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ARS Home » Southeast Area » Oxford, Mississippi » National Sedimentation Laboratory » Watershed Physical Processes Research » Research » Publications at this Location » Publication #162369
Title: HYDROLOGIC CONTROLS OF RIPARIAN VEGETATION ON THE GEOTECHNICAL STABILITY OF STREAMBANKS: EXPERIMENTAL RESULTS

Author
item Simon, Andrew
item POLLEN, NATASHA - UNIV. OF MISSISSIPPI

Submitted to: International Hydro-Science & Engineering International Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/30/2004
Publication Date: 5/31/2004
Citation: Simon, A., Pollen, N. 2008. Hydrologic controls of riparian vegetation on the geotechnical stability of streambanks: experimental results. International Hydro-Science & Engineering International Proceedings. Brisbane, Queensland, Australia. May, 2004. 10 p. (CD-ROM)

Interpretive Summary: Riparian vegetation can increase the strength of streambanks through reinforcement from the root network, and by removing water from the bank via the root network. Recent research has shown that the hydrologic effect of water removal can be significant and may be far greater than the effect of root reinforcement during certain times of the year. To quantify the hydrologic effects of riparian vegetation, experiments with common riparian species were conducted in large soil monoliths. Soil moisture readings at depths of 30cm and 70cm were taken for the period February 2002 until November 2003. Over the period of monitoring, River birch showed the greatest overall stabilizing effect and Black willow the least. The experimental data was used to calculate estimates of increased bank strength due to the removal of water by the roots of the different species. It was found that River birch would provide a 310% increase in bank cohesion followed by Sycamore (200%) and Black willow (100%). These values show that removal of water from the banks via the root network can significantly increase bank strength.

Technical Abstract: 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 were conducted in large soil monoliths. Pore-water pressure data from depths of 30 and 70 cm within soil monoliths containing common riparian species of the USA were monitored for the period February 2002 through November 2003. Over the period of monitoring, River Birch showed the greatest overall effect on increasing matric suction and shear strength 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.