Resolving Structural Influences on Water‐Retention Properties of Alluvial Deposits

Abstract

With the goal of improving property‐transfer model (PTM) predictions of unsaturated hydraulic properties, we investigated the influence of sedimentary structure, defined as particle arrangement during deposition, on laboratory‐measured water retention (water content vs. potential [θ(ψ)]) of 10 undisturbed core samples from alluvial deposits in the western Mojave Desert, California. The samples were classified as having fluvial or debris‐flow structure based on observed stratification and measured spread of particle‐size distribution. The θ(ψ) data were fit with the Rossi–Nimmo junction model, representing water retention with three parameters: the maximum water content (θmax), the ψ‐scaling parameter (ψo), and the shape parameter (λ). We examined trends between these hydraulic parameters and bulk physical properties, both textural—geometric mean, Mg, and geometric standard deviation, σg, of particle diameter—and structural—bulk density, ρb, the fraction of unfilled pore space at natural saturation, Ae, and porosity‐based randomness index, Φs, defined as the excess of total porosity over 0.3. Structural parameters Φs and Ae were greater for fluvial samples, indicating greater structural pore space and a possibly broader pore‐size distribution associated with a more systematic arrangement of particles. Multiple linear regression analysis and Mallow's Cp statistic identified combinations of textural and structural parameters for the most useful predictive models: for θmax, including Ae, Φs, and σg, and for both ψo and λ, including only textural parameters, although use of Ae can somewhat improve ψo predictions. Textural properties can explain most of the sample‐to‐sample variation in θ(ψ) independent of deposit type, but inclusion of the simple structural indicators Ae and Φs can improve PTM predictions, especially for the wettest part of the θ(ψ) curve.

Hydrologic Characterization of Desert Soils with Varying Degrees of Pedogenesis: 2. Inverse Modeling for Effective Properties

“…[1]), thus increasing computational efficiency. For example, effective porosity n e was fixed at 75% of the maximum observed water content for each hydrogeologic unit, equivalent to assuming that, under conditions of field saturation, 25% of the pore space is occupied by trapped air, as is consistent with empirical trends for desert deposits similar to those considered in this study (Winfield et al, 2006). These fixed porosity values additionally agree with gravimetric measurements on core samples from the active wash deposits and the Holocene soil (no core was taken from the Pleistocene soil).…”

Infiltration on alluvial fans in arid environments: Influence of fan morphology

“…Structure was defined as the arrangement of soils resulting from aggregate formation, depositional sorting, shrink‐swell processes, and macropores from animal burrows and root channels. Texture was determined to have a greater influence than structure on the water retention properties of the water‐laid and debris‐laid sediments [ Winfield et al , 2006].…”

“…Specifically, we considered how the shape of the fan and the sequence of fan surfaces influence where infiltration occurs using a two dimensional (2‐D) distributed numerical model of synthetic fans with coupled surface flow and infiltration. Another characteristic of fan morphology with significance for infiltration is the permeability of fan sediments, which is related to the depositional environment, fan age, soil development, and geology of the source basin [ Weissmann et al , 2002a; Young et al , 2004; Winfield et al , 2006]. Using the numerical model, we also examined how fan morphology, including sediment permeability, influences the partitioning of flow between on‐fan flows and those that extend downslope of the fan environment.…”

Characterizing the hydraulic properties of unsaturated sand considering various porosities and drying‐wetting paths of the retention curve

“…Winfield et al . () investigated the structural influence on the water retention properties of alluvial deposit to improve the property‐transfer model predictions of unsaturated hydraulic properties.…”

“…Walczak et al (2006) suggested the prediction of WRC using three soil physical parameters. Winfield et al (2006) investigated the structural influence on the water retention properties of alluvial deposit to improve the property-transfer model predictions of unsaturated hydraulic properties.…”