Importance of Unsaturated Zone Flow for Simulating Recharge in a Humid Climate

Hunt, Randall J.; Prudic, David E.; Walker, John F.; Anderson, Mary P.

doi:10.1111/j.1745-6584.2007.00427.x

Cited by 66 publications

(43 citation statements)

References 40 publications

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“…Temporal variability in recharge is a response to climate variability and land use change; and may be affected by the flow and storage in the unsaturated zone (McMahon et al, 2006;Hunt et al, 2008;Scanlon et al, 2010aScanlon et al, , 2010bCrosbie et al, 2013;Le Coz et al, 2013). Recharge estimation techniques often focus on drainage below the root zone assuming that the unsaturated zone flux at the base of the root zone represents actual recharge (Gurdak and Roe, 2010).…”

Section: Introductionmentioning

confidence: 99%

Impacts of thickening unsaturated zone on groundwater recharge in the North China Plain

Cao

Scanlon

Han

et al. 2016

Journal of Hydrology

107

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s u m m a r yUnsustainable groundwater development shown by rapid groundwater depletion in the North China Plain (NCP) underscores the need to quantify spatiotemporal variability in groundwater recharge for improved management of the resource. The objective of this study was to assess spatiotemporal variability in recharge in response to thickening of the unsaturated zone in the NCP. Recharge was estimated by linking a soil water balance (SWB) model, on the basis of monthly meteorological data, irrigation applications, and soil moisture monitoring data (1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008), to the water table using a deep unsaturated zone flow model. The dynamic bottom boundary (water table) position was provided by the saturated zone flow component, which simulates regional pumping. The model results clearly indicate the effects of unsaturated zone thickening on both temporal distribution and magnitude of recharge: smoothing temporal variability in recharge, and increasing unsaturated storage and lag time between percolation and recharge. The thickening unsaturated zone can result in average recharge reduction of up to $70% in loam soils with water table declines P30 m. Declining groundwater levels with irrigation sourced by groundwater converts percolation to unsaturated zone storage, averaging 14 mm equivalent water depth per year in mostly loam soil over the study period, accounting for $30% of the saturated groundwater storage depletion. This study demonstrates that, in thickening unsaturated zones, modeling approaches that directly equate deep drainage with recharge will overestimate the amount and underestimate the time lag between percolation and recharge, emphasizing the importance of more realistic simulation of the continuity of unsaturated and saturated storage to provide more reliable estimates of spatiotemporal variability in recharge.

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Section: Introductionmentioning

confidence: 99%

Impacts of thickening unsaturated zone on groundwater recharge in the North China Plain

Cao

Scanlon

Han

et al. 2016

Journal of Hydrology

107

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“…As expected, fluctuations were smoothed to a large extent. The episodic nature of recharge, reported in the literature (e.g., Hunt et al, 2008;Smerdon et al, 2008), is lost when precipitation values are averaged over longer time periods. Similar conclusions on the influence of time averaging of the weather data were also presented by Batalha et al (2018).…”

Section: Influence Of the Temporal Resolution Of Weather Datamentioning

confidence: 88%

Simulations of freshwater lens recharge and salt/freshwater interfaces using the HYDRUS and SWI2 packages for MODFLOW

Szymkiewicz

Gumuła-Kawęcka

Šimůnek

et al. 2018

Journal of Hydrology and Hydromechanics

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Abstract:The paper presents an evaluation of the combined use of the HYDRUS and SWI2 packages for MODFLOW as a potential tool for modeling recharge in coastal aquifers subject to saltwater intrusion. The HYDRUS package for MODFLOW solves numerically the one-dimensional form of the Richards equation describing water flow in variablysaturated media. The code computes groundwater recharge to or capillary rise from the groundwater table while considering weather, vegetation, and soil hydraulic property data. The SWI2 package represents in a simplified way variable-density flow associated with saltwater intrusion in coastal aquifers. Combining these two packages within the MODFLOW framework provides a more accurate description of vadose zone processes in subsurface systems with shallow aquifers, which strongly depend upon infiltration. The two packages were applied to a two-dimensional problem of recharge of a freshwater lens in a sandy peninsula, which is a typical geomorphologic form along the Baltic and the North Sea coasts, among other places. Results highlighted the sensitivity of calculated recharge rates to the temporal resolution of weather data. Using daily values of precipitation and potential evapotranspiration produced average recharge rates more than 20% larger than those obtained with weekly or monthly averaged weather data, leading to different trends in the evolution of freshwater-saltwater interfaces. Root water uptake significantly influenced both the recharge rate and the position of the freshwater-saltwater interface. The results were less sensitive to changes in soil hydraulic parameters, which in our study were found to affect average yearly recharge rates by up to 13%.

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“…The size of the lag between the infiltration event and the associated recharge response at the water table will obviously increase with increasing thickness of the unsaturated zone. Although the bulk of the basin has shallow water tables (<7 meters), Hunt et al [52] found lags as much as months in other portions of the basin where the thickness of the unsaturated zone is significantly greater (15 -25 meters thick).…”

Section: Spatial Variability In Rechargementioning

confidence: 99%

An Integrated Field Assessment of Groundwater Recharge

W.R.¹

2012

TOHYDJ

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Groundwater recharge is often assumed to be uniform within a watershed owing to difficulties in quantifying its temporal and spatial variability. In this paper, fluctuations in soil moisture content at multiple depths in the unsaturated zone together with fluctuations in the water table are used to provide a record of the recharge process and a means to quantify and compare temporal and spatial recharge variability. Hourly measurements of soil moisture content and the elevation of the water table were collected at two sites, a clear cut and a coniferous forest site, within the Trout Lake basin of northern Wisconsin. The soil moisture and water table data were used together to assess the temporal and spatial variability in groundwater recharge from October 1999 to May 2001 and to identify the climatic (amount and timing of rainfall) and physical (vegetation and soil type) controls on the recharge process within this basin. Together, the two datasets allow for a holistic assessment of the recharge process from the ground surface through the unsaturated zone down to the water table.

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Importance of Unsaturated Zone Flow for Simulating Recharge in a Humid Climate

Cited by 66 publications

References 40 publications

Impacts of thickening unsaturated zone on groundwater recharge in the North China Plain

Impacts of thickening unsaturated zone on groundwater recharge in the North China Plain

Simulations of freshwater lens recharge and salt/freshwater interfaces using the HYDRUS and SWI2 packages for MODFLOW

An Integrated Field Assessment of Groundwater Recharge

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