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ARS Home » Pacific West Area » Tucson, Arizona » SWRC » Research » Publications at this Location » Publication #362795

Research Project: Understanding Water-Driven Ecohydrologic and Erosion Processes in the Semiarid Southwest to Improve Watershed Management

Location: Southwest Watershed Research Center

Title: Testing a theoretical resistance law for an overland flow on a stony hillslope

item NICOSIA, A. - University Of Palermo Italy
item DI STEFANO, C. - University Of Palermo Italy
item PAMPALONE, V. - University Of Palermo Italy
item PALERMI, V. - University Of Palermo Italy
item FERRO, V. - University Of Palermo Italy
item Nearing, Mark

Submitted to: Hydrological Processes
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/15/2020
Publication Date: 2/1/2020
Citation: Nicosia, A., Di Stefano, C., Pampalone, V., Palermi, V., Ferro, V., Nearing, M.A. 2020. Testing a theoretical resistance law for an overland flow on a stony hillslope. Hydrological Processes. 34(9):2048-2056.

Interpretive Summary: Computer simulation tools for hydrology and soil erosion are commonly used to help land managers to make land management decisions and to make assessments of the health of the land. In order to use these models, we need to have both a detailed understanding of the processes of runoff and erosion, as well as data to calibrate and apply these models to real-world field conditions. One important such factor that needs to be understood and quantified is called hydraulic roughness, which is basically the factor that determines the velocity or runoff and its ability to erode and transport sediment. In this study we used fundamentally-based hydraulic engineering equations to derive a semi-theoretical approach to estimating the hydraulic friction factor term, then tested the resultant mathematical relationships on an independent set of USDA-ARS data that was collected in 2016 at the Walnut Gulch Experimental Watershed. Results were promising. We expect to be able to use these relationships in application of future models and model applications to provide better estimates of runoff and erosion on agricultural landscapes in the United States.

Technical Abstract: In this paper a recently theoretically deduced flow resistance equation, based on a power-velocity profile, was tested using field measurements by Nearing et al. (2017) for the condition of overland flow under simulated rainfall. Measurements of the Darcy-Weisbach friction factor, corresponding to flow Reynolds number ranging from 48 to 194, were obtained for simulated rainfall with two different rainfall intensity values (59 and 178 mm h-1). The database, constituted by measurements of flow velocity, water depth, cross sectional area, wetted perimeter and bed slope, allowed the calibration of the relationship among the velocity profile parameter G, the slope steepness s and the flow Froude number F, taking also into account the influence of rainfall intensity i. Results yielded the following conclusions: i) the theoretical flow resistance equation accurately estimated the Darcy-Weisbach friction factor for overland flow under simulated rainfall; ii) the flow resistance increased with rainfall intensity for laminar overland flow and iii) the mean flow velocity was quasi-independent of the slope gradient.