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1. Sensitivity of Simulated Mountain Block Hydrology to Subsurface Conceptualization

   https://doi.org/10.1029/2020WR027714  

   Rapp, G. A.; Condon, L. E.; Markovich, K. H. (October 2020, Water Resources Research)

   Abstract Mountain block systems are critical to water resources and have been heavily studied and modeled in recent decades. However, due to lack of field data, there is little consistency in how models represent the mountain block subsurface. While there is a large body of research on subsurface heterogeneity, few studies have evaluated the effect that common conceptual choices modelers make in mountainous systems have on simulated hydrology. Here we simulate the hydrology of a semi‐idealized headwater catchment using six common conceptual models of the mountain block subsurface. These scenarios include multiple representations of hydraulic conductivity decaying with depth, changes in soil depth with topography, and anisotropy. We evaluate flow paths, discharge, and water tables to quantify the impact of subsurface conceptualization on hydrologic behavior in three dimensions. Our results show that adding higher conductivity layers in the shallow subsurface concentrates flow paths near the surface and increases average saturated flow path velocities. Increasing heterogeneity by adding additional layers or introducing anisotropy increases the variance in the relationship between the age and length of saturated flow paths. Discharge behavior is most sensitive to heterogeneity in the shallow subsurface layers. Water tables are less sensitive to layering than they are to the overall conductivity in the domain. Anisotropy restricts flow path depths and controls discharge from storage but has little effect on governing runoff. Differences in the response of discharge, water table depth, and residence time distribution to subsurface representation highlight the need to consider model applications when determining the level of complexity that is needed. 

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2. An inverse acoustic-elastic interaction problem with phased or phaseless far-field data

   https://doi.org/10.1088/1361-6420/ab693e  

   Dong, H.; Lai, J.; Li, P. (January 2020, Inverse problems)

   Consider the scattering of a time-harmonic acoustic plane wave by a bounded elastic obstacle which is immersed in a homogeneous acoustic medium. This paper is concerned with an inverse acoustic-elastic interaction problem, which is to determine the location and shape of the elastic obstacle by using either the phased or phaseless far-field data. By introducing the Helmholtz decomposition, the model problem is reduced to a coupled boundary value problem of the Helmholtz equations. The jump relations are studied for the second derivatives of the single-layer potential in order to deduce the corresponding boundary integral equations. The well-posedness is discussed for the solution of the coupled boundary integral equations. An efficient and high order Nyström-type discretization method is proposed for the integral system. A numerical method of nonlinear integral equations is developed for the inverse problem. For the case of phaseless data, we show that the modulus of the far-field pattern is invariant under a translation of the obstacle. To break the translation invariance, an elastic reference ball technique is introduced. We prove that the inverse problem with phaseless far-field pattern has a unique solution under certain conditions. In addition, a numerical method of the reference ball technique based nonlinear integral equations is proposed for the phaseless inverse problem. Numerical experiments are presented to demonstrate the effectiveness and robustness of the proposed methods. 

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3. Numerical modeling of scour around porous hydraulic structures: an evaluation of the porosity model

   Song, Yalan; Ismail, Hassan; Liu, Xiaofeng (October 2021, Proceedings of the 10th International Conference on Scour and Erosion (ICSE-10))

   null (Ed.)

   Porous hydraulic structures, such as Large Woody Debris (LWD) and Engineered Log Jams (ELJs), play a very important role in erosion control and habitation conservation in rivers. Previous experimental research has shed some light on the flow and sediment dynamics through and around porous structures. It was found that the scour process is strongly dependent on porosity. Computational models have great value in revealing more details of the processes which are difficult to capture in laboratory experiments. For example, previous computational modeling work has shown that the level of resolution of the complex hydraulic structures in computer models has great effect on the simulated flow dynamics. The less computationally expensive porosity model, instead of resolving all geometric details, can capture the bulk behavior for the flow field, especially in the far field. In the near field where sediment transport is most intensive, the flow result is inaccurate. The way in which this error is translated to the sediment transport results is unknown. This work aims to answer this question. More specifically, the suitability and limitations of using a porosity model in simulating scour around porous hydraulic structures are investigated. To capture the evolution of the sediment bed, an immersed boundary method is implemented. The computational results are compared against flume experiments to evaluate the performance of the porosity model. 

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4. Hubbard Brook Experimental Forest: Watershed 3 Saturated Hydraulic Conductivity

   https://doi.org/10.6073/pasta/b40546b191ccfbc603b4107122e019c8  

   McGuire, Kevin J; Bailey, Scott W; Gannon, JP; Benton, Josh R (January 2022, Environmental Data Initiative)

   This is a dataset of soil saturated hydraulic conductivity (Ksat) collected from augered boreholes or installed groundwater wells in Watershed 3 of the Hubbard Brook Experimental Forest. Hydraulic conductivity describes the ability of a porous medium such as soil to transmit fluid. It is dependent on both fluid (e.g., viscosity) and porous medium properties, and is a key property for estimating subsurface flow rates. Measurements were collected from near the soil surface (10-15 cm depth) to several meters below the surface. Locations are provided for sites where the confidence in coordinates established by GPS was high. Soil horizons without subordinate designators are approximate since the characterization skill of observers varied. These data were gathered as part of the Hubbard Brook Ecosystem Study (HBES) and several other NSF grants over the period from approximately 2007 to 2019. The HBES is a collaborative effort at the Hubbard Brook Experimental Forest, which is operated and maintained by the USDA Forest Service, Northern Research Station. 

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5. Snowmelt-Driven Seasonal Infiltration and Flow in the Upper Critical Zone, Niwot Ridge (Colorado), USA

   https://doi.org/10.3390/w14152317  

   Dethier, David P.; Williams, Noah; Fields, Jordan F. (July 2022, Water)

   The hydrology of alpine and subalpine areas in the Colorado Front Range (USA) is evolving, driven by warming and by the alteration of precipitation patterns, the timing of snowmelt, and other components of the hydrologic budget. Field measurements of soil hydraulic conductivity and moisture along 30-m transects (n = 13) of representative soils developed in surficial deposits and falling head slug tests of shallow groundwater in till demonstrate that hydraulic conductivity in the soil is comparable to hydraulic conductivity values in the shallow aquifer. Soil hydraulic conductivity values were variable (medians ranged from 5.6 × 10−7 to 4.96 × 10−5 m s−1) and increased in alpine areas underlain by periglacial deposits. Hydraulic conductivities measured by a modified Hvorslev technique in test wells ranged from 4.86 × 10−7 to 1.77 × 10−4 m s−1 in subalpine till. The results suggest a gradient from higher hydraulic conductivity in alpine zones, where short travel paths through periglacial deposits support ephemeral streams and wetlands, to lower hydraulic conductivity in the till-mantled subalpine zone. In drier downstream areas, streambed infiltration contributes substantially to near-channel groundwater. As summer temperatures and evapotranspiration (ET) increase and snowmelt occur earlier, alpine soils are likely to become more vulnerable to drought, and groundwater levels in the critical zone may lower, affecting the connectivity between late-melting snow, meltwater streams, and the areas they affect downstream. 

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