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  • Articles  (4,281)
  • PAPER CURRENT  (4,281)
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  • Articles  (4,281)
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  • PAPER CURRENT  (4,281)
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  • 21
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    Improving Robustness of Hydrologic Ensemble Predictions Through Probabilistic Pre- and Postprocessing in Sequential Data Assimilation (2018)
    Wiley-Blackwell
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    Publication Date: 2018-03-09
    Description: Data assimilation using the ensemble Kalman filter (EnKF) has been increasingly recognized as a promising tool for probabilistic hydrologic predictions. However, little effort has been made to conduct the pre- and post-processing of assimilation experiments, posing a significant challenge in achieving the best performance of hydrologic predictions. This paper presents a unified data assimilation framework for improving the robustness of hydrologic ensemble predictions. Statistical pre-processing of assimilation experiments is conducted through the factorial design and analysis to identify the best EnKF settings with maximized performance. After the data assimilation operation, statistical post-processing analysis is also performed through the factorial polynomial chaos expansion to efficiently address uncertainties in hydrologic predictions, as well as to explicitly reveal potential interactions among model parameters and their contributions to the predictive accuracy. In addition, the Gaussian anamorphosis is used to establish a seamless bridge between data assimilation and uncertainty quantification of hydrologic predictions. Both synthetic and real data assimilation experiments are carried out to demonstrate feasibility and applicability of the proposed methodology in the Guadalupe River basin, Texas. Results suggest that statistical pre- and post-processing of data assimilation experiments provide meaningful insights into the dynamic behavior of hydrologic systems and enhance robustness of hydrologic ensemble predictions.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 22
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    Estimating Surface/Subsurface Sediment Mixing in Karst Settings Using 7Be Isotopes (2018)
    Wiley-Blackwell
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    Publication Date: 2018-03-09
    Description: This study shows that the cosmogenic radionuclide beryllium-7 can be used to track sediment movement through caves. The activities of beryllium-7 and cesium-137 were measured in two different karst settings at both surface and subsurface sites before and after storm runoff events. At one site, 7 Be-enriched sediment was detected up to 1.5 km along a stream conduit after a moderate storm event; however, the activity of 137 Cs was too variable to show a meaningful pattern. The percentages of surface sediment that was found ranged from 0 to 52% along the entire 3 km cave stream and from 33 to 52% along the upper 1.5 km. At the other site, as much as 96% of the sediment initially discharged at the spring during a storm event was fresh surface material that had traveled into and through the cave stream. Moreover, during the 4-day runoff event, approximately 23% of the total suspended sediment flux was estimated to originate from surface erosion with 78% being reworked sediment from within the cave. The data in this study shows that cosmogenic radionuclides with multi-year half-lives are too long-lived to track sediment origins in the caves; whereas, 7 Be with a 53.2 day half life, can be used to track movement of sediment along cave streams.
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 23
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    Soil Texture Often Exerts a Stronger Influence Than Precipitation on Mesoscale Soil Moisture Patterns (2018)
    Wiley-Blackwell
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    Publication Date: 2018-03-09
    Description: Soil moisture patterns are commonly thought to be dominated by land surface characteristics, such as soil texture, at small scales and by atmospheric processes, such as precipitation, at larger scales. However, a growing body of evidence challenges this conceptual model. We investigated the structural similarity and spatial correlations between mesoscale (∼1-100 km) soil moisture patterns and land surface and atmospheric factors along a 150-km transect using 4-km multisensor precipitation data and a cosmic-ray neutron rover, with a 400-m diameter footprint. The rover was used to measure soil moisture along the transect 18 times over 13 months. Spatial structures of soil moisture, soil texture (sand content), and antecedent precipitation index (API) were characterized using autocorrelation functions and fitted with exponential models. Relative importance of land surface characteristics and atmospheric processes were compared using correlation coefficients ( r ) between soil moisture and sand content or API. The correlation lengths of soil moisture, sand content, and API ranged from 12-32 km, 13-20 km, and 14-45 km, respectively. Soil moisture was more strongly correlated with sand content ( r = -0.536 to -0.704) than with API for all but one date. Thus, land surface characteristics exhibit coherent spatial patterns at scales up to 20 km, and those patterns often exert a stronger influence than do precipitation patterns on mesoscale spatial patterns of soil moisture.
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    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 24
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    Channel-Island Connectivity Affects Water Exposure Time Distributions in A Coastal River Delta (2018)
    Wiley-Blackwell
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    Publication Date: 2018-03-09
    Description: The exposure time is a water transport time scale defined as the cumulative amount of time a water parcel spends in the domain of interest regardless of the number of excursions from the domain. Transport time scales are often used to characterize the nutrient removal potential of aquatic systems, but exposure time distribution estimates are scarce for deltaic systems. Here we analyze the controls on exposure time distributions using a hydrodynamic model in two domains: the Wax Lake delta in Louisiana, USA, and an idealized channel-island complex. In particular, we study the effects of river discharge, vegetation, network geometry, and tides and use a simple model for the fractional removal of nitrate. In both domains, we find that channel-island hydrological connectivity significantly affects exposure time distributions and nitrate removal. The relative contributions of the island and channel portions of the delta to the overall exposure time distribution are controlled by island vegetation roughness and network geometry. Tides have a limited effect on the system's exposure time distribution but can introduce significant spatial variability in local exposure times. The median exposure time for the WLD model is 10 hours under the conditions tested and water transport within the islands contributes to 37-50% of the network-scale exposure time distribution and 52-73% of the modeled nitrate removal, indicating that islands may account for the majority of nitrate removal in river deltas.
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    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 25
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    Canopy Spectral Reflectance as a Predictor of Soil Water Potential in Rice (2018)
    Wiley-Blackwell
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    Publication Date: 2018-03-09
    Description: Soil water potential (SWP) is a key parameter for characterizing water stress. Typically, a tensiometer is used to measure SWP. However, the measurement range for commercially available tensiometers is limited to -90 kPa and a tensiometer can only provide estimate of SWP at a single location. In this study, a new approach was developed for estimating SWP from spectral reflectance data of a standing rice crop over the visible to shortwave-infrared region (wavelength: 350 nm to 2500 nm). Five water stress treatments corresponding to targeted SWP of – 30 kPa, - 50 kPa, - 70 kPa, -120 kPa and - 140 kPa were examined by withholding irrigation during the vegetative growth stage of three rice varieties. Tensiometers and mechanistic water flow model were used for monitoring SWP. Spectral models for SWP was developed using partial-least-squares regression (PLSR), support vector regression (SVR), and coupled PLSR and feature selection (PLSR FS ) approaches. Results showed that the SVR approach was the best model for estimating SWP from spectral reflectance data with the coefficient of determination values of 0.71 and 0.55 for the calibration and validation datasets, respectively. Observed root-mean-squared residuals for the predicted SWPs were in the range of -7 to -19 kPa. A new spectral water stress index was also developed using the reflectance values at 745 nm and 2002 nm, which showed strong correlation with relative water contents and electrolyte leakage. This new approach is rapid and non-invasive and may be used for estimating SWP over large areas.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 26
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    Comment on: “Base Flow Recession From Unsaturated-Saturated Porous Media Considering Lateral Unsaturated Discharge and Aquifer Compressibility”, by Liang, X., H. Zhan, Y.-K. Zhang, and K. Schilling (2017) (2018)
    Wiley-Blackwell
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    Publication Date: 2018-03-09
    Description: Liang et al. (2017) presented an analysis of the impacts of unsaturated zone processes on streamflow recession using methodology from Brutsaert and Nieber (1977) with a constant time step in computation of the time derivative of flow. Over the past 10 years many authors have demonstrated that this method may produce artifacts that lead to incorrect interpretations. To demonstrate the impact of the choice of analysis methods, this comment presents an estimation of recession parameters using the Liang et al. (2017) discharge data that eliminates artifacts introduced through the constant time-step. Here we use the exponential time step method, which revealed recession coefficient b greater than 1 which are inconsistent with the fitting framework used in Liang et al. (2017).
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    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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  • 27
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    Improving the Efficiency of 3D Hydrogeological Mixers: Dilution Enhancement via Coupled Engineering-Induced Transient Flows and Spatial Heterogeneity (2018)
    Wiley-Blackwell
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    Publication Date: 2018-03-09
    Description: Natural attenuation and in situ oxidation are commonly considered as low-cost alternatives to ex situ remediation. The efficiency of such remediation techniques is hindered by difficulties in obtaining good dilution and mixing of the contaminant, in particular if the plume deformation is physically constrained by an array of wells, which serves as a containment system. In that case, dilution may be enhanced by inducing an engineered sequence of injections and extractions from such pumping system, which also works as a hydraulic barrier. This way, the aquifer acts as a natural mixer , in a manner similar to the industrialized engineered mixers. Improving the efficiency of hydrogeological mixers is a challenging task, owing to the need to use a 3D setup while relieving the computational burden. Analytical solutions, though approximated, are a suitable and efficient tool to seek the optimum solution among all possible flow configurations. Here we develop a novel physically-based model to demonstrate how the combined spatiotemporal fluctuations of the water fluxes control solute trajectories and residence time distributions and therefore, the effectiveness of contaminant plume dilution and mixing. Our results show how external forcing configurations are capable of inducing distinct time-varying groundwater flow patterns which will yield different solute dilution rates.
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 28
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    A Linear Dynamical Systems Approach to Streamflow Reconstruction Reveals History of Regime Shifts in Northern Thailand (2018)
    Wiley-Blackwell
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    Publication Date: 2018-03-06
    Description: Catchment dynamics is not often modeled in streamflow reconstruction studies; yet, the streamflow generation process depends on both catchment state and climatic inputs. To explicitly account for this interaction, we contribute a linear dynamic model, in which streamflow is a function of both catchment state (i.e., wet/dry) and paleo-climatic proxies. The model is learned using a novel variant of the Expectation-Maximization algorithm, and it is used with a paleo drought record—the Monsoon Asia Drought Atlas—to reconstruct 406 years of streamflow for the Ping River (northern Thailand). Results for the instrumental period show that the dynamic model has higher accuracy than conventional linear regression; all performance scores increase by 45–497%. Furthermore, the reconstructed trajectory of the state variable provides valuable insights about the catchment history—e.g., regime-like behavior—thereby complementing the information contained in the reconstructed streamflow time series. The proposed technique can replace linear regression, since it only requires information on streamflow and climatic proxies (e.g., tree-rings, drought indices); furthermore, it is capable of readily generating stochastic streamflow replicates. With a marginal increase in computational requirements, the dynamic model brings more desirable features and value to streamflow reconstructions.
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 29
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    Reply to Comment by Roques et al. on “Base flow Recession from Unsaturated-Saturated Porous Media Considering Lateral Unsaturated Discharge and Aquifer Compressibility” (2018)
    Wiley-Blackwell
    Details
    Publication Date: 2018-03-06
    Description: Roques et al . [2017A] claims that they have proposed an exponential time step (ETS) method to improve the computing method of Liang et al . [2017] which used a constant time step (CTS) method on the derivative for dQ/dt in field data, where Q is the base flow discharge and t is the time since the start of base flow recession. This reply emphasizes that the main objective of Liang et al . [2017] was to develop an analytical model to investigate the effects of the unsaturated flow on base flow recession, not on the data interpretation methods. The analytical model indicates that the base flow recession hydrograph behaves as dQ/dt ∼ aQ b with the exponent b close to 1 at late times, which is consistent with previous theoretical models. The model of Liang et al . [2017] was applied to field data where the derivative of dQ/dt was computed using the CTS method, a method that has been widely adopted in previous studies. The ETS method proposed by Roques et al . [2017b] appears to be a good alternative but its accuracy needs further validation. Using slopes to fit field data as proposed by Roques et al . [2017a] appears to match data satisfactorily at early times whereas it performs less satisfactorily at late times and leads to the exponent b being obviously larger than 1.
    Print ISSN: 0043-1397
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    Topics: Architecture, Civil Engineering, Surveying , Geography
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  • 30
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    Geomorphic Controls on Floodplain Soil Organic Carbon in the Yukon Flats, Interior Alaska, From Reach to River Basin Scales (2018)
    Wiley-Blackwell
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    Publication Date: 2018-03-06
    Description: Floodplains accumulate and store organic carbon (OC) and release OC to rivers, but studies of floodplain soil OC come from small rivers or small spatial extents on larger rivers in temperate latitudes. Warming climate is causing substantial change in geomorphic process and OC fluxes in high latitude rivers. We investigate geomorphic controls on floodplain soil OC concentrations in active-layer mineral sediment in the Yukon Flats, interior Alaska. We characterize OC along the Yukon River and four tributaries in relation to geomorphic controls at the river basin, segment, and reach scales. Average OC concentration within floodplain soil is 2.8% (median = 2.2%). Statistical analyses indicate that OC varies among river basins, among planform types along a river depending on the geomorphic unit, and among geomorphic units. OC decreases with sample depth, suggesting that most OC accumulates via autochthonous inputs from floodplain vegetation. Floodplain and river characteristics, such as grain size, soil moisture, planform, migration rate, and riverine DOC concentrations, likely influence differences among rivers. Grain size, soil moisture, and age of surfacelikely influence differences among geomorphic units. Mean OC concentrations vary more among geomorphic units (wetlands = 5.1% vs. bars = 2.0%) than among study rivers (Dall River = 3.8% vs. TeedrinjikRiver = 2.3%), suggesting that reach-scale geomorphic processes more strongly control the spatial distribution of OC than basin-scale processes. Investigating differences at the basin and reach scale is necessary to accurately assess the amount and distribution of floodplain soil OC, as well as the geomorphic controls on OC.
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    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley-Blackwell on behalf of American Geophysical Union (AGU).
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