The Houston Stormwater Master Plan (SWMP) initiative is poised to play a pivotal role in providing the City of Houston with a comprehensive stormwater and drainage infrastructure analysis. The information gathered and analyzed through this initiative will serve as a robust foundation for an equitable comparison of flood risk across the City, enabling informed decision-making on drainage projects and studies.
History and Overview
The City of Houston is prone to flooding due to its flat topography, dense development, and proximity to the coast. This flooding causes safety and economic ramifications that impact the Houston region, the state and the nation. Since the 1990s, Houston has completed drainage planning efforts to understand the impacts of flood events better and develop plans and projects to reduce that flood risk for its residents. This study analyzes the influence of the City's local storm sewers and roadside ditches, alongside the drainage patterns caused by the channels, bayous and rivers that convey stormwater to the bay. With this approach, the Houston SWMP initiative provides the first comprehensive look at flooding and drainage patterns in the City.
Previous Planning Efforts
1999
Comprehensive Drainage Plan
* City-wide analysis of storm sewer infrastructure
* Used GIS and rational method
* Determined storm sewer capacity
* Used for CIP identification
2019 - Present
HCFCD MAAPNEXT
* Improving understanding of flood risk in Harris County to allow communities to make more informed decisions
* Developed new models for the bayous and channels throughout the county using the latest information and technology
2010
Rebuild Houston
* Developed drainage impact fee to fund drainage project
* Created prioritization factor to conduct storm drainage planning studies
* Conducted various neighborhood planning studies
2024 - Present
Stormwater Master Plan
* Created a comprehensive, citywide assessment of drainage throughout the City of Houston
* Provides understanding of flood risk based on storm sewers, open ditches, channels, and bayous
* Conducted focus area analysis to identify areas for projects and future studies
2016
Roadside Ditch Drainage Planning
* Updated 1999 CDP to combine storm sewer analysis with open ditches
* Created new outfall boundaries and lidar assessment of drainage infrastructure
* Incorporated into the prioritization framework for a comprehensive analysis
Interactive Map
*Explore the watershed map with detailed planning results and watershed-specific insights
*Storm sewer and roadside ditches
City-Wide Information
The City of Houston drainage infrastructure consists of two components: primary drainage systems such as the major bayous, rivers, and channels which receive flows from both local runoff as well as contributing watersheds upstream of the City; and secondary drainage systems such as storm sewer and roadside ditch that collect and convey local runoff flows to the primary drainage systems. Both of these types of infrastructure were included within the Houston SWMP.
Results
Ponding depths corresponding to seven annual chance events (ACE) were developed for the entire City of Houston. These results were leveraged to analyze existing flood risk throughout the City and identify areas in need of additional study or flood mitigation projects.
Several frequency storm events were simulated for the City of Houston. Based on the results of the analysis, the performance of drainage infrastructure throughout the City was evaluated. Additionally, structures were evaluated to determine the level of flood risk at each structure.
Level of service was evaluated for modeled storm sewer (pipes > 36”). Storm sewer was determined to provide adequate capacity if the flow was contained for the 2-yr event, or within the road right of way for the other modeled events.
Level of service was evaluated for all roadside ditch included in the models. Roadside ditches were determined to provide adequate capacity if peak flows were contained within the banks.
Structures were considered at-risk if modeled flood depths are within 1 ft of the estimated finished floor elevation (FFE). The analyzed structure dataset is sourced from the Texas Water Development Board (TWDB) and includes residential, commercial, industrial, and agricultural buildings.
At-risk population was determined based on the associated population estimated to be within each at-risk structure. Populations per structure were based on the TWDB dataset and refined where they were determined to be inaccurate.
City Watershed Map
Click on one of the watershed plan links to open a webpage with detailed planning results and watershed specific insights.
Focus Area Analysis
The results produced by the Houston SWMP provide a comprehensive overview of existing flood risk throughout the City of Houston. However, identifying areas of “most severe” flood risk can be an overwhelming and highly subjective task. Many different factors can and should be considered when prioritizing the needs for detailed studies and drainage project implementation. To help accumulate the results of this study into concise flood risk information, a Focus Area Evaluation is being performed.
