rivers and floods Flashcards
What are the different types of loads that streams carry?
- Dissolved = load composed of ions from chemical dissolution of rocks
- Suspended = fine particles like silt/clay carried off the bottom by water
- Bed = large particles that roll, slide, and bounce across bottom of the channel
How do we calculate streamflow?
Q = W x D x V
Discharge = Width x Depth x Velocity
Governs competence & capacity
What is the stream base level?
The lowest point a river can go based on rock types present or sea level
What are competence and capacity?
Competence = maximum size particle transported
Capacity = maximum load transported
How can vegetation influence runoff?
Vegetation provides more cover for water and allows more to be absorbed, minimizing runoff
What is evapotranspiration?
Combination of evaporation and transpiration (water moving through a plant), the combined processes that move water from the Earth’s surface into the atmosphere
What is overland flow?
- Flow of water on the surface of Earth not confined to channels
- Results because the intensity of precipitation is greater than the rate at which rainwater infiltrates into the ground (aka flooding)
What is infiltration?
Movement of surface water into rocks or soil
How have human activities altered evapotranspiration, overland flow, and infiltration?
Cutting down trees would cause a decrease of evapotranspiration, and as impermeable surfaces grow with urban spaces, increasing amount of water would not be able to infiltrate, but would instead lead to overland flow
What are common ways that streams originate?
- High points such as a mountain, hill, etc.
- Snow melting
- Springs overflowing
- Lakes need somewhere for water to go and water begins to flow down
What are 1-year floods, 5-year floods, 10-year floods?
Floods that are expected to occur every x amount of hears measured by the magnitude
- I.e. - floods with magnitude of 280 m3 per second are expected every 10 years
How and why do streams move in landscapes?
The transport of water over surfaces in order to return to the ocean is part of the hydrologic cycle (as is water evaporating and returning to the atmosphere)
What are oxbow lakes and how do they form?
When meandering rivers travel so far out they are abandoned as the river cuts a more efficient path
The bend is left behind as an isolated lake
What are hydrographs and what factors influence them under natural conditions?
- Hydrographs measure discharge over time and the lag time (peak rainfall & peak discharge)
- Vegetation, runoff vs. infiltration, rainfall amount, porosity, and topography all play a role
How does urbanization alter hydrographs?
Urbanization leads to a loss of vegetation cover and creates more impermeable surfaces of low porosity which in turn increase runoff and decreases lag time
