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OUTLINE

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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OUTLINE

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

  2. OUTLINE • ORGANIZATION OF PRESENTATION • Introduction/Setup • Purpose • Location • Geology • Hydrogeologic Setup • Mechanisms/Analysis • Recharge to aquifer • Storage in aquifer • Discharge from aquifer • Summary/Conclusion

  3. IntroductionInformation and Analysis Purpose Location Geologic setup

  4. 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?

  5. Location • Columbia River Drainage Basin. • Mountainous perimeter. • Flat interior.

  6. 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

  7. 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)

  8. Geology

  9. 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.

  10. Hydrogeologic Setup

  11. Hydrogeologic Setup • 3 main basalt groups serve as principal aquifers. • Saddle Mountain Unit • Wanapum Unit • Grande Ronde Unit • Overburden Unit consists of loess deposits.

  12. 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.

  13. Recharge Precipitation Surface Water Bodies Structures

  14. 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

  15. Surface Waters • Interflow zones near surface may be recharged by surface waters such as canals.

  16. Structures • Faults can hydraulically connect or interrupt interflow zones. • Steptoes provide infiltration paths. • Cooling joints provide recharge paths to lower aquifers.

  17. Storage Mechanisms Igneous Sedimentary Structural

  18. 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.

  19. Structural/Groundwater Catchment • Faults can create barriers to trap groundwater. • Steptoes provide infiltration paths.

  20. Discharge

  21. Primarily through pumping for irrigation of .5 million acres of farm land. • Pumping accounts for approximately twice as much discharge than recharge.

  22. 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

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