Broad Creek Park Stream Restoration

STREAM RESTORATION PROJECT RESTORES HABITAT AND ELIMINATES CHANNEL EROSION IN ONE OF THE CHESAPEAKE BAY’S MAJOR TRIBUTARIES

Our Client’s Challenge

Broad Creek flows along a hiking and walking path in Broad Creek Park in Annapolis, Maryland, offering park visitors scenic views and opportunities to observe birds and other wildlife. After the creek passes through the park, it heads south, feeding into the tidal portion of the South River, a major tributary to the Chesapeake Bay – the largest estuary in the U.S.

Broad Creek’s health has suffered from commercial, residential, and highway development effects for decades. As more green spaces are converted to impervious surfaces, fewer plants and trees filter stormwater and prevent it from rushing into the creek. The rushing stormwater erodes the stream’s banks, degrades its floodplains, and sends sediment and pollutants downstream to the bay.

The Arundel Rivers Federation, which works to protect, preserve, and restore rivers in Anne Arundel County, identified the eroded and degraded stream as a restoration opportunity. Gannett Fleming partnered with the federation to restore approximately 3,760 linear feet of incised stream.

Our Solution

Gannett Fleming conducted stream surveys and assessments to inform the design of a modified valley restoration that would repair the actively eroding stream and enhance the riparian buffer. By filling the channel and reattaching the floodplain, stormwater spreading over the floodplain is slowed and absorbed rather than rushing through the eroding channel.

The design provided interspaced shallow wetland pools, sheet flow of flood waters through the middle of the flat floodplain, and seepage wetlands in the existing channel at the base of the valley walls. Complete channel filling where the incised stream traversed the valley achieved zero-order valley restoration.

Where the existing stream abutted the valley wall, the stream was plugged every 50 feet to create seepage wetlands at the toe of the slope. An extensive 2D hydraulic model confirmed stable floodplain shear stresses of less than 2 pounds per square foot and that the sheet flows down the middle of the valley would rewet approximately 5 acres of valley wetlands, preventing re-incision of the channel.

Although the floodplain is flat, its steep sides make it difficult to access with heavy machinery. Ramps and crane mats helped crews access the floodplain and create temporary roads that kept machinery from sinking in the soggy conditions. Crews worked diligently not to disturb or remove trees or vegetation, enhancing the ground’s stability and maintaining the park’s appearance.

Gannett Fleming developed a novel structure detail with the park owner, the Anne Arundel County Bureau of Watershed Restoration and Protection, for extensive valley-wide grade controls made of compacted sand. Improvements that capture sediment on the floodplain wetland areas and provide habitat for native flora and fauna include:

Floodplain roughness treatments.
Clay channel plugs.
Floodplain underlayment.
Vegetation stabilization.

The stream restoration project even attracted the attention of Michael and Kevin Bacon, whose foundation, SixDegrees.org, supports impactful initiatives that sustain local communities. Together with the Arundel Rivers Federation and local scouts, the brothers planted hundreds of native plants at Broad Creek Park. Their work contributes to a greater effort by volunteers to plant nearly 6,000 grasses and flowers to hold sediment in place, provide habitat, and filter nutrients to help protect the Chesapeake Bay.

Before (left) and after (right) photos demonstrate how significantly the restoration project improved the water quality.

Key Features

Habitats and wetlands along 3,760 linear feet of stream are restored.
New plants and grasses hold sediment in place, preventing it from discharging into the river.
Valley-wide grade controls provide habitat for native flora and fauna.

Outcomes

The valley’s ecological function was restored by filling and plugging the stream, rewetting relic wetlands throughout the valley, and reconnecting the floodplain.
The restored hydrology improves nutrient and sediment retention, reducing pollution flowing into the South River and the Chesapeake Bay watershed.