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

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07343000 near Cooper, Texas (Cooper Gage herein) on the North Sulphur River is 10.9 miles upstream of the confluence of Big Sandy Creek and the North Sulphur River. Gage 07343200 near Talco, Texas (Talco Gage herein) on the Sulphur River is 22 miles downstream of the confluence of Big Sandy Creek and the North Sulphur River. Both gages measure discharge (flow rate) and gage height (water surface elevation). The Cooper Gage was in flood stage (gage height of 30 feet or more) from 22:00 CDT on April 29, 2016 until 02:45 CDT on April 30, 2016 The Talco Gage was in flood stage (gage height of 20 feet or more) from 23:30 CDT on April 17, 2016 until 20:45 CDT on May 14, 2016 It is outside of the scope of this analysis to determine backwater effects in Paris due to downstream conditions in the Sulphur River, but the stream gage data confirms that the greater Paris region received extraordinary amounts of rain. " With the limited flood gauges in the immediate vicinity of Paris, this information is important. It shows that as the storm was occurring in Paris, the river was already at or above flood stage. With so much water contributing to the larger drainage basin, and the water from Paris also waiting in the queue to drain, there was nowhere for the water to go. It was forced to back up and use the floodplain as nature intended, which had a large impact on anyone living in those areas. I would compare the situation to a bathtub that is filling up and trying to drain, but the sewer line is undersized as it is leaving the house, and the sewer main at the street is already full from all of the other houses, so the water backs up in to the house. Cobb Fendley offered some Alternatives and a recommendation. The Appendices referenced below are not included in this summary but can be found by reviewing the original Cobb Fendley report: "Alternatives CobbFendley investigated several alternatives to mitigate flooding in the two tributaries. The 100 year rainfall event can be contained completely within the limits of the existing channel by deepening the entire channel and replacing all culverts. Some culverts will need to be replaced with bridges unless additional right-of-way is acquired. Culvert replacement (Alternative 1, shown in Appendix F) yielded little to no improvement in the flooded areas. This indicates that channel conveyance capacity is the controlling problem, not strictly culvert capacity. For the purpose of this analysis, culverts were replaced with bridges and the existing stream cross section was maintained through the bridge area. During the design phase, culverts should be sized and designed where right- of-way permits to save costs. Alternative 2, shown in Appendix G, expands on Alternative 1 and includes some channel improvements to further reduce the water surface elevation. The channel improvements include a v -shaped ditch that is concrete lined for most of the channel. The v -shaped ditch option is cheaper than a vertical wall concrete channel, but the over top width of the channel would be wider than the existing channel. Widening the channel would require additional easement and/or right-of-way, which is inadvisable in an established residential neighborhood. 12