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Bolin Creek Watershed Geomorphic Assessment

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Study Summary
In 2007, the Towns of Carrboro and Chapel Hill contracted with Earth Tech to do a watershed-wide study of geomorphic conditions of streams to identify and rank the locations contributing most to poor conditions, and to propose projects to correct these problems. Geomorphic condition includes channel shape and other physical characteristics of streams. This information can point to problems with excess stormwater, erosion, sedimentation, and other instability of the stream channel.

What is the purpose and background of the study?
Previous studies were conducted by Tetra Tech as part the Ecosystem Enhancement Program’s Morgan and Little Creek Watershed Local Watershed Planning Initiative, and the NC Division of Water Quality’s Watershed Assessment and Restoration Program. These studies indicated problems with high, scouring stormwater flows, lack of adequate instream habitat, severe bank and streambed erosion – all indicators of a stream network that is unstable, still responding to changes in its hydrology that have occurred since the Colonial era.

The purpose of this study was to more systematically identify areas of geomorphic (channel shape) instability across the entire Bolin Creek watershed and try to rank them by their severity. This study also proposed and ranked 32 projects to stabilize the stream, reduce effects from high, scouring flows, or otherwise improve physical conditions.

This study was funded by a Clean Water Management Trust Fund mini-grant awarded to the Town of Carrboro.

What are the findings and results of the study?
Professionals from Earth Tech and members of the Bolin Creek Watershed Assessment Team walked along all perennial and intermittent streams and many ephemeral streams in the Bolin Creek watershed. They identified areas of geomorphic instability (areas prone to erosion or sediment build-up due to changes in flow patterns), described and compared individual stream lengths, documenting with channel measurements and photos where needed. These data were used to compare and rank the different geomorphic problems observed in the watershed. Corrective projects were proposed and costs estimated so that these could be ranked as well.

Multiple indications of deteriorating stream condition and multiple types of problems were observed at many locations along the streams. The particular sources of instability observed included stream channelization (straightening/ditching), culverts and channel crossings, utility impacts (sewer lines along streams, other utilities crossing), bank erosion and collapse, direct discharges to the channel, railroad impacts, recreation impacts, and stormwater runoff. The causes and consequences of these impacts are discussed more thoroughly in the report.

Thirty-two projects were proposed to address the worst geomorphic problems identified in the watershed. See the Project Summary below for more information on the results, view the proposed projects, or read the report in its entirety.

What is the status of the project? What are the next steps?
The study and report are completed. The recommendations from the report are being integrated into a full Bolin Creek Watershed Restoration Plan.

A decision must be made on how and whether to proceed with any stormwater management and/or stream restoration in the Bolin Creek Watershed. Priorities and possible funding sources will be included in the Bolin Creek Watershed Restoration Plan.


Geomorphic Analysis and Potential Site Identification for Stormwater BMPs and Retrofits

 Project Summary  

The Bolin Creek Watershed Full Report is also available as a single 78MB PDF file.

 

 

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