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--. I I I I I I I I I I I I I I I I I I Preserve at Weaver Creek CLOMR Report December 26. 2000 II. PROPOSED CHANGES A. Low Flow Crossing A path connecting the east and west sides of the development will be constructed with a riprap embankment through the channel. Culverts sized to pass the low flow will be installed under the crossing with the required riprap erosion protection, and the floodway will be graded to fonn a small pool on the upstream side of the crossing. During high flows, the walkway will be inundated. B. Retaining Walls The revised 100-year floodplain is proposed to follow the retaining walls that surround most of Weaver Creek through the site. They will be constructed so that the 100-year flood will have I-foot of freeboard to the top of the retaining walls. III. REVISED STUDY A. Additional Cross Sections Cross sections were added at locations upstream and downstream of the proposed low water crossing. The crossing was analyzed using the Hec-2 special culvert option, which requires more cross sections than the original study used. Cross Section 35+13 and 35+73 were added for modeling purposes only. B. Analvsis The Hec-2 Program was used to analyze the site. The cross sections used were the same as those used in the 1981 study of Weaver Creek except those noted above. A field survey was done in 1999, updating the actual conditions of the channel. This survey was used to develop the existing conditions scenario. The 1999 survey shows differences in the topography from the 1981 study. These differences include the absence of a dam between stations 35+40 and 35+80 and steeper side slopes. For the proposed conditions, the existing condition cross sections were revised to include the addition of the culvert crossing and the retaining walls. IV. RESULTS A. Flood Tables The following tables compares the 1981 Study, the 1999 Existing conditions, and the proposed conditions. David Evans and Associates, lnc, 2