Rangeland Hydrology And Soil Erosion Processes: A Guide .
1United StatesDepartment ofAgricultureAgriculturalResearchServiceRangeland Hydrology and SoilErosion Processes: A guide forConservation Planning withthe Rangeland Hydrology andErosion Model (RHEM)AgriculturalHandbookNumber XXXDraft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
2Editors: Mark Weltz and Gary FrasierContributors:Mark A. Weltz, Research Leader, Rangeland Hydrologist; USDA-ARS, Reno, NVMariano Hernandez, Hydrologist, USDA-ARS, Tucson, AZ, Tucson, AZMark A. Nearing, Research Agricultural Engineer, USDA-ARS, Tucson, AZKen E. Spaeth, Rangeland Management Specialist, USDA-NRCS, Dallas, TXFred B. Pierson, Research Leader, USDA-ARS, Boise, IDC. Jason Williams, Research Hydrologist, USDA-ARS, Tucson, AZOsama Z. Al-Hamdan, Assistant Professor, Texas A&M Kingsville, Kingsville, TXS. Kossi, Nouwakpo, Soil Scientist, University of Nevada Reno, Reno, NV.Gerardo Armendariz, IT Specialist, USDA-ARS, Tucson, AZDave Goodrich, Research Hydraulic Engineer, USDA-ARS, Tucson, AZPhil Guertin, Hydrologist, University of Arizona, Tucson, AZKenneth McGwire, Physical Scientist, Desert Research Institute, Reno, NV.Jason Nesbit, IT Specialist, USDA-ARS, Reno, NVCitation:Weltz, M.A., Hernandez, M., M. A. Nearing, K. E. Spaeth, G. Armendariz, F. B. Pierson, C. J.Williams, O. Z. Al-Hamdan, S. K. Nouwakpo, K. McGwire, J. Nesbit, D. Goodrich, and P.Guertin, K. McGwire, and J. Nesbit. (2017). Rangeland Hydrology and Soil Erosion Processes:A guide for Conservation Planning with the Rangeland Hydrology and Erosion Model(RHEM)United States Department of Agriculture, Agricultural Research Service, Handbook No.XXXXX, XXXX pg.Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
3Abstract: Soil loss rates on rangelands are considered one of the few quantitative indicatorsfor assessing rangeland health and conservation practice effectiveness. An erosion model topredict soil loss specific for rangeland applications is needed. Existing erosion models weredeveloped from croplands. Hydrologic and erosion processes are different on rangelands thancroplands due to much higher levels of heterogeneity in soil and plant properties and theconsolidated nature of the soils. The purpose of this series of Handbooks are to improve theunderstanding of hydrologic processes and sources and transport mechanisms of sediment inrangeland catchments. The first Handbook Rangeland Hydrology and Soil Erosion Processprovides a review of relevant rangeland hydrology literature on what is known about the impactof range management practices and field experiments conducted across the western UnitedStates. This Handbook provides the background for understanding how to use the RangelandHydrology and Erosion Model (RHEM) and understand it output for making informed decisionsbefore implementing new management actions. The RHEM model is a newly conceptualized,process-based erosion prediction tool specific for rangeland application, based on fundamentalsof infiltration, hydrology, plant science, hydraulics, and erosion mechanics. The model is event‐based and was developed specifically from rangeland data. The erosion prediction tool estimatesrunoff, erosion, and sediment delivery rates and volumes at the spatial scale of the hillslope andthe temporal scale of a single rainfall event. The data used to develop and validate the RHEMseries of tools is contained within the USDA-ARS Agricultural, Runoff, Erosion, and Salinitydatabase (ARES). This database contains over 2,000 rainfall simulation plots and 100 plantcommunities collected over the last 40 years across the western United States. These data can beused to understand ecological processes when combine with the RHEM tools to provide soundscience when making critical land management decisions. The RHEM assessment tool providesinformation that can be combined with state and transition models and enhance Ecological SiteDescriptions. The information on how to develop hydrologic sections of ESD’s is contained inthe 3rd Handbook. The ESD Handbook is designed to inform land managers of the benefits andconsequences of changing from one ecological state to another ecological state. The RHEMassessment tool has been incorporated into the Automated Geospatial Watershed Assessment(AGWA) tool for understanding and predicting hydrologic and soil erosion processes at thewatershed scale. How to estimate watershed scale hydrologic and soil erosion processes isaddressed in the 4th Handbook. With these 4 Handbooks the user can understand causes andconsequences of soil erosion and design management plans to prevent or correct issue of concernon rangelands.KEYWORDS: soil erosion; rangelands; rill erosion; concentrated flow; interrill erosion; soilerodibility; slope length, steepness, and shape; runoff; infiltration; risk assessment; foliar andground cover; soil texture; precipitation intensity; duration and frequency; Ecological SiteDescription; conservation practice; grazing management, brush management, and fire.Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
4Rangeland Hydrology and Soil ErosionProcesses: A guide for Conservation Planningwith the Rangeland Hydrology and ErosionModel (RHEM)CONTENTSRangeland Hydrology and Erosion Model Technical Documentation. . .5Rangeland Hydrology and Erosion Model Tutorial Guide . .54Rangeland Hydrology & Erosion Model: Conservation Planning Short Grass Prairie .93West TexasRangeland Hydrology & Erosion Model: Conservation Planning Post Oak Savanna. 116central TexasAgricultural, Runoff, Erosion, and Salinity Database (ARES) .136Appendix I. Conversion Factors .142Appendix II. Vegetation and ground cover definitions and photograhs . .143Appendix III. References for Rangeland Hydrology and Erosion Model publications .150The U.S. Department of Agriculture (USDA) prohibits discrimination in its programs on thebasis of race, color, national origin, sex, religion, age disabilities, political beliefs, and martialand family status. Mention of a trade name in this publication is solely to provide specificinformation and does not imply recommendation or endorsement by the U.S. Department ofAgriculture over others not mentioned.Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
5Rangeland Hydrology and Erosion ModelTechnical DocumentationDraft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
6Contributors:Mariano Hernandez, Hydrologist, USDA-ARS, Tucson, AZ, Tucson, AZMark A. Nearing, Research Agricultural Engineer, USDA-ARS, Tucson, AZMark A. Weltz, Research Leader, Rangeland Hydrologist; USDA-ARS, Reno, NVKen E. Spaeth, Rangeland Management Specialist, USDA-NRCS, Dallas, TXFred B. Pierson, Research Leader, USDA-ARS, Boise, IDC. Jason Williams, Research Hydrologist, USDA-ARS, Tucson, AZOsama Z. Al-Hamdan, Assistant Professor, Texas A&M Kingsville, Kingsville, TXS. Kossi, Nouwakpo, Soil Scientist, University of Nevada Reno, Reno, NV.Kenneth McGwire, Physical Scientist, Desert Research Institute, Reno, NV.The U.S. Department of Agriculture (USDA) prohibits discrimination in its programs on thebasis of race, color, national origin, sex, religion, age disabilities, political beliefs, and martialand family status. Mention of a trade name in this publication is solely to provide specificinformation and does not imply recommendation or endorsement by the U.S. Department ofAgriculture over others not mentioned.Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
7Rangeland Hydrology and Erosion Model Technical DocumentationCONTENTSIntroduction . 7Model Description .8Fundamental hydrologic and erosion equations . .9o Overland flow model 9Overland soil erosion, deposition, and transport .11RHEM Model Parameter Estimation Equations .14Effective saturated hydraulic conductivity 15Hydraulic roughness coefficient .17Splash and sheet erodibility factor .20Concentrated flow erodibility coefficients for hillslope micro-channels . 21PEST model parameterization 22Statistical analysis . .22Study Area and NRI database – Model performance and capabilities .23o Lucky Hills 106 watershed .23Model performance with RHEM parameter estimation equations 27Model calibration .32Performance improvement from RHEM V1.0 to RHEM V2.3 . 34Model Application with NRI .35Conclusions . 41References .45Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
8IntroductionThe complex interactions of variable climate, vegetation, surface soil dynamics, andhuman activities have major impacts on runoff and soil erosion processes on rangelandecosystems. These processes and activities affect ecosystem function over a wide range of spatialand temporal scales (Williams et al., 2016). Nearing et al. (2004) suggested that climaticvariability will increase erosion in the future in many environments. That is, future climates areexpected to lead to a more vigorous hydrological cycle, including total rainfall amount andvariability, and more frequent high-intensity rainfall events that drive the water erosion process(Nearing et al., 2004; Nearing et al. 2015). The consequence is often rangeland degradation, thatis, a decrease in vegetation cover and or a change of vegetation composition with a subsequentloss of the systems productivity (UNCCD 1994). Decades of research have shown thatrangelands can sustainably produce a variety of goods and services even in the face of extremeclimatic events if managers respond quickly and appropriately to changes (Havstad et al., 2009).While land managers may not be able to alter variability in climate they may be able to adapt tochanges in precipitation intensity, duration, and frequency and devise management practices thatare more resilient and resistant to climatic impacts. Soil erosion is among the climate-relatedimpacts that concern rangeland managers since conservation of topsoil is critical to sustainedproductivity in rangeland ecosystems. Soil loss rates on rangelands are regarded as one of thefew quantitative indicators for assessing rangeland health and conservation practice effectiveness(Nearing et al., 2011 and Weltz et al., 2014).The Rangeland Conservation Effects Assessment Project (CEAP) was formally initiatedin 2006 to evaluate conservation effectiveness on rangelands, pastures, and grazed forests thattogether comprise 188 million hectares of USA nonfederal land, as well as large areas of federalDraft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
9land in the western United States. Broad-scale assessments of this type need reliable modelingcapabilities. Erosion prediction technology must be capable of simulating the complexinteractions between vegetation characteristics, surface soil properties and hydrologic anderosion processes on rangelands (Nearing and Hairsine 2011). Al-Hamdan et al. (2012b) pointedout that better representation of the temporal dynamics of soil erodibility related to disturbedrangeland conditions (e.g., fire) is also needed to accurately estimate soil erosion on rangelands .The goals of this Handbook is provide an exact description of the RHEM V2.3 model byproviding a detailed layout of the mathematical model structure and to present the results ofmodel applications and potential uses. The Handbook also demonstrates the gains in modelperformance and reliability over the former model version RHEM V1.0. The Handbook has thefollowing sections: (1) to present the driving equations for RHEM V2.3 model; (2) to calibratethe RHEM V2.3 model using 23 rainfall-runoff-sediment yield events on a small semiarid subwatershed within the Walnut Gulch Experimental Watershed in Arizona, and compare themagainst parameters estimated by the RHEM V2.3 parameter estimation equations; (3) to examinethe performances improvement from RHEM V1.0 to RHEM V2.3; (4) to User Guide forimplementing the model; (5) present case studies for application and interpretation of the modelfor planning conservation; and (6) present where data was derived to develop and validate themodel.Model DescriptionThis section is divided into four main parts as follows. (1) presentation of fundamentalhydrologic and erosion equations in RHEM V2.3, (2) an overview of the RHEM V2.3 parameterestimation equations, (3) model calibration with the Model-Independent Parameter ESTimation(PEST) program, and (4) statistical analysis and results.Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
10Fundamental hydrologic and erosion equationso Overland flow modelThe hydrology component of the enhanced RHEM V2.3 model is based on theKINEROS2 model (Smith et al., 1995). The model was implemented to simulate onedimensional overland flow within an equivalent plane representing a hillslope with uniform orcurvilinear slope profiles. The flow per unit width across a plane surface as a result of rainfallcan be described by the one-dimensional continuity equation (Woolhiser et al. 1990). h q (x, t) t x(1)where h is the flow depth at time t and the position x; x is the space coordinate along thedirection of flow; q is the volumetric water flux per unit plane width (m2 s-1); and (x, t) is therainfall excess (m s-1). (x, t) r f(2)where r is the rainfall rate (m s-1), and f is the infiltration rate (m s-1). The following equationrepresents the relationship between q and h:1 28gS)q (ft3 2h(3)where g is the gravity acceleration (m s-2), S is the slope gradient (m m-1), and ft is the totalDarcy-Weisbach friction factor estimated using equation 18 developed by (Al-Hamdan et al.,Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
112013). Substituting Equations (2) and (3) in Equation (1) results in the hydrology routingequation:1 2 h 3 8gS) ( t 2 ft1 2h h r f x(4)In RHEM, for a single plane, the upstream boundary is assumed to be at zero depth and thedownstream boundary is a continuing plane (along the direction of flow).h(0, t) 0(5)The infiltration rate is computed in KINEROS2 using the three-parameter infiltrationequation (Parlange et al., 1982), in which the models of Green and Ampt (1911) and Smith andParlange (1978) are included as two limiting cases.𝑓 K e [1 α]αI) 1Cd θiexp((6)where I is the cumulative depth of the water infiltrated into the soil (m), Ke is the surfaceeffective saturated hydraulic conductivity (m s-1), Cd (m) accounts for the effect of capillaryforces on moisture absorption during infiltration, and is a scaling parameter. When 0,Equation 6 is reduced to the simple Green and Ampt infiltration model, and when 1, theequation simplifies to the Parlange model. Most soil exhibit infiltrability behavior intermediateto these two models, and KINEROS2 uses a weighting value of 0.85 (Smith et al., 1993). Thestate variable for infiltrability is the initial water content, in the form of the soil saturation deficit,Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
12B Cd (θs θi ), defined as the saturated moisture content minus the initial moisture content.The saturation deficit (θs θi ) is one parameter because θs is fixed from storm to storm. Forease of estimation, the KINEROS2 input parameter for soil water is a scaled moisture content,S θ/ϕ, (ϕ is the soil porosity) which varies from 0 to 1. Thus initial soil conditions arerepresented by the variable Si ( θi/ϕ). Thus, there are two parameters, Ke, and Cd to characterizethe soil, and the variable Si to characterize the initial conditionOverland soil erosion, deposition, and transportThe RHEM erosion model uses a dynamic sediment continuity equation to describe themovement of suspended sediment in a concentrated flow area (Bennett, 1974). (Ch) (Cq r ) Dss Dcf t x(7)Where C is the measured sediment concentration (kg m-3), qr is the flow discharge ofconcentrated flow per unit width (m-2 s-1), Dss is the splash and sheet detachment rate (kg s-1 m-2),and Dcf is the concentrated flow detachment rate (kg s-1 m-2). For a unit wide plane, whenoverland flow accumulates into a concentrated flow path, the following equation calculates theconcentrated flow discharge per unit width (qr):qr qw(8)Where w is the concentrated flow width (m) calculated by (Al-Hamdan et al., 2012a)2.46 Q0.39w S 0.4(9)Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
13The splash and sheet detachment rate (Dss) is calculated by the following equation (Wei et al.,2009):Dss K ss r1.052 σ0.592(10)where Kss is the splash and sheet erodibility, r (m s-1) is the rainfall intensity and σ is rainfallexcess(m s-1).RHEM is a hillslope scale model. As such it does not address flow in channels. It doeshave the capability to estimate transport and erosion in ephemeral (rills) or semi-permanentmicro-channels on the hillslopes of up to a few cm in width and depth. Concentrated flowdetachment rate (Dcf) is calculated as the net detachment and deposition rate (Foster, 1982):Dc (1 Dcf CQ) , CQ TcTc0.5 Vf(Tc CQ), CQ Tc[ Q](11)where Dc is the concentrated flow detachment capacity (kg s-1 m-2); Q is the flow discharge (m3 s1); Tc is the sediment transport capacity (kg s-1); and Vf is the soil particle fall velocity (m s-1)that is calculated as a function of particle density and size (Fair and Geyer, 1954).Sediment detachment rate from the concentrated flow is calculated by employing soilerodibility characteristics of the site and hydraulic parameters of the flow such as flow width andstream power. Soil detachment is assumed to start when concentrated flow starts (i.e. nothreshold concept for initiating detachment is used) (Al-Hamdan et al., 2012b).Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with theRangeland Hydrology and Erosion Model (RHEM) June 13, 2017
14To calculate Dc, the equation developed by Al-Hamdan et al. (2012b) is used:Dc K ω (ω)(12)where K is the stream power erodibility factor (s2 m-2) andis the stream power (kg s-3). Weimplemented the empirical equation developed by Nearing et al. (1997) to calculate the transportcapacity (Tc).10Tcexp[0.845 0.412 log(1000ω)]) 34.47 38.61 Log10 (w1 exp[0.845 0.412 log(1000ω)](13)Soil detachment is not considered as a selective process, so the sediment particles sizedistribution generated from actively eroding areas is assumed to be a function of the fraction oftotal sedi
Nov 09, 2020 · Draft of USDA Rangeland Hydrology and Soil Erosion Processes: A guide for Conservation Planning with the . runoff, erosion, and sediment delivery rates and volumes at the spatial scale of the hillslope and . The U.S. Department of Agriculture (USDA) prohibits discrimination in its progr
Abstract: The Rangeland Hydrology and Erosion Model (RHEM) is a newly conceptualized model that was adapted from relevant portions of the Water Erosion Prediction Project (WEPP) Model and modified specifically to address rangelands conditions. RHEM is an event-based model that estimates runoff,
Types of Soil Erosion Rain drop or splash erosion: Erosion preceded by the destruction of the crumb structure due to the impact of falling raindrop on the surface of soil is termed as splash erosion. Sheet erosion: It is the fairly uniform removal of soil in thin layers from the land surface, of
Erosion is the detachment and movement of soil particles by wind, water, and gravity. Natural erosion (geologic erosion) is a process that occurs slowly over millions of years. Geologic erosion has shaped the landscape around us. Accelerated erosion is NOT
Soil erosion is the detachment of soil particles and loss of surficial soil by the actions of water, ice, gravity, or wind. Water -generated erosion causes the most severe damage to a site under development. Sedimentation is the consequence of erosion when the eroded soil particles are deposited in
with the LACDPW Hydrology Manual. The soil type used is No. 10 and the 50year, 24hour ‐‐ isohyet is 5 inches per Appendix B Sheet 1H1.7 of‐ LACDPW Hydrology Manual (2006). The isohyets for WQV and 25year storms are converted by multiplication factors per Table 5.3.1 of ‐ LACDPW Hydrology Manual.
Erosion Control Handbook for Local Roads 7 1.2 Physical and Environmental Factors Affecting Erosion Erosion can be caused by wind, gravity, or water. However, water-generated erosion is the most damaging factor, especially in developing areas. The five types of water erosion and tech
WATERSHED MANAGEMENT ORDINANCE TECHNICAL GUIDANCE MANUAL 5/26/2020 4.1 GENERAL SOIL EROSION AND SEDIMENT CONTROL REQUIREMENTS PAGE 4-2 4.1 GENERAL SOIL EROSION AND SEDIMENT ONTROL REQUIREMENTS §400.1 of the WMO requires erosion and sediment control practices for all projects, rega
1 Advanced Engineering Mathematics C. Ray Wylie, Louis C. Barrett McGraw-Hill Book Co 6th Edition, 1995 2 Introductory Methods of Numerical Analysis S. S. Sastry Prentice Hall of India 4th Edition 2010 3 Higher Engineering Mathematics B.V. Ramana McGraw-Hill 11 th Edition,2010 4 A Text Book of Engineering Mathematics N. P. Bali and Manish Goyal Laxmi Publications 2014 5 Advanced Engineering .
