• Comparison of smoothness-constrained and geostatistically based cross-borehole electrical resistivity tomography for characterization of solute tracer plumes

      Englert, Andreas; Kemna, Andreas; Zhu, Jun-feng; Vanderborght, Jan; Vereecken, Harry; Yeh, Tian-Chyi J.; Univ Arizona, Dept Hydrol & Water Resources (EDITORIAL BOARD WATER SCIENCE & ENGINEERING, 2016-10)
      Experiments using electrical resistivity tomography (ERT) have shown promising results in reducing the uncertainty of solute plume characteristics related to estimates based on the analysis of local point measurements only. To explore the similarities and differences between two cross-borehole ERT inversion approaches for characterizing salt tracer plumes, namely the classical smoothness-constrained inversion and a geostatistically based approach, we performed two-dimensional synthetic experiments. Simplifying assumptions about the solute transport model and the electrical forward and inverse model allowed us to study the sensitivity of the ERT inversion approaches towards a variety of basic conditions, including the number of boreholes, measurement schemes, contrast between the plume and background electrical conductivity, use of a priori knowledge, and point conditioning. The results show that geostatistically based and smoothness-constrained inversions of electrical resistance data yield plume characteristics of similar quality, which can be further improved when point measurements are incorporated and advantageous measurement schemes are chosen. As expected, an increased number of boreholes included in the ERT measurement layout can highly improve the quality of inferred plume characteristics, while in this case the benefits of point conditioning and advantageous measurement schemes diminish. Both ERT inversion approaches are similarly sensitive to the noise level of the data and the contrast between the solute plume and background electrical conductivity, and robust with regard to biased input parameters, such as mean concentration, variance, and correlation length of the plume. Although sophisticated inversion schemes have recently become available, in which flow and transport as well as electrical forward models are coupled, these schemes effectively rely on a relatively simple geometrical parameterization of the hydrogeological model. Therefore, we believe that standard uncoupled ERT inverse approaches, like the ones discussed and assessed in this paper, will continue to be important to the imaging and characterization of solute plumes in many real-world applications. (C) 2016 Hohai University. Production and hosting by Elsevier B.V.
    • Effects of heterogeneity distribution on hillslope stability during rainfalls

      Cai, Jing-sen; Yan, E-chuan; Yeh, Tian-chyi Jim; Zha, Yuan-yuan; Univ Arizona, Dept Hydrol & Water Resources (EDITORIAL BOARD WATER SCIENCE & ENGINEERING, 2016-04)
      The objective of this study was to investigate the spatial relationship between the most likely distribution of saturated hydraulic conductivity (K-s) and the observed pressure head (P) distribution within a hillslope. The cross-correlation analysis method was used to investigate the effects of the variance of lnK(s), spatial structure anisotropy of lnK(s), and vertical infiltration flux (q) on P at some selected locations within the hillslope. The cross-correlation analysis shows that, in the unsaturated region with a uniform flux boundary, the dominant correlation between P and Ks is negative and mainly occurs around the observation location of P. A relatively high P value is located in a relatively low Ks zone, while a relatively low P value is located in a relatively high Ks zone. Generally speaking, P is positively correlated with q/Ks at the same location in the unsaturated region. In the saturated region, the spatial distribution of K-s can significantly affect the position and shape of the phreatic surface. We therefore conclude that heterogeneity can cause some parts of the hillslope to be sensitive to external hydraulic stimuli (e.g., rainfall and reservoir level change), and other parts of the hillslope to be insensitive. This is crucial to explaining why slopes with similar geometries would show different responses to the same hydraulic stimuli, which is significant to hillslope stability analysis. (C) 2016 Hohai University. Production and hosting by Elsevier B.V.
    • Models to predict sunlight-induced photodegradation rates of contaminants in wastewater stabilisation ponds and clarifiers

      Niu, Xi-Zhi; Univ Arizona, Dept Chem & Environm Engn; Univ Arizona, Arizona Lab Emerging Contaminants (EDITORIAL BOARD WATER SCIENCE & ENGINEERING, 2019-12)
      Two kinetic models were established for conservative estimates of photodegradation rates of contaminants under sunlight irradiation, in particular for wastewater stabilisation ponds and clarifiers in conventional wastewater treatment plants. These two models were designated for (1) contaminants with high photolytic rates or high photolytic quantum yields, whose photodegradation is unlikely to be enhanced by aquatic photosensitisers; and (2) contaminants withstanding direct photolysis in sunlit waters but subjected to indirect photolysis. The effortlessly intelligible prediction procedure involves sampling and analysis of real water samples, simulated solar experiments in the laboratory, and transfer of the laboratory results to realise water treatment using the prediction models. Although similar models have been widely used for laboratory studies, this paper provides a preliminary example of translating laboratory results to the photochemical fate of contaminants in real waters. (C) 2019 Hohai University. Production and hosting by Elsevier B.V.