The Application of Environmental Site Design Processes to Design a LID Subdivision

This paper will discuss the design processes used to create a single family subdivision utilizing Environmental Site Design (ESD) strategies. ESD requires that civil engineers completely reevaluate the processes that they use to design any type of land development project. In this case, ESD will be used for the design of a residential subdivision. ESD requires that the civil engineer evaluate the topography, soils, hydrology, vegetation and habitat on the site prior to the site design. This process is of utmost importance in the creation of a subdivision utilizing Low Impact Development (LID) designs. This presentation will outline the necessary steps to evaluate the environmental parameters of the site prior to the design of a subdivision. The environmental parameters to be evaluated include wetlands/watercourses/vernal pools, flood plains, steep slopes (generally >25%), unusual trees or vegetative systems, soils with high or moderate infiltration abilities, and stone walls. After the environmental areas are highlighted, a "developable area" is determined which excludes the environmental areas discussed above. At this time, the applicable municipal LID regulations can then be applied to that portion of the site most suitable for development using LID. A Concept Plan is developed for proposed development. While this plan is being prepared, it is important for the designer to evaluate existing drainage patterns and to identify locations for storm water treatment systems. Final layout of lots, infrastructure and open space shall be done. The storm water conveyance and treatment systems shall be designed at this time, utilizing LID strategies, such as increasing the Time of Concentration, disconnecting impervious areas and treating runoff at its source to the maximum extent practical. How will the final project look? An actual design for a site will be presented to show the application of ESD strategies will create an environmentally sound subdivision. It will be shown how the application of ESD to a site will result in the goal of matching the pre-development Runoff Curve Number for post-development conditions. Additionally, the type of LID storm water conveyance and treatment systems utilized will be presented.