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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 overland flow under simulated rainfall with different types of vegetation

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 Polyakov, Viktor
item Nearing, Mark

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/20/2020
Publication Date: 1/23/2020
Citation: Nicosia, A., Di Stefano, C., Pampalone, V., Palermi, V., Ferro, V., Polyakov, V.O., Nearing, M.A. 2020. Testing a theoretical resistance law for overland flow under simulated rainfall with different types of vegetation. Catena. 189.

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 by the ARS Tucson location on 23 different rangeland sites located in Arizona and Nevada between 2002 and 2013. 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 State

Technical Abstract: In this paper a recently theoretically deduced flow resistance equation, based on a power-velocity profile, was tested using data collected for overland flow under simulated rainfall carried out in plots with vegetation. The available data were obtained exploring a wide range of rainfall intensities (from 60 to 181 mm h-1) and slopes (from 3.6 to 39.6 %), and with four different types of vegetation. The database, including measurements of flow velocity, water depth, cross sectional flow area, wetted perimeter and bed slope, was divided in four datasets (one for each vegetation type), which allowed the calibration of the relationship between the velocity profile parameter G, the slope steepness, the flow Froude number, and the rainfall Reynolds number. The effect of different types of vegetation on flow resistance was investigated. Results showed that: i) the theoretical flow resistance equation gave an accurate estimate of the Darcy-Weisbach friction factor for overland flow under simulated rainfall; ii) the flow resistance increased with rainfall intensity for laminar overland flow; iii) the mean flow velocity was quasi-independent of the slope gradient and iv) the different vegetation types, with different roughness, did not appreciably affect the flow resistance relationships.