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FOR462: Watershed Science & Management FOR462: Watershed Science & Management
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Groundwater FundamentalsGroundwater Fundamentals
Module 9.1
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Groundwater
Source: Wisler & Brater, 1949, Hydrology
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Groundwater Flow…
…Produces Baseflow
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Groundwater as a “slow” reservoir
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Groundwater Terminology
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Confined and Unconfined Aquifers
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Artesian Well
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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
dx
dhAkQ 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 m
2 m
25 m
85 m
kh=5 m day-1
Fine sand
( )( ) daym
daym 3
6.26m 800
m 0.2m 85 m 255 =⎟
⎠
⎞⎜⎝
⎛×==
dx
dhAkQ t
v
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Groundwater Development
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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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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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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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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