Stormwater Springs Up Across the Northeast

Apr 24, 2019
Blog Spring Stormwater Design And Planning M 2019

Written by Molly C. Berardi, EIT, Civil Engineer

Stormwater runoff is the water you see during and after a rainstorm, flowing from roof gutters, whooshing through the parking lot to catch basins, and pooling in that low spot in your yard. When not properly managed, stormwater runoff can cause a myriad of problems for infrastructure, the environment, and human safety. Milone & MacBroom has always been an advocate and leader in watershed planning and stormwater management to reduce these impacts. Our engineers, planners, and designers have supported projects ranging from the development of regional and state regulations and guidelines, to the site-specific design of stormwater management and treatment systems. If you would like to learn more, please contact us.

Why Stormwater Management is Important
In many communities across the Northeast, urbanization and new developments increase surface stormwater runoff. When stormwater is unable to infiltrate into the ground, because of impervious surfaces (roads, parking lots, sidewalks, roofs, etc.), it flows across these surfaces until it encounters a collection system (i.e., storm drainage), surface water body, or other point of discharge. As impervious surfaces increase with development, stormwater runoff is allowed to travel more quickly and with increased volume, meaning peak flows in a watershed occur quicker and at an increased rate. Increased peak flow rates can cause issues both on site and downstream, including damage to existing stormwater infrastructure, erosion to streambanks, flooding, and reduced water quality. In addition, sediments, oils, greases, and a whole host of other constituents that are found on the ground are swept up in stormwater runoff, ultimately discharging to groundwater or surface water bodies if untreated, which can lead to the potential pollution of these systems.

Stormwater Management for Site Development
Our engineers and landscape architects are experts in site development planning, stormwater management systems, and low impact development techniques to combat the negative effects of stormwater runoff. The purpose of these systems is to control the flow of stormwater, prevent erosion, and protect water supply sources from stormwater pollution by providing settlement of solids, infiltration, and in some cases, creation of wetland systems.

One typical stormwater management solution is an above-ground basin where stormwater runoff is discharged to by a network of catch basins and yard drains on a site. Once the water reaches the basin, it is treated by the vegetation and discharged through an engineered outlet control structure, which is designed to release the stormwater at predetermined flow rates to prevent increases in the the predevelopment discharge rates from a site and meet municipal and state stormwater management regulations. As part of a project to design improvements for the intersection of US Route 202/State Route 67 and Grove Street in New Milford, Connecticut, Milone & MacBroom designed a planted stormwater management basin (shown above) along with several other state-of-the-art stormwater management measures that included the installation of riprap anti scour dissipation pools, catch basins with deep sumps, and water quality bioswales. This stormwater management basin was designed with a three cell treatment system including a forebay, emergent/wet meadow filter basin and finally a deep water settling pool. Stormwater management basins typically outlet to existing surface water bodies or wetlands, where the stormwater on site would normally outlet before the development took place.

Another option is an underground stormwater management system. This type of system generally works much the same way as above-ground basins, and can be a good alternative to above-ground basins for project sites where space is limited. Instead of routing the stormwater to a large basin, it is instead routed to a series of underground chambers, typically below a parking lot. These chambers detain the stormwater and use a similar engineered outlet control structure to eventually discharge the water, reducing peak flow rates, and usually out-letting to an existing stormwater infrastructure system. A variety of subsurface stormwater systems are available in many different materials and shapes. Materials include reinforced concrete, aluminum, metal, or hard plastic. The designer may select different shapes and sizes, depending upon site characteristics. The underground system layout that fits best a site can be made up of rectangular galleries, square chambers, arched or circular pipes, or a combination of different shapes. Milone & MacBroom designed underground detention galleries (show above) as part of stormwater measures needed for renovations to Verplanck Elementary School in Manchester, Connecticut. The renovated school provides expanded on-site parking, parent pick up and drop off, and a reconstructed bus loop separated from staff and parent parking. Rain gardens in the center of the bus loop were planted with native grasses and herbaceous plantings.

Stormwater Management Through Green Infrastructure
Proper stormwater management is especially important in densely developed, highly trafficked sites where pollutants are more likely to be found in stormwater runoff. Milone & MacBroom is adept at designing and implementing green infrastructure stormwater mitigation strategies in downtown and urban environments. Our green infrastructure projects are designed to include the use of recycled products, locally available materials, and durable products for maximum service life with low maintenance costs. Milone & MacBroom designed a variety of green infrastructure techniques, shown below, for the Town of Fairfield, Connecticut, as part of a stormwater mitigation strategy for its downtown area.

These techniques were developed and conceptually designed to reduce the amount of stormwater and decrease the incidence of shallow nuisance flooding that occurs during intense precipitation events. In addition to conceptual design services, Milone & MacBroom also supported the review of and provided recommendations for the Zoning Regulations, Town Roadway Design Standards, and streetscaping projects. Through this holistic approach to stormwater management, our team has helped municipalities like the Town of Fairfield to incorporate low-impact development strategies into their development codes.

Stormwater Standards & Development Planning
Milone & MacBroom has been active in stormwater management from both a planning and design perspective. In addition to the design of many stormwater management, water quality control, and drainage projects, we have also completed stormwater management studies for entire watersheds. These studies have been used as a framework for developing stormwater regulations and best management practices taking into consideration the needs of the individual community and watershed. Milone & MacBroom recently completed stormwater modeling and planning in the LaPlatte River watershed in the towns of Hinesburg, Shelburne, and Charlotte, Vermont, identifying best management practice (BMP) locations to treat stormwater as these towns grow, shown below.

As part of this project, locations of possible treatment projects were identified for future study, design, and implementation. The information provided by this study will be considered during future growth center and neighborhood planning efforts. Projects identified during this study have been advanced and now provide treatment of runoff.

Specific stormwater management techniques and regulations vary by state, county, and town, but the need for proper stormwater management is constant everywhere. All project sites present their own unique challenges and opportunities in regards to stormwater management, and navigating municipal and state rules and regulations can be tricky. If you need assistance developing stormwater management solutions for your community, contact Milone & MacBroom today.