HR: 1330h
AN: H52A-1173    [PDF]
TI: Increasing the Stability of Streambanks through the Hydrologic Effects of Riparian Vegetation: Experimental Results
AU: * Simon, A
EM: asimon@ars.usda.gov
AF: USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, MS 38655 United States
AU: Pollen, N L
EM: npollen@ars.usda.gov
AF: USDA-ARS National Sedimentation Laboratory, P.O. Box 1157, Oxford, MS 38655 United States
AB: Riparian vegetation can provide both mechanical and hydrologic benefits to the shear strength of streambanks. Recent research has shown that the hydrologic effects of water withdrawal on streambank stability can be significant, and far exceeds that provided by root reinforcement during certain times of the year. To accurately quantify the hydrologic effects of riparian vegetation on streambank stability and to determine optimum species for bank stabilization, experiments with common riparian species (planted in 2000) were conducted in large soil monoliths. Pore-water pressure data from depths of 30 and 70 cm within soil monoliths containing Black Willow, River Birch, Eastern Sycamore, and bare soil were monitored for the period February through June, 2002 (Figure XX1). This period was selected because it represents the wettest and, therefore, the most critical period for streambank stability. With rainfall, all of the tensiometers showed decreases in matric suction (negative pore-water pressure) or increases in positive pore-water pressure reflecting the addition of water. However, both the magnitude of the changes and the absoulute values attained within the soil monoliths differed by treatment. At both 30 cm and 70 cm depths, the soil in the control monoliths became the wettest during and after rainfall indicating the role of the woody species in maintaining matric suction and enhancing shear strength. During late February and early March before leaves appeared on stems and branches, there appeared to be little difference in matric suction values between individual species although matirc suction values within these monoliths were still greater than within the control monoliths. This lack of significant differences between the vegetated monoliths and the controls are at least in part a function of the young age of the specimens and the lack of a carryover of high values of matric suction from the previous summer that can be typical in more mature stands of trees. New growth appeared in early April with a theoretical corresponding increase in evapotranspiration. This change is seen as a steepening of the drying trend and a further departure from the control monoliths between precipitation events. The increasing effect of evapotransipration is seen as the difference in matric suction drying-values and trends at both depths between the control and individual specie monoliths during May and June. Sycamore and River Birch create the largest matric suction values during this period (80 kPa). Over the period of monitoring, River Birch showed the greatest overall effect on matric suction values at both 30 and 70 cm, Black Willow the least. Averaging the difference in matric suction values at the two depths and multiplying this difference by tan ٪b provides an indication of the average increase in apparent cohesion that each of the woody species would provide to a hypothetical streambank. Thus, River Birch would provide a 310% increase in apparent cohesion due to matric suction, followed by Sycamore (200%) and Black Willow (100%). These values are significant in light of typical values of effective cohesion in many silt-clay systems.
DE: 1824 Geomorphology (1625)
DE: 1851 Plant ecology
DE: 1866 Soil moisture
SC: Hydrology [H]
MN: 2003 Fall Meeting