Foundation Detention Basin

Area of Concern: Internal Pathways and Side StreetsRunoff + Erosion

Proposed Solution: Stabilizes road surfaces and creates a foundation infiltration basin diverting surface flow to existing Marshall House foundation

Impervious Liner Perforated Underdrain

Broad-based Dip Marshall House Foundation Stormwater Detention

Erosion on Horse Lane has been an ongoing maintenance burden for many years. Every spring and frequently throughout the year, the surface of Horse Lane requires supplemental material and regrading. The eroding material and stormwater coming down Horse Lane ultimately flow towards a small catch basin at the bottom of the hill at the intersection with Puddle Lane. In the event this inlet is either clogged or full of groundwater and/or seawater, the structure overflows and accumulates within the central lawn.

There are several contributing factors:

• Uncontrolled stormwater path runs down the road corridor.

• Steep slopes with long flow path lead to erosive, concentrated flow.

• Unstable surface material is susceptible to erode.

Ultimately, all stormwater and associated debris coming down Horse Lane contributes to the greater area of concern within the central lawn. Remnants of the historic foundation of the Marshall House are visible today at the intersection of Jefferson Street and Horse Lane. While the foundation today is subtle, it does provide a sense of form and shape that presents an opportunity to be part of the solution to this area of concern.

Design Intent

Stabilizing surface materials will help reduce erosion and frequent maintenance. Adding diversion techniques and adjusting the cross slope of Horse Lane can shift the path of least resistance off the road corridor, creating intentional space for stormwater flow. Although the steep slopes found on Horse Lane can not be adjusted, diversion techniques can be used to intercept and slow stormwater as it makes its way downhill. Rain barrels or other small footprint collection devices can also be used to disconnect rooftop runoff for reuse. In tandem, all of the options described can be used to interrupt the long flow and reduce the erosive force of concentrated stormwater flow.

A broad-based dip at the intersection of Jefferson Street and Horse Lane is proposed to divert stormwater flows normally running down the road corridor to be re-directed across the road and into the Marhsall House foundation. Soil conditions within the foundation will need to be evaluated to assess the level of earthwork required and feasibility for stormwater use, but the Marshall House foundation could be re-purposed to provide short-term stormwater detention and expose another historical element within the campus. The foundation detention basin would provide storage during smaller storm events. At a minimum, this solution would increase the flow path, add detention and reduce the frequency of stormwater directed directly to the downhill drainage infrastructure.

Beyond the stormwater detention benefits, this project also serves as an opportunity to reinvent and celebrate an under-appreciated resource found at Strawbery Banke. Native fieldstone will be used to mimic the historic foundation visible today. If suitable, subsurface enhancements will be included to ensure proper drain-down times and to control overflows, such as amended well-drained soils, and perhaps even perforated underdrains and an impermeable outside liner. None of these features will be visible, thereby retaining the historic sense of place.

SEDIMENT FOREBAY

SOURCE: HORSLEY WITTEN GROUP

STABILIZED SURFACE (STABILIZED STONEDUST)

SOURCE: HORSLEY WITTEN GROUP

BROAD-BASED DIP

SOURCE:©AMAR SJAUW EN WA

FOUNDATION DETENTION BASIN

SOURCE: HORSLEY WITTEN GROUP

VEGETATED SWALE

SOURCE: HORSLEY WITTEN GROUP

COBBLESTONE SWALE

SOURCE: STONE FARM LLC

Carpenter’s Shop Wet Swale

Area of Concern: Carpenter’s Shop - Localized Flooding

Proposed Solution: Vegetated Wet Swale

Frequent localized flooding outside the Carpenter’s Shop is among the highest areas of concern for Museum staff. The Carpenter’s Shop is set at the lowest finished floor elevation (FFE) across the entire campus at 9.19.’ It sits between the 100-year floodplain (elevation 9.0’) and 500-year floodplain (elevation 10.0’). Furthermore, the Carpenter’s Shop has very little foundation reveal, allowing floodwater to come in contact with wooden clapboard and trim that is susceptible to rot. The surrounding topography is flat, which encourages stormwater to settle and pond.

In the winter when the Labrie Family Skate at Puddle Dock Pond rink is installed, the Carpenter’s Shop experiences additional drainage challenges. As the ground freezes, the ice rink acts as a barrier, preventing stormwater from draining away from the Carpenter’s Shop and towards Atkinson Street and a series of catch basins. The existing dirt road also segregates these spaces between the central lawn and the seasonal ice rink. The sand used to level and construct the rink can often clog the surrounding catch basins. The weight of the ice rink also compacts the soil, further exasperating the runoff problem when the soils begin to thaw. These contributing factors lead to a pinch point outside the Carpenter’s Shop and an inability for the soils and catch basins to properly drain the site.

As the Carpenter’s Shop relates to the central lawn, which varies in surface elevation from 7.5’ to 8.5,’ the Carpenter’s Shop FFE establishes our first critical grade as we begin to look at the larger area of concern and how these two areas are interconnected.

Design Intent

Positive drainage requires a consistent pitch away from buildings and structures. As it relates to protecting a building foundation, the landscape that directly abuts the foundation should slope away. Where gutters and downspouts aren’t possible due to historic preservation standards, adding a stone drip edge around the perimeter of the foundation may provide an opportunity to capture and infiltrate smaller rain events and prevent scouring and erosion during larger events.

Similar to the previous area of concern, stormwater surrounding the Carpenter’s Shop must cross several dirt roads to reach the existing drainage system. Due to this area being used as a temporary ice rink during the winter months, two options were considered. The first option includes maintaining the space for the ice rink, reducing the width of the dirt path, and creating a wet swale between the modified path and the rink. The second option, as presented here, aims to reduce the width of the dirt road immediately south of the Carpenter’s Shop to re-establish the walking path and introduce a broad-based dip to control the stormwater by directing it to a vegetated swale. The vegetated wet swale will receive stormwater from the broad-based dip as well as the patio space north of the Lawrence J. Yerdon Visitor Center. During seasonal high groundwater, the wet swale and its planted habitat will intercept the groundwater and the water may be visible at the surface.

Although the main function of the swale will be to control and move stormwater, it can also provide natural beauty and seasonal color to the campus landscape. In alignment with the museum’s preservation and education mission, the wet swale could transform the current mown lawn into a more natural, riparian edge that recalls the former tidal inlet, which once existed on the site.

STABILIZED SURFACE (POROUS PAVER)

SOURCE: HORSLEY WITTEN GROUP

STORMWATER RUNNEL (ALTERNATIVE TO BROAD-BASE DIP)

SOURCE: SF BETTER STREETS

STABILIZED SURFACE (INTERLOCKING PAVERS)

SOURCE: HORSLEY WITTEN GROUP

WET SWALE

SOURCE: HORSLEY WITTEN GROUP