Managing Uncertainty in Runoff Estimation with the U.S. Environmental Protection Agency National Stormwater...

Area of Science:

• Environmental Science
• Hydrology
• Urban Planning

Background:

• The U.S. Environmental Protection Agency National Stormwater Calculator (NSWC) is a tool for estimating stormwater runoff.
• It uses localized climate and soil data to simulate runoff for areas up to 5 hectares.
• Understanding the urban hydrologic cycle and the impact of soil properties is crucial for effective stormwater management.

Purpose of the Study:

• To assess the accuracy of the NSWC's soil hydrology estimations.
• To evaluate the impact of soil hydraulic conductivity uncertainty on runoff simulations.
• To analyze how low-impact development (LID) features interact with soil hydrology and influence runoff predictions.

Main Methods:

• Compared field-measured soil hydraulic conductivity data from 12 cities with NSWC estimates.
• Conducted case studies using three cities to analyze estimation uncertainty.
• Simulated the impact of LID features on runoff, considering their interaction with different soil permeabilities.

Main Results:

• The NSWC's default hydraulic conductivity (10.1 mm/h) significantly deviates from measured values, underestimating in some cities and overestimating in others.
• On average, NSWC underestimated hydraulic conductivity by 10.5 mm/h across the studied cities.
• LID features showed higher sensitivity in runoff prediction when directly interacting with pre-existing soils, especially those with higher permeability.

Conclusions:

• The NSWC is a valuable screening-level tool for understanding site runoff dynamics.
• Improving the accuracy of soil hydrology data within the NSWC is essential for more reliable runoff simulations.
• The interaction between LID and soil type critically influences stormwater management effectiveness.