This paper updates earlier hydrologic studies of the marsh in West River Memorial Park, New Haven, Connecticut. Throughout the 1800s and 1900s, drainage, filling, and the installation of 12 tide gates (in 1919) progressively transformed the park's original salt marsh ecosystem into a system dominated by common reed (Phragmites australis). In 1992, we conducted a hydrologic study to assess the feasibility of salt marsh restoration in the park. Experimental openings of tide gates were used to quantify the increase in tidal inflow and salinity to the marsh. Average water surface elevation range was 79 cm with one gate open and 91 cm with two gates open. By contrast, average accumulation of fresh water in the marsh when all gates were closed was approximately 27 cm. Increases in salinity were detectable as far as 2.1 km upstream when two gates were opened. Salinity near the gates ranged from 9 g·l-1 at water surface to 20 g·l-1 at a depth of 150 cm. These concentrations approach the salinity required to extirpate common reed and provide favorable conditions for salt marsh vegetation. A detailed topographic survey and field measurements of tidal inflow were used to develop and validate a water surface elevation-water storage function for the site. This function can be used, in concert with hydrodynamic models, to estimate the gate openings needed to meet ecological goals and safeguard property and infrastructure. When combined with ecological and socioeconomic data and information, this study of the hydrologic structure and function of the West River Marsh provides a foundation for constructive, community-based change.