Best Management Practices (BMP’s) are actions done to control water pollution and improve water quality. Throughout Aspen many BMP’s are implemented to reduce runoff and keep pollutants out of the Roaring Fork River. Below is a summary of BMP’s that are utilized in Aspen. Further information on BMP’s can be found in the Urban Runoff Management Plan in the sections listed below each summary.
Low Impact Development (LID) aims to mimic the natural,pre-development hydrologic pattern. The goal is to manage stormwater as close to its source as possible. In the past the driving force behind stormwater management was exclusively to move water away from buildings and streets as quickly as possible without any regard to water quality. This meant using pipes and gutters to direct water to detention ponds, retention basins and rivers.This technique has caused significant damage to water quality and the environment. Without any contact with soil or plants, stormwater has no chanceto deposit any of the contaminants that it carries. These contaminants are brought to the river and carried to the next town downstream. To improve water quality people began implementing Low Impact Development. LID is a relativelynew approach that began in Maryland in 1990. To treat stormwater near its source a variety of methods are used, but the main objective is to create small scale projects throughout the town to treat stormwater instead of costly large scale projects that do not have the capability to treat stormwater as efficiently.LID aims to increase the time water is in contact with soil and plants before it reaches the river. Plants and soil essentially work as a filter and remove pollutants. LID also allows water to infiltrate into the ground which recharges the water table. Rain gardens, green roofs, permeable pavers, bioretention areas, green streets, and grass swales are all examples of LID projects.
Low Impact Development can be seen throughout Aspen. Below are examples and pictures of these practices in Aspen.
Grass Swales and Grass Buffers
Grass swales are densely vegetated drainageways. These swales slow down and filter stormwater. Grass swales can be seen throughout town in residential areas. Grass Buffers are similar to Grass Swales, but buffers are designed to treat sheet flow instead of concentrated or channelized flow. As water flows over grass buffers the water slows down which allows sediment to settle.
More information on grass swales and grass buffers can befound in sections 126.96.36.199 and 188.8.131.52,respectively, in the Urban Runoff Management Plan.
Impervious areas cause large amounts of runoff. This means the stormwater system has to deal with a much larger quantity of water. The higher runoff also carries more pollutants through the stormwater system and to the river. Pervious pavers allow water to infiltrate through the surface, while still providing a stable and flat paved area.
Near the John Denver Sanctuary by the Theatre Aspen tent, pervious pavers have been installed. The pavers look great while improving the quantity and quality of stormwater in Aspen.
More information on pervious pavers can be found in section184.108.40.206 of the Urban Runoff Management Plan.
In areas that are only occasionally used for parking, grass pavers are a great alternative to pavement. Grass pavers stabilize and reinforce grassy areas. This allows bikes, cars, and trucks to pass over the area without damaging the grass. Grass pavers are constructed with either concrete or plastic and are designed with void spaces that allow grass to grow.
More information on reinforced grass pavement can be foundin section 220.127.116.11 of the Urban Runoff Management Plan.
Above Ground Conveyance Through the center of the Hyman Avenue Mall water is conveyed above ground. This stream collects stormwater and allows contact with the soil and plants along the bank instead of conveying the water underground through a pipe. On N 7th street, between Hallam Street and Main Street, water is directed from the street gutter to pervious areas.
Street Sweeping Street sweeping plays an important role in keeping pollutants out of stormwater. Debris, dirt, sand and silt collect in gutters and along the sides of streets. Sweeping and collecting this material keeps it from entering the river.
The city of Aspen has installed vaults to help improve stormwater quality. Sediment stays suspended in water when water moves. You can visualize this by picturing a jar filled with water and dirt. When you shake the jar the dirt mixes with the water and the water becomes murky. However, if you leave the jar sitting on a table the dirt will eventually settle to the bottom. Stormwater vaults work in the same manner. Water running off the streets is turbulent, mixed, and carries high concentrations of sediment.
When the water reaches a vault a couple things happen that remove unwanted pollutants. First, the water passes through a trash rack. A trash rack is a series of bars that stop large debris. The water also slows down greatly. Thewater is deep and slow moving. This allows sediment to settle to the bottom ofthe vaults. The water then has to pass under a structure which essentially“skims off” any pollutants floating on the water. This helps keep oil and gas,which floats on top of water, out of the river. At the end of the vault a structure comes up from the bottom of the vault. Only water on top pours over and out of the vault. This keeps the sediment on the bottom from flowing out ofthe vault.
Aspen has vaults located above the Jenny Adair wetlands located on the south side of Puppy Smith Street, as well as underneath the parking areain the Rio Grande Recycle Center. The Jenny Adair vaults treat stormwater that drains from nearly the entire town west of Mill St, while the Rio Grande Recycle Center treats drainage from the east and middle portion of town as well as drainage fromAspen Mountain’s two major gulches, Copper and Spar.
Section 18.104.22.168 of the Urban Runoff Management Plan has moreinformation and specific requirements for stormwater vaults in the City of Aspen.
Bioengineered Wetland- Jenny Adair Wetlands
A constructed wetlands basin is a shallow retention pond that has a continuous base flow which promotes the growth of rushes, willows,cattails and reeds. The shallow pond, along with vegetation, slows down runoff and allows time for sedimentation, filtering, and biological uptake. Wetlands greatly improve water quality while at the same time providing natural aesthetic areas, increasing wildlife habitat, and providing erosion control. Constructed wetlands are engineered to mimic natural wetlands which can be viewed as the “kidneys” of the hydrologic cycle due to their filtering and cleansing capabilities.
More information on constructed wetland basins can be found in section 22.214.171.124 of the Urban Runoff Management Plan.
Whenever anything is built, construction disturbs the soil in which the site sits. This dug up and disturbed soil is no longer held in place and can easily be washed into the stormwater system by a runoff event. High concentrations of sediment can greatly damage river ecosystems, thus sediment from construction sites must be controlled and kept out of stormwater drains.Drain covers, silt fences, sediment barriers, hay bales, and soil covers mustbe used to keep sediment from construction onsite and out of the river.
Drain Covers Drain covers cover stormwater drains that are near construction sites. These covers prevent larger sediment from entering the drain, while still allowing water to pass. This is a temporary solution as the covers quickly fill with sediment and can clog if left too long.
Silt fences are placed along the perimeter of a construction site or anywhere runoff could carry sediment away from the construction site.Silt fences don’t filter runoff but rather cause runoff to pool behind the fence. Sediment then settles in these small pools of water and is kept onsite.It is important the silt fences are properly installed and maintained to be truly effective.
It is important to cover any piles of soil during construction. Loose uncovered soil is easily carried away by rain.