Unsaturated Zone Flow Processes

Abstract

Water flow in the unsaturated zone is greatly influenced by unsaturated hydrostatics (water content, energy, pressure, and retention) and by unsaturated hydrodynamics (diffuse flow and preferential flow). Important multiphase processes include the transport of gases, nonaqueous liquids, and solid particles. Numerous means are available for determination of unsaturated conditions and properties, both measurement (of moisture state, water retention, and dynamic characteristics) and through various formulas and models that are mostly empirical in nature, but in some cases incorporating insight into unsaturated-zone physical processes. Applications to practical problems include models and techniques relating to distributions of water and energy, fluxes at the land surface, inputs, outputs, and fluxes within the unsaturated zone, all of which are frequently complicated by heterogeneity and preferential flow. Further scientific advance requires new measurement techniques and theoretical constructs that more adequately represent the important physical processes within practical modeling schemes.

Evaluation of shallow landslide-triggering scenarios through a physically based approach: an example of application in the southern Messina area (northeastern Sicily, Italy)

“…This module uses a database of measured water retention and other properties for a wide variety of media. For a given grain size distribution and other soil properties, the model estimates a retention curve (i.e., the relationship between soil water suction and the amount of water remaining in the soil θ) with good statistical comparability to known retention curves of other media with similar physical properties (Nimmo, 2005). Daily rainfall data have been used as input for the model, whereas evapotranspiration is accounted for by inserting the maximum and minimum temperature values recorded during the investigated period into the Hargreaves equation (Jensen et al, 1997).…”

Bayesian Markov‐Chain‐Monte‐Carlo Inversion of Time‐Lapse Crosshole GPR Data to Characterize the Vadose Zone at the Arrenaes Site, Denmark

“…In this study, we have extended the research of Scholer et al (2011) and investigated the use of time‐lapse ZOP crosshole GPR traveltime data to estimate the VGM parameters in a layered subsurface medium for the case where steady‐state infiltration conditions cannot be assumed. Indeed, steady‐state conditions are the exception, rather than the norm, in the vadose zone, and thus consideration of the dynamic infiltration case is critical (Nimmo, 2005). Furthermore, dynamic measurements have the potential to significantly improve VGM parameter estimates past the steady‐state case because they provide a means of monitoring infiltration behavior through a range of water content values (Binley and Beven, 2003).…”

A hydroclimatological approach to predicting regional landslide probability using Landlab

“…Transient models require a large number of hydrologic soil and vegetation parameters that are highly variable, uncertain, and difficult to measure or estimate (Godt and McKenna, 2008;Baum et al, 2008b). In addition, in most steep forested mountains where landslide risk is high, the presence of macropores due to connected root structures, biological activity, fractures, large clasts, and lenses leads to preferential and funneled flows that violate the assumptions of most matrixflow models (Nimmo, 2005;Sidle et al, 2001;Gabet et al, 2003;Montrasio and Valentino, 2016;Beven and Germann, 2013). Numerical solutions to flow equations also present a major computational bottleneck in large-scale applications for probabilistic quantification of landslide hazard.…”