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(0) 1978 CRREL Dolo <br /> (.) 1979 CRREL Dota <br /> �L <br /> 100 j\ <br /> c <br /> S' <br /> \ I'�• <br /> S <br /> E � <br /> It ' <br /> c O <br /> lF \ \� <br /> t Inf. 1.868-1.0221nq <br /> r-0.78 \m ' <br /> s-0.358 O®\0 <br /> O\ <br /> 10 <br /> 0.1 1.0 <br /> q,Overlond Flowrate (m3 hr lw l of width) <br /> Flgure 5. Overland flow rate vs detention time for CRREL overland <br /> flow test site. <br /> of a thicker organic mat due to accumulated grass most overland flow terraces Increasing the depth <br /> clippings from previous harvests. Tracer studies causes more surface area to be wetted, which in- <br /> conducted during the 1980 growing season did not creases the resistance to flow. This hypothesis is <br /> show a further increase in detention time. This ob-. consistent with visual observations at the CRREL <br /> servation suggests that the CRREL overland flow site and several other overland flow sites. <br /> terraces reac arl 1!ytor the maximum prat- Substituting eq 12 back into eq 8,an empirical <br /> Qca resis tient TMter three years of open-. relationship that can be used for predicting detention <br /> ation, time at the CRREL site is <br /> The equation for the line of best fit shown in <br /> Figure 5 is T=0.078 L (13) <br /> 5113 q <br /> In T= 1.868-1.022 In q (10) <br /> This equation indicates that T is directly propor- <br /> or tional to L and inversely proportional to q. Slope, <br /> 6.48 being to the one-third power, is less significant <br /> T= , (11) although it cannot be considered negligible. For <br /> q1.022' example, assuming L = 50 m and q= 0.2 m3 h("' m', <br /> an increase in slope from 2 to 12%would decrease <br /> Substituting eq 11 for T in eq 9,an expression for detention time from 72 to 40 minutes, a decrease <br /> the resistance coefficient is of 44%. <br /> a=0.043 g1.066 , 0.043 q. (12) Validation <br /> To determine the validity of eq 13 for other <br /> This expression indicates that the resistance coeffic- systems,detention times were measured at two <br /> ient a increases in direct proportion to the average overland flow sites. The first site, located near Utica, <br /> overland flow rate. This relationship can be explained Mississippi, was a research facility operated by the <br /> by the fact that,as the flow rate increases, the depth U.S. Army Engineer Waterways Experiment Station <br /> of flow also increases. On the irregular surface of (WES). This site (no longer in operation) had 24 <br /> 6 <br />