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<br />SITE DRAINAGE NARRATIVE <br />PAGE 1 OF 2 <br />PROJECT NAME <br />(Little Canada, Ramsey County) <br />Site Drainage Narrative & Storm Water Calculations <br />Date: July 25, 2022 <br /> <br /> <br />This project proposes the subdivision of a 3.1-acre undeveloped property into single-family residential <br />lots. The site is located on the west side of Edgerton Street (CSAH 58), north of Little Canada Road. The <br />site falls within the Ramsey Washington Metro Watershed District. <br /> <br />Soils <br />At the time of plan preparation, no site-specific soil borings are available. A USDA NRCS web soil <br />survey shows that site consists of 35% Zimmerman fine sands (north) and 65% Zimmerman <br />complex sands (south.) The Zimmerman sands are generally very well-draining granular soils. <br />which are typically modeled as HSG “A” type soils. <br /> <br />Storm Water Modeling <br />Modeling uses HydroCAD with Atlas 14 rainfall events and MSE Type 3 storm distribution. HSG <br />“A” type soils are assumed based on soils data noted above. The rainfall events are as follows: <br /> <br /> 2-year storm = 2.81” <br /> 10-year storm = 4.19” <br /> 100-year storm = 7.39” <br /> <br />The following curve numbers area assumed: <br /> <br /> Impervious & Gravel CN = 98 <br /> Open water CN = 98 <br /> Grass (>75%) CN = 39 <br /> Woods CN = 36 <br /> <br />Wetlands <br />The site was inspected for wetlands and none were found. <br /> <br />Existing Conditions <br />In existing conditions, the site is heavily wooded on the north side, with less tree coverage on <br />the south side. There is an existing concrete pad, presumably for a tennis court. There is no <br />other impervious on the site. The site primarily drains north to a land-locked low area, some <br />run-off going directly through the site, and the rest draining onto Edgerton and then to the land- <br />locked low area. The remainder of the site drains south/east to Edgerton (which continues to <br />drain south.) <br /> <br /> Approximate site area = 3.12 acres <br /> <br /> Existing impervious area = 0.074 acres