To study the movement of sediment along the Presque Isle Bay shoreline in Erie Pennsylvania the U.S. Army Corps of Engineers Buffalo District is conducting a particle tracer study to determine if material dredged from Erie Harbor Shipping Channel can be used to nourish and enhance the shoreline growth on the peninsula.
Presque Isle Peninsula and Erie Harbor are located on the southern shore of Lake Erie. The peninsula is a recurving sand spit that forms and protects the harbor. The peninsula is home to Presque Isle State Park which is home to seven ecological zones or landscapes and dune and beach plants that are found no where else in the state. The peninsula formed naturally thousands of years ago and is constantly being reshaped by wind and waves.
As part of the Presque Isle beneficial use demonstration project the U.S. Corps of Engineers environmental analysis team went to Erie Pennsylvania on July 20 with a pontoon boat to deploy three water quality meters (called sondes) around the area. The sondes will stay in place until October 2015 gathering baseline water quality data (i.e. turbidity) to enable the Corps to characterize the water quality impact (if any) of placing dredged material from the Erie navigation channel offshore Presque Isle to facilitate beach nourishment.
Approximately every five years the sediment dredged from Erie Harbor about 200000 cubic yards is typically placed in an open-water disposal area in the lake three miles offshore.
Josh Unghire Corps restoration ecologist Andrew Hannes Corps biologist and Weston Cross Corps geologist explained that while the sediment mostly fine sand silt and clay is not suitable for beach placement the study hopes to show that the material can be beneficially used by reintroducing the sediment into the littoral process and in turn growing Gull Point the terminal end of the peninsula.
The Erie Harbor federal navigation channel where material is dredged has an authorized depth of 29 feet in the entrance channel and the harbor varies from 18 to 29 feet in depth. About 200000 cubic yards were dredged in the channel in 2015 and the Corps expects to remove the same amount next year. Previously 237000 cubic yards had been dredged in 2011.
The dredged material in open-water placement “doesn’t get to participate in the littoral process” Unghire said. In addition the north shore area along the eastern tip experiences erosion problems. The Corps is considering beneficial use options for shallow and deepwater placement to aid in the growth of the peninsula.
The Buffalo District is conducting the study in conjunction with the Corps Engineering Research and Design Center (ERDC). The project aligns with the goals of ERDC’s Engineering With Nature (EWN) Program which tries to enable sustainable benefits for water resources infrastructure. As the EWN websites states “EWN is the intentional alignment of natural and engineering processes to efficiently and sustainably deliver economic environmental and social benefits through collaborative processes.”
The Presque Isle study project is trying to do just that – combining the engineering for sediment placement with natural hydrodynamics around the peninsula to aid in its growth. The beneficial use of dredged material may slow the natural processes that continue to erode the shoreline.
The study proposes sand placement in three places – north of the peninsula near the beach east of the tip of the peninsula in shallow water and farther east of the peninsula in deeper water. See the map on page 8.
“With the placement site that is closer to shore the thought is to get some natural sediment winnowing or separation of the particles getting some portion of the sediment to move into the system” Cross said.
The other placement sites off the eastern tip of Gull Point – one shallow and one deep – will add to an underwater shelf with the hope that littoral more coarse sands coming from an updrift will mix with the finer sand and deposit on the underwater shelf and help naturally build up the beach profile. Cross said the natural current transport is west to east and the water gets deep relatively quickly off the tip of the peninsula. Because of erosion in the natural system every square foot of growth on the peninsula requires much larger amounts of sand he said.
The Buffalo District serviced the three turbidity meters at Presque Isle on August 4. The Corps said the anchorages appear to be holding as all three have maintained their position over the first 1.5 months of deployment. Data was downloaded and the batteries were replaced. Units did have some biofouling mainly small dressenids and macroinvert casings. A wiper on the sensor head keeps fouling from growing on the sensor window. The sensors will stay in the water until mid to late October.
To track the movement of the sediment in the system the study will use tracer particles from Environmental Tracing Systems Ltd. The particles are polymer filled and designed to be negatively buoyant and behave like natural silt and sand. The particles are manufactured to mimic the characteristics of dredged material including the size gradation density hardness shape and fall speed within the water column.
On July 23 the Buffalo District awarded a $473116 contract to URS Corporation and Baird Inc. to do the work of deploying the tracer particles and collecting soil samples. Preplacement soil samples will be taken as well to understand background levels and other particles that might skew the results. Analysis can detect very low levels of tracer particles in the sediment sample (as low as one part per billion) which enables tracking of the particles through significant wave and current action.
The Corps is considering two methods for deploying the tracer particles one being with the dredged material. The tracers would go directly into a scow with approximately 1500 to 4500 cubic yards of material bound for one of the three offshore placement sites. In total the study will deploy 1500 pounds of tracer particles. Deploying the tracers with the sediment will require certain environmental permits which the Corps is still awaiting. If permits do not allow that measure contractors will drop the tracers separately from the sediment by boat. Either is effective for mixing the tracers into the natural flow of the sediment.
The tracer particles are 78 percent by weight the naturally occurring mineral barium sulphate; three percent by weight fluorescent pigment; 14 percent polymer; and the remaining five percent a surfactant. It was important for the study that the percentage of the polymer compared to the total particle weight remains small according to the “Presque Isle Beneficial Use of Dredge Material Demonstration Project – Scoping Information” published in July 2015. ETS said the particles are environmentally benign and are not a danger to water quality or marine animals.
“The idea is our contractor will place the tracers then collect soil samples all over in the area” Unghire said. By analyzing the soil samples and the distribution of the tracer particles “we can make assumptions about where the majority of the material is moving” he said. The Corps can use that data to determine if dredged material placement in those areas will reduce erosion of Gull Point.
The study will also monitor turbidity. Measurements being taken now will serve as baseline measurements to compare with future data in order to see if the sediment placement has any effect on localized turbidity nearshore water quality or sand composition along the shoreline.
Dredging around Presque Isle must take place in a window that protects the piping plover’s breeding season from April 1 to June 30. The deployment of the tracer particles is scheduled for next summer to coincide with the dredging cycle and soil samples will be collected for one year.