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HomeMy WebLinkAbout32 pt 1Flood Plain -Floodway Determination For a Portion of Carter's Creek & Carter's Grove Prepared for: PAYLESS CASHWAYS (FURROWS) A Resubdivision of Lot 1, Harvey Road East Subdivision Richard Carter League -Abstract No. 8 College Station, Brazos County, Texas Prepared by : Municipal Development Group 203 Holleman Drive East College Station, Texas 77840 Page 1 1 1 2 Appendix "A" Appendix "B" Appendix "C" Appendix "D" Appendix "E" Appendix "F" Appendix "G" Appendix "G-1" Appendix "H" Appendix "I" Appendix "J" Table Of Contents Description Project Location Project Description Project Objective Summary Project Location & Vicinity Map Site Plan Grading, Drainage & Erosion Control Plan Topographic Map FEMA Flood Plain Map Carter's Grove Tributary Cross-Sections (Current Conditions) Carter's Grove Tributary Cross-Sections (Proposed Encroachments) Carter's Grove Flood Plain I Floodway Map Carter's Grove Water Surface Profiles (Current Conditions) Carter's Creek Water Surface Profiles (Existing Conditions) Carter's Creek Tributary Water Surface Profile (Per Modifications This Report) TOC-1 Page Appendix "K" Appendix "L" Appendix "M" Appendix "N" Table Of Contents (Continued) Description HEC-2 Floodway Analysis For Carter's Creek (Current FEMA) HEC-2 Floodway Analysis For Carter's Creek (As Per Modifications This Study) HEC-2 Flood Plain Analyses For Carter's Grove Tributary (Current FEMA) HEC-2 Floodway Analyses For Carter's Grove Tributary TOC-2 Flood Plain -Floodway Determination For A Portion Of Carter's Grove Tributary To Carter's Creek Associated With A Resubdivision Of Lot 1, Harvey Road East Subdivision Richard Carter League -Abstract No. 8 College Station, Brazos County, Texas Location Of Project: The subject project lies near the northeast comer of the intersection of Texas State Highway No. 6 East Bypass and Texas State Highway No. 30 commonly known as Harvey Road (See Appendix "A" Project Location & Vicinity Map and Appendix "B" Site fian). Same project lies on the southwest side of Carter's Creek and is partially located in the Carter's Creek 100-year flood plain fringe. A tributary of Carter's Creek which extends into the Carter's Grove Addition crosses the southeastern boundary of the project. Upon intersection with the northwest side of Texas State Highway No. 30 the Carter's Grove tributary meets it's confluence with Carter's Creek approximately 1500 feet downstream from the subject project. Project Description: The project consists of the placement of compacted "fill" within the fringes of the above mentioned flood plains. Installation of pavement and the construction of a 40' x 250' "T" canopy structure and a 24' x 350' commodity storage building are included in this phase of the project(See Appendix "C" Grading, Drainage & Erosion Control Plan). Also included is the construction of an "on-site" detention facility to control the excess stormwater run- off subsequent to the completion of the project. Computations for same detention facility are by Municipal Development Group under separate cover and are available to City staff upon request. Study Objective: The main ofbjective of this report and included data is to establish recreate a base model of Carter's Grove Tributary to Carter's Creek which is consistant with the FEMA flood plain maps for same area and to establish the floodway along that reach of same Carter's Grove Tributary to Carter's Creek from the upstream side of Texas State Highway No. 30 and extending upstream to the location where same Carter's Grove Tributary crosses under the east frontage road of Texas State Highway No. 6 East By-pass. Page 1 Due to the location of the subject project as indicated above it is necessary to first establish a computer base model utilizing HEC-2 to determine the limits of the the present 100-year flood plain and floodway limits for Carter's Creek in the vicinity of the project. Secondly, the limits of the 100-year flood plain and floodway for the Carter's Grove tributary will also be determined by employing same HEC-2 modelling methods. Once the "models" for Carter's Creek and the Carter's Grove tibutary have been compiled modifications to the basin associated with the construction of the subject property will be "input" in to the base model to determine the effects of the proposed construction upon the Carter's Creek & Carter's Grove tributary 100-year flood plains and floodways. FEMA cross-sections for Carter's Creek may be refered in Appendix "E". These cross- sections were taken from previous flood study reports as prepared by the U.S. Army Corps of Engineers and Turner Collie & Braden. Modified cross-sections for Carter's Creek and Carter's Grove tributary are located in Appendix "E-1" and Appendix "F" resp e ctively. The modifications refered to the proposed construction and the associated "fill" to be placed therewith. Actual "on-the-ground" cross-sections were acquired for this study in the vicinity of the subject project with previous data being taken from the above referenced previously prepared flood studies. The current Flood Insurance Study for Brazos County and Incorporated Areas was used to acquire present peak flood discharge rates at specific cross-section locations with Wolf Pen Creek -Carter's Creek confluence be ing a "known" reference point from which to start the computations and simulations contained herein . Modelling of Carter's Creek starts at the confluece with Wolf Pen Creek (Carter's Creek River Mile 10.56) and proceeds upstream past Texas State Highway No. 30 (Carter's Creek River Mile 11.88) and ends at Carter's Creek River Mile 12.37 . Carter's Grove tributary is modelled from it's confluence with Carter's Creek at Carter's Creek River Mile 11.98 and runs upstream to Carter's Grove tributary River Mile 0.560. Included within the above mentioned models are the complete drainage structures at Texas State Highway No . 6 East Bypass and the drainage structure at Texas State Highway No. 30. Summary: Upon completion of the Carter's Creek model, a water surface elevation for the 100-year storm was determined at the upstream side of Texas State Highway No. 30 (Carter's Creek River Mile 11.91). This same elevation (256.31) was used as the starting water surface elevation for subsequent 100-year water surface analyses associated with the Carter's Grove Tributary to Carter's Cree k. At present, officially only a 100-year flood plain has been established by FEMA for the Carter's Grove Tributary to Carter's Creek. No specific cross-sections, water surface elevations or floodway deliniations are presented for same Carter's Grove Tributary to Carte r's Creek as part of the FEMA maps for same Page2 Carter's Grove Tributary area. Appendix "M" presents data which models the existing conditions within the Carter's Grove Tributary with Appendix "N" establishing floodway limits for same Carter's Grove Tributary. The subject floodway for Carter's Grove Tributary was determined by locating the existing channel banks along the study reach and "setting" these points as boundaries for the proposed proposed floodway, thus making the over-bank areas "ineffective" in the floodway computations. Target elevations were tested at each cross-s ection along the study reach of Carter's Grove and tested to determine if the one foot (l ') rise in water surface had been reached or exceeded. Based on upstream development within the Carter's Creek Tributary being fairly complete, . ultimate basin development conditions are assumed to have occured, therefore the floodway established represents the ultimate floodway for same study reach. In conclusion, over-bank areas within the study reach may be filled to desired levels without significately effecting the flow characteristics of the study reach of Carter's Creek Tributary or Carter's Creek flood plain or floodway limits. Page 3 Appendix "A" Project Location & Vicinit.y Map Appendix "A" / le / VICINITY MAP Appendix "B" Site Plan Appendix "B"