Harnessing the Flow of Stormwater

by MARGARET BACK Preservation Manager, Eustis and South Region and BENJAMIN HAAVIK Team Leader, Property Care

Increasingly heavy rains call for stronger management strategies

The summer of 2021 was one of the rainiest on record with twenty inches falling on much of New England—and that was before the arrival of Tropical Storm Ida in September. That much rain can really do a number on buildings and landscapes, especially if a drainage system isn’t well designed. Following up on Historic New England’s innovative work analyzing the capacity of traditional gutters on our historic houses to withstand more frequent and intense rainstorms, we have turned our attention to our overall stormwater management program or, more precisely, “where the water goes after it leaves the gutters.”

Stormwater management has been a major component of our site improvements over the last ten years. Our early goals were simply to transport water far from our historic buildings in a way that wouldn’t detract from the historic landscapes. In recent years we have also come to appreciate that these systems might allow for the replenishment of the groundwater while potentially filtering chemicals, pollutants, and debris before they are introduced into our rivers and streams. Realizing that we wanted a more sustainable approach for our landscapes, we have been working with a range of consultants to inform our thinking and update our approaches.

At Watson Farm in Jamestown, Rhode Island, support from the van Beuren Charitable Foundation is allowing us to implement a test project incorporating both gutter enhancements and site drainage. Existing gutter systems on the farmhouse and main barn date only to the 1990s and have been repaired and replaced in-kind over the years without considering stormwater capacity.

In keeping with the findings of our gutter capacity project we found these gutters and outlets to be undersized for the volume of rain we were receiving. On the c. 1796 farmhouse, we increased the size of the gutters and downspouts, ensuring effective runoff from the large roofline. We are considering adding similar larger components to the main barn as part of the next roofing project.

Drainage across the property is another problem in need of a broad solution. Running west to east along heavily traveled gravel farm roads is a sixty-five-foot elevation drop across 600 feet. During large storms these roads collect and funnel runoff directly toward and through the farmyard, which features active agricultural buildings including the farmhouse, three barns, springhouse, and wool shed. A portion of the runoff, nutrient-packed from passing through livestock holding areas, flows into a small groundwater-supplied pond at the base of the farmyard.

Storms can produce extensive washout along the farm roads, through outbuildings used for equipment storage, and water infiltration into the farmhouse basement. Working with a civil engineer, we developed two drainage plans with the goal of having a system ready to handle the increasingly more intense storms and keep this runoff away from agricultural activities.

The first alternative proposed a level spreader—an above-ground outlet at zero percent grade across a slope. The advantages of a level spreader are in the name itself— converting concentrated runoff into a level, uniform flow over a large area. Called “sheet flow,” this dispersal method maintains an even discharge across a field, avoiding erosion and encouraging sedimentation. While good for stormwater dispersal, this method was not deemed appropriate as wet weather could disrupt the seasonal haying that provides forage for resident cattle and sheep.

The second alternative also considered channeling the runoff into the farm pond, but in a controlled manner. Rather than allowing runoff to flow along gravel paths and foundations, a below-grade piped system will collect stormwater through catch basins at different key points of elevation. The catch basins loosely filter large sedimentation from entering the system and direct runoff into the pond in a controlled manner. Acting as a retention pond, larger nutrient loads and sediments will settle to the bottom and be dredged on a cyclical basis for use as farm compost. When output reaches a certain height in the pond, an upsized culvert to the east will move runoff into the forested wetlands. This alternative works best to confine the project to the affected farmyard core while incorporating the retention pond as a working tool on the farm.

While level spreaders and retention ponds work on farmsized properties we also needed an approach with a more domestic scale. At the Eustis Estate in Milton, Massachusetts, a tremendous volume of water flows down the steep entrance drive past the gatehouse to a small area of lawn. In times of severe rain this area is quickly saturated and

Drainage problems across the Watson Farm property require a broad solution. With support from the van Beuren Charitable Foundation, Historic New England is running a test project using both gutter enhancements and site drainage. Page 21 A rain garden was created at the Eustis Estate in Milton, Massachusetts, to manage stormwater. The first image shows a series of stone check dams installed to slow down the rain water as it flows to the garden. On the right, shrubs planted in the flooded rain garden allow the water to dissipate into the ground.

threatens to flood the gatehouse. Last summer, the area was redesigned as a rain garden—a more purposefully designed area with native plants and shrubs. Instead of disguising the area as lawn we wanted to embrace the sustainable design of the system and the biodiversity we were bringing to the site. The area was excavated below the surrounding ground level, a sub layer of gravel installed to support the drainage, then new soil and finally wet-loving plants were added.

All of these aspects will work in tandem to provide a location for the water while it percolates into the soil. The rain garden also helps to trap pollutants and chemicals that might wash in from the driveway and keep them out of the nearby town stormwater system.

When protecting your property from stormwater it is important to think through the complete cycle from start to finish. Considering not just the gutter sizing and maintenance but also where the water goes once it leaves the gutters can prevent unsightly erosion and

potentially destructive pollution. How we adapt our buildings and landscapes to handle water varies by site, but considerations of climate change, capacity, landscape design, and sustainability are where we are beginning this work. We hope these and future solutions meet site needs and create cleaner landscapes for our properties and their surrounding ecosystems. When protecting your property from stormwater it is important to think through the complete cycle from start to finish.