140129 Whetstone Associates <br />