Stormwater
Management
Inspector Prep
TEST (254
questions with
solutions)
What are the types of disconnection allowed for rooftop
disconnection?
1) simple disconnection - rooftops and/or on-lot residential
impervious surfaces are directed to pervious areas
2) disconnection leading to an alternative runoff reduction
practice adjacent to the roof (ex: soil compost amended filter
path)
Why have a rooftop disconnection to an alternative practice?
-lot size too small
-filter width is too narrow
-need more water quality credit
Brainpower
,Read More
Functions provided by simple rooftop disconnection
-annual runoff volume reduction
-total phosphorus mass load removal
-total nitrogen mass load removal
Alternative rooftop disconnection types
-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?
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
-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
-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
- 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
minimal; spring cleanup, regular mowing, check dam repairs, and
other methods of maintaining hydraulic efficiency
Grass channel design criteria
-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
Management
Inspector Prep
TEST (254
questions with
solutions)
What are the types of disconnection allowed for rooftop
disconnection?
1) simple disconnection - rooftops and/or on-lot residential
impervious surfaces are directed to pervious areas
2) disconnection leading to an alternative runoff reduction
practice adjacent to the roof (ex: soil compost amended filter
path)
Why have a rooftop disconnection to an alternative practice?
-lot size too small
-filter width is too narrow
-need more water quality credit
Brainpower
,Read More
Functions provided by simple rooftop disconnection
-annual runoff volume reduction
-total phosphorus mass load removal
-total nitrogen mass load removal
Alternative rooftop disconnection types
-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?
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
-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
-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
- 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
minimal; spring cleanup, regular mowing, check dam repairs, and
other methods of maintaining hydraulic efficiency
Grass channel design criteria
-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
