Modelling the Hydrologic Impact of Land Cover on Stormwater Detention Basins in Harris County, TX

<p>Harris County on the upper Gulf Coast in Southeast Texas is susceptible to both riverine and coastal flooding due to intense, short-duration thunderstorms, slow-moving frontal systems, and tropical hurricanes. Low-lying terrain, clay soils with poor drainage, high annual rainfall, and a widespread network of bayous and streams all contribute to frequent flooding. To reduce the impacts of urbanization and the loss of surface storage, the Harris County Flood Control District (HCFCD) built detention basins throughout the county to temporarily store stormwater runoff and release it slowly, lowering peak flows and preventing downstream flooding and erosion. These basins vary in land cover, with some covered by trees and others by grass. This study assessed how land cover influences the hydrologic water balance, runoff, infiltration, evaporation, and peak discharge by simulating detention basins as flat sub catchment using the Environmental Protection Agency’s Storm Water Management Model (EPA SWMM). Five significant rainfall events and annual simulations over a 10-year period (2015–2024) were modeled across ten basins with varying land cover conditions. Results showed that land cover significantly alters surface hydrology. Tree-covered basins demonstrated lower runoff, higher infiltration, and reduced and delayed peak discharge compared to grass-covered basins, due to greater surface roughness and depression storage. Statistical analysis (paired t-test, p < 0.05) confirmed that the differences in water retention between tree and grass land cover scenarios were significant across all study basins, with the highest retention observed under tree cover conditions. During Hurricane Harvey, tree-covered basins retained over 132,000 m³ of stormwater, 5,600 m³ more than if they had been grass-covered, demonstrating the critical role of tree cover in reducing runoff during extreme storm events. Notably, the benefits of tree cover were especially pronounced in low-conductivity basins such as A518-02-00, G503-03-00, and D540-01-00, where vegetation-induced surface properties helped offset limited infiltration. In B504-04-00, the removal of trees resulted in the greatest decline in retention, underscoring the importance of preserving tree cover in areas with poor soil permeability. These findings underscore the hydrologic benefits of maintaining or introducing tree cover in detention basins and provide valuable insights for the Harris County Flood Control District (HCFCD) and urban planners to enhance stormwater management through targeted tree-planting strategies.</p> <p>Keywords: Harris County, stormwater, detention basin, Sub catchment, SWMM, land cover, hydrologic water balance, infiltration, runoff</p>

Name thesis:degree_name

Master of Science - Forestry

Level thesis:degree_level

Thesis

Discipline thesis:degree_discipline

Forestry

Year dc:date.available

2025

Author dc:creator

• Sapkota, Kabita

Contributors dc:contributor

• Yanli Zhang, Ph.D
• Matthew W. McBroom, Ph.D
• Jeremy Stovall, Ph.D

• Harris County
• stormwater
• detention basin
• Sub catchment
• SWMM
• hydrologic water balance
• Other Forestry and Forest Sciences

Repository record dc:identifier

https://scholarworks.sfasu.edu/etds/630

OAI identifier oai:identifier

oai:scholarworks.sfasu.edu:etds-1685