Drainage_and_Flooding_Report-dated_03-10-08

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Mr. Ron Bottoms March 10,2008 k10tzassociates Page 5 of 15 Record Plans Review of the drainage infrastructure data provided by the City suggests that updating of the data using City plans and as -built data will be necessary. Incomplete or unavailable as -built information may complicate the update of the drainage information. Hydraulic and Hydrologic Models Up-to-date hydrologic models (HEC-HMS) and hydraulic models (HEC-RAS) based upon information developed as a consequence of the Tropical Storm Allison Recovery Program (TSARP) are readily available from HCFCD and have been incorporated into the information for this project. The hydrologic models that were obtained are for Clear Creek Watershed, Armand Bayou Watershed, and Galveston Bay Watershed. The hydraulic models that were obtained are as followed: • Clear Creek Watershed - A 104-00-00 (Taylor Bayou) A104-07-00 (Tributary 3.93 to Taylor Bayou) • Armand Bayou Watershed - B106-00-00 (Big Island Slough) - B 109-00-00 (Spring Gully) - B 109-03-00 (B 112-02-00 Interconnect) - B 112-00-00 (Willow Springs Bayou) - B 112-02-00 (Tributary 1.78 to Willow Spring Bayou) • San Jancinto/Glaveston Bay Watershed - F216-00-00 (Little Cedar Bayou) Site Visit and Drainage Problem Evaluation Field visits of the City drainage systems were carried out to complement the study and provide an on -the -ground understanding of the drainage situation. Selected photographs taken during the site inspection are shown in Appendix A. Generally, the City drainage is dominated by a combination of runoff from small residential lot neighborhoods with lot sizes in the 0.15 to 0.25 acre range, large rural -like residential lot neighborhoods with lot sizes in the 3 to 5 acre range, and industrial and commercial areas. Selected photos from our field reconnaissance visit are presented in Appendix A. Many of the small lot residential neighborhoods are drained by curb and gutter. Lot sizes average about 0.15 to 0.25 acres. There is a combination of B-, BB-, and A -type inlets in these neighborhoods, but there does not appear to be a sufficient number of inlets to handle the flows. Floor slab elevations in these small residential neighborhoods appear to be commonly higher than the adjacent street elevation by about 1 to 2 feet. Some typical