Tuesday, October 14, 2014

Office Parking Lot Expansion

By Cliff Aichinger

Left: Before the parking lot expansion (after a large rain).  Right: The Watershed District's parking lot expansion is completed.  The retrofit was done to accommodate additional visitor parking, provide access to our new garage (left building in both images above), and assist in infiltration.

Our parking lot expansion project is finally completed. I realize that this project has been an inconvenience over the summer by limiting our available parking. However, we now have 12 additional parking stalls and we can now accommodate most visitors to our meetings and events. This project also allows us access from our entrance to the garage we purchased from the former Norm’s Tire property.

The expansion added two large rainwater gardens in place of the former one and a much smaller drainage swale on the west side of our original parking lot.

A view of the two new rain gardens adjacent to the District parking lots during construction (foreground and far background by construction cones).  Note the sand trench running through the middle of the garden.
The rain garden at the top of this photo takes run-off from Noel Drive.  Any overflow from this garden is directed into the second rain garden (lower part of the photo) through a slit drain.  This trench also captures run-off from the upper parking lot and directs it into the lower rain garden.

We also added a section of porous pavers that demonstrates the new PaveDrain product. This product allows for large storm event infiltration of stormwater runoff. 

Left: PaveDrain, a type of porous paver, being installed during the expansion project. Right: PaveDrain porous pavers infiltrate run-off in the transitional area between the upper and lower parking lots.

The remainder of the new parking lot is conventional asphalt pavement. However, we designed the drainage so we still will be infiltrating almost all runoff on our property. This is accomplished by routing the runoff from the new asphalt into the rain gardens and into the base rock under our current pervious asphalt parking lot.

The rain gardens include 3 kinds of sedges, several native grasses (little bluestem, blue grama and prairie dropseed), common rush, blue flag iris and a variety of shrubs and trees on the berms. 

The new rain gardens are planted in native grasses, sedges, shrubs, and trees.

We, unfortunately, had to remove a large number of mature red twig dogwood and small oak trees in the expansion project, but we added 12 red twigged dogwood, 16 low bush honeysuckle bushes, 36 black chokecherry, and 16 new trees. The tree grove in the central rain garden is dedicated to Roger E. Lake, our former and long-time Board President. The grove was generously co-sponsored by the Minnesota Association of Watershed Districts.

Left: Trees and shrubs grown by Ramsey County Community Correctional Nursery are installed by District staff Simba Blood and Natural Resources Intern, Zola.
Right: Tree grove dedicated to Roger E. Lake, former and long-time Board President.

District staff completed the planting of the rain gardens in early fall.

Carole, Eric, Sage, and Bill (left to right) and other staff finished planting the berm and rain garden.

If you have visited our office during recent rain storm events, you may have noticed that the porous asphalt is no longer very porous. Since 2005, organic material, tracked dirt and debris have clogged portions of our lot. Within the next couple weeks we are going to have a contractor do a special cleaning to restore the porous nature of the asphalt and extend the useful life of the pavement. This is a new process and we are hopeful that it will dramatically improve the pavement infiltration rates. Even though we have decreased infiltration into our parking lot, we still have had only 5-6 events since 2005 where we have had stormwater overflow to Gervais Creek. Our facility continues to demonstrate that a commercial/institutional developed site can be designed to contain and infiltrate stormwater on-site. We also take a significant amount of stormwater off Noel drive into our rain gardens.

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