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<br />'" <br /> <br />. <br /> <br />. <br /> <br />Mr. Duane L. Rehborg <br />May 3, 1978 <br />page tlvO <br /> <br />feet and ielocities <br />the p~oposed units. <br />submitted: <br /> <br />. <br /> <br />from 1.0 to 2.8 feet per second over most of <br />Specifically, we find for the plat plan <br /> <br />1. Appr?ximately 162 of 193 proposed units, the pump station, <br />serv~ce area, storage area, recreation area, and selvage <br />treatment plant sites are Ivithin the 100-year floodplain. <br /> <br />2. Approximately 50 of the proposed units, a portion of the <br />service area, and a portion of the recreation area are in <br />a low hazard flood area. <br /> <br />,- <br /> <br />3. Approximately 92 of the proposed units, the storage area, <br />most of the recreation area, and sewage treatment plant <br />sites are in a high hazard area due to flooding depths <br />in excess of 1.5 feet. <br /> <br />4. Approximately 21 of the proposed units, the pump station, <br />storage area, service area, recreation area, and sewage <br />treatment plant sites are in a high hazard area due to <br />flood velocities in excess of 3.0 feet per second. <br /> <br />5. One of the proposed units appears to be in a high hazard <br />area for both reasons of excessive flooding depth and <br />velocity. <br /> <br />Furthermore, Ive are very concerned with construction of the <br />proposed "...four (4) foot, plus or minus, berm..." to be "...built <br />along the riverbank and extend the entire length of the property...". <br />\,e sugge3t the construction of such a berm may actually aggravate <br />the flood hazard rather than lessen it for the follOlving reasons. <br /> <br />Firs t, the berm as sholvn fails to intercept flOlv in the right <br />overbank which represents approximately 40 percent of the 100-year <br />flood flOlv. This water Hill become trapped behind the berm and <br />pose even a greater flood hazard than if there Ivere no berm at all. <br />The same problem Ivill occur if the berm Ivere to fail an)'l'lhere along <br />its length during a major flood. Furthermore, cross site drainage <br />would collect and be impounded by the bel~l during an intense thunder- <br />storm. <br /> <br />Secondly, experience and studies have shown that it is extremely <br />difficult, if not impossible, to straighten a naturally meandering <br />river by simply piling up an earthen embankment. Suitable riprap <br />~1~ will be necessary to control erosion due to increased velocities. <br />~. ~ Several units as platted appear very close to the-existing river <br />\:S ~ and Ivill be in danger of eroding away Ivith or without a berm. <br /> <br />S~}l~ . <br />i~~ ~~ ' <br />l~ {~ .~~~ <br />