Post-Construction Site Storm Water Management

Overview
Post-construction storm water management ensures best management practices (BMPs) for storm water pollution and runoff control continue after the construction is completed.  These BMPs are usually included in the design of the construction and are a part of the completed subdivision or commercial development.  The BMPs are either non-structural or structural.  The key distinction between them is that non-structural BMPs are intended to prevent storm water generation while structural BMPs focus on mitigating unavoidable storm water related impacts.

What is a non-structural BMP?
Non-structural BMPs focus on preserving open space, protecting natural systems, and incorporating existing landscape features such as wetlands and stream corridors into a site plan to manage storm water at its source. Some focus on clustering and concentrating development, minimizing disturbed areas, and reducing the size of impervious areas.  The City of Bartlett uses “buffers” between developments and streams to create greenbelts as a means of preserving open space as well as protecting natural systems.
What are structural BMPs?
Many so-called structural BMPs are actually based on natural systems and rely upon vegetation and soil mechanisms in order to perform as intended. Others are considered more conventional “brick and mortar” techniques. The use of these mitigative techniques is not meant to replace the use of non-structural BMPs, but rather to work in tandem with these planning and design-based approaches to minimize unavoidable impacts.  In Bartlett, detention basins are the most used structural BMP.  They slow the amount of water being discharged over a given amount of time from an area, decreasing the impact of fast moving waters on streams as well as controlling the volume of water that can contribute to flooding. 

Green Infrastructure
Communities across the country are looking towards non-structural and structured BMPs that mimic the way natural vegetated landscapes respond to precipitation events.  This approach is simultaneously advantageous for protecting the channel stability and ecological characteristics of receiving waters.  In the near future, we will need to look at these types of BMPs that capture or reuse the first inch of of a rainfall event.  To aid in the design and application of these BMPs, the Tennessee Department of Environment and Conservation has published the Tennessee Permanent Stormwater Management and Design Guidance Manual.  The permanent stormwater control measures identified in the manual are runoff reduction BMPs that are intended to address traditional permanent stormwater management limitations by reducing stormwater runoff volume and/or pollutants.

No matter which BMP is used, the design should control the volume, rate and water quality of post construction storm water runoff so as to protect and maintain the chemical, physical and biological properties of the receiving waters.