Anchoring Pollution: Marina BMPs for Stormwater Site Design, Conveyance, Storage and Filtration Systems

Lurking within marina landscapes is a handful of frequently unnoticed yet widely polluting particles that pose a threat to the quality of water. Total suspended solids (TSS) are a category of undissolved particles larger than 2 microns in size and identified by the U.S. Clean Water Act as pollutants. TSS can be natural or man-made — the result of runoff from impervious hardscapes such as buildings, roofs, roads and parking lots — and include things like sand, gravel, silt, clay, salt, oils and garbage. High levels of TSS can adversely affect the integrity of water resources by decreasing water’s natural dissolved oxygen levels, increasing overall water temperature and accelerating water’s turbidity or cloudiness, which in return blocks sunlight, stunts photosynthesis and poses a threat to aquatic ecosystems. Salt is a particular concern in wintery climates, especially when snow is plowed and stockpiled near water sources. All that collective motor oil, salt and wintery gunk is slowly polluting freshwater and groundwater, killing off freshwater fish species and contaminating aquatic life. There must be a solution.

Best Management Practices
Successful stormwater management utilizes a holistic system approach. Best management practices (BMPs) are part of this holistic approach — methods that have been recognized as the most effective, efficient means of reducing or preventing pollution in urban and natural environments. There are a variety of recommendations and approaches to consider, yet marinas and waterfront facilities are best served by developing stormwater BMPs specific to their unique situation and environmental inputs.

This graphic depicts the stormwater plan for Seneca Lake Marina, part of Ohio’s Muskingum Watershed Conservation District.

Five Opportunities for Stormwater Management
Site Studies
Whether assessing an existing marina for stormwater upgrades or considering a new development altogether, conducting a thorough site evaluation is a critical first step. This includes reviewing existing topographic maps of the property or having a professional surveyor create a new one. The study inventories how surface water flows throughout the landscape, where potential stormwater pollutants are located, where pollutants may mix with stormwater and where stormwater drains or discharges. Does all stormwater drain into the lake or river? Is it properly collected and treated prior to doing so? Doing some basic investigation and observation will expose areas of concern and opportunities for mitigation.

This rendering shows the stormwater conveyance for the Lac La Belle boat launch in Oconomowoc, Wisconsin.

A thorough site study will also assess five key areas: the location of buildings and permanent structures; paved areas, including roads and access routes; stormwater drainage patterns and conveyances; locations where potential pollutants are used, stored or located; and locations where “industrial” types of activities occur. It will also review the overall site climate, tilt or slope, size and overall effectiveness for stormwater conveyance and existing treatments.

Stormwater Conveyance
Next, it is important to determine how stormwater travels, where the site’s runoff zones and slopes are and what opportunities are present for storm collection. It is helpful to evaluate the overall grade and slope of a marina property. Does the site tilt toward or away from the waterfront? How are parking areas graded? If the site is intrinsically leaning toward the shoreline, then all runoff — TSS included — is being directly funneled into the water. In these situations, marinas should consider either re-grading and modifying the tilt of their landscape or implementing collection zones throughout the property to capture and treat stormwater before it enters the waterway.

Collection & Infiltration Systems
There are a variety of stormwater collection and treatment systems that marinas can consider implementing. Options vary in shape and size and can be an aesthetic enhancement to any property. Some examples are constructed wetlands or sediment basins, rain gardens and bioretention areas, vegetated swales, forebays and engineered treatment systems.

Constructed wetlands utilize the same natural processes that occur in the wild, except that they are designed and placed precisely where a property needs stormwater collection most. In these areas, a combination of wetland vegetation, soils and microbial properties filter sediments and pollution to help improve water quality on its way to receiving lakes and rivers.

Rain gardens are shallow depressions in the ground planted with native vegetation to capture and filter stormwater runoff. Rain gardens also excel at preventing erosion by establishing deep roots that hold soil in place and are a cost-effective (and beautiful) means to introduce perennial plants and attract birds while reducing runoff. Bioretention areas are like rain gardens but much more engineered, typically consisting of an underdrain with gravel bed and engineered soils to promote infiltration of the treated stormwater.

Vegetated swales or bioswales are shallow, open channels that help slow and filter surface runoff through thick grasses that slow the water and settle out pollutants. They are intentionally designed and contoured linear systems most frequently integrated into parking lot areas or along roadway medians. In areas with permeable soils, runoff nicely infiltrates into the soil beneath; in areas that are less permeable, swales can be constructed with engineered media beneath that helps channel runoff into an underdrain area where it is treated.

Forebays are small, engineered basins for collecting and filtering TSS before it enters a water body. They function very much like rain gardens — living, growing, wetland-like features with native plants whose deep roots “clean” contaminants through a combination of microbial action in the soil, vegetative uptake, evaporation and slowing water to allow settlement. The most effective design is a series of forebays set to drain from one into the other/s, progressively treating in sequence until ultimately discharging into the nearby river or lake. Forebays are constructed by excavating a basin or depression, lining the bottom with stone (in some cases sand mix) and topping with soil and native wetland vegetation. These basins can also serve as attractive vegetated features, improving site appearance and ambiance.

There are some outstanding engineered treatment options on today’s market as well, including below-ground systems like Vortechs by Contech Engineered Solutions. These can be found in localized municipal stormwater networks but can be an excellent addition to marina infrastructure, particularly for sites needing shallow treatment due to bedrock, groundwater restrictions or conflicting utilities.

Systems like Vortechs by Contech Engineered Solutions are installed underground to assist in filtering stormwater

Vortechs is an aluminum cylinder that acts — as the name suggests — like a vortex. Water enters the chamber through an inlet where the mechanized swirling motion promotes gravitational separation of sediments, which then settle and accumulate on the chamber floor. The system is designed to treat sediment, trash debris, hydrocarbons and stormwater runoff, which are either filtered out or trapped by an interior baffle wall while treated stormwater exits via an outlet pipe. The resulting debris and sediment can then easily be extracted through a manhole access by a vacuum truck with little hassle.

Storage Systems
The most traditional way to store stormwater runoff on site is in the form of basins or ponds — either detention or retention. Detention ponds are designed to store water temporarily and release it bit by bit until the pond is drained. As such they are dry most of the time, employed mainly after storm events. Retention ponds, on the other hand, are meant to permanently hold runoff and regulate water levels through an outlet or spillway feature.

However, both types of storage systems require real estate — often more space than marinas have on hand. Fortunately, there are other excellent storage options for marinas of all shapes and sizes.

Underground storage chambers accept, treat and discharge runoff while being largely out of sight and out of mind. They are also an excellent solution for marinas or waterfront facilities with smaller footprints — where things like wetlands, rain gardens or forebays are not an option. Underground storage systems can be constructed of materials such as metal or plastic (PVC) and can be designed as components linked or welded together in one large flow-through matrix or as a stacked system. The larger the size, the greater the detention capacity. These systems typically have vertical inlet pipes to collect stormwater runoff and horizontal outlet pipes to discharge. The bottom of the system can also be open or with permeable features to promote filtration of the runoff into the surrounding soil.

Green Engineering & Stormwater Aesthetics
Stormwater systems offer opportunities to enhance the entire marina ecosystem, design more resilient public spaces and improve site aesthetics. A professional landscape architect can be of great help in pairing open-space and shoreline improvements with stormwater amenities in a constructive and creative manner. Done right, these types of enhancements help filter stormwater, prevent erosion, stabilize shorelines, improve water quality and attract wildlife.

Green stormwater treatments can add color, texture and appeal year after year with very little maintenance.

Green stormwater treatments can begin in upland areas with the development of shoreline open spaces, rain gardens and forebays, which can be enhanced with boardwalks, educational signage or art. Native plantings can follow the progression to the water as well, with species conducive to the full spectrum of marine environments. For lawns and upland areas, any number of native perennials or grasses selected for the right growing zone will lend flourishes of color, texture and appeal year after year with very little ongoing maintenance. Wet meadow emergent plants are a good choice for the bermed edges of detention basins or forebays, while deep marsh plant varietals are excellent semi-submerged or at the water’s edge.

Wet meadow emergent plants can be used for the bermed edges of detention basins, while deep marsh plant varietals are perfect for semi-submerged areas.

By implementing site-specific stormwater best management practices through information gathered from site data collection, green engineering solutions and well-designed collection and treatment systems, the adverse impacts of TSS can be turned from a regulatory necessity into a site asset. Both functionally important and aesthetically pleasing, stormwater upgrades help ensure we remain responsible stewards of our water resources and preserve or improve our recreational waters for future generations.