Stormwater management plan preparation
A Stormwater Management Plan (SWMP) addresses the requirement for containment of surface water runoff associated with site plan approval of a proposed development. The purpose of a SWMP is to define the extent of pre-development and post-development runoff, as well as to provide the necessary details for proposed mitigative measures. Mitigative measures, imposed through stormwater management system design, will ensure that the proposed development will not have an adverse impact on local drainage patterns.
A SWMP should conform to the following constraints:
- Development must not result in increased flowing, erosion, or degradation to water quality on or off the site. This may involve pre- and post-development control. Specifically, peak flow and water velocity must not increase or control facilities must be installed. Watercourses shall be protected from sedimentation and pollution.
- Control facilities may be required to be designed for all hydrologic events up to and including the regional rainfall event. Over control of runoff may be required (i.e. post-development runoff may be less than pre-development runoff).
Stormwater modelling software, PCSWMM 2011, is used by Cambium Environmental to model sites for both the existing condition and with the proposed development. PCSWMM 2011 is used in the design and sizing of drainage system components for flood control and in the sizing of detention facilities and their appurtenances for flood control and water quality protection. Any additional stormwater anticipated as a result of the development will need to be managed on site. A combination of lot level, conveyance, and end-of-pipe stormwater management practices are usually required to meet the multiple objectives of stormwater management: maintaining the hydrologic cycle, protection of water quality, and preventing increased erosion and flooding.