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I I I I II i I , . . I I I I \, I I I I',.. ,_I'" I ,. I Mr, Wayne Bethurum Page 3 The baseline HEC-2 model using flows of 2,800 cfs and 3800 cfs indicated the flood flows would spread out in general agreement with the extent of flooding shown in aerial photography supplied by the CWCB. The model actually indicated somewhat wider flooding than the aerial photographs showed, but the photographs were taken some four (4) hours prior to the estimated peak. It is our understanding that the aerial photography was taken at about 6:00 p.m. and that the peak runoff from the storm did not occur until about 10:00 p.m.. We were informed by the CWCB that at the peak of the overflows, storm water was about 2 feet deep at your construction trailer. Based on the site topography and spot elevations completed by Liebert McAtee, your construction trailer is set on ground with an elevation of 3947.30. Our baseline model completed for 2800 cfs computed a water surface elevation of 3949.41 at cross-section 3 which crosses your property near the location of your construction trailer. Based on this information the model was accepted as a baseline condition ICON created a proposed conditions model to evaluated the impact of the improvements to your property that have been constructed, or are planned to be built as part of the most recent filing. This was done by adding elevation data from the overlot grading plans for the South Point Subdivision of Lot I to the surveyed cross section data Planned single family houses were coded into the modeled cross-sections using the top of foundation elevations presented on the construction drawings which are enclosed with this letter. A roughness Coefficient of 0.035 was . used to represent the streets and bluegrass areas within the subdivision. The results of the baseline U model and proposed conditions model are presented in the following tables: ,~ j \. c: . L'-" \ .6-\./\ C \ ' J-' . I ~~J(LI Water Surface Elevations - Discharge = 2,800 cfs )J l --<,c" , i;; ,/, I ,). .. r ~Vl'C) -,1- ? '-) L, -- ,. -! / / Baseline Water Surface WSEL with 1./ Difference Cross Section Elevation Improvements (ft) 1 3946.60 3946.60 0,00 2 394838 3948.28 / -0,10 3 3949.41 3949.59 . 0,18 4 3949.96 3949,97 0,01 5 3950,71 3950.80 0.09 6 3951.32 3951.03 -0.29 7 3953,29 3952,99 -0.30 B 3957.64 3957.74 0.10 Water Surface Elevations - Discharge = 3,800 cfs ,I Baseline Water Surface WSEL with Difference Cross Section Elevation Improvements (ft) 1 3947.00 3947.00 0,00 2 3948.74 3948.67 -0.07 . - 3 3949.74 3949.93 0.19 4 3950.29 3950,32 0.03 5 3950.96 3951.09 0.13 6 3951.52 3951.27 -0.25 7 3953,61 3953.10 -0.51 8 395B.31 3958.47 0,16 ,; , I vii' I ,j' ~ I-t f. ~)