In order to slow down the flow of rainwater, and infiltrate it, we plan to incorporate bioswales along the grass areas surrounding the athletic field. Also, we plan to place bioswales along the plot of grass near the parking lot, so that contaminants could be removed from stormwater runoff before being released into the sewage system.

Map of Targeted Areas:

Note: In the stretch of grass behind the track (D), there are seventeen 3 ft. x 4ft. cement squares that are holding up poles connected to the fence behind it. These cement squares had been taken into consideration while calculating the area.

Calculations: 

Pictures:

1) Corners of the athletic field where rain gardens will be placed:

A) Top Right Corner:

B) Bottom Right Corner:

C) Bottom Left Corner:

2) Stretch of grass behind the track where rain gardens will be placed:

3) Plot of grass near the parking lot where rain gardens will be placed:

Even before creating bioswales, these areas already contain vegetation. However, the soil and plants would need to be replaced in order to make them more suitable for infiltration and filtration. Also, the land would need to be designed with the proper sloping and drainage systems. This is necessary because a bioswale is most effective when the land is slightly sloped; this allows for better filtration and drainage of rainwater.

Function:

Bioswales are vegetative channels that infiltrate rainwater, and can act as a natural stormwater filtration system. Bioswales are designed to maximize the amount of time water spends traveling through them, which is needed in order to give this natural process enough time to work effectively and trap more contaminants.

Benefits and Potential Problems:

There are many benefits of incorporating bioswales along the athletic field and parking lot. In the parking lot, a substantial amount of pollution contaminates the rainwater runoff. These pollutants have the potential to build up and cause damage to the environment. Bioswales could help remove various contaminants from the runoff before releasing it into the sewage system. Also, adding bioswales is a non-costly undertaking that would help beautify the college and increase its aesthetic value.

However, if improper landscaping is chosen, these bioswales won’t be able to function properly. They could become areas that attract mosquitos and other unwanted insects. Also, although creating bioswales isn’t costly, they do require maintenance. Therefore, in order to avoid these problems and to maintain properly functioning bioswales, they must be created with the following design elements in mind. The bottom of the channel should be flat. This provides enough room for the flow to spread out, which increases the filtering and infiltration capacity. The bioswale should be wide enough to prevent flows from concentrating into gullies, which could cause erosion. Its depth should be lower than the vegetation (typically around 4 inches deep) and it should have a gentle slope (less than 6%) so that the flow could be slowed down without creating ponding. Steep slopes could result in rapid travel, which would lead to less filtration and soil erosion. The soil and vegetation used in a bioswale are specific for its function. Native soil should be replaced with a sand/soil mix that meets permeability requirements. It should be planted with deep-rooted native vegetation that provides surface roughness. These types of plants will slow the flow of water, and enhance filtration. The species selected should also be able to withstand frequent and substantial water flow. Plants that could tolerate both wet and dry conditions may work best. Finally, the planting layout should be designed to make it easily accessible, and to facilitate periodic removal of sediments without significantly disrupting or removing the plant materials. This way, the bioswales could be better maintained.