Modeling aggregate size distribution of eroded sediments by rain-splash and raindrop impacted flow processes

Transcription

1 Modeling aggregate size distribution of eroded sediments by rain-splash and raindrop impacted flow processes Selen Deviren Saygın* Gunay Erpul Department of Soil Science and Plant Nutrition, Faculty of Agriculture, Ankara University, Diskapi-Ankara, Turkey ( *Presenting authour Soil Erosion Modelling Workshop JRC Ispra March 2017

2 Research highligths Previous studies have clearly indicated that sediment characteristics and especially its size distrubution are dynamicly changes under water-induced erosion conditions (Hairsine et al., 1999; Hogarth et al., 2004, Asadi et al., 2007; Baigorria and Romero, 2007; Rose et al., 2007, Asadi et al., 2011). The size distribution of eroded sediments can provide basic information regarding erosion processes (Loch and Donnollan, 1982; Miller and Baharuddin, 1987; Mitchell et al., 1983; Proffitt and Rose, 1991; Meyer et al., 1992). A better understanding of the dynamics of the sediment size distribution will improve understanding of erosion and sedimentation processes, and consequently improve erosion modeling. For next genaration process-based modelling technology it is essential to model mass-fragmentation to accurately estimate transport capacity, soil loss rates and erodibility etc. Nearing et al. (1990) indicate that major deficiency in WEPP model to represent detachment process is in terms of sediment size distrubutions. Thus, it has been proposed the developing separate predictive equations for sediment sizes from rill and interrill areas and incorporating these equations into process-based erosion prediction technologies.

3 Research highligths At this point, we can say that modelling of the sediment size distribution with an proper mathematical model would be useful in modeling and monitoring the changing erosional conditions. From the past to the present, many statistical methods have been proposed to describe the particle-size distribution of sediments (Cooke et al., 1993; Zobeck et al., 2003). Some of them are the conventional Gaussian or normal, log-normal (Shirazi and Boersma, 1984; Buchan, 1989), modified lognormal (Wagner and Ding, 1994), log-hyperbolic (Hartmann and Christiansen, 1988), bi- or multimodal (Pinnick et al., 1985), Rosin-Rammler (Kittleman, 1964),Weibull (Wohletz et al., 1989), and others (Zobeck et al., 2003). Although these studies are cruial for mass-fragmentation model developments in terms of process-based approach, performed measurements on eroded sediments and modelling of them with a proper methodology are quite limited opposite to wind erosion measurements. Thus, we tried to find best modelling approach to model eroded sediment size variations under water-induced erosion conditions. In this context, we compared to the three different mathematical aggregate size distribution model (Log-normal, Fractal and Weibull) performance, mostly used for dust modeling in wind erosion process, for eroded sediments derived from rainfall simulations to simulate fragile ecosytem dynamics in semi-arid catchment scale.

4 Rainfall simulations

5 Log-normal cumulative distribution function (CDF)

6 Fractal cumulative distribution function (CDF) Fractal M ( x < M T X L ) = x X where M(x < x L )s the cumulative mass smaller than diameter x, x L is the diameter of the largest particle, and M T is the total sample mass L 3 D2 derived from Mandelbrot, 1982; Turcotte 1986; Tyler and Wheatcraft 1989; Tyler and Wheatcraft 1992 MSE: 0,0063 R 2 : 0,953 D 50 : 1,828 Sample graph: Dry Aggregate size distrubution modelling for cultivated agricultural land before rainfall simulations

7 Weibull cumulative distribution function (CDF) Weibull M ( x M T where M(x < X ) is the cumulative mass x smaller than diameter X, M T is the total sample mass, the b parameter is a scale factor and the c parameter is a shape factor. < X ) c x = 1 exp ( ) b derived from Wohletz et. al. 1989; Perfect and Kay, 1995; Zobeck et al MSE: 0,0015 R 2 : 0,989 D 50 : 1,49 Sample graph: Dry Aggregate size distrubution modelling for cultuvated agricultural land before rainfall simulations

8 Measured and predicted D 50 values along with MSE and R 2 values for the splashed sediments Land Use Cultivated Land Cultivated Land Grassland Grassland Forest Forest Slope Intensity D 50 Measured Lognormal MSE R 2 Fractal MSE R 2 Weibull MSE R 2 9% 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h mm h

9 Measured and predicted D 50 values along with MSE and R 2 values for the runoff sediments Land Use Cultivated Cultivated Land Land Grassland Grassland Forest Forest Slope Intensity D 50 Measured Lognormal MSE R 2 Fractal MSE R 2 Weibull MSE R 2 9% 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h mm h % 80 mm h -1 No data* 120 mm h % 80 mm h mm h % 80 mm h mm h

10 Results Results clearly indicated that cultivated land and grassland soils have produced similar size aggregate distributions and D 50 values after rainfall simulations for detachment and transport processes opposite to the soils of the forest plantation area under the saturated soil conditions. And, the all studied models had higher potential to estimate the eroded sediment distributions obtained from various rainfall simulations. Especially, the Weibull model has shown the best fit with the lowest MSE values ( MSE ) and the highest determination coefficient (0.998 R ) for modeling eroded sediments by RST and RIFT processes. The Log-normal approach generally resulted in a lower estimated value than the actual value opposite to the Fractal approach which showed a tendency to higher model estimates. In summary, this study of laboratory rainfall simulations demonstrated that the Weibull cumulative distribution function can be used effectively to model the aggregate size distribution of raindrop and shallow flow-induced sediment transport processes References Asadi, H., Ghadiri, H., Rose, C. W., & Rouhipour, H. (2007). Interrill soil erosion processes and their interaction on low slopes. Earth Surface Processes and Landforms, 32(5), Asadi, H., Moussavi, A., Ghadiri, H., & Rose, C. W. (2011). Flow-driven soil erosion processes and the size selectivity of sediment. Journal of Hydrology, 406(1), Baigorria, G. A., & Romero, C. C. (2007). Assessment of erosion hotspots in a watershed: integrating the WEPP model and GIS in a case study in the Peruvian Andes. Environmental Modelling & Software, 22(8), Buchan, G. D. (1989). Applicability of the simple lognormal model to particle size distribution in soils. Soil Science, 147(3), Cooke, R.U., Warren, A., & Goudie, A.S. (1993). Desert Geomorphology. Univ. College London Press, London. Hairsine, P. B., Sander, G. C., Rose, C. W., Parlange, J. Y., Hogarth, W. L., Lisle, I., & Rouhipour, H. (1999). Unsteady soil erosion due to rainfall impact: a model of sediment sorting on the hillslope. Journal of Hydrology, 220(3), Gardner, W. R. (1956). Representation of Soil Aggregate-Size Distribution by a Logarithmic-Normal Distribution1, 2. Soil Science Society of America Journal, 20(2), Hartmann, D., & Christiansen, C. (1988). Settling-velocity distributions and sorting processes on a longitudinal dune: a case study. Earth Surface Processes and Landforms, 13, 656. Hogarth, W. L., Rose, C. W., Parlange, J. Y., Sander, G. C., & Carey, G. (2004). Soil erosion due to rainfall impact with no inflow: a numerical solution with spatial and temporal effects of sediment settling velocity characteristics. Journal of Hydrology, 294(4), Kittleman Jr, L. R. (1964). Application of Rosin's distribution in size-frequency analysis of clastic rocks. Journal of Sedimentary Research, 34(3) Loch, R. J., & Donnollan, T. E. (1983). Field rainfall simulator studies on two clay soils of the Darling Downs, Queensland. II. Aggregate Breakdpwn, sediment properties and soil erodibility. Soil Research, 21(1), Meyer, L. D., Line, D. E., & Harmon, W. C. (1992). Size characteristics of sediment from agricultural soils. Journal of Soil and Water Conservation, 47(1), Miller, W. P., & Baharuddin, M. K. (1987). Particle size of interrill-eroded sediments from highly weathered soils. Soil Science Society of America Journal, 51(6), Mitchell, J. K., Mostaghimi, S., & Pond, M. C. (1983). Primary particle and aggregate size distribution of eroded soil from sequenced rainfall events. TRANSACTIONS of the ASAE, 26(6), Nearing, M. A., Lane, L. J., Alberts, E. E., & Laflen, J. M. (1990). Prediction technology for soil erosion by water: status and research needs. Soil Science Society of America Journal, 54(6), Pinnick, R. G., Fernandez, G., Hinds, B. D., Bruce, C. W., Schaefer, R. W., & Pendleton, J. D. (1985). Dust generated by vehicular traffic on unpaved roadways: sizes and infrared extinction characteristics. Aerosol Science and Technology, 4(1), Proffitt, A. P. B., & Rose, C. W. (1991). Soil erosion processes. II. Settling velocity characteristics of eroded sediment. Soil Research, 29(5), Rose, C. W., Yu, B., Ghadiri, H., Asadi, H., Parlange, J. Y., Hogarth, W. L., & Hussein, J. (2007). Dynamic erosion of soil in steady sheet flow. Journal of Hydrology, 333(2), Shirazi, M. A., & Boersma, L. (1984). A unifying quantitative analysis of soil texture. Soil Science Society of America Journal, 48(1), Wagner, L. E., & Ding, D. (1994). Representing aggregate size distributions as modified lognormal distributions. Transactions of the ASAE, 37(3), Wohletz, K. H., Sheridan, M. F., & Brown, W. K. (1989). Particle size distributions and the sequential fragmentation/transport theory applied to volcanic ash. J. Geophys. Res, 94(B11), Zobeck, T. M., Popham, T. W., Skidmore, E. L., Lamb, J. A., Merrill, S. D., Lindstrom, M. J.,... & Yoder, R. E. (2003). Aggregate-mean diameter and wind-erodible soil predictions using dry aggregate-size distributions. Soil Science Society of America Journal, 67(2),