Post-construction storm water management is necessary because runoff from developed areas can impair local streams and rivers if not properly managed. Two general types of impacts can occur. First, there is typically an increase in some types and quantities of pollutants in storm water runoff. As water flows over these sites, it transports harmful contaminants such as oil and grease, pesticides, heavy metals, and nutrients, (e.g., nitrogen and phosphorous). These pollutants become suspended in the runoff and are conveyed to nearby streams.
The second post-construction impact occurs as a result of increased storm water runoff volume and rates caused by an increase in impervious (hard or paved) surfaces. The added impervious area reduces the amount of rain water that soaks into the ground, and speeds the flow of the water toward a storm drain or open channel. This can result both in localized and downstream flooding, as well as stream bank erosion, if management practices aren’t put in place to address the added volume and increased flow.
Structural management practices, such as retention ponds, filter strips, and bioretention basins (rain gardens) can be put in to give storm water runoff a chance to slow down and soak in. However, it is not always necessary to construct a treatment practice to manage storm water runoff. Some problems can be addressed with sound planning procedures. Master plans, comprehensive plans, and zoning ordinances can promote improved water quality by guiding growth of a community away from sensitive areas and by restricting certain types of growth (industrial, for example) to areas that can support it without compromising water quality. Non-structural management practices can include buffer strip and riparian zone preservation, minimization of disturbance and imperviousness, and maximization of open space.
Ohio EPA developed and maintains the Rain Water and Land Development Manual (PDF, full copy), which defines Ohio’s standards and specifications for stormwater practices implemented during land development. This book aims to integrate water resource protection into development site planning in order to maintain or improve stream integrity. Below are links to specific chapters of the manual that address post-construction management practices.
Chapter 2: Post-Construction Storm Water Practice: includes information, standards and specifications for the following practices:
Chapter 4 — Permanent Runoff Control: includes standards and specifications for the following practices: