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Lorencilo Canvon Mine -Surface Wmer Technical ReDOrt <br />• Flow, Crest, and Storm Event Determination <br />Determination of the flow at the site was done by measuring depth of the water at a known point <br />and interpolating this depth through the stream rating curves developed for the site. Determination <br />of the stream rating curves was done following the Manning's method (Isco, 1985). This method <br />allows for the determination of the rate of flow in an open channel without the benefit of a separate <br />primary measuring device. This determination is based upon the formula Q=(1.49/n)AR2"S'lZ <br />where: <br />Q= Flow in cfs <br />n= Manning's Coefficient <br />A= Cross-sectional area of flow (ft~) <br />R= Hydraulic radius (ft) (cross-sectional area divided by the wetted perimeter) <br />S= Slope of the hydraulic gradient <br />The cross-sectional area of the flow was surveyed for determination of the rating curve. Along <br />with the determination of the cross-sectional area, the wetted perimeter area was determined. <br />These values were then input into a spreadsheet and a discharge curve determined for each station. <br />Prior to the determination of the rating curves, surveys were performed to determine the stream <br />• cross-section at each site. These surveys were performed by establishing permanent benchmarks <br />at either side of the stream, and subsequently surveying the elevation at points every two feet <br />across the stream. A second survey was performed in the direction of flow to determine the slope <br />of the channel. In addition, the crest gauge was surveyed in. Professional judgement was utilized <br />to establish the Manning's n value. <br />Crests for the stations were measured via crest gauges. Each of the crest gauges are two-inch <br />PVC cylinders with a 1-inch staff gauge inside the cylinder. Each of the two-inch cylinders has <br />holes drilled at the base to admit water into the pipe. Cork was added into the outer cylinder <br />which sticks to the staff gauge after every storm event. Crest gauges are read every month along <br />with the monthly baseline monitoring. In addition to the crest gauges, sediment samplers were <br />installed. Crest gauges were designed as previously discussed. Sediment samplers were <br />constructed of 6-inch diameter, 3 feet long, schedule 40 PVC pipe fitted with a permanent bottom <br />cap and a threaded top cap. Holes were drilled in the pipe at a level above the normal flow. <br />Placed inside each pipe is a 4-inch PVC container. Apiece of 1-inch piping extends from the top <br />cap to the sampler to prevent the sampler from "floating" during storm events. These devices are <br />detailed on Figure SW-1. <br />• <br />sw.476\Dccember 4, 1996 <br />