What Causes Streambanks to Retreat?
By Kammy Kern-Korot, WMSWCD
Stream banks retreat when there is a combination of erosion and bank failure. Coarse soils along a stream can be more prone to erosion than fine particle (silt and clay) soils, which may hold together so well they even overhang banks. While some erosion is natural and desirable, human activity can contribute. For example, heavy equipment on wet soils can cause compaction, which reduces permeability and drainage and generally damages the protective “fabric” of the soil. A lack of vegetation on stream banks (as well as crop fields and anywhere on the landscape) limits a soil’s ability to weave a fabric, which not only include plant roots, but small fibrous fungi that essentially extend the soil-holding abilities of the plants, and pore spaces. These elements, plus micro-organisms, make for healthy soil that can resist erosion.
There are other factors that weaken stream bank soils and make them susceptible to erosion:
1) Weathering, in the form of freezing and thawing (even without flowing water), serves as a pre-condition for erosion;
2) Water flowing over the bank from adjacent land makes the stream’s erosion worse; and
3) Water accumulating in the stream bank itself, which is the result of poor drainage. In such cases, you may see oozed soil at the base of the bank.
Mature trees and other vegetation typically do a good job of holding the banks and transpiring moisture out of the soil. Isolated streamside trees, however, are vulnerable to erosive forces and will eventually give out -- particularly if the stream is incised (as most of ours are) and the roots are exposed. Trees like company, so the solution is to line the entire stream bank with trees and shrubs. Vegetation on adjacent land (cropland, yard or forest) also mitigates erosion. Cover crops on fields, well forested hill-slopes, and a wide buffer of trees and shrubs along the waterway can all help hold those precious soils in place.
If you need help restoring your streamside areas, check out our Healthy Streams Program at http://www.wmswcd.org/content.cfm/What-We-Do/Healthy-Streams and /or contact [email protected]
By Kammy Kern-Korot, WMSWCD
Stream banks retreat when there is a combination of erosion and bank failure. Coarse soils along a stream can be more prone to erosion than fine particle (silt and clay) soils, which may hold together so well they even overhang banks. While some erosion is natural and desirable, human activity can contribute. For example, heavy equipment on wet soils can cause compaction, which reduces permeability and drainage and generally damages the protective “fabric” of the soil. A lack of vegetation on stream banks (as well as crop fields and anywhere on the landscape) limits a soil’s ability to weave a fabric, which not only include plant roots, but small fibrous fungi that essentially extend the soil-holding abilities of the plants, and pore spaces. These elements, plus micro-organisms, make for healthy soil that can resist erosion.
There are other factors that weaken stream bank soils and make them susceptible to erosion:
1) Weathering, in the form of freezing and thawing (even without flowing water), serves as a pre-condition for erosion;
2) Water flowing over the bank from adjacent land makes the stream’s erosion worse; and
3) Water accumulating in the stream bank itself, which is the result of poor drainage. In such cases, you may see oozed soil at the base of the bank.
Mature trees and other vegetation typically do a good job of holding the banks and transpiring moisture out of the soil. Isolated streamside trees, however, are vulnerable to erosive forces and will eventually give out -- particularly if the stream is incised (as most of ours are) and the roots are exposed. Trees like company, so the solution is to line the entire stream bank with trees and shrubs. Vegetation on adjacent land (cropland, yard or forest) also mitigates erosion. Cover crops on fields, well forested hill-slopes, and a wide buffer of trees and shrubs along the waterway can all help hold those precious soils in place.
If you need help restoring your streamside areas, check out our Healthy Streams Program at http://www.wmswcd.org/content.cfm/What-We-Do/Healthy-Streams and /or contact [email protected]
|
|