Storm Drainage Analysis and Design

GRA's experience in storm drainage and runoff-related disciplines is extensive. GRA has performed drainage analysis on many RI Department of Transportation projects and on numerous private development projects. The related work has included runoff analyses, hydrological studies, hydraulic designs, drainage designs, pollutant loading studies and the design of various types of Best Management Practices (BMPs) to reduce wetland and water resource impacts. GRA has undertaken specific BMP designs relating to the development of wet and dry detention basins, infiltration basins, underground storage basins, retention ponds, percolation trenches, level spreaders, oil separators and grass swales. Our office has also coordinated with and submitted applications to all the environmental permitting agencies that regulate storm water management issues.

A particularly noteworthy experience includes GRA's participation as one of two consultants on the RI Stormwater Management and Erosion Control Advisory Committee. That committee of the Rhode Island Department of Environmental Management (RIDEM) was directly responsible for the development of the current RI Soil Erosion and Sediment Control Handbook and RIDEM's Recommendations Regarding the Development and Implementation of Technical Guidelines for Stormwater Management. GRA was also selected to serve on the Technical Advisory Committee for the Scituate Reservoir Task Force. Additionally, the firm has participated in the development of the RI Standard Specifications "Part 200 - Earthwork and Erosion Control," which included the development of new Erosion Control Standards.

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Relocated Route 403, East Greenwich and North Kingstown, RI. This project passes over the Hunt-Annaquatucket-Pettaquamscutt (HAP) sole source aquifer and it passes through areas near or adjacent to sensitive surface waters and wetland. Both conventional and creative solutions were required to protect the existing fragile ecosystems. As part of the project, GRA designed extensive Best Management Practices, including eleven (11) water quality basins, with those over the aquifer containing impermeable liners below the bottoms of the basins. Vegetated channels, level spreaders and other techniques were utilized.

Complex hydrological and hydraulic modeling was required to design the freeway's storm water management system. The effect that the storm drainage system would have on the area's sensitive receptors was evaluated. The modeling output was used to support the RIDEM Freshwater Wetlands and Rhode Island Pollution Discharge Elimination System (RIPDES) permit application submittals. GRA obtained the RIDEM Freshwater Wetlands and RIPDES permits required to install the project's storm water management system.

University of Rhode Island, Kingston, RI.. The White Horn Brook flows through the University of Rhode Island's lower campus. Culverts and bridges used by students and vehicles had deteriorated over time and required replacement. Sediment deposits and organic debris have reduced the flow in the brook creating flooding conditions along the brook's path. A two-phase project was proposed to address the brook crossing issues and to restore brook flow to pre-deposition conditions. The initial phase consisted of culvert replacements. The brook channel restoration program that includes sediment dredging and organic debris removal will be implemented as a second phase.

GRA conducted a complete hydraulic analysis, including an updated flood routing analysis to determine existing flow conditions and to evaluate the culvert replacement and channel restoration program's effect on flow conditions. The modeling was used to evaluate proposed culvert configurations and their effect on flow capacity. Additional modeling was then used to evaluate the effect the channel restoration project would have on flow. An Application to Alter Freshwater Wetlands was submitted to the RIDEM. Two of the completed culverts and a new pedestrian bridge over the brook are shown below.

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