Stormwater management on the Dartmouth campus consists of two primary types of systems.
The first consists of traditional open-grate catchbasins, of which there are literally hundreds scattered throughout the campus. These structures are interconnected, and the water entering this system discharges to another network of pipes owned and maintained by the Town of Hanover and then ultimately to the Connecticut River.
The second type of system is typically associated with a discrete area or construction project and collects stormwater for pre-treatment, retention, and eventual discharge to either the Town system or a separate discharge point (such as Girl Brook). There are currently 13 of these systems in operation over the entire campus. While there are many different types of these systems, typical components include:
- Mechanisms for pre-treatment to remove sediment and floatables (such as trash and petroleum compounds)
- Detention of stormwater, either aboveground or in underground tanks, to slow the rate at which the water is released. Detention is intended to ensure that downstream pipes are not overloaded during and immediately after a storm event, and to mitigate the impact of stormwater on the downstream environment.
Inspections and Cleaning
All stormwater systems require periodic inspection and maintenance. Catchbasins typically include a sump at the bottom where silt and sand can drop out and be collected. On an annual basis, an outside contractor pumpa out this material with a vacuum truck. Periodic removal of this material helps both to prevent downstream pipes from clogging and keeps silt and sand from entering waterways.
Stormwater treatment and detention systems are often complex and require frequent inspection to ensure that they are operating properly. Depending on the site, they are inspected once or twice per year. This work is performed by an outside engineering consultant who documents system conditions and recommends any needed maintenance.
In some of our systems, a portion of the water that accumulates in the detention tank is re-used on site for irrigation. This is a great way to recycle stormwater and reduce direct discharge to waterways. Where feasible based on site conditions, an infiltration system may also be included, slowly releasing accumulated water directly to the soil. The feasibility of infiltration systems is very dependent on soil conditions. Dense soils such as the silts and clays underlying much of the Dartmouth campus are generally not amenable to infiltration.
Rain gardens are an infiltration method that is becoming more common on new construction projects. These garden areas are used to absorb the runoff from small precipitation events, where soils are suitable. The water supports the vegetation, and the vegetation helps cleanse the water before it infiltrates. Dartmouth's largest rain garden installation is behind the new Indoor Practice Facility.