Set against a background of vegetation change from grassland to shrubland, this project used the small agricultural stock ponds of the Jornada Experimental Range, in the semi-arid Chihuahuan Desert of New Mexico, to quantify sediment production from the expanding shrubland vegetation communities. In quantifying sediment production, conclusions can be drawn about the importance of land cover in rangeland management, but more significantly for this study, a valuable dataset is generated at a generally under-researched scale. Small pond studies are necessary to expand the existing knowledge on up-scaling of erosion datasets. Sediment yield data are primarily collected from erosion plots, or at a much larger scale using erosion models. These models rely on data from plots for calibration and validation. However, data collected at the plot scale do not accurately represent sediment production at larger scales, often resulting in the propagation of errors. New methods of considering sediment routing through a catchment are necessary if understanding at an intermediate (catchment) scale is to be gained. Three approaches were used to generate comparable datasets: repeated surveys, sediment dating, and reconstructing runoff coefficients from aerial photographs. The results from these projects show internally consistent results, as well as agreement with similar studies in the wider erosion-study literature. This demonstrates the potential of this technique to produce viable datasets. The principal findings of this research are that runoff coefficients calculated at the catchment scale do not show the expected reduction from those gained from plots. This is primarily thought to be a methodological problem. However, the principal aim of the research was met with two complimentary datasets showing variations in sediment fluxes from shrubland vegetation. The dataset was insufficient to conclude this was statistically different from the historic grasslands, but this does appear to be the case. The idea of travel distance of particles as a control on sediment production was only partially substantiated by this work: fining of sediment is evident only within the catchments of the ponds. No statistical difference was found between the particle-size distribution of pond and catchment samples.

PB - University of Leicester UR - files/bibliography/JRN00512.pdf AN - JRN00512 N1 - //USDA//LTER V//entered 2/19/2009ProCite field[12]: In File (02/19/2009) ER - TY - JOUR T1 - A transport-distance approach to scaling erosion rates: 1. Background and model development JF - Earth Surface Processes and Landforms Y1 - 2008 A1 - Wainwright, John A1 - Parsons, Anthony J. A1 - Müller, Eva N. A1 - Brazier, Richard E. A1 - Powell, D. Mark A1 - Fenti, Bantigegne KW - article KW - erosion, hydrology KW - hydrology, erosion KW - hydrology, sediment transport KW - hydrology, soil-erosion model KW - journal KW - model, MAHLERAN KW - model, soil-erosion AB -The process basis of existing soil-erosion models is shown to be ill-founded. The existing literature builds directly or indirectly on Bennett’s (1974) paper, which provided a blueprint for integrated catchment-scale erosion modelling. Whereas Bennett recognized the inherent assumptions of the approach suggested, subsequent readings of the paper have led to a less critical approach. Most notably, the assumption that sediment movement could be approximated by a continuity equation that related to transport in suspension has produced a series of submodels that assume that all movement occurs in suspension. For commonly occurring conditions on hillslopes, this case is demonstrably untrue both on theoretical grounds and from empirical observations. Elsewhere in the catchment system, it is only partially true, and the extent to which the assumption is reasonable varies both spatially and temporally. A second ground-breaking paper – that of Foster and Meyer (1972) – was responsible for subsequent uncritical application of a first-order approximation to deposition based on steady-state analysis and again a weak empirical basis. We describe in this paper an alternative model (MAHLERAN – Model for Assessing Hillslope-Landscape Erosion, Runoff And Nutrients) based upon particle-travel distance that overcomes existing limitations by incorporating parameterizations of the different detachment and transport mechanisms that occur in water erosion in hillslopes and small catchments. In the second paper in the series, we consider the sensitivity and general behaviour of MAHLERAN, and test it in relation to data from a large rainfall-simulation experiment. The third paper of the sequence evaluates the model using data from plots of different sizes in monitored rainfall events. From this evaluation, we consider the scaling characteristics of the current form of MAHLERAN and suggest that integrated modelling, laboratory and field approaches are required in order to advance the state of the art in soil-erosion modelling. Copyright © 2008 John Wiley & Sons, Ltd.

VL - 33 UR - files/bibliography/JRN00489.pdf AN - JRN00489 N1 - //NMSU,USDA//LTER V//entered 05/29/2008 ER - TY - JOUR T1 - A transport-distance approach to scaling erosion rates: 2. Sensitivity and evaluation of MAHLERAN JF - Earth Surface Processes and Landforms Y1 - 2008 A1 - Wainwright, John A1 - Parsons, Anthony J. A1 - Müller, Eva N. A1 - Brazier, Richard E. A1 - Powell, D. Mark A1 - Fenti, Bantigegne KW - article KW - erosion, hydrology KW - hydrology, erosion KW - hydrology, sediment transport KW - hydrology, soil-erosion model KW - hydrology, validation model KW - journal KW - model, MAHLERAN KW - model, soil-erosion KW - model, validation AB -In the first paper in this series, we demonstrated that most process-based erosion models have a series of in-built assumptions that led us to question their true process basis. An alternative soil-erosion model (MAHLERAN – Model for Assessing Hillslope-Landscape Erosion, Runoff And Nutrients) based upon particle-travel distance has been presented in the first paper in this series and this paper presents the first of two evaluations of the model. Here, a sensitivity analysis shows that the numerical model is consistent with the analytical model of Parsons *et al.* (2004) and demonstrates that downslope patterns of sediment flux on hillslopes are a complex interaction of rainfall intensity, duration and pattern; hillslope gradient; surface roughness and sediment size. This result indicates that the spatial scaling of sediment transfers on hillslopes is a non-trivial problem and will vary from point to point and from event to event and thus from year to year. The model is evaluated against field data from a rainfall-simulation experiment on an 18 m × 35 m plot for which there are sub-plot-scale data on runoff hydraulics and sediment flux. The results show that the model is capable of reproducing the sedigraph with an overall normalized root-mean-square error of 18·4% and Nash–Sutcliffe efficiency of 0·90. Spatial and temporal patterns of particle-size distributions of the eroded sediment are also reproduced very well, once erosion parameters have been optimized for the specific soil conditions. Copyright © 2008 John Wiley & Sons, Ltd.

In the two previous papers of this series, we demonstrated how a novel approach to erosion modelling (MAHLERAN – Model for Assessing Hillslope-Landscape Erosion, Runoff And Nutrients) provided distinct advantages in terms of process representation and explicit scaling characteristics when compared with existing models. A first evaluation furthermore demonstrated the ability of the model to reproduce spatial and temporal patterns of erosion and their particle-size characteristics on a large rainfall-simulation plot. In this paper, we carry out a more detailed evaluation of the model using monitored erosion events on plots of different size. The evaluation uses four plots of 21·01, 115·94, 56·84 and 302·19 m2, with lengths of 4·12, 14·48, 18·95 and 27·78 m, respectively, on similar soils to the rainfall-simulation plot, for which runoff and erosion were monitored under natural rainfall. Although the model produces the correct ranking of the magnitude of erosion events, it performs less well in reproducing the absolute values and particle-size distributions of the eroded sediment. The implications of these results are evaluated in terms of requirements for process understanding and data for parameterization of improved soil-erosion models. We suggest that there are major weaknesses in the current understanding and data underpinning existing models. Consequently, a more holistic re-evaluation is required that produces functional relationships for different processes that are mutually consistent, and that have appropriate parameterization data to support their use in a wide range of environmental conditions. Copyright © 2008 John Wiley & Sons, Ltd.

VL - 33 UR - files/bibliography/JRN00491.pdf AN - JRN00491 N1 - //NMSU,USDA//LTER V//entered 05/29/2008, In Press available online; updated 06/12/2008, in print; PDF on file ER - TY - JOUR T1 - A bed-load transport model for rough turbulent open-channel flows on plane beds JF - Earth Surface Processes and Landforms Y1 - 2006 A1 - Athol D. Abrahams A1 - Gao, Peng KW - article KW - hydrology, bed-load transport KW - hydrology, saltation KW - hydrology, sediment transport KW - hydrology, sheet flow KW - journal KW - model KW - model, bed-load transport KW - model, hydrology AB -Data from flume studies are used to develop a model for predicting bed-load transport rates in rough turbulent two-dimensional open-channel flows moving well sorted non-cohesive sediments over plane mobile beds. The object is not to predict transport rates in natural channel flows but rather to provide a standard against which measured bed-load transport rates influenced by factors such as bed forms, bed armouring, or limited sediment availability may be compared in order to assess the impact of these factors on bed-load transport rates. The model is based on a revised version of Bagnold’s basic energy equation *ibsb *= *eb*ù, where *ib *is the immersed bed-load transport rate, ù is flow power per unit area, *eb *is the efficiency coefficient, and *sb *is the stress coefficient defined as the ratio of the tangential bed shear stress caused by grain collisions and fluid drag to the immersed weight of the bed load. Expressions are developed for *sb *and *eb *in terms of *G*, a normalized measure of sediment transport stage, and these expressions are substituted into the revised energy equation to obtain the bed-load transport equation *ib *= ù *G *3·4. This equation applies regardless of the mode of bed-load transport (i.e. saltation or sheet flow) and reduces to *ib *= ù where *G *approaches 1 in the sheet-flow regime. That *ib *= ù does not mean that all the available power is dissipated in transporting the bed load. Rather, it reflects the fact that *ib *is a transport rate that must be multiplied by *sb *to become a work rate before it can be compared with ù. It follows that the proportion of ù that is dissipated in the transport of bed load is *ibsb*/ù, which is approximately 0·6 when *ib *= ù. It is suggested that this remarkably high transport efficiency is achieved in sheet flow (1) because the ratio of grain-to-grain to grain-to-bed collisions increases with bed shear stress, and (2) because on average much more momentum is lost in a grain-to-bed collision than in a grain-to-grain one. Copyright © 2006 John Wiley & Sons, Ltd.

When open-channel flows become sufficiently powerful, the mode of bed-load transport changes from saltation to sheet flow. Where there is no suspended sediment, sheet flow consists of a layer of colliding grains whose basal concentration approaches that of the stationary bed. These collisions give rise to a dispersive stress that acts normal to the bed and supports the bed load. An equation for predicting the rate of bed-load transport in sheet flow is developed from an analysis of 55 flume and closed conduit experiments. The equation is i(b) = omega where i(b) = immersed bed-load transport rate; and omega = flow power. That i(b) = omega implies that e(b) = tan alpha = u(b)/u, where e(b) = Bagnold's bed-load transport efficiency; u(b) = Mean grain velocity in the sheet-flow layer; and tan alpha = dynamic internal friction coefficient. Given that tan alpha approximate to 0.6 for natural sand, u(b) approximate to 0.6u, and e(b)approximate to 0.6. This finding is confirmed by an independent analysis of the experimental data. The value of 0.60 for e(b) is much larger than the value of 0.12 calculated by Bagnold, indicating that sheet flow is a much more efficient mode of bed-load transport than previously thought.

VL - 129 SN - 0733-9429/2003/2-159-163 UR - files/bibliography/JRN00378.pdf AN - JRN00378 N1 - //NONE//LTER IV//added 6/29/2005; updated 8/8/2006 ER - TY - JOUR T1 - A sediment transport equation for interrill overland flow on rough surfaces JF - Earth Surface Processes and Landforms Y1 - 2001 A1 - Athol D. Abrahams A1 - Li, Gary A1 - Krishnan, Chitra A1 - Atkinson, Joseph F. KW - article KW - articles KW - hydrology, bedload KW - hydrology, hillslopes KW - hydrology, interrill flow KW - hydrology, overland flow KW - hydrology, sediment transport KW - hydrology, soil erosion KW - journal KW - journals KW - model, hydrology KW - model, interrill overland flow KW - model, sediment transport AB -A model for predicting the sediment transport capacity of turbulent interrill flow on rough sur4faces is developed from 1295 flume experiments with flow depths ranging from 3.4 to 43.4 mm, flow velocities from 0.09 to 0.65 m s^{-1}, Reynolds numbers from 5000 to 26949, Froude numbers from 0.23 to 2.93, bed slopes from 2.7° to 10°, sediment diameters from 0.098 to 1.16 mm, volumetric sediment concentrations from 0.002 to 0.304, roughness concentrations from 0 to 0.57, roughness diameters from 1.0 to 91.3 mm, rainfall intensities from 0 to 159 mm h^{-1}, flow densities from 1002 to 1501 kg m^{-3}, and flow kinematic viscosities from 0.913 to 2.556 x 10^{-6} m^{2} s^{-1}. Stones, cylinders and miniature ornamental trees are used as roughness elements. Given the diverse shapes, sizes and concentrations of these elements, the transport model is likely to apply to a wide range of ground surface morphologies. Using dimensional analysis, a total-load transpot equation is developed for open-channel flows, and this equation is shown to apply to interrill flows both with and without rainfall. The euation indicates that the dimensionless sediment transport rate Ø is a function of, and therefore can be predicted by, the dimensionless shear stress è, its critical value è_{c}, the resistance coefficient u/u_{*}, the inertial settling velocity of the sediment w_{i}, the roughness concentration C_{r}, and the roughness diameter D_{r}. Testing reveals that the model gives good unbiased predictions of Ø in flows with sediment concentrations less than 0.20. FLows with higher concentrations appear to be hyperconcentrated and to have sediment transport rates higher than those predicted by the model. Copyright © 2001 John Wiley & Sons, Ltd.

Rainfall-simulation experiments have been carried out on a series of plots ranging in size from 1 m^{2} to* c* 500 m^{2} in order to observe process and flux-rate changes resulting from the replacement of the dominant vegetation type from grassland to shrubland in the southwest. Results have demonstrated variations in infiltration rates, flow, hydraulics, splash and interrill erosion rates and nutrient transport rates. Furthermore, the shrubland areas develop rills, which are responsible for significant increases in overall erosion rates. The small-plot experiments allow the definition of controlling factors on the processes, and highlight the importance of vegetation controls. Although the small-plot approach has a number of significant advantages, it also has a number of disadvantages, which are discussed in detail. Some of these problems can be overcome with a careful consideration of experimental design. It is argued that plot-scale studies play an important part in improving our understanding of complex, open systems, but need to be integrated with other approaches such as the monitoring of natural events and computer modelling so that mutually consistent understandings of complex, ecohydrological systems can be achieved.

Sediment transport capacity is an important control on soil erosion and deposition by overland flow. To investigate the controls of transport capacity in laminar interrill overland flow on stone‐covered surfaces, 357 flume experiments were performed using a single sediment size. Multiple regression analyses reveal that transport capacity is positively related to excess flow power ω − ω_{c}, but the slope of the relation is steeper where ω < 0.3 W m^{−2} than where ω ≥ 0.3 W m^{−2}. Transport capacity is positively related to rainfall intensity where ω < 0.3 W m^{−2} and negatively related to rainfall intensity where ω ≥ 0.3 W m^{−2}. Transport capacity is negatively related to stone concentration and positively related to stone size irrespective of the value of ω. Finally, transport capacity is negatively related to fluid viscosity where ω < 0.3 W m^{−2} and unrelated to viscosity where ω ≥ 0.3 W m^{−2}.

Modeling soil erosion requires an equation for predicting the sediment transport capacity by interrill overland flow on rough surfaces. The conventional practice of partitioning total shear stress into grain and form shear stress and predicting transport capacity using grain shear stress lacks rigor and is prone to underestimation. This study therefore explores the possibility that inasmuch as surface roughness affects flow hydraulic variables which, in turn, determine transport capacity, there may be one or more hydraulic variables which capture the effect of surface roughness on transport capacity sufficiently well for good predictions of transport capacity to be achieved from data on these variables alone. To investigate this possibility, regression analyses were performed on data from 1506 flume experiments in which discharge, slope, water temperature, rainfall intensity, and roughness size, shape and concentration were varied. The analyses reveal that 89.8 per cent of the variance in transport capacity can be accounted for by excess flow power and flow depth. Including roughness size and concentration in the regression improves that explained variance by only 3.5 per cent. Evidently, flow depth, when used in combination with excess flow power, largely captures the effect of surface roughness on transport capacity. This finding promises to simplify greatly the task of developing a general sediment transport equation for interrill overland flow on rough surfaces. ©1998 John Wiley & Sons, Ltd.

VL - 23 UR - files/bibliography/JRN00261.pdf AN - JRN00261 N1 - //NONE//LTER III// ER - TY - JOUR T1 - Sediment-related transport of nutrients from southwestern watersheds JF - Journal of Irrigation and Drainage Y1 - 1991 A1 - Bolton, S. M. A1 - Ward, T. J. A1 - Cole, R. A. KW - article KW - articles KW - hydrology, nutrients KW - hydrology, sediment transport KW - journal KW - journals KW - nitrogen, hydrology KW - nutrients, hydrology KW - nutrients, hydrology,runoff KW - phosphorus, hydrology KW - phosphorus,runoff KW - rainfall simulation,hydrology KW - runoff, SEEData from rainfall simulation experiments conducted in Arizona and New Mexico were used to identify relationships between total suspended sediment (TSS) concentrations (kg/ha/mm of runoff) in runoff and concentrations (kg/ha/mm of runoff) of total phosphorus (TP), total volatile suspended sediment (TVSS), and total nitrogen (TN). The units of kg/ha/mm of runoff are equivalent to mg/l divided by 100. Data were collected from pinyon-juniper, ponderosa pine, short grass prairie, creosote bush, and bottomland vegetation types. Lumping data from these five vegetation types yielded a relationlship for total phosphorus of TP = 0.0013(TSS)0.83 with a linear correlation coefficient of r = 0.77. The relationship for total volatile suspended sediment was TVSS = 0.274(TSS)0.72 (r = 0.91). A poor relationship was found for total nitrogen with TN = 0.008(TSS)0.15 (with r = 0.11). These relationships were validated using data from other rainfall simulation experiments and naturally occurring ephemeral streamflow in southern New Mexico.

VL - 117 UR - files/bibliography/JRN00140.pdf AN - JRN00140 N1 - //NMSU//LTER II//Listed in LTER3 proposal as citing LTER2 support// ER -