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 Columbia River Drainage Basin. Mountainous perimeter. Flat interior.
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
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)
3 main basalt groups serve as principal aquifers. Saddle Mountain Unit Wanapum Unit Grande Ronde Unit Overburden Unit consists of loess deposits. Hydrogeologic Setup
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.
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 Interflow zones near surface may be recharged by surface waters such as canals.
Structures Steptoes provide infiltration paths. Cooling joints provide recharge paths to lower aquifers. Faults can hydraulically connect or interrupt interflow zones.
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 Steptoes provide infiltration paths. Faults can create barriers to trap groundwater.
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 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