Salmon River Estuary - Crowley Creek

Restoring watershed functions

Background

Historically Crowley Creek migrated across the debris fan and tidal marsh creating mud flats and supported development of clam beds. Dikes and drainage ditches were constructed in the estuary in the 1950s to improve the marsh habitat for grazing. Dikes impede tidal flows across the surface of the marsh. Drainage ditches rapidly remove water from the salt marsh altering the groundwater regime and the plant associations that would develop under a more hydrated and saline condition. The dikes along Crowley Creek confined the flow of Crowley Creek, eliminating stream access to the associated wetlands and reducing the use of the wetland areas as aquatic species refuge during storm events.

In 1996, the dike along the Salmon River was removed, but the dike between Crowley Creek and the marsh was left in place.

Restoration Work Accomplished at Crowley Creek

The first phase of restoring the Crowley Creek marsh was done in 1996 when the dike along the Salmon River was removed. For the first time in more than 40 years the marsh was open to the tides and the river.

Planning for phase two of the Crowley Creek restoration began in 2006 with a graduate student charrette. Shortly afterward the U.S. Fish and Wildlife Service surveyor did a topographic site survey of the area. Implementation of the work was delayed until the Tamara Quays and Pixieland projects were completed.

In the summer of 2012 the dike along the eastern bank of Crowley Creek was removed. Additionally, a larger culvert was installed under Three Rocks Road for a small tributary to the west of Crowley Creek. During the restoration project, beavers dammed Crowley Creek and effectively dewatered the project area, removing several large trees each night.

Within one year of this work being completed, the marsh vegetation in the dike removal area was well on its way to recovery. Once the restoration ground work was performed at Crowley Creek and the dike was removed from the tidal marsh, it was a strip of bare soil. Within one year, tufted hair grass became the dominant plant in this disturbed area. The planting efforts of the restoration team likely played a major role in this success, but seed brought in by the tide also likely contributed.

Other plants captured in the disturbed area have been established solely from local seed sources, also brought in by the tide. Bare ground and standing water make up the highest cover in the removed dike area. This is expected after only one year of plant colonization. Many of the non-native plants in the removed dike area either maintain a low, nonthreatening cover in the long term (i.e. spear saltbush) or are common pioneer species (e.g. toadrush).

The reference marsh transect captured a general tidal marsh plant community for the area which is mostly dominated by native plants. It is expected that the disturbed area, where the dike was removed, will develop in the same direction. While the cover of the non-native creeping bentgrass was high in the removed dike area, it also maintains a high cover in the reference marsh area. Reference marsh data from other projects in the area suggest it has become a component of these tidal marshes and the native plants appear to coexist.