Chapter 6Running Water and Ground Water

6.1 Running WaterThe unending circulation of Earth’s

water supply is the water cycle◦Water changes states (solid, liquid,

gas) readily at temperatures and pressure common on Earth

◦The cycle is powered by the sun◦Water evaporates to the atmosphere,

it is transported by winds, condenses into precipitation (falling to Earth)

6.1 Running WaterInfiltration is the movement of surface

water into rock or soil through cracks and pore spaces◦Seeps into lakes, streams, or oceans◦If it isn’t absorbed into the ground, it

creates runoff◦Plants absorb water and it returns to

the atmosphere by transpiration

Water Cycle

6.1 Running WaterBalance in the water cycle means that

the average annual precipitation over Earth is equal to the amount that evaporates◦Local imbalances exist◦If the overall cycle wasn’t balanced,

we would notice a drastic change in the oceans’ level

6.1 Running WaterStreams/rivers flow downhill due to gravityThe ability of streams to erode and transport

material depends on its velocity◦A steeper gradient (steepness) provides

more energy to the stream as it flows downhill

◦The shape, size, and roughness of the stream channel (course it follows) affect the friction, which slows the water

◦Discharge is the volume of water passing a point in the stream (affect size and velocity of the stream)

6.1 Running WaterThe gradient decreases between a

stream’s headwaters and mouth, while the discharge increases◦More tributaries (stream that

empties into another stream) enter the main channel

◦Typically a mountain stream has a lower velocity than at the mouth of a river Friction affects mountain streams more

(boulders and smaller channel) Channel usually smoother downstream

Stream Profile

6.1 Running WaterThe base level is the lowest point to

which a stream can erode its channel◦It is the level at which the mouth of

the stream enters the ocean◦Sea level is the ultimate base level◦Temporary base levels include lakes,

resistant layers or rock, and main streams

A stream in a broad, flat-bottomed valley near its base level meanders (has many bends)

Meander

Incised Meander