Chapter 6

Where is our water?

Water Cycle Evaporation from the ocean and other water sources Precipitation over the ocean and land Water runs from high elevations down to the oceans and infiltrates the land

Streamflow Water flows from higher elevations to lower – the gradient is the change in elevation The higher the velocity the more sediment moved A straight stream channel means higher velocity – lots of curves or turbulence means it goes slower Discharge is measured in cubic meters/second

Stream Profile Source (headwaters) to mouth (empties into a body of water) Slope decreases from source to mouth Discharge increases from source to mouth as tributaries add together

Stream profile cont… Base level Ultimate base level is sea level – even with the ocean Temporary base level – lakes Once a stream is close to base level it meanders (the course has many bends)

Erosion The stronger the current the more sediment carried away Sediment transported In solution (parts per million) 4 billion metric tons added to the oceans annually In suspension Sand, salt, and clay (visible in the stream) Rolling along the bottom Stuff that is too large to be suspended Competence – measure of the largest particle that can be transported Capacity – maximum load stream can carry (related to discharge)

Deposition Velocity decreases so competence decreases and sediment is deposited The largest parts of the sediment fall out first (sorting) Delta – stream slowed and sediment accumulates where the stream enters a lake or ocean Stream separates into distributaries Natural levees Built by repeated floods depositing sediment along the sides of the river

Stream Valleys Narrow valleys Rapids and waterfalls – quick drop in profile Wide valleys Closer to base level Floodplain (meandering happens) Oxbow lake – meanders meet and sediment creates a new channel

Flood Control Artificial Levees Mounds on the banks of rivers Keep the water from flooding Stops sediment from being dropped on the floodplain (so the bottom of the river builds up) Dam Hold water and release it slowly Trap sediment – erodes deltas and floodplain downstream Limiting Development Leave floodplains in their natural state

Drainage Basin Land area that contributes to the water in a stream

Underground water Provides drinking water for more than 50% of the US Belt of soil moisture Near surface water – attracted to soil particles Aka - Zone of aeration Zone of saturation Water fills all the open spaces Porosity – how much space available for water to fill Permeability – ability to get water out of the soil This is where we find groundwater Water table is the upper part of this zone This is the zone where wells get water Aquifers – permeable rock layer where groundwater moves freely

Springs Ground water that comes to the surface Hot Springs Warmer than air temperature for the region Often because of previous volcanic activity (igneous rock) Geysers Cool water enters a chamber with hot igneous rock Weight of the water causes pressure to build Water expands until some comes out at the surface which temporarily lowers the pressure Lower pressure means steam is released (eruption)

Wells Hole bored into zone of saturation Well below water table so supply can be year round Drawdown – water table around the well decreases when it is used a lot Artesian well – water rises on its own Water is in an aquifer that is tilted and exposed to the surface (so it can be refilled) Aquitards above and below to stop water from escaping Water has to be pumped from most wells

Renewable? Being withdrawn faster than it is being recharged Land subsidence Ground sinks because the space where water used to be is empty Contamination Septic tanks, farm waste, broken sewers, highway salt, landfills, storage tanks, Water source is often abandoned so the soil and rock can slowly clean the water

Caverns Limestone (and other soluble rock) Water contains a little bit of carbonic acid (dissolved carbon dioxide makes carbonic acid) Carbonic acid dissolves the calcite making calcium bicarbonate that gets carried away Erosion that creates caverns happens at or below water table The dripping water with calcium bicarbonate produces dripstone (travertine) only happens once the cavern is above the water table Stalactites – hang down from the ceiling Stalagmites – develop on the floor

Sinkholes Rain seeps underground and the carbonic acid eats away limestone making an underground hole This can also happen if water pipes leak water into a region making a hole A lack of ground water can also create an underground hole