Geol 101 Surface Water

Hydrologic Cycle (water cycle)

repeated circulation of water through the different Earth environmental components

Geosphere, hydrosphere, atmosphere, biosphere

different mechanisms throughout the cycle

produces water vapor (Evaporation, Transpiration), Precipitation, Surface water flow, Glacier flow/melting, infiltration and Percolation, groundwater discharge

water vapor enters atmosphere from multiple places

evaporation of surface (oceans, lakes, rivers, soil, regolith)

evaporation from subsurface (soil, regolith)

transpiration from plants

Water vapor moves through the atmosphere from

surface and subsurface

Precipitated water can move to different places

re-enter atmosphere (evaporation)

move into the ground (infiltration)

stay on the surface (pool, runoff)

Channel

Where water is flowing (or has flowed)

Stream

Any water that flows in a channel, regardless of channel size

River

A general term for streams that carry substantial amounts of water and have numerous tributaries

River (stream) valley

valley created as a result of erosion and transport by liquid water flow

Streams collect (drain) water from a specific area

near surface flow parts as sheet flow

sheet flow then becomes channelized

drainage basins (watersheds)

areas drained by a given stream

drainage divides define boundaries of specific drainage basins

Continental divides

drainage divides that divide an entire continent into its largest drainage basins

incorporates divides of smaller drainage basins

River system

the river and all associated components in its drainage basin

main stream, tributaries

river system zones based on predominant sediment actions

sediment production zone (headwaters region)

sediment transport zone (main trunk of stream

sediment deposition zone (mouth region)

Sediment deposition zone

when a river empties into large body of water

sediment deposits form a delta

gravity drives water flow

into a stream channel

Laminar flow

flowing in a nearly straight path and parallel to the stream channel

Turbulent flow

flowing in chaotic or erratic fashion in all directions

Channel slope (gradient)

Steeper gradient means more gravitational energy to drive flow

Channel shape

for comparable channels, water flows faster in narrow and deep channels and slower in wide and shallow channels

Channel size and roughness

water moves more efficiently through larger and smoother channels

generally, from head to mouth…

channel slope (gradient) decreases

channel size increases

flow rate increases

work

erosion, transport, deposition

erosional effectiveness of a stream is related to

stream flow velocity

stream discharge

properties of channel bed and channel banks

discharge

volume of water flowing past a certain point in a given unit of time (m³/s)

Erosion of sediments

easily eroded: sand-sized sediments

not as easily eroded: Silt and clay-sized sediments, gravel-sized sediments

Erosion of bedrock

Quarrying (removing large bedrock blocks from the channel bed)

Abrasion (scraping, bumping, and rubbing action of sediment carried in stream)

Corrosion (flowing water dissolves bedrock, overlaps with chemical weathering)

Streams transport material in one of three ways

In solution (dissolved load)

In suspension (suspended load))

along the bed (bed load)

dissolved load

materials are dissolved in the water

flow velocity has no impact on ability to carry dissolved load

suspended load

sediments carried along in suspension

typically, greatest amount of sediment is carried by streams this way (mostly small particles)

Bed load

transported along channel bed, larger particles (coarse sands, gravel, boulders)

Ability of a stream to carry solid particles described by 2 properties

competence (maximum sediment particle size a stream can transport)

capacity (maximum load of sediment a stream can transport)

Deposition occurs when the stream flow rate decreases

stream competence decreases

particles of the same size are deposited together (same time & place)

Bedrock channels

channels cut into bedrock

typically form in headwater region

Alluvial channels

channels cut into previously deposited stream sediments

typically associated with floodplains

channels progressively change shape and location

meandering channels

outside of a meander is a zone of active erosion

inside of a meander is a zone of deposition

continued growth of leader can create an Oxbow lake

Deltas

form when sediment-transporting streams empty into a large body of water

sudden decrease in flow velocity decreases in flow velocity decreases competence of stream

Alluvial fans

fan-shaped sediment deposits at base of mountain fronts

mountain stream emerges onto a flat lowland

stream channel slope decreases

Natural levees

raises areas adjacent to the channel

form during flood events

Base level

the lowest to which a stream can erode its channel

Graded stream

a stream that maintains a minimum flow rate necessary to transport the sediment that is delivered to it

no net erosion or deposition of sediment

When a channel has a steep gradient…

dominant erosion process is downcutting

leads to v-shaped valleys with steep sides

as stream approaches graded condition

downcutting is less important

erosion occurs laterally (produces flood plain)

Incised meanders

Meanders flowing through steep, narrow bedrock valleys

• meanders develop on a floodplain

• height difference between stream channel and base level increases relatively quickly

• meandering stream starts downcutting

Stream drainage patterns

network of stream valleys creates a drainage pattern

different stream valley drainage patterns develop depending on regional terrain properties

• surface slope

• landform obstructions