Grid-Size Dependency of Evapotranspiration Simulations in Shallow Aquifers: An Optimal Approach

Kambhammettu, Bvn P; King, James P.; Schmid, Wolfgang

doi:10.1061/(asce)he.1943-5584.0000957

Cited by 5 publications

(4 citation statements)

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“…() and Kambhammettu et al . () would cease to be an issue as the UFRs predefined for the terrain type would correctly produce the ET estimate without explicitly retaining the necessary subgrid elevation data to maintain accuracy. Additionally, as supported by Rihani et al .…”

Section: Resultsmentioning

confidence: 99%

“…It is the belief of the authors that simply upscaling in the straightforward manner described in this paper would make it possible to avoid or reduce many of the issues that currently exist when modelling GW-SW fluxes at regional scales. For example, the errors introduced to ET when upscaling as described by Kambhammettu et al (2011) and Kambhammettu et al (2013) would cease to be an issue as the UFRs predefined for the terrain type would correctly produce the ET estimate without explicitly retaining the necessary subgrid elevation data to maintain accuracy. Additionally, as supported by Rihani et al (2010), topographic slope affects ET fluxes, and therefore, the use of UFRs based upon terrain type would account for some of this terrain-specific variability.…”

Section: Why This Characterization? What Does It Mean For Modelling Amentioning

confidence: 99%

“…Some approaches, such as that of TOPMODEL (Beven and Kirkby, 1979;Iorgulescu and Musy, 1997;Lamb et al, 1997), arrive at simpler power law relations via the extension of simplified conceptual models to problems of baseflow and run-off generation. Many previous studies have used simple linear and power law relationships to represent relationships between GW storage, GW infiltration and GW-SW exchange fluxes such as evapotranspiration, discharge to rivers or discharge from hillslopes (Beven, 1984;Selker et al, 1999;Rupp and Selker, 2005;Cardenas, 2008;Troch et al, 2008;Harman et al, 2009;Kambhammettu et al, 2011Kambhammettu et al, , 2013. These are rarely justified via the application of fine-resolution physically based models.…”

Section: Introductionmentioning

confidence: 99%

“…Unsurprisingly, the ET from shallow GW, which is dependent upon WT depth, has been found to be prone to errors when naïvely upscaled (i.e. simply applying point‐scale ET relationships directly on coarse grids) (Kambhammettu et al ., , ). These studies found that the ability to simulate ET at large scales was dependent on the correct interpretation of digital elevation model (DEM) data.…”

Section: Introductionmentioning

confidence: 99%

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Effective groundwater-surface water exchange at watershed scales

Snowdon

Craig

2015

Hydrol. Process.

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Coupled groundwater–surface water (GW–SW) models are capable of simulating complex hydrological systems when used at fine resolutions. However, properly characterizing bulk GW–SW fluxes for either coarsely resolved integrated models or basin‐discretized surface water models remains a challenge. Loss of subgrid detail, while beneficially decreasing computational cost, leads to a decrease in model accuracy as scale effects become important. Ideally, coarse low‐resolution models should be informed by expected subgrid behaviour, reducing the impact of scale effects. Determining how to best represent these fine‐scale details in lower‐resolution models is important for improving the accuracy and appropriateness of these models. To investigate some of these scale effects, we here explore the relationships between area‐averaged hydraulic head and bulk GW–SW exchange fluxes (e.g. evapotranspiration and discharge), all of which are presumed to be controlled predominantly by subgrid topographic effects. These relationships may be useful for simply upscaling models without the complete loss of crucial fine‐resolution subgrid details. Using finely resolved simulation output from Modflow for a fine‐resolution simulation and post‐processed results generated to represent coarser resolutions, upscaled flux relationships (UFRs) are generated for multiple terrains; these UFRs define the relationships that exist between average hydraulic head and average fluxes in unconfined aquifer systems. It is found that, for steady‐flow regimes, similar one‐to‐one power law relationships consistently exist between area‐averaged hydraulic heads, exchange fluxes and saturated area for a variety of terrains. Additionally, when the averaged values are properly normalized, the generated steady‐state UFRs for a single terrain are independent of hydraulic conductivity and potential evapotranspiration rates and apparently insensitive to the presence of mild heterogeneity. While some hysteresis is apparent in the relationships under transient conditions, transient artefacts are shown to be minor under some circumstances, indicating that UFRs may be applied to both steady‐state and transient scenarios. Simpler tests performed under saturated and variably saturated conditions in a cross‐sectional model show similar trends, suggesting that the UFR representation is extendable to systems where the vadose zone plays a significant role. It is suggested that relatively simple UFRs such as these may find use as an alternative to direct point upscaling or multi‐resolution models for estimating GW–SW exchange fluxes in coarse‐scale models. They also appear to justify the functional form of some classical models of baseflow and evapotranspiration used in conceptual surface water models. Copyright © 2015 John Wiley & Sons, Ltd.

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Section: Resultsmentioning

confidence: 99%