Stream Restoration Projects
Developing Strategies for Urban Channel Erosion Quantification in Upland Coastal Zone Streams
Project Summary
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.
Final Report
Appendices without pictures
Appendix A : Cross-section Data
Appendix E: Study site bed substrate pictures
Appendix F: Study site cross-section pictures
Appendix I: USM Assessments
M.S. Presentation Top
