Chapter 6
Terms
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- Bed load
- The material involved in saltation or the traction load
- Hydrosphere
- All the water at and near the surface of the earth, 97% of which is in oceans
- Levee
- Raised bank along a stream channel
- Factors governing flood severity
- Quantity of water involved, extent of infiltration, topography, subsurface runoff, and vegetation
- Alluvial fan
- formed when a tributary stream flows into a more slowly flowing, larger stream, or a stream flows from mountains into a plain
- How do you calculate the discharge?
- The product of the area of the channel crosse section and the average stream velocity
- Retention ponds
- Large basins that trap some of the surface runoff
- How do floodplains form?
- The erosion on the cut banks and deposition of point bars on the inside banks of meanders and downstream meander migration produce them
- Infiltration
- Process by which surface water sinks into the ground
- Upstream floods
- Floods that affect only small, localized areas, most often caused by sudden, locally intense rainstorms and events like dam failure
- Base level
- Lowest elevation to which the stream can erode downward, for many streams, the water surface level of the body of water into which they flow
- cut bank
- downstream and outside side of the meander, flows somewhat faster
- What are the main processes of the hydrologic cycle?
- Evaporation into and precipitation out of the atmosphere
- Saltation
- Material of intermediate size is carried by short hops along the stream bed in the process
- Drainage basin
- Region from which a stream draws water
- Load
- Total quantity of material that a stream transports
- Diversion channels
- Redirect some of the water flow into areas adjacent to the stream where flooding will cause minimal damage
- Delta
- A fan-shaped deposit fo sediment formed at a stream's mouth
- Crest
- Maximum stage reached during a flood event
- Stream
- Body of flowing water confined within a channel, regardless of size
- Stream capacity
- Measure of the total load of material a stream can move
- Peak lag time
- Time lag between a precipitation event and peak flood discharge
- Flood stage
- When stream stage exceeds bank height
- Channelization
- General term for the various modifications of the stream channel itself that are usually intended to increase the velocity of water flow, volume of channel, or both
- 2 factors affecting flood severity
- proportion and rate of surface runoff
- Meander
- The curve or bend in a stream channel
- Braiding
- If the sediment load of the stream is large, these channel islands can build up until they reach the surface; effectively dividng the channel in this process
- Stream Gradient
- Steepness of the stream channel
- Point bars
- Consist of sediment deposited on the insides of meanders, build out the banks in those parts of the channel
- Suspended load
- Material that is light or fine enough to be moved along suspended in the stream, supported by the flowing water
- Downstream floods
- Floods that affect large stream systems and large drainage basins
- stage
- Elevation of the water surface at any point
- Flash floods
- variety of upstream flood, characterized by especially rapid rise of stream stage
- Floodplain
- A broad, fairly flat expanse of land covered with sediment along the stream channel, called this, the area into which the stream spills over during floods
- Braided stream
- A stream with multiple channels that divide and rejoin
- Oxbow
- Old meanders now cut off or abandoned by a stream
- How is stream gradient calculated?
- The difference between two points along a stream divided by horizontal distance
- What determines the size of a stream?
- Area of the drainage basin, climate, vegetation, and underlying geology
- Hydrologic cycle
- The cycle through which water in the hydrosphere moves; includes such processes as evaporation, precipitation, and surface and groundwater runoff
- Recurrence interval
- How frequently a flood of a certain severity occurs on average for that stream; inverse of the probability of a flood
- Flood frequency curve
- A graph of stream stage or discharge as a function of recurrence interval (or annual probability of occurrence)
- Flood
- Condition in which stream stage is above channel bank height
- What is the traction load?
- Heavier debris may be rolled, dragged, or pushed along the bottom of the stream bed as this
- Longitudinal profile
- Diagram of elevation of a stream bed along its length
- Discharge
- Volume of water flowing past a given point in a specified length of time
- Percolation
- Process by which water is moved through soil and rock
- How is capacity related to discharge?
- The faster the water flows, the more water present, the more material can be moved
- Dissolved load
- Material that is completely dissolved in the water