1,721,046 research outputs found
A laboratory experimental analysis of overland flow production with different slope gradients
No full textExperimental evidence of the relationship between soil gradient and production of surface runoff at the slope outlet is given under the initial conditions of approximately saturated soil. A laboratory slope 152 cm long, 122 cm wide and 78 cm deep was used. The soil tray was adjusted between 1° and 15°. An artificial rainfall generator producing rainfall rates between 10 mmh-1 and 20 mmh-1 was employed. It was found that, for a fixed rainfall rate, the slope gradient has a positive influence on the steady state discharge and that this influence becomes comparatively higher with decreasing the rainfall intensity. An overall analysis of the recession limb of the hydrographs suggests that the slope angle gives a significant contribution to surface water through the generation of an outflow of soil water under conditions of approximately saturated soil. The magnitude of this mechanism is independent of rainfall rate
Overland Flow and the Runon Process
No full textThe processes of infiltration and overland flow over natural surfaces have important applications in surface runoff computations and transport of associated contaminants. Since natural fields exhibit spatially heterogeneous infiltration properties, water from upstream saturated areas may infiltrate into downstream regions where moisture deficit has not been satisfied leading to the runon process. This chapter first presents the classical equations for shallow water flow, their popular approximations, and describes the runon effect along with descriptions of some laboratory experiments of overland flow that demonstrate the relevance of runon. Monte-Carlo methods for quantitative evaluation of the role of runon effect at the field scale are presented. Specifically, role of runon is described in conjunction with flow quantities, erosion and transport of sediments, and transfer of dissolved solutes. Numerical solutions for these processes and field-scale ensemble averages and variances of relevant quantities are examined, and the conditions under which runon can be ignored are identified. A method for extending the runon process to watershed scale applications is described in this chapter
An investigation of the relationship between spatial variability of soil hydraulic properties and overland flow formation
No full textA sensitivity analysis is presented of the overland flow hydrograph generated by complex rainfall events to the representation of the saturated hydraulic conductivity, Ks, considered as random variable. Computation were performed through numerical solutions of a point infiltration model. For rainfall rates, r, much greater than the average value of Ks, , the hydrograph may be appropriately derived assuming Ks= uniform in space. On the other hand, for the range where this assumption is incorrect, evidence is given of the major role of the run-on process, which was neglected in most studies
Similarity solutions for overland and stream flows to study watershed runoff
No full textThis study investigates the use of similarity profiles for analyzing surface flows-specifically those occurring on overland and stream sections. The spatial behaviour of the flow depth is approximated by a sine function, so that the partial differential equations reduce to ordinary differential equations. Solutions of these reduced equations are obtained at a much smaller computational effort, with analytical solutions available in some cases. These solutions were then extended to study surface water movement over small watersheds. These watersheds can be represented as a sequence of cascading overland flow planes and streams. The performance of the similarity solutions was studied by comparing with results from other physically-based models and experimental observations. It was concluded that the similarity solutions are more robust, and almost as accurate as numerical solutions that are obtained from physically-based models. Good agreement with experimental results was found. The potential application of such solutions for surface flow modeling over watersheds will be discussed
A semi-analytical model of expected areal-average infiltration under spatial heterogeneity of rainfall and soil saturated hydraulic conductivitiy
No full textA semi-analytical model for the estimate of expected areal-average infiltration rate at hillslope scale is presented. It accounts for spatial heterogeneity of the saturated hydraulic conductivity, Ks, and rainfall rate, r. The Ks field is characterized by a lognormal probability density function while the rainfall rate r is represented by a uniform distribution between two extreme values. The model formulation relies upon the use of cumulative infiltration as the independent variable which is then expressed as a function of an expected time for use in practical applications. The solution is applicable for those ranges of r and Ks that allow for neglecting the infiltration of surface water running downslope into pervious soils (run-on process). The model was tested by comparisons with Monte Carlo simulations carried out for a variety of coefficients of variation of r and Ks over a clay loam soil and a sandy loam soil. The model was found to be very reliable both with coupled spatial variability of r and Ks and when only one variable is characterized by spatial heterogeneity while the other is uniform
Assessment of the impact of LULC changes on peak discharge and runoff volume in Kebir river catchment Northeastern of Algeria
No full textThe focus of this study is to examine and analysis the impacts of land use land cover (LULC) change for a period between 1985 and 2040 on the peak discharge and runoff volume in a Kebir river catchment using HEC-HMS model and remote sensing-GIS techniques. Therefore, this research started by analyzing changes in LULC by classifying Landsat 5 and Landsat 7 satellite images from 1985 to 2020, whereas the LULC change map of 2040 was obtained by prediction. Data analysis and projection were performed using an integrated Cellular Automata Artificial Neural Network (CA-ANN) methodology within the Modules of Land Use Change Evaluation (MOLUSCE) plugin in QGIS. The accuracy assessment of the classified images was performed by error matrix, where the overall accuracy and Kappa values were found to be 99.27% and 0.98 respectively. The classification results obtained are quite satisfactory, and thus, the classified image is utilized to evaluate changes in LULC throughout the study period. The findings reveal an increase of 0.403%, 0.584%, and 1.020% in agricultural lands, water bodies, and built-up lands respectively. Also, a decrease of 0.722% and 1.285% in Barren lands, and forests, respectively, between 1985 and 2040, was shown. To simulate the changes in the peak discharge and runoff volume, the classified LULC maps of 1985, 2003, 2020, and the predicted LULC map of 2040 are used in the HEC-HMS model during the calibration period from 18/12/1984 to 31/07/1985 and validation period from 01/01/2003 to 31/07/2003. The simulated results show a 1.93% rise in peak discharge during the calibration period and a 2.20% increase during the validation period. In addition, the runoff volume saw a 1.15% increase in the calibration period and a 1.53% increase in the validation period. Further, the performance results of the model were good for both calibration (RMSE = 0.50, NSE = 0.701 to 0.720, KGE = 0.36 to 0.56, and R2 = 0.92) and validation (RMSE = 0.60, NSE = 0.598 to 0.608, KGE = 0.31 to 0.34, and R2 = 0.86 to 0.87)
Infiltration over soils with spatially-correlated hydraulic properties
No full textWe study the problem of field-scale infiltration over soils where spatial variability of saturated hydraulic conductivity is represented by a homogeneous correlated log-normal random field. The Green-Ampt equation is used to describe infiltration at the local scale m terms of cumulative infiltration. Expressions for the ensemble mean and variance of field-scale infiltration are developed. Analytical expression is derived for the expected time it takes for a given depth of water to infiltrate into me soil. The results are compared with extensive sets of Monte-Carlo simulations for a wide variety of cases. The simulations reveal that the proposed formulations provide an adequate estimate of the field-scale infiltration, and that the variance of field-scale infiltration can be parameterized through a simple scaling relationship in terms of the correlation length of the saturated hydraulic conductivity field. Simplified expressions for the variance under asymptotic correlation lengths are also presented
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