Document Type
Report
Department/Program
Virginia Institute of Marine Science
Publication Date
12-2023
Abstract
The Initial Phase of the project (Phase 1), used remote sensing and other data collection to develop a method for determining which waterbodies on the Northern Neck of Virginia need dredging. The analysis included most of the waterbodies in the counties of Lancaster, Northumberland, Richmond, and Westmoreland. From this analysis, 19 waterbodies emerged as potentially needing dredged based on physical parameters and residential and economic usage (Milligan et al., 2023).
In this Feasibility Phase (Phase 2), more detailed site data were collected to provide data to the localities for consideration. These tasks were included in the analysis:
1. Historic shore evolution.
2. Bathymetric data were collected in the waterbody;
3. Sediment sampling of the upper 1-2 ft of the bottom was performed to determine surface sediment type;
4. Structures adjacent to the channel were assessed;
5. Channels were determined based on whether they were federal, non-federal, or non-federal with aids to navigation (ATONs). Eight federal channels were included in this Feasibility Phase, and the federally-defined channel was used for those waterbodies. However, two waterbodies, Cranes Creek and Monroe Bay, have a federal channel only at their mouth. For this Feasibility Phase, the channel was extended farther into the waterbodies. For non-federal channels, the bathymetric data was used to determine where the natural channel occurred and using aids to navigation (ATONs) where available.
6. Channel volume was calculated based on the maintenance depth plus 1 ft of overdepth. This determines the size of the project and how much area will be needed for disposal of material.
7. The potential disposal location (upland vs. shoreline) was determined for each channel based on sediment type. For shoreline placement, potential adjacent sites are shown.
The goal of these data collections and analysis is to provide information to the localities regarding the waterbodies that may need to be dredged to maintain residential and economic usage. It can be used to prioritize dredge channel funding as it becomes available for design and construction. This is a scoping level analysis and should be used for planning purposes only. The parameters chosen for analysis such as proposed channel location and channel depth can be modified during the final design process to fit the needs of the community and to fit available costs. Additional data is needed for final dredge project design in Phase 3. The most crucial data are subbottom cores that are used to determine if the surficial sediments taken for this analysis represent the overall type of material that will be dredged. If the cores reveal sediment different from the surficial analysis, then the placement options may change.
DOI
https://doi.org/10.25773/bdwy-jj38
Keywords
Dredging -- Environmental aspects -- Virginia
Recommended Citation
Milligan, D. A., Green, C. W., Hardaway, C., Wilcox, C. A., Rae, C. M., Lerberg, S., Demeo, A., Brooks, G., & Mansfield, M. (2023) Northern Neck Regional Shallow Draft Channel Dredging Plan: Feasibility Phase. Virginia Institute of Marine Science, William & Mary. https://doi.org/10.25773/bdwy-jj38
