Virginia Coastal Program: 2005 Coastal Grant Project Description and Final Summary
Project Task:
83
Grantee:
Virginia Polytechnic Institute & State University
Project Title:
Developing Strategies for Urban Channel Erosion Quantification in Upland Coastal Zone Streams
Project Description as Proposed:
The overall project goal is to quantify sediment contributions due to channel enlargement of urban streams using a combination of the best available and most relevant modeling and field-based procedures. Currently, the State of Virginia is not accurately capturing the true volume of sediment that is affecting our rivers and streams. This project could position the State better to address the true source of sediment and allocate the resources to address it.
Introduction:
While considerable effort has been directed toward reducing erosion from agricultural and urban lands, a major source of sediment - streambank erosion - has received little attention. Studies have shown that sediment from streambanks can account for as much as 85% of watershed sediment yields (Simon et al., 2000). Because of the process complexity and the lack of physically-based algorithms to describe these processes, quantification of this source is often underestimated in current state accounting procedures both for state programs and for the regional Chesapeake Bay Program. The proposed research will attempt to quantify the volume of stream sourced sediment affecting our water resources and identify the most widely applicable approach for estimating sediment loading from channel degradation and the most appropriate field-based monitoring techniques for future model calibration and verification. It is important to note at this point that there are two main techniques proposed herein: 1) evaluation of change over time at specific points on a stream; and 2) a substitution of space for time.
Modeling Objectives:
1. To identify significant watershed characteristics related to channel erosion and associated nutrients;
2. To compare existing models on the basis of how well they represent these important characteristics;
3. To assess the ability of existing models to represent various types of BMPs that can affect runoff behavior, sediment transport, and in-stream sediment generation; and,
4. To assess modeling data needs and available data sources.
Field-Based Objectives:
1. Review of existing USGS, VDOT, and local government stream geometry data; and
2. Monitoring-based approach (using a statistically randomized procedure for site identification):
Tier 1: Space-for-time cross-sectional evaluation of 50 sites
Tier 2: Comparison of field-based channel erosion monitoring over a six-month period at each of the three major land uses, in each of the two physiographic provinces under Coastal Zone Management, with two replicates of each (12 sites total)
Tier 3: Selection of a subset of two Tier 2 sites for future detailed study (not to be conducted within this proposed workplan).
Under the field-based objectives, we will undertake two main activities aimed at better understanding the impact of urbanization on channel erosion: 1) collection of existing data to evaluate historic changes in streams due to increased urbanization; and, 2) a 3-tiered field study with linked GIS-based analysis to measure streams across a range of watershed conditions.
Review of Existing Data
We will conduct an extensive review of existing channel cross-section data to develop relationships between channel enlargement and upstream watershed condition. Our data-mining activity will focus on three main data sets:
1. USGS Gage Stations and Hydraulic Geometry Relationships
a. An analysis of the regional curve data/studies available in Virginia and nearby states will be conducted. Since these data were developed for stable rural channels, they will represent the reference, undisturbed channel condition.
b. For USGS gage sites we will obtain historic resurveys to determine if channel cross sections have changed significantly at any sites
2. Historic Channel Cross Sections
a. We will investigate sources of historic channel cross-sectional data through several state agencies (particularly the Virginia Department of Transportation – VDOT). Sites where bridges, culverts, or utilities (e.g., Colonial Pipeline) were installed in the past often have cross-sectional surveys included in their design plans.
b. Comparison between the historic cross-section surveys and new surveys will allow us to compute enlargement ratios and to estimate the amount of sediment (as an annual average since the original survey) contributed to the water body.
3. Local Government Data
a. We will also investigate the existence of historic cross-section data from local governments. In particular, we expect to find some detailed stream studies in Chesterfield, Fairfax, Henrico, and Hanover Counties.
b. These data will be analyzed in a similar manner to that described in section 2 above.
Field Data Collection
Tier 1: We will select 50 independent sites on small streams (1st to 3rd order with watershed areas less than 100 km2). Half of these will be in the Piedmont and half will be in the Coastal Plain; all within the Coastal Zone Management area. We will focus on smaller streams because 70-90% of all stream miles within a watershed are headwater streams. Sites will be selected as a subset of stations identified by VDEQ’s probabilistic monitoring (ProbMon) program.
At each of these sites we will conduct a rapid during Spring 2007. In addition, we will select these sample sites in areas with detailed GIS data to utilize existing total impervious area (TIA) data layers, or to develop them based on available data.
Data from this Tier 1 rapid survey technique will allow us to evaluate existing relationships of enlargement ratio and watershed condition.
Tier 2: A subset of the Tier 1 sites will be selected for more detailed analyses. A total of 12 sites will be selected. Within each CZMA physiographic region we will select two stream reaches within rural, relatively non-impacted watersheds; two with watersheds with older urban developments (> 30 yrs); and, two in watersheds with new urban development (< 10 yrs). Within these 12 Tier 2 study streams, we will select study reaches of 10-20 bankfull widths in length. Detailed surveys in late spring (May) will be conducted with a total station for each stream reach, as well as pebble counts and habitat assessments at the beginning of the study period. Within each of these study reaches, two cross sections (at riffles) will be permanently monumented to allow for resurveys over time. The locations of the permanent monuments and the reach ends will be identified using GPS. We will resurvey the monumented cross sections two additional times during the study period – once during late summer (mid-August) and again in late fall (early November) – to quantify channel erosion during the study period.
Approximately 2-3 m downstream of each of the cross-section area locations, we will describe the soil profile within the channel (horizons, depths, texture, structure, boundaries, redoximorphic features, Munsell colors). These samples will be analyzed for nitrogen and phosphorus content. We will also collect a sample for each horizon to calculate nutrient losses per unit volume.
Advisory Committee:
To make the research results as widely applicable as possible, an advisory committee will be created that will include representatives from local government, federal (USGS and/or CBP), and state government. The committee will be convened twice during the study period to guide the assessments and recommendations produced from this project. Our proposed advisory committee consists of the following: Bob Kerr (Kerr Environmental, Inc.); Leo Snead (VDOT); Mark Bennett (USGS); Mike Flagg (Hanover County); Todd Janeski and Scott Crafton (DCR); and representatives to be determined from DEQ and DGIF.
Federal Funding:
$87,000.00
Project Contact:
Gene Yagow - eyagow@vt.edu, (540) 231-2538
Project Status:
4/1/2007 - 3/31/2008; Project Completed
Final Product Received:
"Developing Strategies for Urban Channel Erosion Quantification in Upland Coastal Zone Streams" (PDF)
Project Summary Provided by Grantee:
The overall project goal was to determine how much sediment in streams came from erosion of the stream channel itself due to urban development. To determine the impact of urban development on stream channel erosion, 50 small streams within the Coastal Zone Management area of Virginia were selected: half of the streams were in the Coastal region and the other half were in the Piedmont. The study streams varied in size, as well as in the amount and age of upstream development. Each of the study streams was surveyed to determine stream width, depth, and area. This study found that Piedmont streams were generally wider than Coastal Plain streams for a given watershed area.
A subset of 12 streams was selected for more detailed analyses (six in each region). Within each region, two streams were selected within rural watersheds, two in watersheds with older urban developments (> 30 yrs), and two in watersheds with newer urban development (< 10 yrs). More extensive surveys were conducted on these 12 streams. Data analysis was conducted to determine if the stream channel size, and thus the amount of soil eroded from the channel, was related to the amount or age of upstream development. The analysis did not indicate any particular pattern between stream size and the steepness of the land draining to the stream or the amount of upstream development. Additionally, comparisons of similar rural and urban streams showed no distinct relationship between channel erosion and urbanization. The lack of a distinct relationship between urbanization and channel size was likely due to the inherent uncertainty in measuring and comparing stream channel dimensions. Also, measurement of changes in channel size over the short study duration (Fall 2007 – Spring 2008) was difficult due to the current drought. This study reinforced the concept that changes in stream channel size are due to complex interactions between weather, local geology and soils, structures such as bridges and culverts, and the history of changes in the channel form or location.
In addition to the field studies, the project reviewed methods for estimating channel erosion, including large-scale computer models, small scale models, and statistical equations. The study also identified the stream characteristics that would be important to include in any estimation of soil loss from stream channels in the urbanizing coastal zone management area in Virginia. These characteristics are as follows:
- upstream development and land use;
- cohesive (clay and silt) and non-cohesive (sand and gravel) sediment particles;
- the connectedness between the stream channel and the floodplain;
- in-stream structures, including bridges, reservoirs, and dams; and,
- the effects of stream restoration.
The full report is available online at http://www.tmdl.bse.vt.edu/stream_restoration/C114/.
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
