19 - Drainage Presentation - Sandy Creek Upper Tributaries 4 and 6

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Alternative 3, shown in Appendix H, replaces the existing concrete -lined, vertical wall channel with a deeper channel of similar construction. Deepening the channel must begin at the downstream end as to not impede flow during construction. The overall width of the channel is maintained so acquiring additional right-of-way or easements is not necessary. Most of the channel is immediately adjacent to residences. Appendix H includes detailed cost estimates and improvements for this alternative. " "Recommendations The Alternative 3 improvements should be constructed in 3 phases. Phase 1: downstream of Clarksville, the existing earthen channel will be regraded to a 25 foot wide grasslined channel with 4:1 side slopes at the existing depth. The channel upstream of Clarksville Avenue up to and including the confluence with Tributary 6 will be replaced with a 15 foot wide concrete channel with vertical walls, cut three to four feet (3'— 4') deeper. All existing culverts will be replaced to match the proposed deeper channel flowline. A detailed breakdown of these costs is shown in: Lower Tributary 4 Channel improvements $ 2,947,438.89 Lower Tributary 4 Culvert Improvements $ 564,550.00 Phase 1 - Lower Tributary 4 Subtotal $ 3,511,988.89 Phase 2: the upper portion of Tributary 4 will be improved. The channel will be improved from the confluence upstream to Lamar Avenue with a 15 foot wide concrete channel with vertical walls, with a cut ranging from one to four feet (1' — 4'). Upstream of Lamar, no channel improvements need to be made. All culverts along the upper reach of Tributary 4 need to be replaced, including the culvert under Lamar Avenue and the culvert at Price Street. Upper Tributary 4 Channel Improvements $ 2,403,489.64 Upper Tributary 4 Culvert Improvements $ 458,782.50 Phase 2 - Upper Tributary 4 Subtotal $ 2,862,272.14 Phase 3: Tributary 6 will be improved. The existing trapezoidal channel will be replaced with a 25 - foot wide, vertical wall concrete channel. The culverts along Tributary 6 will need to be replaced with bridges unless additional right-of-way is acquired. Tributary 6 Channel improvements $ 640,092.88 Tributary 6 Culvert improvements $ 741,275.00 Phase 3 - Tributary 6 Subtotal $1,381,367.88 These costs are construction estimates only and do not include design survey or engineering fees. These costs also do not account for inflation or any escalation in construction prices. These costs were estimated using recent bid tabulations and Texas Department of Transportation average bid prices. Construction Subtotal $ 7,755,628.91 Contingency $1,551,125.78 13