Evaluation of unsaturated zone water fluxes in heterogeneous alluvium at a Mojave Basin Site

Nimmo, John R.; Deason, Jeffrey A.; Izbicki, John A.; Martin, Peter M.

doi:10.1029/2001wr000735

Cited by 25 publications

(18 citation statements)

References 18 publications

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“…Under the unit-gradient assumption, a single K(h) measurement can indicate long-term average recharge rate in zones of steady downward flow in deep unsaturated zones typical of arid regions (Nimmo et al, 2003). Temporal variability of recharge in such cases is dampened by physical averaging of flow paths (Nimmo et al, 2002). Although the current study sampled shallow unsaturated zones in a comparatively humid climate, dampening of variations in measured soil tension has been observed at shallow depths in central Indiana (Bayless, 2001).…”

Section: Darcian-pedotransfer Methodsmentioning

confidence: 96%

Factors influencing ground-water recharge in the eastern United States

Nolan

Healy

Taber

et al. 2007

Journal of Hydrology

106

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Kerie J.; and Wolock, David M., "Factors influencing ground-water recharge in the eastern United States" (2007). USGS Summary Ground-water recharge estimates for selected locations in the eastern half of the United States were obtained by Darcian and chloride-tracer methods and compared using statistical analyses. Recharge estimates derived from unsaturated-zone (R UZC ) and saturated-zone (R SZC ) chloride mass balance methods are less variable (interquartile ranges or IQRs are 9.5 and 16.1 cm/yr, respectively) and more strongly correlated with climatic, hydrologic, land use, and sediment variables than Darcian estimates (IQR = 22.8 cm/yr). The unit-gradient Darcian estimates are a nonlinear function of moisture content and also reflect the uncertainty of pedotransfer functions used to estimate hydraulic parameters. Significance level is <0.001 for nearly all explanatory variables having correlations with R UZC of <À0.3 or >0.3. Estimates of R SZC were evaluated using analysis of variance, multiple comparison tests, and an exploratory nonlinear regression (NLR) model. Recharge generally is greater in coastal plain surficial aquifers, fractured crystalline rocks, and carbonate rocks, or in areas with high sand content. Westernmost portions of the study area have low recharge, receive somewhat less precipitation, and contain fine-grained sediment. The NLR model simulates water input to the land surface followed by transport to ground water, depending on factors that either promote or inhibit water infiltration. The model explains a moderate amount of variation in the data set (coefficient of determination = 0.61). Model sensitivity analysis indicates that mean annual runoff, air temperature, and precipitation, and an index of ground-water exfiltration potential most influence estimates of recharge at sampled sites in the region. Soil characteristics and land use have less influence on the recharge estimates, but nonetheless are significant in the NLR model. ª

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Section: Darcian-pedotransfer Methodsmentioning

confidence: 96%

Factors influencing ground-water recharge in the eastern United States

Nolan

Healy

Taber

et al. 2007

Journal of Hydrology

106

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“…As the vadose zone was composed of distinct layers (Fig. 1), the assumption of relative homogeneity of soil hydraulic properties for each layer is a common practice to delineate different layers of soil texture, in unsaturated flow and transport problems (Hills et al, 1991; Roth et al, 1991; Nimmo et al, 2002; Zhu and Mohanty, 2002).…”

Section: Model Applicationmentioning

confidence: 99%

Richards Equation–Based Modeling to Estimate Flow and Nitrate Transport in a Deep Alluvial Vadose Zone

Botros

Onsoy

Ginn

et al. 2012

Vadose Zone Journal

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Heterogeneity in unsaturated soils and sediments is well known to exist at different scales, from microscopic scale to macroscopic scale. Characterization of different types of heterogeneity in deep vadose zones is challenging because of the usual lack of information at such sites. In this paper, we considered a site with detailed geological, chemical, and hydraulic properties measurements throughout an approximately 16‐m deep vadose zone consisting of unconsolidated, alluvial deposits typical for the alluvial fans of the eastern San Joaquin Valley, California. At the agricultural site, data were also available for a 7‐yr long field fertilization experiment that we used to independently estimate the amount of nitrate stored within the vadose zone at the end of the experiment. Simple mass balance calculations were performed and compared to six conceptually different two‐dimensional and three‐dimensional vadose zone numerical models that were implemented to represent varying degrees of hierarchical details of heterogeneity. Despite widely differing structure and heterogeneity of unsaturated flow, all models resulted in a narrow range of estimated nitrate storage in the deep vadose zone for near‐cyclically repeated water and nitrogen fertilizer applications. Simulated nitrate storage was found to be approximately six to eight times larger than the measured storage at the field. Simulated nitrate variability, while qualitatively similar in pattern, was considerably lower than measured, despite the large simulated hydraulic variability. This study underscores that physical heterogeneity of deep vadose zones may have limited effects on the transfer of conservative contaminants applied repeatedly to the land surface. It also raises questions about our understanding of the chemical fate of nitrate in the vadose zone; and suggests the presence of a significant immobile moisture domain within the deep vadose zone that is not explainable by heterogeneity of Richards equation parameters, yet needs to be considered for simulating nitrate transport under conditions of cyclical infiltration with gravity dominated convective flux.

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“…However, small amounts of water moving downward through preferential pathways in the unsaturated zone may move more rapidly (Izbicki et al ., 2000). Because water spreads laterally away from the wash as it moves downward, the rate of downward movement decreases with depth (Izbicki et al ., 2000, 2002; Nimmo et al ., 2002). Simulations of unsaturated flow (Izbicki, 2002) show that lateral spreading can be increased by low permeability layers within the unsaturated zone that impede the downward movement of water (Figure 8).…”

Section: Unsaturated Flowmentioning

confidence: 99%

“…Although precipitation, runoff, and subsequent streamflow are highly variable, water potential and downward rates of water movement damp to a constant value with increasing depth (Nimmo et al ., 2002). For example, seasonal water potential (and temperature data) collected beneath Quail and Yucca Washes damp to near constant values within 15 m of land surface (Nishikawa et al ., 2004).…”

Section: Unsaturated Flowmentioning

confidence: 99%

Physical and Temporal Isolation of Mountain Headwater Streams in the Western Mojave Desert, Southern California¹

Izbicki

2007

J American Water Resour Assoc

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Streams draining mountain headwater areas of the western Mojave Desert are commonly physically isolated from downstream hydrologic systems such as springs, playa lakes, wetlands, or larger streams and rivers by stream reaches that are dry much of the time. The physical isolation of surface flow in these streams may be broken for brief periods after rainfall or snowmelt when runoff is sufficient to allow flow along the entire stream reach. Despite the physical isolation of surface flow in these streams, they are an integral part of the hydrologic cycle. Water infiltrated from headwater streams moves through the unsaturated zone to recharge the underlying ground‐water system and eventually discharges to support springs, streamflow, isolated wetlands, or native vegetation. Water movement through thick unsaturated zones may require several hundred years and subsequent movement through the underlying ground‐water systems may require many thousands of years – contributing to the temporal isolation of mountain headwater streams.

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Evaluation of unsaturated zone water fluxes in heterogeneous alluvium at a Mojave Basin Site

Cited by 25 publications

References 18 publications

Factors influencing ground-water recharge in the eastern United States

Factors influencing ground-water recharge in the eastern United States

Richards Equation–Based Modeling to Estimate Flow and Nitrate Transport in a Deep Alluvial Vadose Zone

Physical and Temporal Isolation of Mountain Headwater Streams in the Western Mojave Desert, Southern California¹

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Evaluation of unsaturated zone water fluxes in heterogeneous alluvium at a Mojave Basin Site

Cited by 25 publications

References 18 publications

Factors influencing ground-water recharge in the eastern United States

Factors influencing ground-water recharge in the eastern United States

Richards Equation–Based Modeling to Estimate Flow and Nitrate Transport in a Deep Alluvial Vadose Zone

Physical and Temporal Isolation of Mountain Headwater Streams in the Western Mojave Desert, Southern California1

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Physical and Temporal Isolation of Mountain Headwater Streams in the Western Mojave Desert, Southern California¹