Downstream of dams:

• erosion occurs because stream has no sediment
• further downstream, deposition can occur where tributaries enter with sediment

Limitations of using “100 year flood”
1) limited data
2) false sense of security
3) climate may be changing
4) land use may be changing

Flash Flood: local, rapid flood event (often in small, steep drainage basins, where water gets to the stream quickly
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Groundwater: (chapter 13, 270 - 274; 277-281)

Groundwater: water stored in open spaces of underground rocks and unconsolidated materials

Groundwater is <1% of the earth's water
BUT 22% of  fresh water
Used for: 1) Irrigation 2) industry, 3) homes

Aquifer: geologic layer which stores and transmits water

Porosity: the % of a rock’s total volume that is open.
Porosity is high in unlithified sediments, reduced by cementation and compaction.
Porosity is very low in metamorphic and igneous, chemical sedimentary rocks.
Increased by fracturing and dissolution

Permeability: how well a rock/sediment transmits water

depends on porosity,
                   size and shape of pores
                   how interconnected the pores are.