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FOR462: Watershed Science & Management

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Groundwater Fundamentals

Module 9.1

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FOR462: Watershed Science & Management

Groundwater

Source: Wisler & Brater, 1949, Hydrology

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FOR462: Watershed Science & Management

Groundwater Flow…

…Produces Baseflow

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FOR462: Watershed Science & Management

Groundwater as a “slow” reservoir

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FOR462: Watershed Science & Management

Groundwater Terminology

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FOR462: Watershed Science & Management

Confined and Unconfined Aquifers

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FOR462: Watershed Science & Management

Artesian Well

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FOR462: Watershed Science & Management

More on Aquifer Types…

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FOR462: Watershed Science & Management

Hydraulic Head

datum

ht

hp

z

a

Pressure:

pghP ρ=

Total hydraulic head (ht):

pt hzh +=

Where:ρ = density of water (kg m-3)g = gravitational acceleration (m s-2)hp = pressure head

Where:z = elevationhp = pressure head

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FOR462: Watershed Science & Management

Darcy’s Law

Darcy’s Law defines groundwater flow:

where:Q is discharge (L3 T-1)kv is the hydraulic conductivity (L T-1)A is area of flow (L2), anddht/dx is the gradient of pressure, or head

dxdhAkQ t

v=

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FOR462: Watershed Science & Management

Hydraulic Conductivity (kv)

Hornberger, 1998

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FOR462: Watershed Science & Management

Example

800 m2 m

25 m

85 m

kh=5 m day-1

Fine sand

( )( ) daym

daym 36.26

m 800m 0.2m 85 m 255 =⎟⎠⎞⎜

⎝⎛×==

dxdhAkQ t

v

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FOR462: Watershed Science & Management

Groundwater Development

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FOR462: Watershed Science & Management

Groundwater/Surface Water Connections

Gaining Stream

Cone ofDepression

Pumping Well

Groundwater

In systems with high degree of groundwater/surface water connectivity(highly transmissive sediments)

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FOR462: Watershed Science & Management

Subsidence

From USGS Professional Paper 1401-A, "Ground water in the Central Valley, California- A summary report"Photo by Dick Ireland, USGS, 1977

Causes:Fluid withdrawal

Sinkholes

Drainage of Organic soils

Mining

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FOR462: Watershed Science & Management

Recharge Zone Protection Example

Piezometric surface

Municipal well field

Gravel

Clay Clay

Confined Aquifer

UnconfinedAquifer

Recharge Zone

landfill

flow

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FOR462: Watershed Science & Management

Groundwater Development

• Multiple pumping wells can cause interference between cones of depression

• Extraction should not exceed recharge• Water mining

• Extraction may cause subsidence• Recharge zones should be protected

• Ensure adequate water flow• Ensure quality

• Extraction may affect surface water• Many watershed management actions are

taken to protect quality

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FOR462: Watershed Science & Management

Gaining and Losing Streams

Dingman

Gaining streamEffluent stream

Losing streamInfluent stream

Perched losing stream Flow-through stream

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FOR462: Watershed Science & Management

Hyporheic Zone

• Zone where water is exchanged between surface and groundwater

• Controlled by geomorphology (upwelling and downwelling)

• Biochemical processing: water quality & habitat issues

• Temperature

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FOR462: Watershed Science & Management

Bedrock

Floodplain

Equipotential lines

Kasahara & Wondzell (2003) Water Resour. Res.

Scale (m)

0 25 50

2nd-Order / Unconstrained reach of WS03, HJA

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FOR462: Watershed Science & Management

Proposed C & D Landfill Example

Creek

Flow Direction

Old Gravel

Pit

Domestic Wells

Constituents of ConcernSulfate ArsenicChromiumIron1,2-DCATotal Dissolved Solids

Glacial Outwash

Zone exceedingMCL’s for drinkingwater

Increased, butMCL’s for drinkingWater not exceeded

Modeled contaminant plumes

Municipal Wells