Bass Creek, tributary to Green Harbor River (Marshfield, MA) was a tidally influenced stream, prior to tide gate failure, followed by years of sedimentation and vegetative infilling. Riparian wetlands shifted from Spartina alterniflora to Phragmites australis. A 2008 Town / MA CZM project repaired the tide gate, increasing tidal flow and salinity from 11.1 ppt to 25 ppt, 6,700 feet upgradient of the tide control structure. However, the years of Phragmites channel occlusion impeded restoration of the upgradient tidal creek. In 2014 GZA designed, permitted and monitored a Bass Creek restoration effort to remove Phragmites via dredging of the channel, allowing tidal influence to channel areas 4,000± feet further upgradient. Project goals included tidal creek and salt marsh restoration, storm flow conveyance, reduced flooding, and improve wildlife habitat.

GZA has been involved in the monitoring of Bass Creek Restoration Project since 2014. Prior to restoration efforts salinity values in this portion of Bass Creek ranged from 0.0 to 0.2 ppt. Initial post dredging salinity monitoring in Bass Creek showed a dramatic change in salinity from ?0.2 ppt to >18.1 ppt ~9,500 feet upgradient of the tide gate, and significantly increased salinity values and tidal influence an additional 500 feet upgradient (> 5.0 ppt). Further, the 2014 restored tidal areas showed significant browning and poor growth of Phragmites, Scirpus cyperinus, Typha latifolia and other freshwater wetland species up to 10,000 feet upgradient of the tide gate. In areas where restored tidal influence yielded salinity <12 ppt, there was no detectable effect on Phragmites or other freshwater wetland species since 2014. Concerns for a new, further upstream zone where salinities will favor the incursion of Phragmites have thus far not materialized.

Mr. Riberdy is a senior ecologist at GZA GeoEnvironmental, Inc. He has been working in ecological restoration for the past 15 years across the northeast. His specialties are wetland ecology, rare species surveys and management, floristic surveys and restoration projects. He holds a MS degree in wetland ecology from UMASS Amherst, is a Professional Wetland Scientist with SWS, a Certified Ecologist with ESA, a Certified Wildlife Biologist with the wildlife society and a professional soil scientist.