Effects of Stream bank Erosion


Stream bank erosion degrades in-stream habitat by increasing the streams sediment load  and changing its shape and function.  When this happens the stream loses its ability to transport its sediment which causes it to become wide and shallow.  Once these changes begin, the stream channel can become braided, quality habitat is lost and the increased sediment can reduce overall biological productivity.

The Use of Cedar Trees and Bank Vegetation to Reduce Stream bank Erosion

ODWC's streams management staff began to address these issues in 2002 by completing two stream bank stabilization projects on Spring Creek using both hard  (rocks and boulders) and soft (cedar trees and vegetation) structural control techniques. The first project used a modified cedar tree revetment (soft structural control) to stabilize a 350-ft stretch of stream bank.  This method required the bank be graded to 1:2 slope to reduce the shear-stress.  Once this was completed, an erosion control mat was installed over the exposed soil and anchored in place with wooden stakes.  Large root-wads were then placed along the toe of the bank to further reduce shear-stress by deflecting the flow away from the bank.  Cedar trees were then anchored along the bank to provide more armoring and catch sediment necessary for establishment of stream-side vegetation.  The cedar trees extended from the stream bed up to the bankfull elevation. Green ash, sycamore, and willow trees, and a variety of grasses were then planted up the slope of the stream bank to provide more permanent vegetative stabilization.

image of the bank before erosionBefore: Bank erosion  

                       bank after the trees were removed and the bank stabilized     


After: Cedar tree and vegetation stabilization            


*(Click pictures to view larger image)  


In 2002, the Oklahoma Department of Wildlife Conservation installed a series of five J-hook rock vanes to stabilize a 500-ft. stretch of stream bank.  These structures are designed to reduce the shear stress on the bank by shifting the deepest part of the channel from the bank toe to the center of the stream.  Each rock-vane was constructed using large boulders (32-36 inch diameter).  All rock-vanes were installed pointing upstream at a 20-30 degree angle from the stream bank and extend to 2/3rd the distance across the channel width.  Each vane has a slope of between two and seven percent from the top of the stream bank to the end of the vanes.  Both the soft and hard techniques techniques reduce bank erosion, help maintain proper channel morphology and provide more dynamic flow conditions and excellent habitat for many species of sportfish.                                       


Before: Unstable bank



After:  Addition of J-hook rock vanes

 *(Click pictures to view larger image)    

Measuring Lateral Stream bank Erosion Rates

Lateral stream bank erosion can be measured on your property to estimate the rate of  land loss.  Do this by installing three or four pieces of 10-foot re-bar horizontally into the stream bank at the upper, middle and lower portion of the cut-bank.  The bars should be driven in until flush.  Repeat this procedure at the upstream, middle and downstream sections of the effected (three sites and 12 bars total) better overall estimate.  The among of erosion can then be estimated from measurements taken over time.  >

Determine your rate of bank erosion by measuring and recording the average lateral depth of exposed re-bar protruding from the bank at regular time intervals (e.g., monthly).  Be sure and drive the re-bar back flush into the bank after each reading to keep the area safe and to avoid confusion or inflation of readings when making the next measurements.  Next, determine the length of effected bank and multiply that by the average lateral depth of erosion from your measurements.  Your rate of bank erosion and associated land loss can then be accurately reported using a variety of terms (e.g. cubic yards/year)                                                                    


*(Click on picture to view larger image)