08-11-1976 Council Agenda - Laserfiche WebLink

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UNITED STATES DEPARTMENT OF AGRICULTURE SOIL CONSERVATION SERVICE TO: FROM: SUBJECT: July 21, 197.6 Supervisors, Ramsey Soil and Water Conservation District Howard J. Moechnig, District Conservationist Review of Uestwinds proposed plat, Little Cnna1a The soil on the proposed plat has been classifieh by USDA soil scientists as Wadconda silt loan:, 0-27f slopes. The Srefliminary Soil Investigation by Soil Exploration Company outlines in detail the ne:es sary precautions to take when constructing homes on this soil type. These precautions should be followed by the developer. In this particular case, the amount of runoff from tbis parcel of land may not be greater after development than in its present chndition- The runoff curve number gives a good indication of this. In general, the higher the runoff curve number the greater the amhnet of runoff. From the attached Runoff Curve Sheet it can be seen that ‘..i.th lots about 1/3 acre in size the runoff curve number is Cl (hydrologic soil. grouP C) . For pasture the .runoff curve -number ranges frou 74- to 86, depending upon the condition of the grass cover. It is soggested thnt the city have an engineer make an accurate determination.. of the amount of runoff. One major difference between existing conditions find these of an urban development is the installation of storm severs to collect runoff from streets. This means that water falling directly on streets will be quickly removed to County Ditch 7 instead o'f having to flow overiatd. The characteristics of the ditch should he checked by an engineer to see if it can handle this "rush" of water during a storm- Runoff from this proposed development will most likely be more con- taminated than the runoff from the land in its present condition. The major contaminants will be sand and sediment, ail, organic debris such as grass clippings and leaves, and road salt. it is recommended that sedimentation ponds be installed on both sides of County Ditch 7 to trdp sediments prior to discharging the stormwater into the ditch. All storm sewers on the plat should be routed through these sediment ponds. It is not known how effective sediment ponds are in controlling other contaminants but they are very effective in removing much of the sedi- ment. This is important since sediment not only damages fish and wild- life habitat in receiving bodies of water, but it also contributes to the nutrient enrichment of these bodies of water and this can lead to algal blooms. L-A i;1 , 0010 CiTli (1,