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SCOTTLAND GREEN POND <br />DESIGN OF OUTLET STRUCTURE'AND ROUTING OF DESIGN STORM <br />1. General <br />-r� � 7tssa <br />H'GION V1 <br />WATERS <br />The attached plans for the Scottland Green Pond and outlet struc- <br />ture are intended for the following design conditions: <br />a. Normal Pond Level = 893.0 <br />b. 100 Year Pond Level = 895.7 <br />c. Pond Storage = 51.6 AF <br />d. Pond 100 Yr. Discharge - 15.0 cfs <br />Previously we submitted information that estimates the pre - <br />development discharge based on land use and existing pond storage. <br />Also, The pond area was sized based on final land use and a 100 year <br />runoff event for the site. <br />This report includes our sizing calculations for the proposed <br />outlet structure and also routing of a'100 year, 24 hour storm event <br />through the completed pond and structure. <br />2. Rating of the Outlet'Structure <br />The plans show the outlet structure as having a 12 inch diameter <br />opening at the pond control elevation of 893.0. When water rises to <br />elevation 894.9, flow will begin over a weir having a width of 519". <br />At a water level of 895.7, the total flow through the structure will <br />be approximately 15.0 cfs. <br />The following assumptions were made. For orifice flow through <br />the 12" diameter hole, we assumed that tailwater on the orifice would <br />be below elevation 893.5 for the interval from normal pool (893.0 <br />to the weir overflow level (894.9). Above that level, tailwater would <br />be higher on the orifice rising to 894.9 when the pond level would be <br />at elevation 895.7. <br />Tailwater on the outlet structure for maximum water level was <br />assumed to be 894.9. This was calculated using a water level down- <br />stream from County Road H-2 of 894.5 and approximately 0.4 feet of <br />head loss from the outlet structure to a point south of the County <br />Road. The City has indicated their intent to place flows in this <br />reach of the existing ditch in pipe. We have reviewed sizing with <br />the City's consulting engineer. It appears that a 36" diameter <br />reinforced concrete pipe would be required. <br />Flows over the weir were made using the normal weir equation. <br />As noted above, the tailwater at the weir should not exceed the weir <br />sill elevation for the 100 year event. <br />The attached drawing shows the rating curve for the outlet <br />structure and also the volume -elevation storage curve for the proposed <br />Scottland Green Pond. <br />