**Preface to "Modeling of Soil Erosion and Sediment Transport"**

The theme of the present Special Issue is "Modeling of Soil Erosion and Sediment Transport". Most studies presented in the Special Issue were applied to different basins in Europe, America, and Asia. It is also worth mentioning that most studies are the result of the cooperation between universities and/or research centers in different countries and continents, portraying an optimistic view of the status of international scientific communication. This Special Issue contains 14 articles that can be classified into the following five categories: Category A: "Soil erosion and sediment transport modeling in basins"; Category B: "Inclusion of soil erosion control measures in soil erosion models"; Category C: "Soil erosion and sediment transport modeling in view of reservoir sedimentation"; Category D: "Field measurements of gully erosion"; Category E: "Stream sediment transport modeling". Articles 1–4 belong to Category A: In the first article (Gudino-Elizondo et al.), the Annualized Agricultural Non-Point Source (AnnAGNPS) model is applied to the Los Laureles Canyon coastal watershed (USA–Mexico border) in order to investigate, amongst others, the impact of urbanization on runoff and sediment load. Field measurements are also used for the calibration and validation of the model. In the second article (Lu and Chiang), the SWAT-Twn model, including the Taiwan Universal Soil Loss Equation (TUSLE), is applied to a small mountainous watershed in Taiwan in order to improve sediment simulation and assess the sediment transport functions. Field measurements are also used for the calibration and validation of the model. In the third article (Yin et al.), a process-based, fully distributed soil erosion model, named WRF-Hydro-Sed, is applied to the Goodwin Creek Experimental Watershed in Mississippi (USA) to account for both overland and channel processes. Streamflow and sediment concentration data during rainfall events are used for the calibration and validation of the model. In the fourth article (Al Sayah et al.), the impact of man-made ponds on soil erosion and sediment transport is assessed, especially for limnological basins. The French Claise basin is considered as application example. In concrete terms, the CORINE erosion and SWAT models are applied to the above basin. Additionally, erosion risk zones are distinguished in the basin. Articles 5–7 belong to Category B: In article 5 (Bai et al.), the impact of terraces and vegetation on runoff and sediment routing is investigated. The Pianguanhe basin in the Chinese Loess Plateau is considered as an application example. For the above investigation, a revised time-area method is integrated into the Land Change Model-Modified Universal Soil Loss Equation (LCM-MUSLE). Eight storms in the 1980s and 2010s are selected to calibrate and verify the original LCM-MUSLE model and its revised version. In article 6 (Nabi et al.), the impact of stone bund type structures and vegetation cover change on sediment yield reduction is investigated. The effectiveness of the above erosion control measures is evaluated by applying a semi-distributed Soil and Water Assessment Tool (SWAT) model to various small watersheds in Pakistan. In article 7 (Xin et al.), the effects of bare and residue cover slopes on the infiltration process of the black soil are evaluated under rainfall simulations. A black soil region in northeastern China is considered as an application paradigm. Two articles are classified into Category C: In article 8 (Nemetov ´ a et al.), a physically ´ based model, named EROSION-3D, is applied to the Svacenicky Creek catchment in the western part of the Slovak Republic. Measurements of sediment volume in a small reservoir, at the bottom of the catchment, are available via a bathymetric field survey. Hence, the model performance can be tested through the available sediment volume measurements. In article 9 (Tarar et al.), the HEC-RAS 1D numerical model is used for predicting delta movement in the Tarbela reservoir (Pakistan). Sediment Rating Curves (SRCs) and Wavelet-Artificial Neural Networks (WA-ANNs) are applied for setting sediment load boundary conditions in HEC-RAS and for finding missing sediment sampling data. Category D is represented by one article: In article 10 of Luffman and Nandi, the relationship between gully erosion and precipitation parameters (duration, total accumulation, intensity) is examined. In concrete terms, the effect of the seasonal precipitation variability on gully erosion is determined in northeast Tennessee (southeastern USA) on the basis of available field measurements of gully erosion. Four articles are classified into Category E: In article 11 (Park et al.), the effect of catchment characteristics on the performance of an already developed model for the estimation of fine sediment dynamics between the water column and sediment bed is tested, using 13 catchments in France, Ireland, Spain, Italy, the Belgian–Dutch border, and USA. Article 12 (Tavelli et al.) presents a new 2D, semi-implicit numerical scheme for the solution of Navier–Stokes equations (momentum conservation), the incompressibility condition (mass conservation), and the mass conservation law for suspended sediment concentration in gravel bed rivers. The above scheme is tested against analytical solutions and performing numerical tests. In article 13 (Kaffas et al.), fuzzy transformation of the total sediment load formula of Yang is conducted. In other words, transformation of the arithmetic coefficients of the Yang formula into fuzzy numbers. A very large set of experimental data, in flumes, is used for fuzzy regression analysis. In article 14 (Wang et al.), a dynamical and numerical simulation of the evolution process of leaked tailings flow from dam failure is presented. At this point, it should be noted that tailings ponds are indispensable facilities in the mine production and operation. The evolution process mentioned above is analyzed at various downstream riverbed slopes and debris blocking dam settings. As application paradigm, a tailings pond dam in Sichuan Province of China is reported.

> **Vlassios Hrissanthou** *Editor*
