A Screening Tool for Delineating Subregions of Steady Recharge within Groundwater Models

Abstract

We have developed a screening method for simplifying groundwater models by delineating areas within the domain that can be represented using steady‐state groundwater recharge. The screening method is based on an analytical solution for the damping of sinusoidal infiltration variations in homogeneous soils in the vadose zone. The damping depth is defined as the depth at which the flux variation damps to 5% of the variation at the land surface. Groundwater recharge may be considered steady where the damping depth is above the depth of the water table. The analytical solution approximates the vadose zone diffusivity as constant, and we evaluated when this approximation is reasonable. We evaluated the analytical solution through comparison of the damping depth computed by the analytic solution with the damping depth simulated by a numerical model that allows variable diffusivity. This comparison showed that the screening method conservatively identifies areas of steady recharge and is more accurate when water content and diffusivity are nearly constant. Nomograms of the damping factor (the ratio of the flux amplitude at any depth to the amplitude at the land surface) and the damping depth were constructed for clay and sand for periodic variations between 1 and 365 d and flux means and amplitudes from nearly 0 to 1 × 10−3 m d−1. We applied the screening tool to Central Valley, California, to identify areas of steady recharge. A MATLAB script was developed to compute the damping factor for any soil and any sinusoidal flux variation.

Analyses of infrequent (quasi-decadal) large groundwater recharge events in the northern Great Basin: Their importance for groundwater availability, use, and management

“…The higher‐frequency events identified in the precipitation spectrum are not present in the groundwater spectrum suggesting that these precipitation events have less effect on groundwater levels. This is consistent with the findings of several studies [ Dickinson et al ., ; Velasco et al ., ] which showed that low‐frequency signals tend to be better preserved in the groundwater level record than high‐frequency signals because of damping in the unsaturated zone which is related to soil texture, depth to water, and mean and period of the infiltration flux. This also implies that the quasi‐decadal groundwater recharge events are highly important in supplying large amounts of recharge to the groundwater system.…”

Recent Developments and Applications of the HYDRUS Computer Software Packages

“…The largest number of HYDRUS papers in VZJ simulated subsurface water fluxes and groundwater recharge (e.g., Dickinson et al, 2014; Pfletschinger et al, 2014; Rieckh et al, 2014; Turkeltaub et al, 2014; Fan et al, 2015; and Guber et al, 2015). Of these, Guber et al (2015) used HYDRUS‐2D to evaluate a new subsurface water retention technology consisting of subsurface polyethylene membranes installed within the soil profile to improve root‐zone water storage and to limit downward recharge fluxes.…”

“…Fan et al (2015) used both HYDRUS‐1D and HYDRUS (2D/3D) to model the effects of plant canopy and roots on soil moisture and deep drainage in forested ecosystems. Dickinson et al (2014) used HYDRUS‐1D to verify the appropriateness of a proposed screening tool for delineating areas with constant groundwater recharge. Turkeltaub et al (2014) used data collected with a deep vadose zone monitoring system to calibrate HYDRUS‐1D and subsequently used the software to investigate the temporal characteristics of groundwater recharge and how recharge may be affected by climate change.…”

“…Fan et al (2015) used both HYDRUS-1D and HYDRUS (2D/3D) to model the effects of plant canopy and roots on soil moisture and deep drainage in forested ecosystems Dickinson et al (2014). VZJ | Advancing Critical Zone Science p. 17 of 25…”

Filtering of Period Infiltration in a Layered Vadose Zone: 1. Approximation of Damping and Time Lags

“…[16] and [17]. The period of the forcings may be representative of irrigation cycles or seasonal or annual climatic variability identified through time series analysis of atmospheric or hydrologic data (e.g., Hanson et al, 2004; Gurdak et al, 2007; Dickinson et al, 2014; Velasco et al, 2017). The fine soil is a silty clay and the coarse soil is a sandy loam, which have differing soil hydrologic parameters (Table 1) that produce complex flow and water content responses at the layer boundary.…”