Archive | June, 2011

Asheville, North Carolina Field Trip – Student Notes and Observations

3 Jun

Site

The main objective of the North Carolina Arboretum is achieving pre-development hydrology and to capture and infiltrate at least 50% of the rain water in 1.2 inch rainfall events.

Discussion

Strategies for slowing down, treating and cooling storm water before it gets to the local area water system include:

    • Oversized water cisterns for capturing rain water
    • A bottom-up approach on the formal lawn area which has two large perforated culverts and is covered with
    • A bottom-up approach on the formal lawn area which has two large perforated culverts and covered with Staylite aggregate mixed with loam, sand and silt. The lawn then sucks up the water passing through the pipes.   Pretty cool.
    • A big rain garden at the main entry roundabout. John pointed out that a rain garden needs to be at least 1/10th the size of the catchment area.  The rain garden also needs to provoke and  interact with people by having some form of art or a shape that draws attention.  The rain garden had an visible concave shape that makes it obvious and allows observation of collected rainwater and how fast it infiltrates into the ground.
    • Rain gardens need to be planted with diverse species with the main criteria for their selection being the ability to withstand wet conditions.  Woody plants should be avoided in wetlands as they provide cover for mosquito larvae and should be around 9” deep.
    • Wetlands need to be located away from the formal buildings.
    • There should be an extruded filter sock for sediment control downhill.

 Opportunities for improvement include:

    • Having lawn grass grow all the way to the slope, probably to the first foot of the rain garden floor, in order to prevent erosion.
    • The planting design of the large rain garden could be improved with a less formal and more organic plant massing.

– Written by Antony Wambui

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Asheville, North Carolina Field Trip – Student Notes and Observations

3 Jun

Site 

 The Evergreen Community Charter School’s LID landscape featuring various stormwater Best Management Practices.

Discussion

 The site of the Evergreen Charter School formerly housed a Christian academy, but when the school changed to a charter school, the decision was made to implement a LID landscape on the campus.  The school applied for funding from an environmental grant with the goal of reducing the amount of impervious surface and improving the quality of water on the site.  On the tour, we observed several large bioretention areas that captured water off of the main buildings of the school.  There was a large bioretention area below the parking lot that captured runoff from a roof as well as from the parking lot.  The site also featured a conveyance channel with a series of step-down weirs, a constructed wetland, removal of curb and gutter systems, a biodiesel fueling station, and a cob structure.  

 This site is an excellent example of a holistic approach to treating water on a site due to the various BMPs found throughout the site. While some were more successful than others, it was really inspiring to see the BMPs implemented on such a large scale, especially at a relatively small school.  The bioretention areas adjacent to the school building looked like they were performing very well, with thriving plants as well as nice educational signs.  The bioretention area below the parking lot looked as though it was capturing a lot of water, but there were some structural issues where erosion had undercut the pavement where water entered the depression.  This could be remedied by the inclusion of rip-rap where the water entered to help dissipate the energy and prevent erosion.  There were a couple of missed opportunities in the parking lot, where more bioretention areas could have been included.  There was a narrow planted strip running down the center of the parking lot, perpendicular to the grade, and the class discussed how this could have been more successful if it was slightly depressed to allow for infiltration and pretreatment of the water upstream.  The class found a couple of areas where maintenance was needed including the buildup of silt and debris at bioretention entrances, and erosion on weirs, showing the importance of diligent maintenance on these types of systems.  I was very interested in looking at the planting palette in the BMPs and discovered that most of the plantings were native.  Plants included Itea, Clethra, Hamamelis, Amelanchier, Aescules, and Callicarpa, although the Callicarpa was the non-native species, so I feel like this might have been a mistake since everything else was native.  Overall, I was impressed with what I saw and thought this site could act as a good precedent for other schools, inspiring them to implement similar systems.  

– Written by Mary Archer