Running Water and Groundwater

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.