B. Latorre

Comparing catchment sediment fingerprinting procedures using an auto-evaluation approach with virtual sample mixtures

Information on sediment sources in river catchments is required for effective sediment control strategies, to understand sediment, nutrient and pollutant transport, and for developing soil erosion management plans. Sediment fingerprinting procedures are employed to quantify sediment source contributions and have become a widely used tool. As fingerprinting procedures are naturally variable and locally dependant, there are different applications of the procedure. Here, the auto-evaluation of different fingerprinting procedures using virtual sample mixtures is proposed to support the selection of the fingerprinting procedure with the best capacity for source discrimination and apportionment. Surface samples from four land uses from a Central Spanish Pyrenean catchment were used i) as sources to generate the virtual sample mixtures and ii) to characterise the sources for the fingerprinting procedures. The auto-evaluation approach involved comparing fingerprinting procedures based on four optimum composite fingerprints selected by three statistical tests, three source characterisations (mean, median and corrected mean) and two types of objective functions for the mixing model. A total of 24 fingerprinting procedures were assessed by this new approach which were solved by Monte Carlo simulations and compared using the root mean squared error (RMSE) between known and assessed source ascriptions for the virtual sample mixtures. It was found that the source ascriptions with the highest accuracy were achieved using the corrected mean source characterisations for the composite fingerprints selected by the Kruskal Wallis H-test and principal components analysis. Based on the RMSE results, high goodness of fit (GOF) values were not always indicative of accurate source apportionment results, and care should be taken when using GOF to assess mixing model performance. The proposed approach to test different fingerprinting procedures using virtual sample mixtures provides an enhanced basis for selecting procedures that can deliver optimum source discrimination and apportionment.

Initial Drop Velocity in a Fixed Spray Plate Sprinkler

AbstractBallistic simulation has been successfully applied to impact sprinklers. However, ballistic simulation of center pivot sprinkler irrigation has been limited by the difficulty in estimating the initial drop velocity vector in fixed and rotating spray plate sprinklers. Initial velocity is severely affected by the impact of the jet on the sprinkler deflecting plate (or plates). In this work, experimental techniques based on drop photography have been used to obtain the droplet velocity and angle in the vicinity of a fixed spray plate sprinkler by using three different nozzle diameters. Furthermore, simulation techniques based on the inverse solution of drop trajectory were combined to determine the initial velocity vector and energy loss at the spray. Our analysis suggests that the ballistic model can be used to simulate drop inverse trajectory in these sprinklers, although the ballistic model can benefit from 5 to 10% effective drag-force screening. The ratio of initial drop velocity to jet velocity...

Applicability of the photogrammetry technique to determine the volume and the bulk density of small soil aggregates

Aggregate density (ρ) is defined as the relationship between the mass and the volume occupied by an aggregate. Previous studies have characterised ρ on large to medium-sized soil aggregates (>4 mm diameter); however, little information is available for smaller aggregates (  0.99, P < 0.0001) between the volumes estimated on rough stones with the PHM and Archimedes methods demonstrates that this technique can be satisfactorily used to estimate the volume and, consequently, the ρ of small soil aggregates. The results showed an increase in ρ with decreasing aggregate size. A general trend of increasing ρ with the degree of soil disturbance by tillage was also observed.

Comparison of precipitation measurements by OTT Parsivel 2 and Thies LPM optical disdrometers

Optical disdrometers are present weather sensors with the ability of providing detailed information of precipitation such as rain intensity, radar reflectivity or kinetic energy, together with discrete information on the particle size and fall velocity distribution (PSVD) of the hydrometeors. Disdrometers constitute a step forward towards a more complete characterization of precipitation, being useful in several research fields and applications. In this article the performance of two extensively used optical disdrometers, the most recent version of OTT Parsivel disdrometer and Thies Clima Laser Precipitation Monitor (LPM), is evaluated. During two years four collocated optical disdrometers, two Thies Clima LPM and two OTT Parsivel, collected up to 100,000 minutes of data and up to 30,000 minutes with rain in more than 200 rainfall events, with intensities peaking at 277 mm h−1 in one minute. The analysis of these records show significant differences between both disdrometer types for all integrated precipitation parameters, which can be explained by differences in the raw particle size and velocity distri∗Correspondence to: santiago.begueria@csic.es Preprint submitted to Elsevier March 6, 2018 bution (PSVD) estimated by the two sensors. Thies LPM recorded a larger number particles than Parsivel and a higher proportion of small particles than OTT Parsivel, resulting in higher rain rates and totals and differences in radar reflectivity and kinetic energy. These differences increased greatly with rainfall intensity. Posible causes of these differences, and their practical consequences, are discussed in order to help researchers and users in the election of the sensor, pointing out at the same time limitations to be addressed in future studies.

Estimating the van Genuchten retention curve parameters of undisturbed soil from a single upward infiltration measurement

Estimation of the soil–water retention curve, θ(h), on undisturbed soil samples is of paramount importance to characterise the hydraulic behaviour of soils. Although a method of determining parameters of the water retention curve (α, a scale parameter inversely proportional to mean pore diameter and n, a measure of pore size distribution) from saturated hydraulic conductivity (Ks), sorptivity (S) and the β parameter, using S and β calculated from the inverse analysis of upward infiltration (UI) has been satisfactorily applied to sieved soil samples, its applicability to undisturbed soils has not been tested. The aim of the present study was to show that the method can be applied to undisturbed soil cores representing a range of textures and structures. Undisturbed soil cores were collected using stainless steel cylinders (5cm internal diameter×5cm high) from structured soils located in two different places: (1) an agricultural loam soil under conventional, reduced and no tillage systems; and (2) a loam soil under grazed and ungrazed natural shrubland. The α and n values estimated for the different soils using the UI method were compared with those calculated using time domain reflectometry (TDR) pressure cells (PC) for pressure heads of –0.5, –1.5, –3, –5, –10 and –50kPa. To compare the two methods, α values measured with UI were calculated to the drying branch of θ(h). For each treatment, three replicates of UI and PC calculations were performed. The results showed that the 5-cm high cylinders used in all experiments provided accurate estimates of S and β. Overall, the α and n values estimated with UI were larger than those measured with PC. These differences could be attributed, in part, to limitations of the PC method. On average, the n values calculated from the optimised S and β data were 5% larger than those obtained with PC. A relationship with a slope close to 1 fitted the n values estimated using both methods (nPC=0.73 nUI+0.49; R2=0.78, P<0.05). The results show that the UI method is a promising technique to estimate the hydraulic properties of undisturbed soil samples.

Upward infiltration–evaporation method to estimate soil hydraulic properties

ABSTRACT Determination of saturated hydraulic conductivity, Ks, and the van Genuchten water retention curve θ(h) parameters is crucial in evaluating unsaturated soil water flow. The aim of this work is to present a method to estimate Ks, α and n from numerical analysis of an upward infiltration process at saturation (Cap0), with (Cap0 + h) and without (Cap0) an overpressure step (h) at the end of the wetting phase, followed by an evaporation process (Evap). The HYDRUS model as well as a brute-force search method were used for theoretical loam soil parameter estimation. The uniqueness and the accuracy of solutions from the response surfaces, Ks–n, α–n and Ks–α, were evaluated for different scenarios. Numerical experiments showed that only the Cap0 + Evap and Cap0 + h + Evap scenarios were univocally able to estimate the hydraulic properties. The method gave reliable results in sand, loam and clay-loam soils.

Closure to “Initial Drop Velocity in a Fixed Spray Plate Sprinkler” by G. Sánchez Burillo, R. Delirhasannia, E. Playán, P. Paniagua, B. Latorre, and J. Burguete

1 Researcher, Dept. of Soil and Water, Estación Experimental de Aula Dei (EEAD-CSIC), P.O. Box 202, 50080 Zaragoza, Spain. E-mail: guillermo.sanchez@csic.es 2 Assistant Professor, Dept. Water Engineering, Faculty of Agriculture, Univ. of Tabriz, P.O. Box 51666, Tabriz 51666, Iran. E-mail: delearhasannia@yahoo.com 3 Researcher, Dept. of Soil and Water, Estación Experimental de Aula Dei (EEAD-CSIC), P.O. Box 202, 50080 Zaragoza, Spain. E-mail: enrique.playan@csic.es 4 Researcher, Dept. of Soil and Water, Estación Experimental de Aula Dei (EEAD-CSIC), P.O. Box 202, 50080 Zaragoza, Spain. E-mail: pilucap@eead.csic.es 5Researcher, Dept. of Soil and Water, Estación Experimental de Aula Dei (EEAD-CSIC), P.O. Box 202, 50080 Zaragoza, Spain. E-mail: borja.latorre@csic.es 6Researcher, Dept. of Soil and Water, Estaci ón Experimental de Aula Dei (EEAD-CSIC), P.O. Box 202, 50080 Zaragoza, Spain; and Associate Researcher, Instituto de Biocomputacíon y Física de Sistemas Complejos (BIFI), Mariano Esquillor, 50018 Zaragoza, Spain (corresponding author). E-mail: jburguete@eead.csic.es

Numerical Treatment of the Resistance Term in Upwind Schemes in Debris Flow Runout Modeling

AbstractFast flows and avalanches of rock and debris are among the most dangerous of all landslide processes. Understanding and predicting postfailure motion (runout) of this kind of flowlike landslides is thus key for risk assessment, justifying the development of numerical models able to simulate their dynamics. In this paper a numerical method for the resolution of the depth-averaged debris flow model is presented. This set of nonlinear differential equations is formed by a variation of the shallow water equations, including strong bed slope, and a rheology resistance term. This paper focus on the numerical discretization of the resistance term, exploring three different approximations: pointwise, implicit, and unified. Well balance between numerical flux and source terms is only achieved using the unified discretization. In order to avoid nonphysical values of the water depth and discharge, a limitation of the unified resistance term is also needed. This correction is made following three conditions t...