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Groundwater Recharge, Storage, and Discharge mechanisms of the Colombia Plateau Regional Aquifer System (CPRAS). OUTLINE. ORGANIZATION OF PRESENTATION Introduction/Setup Purpose Location Geology Hydrogeologic Setup Mechanisms/Analysis Recharge to aquifer Storage in aquifer

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slide1

Groundwater Recharge, Storage, and Discharge mechanisms of the Colombia Plateau Regional Aquifer System (CPRAS)

outline
OUTLINE
  • ORGANIZATION OF PRESENTATION
  • Introduction/Setup
    • Purpose
    • Location
    • Geology
    • Hydrogeologic Setup
  • Mechanisms/Analysis
    • Recharge to aquifer
    • Storage in aquifer
    • Discharge from aquifer
  • Summary/Conclusion
introduction i nformation and analysis
IntroductionInformation and Analysis

Purpose

Location

Geologic setup

purpose
Purpose
  • MAIN QUESTIONS:
    • What are the mechanisms of recharge storage and discharge within the CPRAS?
    • What components have not been looked at and what else is possible for the above mentioned parameters?
location
Location
  • Columbia River Drainage Basin.
  • Mountainous perimeter.
  • Flat interior.
slide6

Geology

  • Deep basin with large mountains to the east.
  • 7 exploration oil wells project the distribution of rocks throughout the deepest parts of the plateau.
  • Hundreds of basalt flows filled in the basin known as the Columbia River Basalt Group (CRBG).
  • As the first basalt flows flooded the basin a water bodies were overridden and formed pillow basalt.

http://www.summitpost.org/mount-fairweather/250372/c-248612

geology
Geology
  • Cooling structures formed
  • Sedimentary environments developed atop basalt flows and filled in void spaces.
  • Additional lava flows developed atop sed. Environments.
  • This sequence of events continued until only mountain tops were left (steptoes)
faulting and folding
Faulting and Folding
  • Steep east-west trending anticlines on western half.
  • Monoclines have shallow dip southward from the northern boundary.
  • Steptoes on the eastern side.
slide11

Hydrogeologic Setup

  • 3 main basalt groups serve as principal aquifers.
    • Saddle Mountain Unit
    • Wanapum Unit
    • Grande Ronde Unit
  • Overburden Unit consists of loess deposits.
intraflow and interflow zones
Intraflow and Interflow zones
  • Intraflow zones consist of:
    • lower pillow basalt complex from riding over a river
    • Columnar jointing or dense crystalline interior
    • Vesicular tops
    • Possible sediment development.
  • Interflow zones generally transport water horizontally and consist of:
    • Vesicular tops of lava flows
    • Sedimentary packages
    • Pillow basalt complexes on bottom of younger flow.
recharge
Recharge

Precipitation

Surface Water Bodies

Structures

precipitation
Precipitation
  • < 8 in/yr. in central portion (natural)
  • Up to 60 in/yr. on boundaries (natural)
  • Additional recharge comes in the form of Irrigation
  • Predevelopment recharge (2.72 in/yr) average
  • Current conditions recharge (4.24 in/yr) average
surface waters
Surface Waters
  • Interflow zones near surface may be recharged by surface waters such as canals.
structures
Structures
  • Faults can hydraulically connect or interrupt interflow zones.
  • Steptoes provide infiltration paths.
  • Cooling joints provide recharge paths to lower aquifers.
storage mechanisms
Storage Mechanisms

Igneous

Sedimentary

Structural

igneous sedimentary
Igneous/Sedimentary
  • Mafic units have a median storage coefficient as low as 10^-6
  • The unconfined sedimentary unit has a storage coefficient as high as 10^-2
  • Water is stored in vertical cooling fractures and in interflow zones between lava flows.
structural groundwater catchment
Structural/Groundwater Catchment
  • Faults can create barriers to trap groundwater.
  • Steptoes provide infiltration paths.
slide21

Primarily through pumping for irrigation of .5 million acres of farm land.

  • Pumping accounts for approximately twice as much discharge than recharge.
summary answers to questions
Summary/Answers to Questions
  • Primary mechanisms of Recharge
    • Natural Precipitation at boundaries of system.
    • Anthropogenic recharge and natural recharge in central.
  • Primary mechanisms of Storage
    • Interflow zones
    • Groundwater Catchments
  • Primary mechanisms of Discharge
    • Pumping