Hillslope Processes Flashcards
What are the three stages of slope erosion?
Entrainment
Transport
Deposition
What are the three processes of slope erosion? Where are they likely to be found? What factors affect erosion rates?
Erodibility depends on Vegetation cover, Slope angle, water depth, soil erodability.
Rain Splash - Open areas. Effective at entrainment but not transportation.
Sheet Erosion - Result of sheet flow. Good at transportation material entrained by splash erosion. Found at drainage divides. No channelized flow.
Rill and gully erosion - Occur further down the slope. Gullies develop due to surface and subsurface flows.
What two general forces are at play in erosion (Think material and water)
Driving force/Resisting force
Driving forces is the force the water can exert. Depends on the specific weight of water and the amount and slope
Resisting force is how large the particles are and how cohesive
What is sediment yield like for the following landscapes? Forest Grassland Agriculture Construction Urban
Increase dramatically until you reach urban, at which point paved surfaces make it very low.
What is the difference between Colluvium and Alluvium?
Colluvium - Soil or land particles that accumulate at the base of a slope.
Alluvium - Any stream laid deposit.
What types of environments are typically very prone to erosion? ie they can form badlands. Why is this?
Arid environments - sparse vegetation and impacted by grazing and fire which further reduce veg cover.
How is basin denudation measured? What are some of assumptions made? How is it measured?
Sediment yield: Measured in total volume of sediments/basin area divided by the time period. ex cm/year
Assumes equal lowering of entire basin.
Assumes sediment is completely removed from the basin.
Some upland sediment is stored in the valley bottom.
Measured at mouth of basin with a gaging station or by using a reservoir.
What are some of the controlling factors of basin erosion?
Climate - precipitation, temp, aridity Land use - roads, parks, logging, Topography - gradient, size, relief Vegetation - interception, rootlets, slow down Geology - material, deposits,
What are the three ways in which vegetation helps to limit erosion?
Interception
Rootlets bind soil
Slows overland water velocities.
What is mass wasting? What is the principle force involved? What does mass wasting affect?
Mass wasting is mass movement of soil or rock materials downslope without the aid of water. Gravity largely responsible.
Water quality
Sediment inputs
Habitat
Infrastructure
What is the angle of repose? What significance does this have to restoration?
Maximum angle that a loose material can form in a pile without slipping. Depends on the material.
In materials that are already at the angle of repose, all the material is connected. Bottom of the hill is connected to the top.
What is the measure of slope stability? What is the equation? How do you interpret it?
Safety Factor = Sum of resisting forces (friction, cohesion) divided by the sum of the driving forces. If Fs < 1 the slope is unstable.
Describe the different types of mass wasting. Give an example of a landform.
Soil Creep - Slow downward movement of upper part of soil. Driven by frost heave. Sheep Terraces.
Solifluction - Soil and rock are saturated and flow downhill over a frozen or impermeable layer. Form of creep.
Flows - mudflow and earth flow and *debris flow (most common in BC) - when soils and clays are liquified. Debris flows have more coarse sediments.
Slides - Rapid sliding of large masses of rock or soil. Usually occur after heavy rain. Steep slopes.
Rock and Soil Fall - Occur on very steep slopes or cliffs. Forms talus cone or scree slope which is at the angle of repose.
What are the 4 main physical factors, relating to material, that increase the risk of mass movement?
Pore water - Saturated
Earth Material - Igneous
Rock Orientation - Dips downslope
Vegetation - limited veg
What must be considered when implementing plans for erosion control? What is an invaluable tool for assessing these characteristics?
Surficial materials, landforms and inherent stability.
Use of terrain maps which include information on topography, slope steepness, landforms and materials. Aerial photographs. Terrain stability maps - maps that interpret the terrain data and delineate areas of slope stability and instability.
