03-23-09 Drainage and Flooding Committee meeting minutes

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Numerous configurations will relieve ponding and flooding during normal rainfall events that occur more frequently than the 100-year event. Depending on the design frequency, a 3-year design is approximately 20% less than the estimates presented above and detailed in Appendix D. Other factors that may affect cost and design are re-routing the existing storm sewer through adjacent systems. This option affects design capacities downstream and causes problems where downstream detention is located. Unless the receiving system has the excess capacity to handle additional flows, this is not desirable. Another option is to purchase additional easements for drainage in the pipeline corridors located along the western boundary of Fairmont Park East. This is possible if the space is available in the pipeline for storm sewer or for crossings. Additional considerations are the added review and coordination time associated with review. If a pipeline is to be relocated, the pipeline owners usually request reimbursement for the relocation and most companies prefer to design the location internally. 3.4 Conclusions Each alternative will allow for the implementation of an overflow swale to be constructed at Fleetwood Drive and Mesquite by lowering the pavement at the intersection approximately 1.0-foot with 50-foot pavement transitions between existing pavement and proposed grade. The outfall pipe will require upsizing and replacement to accommodate other utilities and design flow rate. There is a 22-foot drainage easement located between the Mesquite and HCFCD Unit B 106-02-00 that can accommodate an 8'x 6' RCB. Other City owned utilities may have to be adjusted and are not addressed here. Detailed cost estimates can be found in Appendix D with unit prices and quantities. 3-3 Klotz Associates Project No. 0127.009.000 Fairmont Park East & Brookglen Drainage Study May 2009 City of La Porte