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Jeong, Jina,Park, Eungyu,Han, Weon Shik,Kim, Kueyoung,Choung, Sungwook,Chung, Il Moon Elsevier, etc 2017 Journal of hydrology Vol.548 No.-
<P><B>Abstract</B></P> <P>A hydrogeological dataset often includes substantial deviations that need to be inspected. In the present study, three outlier identification methods – the three sigma rule (3<I>σ</I>), inter quantile range (IQR), and median absolute deviation (MAD) – that take advantage of the ensemble regression method are proposed by considering non-Gaussian characteristics of groundwater data. For validation purposes, the performance of the methods is compared using simulated and actual groundwater data with a few hypothetical conditions. In the validations using simulated data, all of the proposed methods reasonably identify outliers at a 5% outlier level; whereas, only the IQR method performs well for identifying outliers at a 30% outlier level. When applying the methods to real groundwater data, the outlier identification performance of the IQR method is found to be superior to the other two methods. However, the IQR method shows limitation by identifying excessive false outliers, which may be overcome by its joint application with other methods (for example, the 3<I>σ</I> rule and MAD methods). The proposed methods can be also applied as potential tools for the detection of future anomalies by model training based on currently available data.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel outlier identification methods based on ensemble regression are proposed. </LI> <LI> The methods use distribution of trends based on resampling instead of data itself. </LI> <LI> Owing to non-Gaussian assumption, the methods are well suited for realistic GW data. </LI> <LI> The methods are thoroughly validated through synthetic and actual GW state data. </LI> <LI> The methods can be used as tools for future anomaly detection based on the training. </LI> </UL> </P>
Jeong, Jina,Park, Eungyu,Han, Weon Shik,Kim, Kue-Young,Oh, Junho,Ha, Kyoochul,Yoon, Heesung,Yun, Seong-Taek Elsevier, etc 2017 Journal of hydrology Vol.554 No.-
<P><B>Abstract</B></P> <P>A method to estimate sequential average unsaturated zone travel time with high temporal resolution has been developed. The method is built upon the conventional cross-correlogram analysis, while the estimation errors are significantly reduced by the proposed schemes. In addition, an analytical relationship between the estimated travel time and the corresponding parameter of a physically-based water table (WT) fluctuation model has been newly established. For validation, applications were performed using WT and precipitation data from two locations with contrasting properties. The method was found to derive distinct characteristics in the estimated travel time, which reflect the unsaturated hydraulics by estimating large means and variations in travel times for low permeability unsaturated zones; whereas, the values are typically small for highly permeable unsaturated zones. The overall results suggest that the proposed method can be potentially adopted to complement other methods in the assessment of groundwater vulnerability to surface contaminants and the hydraulic characterizations of unsaturated zones.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Travel times in the unsaturated zone are estimated with high temporal resolution. </LI> <LI> Travel times are linked to a physical model that gives consistent results. </LI> <LI> The travel times reflect heterogeneous unsaturated hydraulics in time and space. </LI> </UL> </P>
Jeong, Jina,Park, Eungyu,Shik Han, Weon,Kim, Kue-Young,Suk, Heejun,Beom Jo, Si Elsevier 2018 Journal of hydrology Vol.562 No.-
<P><B>Abstract</B></P> <P>A generalized water table fluctuation model based on precipitation was developed using a statistical conceptualization of unsaturated infiltration fluxes. A gamma distribution function was adopted as a transfer function due to its versatility in representing recharge rates with temporally dispersed infiltration fluxes, and a Laplace transformation was used to obtain an analytical solution. To prove the general applicability of the model, convergences with previous water table fluctuation models were shown as special cases. For validation, a few hypothetical cases were developed, where the applicability of the model to a wide range of unsaturated zone conditions was confirmed. For further validation, the model was applied to water table level estimations of three monitoring wells with considerably thick unsaturated zones on Jeju Island. The results show that the developed model represented the pattern of hydrographs from the two monitoring wells fairly well. The lag times from precipitation to recharge estimated from the developed system transfer function were found to agree with those from a conventional cross-correlation analysis. The developed model has the potential to be adopted for the hydraulic characterization of both saturated and unsaturated zones by being calibrated to actual data when extraneous and exogenous causes of water table fluctuation are limited. In addition, as it provides reference estimates, the model can be adopted as a tool for surveilling groundwater resources under hydraulically stressed conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A generalized estimation for water table fluctuation is developed. </LI> <LI> The method can estimate water table level in unconfined aquifers of various depths. </LI> <LI> To model unsaturated infiltration fluxes, a gamma distribution function is adopted. </LI> <LI> The applicability of the model to deep water table aquifers is demonstrated. </LI> </UL> </P>