2017-02-21_REVISION - M1988112 (4)

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Flow (cfs) in Ditch at the Drop Structure 100 -Yr 100 -Yr 500 -Yr Contained 500 -Yr 1,000 -Yr Contained 1000 -Yr Contained 10,000 -Yr PMF Contained Existing Conditions 323 348 552 739 713 950 12 15 ft. Bottom (S=0.25%) 431 830 1046 1,490 2,642 20 ft. Bottom (S varies) 433 833 1049 1,492 2,798 Existing Ditch Geometry and Bank Heights to Contain the 100 -Yr, 500 -Yr and 1,000 -Yr Storms Link Existing 100 -Yr Height (ft) Height (ft) 500 -Yr Height (ft) 1,000 -Yr Height (ft) 5 10 10 12 12 6 5 5 5 6 20 5.5 6 8 9 23 7 7 8 9 Potential Channel Modifications Links Recommended Bank Height (ft) 1-7* 10 8-11 12 12-18 14 19-23 12 *To contain PMF for both 15 ft. and 20 ft. alternatives, increase bank height to 11 ft. resulting in Qo,tfau-3,060 cfs 20 -ft Bottom Width Alternative without Basin A Inflow 10,000 -Yr PMF Qoutfa11 (cfs) 927 1,660 Link 20 in the model is the location of the wasteway crest above Sub -Basin B. The crest length of the wasteway was measured from the terrain model to be approximately 135 ft. To contain the 500 -Yr Storm, the crest elevation must be raised to 8,628 ft. (An increase of 2.5 ft.). The following table shows the wasteway flow (Qw,,Y,) for storms greater than the 500 -Yr. *Note: Flooding occurs in other areas of model on 10,000 -Yr and PMF, which decreases Qo„,fall 1,000 -Yr 10,000 -Yr PMF Qwaste (cfs) —100 —400 —700 Total Volume Flooded (acre -ft) 1.3 16.4 33.9 C�.,fau (cfs) 912 1131 1611 *Note: Flooding occurs in other areas of model on 10,000 -Yr and PMF, which decreases Qo„,fall