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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #207717

Title: Modeling the Hydrologic and Mechanical Effects of Riparian Vegetation on Streambank Stability

Author
item Langendoen, Eddy
item Bankhead, Natasha
item Simon, Andrew

Submitted to: Congress of International Association for Hydraulic Research Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/2/2007
Publication Date: 7/2/2007
Citation: Langendoen, E.J., Pollen, N.L., Simon, A. 2007. Modeling the Hydrologic and Mechanical Effects of Riparian Vegetation on Streambank Stability. In: Proceedings 32nd Congress of International Association for Hydraulic Research, July 1-6, 2007, Venice, Italy. CDROM.

Interpretive Summary: Sediments, washed off agricultural fields or eroded from stream channels, may diminish the water quality of streams and rivers. The stream and the area between stream and agricultural field, the riparian zone, play an important role in the management of excess sediments. The vegetation in the riparian zone is known to reduce erosion from the streambank. The U.S. Department of Agriculture-Agricultural Research Service has been developing the computer models REMM and CONCEPTS to study the effects of riparian forests and in-stream conservation measures on water quality. These models have been integrated to provide a comprehensive tool that can be used to assess the effects of riparian buffer systems on the physical and biological integrity of a stream. The combined model has been used to study the effects of different riparian buffer systems, consisting of trees and grass, on controlling streambank erosion of a severely eroded stream in North-Central Mississippi. Comparison of model results with observed data shows that the model can accurately predict the distribution of soil water within the streambank and how the soil water distribution is affected by vegetation. This is important because soil water greatly affects streambank collapse and hence the amount of sediment added to the stream. The combination of CONCEPTS and REMM is therefore a tool that can be used by state and federal agencies to design and assess vegetative, riparian conservation measures. To date, designing proper dimensions of these measures has been very difficult.

Technical Abstract: Riparian vegetation reduces the risk of streambank failure by increasing bank shear strength. First, soil tensile stresses are transferred to the root system thereby reinforcing the streambank material. Second, canopy interception of rainfall and transpiration increases soil suction, increasing resistance to shearing. Vegetative stream restoration measures are commonly designed using an estimated contribution of vegetation to shear resistance. Root biomass and soil water content depend, among others, on plant specie, soil texture, availability of nutrients, and climate. These factors may vary greatly both spatially and temporally. It is therefore difficult to predict if vegetative restoration designs will successfully stabilize streambanks. This paper presents ongoing research to enhance the streambank erosion submodel of the one-dimensional channel evolution model CONCEPTS. Components of the riparian ecosystem management model REMM that simulate the water balance and plant growth in a riparian buffer have been adjusted to more accurately simulate the distributions of pore-water pressure and root biomass. These components have been integrated into CONCEPTS to study the effectiveness of hypothetical woody and herbaceous riparian buffers in controlling streambank stability of an incised stream in Mississippi. Model results showed that spatial and temporal variations in pore-water pressures can be accurately simulated, but may significantly depend on simulated transpiration and rooting depths. Further, the coarse roots of woody vegetation greatly enhance streambank stability and therefore reduce streambank erosion. The fine roots of the herbaceous species have a negligible effect on the stability of the bank of an incised stream if bank height is significantly larger than rooting depth.