Influence of run -on on field-scale surface and subsurface water and contaminant movement over spatially variable hillslopes
Abstract
This study presents a numerical examination of surface and subsurface water movement, contaminant transport, and erosion over spatially heterogeneous hillslopes with special focus on investigation of the role of the run-on process. The high degree of heterogeneity exhibited by the soil parameters that govern the mechanisms of infiltration on hillslopes, initiates the run-on process. To analyze the significance of run-on, a stochastic approach is most appropriate. The saturated hydraulic conductivity Ks is considered to be a random quantity and is represented by a lognormal random field. The behavior of field scale ensemble mean and variance of various quantities for cases with and without run-on were compared by performing numerical Monte-Carlo simulations. Some supporting semi-analytical solutions were also provided to strengthen the numerical results. Non-dimensional formulation of the ensemble averaged mean and variance of field-scale quantities were presented with the aid of scaled variables whenever applicable. Results revealed that the influence of run-on could be quite significant in describing water and solute movement over spatially heterogeneous hillslopes in most of the cases considered in the present study. Run-on process increases mean field-scale infiltration, thereby influencing field-scale overland flow hydrographs. Consequently, solute transport by overland flow is also affected substantially. One of the important outcomes of this study was identification of conditions when run-on can be significant and when run-on can be ignored. This was achieved by examining a wide range of parameters of the random K s field. Besides Ks, other variables such as soil type, rainfall intensity and duration, slope, and correlation scale were also varied to observe the influence of run-on on water and solute movement over hillslopes. Results show that for soils with a low mean saturated hydraulic conductivity compared to rainfall intensity, run-on effects are negligible whereas soils with moderate to high saturated hydraulic conductivity showed substantial effects of run-on. Influence of run-on varied significantly with soil type, rainfall intensity and duration and correlation scale of the Ks random field, while slope in the direction of flow had a minimal effect on run-on results. In each case, guideline was provided for when run-on could not be neglected.
Degree
Ph.D.
Advisors
Govindaraju, Purdue University.
Subject Area
Civil engineering|Agricultural engineering
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