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In some cases, as a practical consideration, a group of channels has been designed using a single <br />minimum riprap size. That size will in all cases be as large or larger than the size determined in the <br />SEDCAD analysis for each individual ditch, and will thus result in a more conservative design for some <br />of the ditches in the group. <br />Where flow velocities in the design event can be shown to be below allowable velocities as defined in the <br />SEDCAD Model, grass linings may be selected for such ditch segments. SEDCAD provides for a sliding <br />scale of permissible velocities for smooth brome grass linings varying from 5 to 7 feet per second (fps) <br />depending on channel slope. <br />4.0 RESULTS <br />Based on the previously discussed input parameters and methodologies, the emergency spillways, <br />temporary and permanent channels for the Colowyo mine site were designed and /or evaluated for <br />capacity and erosional stability. The following summary tables indicate a range of slopes and erosion <br />control requirements for each emergency spillway and segment of the temporary and permanent channels. <br />All channels are designed to meet the requirements of Rule 4.05.3 or Rule 4.05.4 as appropriate. Rule <br />4.05.3 is for drainage areas less than one square mile and requires a minimum design event based on the <br />10 year storm. Rule 4.05.4 is for drainages in excess of one square mile and requires a 100 year, 24 hour <br />event. <br />Upon completion of each permanent channel segment, an engineering construction report will be prepared <br />and submitted in the appropriate annual report. This report will provide certification by a professional <br />engineer that the channel segment has been constructed to the appropriate widths, lengths, alignment, <br />channel slope and riprap or other erosion protection specifications to meet the intended design criteria. <br />5.0 REFERENCES <br />Bureau of Land and Water Conservation, Division of Stormwater Management and Sediment Control <br />(1996). "Erosion and Sediment Pollution Control Program Manual'. Commonwealth of <br />Pennsylvania, Department of Environmental Protection, Office of Water Management. <br />Harrisburg, PA. <br />Chen, YR., and G.K. Cotton (1988). "Design of Roadside Channels with Flexible Linings ". Hydraulic <br />Engineering Circular # 15. Federal Highway Administration. McLean, VA. <br />Temple, D.M., KM. Robinson, R.M. Ahring, and AG. Davis (1987). "Stability Design of Grass -Lined <br />Open Channels ". Agriculture Handbook Number 667. United States Department of Agriculture, <br />U.S. Government Printing Office, Washington D.C. <br />Exh. 7 -14 -4 Revision Date 12/10/12 <br />Revision No.: TR -97 <br />