Virginia Coastal Program: 2004 Coastal Grant Project Description and Final Summary
Project Task:
FY 2004 Task 85
Grantee:
Virginia Department of Conservation & Recreation/U.S. Geological Survey
Project Title:
Support to Develop Regional Channel Geometry Curves
Project Description as Proposed:
The USGS proposes
to collect data that will be used to develop regional curves for
the non-tidal coastal plain of Virginia.
This is accomplished by
identifying relations between drainage area and bankfull discharge,
cross-sectional area, width, and average depth for stream riffle
sections. Currently, practitioners in Virginia are forced to use
regional curves developed for North Carolina and Maryland to help
design stream restoration plans. This is part of a larger statewide
effort by the USGS and its partners.
This project supports many
objectives contained in the Virginia Nonpoint Source Pollution Management
Program document intended to address stream channel erosion, preservation
of natural stream channels, provide technical guidance, and strengthening
design standards and specifications for stream restoration. The
primary (g) guidance management measures this work is applicable
to are channelization & channel modification and streambanks
& shoreline erosion. Additionally, many of the Urban Runoff
measures will benefit from this project. Stream channels often are
disturbed by human activities such as construction or agriculture
and require restoration to approximate natural stable conditions
to reduce erosion and sedimentation and provide suitable aquatic
habitat. Central to the methodology of natural channel design is
that of determining bankfull discharge. Bankfull discharge is determined
by developing regional regression relationships between drainage
area and bankfull channel geometry, which are important tools for
designing and restoring stable stream channels. By identifying bankfull
characteristics at multiple stream gage locations and stratifying
them by hydro-physiographic province “regional curves”
can be developed. There are about 15 gage stations within the coastal
zone to be evaluated in this project. Sites will be selected based
on geographic distribution, current channel conditions, length of
discharge record, and watershed & flow characteristics.
The selected stations will then be visited to make onsite determinations
of bankfull stage and measurements of bankfull cross-sectional area,
width, and average depth at 2 riffle sections. Results of frequency
analyses will be used to help identify bankfull stage, but the stage
will be determined by locations of morphologic features. Modified
Wolman pebble counts (Rosgen, 1996) adapted from Wolman (1954) will
be conducted to evaluate bed-material particle size distributions,
validate bankfull discharge and corresponding stream power, and
to help determine the Rosgen Stream Classification. The riffle cross-sections
and down-stream pattern and profile (through the gage location and
including the water surface, bankfull indicators, cross-section
location, and thalweg) will be surveyed with a total station. Standard
methods/formats for data collection and storage will be prepared
to facilitate the collection, management, storage, and transfer
of project data. This project constitutes year 1 of a 2-year effort,
which will depend on future finding.
Federal Funding:
$35,750.00
Project Contact:
Jennifer Krstolic - USGS; jkrstoli@usgs.gov
Project Status:
Project Completed
Final Product Received:
Project Summary Provided by Grantee:
Reconnaissance and Surveying:
Bankfull channel geometry data was surveyed on streams in the Coastal Plain province. Eight site surveys were completed during fiscal year 2005. In Virginia, 51 sites were evaluated as potential study sites, meeting peak flow criteria. Twenty-three stations were excluded because of drainage areas too large, a great percentage of developed land in the watershed, or the presence of a dam directly upstream of the reach. Twenty-five stations were visited, with 17 excluded based on lack of bankfull channel geometry indicators, lack of adequate ratings, or lack of reference marks at the gauge site.
Survey Data collected include:
- Two riffle cross-section surveys;
- A longitudinal profile for a length of 20 times the bankfull width of the channel;
- Bed material size determined through a modified Wolman pebble count; and
- Digital photographs of the site.
Analysis:
Channel geometry surveys and bed material data was entered into the modified US Geological Survey of Pennsylvania spreadsheet. The longitudinal profile data was plotted and used in conjunction with the cross section data and field notes to select an appropriate bankfull elevation for each study site. Bankfull elevations have been selected for each site surveyed, but they are preliminary to date. Subsequent analysis of each station rating curve and recurrence interval will refine the bankfull selection to ensure that the bankfull elevations and discharges represent features formed by 1-2.5 year flood events.
Each point in the regression model will represent the average of the two cross section surveys to include the variability of each stream. Preliminary plots were created to screen the data as it was collected. To this point, sites that appear to be ‘outliers’ are the sites we hypothesized would have slightly different geometry. These add to the regression analysis, and should help represent the actual condition in streams at this time. Six Virginia streams have been surveyed, with two more potential sites that meet the criteria specified for this study. The survey demonstrated that our surveying techniques and McCandless techniques appear to produce the comparable results for bankfull cross sectional area.
Disclaimer: This project summary provides the federal dollars initially awarded to the grantee. Due to underexpenditure or reprogramming of grant funds, this figure may change. For more information on the allocation of coastal grant funds, please contact Laura McKay, Virginia Coastal Program Manager, at 804.698.4323 or email: Laura.McKay@deq.virginia.gov
A more detailed Scope of Work for this project is available. Please direct your request for a copy to Virginia.Witmer@deq.virginia.gov
