1. Aquifers and Groundwater flow
ATM 301 Lecture #16 (sections )
Groundwater:
Aquifers and Groundwater flow

2. Snowpack and snowmelt Groundwater Outline of the course The Basics
The global hydrological cycle
Precipitation
Soil water (lab work)
Surface energy fluxes
Evaporation and transpiration
Snowpack and snowmelt
Groundwater
Streamflow
Floods & Droughts
Water management

3. Hydrologic Soil Horizons (or layers):
Vadose Zone
(unsaturated zone)
p=w g (z’-z’o)
Phreatic Zone
(saturated zone)
p=w g (z’-z’o)

4. Groundwater is water stored in saturated soils and rocks.
Pressure in groundwater is greater than atmospheric, increasing with depth (hydrostatic).

5. About 30% of global freshwater is stored as groundwater
Residence time of weeks to 1000’s of years!

6. Why care about groundwater?
Stores much of Earth’s freshwater (30%)
Used for irrigation and drinking water when other sources are unavailable
About ¼ of world’s water resources are drawn from groundwater
Subject to contamination and depletion
Groundwater storage crosses property lines, town lines, state, and national boundaries
Source of most water in many rivers and lakes
Affects stream flow timing and magnitude

7. Ground water as a fraction of total freshwater use in US

8. Overview of groundwater
Groundwater is water stored in saturated soils and rocks.
Pressure in groundwater is greater than atmospheric, increasing with depth (hydrostatic).
The water table is the upper boundary of the groundwater zone.
Groundwater is increased by recharge and decreased by discharge
Water table
Unsaturated soil

9. An aquifer is a geologic unit that can store enough water and transmit it at a rate fast enough to be hydrologically significant.
Unconfined aquifers Upper boundary is the water table, and the height of water in a drilled well. They have p=patm at upper boundary
Confined aquifers Upper boundary is a confining layer of very low hydraulic conductivity. p>patm at the upper boundary, and water in a drilled well will rise above the confining layer.
Fig 9-1

10. About ¼ of NYS population relies on groundwater

11. Principal Aquifers in the U.S.10 3 11 1 13 50

12. Withdrawals from Major Aquifers
in the U.S. in 2000

13. High Plains / Ogallala Aquifer
Saturated Thickness (ft)
High Plains / Ogallala Aquifer
Very large aquifer that is central in sustaining a large fraction of US agriculture
“About 27 percent of the irrigated land in the United States overlies this aquifer system, which yields about 30 percent of the nation's ground water used for irrigation. In addition, the aquifer system provides drinking water to 82 percent of the people who live within the aquifer boundary”- USGS

14. Annual Withdrawal from
Ogallala Aquifer
for year 2000

15. Saturated Thickness (ft) in 2000
Water-level change (ft) from 1950 to 2005
~9% decline since “pre-development” (~1950’s)
…major concern, since recharge could take 100’s-1000’s of years!

16. US Groundwater Extraction
from

17. in Eastern Australia

18. World’s Major Aquifers and their Footprint (GF) or Recharge Area

21. Monitoring Groundwater
Measurements of water table by wells: very few long-term records (e.g., from Illinois State Water Survey).

22. Monitoring Groundwater from Space
GRACE satellite measurements of changes in water storage over land by measuring changes in gravity. Launched in March 2002.
GRACE=Gravity Recovery and Climate Experiment (GRACE), lauched in March 2002
GRACE=Gravity Recovery and Climate Experiment

23. Low spatial resolution ~300-400km for monthly data
Base period: From
Low spatial resolution ~ km for monthly data
GRACE Data portal:

24. GRACE Satellite Measurements
(~7min.)

25. Groundwater flow
For steady flow in an isotropic (K doesn’t depend on direction) and homogeneous (K doesn’t depend on location) medium:
3D version of Darcy’s Law can determine the distribution of hydraulic head, if given conditions at the boundaries.
This can be used to calculate the groundwater flow
Water flow directions (streamlines) are perpendicular to lines of constant hydraulic head (equipotential lines)
“Flow Net”
High h
Low h
streamlines
Equipotential lines (constant h)
Fig 9-5

26. Topographic effects on groundwater flow
Gradual slopes lead to gradual gradients in h, with a single regional flow system with discharge distant from recharge regions
Hills and valleys produce local variations in h, and create numerous local flow systems with discharge nearby to recharge regions
Fig 9-7
regional flow system
Local flow systems
regional flow system

27. Local flow system
Intermediate
flow system
Regional flow system

28. Geologic effects on groundwater flow
Geologic material affects the hydraulic conductivity
Sediment size
Sediment or rock type
Fracturing
This influences flow paths and rates

29. Combined geological and topographic effects
Fig 9-11
Low conductivity
High conductivity

30. Landscape and Groundwater Flow
The Fundamental Hydrologic Landscape Unit (FHLU)

31. Generalized Hydrologic
Landscape Types and
Groundwater Flow

32. Ground water links http://ny.water.usgs.gov/