Non-perennial streamflow & geomorphic patterns in a semi-arid rangeland slated for development
Date
2023
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Abstract
Urbanization has widely recognizable impacts on stream morphology and flow patterns. Predicting and quantifying these impacts can be difficult, especially for non-perennial streams in semi-arid rangelands. Non-perennial streams tend to lack a historical baseline with complete records of streamflow presence and absence. A historical pre-development baseline allows for better consideration when making development and infrastructure decisions as well as post-development comparison to quantify urbanization-driven impacts. This project focuses on a non-perennial stream channel in West Stroh Gulch, located in Parker, Colorado south of Denver, U.S.A. A historically semi-arid rangeland area slated to undergo housing development in the next few years, West Stroh Gulch is a unique opportunity to establish a historical baseline for a non-perennial stream. Streamflow presence and absence was recorded at multiple locations along the stream network with time-lapse photography. Photo observations and precipitation data were reviewed to determine what storm events did, or did not, trigger a flow response. After over two years of stream channel monitoring, one precipitation event with a total depth of 92-mm and maximum 60-minute intensity of 50-mm per hour triggered streamflow. Additionally, a hydrodynamic model was built in SRH-2D to compare the impacts of predicted flows through a reach of interest. Topographic pre-development data and Storm Water Management Model (SWMM) generated peak flows were used to simulate impacts of different sized storms. Peak flows varied both by storm and development scenario: existing undeveloped, traditional centralized post-development detention, and post-development distributed detention. Boundary shear stresses were used to compare the different simulations. Overall, the pre-development existing scenario had the lowest flows shear stresses for the two smallest storm scenarios (water quality capture volume and 2-year storms). For the 5-, 10-, 50-, and 100-year storms, the proposed post-development scenarios that incorporated distributed detention had the lowest flows and shear stresses. The traditional centralized detention post-development stormwater strategy had the highest flows, shear stresses, velocities, and water depths for all storm sizes. The simulation results indicate that the post-development distributed detention strategy will be effective at reducing stream channel stresses and erosion for larger storm events.
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Subject
rangeland
SRH-2D
time-lapse photography
semi-arid
non-perennial
streamflow monitoring