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The current state-of-the-art technique for predicting sediment basin effluent <br />• quality is currently recognized as being the procedure incorporated by the <br />DEPOSITS Sedimentation Pond Design Manual produced by the University of <br />Kentucky, This computer model requires extensive input data to produce any <br />meaningful conclusions, most notably the particle size distribution of the <br />studied sediments and the total sediment loads. The reliability of any conclu- <br />sions based on such a model are directly proportional to the accuracy of these <br />assumed parameters. Because of this fact, and the small peak flow rates of <br />sediment basin effluents, a more meaningful analysis would consider the peak <br />flow rates of North Thompson Creek in relation to these sediment basin <br />discharges. <br />Due to the ephemeral characteristics of the drainage areas controlled by the 3 <br />sedimentation structures, the only discharges associated with the structures <br />will be those during and immediately following a precipitation event and runoff <br />due to snowmelt. As stated previously, the maximum effluent discharge asso- <br />ciated with the 10-year, 24-hour rainfall event would be 0.90 cfs, assuming the <br />three outflow hydrograph peaks were coincident (a conservative assumption), <br />The peak flow rate in North Thompson Creek associated with the 10-year event has <br />been calculated to be 409 cfs (ref. pages 1-32 of Appendix 4-B, North Thompson <br />Creek Flows), To assess the relative impact of the sediment structure effluents <br />on the receiving stream, the suspended solids concentration required to <br />incrementally increase North Thompson Creek concentrations by 45 mg/1 can be <br />calculated: <br />409 ft3 x 28.32 1 11,608 1(sec <br />sec ft3 <br />11,608 1 x 45 mg = 522,377 mg/sec <br />sec 1 <br />0.90 ft3 x 28.32 1 = p5.5 1/sec <br />sec ft3 <br />4-106 <br />