presentation 7.0 regional v1.0 student version

Groundwater and the Hydrological Cycle, Part I

Regional Groundwater Flow

Reference Schwartz and Zhang Chapter 8

Portions by permission of John Hermance, 2007

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Portions Allan D. Woodbury (2011)

Lesson Objectives

Components of the hydrologic cycle, specifically regional groundwater flow and what controls it.

How to interpret output from a numerical-computer model

Basic recharge calculations from flow nets

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Aspects of the Hydrologic Cycle

The saturated and unsaturated zones: Groundwater

Surface water; the land surface Atmosphere

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Source: Todd and Mays (2005)

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Early Work Hubbert, Toth

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S&Z (2003) Figure 8.2

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(Source: Fig. 7.1; Fetter, 2001; after Hubbert, 1941.)

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(Source: Fig. 7.1; Fetter, 2001; after Hubbert, 1941.)

Water table is a subdued replica Recharge in upland and discharge in lowland Steady flow field, axes of symmetry, hinge lines

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Toth Simulations

First attempts at analytic solution for regional flow in 60s

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Schwartz and Zhang (2003) Figure 8.3

Mathematical problem solved by Toth

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(Source: Fig. 7.4; Fetter, 2001.)

Two Examples of Local, Intermediate and Regional Flow Patterns.

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What factors affect the partitioning of flow among local, intermediate and regional patterns ?

DlL ratio is 1:20 and lower is 1:2

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Source: Fetter (2001)

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Question: Does the spatial wavelength or the amplitude, or both, affect the partitioning among local, intermediate and regional flow patterns?

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Amplitude of the undulations cause more penetration of local systems and overides regional slopes

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Toth Results

Extended flat area, groundwater flow is very slow

When local relief (hills) is small, a general slope across will create regional flow

Local flow develops when local relief is well defined

Flow velocities in local flow system much greater that regional flow system

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More Recent Freeze & Witherspoon

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Effects of Basin Geology

Freeze and Witherspoon simulations More advanced analytic solutions

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Source: Schwartz and Zhang (2003) Figure 8.9

Local Topography

Absence of local topography causes regional flow to develop

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K contrasts; aquifers

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Effects of lenticular bodies

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Freeze and Witherspoon Results

Effects of more realistic topography Buried aquifers pinched out aquifers Many other implications not covered

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Modern Numerical Simulations Regional Flow

Slides 26 39 courtesy of Dr. John Hermance

Numerical simulations (finite difference) can capture even more realistic topography and boundary conditions

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Boundary conditions?

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Flow-net in color.

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Note: No flow directions.

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Example of flow direction.

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A Close-up View.

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Utility of Piezometers.

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Not always a correlation between elevation of watertable and depth of water in a piezometer. Nested piezometers can provide local flow direction.

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Groundwater Recharge

Infiltration will be discussed later Recharge occurs at the water table and is

the amount of water replenishing the groundwater component

Water required to maintain the water table at current position

Old thinking: spatially and temporally constant value (never changes)


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Recharge Calculations

Use basic flow net methodology More on recharge and infiltration

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Adapted Schwartz and Zhang (2003) Figure 8.23

Estimation of recharge

Rule of thumb, R = 5% of precipitation (crude)

Estimate from flow net, see above. Flow exiting from area B, 8 flow tubes, gives 12.2 cubic m/day

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Solved Problems

Problems 1 - 4

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Lesson Review

What are recharge, discharge zones?

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Lesson Review

How are flow systems categorized?

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Lesson Review

Considering the last question and length of flow paths; where would the best place be (on the topography) for a toxic waste site?

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Lesson Review

Where to you think that most, if not all, toxic waste and landfills are constructed (w/r) to flow systems?

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Lesson Review

How can you estimate (or calculate) recharge into a groundwater system?

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Groundwater and the Hydrological Cycle, Part IRegional Groundwater FlowLesson ObjectivesAspects of the Hydrologic CycleSlide Number 4Early WorkHubbert, TothS&Z (2003) Figure 8.2Slide Number 7Slide Number 8Toth Simulations Schwartz and Zhang (2003) Figure 8.3 Slide Number 13Slide Number 14 Slide Number 16Slide Number 17Toth ResultsMore RecentFreeze & WitherspoonEffects of Basin GeologySource: Schwartz and Zhang (2003) Figure 8.9 Freeze and Witherspoon ResultsModern Numerical SimulationsRegional FlowSlide Number 26Slide Number 27Slide Number 28Slide Number 29Slide Number 30Slide Number 31Slide Number 32Slide Number 33Slide Number 34Slide Number 35Slide Number 36Slide Number 37Slide Number 38Groundwater RechargeRecharge CalculationsAdapted Schwartz and Zhang (2003) Figure 8.23Solved ProblemsLesson ReviewLesson ReviewLesson ReviewLesson ReviewLesson Review

presentation 7.0 regional v1.0 student version

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