Res 2005-071 - Laserfiche WebLink

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San Marcos Floodplain Management Plan: A Sustainable Future for Floodplain Management Applicatfon for Flood Protection Study Grant entity's past and ongoing efforts to better understand the ecological fabric of the unique environmental area surrounding San Marcos Springs and the San Marcos River, as well as others within the proposed project area. 4) Review and Identification of Flood and Drainage Problem Areas - Following an extensive review of the fuformation collected, the problem areas will be classified according to primary drainage system problems and secondary drainage system problems. Based on a preliminary review of this information, a brief preliminary findings report will be prepared, which will outline the specific recommended problem. areas for study. A list of required field survey data will be identified at critical bridges, channel cross-sections, slab elevations, etc.. The preliminary report will be delivered at a public meeting, to receive further public input and discuss the next steps. 5) Necessary Field Survey Collection - Apart from field survey that may need to be collected pending the review and identification of problem areas, the following areas will need field survey, as they are unstudied, or are known to be outdated: 1. Blanco River - slab elevations in low-lying subdivisions. n. San. Marcos River - cross-sections and bridge survey along Sessom Creek. iii. Purgatory Creek - the tributary of Purgatory Creek that enters above SCS No. 5 from the northeast, extending through the Franklin Square subdivision. iv. Sink Creek - cross sections and bridge/culvert crossings along Schulle Canyon Creek. v. Willow Springs Creek - the tributary of Willow Springs Creek that is channelized and extends to Wonder W orId Drive, under 1-35. Field survey will be taken on the City's HARN Texas State Plane South Central Zone coordinate system (US foot), NAD 83 horizontal and NA VD 88 vertical datum, to be on the same basis as the FIS. The City has developed this high accuracy control network, which will ultimately enable very accurate floodplain delineation and correlation to existing and future GIS data development. 6) Hydrologic Model Development - Utilizing existing hydrologic model data, an updated hydrologic model of the watersheds will be developed using Geo-HMS on an ArcView 3.2 platform to develop a georeferenced HEC-HMS model. The use of Geo-HMS will facilitate inclusion of existing City and County GIS coverages, thereby reducing the time and effort needed to develop curve numbers and times of concentration. The model will include both existing and future land use conditions, utilizing existing City and County GIS data, and employ STATSGO or SSURGO soil information to generate runoff curve numbers using the SCS method. A detailed stream network routing will be developed, based on recent 2' LIDAR topography and detention pond rating curve information from M:\activeI04P012 San Marcos M.D.P\Grant Applic-sMa.dtJ!xhibft A, Page 18 December 16. 2004