Quiz 2:mechanisms of erosion

what are the 3 phases of soil erosion?

1. Detachment --- raindrops, tillage, wetting/drying

2. Transport --- water and wind

3. Deposition --- no sufficient energy to transpor

Detachment

--- raindrops, tillage, wetting/drying

2. Transport

r

--- water and wind

3. Deposition

--- no sufficient energy to transpo

Detachment limited erosion:

▪ When the agents have the capacity to transport

more material than is supplied by detachmen

Transport limited erosion:

▪ When more material is supplied than can be

transported

What 2 energy types cause erosion?

Potential and kinetic energy

How much energy is actually used for erosion?

3-4%

Infiltration rate:

the rate at which water

passes into the soi

What creates soil structure?

Cohesion and Adhesion which results in agregate forming

What form of soil has the fasted infilration vs the slowest?

Sand>Silt>Clay

What are the 2 rules of thumb for surface runoff?

No surface runoff occurs if

Rainfall intensity < infiltration capacity

▪ Surface runoff occurs if

If the rainfall intensity > infiltration capacity

What causes the rule of thumbs for water erosion to fail?

A crust forming on the surface of the soil.

What does crusting result in?

Rainfall cannot infiltrate into the soil properly. Water hits the crust and results in puddles and flows beneath the crusts' surface. This results in erosion.

What helps prevent crusting and why do we care (outside erosion)

OM and clay prevent crusting. crusting prevents seeds from breaking through in cropping.

Raindrop erosion

Destroys soil aggregates and moves soil particles

because of the KE + PE associated with it

Know how to do the energy of raindrop erosion problems.

Help me god.

Splash pillars?

Rocks block erosion directly below them. This forms those little pillars with rocks on top.

What are the soil particle sizes of sand, silt, and clay?

Sand-0.05-2mm

Silt:0.05-0.002 mm

Clay:<0.002 mm

What particle sizes need the most energy to dislodge?

less than 0.04 (silt) is when it begins to trend upward in energy needed. Generally, smaller particles are harder than large particles. Clay>Silt>Sand

What type of soil accumulates on hill sides.

Sandy soils

What does the bare soil equation mean in terms of rainfall erosion?

Erosion is directly porportional to slope and intensity of event.

What does the wet soil equation mean in terms of erosion?

Water depth on soil surface is inversly related to the amount of erosion. Deeper puddles block rain from making energy contact onto the soil.

What puddle depth is needed to stop most of rainfall erosion from energy?

Equal depth to the raindrops size.

Overland Flows?

occurs on hillsides during rainstorms when surface depression storage, soil moisture storage or infiltration capacity of the soil is exceeded. DOES NOT HAVE CANNALS

Surface Runoff?

All forms of surface level erosion. can be overland or canal influenced.

What does renault number measure?

number is an index of the

turbulence of the flow

What are the 2 renault number meanings?

<500 =laminar (smooth flow)

>2000=turbulent flow (high erosion)

What is The Froude number

index of whether or not

gravity waves will form in

the flow

What do the froude numbers mean?

▪ F < 1 = No gravity waves

= tranquil or subcritical.

▪ F >1 = rapid or

supercritical flow = more

erosive

When does transport stop?

When the transport lacks the energy resulting in deposition.

Rill erosion?

small intermittent watercourses with

steep sides that are initiated due to differential

erosion caused by overland flow

How big are rills? how much erosion do they cause?

There width and depth are 2-20 cm. Rill erosion accounts for 50 to 70% of total soil

erosion

What do rills become and what makes them that?

form ephemeral gullies that can

further facilitate flow convergence. Gullies are different from rills as gullies have

cross-sectional area greater than 1 m

How are gullies measured outside of metric?

If farm equipment cannot pass over them.

What forms gullies outside surface erosion?

Forest have underground channels that can colapse to form gullies. Landslides

What mainly causes gullies?

Excess water accumulation.

How wide is the range of gully erosion in an area?

10-94% can be caused by gullies.