Key Features
What Stormwater Calculator Does
Details
Overview
The EPA’s Stormwater Calculator is a web-based tool that estimates annual stormwater runoff volume and pollutant loads from precipitation falling on user-defined site landscapes. By simulating the runoff-reduction performance of green infrastructure practices—such as rain gardens, permeable pavement, and tree trenches—it enables designers to size and optimise nature-based solutions that minimise flooding, erosion, and water-quality impairment while reducing infrastructure costs.
Key Features
- Site characterisation: Specification of soil type, slope, land cover (impervious surface, vegetation, water), and local rainfall patterns for accurate site modelling
- Green infrastructure library: Pre-configured performance data for rain gardens, tree trenches, green roofs, permeable pavement, and other practices
- Runoff and pollutant modelling: Annual volume reduction and removal of nitrogen, phosphorus, and sediment across different design configurations
- Cost-benefit analysis: Comparative tables showing capital and maintenance cost trade-offs across green and conventional infrastructure alternatives
Who Is It For?
Stormwater engineers, landscape architects, site planners, and municipal public-works departments designing compliance solutions for stormwater regulations. The tool is accessible to intermediate users with basic hydrology knowledge; worked examples and video tutorials support professionals new to green infrastructure design.
Getting Started
Visit epa.gov/water-research/stormwater-calculator to access the web version (no installation required). Input your site’s soil, topography, and current land cover, then test green infrastructure options. The EPA also publishes case studies demonstrating how communities have met stormwater-quality mandates cost-effectively through the tool’s recommendations.