Working closely with Department of Environmental Conservation (DEC) and Port Bay Improvement Association (PBIA), Healthy Port Futures will aid in the design, implementation, and monitoring of a passive dredge management pilot project in Port Bay, NY. One of the many small bay communities located on the southwest shores of Lake Ontario, PBIA partners with DEC to strategize the dredge management of the baymouth channel and the associated barrier bar. The purpose of this project is to develop a responsive dredge maintenance methodology: This plan will seek to utilize wave energy in order to efficiently spread material along a highly erodible and frequently breached barrier bar. As a reoccurring maintenance project, this pilot is uniquely positioned to test, observe, and adapt the placement and movement of material via machinery and natural forces. Overtime, these maintenance practices will be calibrated and developed into a more elegant and efficient sediment sequencing. HPF created this initial placement and sequencing plan through research, physical modeling, and iterative design, and will monitor the results through drone imagery and survey techniques.
Port Bay, NY is a small recreational harbor situated along the southwest shores of Lake Ontario, a region characterized by alternating drumlin bluffs and baymouth barriers. The bluffs nourish the nearshore and offshore zones through erosive actions of wave notching, slumping, and gullying. Clays and silts are suspended and fluxed offshore as prevailing longshore drift disperses coarse materials, sand and gravel, towards the east. The traveling sand and gravel are the building materials for the baymouth barriers, protecting the bays, ponds, and marshes that comprise this stretch of the shoreline, creating a semi-enclosed barrier bar-bluff compartment (Pinet, 1998). However, this direct nourishment is dependent on eroding bluffs and uninterrupted east-to-west longshore drift. Shoreline hardening, jetties, and channels along the lake undermine this process, and can lead to decreased sediment supply, as well as the formation of areas of sediment accretion, and conversely, sediment starvation.
Since the jetty and permanent boat channel were built in the early sixties, Port Bay has witnessed the subsequent erosion and thinning of the sediment-starved eastern bar. In the past three years, the eastern bar has been breached multiple times: During those times, storm waves have deposited sediment over top the bar, created semi-permanent secondary inlets, and flooded the bay, threatening boats and docks housed along it. The community has been working with Wayne County Soil and Water, and the DEC, to reconstruct the bar, using machinery to spread dredge material over the length of the bar. However, the process is cost-prohibitive and cannot be considered a long-term sustainable solution given the limited resources of the community. Within this region, DEC manages several other barrier bar spits that are similarly sediment-starved and eroded. DEC has enlisted the help of HPF to study and design a more efficient passive sediment approach to utilize dredge material to nourish the bar. Accordingly, HPF has developed an initial design and placement sequencing that employs incident wave energy to move and spread material along the barrier bar. Additionally, HPF has developed a monitoring plan to study the movement of the dredge material post-placement and its impact on the morphology of the Eastern Bar
HPF will develop methods to more effectively apply wave energy to aid in the directional movement and spread of dredge material. This study will explore placement options within the current parameters; wave direction, bathymetry, sediment type, sediment amount, available machinery, contractor and knowledge expertise, and time. Working within these parameters, HPF has developed a method that places material out in the active nearshore zone, effectively re-creating an eroding drumlin bluff. Under these circumstances, machinery moves the sediment from the channel and mounds the sediment out into the nearshore zone, and similar to its larger-scale prototype, wave energy erodes the placement pile and moves it along the bar. This process be less costly, and less disruptive than relying solely on mechanical means to move and spread material. Monitoring will be an important component of the study, and will allow for an understanding of the movement of the initial placement. In turn, these insights will lead to further adaptation and calibration in future years. The project and subsequent monitoring efforts will provide valuable information into wave- driven dredge placement and movement, and provide a prototype for similar small communities in the region.
- PASSIVE SEDIMENT MANAGEMENT: An intentional use of machinery and natural forces to manage dredge material efficiently.
- LANDSCAPE SPECIFIC: An understanding hydro-geomorphological characteristics of the region and its relation to the project.
- RESPONSIVE EXPERIMENTAL PROCESS: A recognition that dredge maintenance is a process, and one that can be calibrated over time.
The design is a constructed sediment pile, placed in a drumlin-form perpendicular to the angle of incident waves. The drumlin shape, with its gentle upward grade, its wide-flat ridgeline and its steep, vertical sides, is designed to optimize the machinery forces used to construct it, and the wave forces used to erode it. The bulldozer constructs the drumlin by repeatedly pushing the material along the wide sloping ridge, higher and farther out into the nearshore, until the drumlin is at the desired length and width. The side slopes will be determined by the dredge material’s natural angle of repose. Past channel surveys indicate the dredge material is a mix of coarser material, characteristics which should allow it to be stacked high, steep, and driven over. Scaled down, but operating on the same erosive patterns seen in nearby bluffs, the waves will erode the steep sides of the dredge drumlin through notching, slumping, and gullying. The steeper the slopes, the faster the erosive process will occur. The placement of the feeder drumlin along the bar is designed to minimize the amount of travel distance needed by the bulldozer. It is placed beyond the jetty shadow, to both maximize ability of the incident wave energy to move it westwards, and to reduce the risk of sediment moving eastwards into the navigation channel. The placement location is sited just beyond the current build-up of material located at the western edge of the barrier bar.
While the general shape and location of the placed dredge material was derived from by machinery mechanics, wave direction, bathymetry, and shoreline geomorphology, physical modeling can help iterate form specifics and visualize the process of material movement. HPF tested various form iterations under various wave conditions to explore differences in how the material eroded and moved in relation to the wave direction and shoreline morphology.
While the physical modeling is broadly tuned to the conditions at Port Bay, it is not meant as a definitive, and predictive model. Rather, physical modeling is used make general inferences, to illuminate insightful patterns, and to provoke further leading questions. Instead, the shape and location of placement will be further calibrated by the continuation of experimental and responsive placement along the bar. Each year, Port Bay is dredged at a similar time by the same contractor; conditions which allow the project to be responsive and adaptive in its approach.
The Port Bay Dredged Material Monitoring Plan will provide quantitative data regarding the morphological changes of the eastern sand bar separating Port Bay from Lake Ontario. These changes will be monitored after the placement of dredged sediments along the bar in the spring of 2020. This information will:
- supplement the ongoing qualitative data that has been observed by local residents over the last decade,
- provide insight into how material placed in the nearshore environment around Port Bay moves in response to wave and wind energy, and;
- aid in the calibration of future placements to reduce shoaling in the managed channel while also fortifying the weaker areas of the bar prone to large failures.
Over the course of the monitoring period data will be collected both physically and remotely in order to monitor the morphological changes within the project area. The primary method of data collection will come by way of drone-acquired imagery that will be processed into three-dimensional data. This information will include only terrestrial formations and cannot survey sub-aquatic elevations. This will however show the deformation of the dredge bluff feature over time and indicate any changes in beach profile in response to the eroded feature up-system. Secondarily, survey transects will also be collected at particular times, weather permitting, within the nearshore (water less than 3’) with RTK survey equipment. This data can then be used to produce a more accurate shallow water topo-bathy survey, but will likely not be possible to collect during every survey.
The stretch of small harbors between Great Sodus Bay and Little Sodus Bay are characterized by the drumlin bluff and baymouth barriers complex, and accordingly, have similar sediment management issues. Through a regional sediment management approach, key commonalities can be instrumental to understanding individual harbors’ needs. Additionally, DEC manages many key places along the shore, including baymouth barriers and actively eroding drumlin bluffs, suggesting an opportunity for holistic planning.