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Engineering Services <br />for the <br />City of San Marcos - Drainage Master Plan <br />Halff Associates, Inc. <br />July 29, 2013 <br />INTRODUCTION <br />The purpose of this proposal is to provide engineering services to (1) assess the viability of the City of San <br />Marcos' storm water infrastructure, (2) identify problems and develop conceptual solutions and (3) provide a <br />systematic approach for allocating funds for storm water projects for the City's capital improvement program. <br />BACKGROUND <br />Halff Associates, Inc. (Half has been primarily tasked with the update of hydrologic analysis, hydraulic <br />analysis, and flood mitigation analysis for the City of San Marcos Drainage Master Plan development. In an <br />effort to not duplicate effort that was previously conducted or that is currently being conducted, all streams <br />that impact San Marcos were divided into three categories. The categories include the following types: <br />• Type A — Guadalupe - Blanco River Authority (GBRA) Study: The GBRA has partnered with the <br />Corps of Engineers, the Texas Water Development Board (1`WDB), and 14 of its river communities in <br />a collaborative effort to develop a comprehensive and sustainable flood risk evaluation program to <br />assess flood risk and investigate flood damage mitigation alternatives. San Marcos is one of the <br />partnering communities. The GBRA study streams are displayed as thin orange lines in Figure 1. <br />• Type B — 2007 San Marcos Flood Protection Plan (FPP): In 2007, the City of San Marcos <br />completed the San Marcos Flood Protection Plan. The 2007 FPP study streams are displayed as thin <br />red lines in Figure 1. Streams that were previously studied in 2007, but were not included in the <br />current GBRA study are categorized as Type B streams. These Type B streams are displayed as blue <br />highlighted streams in Figure 1. <br />• Type C — Federal Emergency Management Agency (FEMA): The FE1\11k Flood Insurance Rate <br />Maps were used to identify streams that currently have a FEMA designated floodplain. These <br />FEMA streams are displayed as thin green lines in Figure 1. FEMA streams that were not included <br />in the GBRA study or the 2007 FPP study are categorized as Type C streams. These Type C streams <br />are displayed as pink highlighted streams in Figure 1. <br />The streams associated with each category are listed in Table 1. Attachment C contains a table that lists the <br />existing data associated with each stream category as well as the proposed work for this drainage master plan. <br />Table 1. Study Stream Categories <br />Type A Streams - GBRA <br />Miles <br />Type B Streams - 2007 FPP <br />Miles <br />Type C Streams - FEMA <br />Miles <br />Sink Creek <br />11.57 <br />Cottonwood Creek & Tributaries <br />9.73 <br />PC -1 <br />2.71 <br />Unnamed Creek 46 <br />1.65 <br />PC -02 -01 <br />0.28 <br />Unnamed to PC <br />2.46 <br />San Marcos River <br />7.75 <br />PC03 -01 <br />1.62 <br />Willow Springs Creek <br />0.79 <br />Total <br />5.96 <br />Purgatory Creek 11.76 <br />SC -01 1.09 <br />Willow Spring Creek <br />5.12 <br />SCH -01 <br />1.32 <br />Blanco River <br />10.67 <br />SAIR -0301 <br />0.64 <br />Bypass Creek <br />6.35 <br />WSC- 02 -Tribs <br />0.99 <br />Total 54.87 <br />Total 15.67 <br />Page 1 of 10 mom HALFF. MEN <br />