Title: ASSESSING THE IMPACT OF RIPARIAN PROCESSES ON STREAMBANK STABILITY Authors
Submitted to: Ecohydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 23, 2009
Publication Date: September 30, 2009
Citation: Langendoen, E.J., Lowrance, R.R., Simon, A. 2009. ASSESSING THE IMPACT OF RIPARIAN PROCESSES ON STREAMBANK STABILITY. Ecohydrology. 2:360-369. Interpretive Summary: Fine-grained soil particles, 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 eroded upland soils. The vegetation in the riparian zone is also known to reduce erosion from the streambank due to bank material strengthening by plant roots and the removal of groundwater. 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 or buffers 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 buffers on the physical and biological integrity of a stream. Application of the model to a severely eroded stream in North-Central Mississippi showed that it can satisfactorily simulate the below-ground processes that control streambank erosion: soil water and plant root biomass. However, some discrepancies were observed in the simulated lateral movement of groundwater and rate of evapotranspiration between woody and herbaceous plants. The modeling exercise further showed that a coarse rooting system, e.g. as provided by trees, significantly reduced bank erosion rates for this deeply incised stream. The combination of REMM and CONCEPTS models can be used by state and federal agencies to assess vegetative, riparian conservation measures.
Technical Abstract: The series of biennial United States (US) National Water Quality Inventory surveys show no reduction in the percentage of degraded miles of streams since the early 1990s despite an exponential increase in river restoration projects to improve water quality, enhance in-stream habitat, and manage the riparian zone. This may suggest that many river restoration projects fail to achieve their objectives. This is partly due to a lack of understanding of the dynamics of the degraded riverine system and its interaction with the riparian zone. These projects could therefore benefit from using proven models of stream and riparian processes to guide restoration design and to evaluate indicators of ecological integrity. The US Department of Agriculture has developed two such models: the channel evolution computer model CONCEPTS and the riparian ecosystem model REMM. These models have been integrated to evaluate the impact of edge-of-field and riparian conservation measures on stream morphology and water quality. Vegetative riparian conservation measures are commonly used to stabilize failing streambanks. The shear strength of bank soils is greatly affected by the degree of saturation of the soils and root reinforcement by riparian vegetation. The integrated model was used to study the effectiveness of woody and herbaceous riparian buffers in controlling streambank erosion of an incised stream in northern Mississippi. Comparison of model results against observations showed that pore-water pressures are accurately predicted in the upper part of the streambank, away from the groundwater table. Simulated pore-water pressures deviate from those observed lower in the streambank near the phreatic surface. These discrepancies are mainly caused by differences in the simulated location of the phreatic surface and simulated evapotranspiration in case of the woody buffer. The modeling exercise further showed that a coarse rooting system, e.g. as provided by trees, significantly reduced bank erosion rates for this deeply incised stream.