The City of Kilgore was facing flooding and other issues in the downtown area related to aging storm sewer infrastructure. In addition, staff members who had recently joined the team were not as familiar with the existing infrastructure and wanted to gain more insight into what was in place. To address these issues, the city turned to Freese and Nichols to create a Downtown Storm Sewer Master Plan.

The Downtown Storm Sewer Master Plan included storm sewer system inventory review, hydrologic assessment, development of a hydraulic model for existing conditions and proposed improvements, and development of a storm sewer system capital improvement plan.

The project started with an extensive data collection of the city’s previous studies and plans. This was followed by a field inventory using GIS-connected devices to locate and identify all storm sewer infrastructure in the study area. A GIS database was populated with the inventory data that included survey grade information and the condition (good to poor) of existing infrastructure. Pictures of storm sewer structures were linked to the database as well. The database was part of the overall deliverable for the city’s use and information, and it can be easily updated as redevelopment or improvements occur.

The existing conditions and proposed improvements hydrologic and hydraulic models were developed using the data from the GIS database created during the field inventory. The U.S. Environmental Protection Agency’s Storm Water Management Model (EPA-SWMM) program was used to build the models. EPA-SWMM performs an unsteady analysis on the storm sewer system and provides more accurate results than typical hydraulic calculation techniques because it takes into account the timing of peak discharges. The existing conditions analysis identified roadway inundation and floodplain information for the 100-year storm event in downtown Kilgore as shown in the map.

Capital improvement projects were developed to reduce inundation identified during the existing conditions analysis. Proposed projects varied from upsizing storm sewer infrastructure, realigning existing pipe systems, channel improvements and a conceptual opinion of probable construction cost was developed for each project. The capital improvements projects were then ranked based on city selected criteria to develop an overall plan.

This article originally appeared on the Freese and Nichols' "Ebb and Flow" blog. Photos courtesy of Freese and Nichols.

About the authors:

Lesley Brooks, P.E., CFM, is a project manager in the Stormwater Group at Freese and Nichols Inc. She holds a B.S. in Civil Engineering from Texas A&M University.

Evan Burn is an engineer-in-training at Freese and Nichols Inc. He holds a B.S. in Civil Engineering from New Mexico State University.