Prediction of Rainfall Runoff in Geoenvironmental Engineering Practice

  • Author / Creator
    Abdulnabi, Ahlam
  • Soil cover systems are engineered barriers designed to isolate hazardous mine waste from climatic water and oxygen. Assessment of water flow at the interface between the atmosphere and the ground surface is paramount to successful cover design. For decades, cover systems were designed based on infiltration and evaporation models often overlooking surface runoff. Runoff is a fundamental part of the rainwater cycle intertwined with both infiltration and evaporation but rarely adequately examined in the context of cover system design. This thesis provides a laboratory and numerical modelling program for comprehensive physical evaluation of rainfall runoff responses in soil cover systems. In the laboratory, rainfall runoff tests were conducted using a specially designed rainfall simulator apparatus. A series of controlled rainfall experiments targeted at low permeability and capillary barrier profiles were completed. The experiments focused on observing the runoff phenomenon and quantifying the volume, rate, and time until runoff occurred in response to variation of applied rainfall intensities. Changes in matric suction and volumetric water content were monitored as wetting fronts propagated through the soil profiles. Soil profiles were investigated under different saturation states. The study focused on one central question: is it possible to predict rainfall runoff based on measurable soil properties? Laboratory observations suggest that yes, rainfall runoff rates and volumes are primarily governed by the applied rainfall intensity and saturated hydraulic conductivity in the case of saturated soil surfaces, whereas rainfall runoff rates are governed by the applied rainfall intensity and infiltration capacity for unsaturated soil profiles. The laboratory experiments were numerically replicated for each profile using the SVFlux model. One- and three-dimensional models were assessed for saturated and unsaturated initial states. One-dimensional models produced runoff cumulative volume results within 6% accuracy for most low permeability profiles. Less rigorous results were observed in the capillary barrier profiles, where accuracy varied between 1% and 32%. Three-dimensional models marginally improved the results for capillary barrier profiles. Overall, the results of numerical predictions testify to a reasonably good capability to predict runoff fluxes for controlled laboratory conditions. Lastly, a case study of the Savage River mine in Australia was evaluated to ascertain temporal and spatial variability effects on numerical predictions in field settings. Comparisons of field measured rainfall, and runoff volumes with predictions made by SVFlux were discussed. Both non-vegetated water-shedding cover system and uncovered tailings dam were examined. The study encompassed detailed sensitivity analyses of surface runoff predictions in response to the changing input of rainfall intensity resolution and saturated hydraulic conductivity. The results showed that runoff predictions were highly sensitive to both the resolution of precipitation rate and change in saturated hydraulic conductivity input. Close attention to site conditions is vital when choosing soil parameters to attain meaningful results.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
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