The Water Cycle Water constantly moves among the
oceans, the atmosphere, the solid Earth, and the biosphere.
Water Cycle ProcessesEvaporation – liquid water gains enough
energy to become water vapor, water evaporates from the oceans to a lesser extent the continents
Condensation – water vapor cools and becomes liquid water
Precipitation – rain or snow falls to the EarthTranspiration – water absorbed by plants is
released to the atmosphereInfiltration – the movement of surface water
into rock or soil through cracks and pore spacesRun-off – excess precipitation flows into
streams, rivers and lakes
The Earth’s Water balance – the amount of precipitation equals the amount of evaporation
StreamsGravity pulls water downhillMaximum velocity is in the center of the
channelThe work of stream includes erosion,
transportation, and depositionBase level is the lowest point to which a stream
can erode. Sea level is the ultimate base level. Lakes are temporary base levels
Dams create a temporary base level. Upstream of the dam, the stream loses velocity and sediment deposits, forming a delta. After the dam, the increased velocity of the stream erodes the channel.
Streams transport sediment in three ways: dissolved load, suspended load, and bed load, rolling or scooting along the bottom of the stream.
Deposition – well-sorted material deposited by a stream is called alluvium
Delta – when a stream enters a still body of water, its velocity stops abruptly and the sediment drops out forming a delta
Natural levees – form parallel to the channel, when the stream overflows its banks and the velocity immediately slows and deposits the sediment
Factors influencing stream velocity
Gradient – the slope The steeper the slope, the more
energy the stream has as it flows downhill
Stream Channel – course the water flows
The smoother the channel, the easier water can flow
Discharge – the volume of water flowing past a certain point in a given unit of time.
As the size of the stream increases, there is less friction, and the water flows more easily. To calculate stream discharge you multiply the velocity of the stream by the area.
The velocity of a stream is actually greatest at the mouth
Even though the gradient decreases from the headwaters to the mouth of the stream, the discharge increases.
Stream Profile Headwaters – young streams,
mountain streams, steep, V-shaped valleys, rough stream beds increase friction, cold, downcutting due to erosion is rapid, little or no floodplains, waterfalls and rapids
Mature Stream – downward erosion diminishes and lateral erosion dominates to begin to create a floodplain and meanders, the gradient is much lower and the profile is much smoother
Mouth – old age, floodplain is several times wider than meander belt, sifts rapidly, floodplain dotted with oxbow lakes and old cutoffs. Natural levees, backswamps, and yazoo tributaries are features.
Oxbow Lakes
Rejuvenated Streams – old age streams uplifted and made young again. Downcutting again occurs and causes entrenched meanders and new higher floodplains
Meanders – stream that flow on floodplains move in sweeping bends, eroding sideways
The sideway movement occurs because the maximum velocity of the stream is on the outside of the bend, causing erosion of the outer bank. This is called the cut bank.
Reduced erosion on the inside meander results in the deposition of sediment and is called the point bar.