The Buzzards Bay Coalition, a membership-supported, nonprofit organization based in New Bedford, Massachusetts, is developing a feasibility study for river restoration on the Weweantic River in the nearby town of Wareham.
In June 2012, the Coalition acquired a 10-acre property that straddles the river at the head of tide and contains Horseshoe Mill Dam. Set in a scenic spot near a major highway interchange, the property was a high priority for preservation in order to prevent it from getting developed, and to provide public access to the river, and restore wildlife habitat – particularly for diadromous fish species.
Constructed in the early 1800s, Horseshoe Mill Dam is the first obstruction to fish passage on the Weweantic River, the largest tributary to Buzzards Bay and historically one of the most productive fish runs. It is one of the most promising and unique diadromous fish resources in Buzzards Bay, as it contains a diverse community of migratory species, including rainbow smelt and wild Eastern brook trout in its lower tributaries, in addition to alewife and blueback herring, American eel, white perch, tomcod, hog chokers, lamprey, and possibly shad.
Fish passage is severely limited by the Horseshoe Mill Dam. Additionally, the extent of a unique and important tidal freshwater wetland plant community, which includes a number of species that are rare in Massachusetts, is limited by this dam.
Restoration at this site will open migratory fish passage to more than three miles of river habitat, as well as allow for adaptation of coastal wetland habitats to climate change. Removal of the barrier caused by the dam will have wide-reaching benefits for fisheries, rare plant communities, and associated wildlife by restoring river continuity and enabling coastal wetland habitats on protected lands above the dam to adapt with expected sea level rise.
To determine a river restoration design, critical baseline data must be collected to inform the feasibility study and assess restoration alternatives (e.g. topography, bathymetry, sediment analysis, hydraulic modeling, etc.). In particular, detailed water level data above the impoundment is needed as an input to hydrologic and hydraulic modeling associated with the project. "We're trying to assess water flows into the impoundment," said Sara Quintal, a restoration ecologist with the Coalition. "When we start modeling restoration alternatives at the dam, water level data will feed into the model."
To track water levels, the Coalition team first selected a stream crossing above the impoundment as a continuous water level monitoring location due to its proximity to the project area and the prior existence of a U.S. Geological Survey (USGS) staff gauge.
Then, the team deployed a HOBO® U20 water level logger from Massachusetts-based Onset to collect water temperature and pressure data at five-minute intervals. The instrument features a sealed, non-vented design to make logger deployment in the river faster, easier, and more maintenance-free. The logger also provides a USB-based optical interface for high-speed offload of the collected data in wet environments. The optical design also eliminates the need for failure-prone mechanical connectors found in many traditional water level logging instruments.
To prepare the logger for deployment, it was connected to a computer via USB cable, and configured in a matter of minutes using accompanying HOBOware® Pro graphing and analysis software.
The logger was first attached to a tree in the project area and cross-calibrated for barometric pressure with pressure readings from a nearby site. Once the barometric pressure between the two sites was deemed comparable, the logger was installed in the river channel within a PVC settling column affixed to a bridge support to continuously measure water levels at five-minute intervals.
"The five-minute sample rate was informed by guidance provided by the Massachusetts Division of Ecological Restoration, based on monitoring they have done at other sites," said Quintal.
Water level data is being periodically offloaded using a waterproof data shuttle device. The shuttle provides safe transport of the data from the logger to a computer, where the data can be viewed and analyzed using HOBOware software. The software displays the level measurements in graph form to show profiles over time, which Quintal can check against staff gauge readings from the site. Data can be viewed in tabular form as well, or exported to a spreadsheet for further manipulation.
The feasibility study is still in process and more baseline data will be necessary to inform an assessment of feasible options for ecological restoration at the Horseshoe Mill Dam site.