Develop Sonar Data Mapping on Three Rivers to Assess Suitability for Native Mussel Habitat

Science Center Objects

The National Park Service Mississippi National River and Recreation Area and the St. Croix National Scenic Riverway is known for their conservation efforts of threatened and endangered native freshwater mussels. Understanding what constitutes mussel habitat is important for identifying suitable habitat for the conservation and restoration of freshwater mussels. Mussel habitat has not been well quantified partly due to the lack of information on benthic conditions in turbid, complex large river systems.

 Bathymetry is a desirable dataset because along with depth measurements, it shows geomorphology patterns used in hydraulic modeling. Understanding the physical and hydraulic factors of large rivers might help to understand what drives the distribution and abundance of freshwater mussels. While logging high-resolution bathymetry, a multibeam echosounder simultaneously collects backscatter measurements used to obtain information about the sediment composition and physical properties of the riverbed. Sidescan sonar is a useful technology for examining features of aquatic systems because it produces a high-resolution two-dimensional image of the underwater landscape.

 

An example of a bathymetric dataset (water depth) used to analyze benthic habitats.

An example of a bathymetric dataset (water depth) used to analyze benthic habitats.

(Public domain.)

 The primary goal for this project was to collect high-resolution sonar information of benthic characteristics that can be useful in identifying preferred native mussel habitat in these corridors. The scope of the project is contained within both park boundaries, and covers portions of three rivers: the Mississippi, Minnesota, and St. Croix River. The National Park Service obtained support from the Legislative-Citizen Commission on Minnesota Resources Environment and Natural Resources Trust Fund.

A UMESC scientist navigating the Mississippi River for a bathymetric survey.

A UMESC scientist navigating the Mississippi River for a bathymetric survey.

(Public domain.)

High-resolution swath multibeam and sidescan sonar was surveyed for the lower 48 kilometers of the St. Croix River (depths up to 7.6-meters), and within the Mississippi National River and Recreation Area where no current bathymetry exists. Priority areas, where NPS scientists desired more information, had additional mapping efforts consisting of measured river current velocities and substrate mapping.