Barry, David Andrew

Heng, B. C. P.

Jomaa, Seifeddine

Parlange, J.-Y.

Sander, G. C.

Tromp-van Meerveld, H. J.

Infoscience - École polytechnique fédérale de Lausanne

One-dimensional Hairsine-Rose Erosion Model: Parameter Consistency in the Presence of Rainfall SplashProcess-based erosion modeling has proven to be an efficient tool for description and prediction of soil erosion and sediment transport. The one-dimensional Hairsine-Rose(HR) erosion model, which describes the time variation of suspended sediment concentration of multiple particle sizes, accounts for key soil erosion mechanisms: rainfalldetachment, overland-flow entrainment and gravity deposition [1-3]. In interrill erosion, it is known that raindrop splash is an important mechanism of sediment detachmentand therefore of sediment delivery. In addition, studies have shown that the mass transported from a point source by raindrop splash decreases exponentially with radialdistance and is controlled by drop characteristics and soil properties. Here we test experimentally and numerically the HR parameter consistency at different transversalwidths and in the presence of splash. To achieve this, experiments were conducted using different configurations of the 2 m 6 m EPFL erosion flume. The flume wasdivided into four identical smaller flumes, with different widths of 1 m, 0.5 m, and 2 0.25 m. From these experiments, total and the individual size classes sedimentconcentrations were obtained.1. Introduction and motivation 2.  Model S. Jomaa1, D.A. Barry1, G.C. Sander2, J.-Y. Parlange3, B. C. P. Heng2, H.J. Tromp-van Meerveld41 Laboratoire de technologie écologique, Ecole polytechnique fédérale de Lausanne, Lausanne, Suisse (seifeddine.jomaa@epfl.ch, andrew.barry@epfl.ch)2 Department of Civil and Building Engineering, Loughborough University, Leicestershire, United Kingdom (g.sander@lboro.ac.uk, b.c.p.Heng@lboro.ac.uk)3 Department of Biological and Environmental Engineering, Cornell University, New York, USA (jp58@cornell.edu)4 Department of Geography, Simon Fraser University, Burnaby, Canada (Ilja@sfu.ca)3.  Design of experiment  1. P. B. Hairsine, and C. W. Rose (1991), Rainfall detachment and deposition: sediment transport in the absence of flow-driven processes, Soil Science Society of America Journal 55(2):320-324.2. P. B. Hairsine, and C. W. Rose (1992), Modeling water erosion due to overland flow using physical principles, 1, Sheet flow, Water Resources Research 28(1):237-243.3. P. B. Hairsine and C. W. Rose (1992), Modeling water erosion due to overland flow using physical principles, 2, Rill flow, Water Resources Research 28(1):245-250.4. B. C. P. Heng, G. C. Sander, and C. F. Scott (2009). Modeling overland flow and soil erosion on non-uniform hillslopes: A Finite volume scheme, Water Resources Research 45, W05423,doi:10.1029/2008WR007502.6. References 21 11 1 1 1 1fr rI II I rI rI IPhugh S Puhu huxhc huce r e r dt xhc hcue r e r d                                                        1 1 1 1r rI I rI rIm d e rtm d e r                  Notation η = water surface level (m)h = water depth (m) P = rainfall intensity (m/s)Sf = friction slopeci = class i sediment concentration (kg/m3)ei = rainfall detachment (kg/m2/s)eri = rainfall re-detachment (kg/m2/s)ri = runoff entrainment (kg/m2/s)rri = runoff re-entrainment (kg/m2/s)di = deposition (kg/m2/s)mi = mass of deposited class i sediment per unit area (kg/m2)I = the total number of size classesThe 1D fixed-bed Hairsine-Rose model coupled with the shallow water equations is [4]:As a function of time the protective layer of deposited sediment develops according to:5.  Results The experimental results indicate that the raindrop splash dominated in the flumeshaving the larger widths (1 m and 0.5 m). In addition, this process generated ashort time peak in all individual size classes. However, the effect of raindropsplash was less in observed sediment concentrations of the collected data fromflumes having the smaller widths (0.25 m). For these flumes, the detachedsediment was controlled by the transversal width of the flume. An amount ofdetached sediment adhered to the barriers instead of being removed in theoverland flow. Moreover, the experimental results showed that the boundaryconditions could affect the concentration of the mid-size and the larger particles.The one-dimensional Hairsine-Rose model was used to fit the integrated data andso provide parameter estimates according each flume. The analytical results agreedwith the total sediment concentrations but not the measured sedimentconcentrations of all individual size classes. However, the observed sedimentconcentrations for the individual size classes could be predicted only when theinitial sediment concentration was adjusted and a new calculation of the settlingvelocities was used. This new settling velocity calculation was conducted bytaking into account the effect of the raindrop splash on the deposition force of theparticles.4. Discussion and conclusion  Fig. 1. The EPFL erosion flume divided into 4 smaller flumes Fig. 2. Interrill erosion Fig. 3. Raindrop splash1iieffectiveiSplashVVVDqThe effective settling velocity for each size class, which takes into consideration the effect of the raindrop splash on the deposition force of the particles, is:  α = the proportion of raindrops that will generated the splash process (1/10) Dsplash = the average splash length ranged from 4 to 23 cm, here taken as 10 cmVi = the settling velocity of each size class (m/s) q = the overland flow per unit width (m2/s) Table. 1. Best fit-parameters of the flumes Fig. 4. Sediment concentration (g/l) as a function of time (min)Flume 1 Flume 2 Flume 3a (mg/cm3) ad (mg/cm3) mdt* (mg/cm2)Fitted Fitted:Effective settling velocity Fitted Fitted:Effective settling velocity FittedFitted:Effective settling velocity Flume 1 35 30 8700 1600 0.30 0.30Flume 2 35 35 8800 1700 0.40 0.40Flume 3 75 70 8700 1500 0.10 0.10Flume 4* 35 40 8000 2000 0.20 0.15* The behaviour of the flume 4 s different from the other flumes. the position of the collector 4 has generated an additional amount of larger particles in the corner. However, the concentrations of finer particles were consistent with the other flumes. 

One-dimensional Hairsine-Rose Erosion Model: Parameter Consistency in the Presence of Rainfall Splash.

http://infoscience.epfl.ch/record/140936/files/Jomaa_et_al_Green_days_2009.pdf

One-dimensional Hairsine-Rose Erosion Model: Parameter Consistency in the Presence of Rainfall Splash.

Abstract

Similar works

Full text

Available Versions

Infoscience - École polytechnique fédérale de Lausanne