EROSION AND SEDIMENT CONTROL
INSPECTOR COMPLETE STUDY GUIDE
QUESTIONS AND VERIFIED ANSWERS
●● Why have a rooftop disconnection to an alternative practice?
Answer: -lot size too small
-filter width is too narrow
-need more water quality credit
●● Functions provided by simple rooftop disconnection
Answer: -annual runoff volume reduction
-total phosphorus mass load removal
-total nitrogen mass load removal
●● Alternative rooftop disconnection types
Answer: -soil compost-amended filter path
-dry-well or french drain
-rain-garden//front yard bioretention
-rainwater harvesting//cistern
-stormwater planter
,●● How does sheet flow to a vegetated filter strip or conserved open
space work?
Answer: Filter strips are vegetated areas that treat sheet flow delivered
from adjacent impervious and managed turd areas by slowing runoff
velocities and allowing sediment and attached pollutants to settle and/or
be filtered by the vegetation
●● Gravel diaphragm
Answer: -pretreatment device
-maintains sheet flow
-not necessary if contributing drainage area is solely turf
-trench is 2 ft. wide and 1 ft. deep
-runs on same contour at top of filter strip
-drop at least 3 inches
-fabric between gravel and soil
●● Engineered level spreader
Answer: -forebay: max. 3ft. deep, transition to 1 ft. at level spreader lip
-level spreader lip - concrete, wood, or prefabricated metal, with a well
anchored footer, or other accepted rigid, non-erodible material
-location: 3-6 inches above downstream natural grade to avoid turf
buildup
-3ft. of VDOT #3 stone, underlain by filter fabric just below spreader
-vegetated receiving area must be stabilized
,●● Construction sequence for conserved open space
Answer: - no clearing, grading, heavy equipment
-protect area during construction
-prevent sediment discharge
-mark limits of disturbance
-drainage area stabilized
-grade with tracked vehicles
-install gravel diaphragm and/or level spreader
-mark filter boundaries
-keep vehicles out
-stockpile topsoil for later use
-divert construction runoff
-install gravel diaphragm and/or level spreader
-grade with tracked vehicles
-open to runoff once stabilized
●● Maintenance of Vegetated Filter Strips
Answer: minimal; spring cleanup, regular mowing, check dam repairs,
and other methods of maintaining hydraulic efficiency
●● Grass channel design criteria
, Answer: -the bottom width of the channel should be between 4-8 feet
wide
-the channel side-slopes should be 3H:1V or flatter
-the maximum total contributing drainage area to any individual grass
channel is 5 acres
-the longitudinal slope of the channel is <4%
-max flow velocity of channel must be <1ft/sec during a 1 inch storm
event
-the dimensions of the channel should ensure that flow velocity is non-
erosive during the 2-yr and 10-yr design storm events and the 10-yr
design flow is contained within the channel
●● Grass channel pretreatment
Answer: -check dams
-tree check dams
-grass filter strip
-gravel or stone diaphragm
-gravel or stone flow spreaders
●● Check dams
Answer: -Purpose: break-up slopes and increase time water stays in
channel
max desired height 12-18 in
-averaging ponding depth: 12 in
INSPECTOR COMPLETE STUDY GUIDE
QUESTIONS AND VERIFIED ANSWERS
●● Why have a rooftop disconnection to an alternative practice?
Answer: -lot size too small
-filter width is too narrow
-need more water quality credit
●● Functions provided by simple rooftop disconnection
Answer: -annual runoff volume reduction
-total phosphorus mass load removal
-total nitrogen mass load removal
●● Alternative rooftop disconnection types
Answer: -soil compost-amended filter path
-dry-well or french drain
-rain-garden//front yard bioretention
-rainwater harvesting//cistern
-stormwater planter
,●● How does sheet flow to a vegetated filter strip or conserved open
space work?
Answer: Filter strips are vegetated areas that treat sheet flow delivered
from adjacent impervious and managed turd areas by slowing runoff
velocities and allowing sediment and attached pollutants to settle and/or
be filtered by the vegetation
●● Gravel diaphragm
Answer: -pretreatment device
-maintains sheet flow
-not necessary if contributing drainage area is solely turf
-trench is 2 ft. wide and 1 ft. deep
-runs on same contour at top of filter strip
-drop at least 3 inches
-fabric between gravel and soil
●● Engineered level spreader
Answer: -forebay: max. 3ft. deep, transition to 1 ft. at level spreader lip
-level spreader lip - concrete, wood, or prefabricated metal, with a well
anchored footer, or other accepted rigid, non-erodible material
-location: 3-6 inches above downstream natural grade to avoid turf
buildup
-3ft. of VDOT #3 stone, underlain by filter fabric just below spreader
-vegetated receiving area must be stabilized
,●● Construction sequence for conserved open space
Answer: - no clearing, grading, heavy equipment
-protect area during construction
-prevent sediment discharge
-mark limits of disturbance
-drainage area stabilized
-grade with tracked vehicles
-install gravel diaphragm and/or level spreader
-mark filter boundaries
-keep vehicles out
-stockpile topsoil for later use
-divert construction runoff
-install gravel diaphragm and/or level spreader
-grade with tracked vehicles
-open to runoff once stabilized
●● Maintenance of Vegetated Filter Strips
Answer: minimal; spring cleanup, regular mowing, check dam repairs,
and other methods of maintaining hydraulic efficiency
●● Grass channel design criteria
, Answer: -the bottom width of the channel should be between 4-8 feet
wide
-the channel side-slopes should be 3H:1V or flatter
-the maximum total contributing drainage area to any individual grass
channel is 5 acres
-the longitudinal slope of the channel is <4%
-max flow velocity of channel must be <1ft/sec during a 1 inch storm
event
-the dimensions of the channel should ensure that flow velocity is non-
erosive during the 2-yr and 10-yr design storm events and the 10-yr
design flow is contained within the channel
●● Grass channel pretreatment
Answer: -check dams
-tree check dams
-grass filter strip
-gravel or stone diaphragm
-gravel or stone flow spreaders
●● Check dams
Answer: -Purpose: break-up slopes and increase time water stays in
channel
max desired height 12-18 in
-averaging ponding depth: 12 in
