Study shows flap gates at Mattamuskeet bring minimal change

Published 7:08 pm Wednesday, July 26, 2017

SWAN QUARTER — A recent study of the effectiveness of the aluminum flap gates at Lake Mattamuskeet shows that they produce no significant change in the flow rate of water as compared to the original wooden gates.

The Lake Mattamuskeet National Wildlife Refuge manages a series of one-way flap gates on each of the four canals that connect the lake to the Pamlico Sound. The gates prevent salt-water intrusion back into the lake.
“The replacement or repair of the flap gates is a standard management practice that has occurred since the first set of gates were installed,” said Michelle Moorman, a biologist with the U.S. Fish and Wildlife Service. “The gates can start to leak as they age. This can increase salinities slightly in the canals on the lake side of the gates and in the lake itself, although it should be noted that records dating back to 1977 show that lake salinities have never been higher than five parts per thousand.”

The joint management team, comprised of representatives from the N.C. Wildlife Resources Commission and the U.S. Fish and Wildlife Service, decided to conduct the study based on mutual concerns about the actual water-flow rates of the aluminum flap gates compared to the original wooden ones.

“Water levels in Lake Mattamuskeet are affected by the amount of precipitation and runoff flowing into the lake and the amount of water leaving the lake through evaporation and the four canals,” Moorman said. “The result of the study suggests that the change in materials from wood to metal, when the gates were replaced in 2003-2004, had no impact on the ability of the canals to move water or lake levels. The high-water levels we saw in 2015 and 2016 were caused by higher than normal precipitation.”

Criser Troutman Tanner Consulting Engineers conducted the study. Additional work is being conducted by East Carolina University to determine if sedimentation and/or rising sea levels are affecting flow rates out of the canals.