Monday, March 4, 2019

Waterfront Swales with a Hugelkultur and Dune

Run-off area
At this residential property on the Maryland coast, I was tasked with designing a native landscape to manage polluted stormwater coming from the road, running down the driveway, across the lawn, and ultimately exiting into a cove on the Chesapeake Bay. 

Due to underground utility lines and space constraints, the only location for this new device was at the waterfront. 

Beach litter collected for Hugelkultur

Waterfront site, BEFORE

The design consists of two adjacent swales and berms. The level swales are filled with wood chips, which act as a sponge, collecting the stormwater and enabling it to percolate into the soil, interrupting its journey to the bay. The plant roots at the berms absorb this water as passive irrigation. 

Installed in October, the upper berm was constructed as a hugelkultur, mounded with harvested beach litter (drift wood and seaweed) and covered with the soil excavated from the swale above. My client had already imported sand to make an artificial beach, and asked me to construct the lower berm as a dune.

Berms and swales under construction
Mimicking the local coastal plant community, the upper berm was planted with native shrubs that tolerate brackish water, some growing in the wild area right next door. Their woody roots will anchor the soil against the deluge of stormwater during harsh storms, and buffer strong winds off the Bay. These shrubs also create privacy for the beach by blocking the view from the road. The Southern Bayberry fixes nitrogen in the soil. 

Before planting; after the first rain
In a functional landscape, every component serves at least one purpose, besides providing beauty. The dune was planted with local, salt tolerant grasses and flowers, which will attract beneficial insects like bees and butterflies.  To create a gentle transition between this native landscape and the lawn, I added some non-native aromatic herbs and ground covers. These will deter mosquitos, and eventually negate the need for mulch. 

Finished Rain-scape; swales filled with wood chips (winter)
Hugelkultur swales and berms with driftwood and beach litter
Hugelkultur berms and swales were built with driftwood and seaweed, adjacent to the wilderness next door.  Native trees will be planted there next year, after the hugelkultur has decomposed a bit.

Fall is a great time to plant because new plants can go dormant while their roots establish over the winter.  There is no stress from hot summer temperatures or the need for daily watering.  When spring comes the following year, plants stand of better chance of thriving without constant attention

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