07-09-18 Drainage and Flooding Committee Meeting

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Previous Studies The most recent drainage analysis for the City of La Porte is the City Wide Drainage Study, prepared by Klotz Associates, Inc. in January of 2009. In this study, the La Porte Municipal Airport and bordering areas were not evaluated in detail. The Spencer Highway drainage design plan (Record Drawings dated 1994) is used for the storm sewer along the Highway. m Exisdirm ondifion Location. The La Porte Municipal Airport is located in the City of La Porte, Texas, to the south of TX-225/Pasadena Highway and to the west of TX-146. It is located at the northeast corner of Spencer Highway and Farrington Drive. The neighborhoods in question are located to the west and north of the airport site. The neighborhood to the west is located just west of Farrington Drive, north of Spencer Highway and east of the Big Island Slough channel, and for this report is known as Glen Meadows. The neighborhood to the north is located between the northern border of the airport and N Avenue H. Figure 1 shows these neighborhoods. Floodplains The corner of the Glen Meadows subdivision near Spencer Highway adjacent to the Big Island Slough is within the 100-year FEMA floodplain, with a larger portion of the southern and western areas within the 500-year floodplain. The neighborhood to the north of the airport site is outside the 100-year floodplain. Exhibit 1 presents the effective FEMA floodplains at the airport site. The 100-year Base Flood Elevation (BFE) ranges from elevation 19.70 near Spencer Highway to elevation 21.0 near the north end of the Glen Meadows subdivision. Topography and. Drainage Topography of the site and bordering areas was developed using a combination of a detailed survey provided by Gessner Engineering and LiDAR data downloaded from Houston -Galveston Area Council (HGAC). A Digital Terrain Model (DTM) was developed from the detailed survey and drainage areas were determined for each ditch and drainage structure using GIS tools. Overall, the airport property generally slopes north to south, with isolated high and low points. The ground elevations on site range from approximately 24 feet to 20 feet. The neighborhood to the north of the airport slopes southwest to northeast along Northern Avenue H from approximately 25 feet to 20 feet. The neighborhood to the west of the airport generally slopes northeast to southwest toward Spencer Highway from approximately 23 feet to 19 feet. La Porte Municipal Airport — Offsite Drainage Analysis HT&J, LLC, January 2018 Page 3