(TEST 2) Earth Science, Lecture pt 4 (ch 8) Flashcards
Why are stream runoffs considered an important geologic agent?
- Erodes, transports, and deposits ions and sediments
- Sculpts landscapes
- Transfers mass from continents to ocean basins
What is overland flow?
Precipitation moving downslope over the land surface
What is stream discharge?
Volume of water moving through the channel in a given time
What is groundwater baseflow?
Groundwater that discharges to the surface
What are some qualities of a gaining stream?
- Water flows all year
- At or below the water table
- Humid or temperate climates
- Sufficient rainfall
- Lower evaporation
Gaining streams are also known as _____?
Permanent streams
What are some qualities of a losing stream?
- Dry up part of the year
- Above the water table
- Dry climates
- Low rainfall
- High evaporation
Losing streams are also known as ______?
Ephemeral streams
Is velocity uniform in a channel?
No
What is a hydrograph?
Plot of discharge versus time
What is a watershed?
An area of land that drains into a stream
What do drainage divides separate?
Drainage basins
What is a stream gradient?
Change in elevation per distance flowed
What are some physical characteristics near the headwater of a stream?
They tend to be steep and straight
What are some physical characteristics near the mouth of a stream?
They tend to be flat and curved
Why is erosion is greatest during a flood?
Because energy is higher which causes more erosions and more transportations
How do streams erode?
Streams break, abrade, and dissolve material
Scouring – water picks up and moves sediment
Breaking and lifting rocks and sediments
Abrasion – the “sandblasting” of rock by particles in fast-moving water
Dissolution – running water can dissolve soluble minerals
What is river erosion?
The energy of flowing water is from mass and gravity
How do streams transport sediments?
Through sediment load
What is sediment load?
Material moved by running water
What are three types of sediment load?
- Dissolved load: ions from chemical weathering
- Suspended load: fine particles (silt and clay) in the water
- Bed load: larger particles roll, slide, and bounce along the bottom
Bed load moves by a process called……?
Saltation
How does decrease in water velocity affect sediment transport?
- Competence reduced, sediment drops out
- Boulders, then gravels, then sands fill channel bottoms
- Sands form inside banks (point bars)
Silts and clays drape floodplains
What do meander streams look like from a top-down view?
They have winding, looping curves
When do meandering streams form?
- The stream gradient is low
- The substrate is soft and easily eroded
- The stream exists within a broad floodplain
T/F: Meander streams evolve during times of flood
True, because the channel is modified during periods of flood
How does fast water impact stream bank?
It erodes the outside stream bank (or cut bank)
How does slower water impact stream bank?
It deposits point bars within the curve
How are oxbow lakes formed?
They are formed from cutoff meanders
What are some properties of the base level in meandering streams?
- Lowest level to which a stream can cut downward
- Sea level is the ultimate base level
- Lakes, reservoirs, and resistant rock bodies can create temporary base levels
What happens as streams approach their base levels?
- Stream gradient decreases
- Meanders get wider
- Stream carves out a wider floodplain
- Oxbows develop during times of flooding
How is a delta formed?
A delta is formed when a stream enters standing water
What happens when a stream enters standing water?
- Stream divides into a fan of distributaries
- Velocity slows; sediment drops out
In flood, the river may break through a levee, which is a process called …..?
Avulsion
What type of plain forms when distributaries continue to provide sediment?
Delta forms
When do abandoned delta lobes degrade over time?
When sediment supply is reduced/ eliminated
How does a reduction of sediment supply causes degradation in abandoned delta lobes?
- Compaction causes subsidence, which causes the delta surface to sink
- Submarine slumps and storm waves attack the delta front
Floods occur when
Flow exceeds channel capacity
What different conditions are floods triggered by?
- Torrential rains rapidly dumping large volumes of water
- Long period of continuous rain; ground is saturated
- Rapid snowmelt across a large drainage basin
- Failure of dam or levee
What are some different types of floods?
- Flash floods
- Dam failure
- Downstream floods
What are flash floods?
Water that rises with little warning
How are flash floods caused?
- By intense rainfall or dam failures
- By rapidly moving wall of debris-laden water
What is a dam failure?
Catastrophic amounts of water released from impoundment in a very short period of time
What are downstream floods?
Where a river in the lower part of a drainage basin leaves its channel, flowing out onto its floodplain
What are most downstream floods caused by?
Most are caused by regional accumulations of water and not just a single storm
What structures aim to prevent overflow to floodplains?
Levees and flood walls
What do artificial levees do?
They transmit flood problems downstream and they’re used to protect cities from flooding
Why are many parts of the city located below sea level?
- Draining of the back swamps
- Subsidence
What do artificial levees prevent?
Sediments from reaching the floodplains
What land-use activities increase the hazards associated with flooding?
- Removal of natural vegetation
- Destruction of wetlands
- Construction activity
- Urbanization
Why does the removal of natural vegetation contribute to the hazards of flooding?
Because it leaves soils exposed and greater overland flow
Why does the destruction of wetlands contribute to the hazards of flooding?
Because wetlands are used to capture and store large amounts of water
What are some ways to reduce flooding?
- Dams
- Artificial levees
- Channelization
- Retention Basins
- Erosion Controls
- Wetlands Restoration
- Floodplain Management
- Education
