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)~drograph Response 5ha~ <br /> <br /> <br />• <br />A unit hydrograph is chosen for each drainage area or sub-area model to predict the runoff <br />response. The hydrograph responses available in the SEDCAD+ model are slow, medium and <br />fast. A slow response corresponds to a forested area or an area with a number of obstruttions, <br />whereas a fast response corresponds to an unvegetated or poorly protected area. Fast and <br />medium hydrograph responses were chosen for disturbed and undisturbed areas, respettively. <br />Drainage Basin Area <br />The drainage areas are determined by dirett measurement by planimetering from a 1"-200' scale <br />map. The maximum (worst case) areas were measured. <br />Areas measured are as follows: <br />Drainage $[ruc[ure Section Drainage Area <br />(ac) <br />Watershed Diversion N1 A, B 9.3 <br /> C 10.5 <br />Watershed Diversion N2 A, B 12.9 <br /> C 18.2 <br />Watershed Diversion N3 A 20.9 <br />Watershed Diversion N4 B 20.3 <br />Refuse Sediment <br />Collection Ditch No. 1 A, B, C 15.4 <br />Mine Bench Area (10-yr, 24hr runoff) 7.6 <br />Refuse Sedimen[ <br />CoBec[ion Ditch No. 2 All 4.5 <br />Yard Ditch N2 A 0.55 <br />Time of Concentration. Tc <br />Time of concentration is calculated by using the SCS Upland Method. All hydraulic leng[hs, <br />drainage heights and slopes are measured directly from a I"-200' scale map. The values <br />calculated for time of concentration are summarized as follows: <br />Drainage Structure Time of Concentration (hrs) <br />Watershed Diversion N1 0.028 <br />Watershed Diversion N2 0.033 <br />Watershed Diversion N3 Subaatershed 1 0.087 <br />Watershed Diversion NJ Subwatershed 2 0.087 <br />Watershed Diversion N4 0.051 <br />Refuse Sediment Collection Ditch NO. 1 0.108 <br />Mine Bench area (10.yr, 24-hr runoff) 0.041 <br />Refuse Sediment Collection Ditch No. 2 0.108 <br />Yard Ditch 2 0.016 <br />c~moRKUSenraov.rtev 358Re Revised - Ma 1993 <br />CS/IN9] Spm y <br />