One of our important tasks during the spring is to measure the volume of water coming out of the marsh.  This volume impacts the ease of fish passage into the marsh.  When there’s plenty of water spilling out of the marsh, the alewives may have an adequate column of water to swim up through and into the marsh.  More likely, as the volume of water decreases throughout the spring, in May when we might expect alewives, the water flow may be an issue.  We have learned that the biology of alewives don’t allow them to jump as salmon do.

We’ve learned that the culvert that was replaced in the late summer of 2015 was engineered with weirs (internal sections that trap water and create pools) based on the water flows of three similar “gauged” streams that had measured water flows and were located in New Hampshire and Massachusetts!  We want to collect data to “ground-truth” these water flows and to know, over time, what the expected flow out of our marsh is when alewives are migrating.  This information would be essential to providing adequate fish passage, as is the goal of the Conservation Commission, and why a “nature-like fishway passage” is the next step to allowing alewives to return to the marsh.