Stormwater Exam 2 UPDATED ACTUAL
Questions and CORRECT Answers
5 ways of controlling hillslope detachment - CORRECT ANSWER - 1. Absorb raindrop
impact
2. Absorb flow impact energy
3. Slow runoff velocity
4. Reduce runoff amounts
5. Increase soils resistance to erosion
Materials that can absorb raindrop impact - CORRECT ANSWER - vegetation, straw
mulch, other organic mulches and rolled erosion control product
Protecting soil surface from flow turbulence impact has what general effect on rill formation? -
CORRECT ANSWER - Inhibits rill formation b/c it forces the flow to spread out. Causes
the flow to change direction which prevents rill formation by way of spreading water out and
preventing it from concentrating
Slowing the flow effectively reduces detachment and erosion by - CORRECT ANSWER -
-giving water more time to infilitrate
-spread out flow further
-slower water means there is less energy in turbulent eddies
What factors cause diminution of the soil roughness over time? - CORRECT ANSWER --
dramatic exposure of the soil allows rough pockets to be smoothed out more quickly such as
tillage
- when soil aggregates are broken up to create disturbed, rough soil such in tillage, the particles
are more easily dethatched and can be transported away easier, causing roughness to diminish
over time as particles are moved away
- disaggregation and straw that can be put down can move
,contour tillage - CORRECT ANSWER - Contour tillage is tilling along an imaginary line
created by connecting two points of equal elevation that run perpendicular to the hillslope. It is
practices to reduces erosion and sediment transport off of a sloped field.
Contour tillage is the farming practice of plowing and/or planting across a slope following its
elevation contour lines. These contour lines create a water break which reduces the formation of
rills and gullies during times of heavy water run-off; which is a major cause of soil erosion. The
water break also allows more time for the water to settle into the soil. In contour plowing, the
ruts made by the plow run perpendicular rather than parallel to the slopes
If you concentrate the flow... - CORRECT ANSWER - you are responsible for it
keys to strong soil aggregation - CORRECT ANSWER - Good organic matter is the key to
strong soil aggregates.
Soils resistance to erosion is a function of soil texture (sand, silt, clay) and soil particle
aggregation/
In what ways do subsurface vegetative material (e.g., roots) help stop hillslope detachment? -
CORRECT ANSWER - Hillslope detachment is minimized by subsurface vegetative
material because it helps infiltration and well as hold soil in place on the hillslope
Acts as anchoring
Besides protecting water quality, what are other goals of urban erosion and sediment control? -
CORRECT ANSWER - Protecting the soil resource itself from degradation, eroded
sediment can fill in erosion control devices such as sediment basins and channels
What is the primary concern for urban erosion and sediment control generally limited to while
construction is in process? - CORRECT ANSWER - Ensuring the sediment doesn't
transport off of site
Vegetation on construction sites should be removed no more than how many days before earth-
moving begins? - CORRECT ANSWER - 14 days /2 weeks and then re-establish
vegetation after earth moving after 14 days.
, What are the benefits of compost compared to other mulches? - CORRECT ANSWER -
Compost is heavier than other mulches, such as straw, and it can absorb water, so when it is the
wettest is when it the heaviest and most effective. Also compost nourishes the soil, which straw
mulch does not because it has a high C:N ratio.
What is the critical element when using RECPs on construction sites? - CORRECT
ANSWER - The effectiveness of the RECP is only as good as its level of direct contact
with the soil.
"it is only as good as the cover makes contact with the soil"
They fail most often when there is a nice cover on the surface, but when there is water coming in
from above, it will go underneath the mat, because it is the path of least resistance, and erosion
will occur underneath that mat.
How do we usually stop sediment delivery from hillslopes? - CORRECT ANSWER -
Stopping transport delivery is all about reducing the transport capacity of water and giving
sediment time to settle
This is done in two ways:
Minimize runoff
Slow runoff by increasing roughness or forcing water into a ponded volume
What are the two key elements for the use of permeable barriers? - CORRECT ANSWER -
Insuring that they are installed into the ground
They need to be installed correctly
Water takes the path of least resistance so if they are not secure in ground, water will just flow
under them
Contouring
If we lay these out naturally at lower portions in the topography, all the water will run towards
the permeable barrier and it will topple over, so it is important to be mindful of this when we
install them in terms of a contour
Eyelid shape
Stuff is only as good as how much water goes through it, so we should install permeable barriers
in an eyelid shape so it collects the water through it rather than around it
Questions and CORRECT Answers
5 ways of controlling hillslope detachment - CORRECT ANSWER - 1. Absorb raindrop
impact
2. Absorb flow impact energy
3. Slow runoff velocity
4. Reduce runoff amounts
5. Increase soils resistance to erosion
Materials that can absorb raindrop impact - CORRECT ANSWER - vegetation, straw
mulch, other organic mulches and rolled erosion control product
Protecting soil surface from flow turbulence impact has what general effect on rill formation? -
CORRECT ANSWER - Inhibits rill formation b/c it forces the flow to spread out. Causes
the flow to change direction which prevents rill formation by way of spreading water out and
preventing it from concentrating
Slowing the flow effectively reduces detachment and erosion by - CORRECT ANSWER -
-giving water more time to infilitrate
-spread out flow further
-slower water means there is less energy in turbulent eddies
What factors cause diminution of the soil roughness over time? - CORRECT ANSWER --
dramatic exposure of the soil allows rough pockets to be smoothed out more quickly such as
tillage
- when soil aggregates are broken up to create disturbed, rough soil such in tillage, the particles
are more easily dethatched and can be transported away easier, causing roughness to diminish
over time as particles are moved away
- disaggregation and straw that can be put down can move
,contour tillage - CORRECT ANSWER - Contour tillage is tilling along an imaginary line
created by connecting two points of equal elevation that run perpendicular to the hillslope. It is
practices to reduces erosion and sediment transport off of a sloped field.
Contour tillage is the farming practice of plowing and/or planting across a slope following its
elevation contour lines. These contour lines create a water break which reduces the formation of
rills and gullies during times of heavy water run-off; which is a major cause of soil erosion. The
water break also allows more time for the water to settle into the soil. In contour plowing, the
ruts made by the plow run perpendicular rather than parallel to the slopes
If you concentrate the flow... - CORRECT ANSWER - you are responsible for it
keys to strong soil aggregation - CORRECT ANSWER - Good organic matter is the key to
strong soil aggregates.
Soils resistance to erosion is a function of soil texture (sand, silt, clay) and soil particle
aggregation/
In what ways do subsurface vegetative material (e.g., roots) help stop hillslope detachment? -
CORRECT ANSWER - Hillslope detachment is minimized by subsurface vegetative
material because it helps infiltration and well as hold soil in place on the hillslope
Acts as anchoring
Besides protecting water quality, what are other goals of urban erosion and sediment control? -
CORRECT ANSWER - Protecting the soil resource itself from degradation, eroded
sediment can fill in erosion control devices such as sediment basins and channels
What is the primary concern for urban erosion and sediment control generally limited to while
construction is in process? - CORRECT ANSWER - Ensuring the sediment doesn't
transport off of site
Vegetation on construction sites should be removed no more than how many days before earth-
moving begins? - CORRECT ANSWER - 14 days /2 weeks and then re-establish
vegetation after earth moving after 14 days.
, What are the benefits of compost compared to other mulches? - CORRECT ANSWER -
Compost is heavier than other mulches, such as straw, and it can absorb water, so when it is the
wettest is when it the heaviest and most effective. Also compost nourishes the soil, which straw
mulch does not because it has a high C:N ratio.
What is the critical element when using RECPs on construction sites? - CORRECT
ANSWER - The effectiveness of the RECP is only as good as its level of direct contact
with the soil.
"it is only as good as the cover makes contact with the soil"
They fail most often when there is a nice cover on the surface, but when there is water coming in
from above, it will go underneath the mat, because it is the path of least resistance, and erosion
will occur underneath that mat.
How do we usually stop sediment delivery from hillslopes? - CORRECT ANSWER -
Stopping transport delivery is all about reducing the transport capacity of water and giving
sediment time to settle
This is done in two ways:
Minimize runoff
Slow runoff by increasing roughness or forcing water into a ponded volume
What are the two key elements for the use of permeable barriers? - CORRECT ANSWER -
Insuring that they are installed into the ground
They need to be installed correctly
Water takes the path of least resistance so if they are not secure in ground, water will just flow
under them
Contouring
If we lay these out naturally at lower portions in the topography, all the water will run towards
the permeable barrier and it will topple over, so it is important to be mindful of this when we
install them in terms of a contour
Eyelid shape
Stuff is only as good as how much water goes through it, so we should install permeable barriers
in an eyelid shape so it collects the water through it rather than around it
