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ARS Home » Pacific West Area » Boise, Idaho » Northwest Watershed Research Center » Research » Publications at this Location » Publication #259612
Title: New concentrated flow hydraulics equations for physically-based rangeland hydrology and erosion models

Author
item AL-HAMDAN, OSAMA - University Of Idaho
item Pierson Jr, Frederick
item Williams, Christopher - Jason
item Nearing, Mark
item Stone, Jeffry
item Moffet, Corey
item KORMOS, PATRICK - Boise State University
item BOLL, JAN - University Of Idaho
item Weltz, Mark

Submitted to: Trans American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 10/16/2010
Publication Date: 12/13/2010
Citation: Al-Hamdan, O.Z., Pierson, F.B., Williams, C.J., Nearing, M.A., Stone, J.J., Moffet, C.A., Kormos, P.R., Boll, J., and Weltz, M.A. 2010. New Concentrated Flow Hydraulics Equations for Physically-Based Rangeland Hydrology and Erosion Models. Presented at 2010 Fall Meeting, American Geophysical Union, San Francisco, California, 13-17 December 2010, Abstract H41F-1156.

Interpretive Summary: We examined the hydraulics of concentrated flow using unconfined field experimental data over diverse rangeland landscapes, and developed new empirical prediction models of different rangeland concentrated flow hydraulic parameters, which can be applicable across a wide span of rangeland sites, soil, and vegetation and ground cover conditions. The overall hydraulic characteristics in which concentrated flow forms on rangelands differs significantly from that of cropland rills. The complexity of ground cover in rangeland landscapes relative to cropland adds more factors that control the hydraulics of concentrated flow. The shallowness of soil layers in rangelands force the concentrated flow path to go wider rather than deeper as flow discharge increases. In such conditions, the increase of flow discharge would increase the ground and vegetation cover that the flow encounters and consequently would increase the hydraulic friction. Concentrated flow on rangelands is also controlled by slope particularly in newly disturbed sites. These sites have high percentage of bare soil and little percentage of vegetation and rock cover sufficient to counteract the driving force of gravity for the flow. Moreover, slope has an effect on the rock and vegetation cover which are important controllers of concentrated flow. Multiple regression analysis (n=420) was used to develop the concentrated flow hydraulic parameters equations. The resulting predictive equations for concentrated flow velocity (R2=0.56), hydraulic friction (R2=0.58), and width (R2=0.35) are functions of flow discharge, slope, and rock and vegetation cover. These predictive equations can be robustly applied for estimating concentrated flow hydraulic parameters as inputs for hydrologic models of diverse rangeland ecosystems. The hydraulic friction equation can be used for the partitioning of the friction factor process which is very important step in estimating erodibility factors for the erosion model component used in physically based hydrology and erosion models.

Technical Abstract: We examined the hydraulics of concentrated flow using unconfined field experimental data over diverse rangeland landscapes, and developed new empirical prediction models of different rangeland concentrated flow hydraulic parameters, which can be applicable across a wide span of rangeland sites, soil, and vegetation and ground cover conditions. The overall hydraulic characteristics in which concentrated flow forms on rangelands differs significantly from that of cropland rills. The complexity of ground cover in rangeland landscapes relative to cropland adds more factors that control the hydraulics of concentrated flow. The shallowness of soil layers in rangelands force the concentrated flow path to go wider rather than deeper as flow discharge increases. In such conditions, the increase of flow discharge would increase the ground and vegetation cover that the flow encounters and consequently would increase the hydraulic friction. Concentrated flow on rangelands is also controlled by slope particularly in newly disturbed sites. These sites have high percentage of bare soil and little percentage of vegetation and rock cover sufficient to counteract the driving force of gravity for the flow. Moreover, slope has an effect on the rock and vegetation cover which are important controllers of concentrated flow. Multiple regression analysis (n=420) was used to develop the concentrated flow hydraulic parameters equations. The resulting predictive equations for concentrated flow velocity (R2=0.56), hydraulic friction (R2=0.58), and width (R2=0.35) are functions of flow discharge, slope, and rock and vegetation cover. These predictive equations can be robustly applied for estimating concentrated flow hydraulic parameters as inputs for hydrologic models of diverse rangeland ecosystems. The hydraulic friction equation can be used for the partitioning of the friction factor process which is very important step in estimating erodibility factors for the erosion model component used in physically based hydrology and erosion models.