Groundwater Fluxes Across Interfaces (2004) / Chapter Skim
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1 Introduction
1 Introduction
Pages 5-15
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From page 5... ...
For example, in situ point measurements are representative of the point value of a flux but are inadequate for mapping larger regions of interest to planners, while regional chemical tracers and modeling techniques can provide estimates representative of larger areas but these are difficult to relate to local conditions at water supply and aquifer remediation sites. The challenge to closing the groundwater balance, and to estimating groundwater fluxes to or fiom other water reservoirs, is to integrate flux measurement and estimation techniques at multiple scales, with multiple types of data.
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From page 6... ...
Despite the importance to water and chemical cycles, to ecosystems, and to water reources management, there are no universally applicable methods or established networks to measure recharge and discharge rates, and only limited understanding of recharge and discharge processes. Limited understanding and difficulties with measurements arise in part because of the distnbuted nature and spatially large extent of most groundwater recharge and discharge areas, as well as the many different
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From page 7... ...
Nationally, NRC's Water Science and Technology Board recently identified mapping of groundwater recharge and discharge vulnerability as a priority area for research in environmental science (NRC, 2000~. The Water Cycle initiative of the U.S.
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From page 8... ...
* Seepage meters Heat tracers Isotopic tracers Solute mass balance Watershed Modeling *
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From page 9... ...
9 o is at: ct o o is 'e go He o If s: · o ~ ~ o >- ~ ct of c) I: i ~ .g cool v, C'3 o o l lo ~ i ~ cD ~5: c)
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From page 10... ...
However, many of the concepts related to natural groundwater fluxes also apply to anthropogenic fluxes such as those associated with agriculture, municipal water supply, and aquifer contamination. The report is also not meant to be a comprehensive analysis of all issues related to Groundwater fluxes but instead focuses on the following questions, drawn from a broader set of issues (see preface)
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From page 11... ...
· How accurately can recharge/discharge patterns/rates be estimated at a regional or national scale, and how might uncertainty in these patterns/rates vain with spatial and temporal scale and geographic location? BASIC CONCEPTS RELATED TO GROUNDWATER RECHARGE/DISCHARGE The zone of subsurface water can be divided into the unsaturated zone above the water table and the saturated zone below the water table.
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From page 12... ...
measures basin-scale groundwater discharge to streams, which is then used as a proxy for recharge estimates under the assumption that, under steady state conditions on the watershed scale, recharge equals discharge. Darcy's law is used to estimate point discharge rates by measunog hydraulic gradients in piezometers installed in a discharge area.
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From page 13... ...
'.:; . ~ : ~ -, ~ 13 FIGURE 1-3 The Fundamental Hydrologic Landscape Unit (FHLU)
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From page 14... ...
Seepage meters, theoretically, can be used to make direct point measurements of either recharge or discharge of water between a surface water body and the groundwater system, but have been used more successfully to estimate discharge. Seepage meters for discharge estimation are designed to collect groundwater flux.
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From page 15... ...
A summary of the methods, including general approach, scale of application, and strengths and limitations, is presented in Table I-2 and illustrates some of the issues in estimating groundwater fluxes. The methods in the table produce estimates of flux that reflect different spatial and temporal scales, they have different data requirements, strengths and limitations; and have varying sensitivity to water flux in Eactures, a major pathway through the unsaturated zone at Yucca Mountain.
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