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Problem: As a result of the combined effects of surface-water flow modifications (canals, ditches, and channelization), tidal influences, and slight topographic relief, localized areas in southeastern Virginia have poorly defined surface-water flow boundaries. The flow boundaries are defined by the existing 11-digit hydrologic unit code designations (HUC). In some localized areas, surface-water flow across these boundaries is routinely observed. The location of these boundaries is important to wetland management in the Commonwealth of Virginia because wetland damage or destruction is required to be mitigated within the watershed of the original wetland.

Objective: The overall objective of the project is to better define and describe the locations of the 11-digit HUC boundaries in selected areas of southeastern Virginia.

Relevance and Benefits: This study addresses water-resource issues in the coastal zone, a priority of the FY2000 USGS-WRD Federal-State Cooperative Program. In addition, the study meets the goals of the USGS Strategic Plan by providing science to expand our understanding of environmental and natural resource issues on a regional scale. Specifically, the study will help us to better understand the flow of water in the tidally affected low-gradient streams that are typical of the Mid-Atlantic Coastal Plain. In addition, the study will help to further define the drainage divides of streams flowing across the Virginia-North Carolina interstate boundary and will assist the Commonwealth of Virginia and local jurisdictions in their management of wetland resources. The overall benefit of the study will be to provide the Commonwealth of Virginia with data that will be useful for administering potentially contentious policies related to wetland resources.

Approach: The HUC boundary between the London Bridge Creek and West Neck Creek watersheds lies near and parallel to Dam Neck Road. A network of water-surface elevation recorders (transducers) will be established on either side of the HUC boundary on both London Bridge Creek and West Neck Creek from about Potters Road to Princess Anne Road. Datums will be determined for each stage recorder and will be referenced to mean sea level. Datum elevations will be determined by a differential GPS (Global Positioning Satellite) survey. Continual water-surface elevation will be measured and recorded. The stage-recorder network will be used to define water-surface profiles and gradients on either side of the HUC boundary throughout a range of hydrologic conditions. Periodic measurements of flow direction and depth-integrated velocity will be made at each stage recorder.

  A flow meter will be installed near the existing HUC boundary to measure longitudinal streamflow velocity and direction in the channel. Measurements of velocity and flow direction will be recorded in conjunction with the network stage measurements. Measured velocities will be integrated over the elapsed time between the flow reversals caused by lunar tides. The result of the integration of velocity over time will provide an estimate of the distance a parcel of water can travel, relative to the HUC boundary, over a tidal cycle. The maximum of the resultant distances will be determined for both flow directions.  This distance is the maximum distance a particle could travel toward the basin divide and cross the divide as the next reversal is initiated. This distance will define the "buffer region" on both sides of the HUC boundary. Measurements of stream stage will be used to refine the results of the velocity integration. It is believed that this approach, with some modification and refinement, will be employed in areas 3-5 during Phase II.