Laserfiche WebLink
Pond 012 Postmining SEDCAD Modeling <br />This sediment control plan update addresses the current conditions of the watershed tributary to <br />Pond 012 to reflect the fact that the entire tributary area is now reclaimed and has a maturing <br />vegetative cover in place. The system collects all runoff from the 24.29 acres into a below grade <br />sediment control pond excavated near the south end of this area. This area is currently draining <br />to Pond 012 via the C8 ditch from the east, the C7 ditch from the west. The Tailwater Ditch <br />along the southern edge of the watershed intercepts and diverts runoff from the reclaimed areas <br />to the west. <br />The drainage area of Pond 012 is entirely composed of reclaimed lands with more than 3 years <br />growth. <br />The design considerations used for this evaluation are described in the following paragraphs. <br />The watershed boundaries, associated drainage areas, and runoff curve numbers are shown on <br />Map 1, Postmining Drainage Analysis, Pond 012 Area, hereafter referred to as Map 1. <br />Hydrologic Methodology <br />The SCS Curve Number method has been used to determine runoff volumes and runoff flow <br />rates. The runoff curve number is a factor relating the amount of rainfall to the amount of runoff <br />for a given area. The best reference for application of this method to coal mine applications is <br />Barfield, Warner, & Haan (198 1) in "Applied Hydrology and Sedimentology for Disturbed <br />Areas", Oklahoma Technical Press, Stillwater, OK. Tables are included in this reference, as <br />well as several widely accepted NRCS (formerly SCS) publications, present the appropriate CN's <br />(curve numbers) for specific land uses and conditions. <br />Although the volume of runoff can be calculated manually using the SCS Curve Number <br />method, for this evaluation the SEDCAD computer model, developed and marketed by Civil <br />Software Design, was used to make the runoff calculations. In addition to its wide acceptance <br />for use in coal mine permitting work, it also provides a consistent tabular output of all design <br />assumptions and all calculated results. <br />Location Specific Hydrologic Parameters <br />The 10 year, 24 hour precipitation event for sediment control analysis for this location has been <br />identified as 2.0 inches. The 25 year, 24 hour precipitation event used for spillway evaluation <br />produces 2.4 inches of rain. <br />Site Specific Hydrologic Parameters <br />Curve numbers were designated on a land use basis as determined from field observations and <br />are presented on Table 2.05.3(3) -IA. <br />Attachment 2.05.3(3)-31 Revision Date: 1/08/2016 <br />Page 2 Revision No.: TR -70 <br />