(12) + (13) Groundwater Flashcards
1
Q
Groundwater
A
- Water that lies beneath ground surface
2
Q
How does it get underground?
A
- Rain and snowfall: percolation into the ground under the influence of gravity
- 15% of precipitation ends up as ground water
o Big variations locally and regionally - Porosity decreases with depth
o More cement in sediment rock closes pores
o Weight of overlaying rock closes pores
o Igneous and metamorphic rocks have low porosity
3
Q
Where is groundwater stored?
A
- Fills pore space between grains in sediment and clastic sedimentary rocks
- Fills cracks in all types of rocks
4
Q
Porosity
A
- Measures rocks ability to hold water
- Porous vs nonporous
5
Q
Permeability
A
- Measures capacity of rocks to transmit fluid through pores and fractures (flow)
- Permeable vs impermeable
6
Q
Terms to know
A
- Saturated zone
- Water table (top of saturated zone)
- Vadose zone (unsaturated zone)
7
Q
Water Table
A
- Level of water table = elevation of ponds, lakes, rivers, etc.
- Mimics topography (not always flat)
- Subdued
8
Q
Water table and seasons
A
- Fluctuates
- Dry seasons: water flows out of saturated zone into springs and rivers
- Wet seasons: water table recharges
9
Q
Surface rivers and groundwater
A
- Gaining streams o Streams receive water from saturated zone o Stream surface = water table o Rainy seasons - Losing streams o Channels above water table o Water percolates down into the water table o Drier climates
10
Q
How groundwater moves underground
A
- Slow movement (compared to surface streams)
o Typical mm/day to cm/day
o Can take up to millennia for water to resurface - Influenced by..
o Slope of the water table
o Permeability
11
Q
Aquifer
A
- Highly permeable
- Saturated with water
- Unsuitable area is called aquitard
12
Q
Good Porosity
A
- Gravel
- Clay
- Sometimes Sandstone
- Sometimes Limestone
13
Q
Bad Porosity
A
- Till
- Shale
14
Q
Good Permeability
A
- Gravel
- Sometimes Sandstone
- Sometimes Limestone
15
Q
Bad Permeability
A
- Clay
- Till
- Shale
