Sand and Gravel of the Wells, Maine, Embayment: Nearshore and Barrier Sediment Volumes and Transport Paths in a Heavily Coastal System

Lead Pi: Duncan Fitzgerald · 8/1996 - 7/1997

Project Personnel:

Project number: 1996-RC-50

Objectives:The major objective of this study is to determine the Holocene stratigraphy and evolution of the Wells Embayment shoreline. Determination of the thickness and sequence of sedimentary facies comprising the barrier lithosome, underlying estuarine and lagoonal deposits, and bounding Pleistocene units in the Wells Embayment, will allow the construction of stratigraphic cross sections of the coast and formulation of evolutionary models for this region. A determination of the stratigraphy of the coastal barriers will enable the volume of sand contained in these systems to be calculated. Knowledge of the geological development of this coast and the thickness of the barrier sands will provide a means of assessing the stability of these heavily developed barriers in a regime of increasing sea level rise. A secondary objective is to assess whether the five tidal inlets in the study area are contributing sand to the nearshore and beach system, or if they are coarse-grained sediment sinks. Data collected by the author at three of the inlets (Ogunquit, Wells, and Little River) in previous investigations indicate that they are dominated by landward sand transport and represent long term sand traps. This trend of sand movement into inlets will be assessed at all the inlets using existing information and will be tested at Mousam and Kennebunk Inlets where to hydraulic data are available. Methodology:The straigraphy of the barriers is determined through the use of ground penetrating radar (GPR), the collection of sediment cores, and topographic surveys. GPR provides and X -ray view of the barrier deposits and underlying sediments. GPR profiles are being collected at each of the barriers along shore parallel and shore normal transects. Profiles taken along the length of the barriers provide information concerning former tidal inlet positions, underlying bedrock topography, and barrier evolution, whereas the shore normal transects are used to identify to accretionary history of the barrier and complete the grid necessary for isopach map construction. Initial analysis of the GPR records of a particular barrier form the basis for determining locations of vibracoring or pulse auger coring, which are taken to identify the lithology of the different radar facies and the true depths of the GPR reflectors. These data provide a basis for constructing stratigraphic sections of the barriers, for developing barrier evolutionary models, and for computing barrier lithosome volumes.The hydraulic and sedimentologic character of Kennebunk and Mousam Inlets will be determined through the collection of tidal current, estuarine, and bedform data. The field data will consist of current velocity, salinity, and temperature measurements recorded through the water column and across the inlet throat at four to five stations. Measurements will be made every hour over a complete tidal cycle during various tidal range conditions (spring to neap). The existing inlet data base together with the information we collect in this study will provide a means for assessing the sedimentation behavior of the inlets and their relative importance in the Wells Embayment sediment budget. Rationale:The study area consists of thin barriers and small tidal inlets anchored to bedrock and glacial headlands. The beaches of this region are eroding and the many (missing word) the navigation channels suffer continual shoaling. Seawalls and jetties built to treat these problems have exacerbated the conditions. Towns and State agencies are continuously confronted with building permits, dredging applications, and other coastal construction projects that they must act on without sufficient scientific data. This project will provide a sediment budget and paths of sand exchange for this region. This information will allow the impacts of construction and dredging projects to be determined.