RUN OFF, EROSION & LANDSLIDES Flashcards
where does runoff come from
rain, melting ice and snow, and from springs
- On flat ground, water accumulates in puddles or swamps, but on slopes it flows downslope in streams
4 steps of stream formation
- Runoff
- Sheetwash
- Scours a channel
- Downcutting
3 Stream Processes
related to running water
1. Erode the channels in which they flow.
2. Transport sediment and solutes provided by
weathering processes
3. Deposit sediment -> a wide range of erosional and
depositional landforms
whats load and its 3 types
materials carried by a stream
- Suspended load (fine particles)
- Dissolved load (ions in solution)
- Bedload (large particles)
what process are Most sand grains within a stream transported by
saltation (intermittent jumping of particles)
- The smaller the particle, the higher it jumps and the farther it travels.
what is The velocity of the stream governed by
the steepness of its slope - gradient
- Gradient = change in the altitude of the channel per
horizontal length of the stream course.
- The steeper the gradient, the more rapid the flow + the more power to carry sediment
what is discharge and how to calculate it
- Volume of water flowing past a point in a given time interval
- Varies seasonally due to precipitation and runoff
- tends to increase in the downstream direction as tributary streams add their water to the amount in the trunk stream
- Stream velocity x Cross-sectional area
how does velocity change in different areas of the channel
– Friction is…
* Greater in wider, shallower streams.
* Lesser in narrower, deeper streams
- in straight channels, highest velocity = in the center
* In curved channels, max. velocity = the outside
curve - leads to high erosion
how does sediment size differ as you go down the channel
sediment size is smaller
what is Meander evolution
channel becomes more curved overtime -> leading to separate oxbow lake + Meander cutoff
Stream Channel Types
- straight - Streams flowing BELOW capacity
- braided - Streams flowing ABOVE capacity:
- meandering - Streams flowing AT capacity:
- meandering + straight -
whats a delta
a fan shaped body of sediment that deposited at the
mouth of a stream entering an ocean or lake
what dominates in the Uplands, river valley and mouth
Uplands - Headward Erosion
river valley - Transportation
mouth - deposition
what is watershed
*Land area that drains into a specific trunk stream.
*Also known as a drainage basin / catchment
3 Common drainage patterns
– Dendritic – Branching, “treelike”
– Radial – From a point uplift (mesa, volcano, etc.)
– Rectangular – Controlled by jointed rocks
what are Drainage basins separated by
divides (e.g., ridges, gentle uplands, or mountain ranges)
what is field capacity
the amount of water the ground can hold when it is
fully drained
Conservation of Mass Equation
I - O = DS
I = Input = input of precipitation
O = Output = runoff + evapo-transpiration
DS = Change in storage - can be + or -
what does weathering do
breaks rock apart
what does erosion do
moves soil / rock
what is mass wasting
- Downslope movement of Earth materials by gravity
- A type of natural hazard
- An important erosion process
e.g. rock fall, debris flow, lahar/mudflow, slumping
what are landslides
slope failures (or mass wasting) initiated by slippage along a well-defined plane surface - specific type of mass wasting
how does fire relate to landslides
- Vegetation plays a very important role in stabilizing
land surface - Fires destroy vegetation ===> soil is weakened
4 paths rainwater takes to get to a channel
- Ground water flow - permeable ground (slow response to rain - low peak discharge)
- Shallow Subsurface Flow - permeable soil but less permeable rock (more erosion)
- Saturation Overland Flow - soil becomes fully saturated
- Horton Overland Flow - impermeable surface (more erosion + rapid response to rain - high peak discharge)
