Variation of Beach Morphology along the Saco Bay Littoral Cell

Recommendations for Additional Study

Considering the length of Corps involvement and numerous studies completed on the Camp Ellis region, there is little data regarding beach or hydrodynamic conditions or processes along Saco Bay. Such long-term monitoring data is very useful in beach nourishment project design and modeling of hydrodynamic and morphologic conditions. In development of current project alternatives, the Corps has recently conducted bathymetric, topographic, and geophysical surveys to document pre-project conditions. In order to insure project success and prepare to address future erosion problems, should they arise, a detailed post-project monitoring program should be implemented. The monitoring should focus on studying the fate of sediment placed as part of the beach nourishment project (should it be undertaken), and the impacts of jetty alterations/additions on the existing hydrodynamic processes. Since Saco Bay is considered an enclosed littoral cell (Kelley and others, 1995), post-nourishment monitoring should encompass the entire Bay. The Bay is approximately 43,000 ft in length (along the shoreline) from Hills Beach north to Pine Point, with approximately 3,500 ft comprised of the Saco River and Goosefare Brook waterbodies (e.g., inlet widths). The proposed Section 111 Mitigation Project site extends approximately 2,500 linear ft north of the northern jetty of the Saco River. It is suggested that the monitoring program include:

Beach Profiles
- Spatial Coverage: Due to the relatively small size of the project, profiles should be established at a high density (e.g., every 100 ft) along project length than the remaining Saco Bay shoreline. The remaining shoreline should be sampled at random 2,000-3,000 foot spacing, allowing for the total number of profiles to range from 19-25. Siting of profile benchmarks should take into consideration ease of access, and documentation of entire active profile is imperative. Profiles should extend from benchmarks of known elevation, generally from the back-dune seaward to 'depth of closure' or 3,000 ft seaward of the MHWL, whichever is farther (Dean and Campbell, 1999), with survey points at an average spacing of 10-15 ft horizontally and 0.1-0.2 ft vertically (Kriebel, 1995).
- Temporal Coverage: Profiles should be completed at a minimum annually at one-year, two-year, and three-year post construction intervals, and biennially thereafter (Dean and Campbell, 1999). In order to document shorter-term profile variations and seasonal fluctuations, if possible, profile monitoring should be completed 6 times a year for the initial two years post-construction, then annually thereafter. Profile collection should occur as close to low-tide as possible. Monitoring should also occur post-storm (e.g., 20 year storm minimum) to document beach response, when possible (USACE, 1995b).
Mean High Water Line (MHWL) Variation: The alongshore variation of the MHWL should be surveyed in order to document fluctuations in dry-beach width at the project site and within study boundaries. Surveys should correspond with times of beach profile collection.
Aerial Photography: Aerial photograph flights documenting the immediate project area and study boundaries should be flown prior to, and immediately after completion of construction. Biennial flights thereafter should be sufficient to document overall geomorphologic changes.
Sediment Sampling: Samples should be collected prior to and immediately post-construction. Collection should then correspond with timing of cross-shore surveys. Sampling should occur at toe-of-dune, vegetation or seawall line, mid-berm location, and at mean high water contour (Dean and Campbell, 1999). Samples should be analyzed for grain size, color, texture, and percent organic material matter.
Current and Wave Sampling: It is suggested that modern, efficient and effective monitoring equipment be employed, such as a personal watercraft outfitted for hydrodynamic sampling (e.g., Dugan and others, 1999). An Acoustic Doppler Current Profiler (ADCP) can be mounted on the personal watercraft to provide current measurements during nearshore surveys. Wave gauges and ADCPs could be installed at seaward end of northern jetty and adjacent to the spur jetty for certain monitoring periods to monitor effectiveness of whatever structural solution, if any, is used, in lessening northerly-directed alongshore currents and wave heights. If an offshore borrow site is chosen as the source of sediment for the nourishment, additional monitoring should include the borrow site. If cost inhibits the installation of wave gauges and ADCPs, it may be possible to implement a Littoral Environment Observation (LEO) program with members of the Camp Ellis community (USACE, 1995b).

Continued Research

The Maine Geological Survey (MGS), in conjunction with scientists at the University of Maine (Orono), recently received a Maine Sea Grant award for a project titled Monitoring Coastal Dynamics at the Saco River Mouth Near Jetty Modification and Beach Nourishment Projects. The project will span 2 full years and will test the hypotheses that proposed engineering alterations to the north jetty at the Saco River mouth will significantly reduce incident wave energy at Camp Ellis and reduce the rate of alongshore transport (erosion) away from that area, in addition to confirming that the Saco River is a major source of sand to the beach and nearshore system, and that alongshore drift carries sand to the north along the Saco Bay littoral system, through observation of the redistribution of the beach-nourishment material.

MGS also received an award from the Maine Marine Research Fund for an additional project, Three Dimensional Beach and Nearshore Bathymetric Surveys and Sand Budgets. Funds will be used to construct a Nearshore Survey System (NSS) based on a personal watercraft platform outfitted with a high precision Real-Time Kinematic (RTK) Global Positioning System (GPS) and high accuracy fathometer. The extremely mobile system will enable detailed three-dimensional surveys within the highly dynamic surf zone, which will allow much more precise quantification of nearshore sediment budgets.

These projects will provide data vital to understanding sediment migration pathways within Saco Bay, and will develop a hydrodynamic framework for the processes governing sediment movement within the bay.

Contents Introduction Historical Background Methods Results Discussion Recommendations Conclusions Additional Study and Research References Appendix A

Last updated on January 10, 2006.