NatSci Outline: Hydrologic Cycle, Running Water, Stream Erosion and Sediment Transport

HYDROLOGIC CYCLE

-          water is continuously recycled from the oceans through the atmosphere and back to the oceans

·         Evaporation

Ø  Occurs when the physical state of water is changed from a liquid state to a gaseous state

·         Condensation

Ø   Is a process by which water vapor changes its physical state from a vapor most commonly to a liquid

Ø  Brought about by cooling the air or by increasing the amount of vapor in the air to its saturation point

·         Precipitation

Ø  Is the process that occurs when only and all forms of water particles fall from the atmosphere and reach the ground

Ø  2 Subways to release precipitation:

v  Coalescence Process – rain

v  Ice-crystal Process – occurs when ice develop in cold clouds or in cloud formation high in the temperature where freezing temperature occur

§  80% falls directly into the ocean

§  20% falls on land as rain or snow

Ø  When precipitation reaches the ground:

v  Re-evaporate

v  If it isn’t re-evaporated, water will become RUN-OFF

v  Some absorbed into the ground by infiltration

·         Run-off

Ø  Is a flow from a drainage basin or watershed that appears in surface streams

·         Infiltration

Ø  Is a process involving movement of water through the boundary area where the atmosphere interfaces with the soil

·         Storage

Ø  3 storage that occur in the planetary water cycle:

v  Stored in the atmosphere

v  Stored in the surface of the earth

v  Stored in the ground

RUNNING WATER

-          The single most important agent sculpturing the earth’s land surface

·         Infiltration Capacity

Ø  The maximum rate that soil and other surface materials can absorb water

·         Sheet Flows

Ø  An overland flow or down slope movement of water taking the form of a thin, continuous film over relatively smooth soil or rock surfaces and not concentrated into channels larger than rills

·         Sheet Erosion

Ø  Detachment of soil particles by raindrop impact and their removal down slope as a sheet instead of indefinite channels or rills

Ø  2 stages of sheet erosion:

v  Rain Splash – soil particle knocked into the air by raindrop impact

v  Sheet Flooding – loose particles are moved down slope. Blood sheets of rapidly flowing water filled with sediment present a potential higher erosion force

·         Channel Flows

Ø  Those that are not entirely included within rigid boundaries a part of the flow is in contact with nothing at all, just empty space

Ø  3 types of channel:

v  Broad Shallow Channel

v  Narrow Deep Channel

v  Semicircular Channel

·         Stream Flow

Ø  Flow downhill from a source area to a lower elevation where they empty into another stream, a lake or sea

Ø  Gradient – over the slope of a stream flow

v  Vertical drop in a given horizontal distance

v  Expressed in (m/km) or (ft/mi)

v  It is sleeper in the upper reaches of streams where there may be tens of meters per kilometer

·         Velocity

Ø  Measure of downstream distance traveled per unit of time

Ø  Expressed in (m/sec) or (ft/sec)

Ø  Makes the flow of velocity slower near the bed and banks of the stream

Ø  Channel – least perimeter, least friction, greater velocity

v  3 factors contribute to this:

§  Velocity increase continuously in response to the acceleration of gravity unless other factors retard flow

§  Streams – flow resistance high, velocity slow

§  Tributary Streams – total number of water increases and increased in velocity

·         Discharge

Ø  Total volume of water in a stream moving past a particular point in a given period of time

Ø  Multiply a stream’s cross-sectional area by its flow velocity

STREAM EROSION AND SEDIMENT TRANSPORT

-          Erosion involves the removal of dissolved substances and loose particle of soil and rock from a source area

-          Sediment transported in a stream consists of both dissolved materials, the dissolved load and solid particles transported as suspended or bed load

·         Suspended Load – consist of silt and clay

·         Bed Load – made up of sand and gravel

-          Hydraulic Action – sediment carried in streams eroded by the power of running water

-          Streams also eroded by Abrasion:

·         Competence

Ø  Factor related to flow velocity

·         Capacity

Ø  Is a measure of the total load a stream carries which varies as a function of discharge

·         Competence and Capacity are actually related to different aspects of stream transport

·         A large slow-flowing stream has a low competence, but may have a very large suspended load and hence a large capacity