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<br />I <br />I <br />I <br />I <br />II <br />I <br />I <br />1 <br />I <br />I <br />I <br />I <br />I, <br />I. <br />I <br />I <br />I <br />I <br />I <br /> <br />Street do not have adequate spillways. Tributary S crosses Washington Street in two 36" <br /> <br /> <br />CMP and one 24" CMP culverts. The flood flows in this reach are contained within the <br /> <br /> <br />channel and the pond areas with potentiol breaching of the dam embonkments. <br /> <br /> <br />There are no improvements proposed above Washington Street except flood plain <br /> <br /> <br />zoning with flood insurance. <br /> <br /> <br />The proposed improvements at Washington Street consist of replocing the existing <br /> <br /> <br />culverts with three 48" x 76" HE-RCP culverts with a rip-rap outlet stilling basin. Below <br /> <br /> <br />Washington Street the orea is proposed to be flood plain zoned. The first two ponds below <br /> <br /> <br />Washington are not considered to be important from the flood control standpoint; <br /> <br /> <br />therefore, no improvements are recommended in this report. <br /> <br /> <br />14. Drawing TS-4 (Sheet 19 of 30), Tributary S, Station 58+00 to 29+00 <br /> <br /> <br />The channel in the reach depicted by the drawing is characterized by a narrow, deep <br /> <br /> <br />channel with a steep, longitudinal slope in the areo below the pond. The improvements <br /> <br /> <br />proposed are as follows: <br /> <br /> <br />(I) Construction of a 30 foot wide concrete spillway, chute, and stilling basin for <br /> <br /> <br />the pond at Station 48+60. Also, embankment work, including rip-rap on the <br /> <br /> <br />foce of the dam, is proposed to meet the State Engineer's criteria. An 18" <br /> <br /> <br />CMP low level outlet pipe is also proposed to improve the dom and reservoir <br /> <br /> <br />facility. <br /> <br /> <br />(2) Six 3 foot concrete check drop structures are proposed to be constructed in the <br /> <br /> <br />channel reach below the dam to control erosion. <br /> <br /> <br />The improvements to the pond at Station 48+60 are shown on the drawings even <br /> <br /> <br />though the damages below the dam are minimal and the improvements are not fully <br /> <br /> <br />justified from 0 flood control standpoint. During the occurrence of a 100-year flood on <br /> <br /> <br />Tributary S the water surface in the reservoir would rise to the crest of the dam. The <br /> <br />downstream flood plain has been delineated based upon the existing conditions of the dam. <br />If improvement are not made to the dam by the owner, then the flood plain would remain <br />as shown. <br /> <br /> <br />If the dam is to be retained, the State regulations as administered by the State <br /> <br /> <br />Engineer's Office would probably require dam ond spillwoy improvements. The pond <br /> <br /> <br />provides minimal flood storage benefits for the 100-year flood but does have a routing <br /> <br /> <br />effect on the more frequent floods. In conclusion, it should be the responsibi Iity of the <br /> <br /> <br />owner to upgrade the pond and dom to the State Engineer's stondards, and the cost of the <br /> <br /> <br />improvements are not justified by flood control benefits. <br /> <br /> <br />15. Drawing TS-5 (Sheet 20 of 30), Tributary S, Stotion 29+00 to 0+00, Grange Hall <br /> <br /> <br />Creek Confluence <br /> <br /> <br />The channel in this reach is narrow and deep with steep, longitudinal slopes. <br /> <br /> <br />Tributary S crosses 104th Avenue in two recently constructed 66" RCP culverts. The <br /> <br /> <br />flood plain is contained within the channel section with an increase in width near the <br /> <br /> <br />confluence created by backwater from the 108" CMP culvert under the railroad spur <br /> <br /> <br />embankment. <br /> <br /> <br />The proposed improvements consist of the following: <br /> <br /> <br />(I) Five 3 foot and one 2 foot concrete check drop structures, one above and five <br /> <br /> <br />below 104th Avneue to control erosion of the main channel. <br /> <br /> <br />(2) Addition of a 72" RCP culvert under 104th Avenue with a rip-rapped outlet <br /> <br /> <br />stilling basin. <br /> <br /> <br />The drawing does not show a distinction in the 100-year flood plain with and without <br /> <br /> <br />improvements because of the lack of sufficient difference. <br /> <br /> <br />16. Drawing TN-I (Sheet 21 of 30), Tributary N, Stotion 42+85 to 30+00 <br /> <br /> <br />The channel in this reach has been greotly influenced by the encroaching <br /> <br /> <br />development. The area obove Irma Drive which is tributary to this reach is almost <br /> <br />16 <br />