Flooding Flashcards
What is the main role of streams and rivers?
Drain the water and transport sediments
A stream overflow occurs if its ability to carry water is overwhelmed.
Flood
The volume of water moving through a channel over a period of time.
Stream discharge
A process where water flows through stream channels.
Runoff
Precipitation reaching the land surface moves downslope in thin sheets.
Overland flow
Discharge of groundwater into the surface environment.
Groundwater baseflow
Provide information about the river or stream by plotting the discharge and time.
Stream hydrographs
Amount of time for a water to move across the landscape and into channels.
Lag time
Continuous input of groundwater baseflow allows stream in many areas to keep flowing at minimum levels.
Baseflow conditions
More water infiltration causes groundwater to be higher than stream channels.
Gaining streams
Result of less deep infiltration in arid areas resulting in a water table below the streams.
Losing streams
Large streams serve as the principal channel within the drainage system.
River
Upper portion of the drainage system.
Headwaters
Found in the lower part of the system where a river empties into an ocean.
Mouth
Individual system separated from one another by topographic high or crest.
Drainage divide
Land area that collects water for an individual stream or river.
Drainage basin/ Watershed
Smaller streams that feed larger streams within a drainage basin.
Tributaries
A method of classifying or ordering the hierarchy of natural channels
Strahler Stream Order
The longitudinal profile reflects a downstream trade-off between discharge and slope in setting transport capacity.
Stream Longitudinal Profile
The limiting level below which a stream cannot erode is called _________.
Base level
Approximately equals the inverse of the source basin length.
Drainage density
True or False. Steep terrain has high drainage density while gentle terrains have low drainage density.
TRUE
Drainage pattern that forms horizontally bedded and uniform sediments or on uniformly resistant crystalline rocks.
Dendritic
Drainage pattern that develops on moderate to steep slopes, but also where regional structure, such as outcropping resistant rock bands.
Parallel
Patterns most commonly on dipping or folded sedimentary or weakly metamorphosed sedimentary rock; also areas of joints and faults which intersect with right angles and old sand dunes with parallel alignment.
Trellis
Usually have more or less perpendicular turns mainly caused by crisscrossing fractures.
Rectangular
Occurs around domes or cones and is particularly common in volcanic areas.
Radial
Patterns also develop around domes, where there exist alternating resistant and weak beds.
Annular
Can occur in a variety of conditions where local hummocks and depressions inhibit a continuous channel network.
Multibasinal
Incised into rocks with complicated structural patterns. Associated with crystalline metamorphic rocks with a history of intense folding, jointing, intrusion, alterations, and faulting.
Contorted
Types flowing streams.
Perennial, intermittent, & ephemeral
Types of linearity of river.
Straight, meandering and braided
The Cross profile of the river can be described as _______.
Gently and steeply sloping
The length of the profile can be described as __________.
Graded or interrupted profile
Loose rock particles/sediments deposited on a stream.
Alluvium
Key factors in a stream’s ability to erode the landscape is _______ .
Velocity of the water
_______ unstable overhang located at the outer bank which is produced by the velocity increase.
Cutbanks
Inner bank where velocity decreases sediments tends to accumulate and form deposit.
Point bar
__________ by streams is not performed by the water itself, but rather by the sediment that wears away rock.
Downcutting
Evidence of stream abrasion.
Potholes
Swirling motion of water column
eddy current
Velocity of a stream segment is controlled by _____.
stream gradient
Sea level is referred to as ________________ because oceans represents the low point of most rivers.
ultimate base level
___________ describes the fraction of solid particles that is in suspended state.
Suspended load
___________ consist of sediments particles that roll, bounces, or remain stationary.
Bed load
The process whereby water separates sediment grains based on their size, shape, and density.
Hydraulic sorting
Mound-shaped channel deposits consisting of sorted material ranging in size from boulders to coarse gravel to fine sand.
Bars
__________ are formed when a rivers enters a lake or ocean.
Deltas
________ large fan-shaped deposits that form where steep mountains streams empty out onto valley floors at the mouth of river.
Alluvial fans
A channel that is choked with sediments called a ________.
Braided streams
Transport considerable amounts of dissolved ion refer to as the ____________.
Dissolved load
________ erosion that occurs along the outside of meander bends produces wider valleys over time.
Natural floodplain
_________ a pair of ridges that run parallel to the bank which are formed due to the deposition of sediments.
Natural levees
Areas on the floodplain that are poorly drained and can remain wet after the flood.
Back swamps
Old floodplains are poorly drained and dry as the river migrates.
Stream terraces
Normally dry areas of land become inundated.
Flood
_______ the height at which a river begins to overflow.
Flood stage
The ability of the ground to absorb water is referred to as __________.
Infiltration capacity
The actual rate at which water can infiltrate is determined by the ________ of the land surface, _______ and _______ of the material.
Slope;
Type of ground material and
Moisture content
Vegetation intercepts and stores a certain fraction of the rain water.
Vegetation cover
Floods that have short duration with relatively high peak discharge.
Flash flood
Can be defined as one where a river leaves its channel farther down in its drainage basin, flowing out onto its floodplain and inundating large areas of the valley floor.
Downstream floods
Another term for flash flood.
Upstream flood
Land-use factors that affect flooding.
Removal of natural vegetation
Destruction of wetlands
Construction activity
Urbanization
Flood mitigation measures.
Dams
Artificial levees
Channelization
Erosion controls
Flood proofing
Education
Protecting floods and serving as an important source of freshwater and electrical power.
Dams
Constructed of earthen materials, but large concrete panels called floodwalls are sometimes used.
Artificial levees
Straightening and deepening a stream channel so that its discharge capacity is increased.
Channelization
Temporarily stores some the excesses water in a series of depression which are constructed within the tributary network.
Retention basins
Practices that tend to keep soil particles in place so as to minimize the amount of material able to move downslope.
Erosion control
Type of barrier in which vegetated strips line the banks of stream channels trapping sediments before it can enter the drainage network.
Stream buffers
Synthetic fabric that is fine enough to trap sediments but allow some water to pass.
Silt fences
Ponds constructed for the purpose of trapping any sediments.
Silt basin
Involves raising the building above the expected flood level.
Flood proofing
_____ the public about flooding in a very cost-effective means of reducing the number of fatalities and property damage.
Education
Increase the ability of water to flow downslope, which translates into more overland flow and less infiltration.
Removal of natural vegetation
Excessive dislodged sediment is moved off the landscape into the drainage systems which causes channels to become filled with sediments.
Sediment pollution
The destruction of ________ has reduced the landscape’s ability to store water.
destruction of wetlands
This activity exacerbates flooding because it increases the overland flow and causes stream channels to fill with sediment.
Construction activity
Large pipes called ________ are typically used for small streams that flow intermittently.
Culverts
Land covered with an impermeable surface which do not allow water to infiltrate, but rather forces to moved as overland flow.
Urbanization
