City of San Marcos Midtown Drainage Improvements

Analyzing Drainage in San Marcos Area

Project Purpose

The watershed for this project area contains multiple problems areas primarily driven by localized flooding as stormwater runoff flows to the Blanco River. Problem areas include multi-family apartment units flooding, the Loop 82/Aquarena Springs underpass at IH-35, and the San Marcos Rehabilitation & Health Care Nursing Home. The purpose of the Preliminary Engineering Report is to study the entire watershed to identify the source of the problems and propose a range of flood mitigation alternatives. Each of the alternatives will include a utility conflict assessment and estimated construction cost. The most beneficial and cost-effective project will be selected to move into detailed design. A maintenance path is also being designed at a 30% level during this phase of the project.

Project Approach

KFA has built an infoworks 2-dimensional model of the entire watershed to simulate existing runoff. This included data collection, multiple site visits, topographic processing of available LiDAR, hydrologic HMS modeling, and detailed ICM modeling. This model has been validated against historic rainfall events to ensure it is adequately simulating the existing conditions. KFA is currently simulating flood reduction alternatives to find the most beneficial solution for the project area. This project is being primarily funded through the HUD CDBG-DR funding. The KFA team is making sure that all proposed construction meets the requirements of the program to satisfy the grant rules and regulations.

Project Results

KFA proposed mitigation measures with varying levels of cost and complexity based on funding options available to the City using a multi-phased approach. Currently, KFA is developing PS&E for the selected Phase 1 Alternative which is being funded through the HUD CDBG-DR program. Construction of these improvements is scheduled to be completed in late 2022.