3-Dimensional Geologic Model of the Flathead River Valley at Kalispell Montana

Montana AWRA Conference Fairmont Hot Springs, MT October 14, 2016 James Rose

questions acrossMontana Study area

Red polygon north of Flathead Lake is focus area

But, we’ll look around the valley also.

Figure 01-1. Study area location. How did the Flathead Valley get to its current form?

Glacier Park

Kalispell

Flathead Lake

N Polson Moraine Kerr Dam

Polson GWIC database

Thickness of unit Hydrogeologic Unit Age Material Description Shallow sand Holocene- sand and gravel with silt and Geologic 0-200’ and gravel present clay Silt and silty-clay lacustrine Section Pleistocene - sediments and till (gravel <50’-400’ Confining Unit Holocene embedded in clay) Upper Deep coarse sand and gravel with Quaternary 0’-100’ Aquifer abundant silt or clay Clean coarse sands and gravels ~1,500’- ? Deep Aquifer Quaternary with occasional silty or clay- rich intervals

Tertiary semi-consolidated sands and +/- 1000’? Tertiary Sediments gravels and conglomerate

argillite,quartzite, siltite, Belt bedrock Pre-Cambrian Unconformable contacts mudstone, marble, dolomite Geologic Model

980 selected wells

GMS

Drillers log Drillers Hydrogeologic Units Hydrogeologic Deep Sand and Gravel Aquifer Good clean water source

Great water filter Wells data

Confining silt-clay GMS contact Log geology elevation Hydrostratigraphic Contact flag

unit

Hydrogeologic Units Hydrogeologic Wells with Hydrogeologic intervals N

bedrock

wells

Deep sand and gravel Depth Simplified Geologic Section in feet Flathead 0 River Land surface Geophysics Shallow sand and gravel Upper Deep Aquifer silt-clay 500 Deepest wells 800 feet 1000 Deep Sand and Gravel aquifer 1500 up to 2,600 feet thick Undefined ? Belt Geology 2000 Bedrock Tertiary sediment ? (about 1500 feet thick) 2500 Compacted sands, sandstones, 3000 conglomerates 8 miles

Kalispell Bigfork

Flathead Lake N

Bigfork N

Bigfork

Flathead Lake N

?

Bigfork

Flathead Lake

10 miles

Construct cross sections through model W Confining unit – lake sediments Deep sand and gravel E

Bigfork Model cross-section W E 3040

2840 unit

400 feet depth difference Belt trough Bedrock Trough bedrock 2440 Deep sand and gravel aquifer

1 mile 2240