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New Inlet Improving Water Quality In Pleasant Bay
by Tim Wood The bad news is that sand flowing into Pleasant Bay from the new inlet in North Beach smothered a 50-acre eelgrass bed. The good news is that the improved water quality due to the inlet created the potential for 1,400 acres of new eelgrass beds. Computer modeling shows that the increased tidal flow between the bay and the Atlantic fostered by the inlet should improve water quality throughout the bay, especially in the most impaired areas such as Muddy Creek and Frost Fish Creek. “We’ll end up with a system that’s in better shape than it was,” John Ramsey, principal coastal engineer with Applied Coastal Research and Engineering in Mashpee, told a full house at the Chatham Community Center last Thursday during the Pleasant Bay Resource Management Alliance’s annual summer symposium. While the inlet created in April 2007 will probably result in the best water quality in the bay in 150 years, Ramsey and others cautioned against relaxing efforts to mitigate nitrogen loading problems through sewering and other methods. The constantly shifting nature of the inlet and North Beach means that water quality won’t remain top-notch forever, and the state is likely to insist that nitrogen reduction targets for the bay set prior to the inlet still be met. The current situation is a “snapshot” in time, Ramsey said, and state officials could point to what was even poorer water quality prior to the 1987 break and insist on even more drastic reductions in nitrogen loading. The question of lowering the nitrogen loading targets, known as TMDLs, was posed to the state department of environmental protection, added Dr. Robert Duncanson, director of Chatham’s department of health and environment. An answer hasn’t been forthcoming. But it will take two or three decades to sewer the watersheds that drain into the bay, and water quality is likely to change over that period. “This break is changing on a daily basis,” Duncanson said. “It’s not stable.” Bay water monitoring results from last summer did not show a significant increase in quality, he added, but that was before the inlet widened over the winter. Monitoring will continue this summer. Ramsey presented preliminary results from a hyrdrodynamic and water quality modeling study being conducted with funding from the Army Corps of Engineers and the Alliance. Although the data did not cover the period after the inlet began to widen following storms last November, it still showed a significant impact in both Big and Little Pleasant Bay, including a 19 percent increase in tidal range, or .7 feet, and a 15 percent increase in the amount of water flowing into the bay, which translates to a more efficient exchange and better overall water quality. Dr. Graham Giese, a coastal geologist with the Provincetown Center for Coastal Studies, found even greater increases in tidal range. In a study done in conjunction with Mark Adams and Kelly Chapman of the Cape Cod National Seashore, Giese measured tide ranges with gauges set at Meetinghouse Pond, concluding that the high tide has increased by one foot. At first low tide did not change much, but since the November storms and the widening of the inlet, “low tide has been getting lower and lower and lower,” Giese said. Aerial photos clearly show that a two-channel system has developed in the inlet. The northernmost channel flows in and out of Little Pleasant Bay, while the southernmost channel funnels water in and out of Big Pleasant Bay. This has created a much more efficient system for draining the upper bay, said Ted Keon, Chatham’s Coastal Resources Director. According to Ramsey’s study, 40 percent of the tidal was going through the new inlet as of last November. On the ebb tide, 36 percent of the flow was through the new inlet. In effect, he said, more water was flowing into the inlet than out, with the “residual” flowing out the 1987 break. Keon reviewed the significant changes in the inlet since last year’s symposium, including the severe erosion of the southern tip of North Beach over the winter and early spring, which forced the removal or destroyed by storms some half dozen beach camps. Four others were relocated to the north on property owned by William Hammatt. By mid-June, the inlet measured 3,100 feet on the outer shore, and about 2,500 feet inside. The overall erosion rate has been about six feet per day. It remains very shallow in most places and difficult to navigate, Keon said. “Do not try to get through there at low water,” he warned. “In fact don’t try to go in there except at very high tide.” So far the inlet has had little impact on the mainland, he said; unlike the 1987 break, there has not been large-scale erosion or ocean-size waves in the Minister’s Point area across from the inlet. Higher tides changed the shoreline profile in some locations, and several property owners\brought in sand to fortify beaches, and some proposed new revetments. There is good news to the south, where the navigation channel from the original inlet up into the harbor has improved. The velocity of water in the channel has slowed, reducing scouring that threatened several seawalls. Keon plan to continue monitoring the size and shape of the inlet through aerial photos. Pleasant Bay Alliance Coordinator Carole Ridley said Ramsey’s data was “hot off the presses” and had just been presented to alliance officials a few days before the symposium. A final report on the study is anticipated within a few months, she said.
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