Simulation and Permitting Tool for Permeable Pavement and Bioretention
Authors:
- Matthew P. Jones, E.I., Ph.D. - Hazen and Sawyer
As concerns grow over the negative impacts of urban development on water resources, low impact development (LID) practices, such as bioretention and permeable pavement, are increasingly becoming recommended or required. This trend was exemplified in North Carolina with Session Law 2008-198, which required installation of bioretention or permeable pavement for locations that meet certain criteria and were not subject to other stormwater regulations. The result of this regulation was that many small municipalities, potentially lacking engineering staff familiar with stormwater BMPs, were required to review bioretention and permeable pavement designs as part of the building permitting process. A computer tool was developed to evaluate the hydraulic and hydrologic function of bioretention and permeable pavement systems while also evaluating compliance with key design constraints.
Simulated inflow was created using NRCS hyetographs and hydrograph methodologies. A water balance was evaluated in conjunction with hydraulic calculations to determine the proportion of runoff leaving the system as overflow, through the underdrain, or through seepage into the subsoil. Outputs from the simulation tool included a numeric summary of system hydrology and hydraulics as well an animation function to visually represent the water balance and overall functionality of the system. Utilizing these results, it was possible to evaluate the feasibility of installing a bioretention or permeable pavement system and whether the proposed system achieved LID goals of mimicking predevelopment hydrology. These simulations were particularly valuable where bioretention and permeable pavement applications were not considered to be beneficial due to underlying soil conditions, with simulation results demonstrating the effect of these practices on site hydrology.
In addition to hydraulic and hydrologic simulations, the tool checked numerous design criteria and regulatory requirements, including media depths, nutrient composition, and construction sequencing. The tool provided a detailed report of any design criteria or regulatory requirements that were not satisfied, providing explanations for any discrepancies and implications for system functionality.
The simulation tool presented herein has been designed to be both accessible to people lacking thorough knowledge of stormwater BMPs and customizable for application in a wide variety of scenarios. By using this tool to evaluate proposed bioretention and permeable pavement applications, it should be possible to utilize these practices in areas where they have not been historically applied due to permitting review burdens or concerns over system functionality.
To request a copy of the full paper, please contact the author at .(JavaScript must be enabled to view this email address).
