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Mc Crellin Scott <br />July 30, 2002 <br />Page 2 of 3 <br />~. Stoker Watershed SEDCAD 4 Model Input. These sheets provide a summary of <br />the input data into the new SEDCAD 4 model of the Stoker watershed. <br />6. CN BreakdoH~n. This color figure shows the curve number breakdown for the <br />watershed. Dark green is undisturbed (CN=47), green is reclaimed 3+ year growth <br />(CN=56), blue is reclaimed 1 to 2 year growth (CN=61 ), and red is reclaimed <br />topsoiled and seeded (CN=86). This figure represents the watershed immediately <br />after the watershed is reclaimed and is considered the worst-case scenario. Curve <br />numbers vv°ere obtained from "Methodologies and Assumptions for Sedimentation <br />Pond Evaluations" of the approved permit (Volume 2C). <br />7. Stoker Sedimentation Pond Summary. This table provides a quick reference to the <br />differences between the current model of the Stoker watershed and earlier versions. <br />The summary sheet indicates that the drainage area increased by 1.5 acres between <br />1998 and 2002 and the discharge parameters for ttie ] 0-year and 25-year storms <br />generally did not change. The pond summary sheet also predicts the Stoker Pond has <br />17.9 years of sediment storage. <br />• 8. SEDCAD 4, Stoker 10-year, 24-hour Model. This is the printout of the 10-year, <br />24-hour design storm. This model demonstrates that using the design storm, the <br />Stoker Pond is in compliance with an effluent discharge of less than 0.5 ml/I <br />settleable solids and no discharge in the emergency spillway. <br />9. SEDCAD 4, Stoker 25-year, 24 hour Model. The spillway is adequate. <br />10. SEDCAD 4, Stoker 100-year, 24-hour Model. The spillway is adequate. <br />11. SEDCAD 4, Stoker TR-60 Emergency Spilhvay Evaduation. The Stoker Pond was <br />assumed to be a Class B pond for a TR-60 Emergency Spilhvay Evaluation. The <br />rainfall amount used for this mode] was the 100-year, 6-hour amount plus O, l2 times <br />the difference between the probable maximum 6-hour amount and the 100-year. 6- <br />hour amount. The model shows the Spilhvay is adequate to meet the TR-60 criteria <br />for a Class B struchu•e. The probable maximum precipitation was determined from <br />HMR 49. <br />12. SEDCAD 4, Stoker TR-60 Emergency Spilhvay Freeboard Evaluation. The <br />Stoker Pond was assumed to be a Class B pond for a TR-60 Emergent}' Spilhva} <br />Freeboard Evahtation. The freeboard is adequate to ~~ithstand the runoff from the <br />100-.'ear. 6-hour rainfall plus 0.=t times the difference between the PMP-6-hour and <br />the ]00-rear. 6-hour amount. The SEDCAD d anahsis indicates the peak elevation <br />will approach to ~~ ithin 3.6=1 feet of the top of the embankment without o~~ertopping. <br />W <br />WC Engineering <br />