Detention Methodology — BMP Trains 2020
Overview
This document presents the methodology used to calculate the average annual nutrient removal effectiveness of detention stormwater systems within the BMP Trains 2020 model. Detention systems function by storing water before discharge, allowing pollutants to settle or transform through physical and biochemical processes. The method evaluates permanent pool volume, annual residence time, and long-term hydrologic simulation to determine pollutant removal rates. Removal curves derived from Harper and Baker (2007) are applied to estimate treatment performance for nitrogen and phosphorus.
Key Components of the Methodology
- Definition and role of detention systems
- Permanent pool calculation
- Annual runoff computation from long-term storm event simulation
- Formula for annual residence time
- Use of nutrient removal curves (Harper & Baker, 2007)
- Applicability to wet ponds, detention depressions, and baffle boxes