Get documents about "Storm Water Runoff Volume Calculator - Runoff Volume Calculator
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"The Storm
The StormUlator enables the user to estimate the size, volume a
needed to reduce stormwater runof
(Step 1a) If you
know the 85th
User may make changes from any percentile storm
event for your
cell that is orange or brown in color location enter it in
(similar to the cells to the immediate the box below
right). Cells in green are calculated
for you.
Project Information
Project Name: Optional
Waste Discharge Identification (WDID): Optional
Date: Optional
Sub Drainage Area Name (from map): Optional
Regional Curve Numbers
Existing Pervious Runoff Curve Number
Proposed Development Pervious Runoff Curve Number
Precipitation
Based on the County you indicated above,
we have included the 85 percentile average 0.00 in
The Amount P85 (in)^ for your area.
24 hr event - of rainfall needed for runoff to
occur (Existing regional curve -P from
0.00 In
existing RCN (in)^)
P used for calculations (in) (the greater of
0.00 In
the above two criteria)
^Available at www.cabmphandbooks.com
Pre-Project Runoff Volume (cu ft) 0 Cu.Ft.
Project-Related Runoff Volume Increase
0 Cu.Ft.
w/o credits (cu ft)
Project-Related Volume Increase with
0 Cu.Ft.
Credits (cu ft)
"The StormUlator"
ser to estimate the size, volume and type of Alternative Storm Water Management System
eded to reduce stormwater runoff from development projects.
(Step 1b) If you can not answer 1a then select the
county where the project is located (click on the cell
to the right for drop-down): This will determine the COUNTY
average 85th percentile 24 hr. storm event for your
site, which will appear under precipitation to left.
(Step 1c) If you would like a more percise value
select the location closest to your site. If you do not
recgonize any of these locations, leave this drop- LOCATION
down menu at location. The average value for the
County will be used.
Runoff Calculations
(Step 2) Indicate the Soil Type (dropdown menu to
right):
Soil Type
(Step 3) Indicate the existing dominant non-built land
Non-Built Land Use Type Pre Development
Use Type (dropdown menu to right):
(Step 4) Indicate the proposed dominant non-built
Non-Built Land Use Type Post Development
land Use Type (dropdown menu to right):
Complete Either
Sq Ft Acres
(Step 5) Total Project Site Area:
(Step 6) Sub-watershed Area:
Percent of total project :
(Step 7) Sub-watershed Conditions Complete Either
Sub-watershed Area (acres)
Sq Ft Acres
Existing Rooftop Lot Coverage
Existing Non-Rooftop Lot Coverage
Proposed Rooftop Lot Coverage
Proposed Non-Rooftop Lot Coverage
(Step 8) Impervious Area Reduction Credits Acres
Porous Pavement 0.00
Tree Planting 0.00
Downspout Disconnection 0.00
Impervious Area Disconnection 0.00
Green Roof 0.00
Stream Buffer 0.00
Vegetated Swales 0.00
Subtotal 0.00
Subtotal Runoff Volume Reduction in cubic feet
0
(Step 9) Impervious Volume Reduction Credits Volume (cubic feet)
Rain Barrels/Cisterns 0
Landscaping Soil Quality 0
Subtotal Runoff Volume Reduction in cubic feet 0
Total Runoff Volume Reduction in cubic feet 0
ent System
COUNTY
LOCATION
Use Type Pre Development
Use Type Post Development
Acres
0.00
0.00
Acres
0.00
0.00
0.00
0.00
Note: Macros
have been
disabled in this
version
Cu. Ft.
Cu. Ft.
Cu. Ft.
Cu. Ft.
Cu. Ft.
Porous Pavement Credit Worksheet
Please fill out a porous pavement credit worksheet for each project sub-watershed.
For the PROPOSED Development:
Proposed Porous Pavement
Area of Brick without Grout on less than 12 inches of base with at least 20% void
space over soil
Area of Brick without Grout on more than 12 inches of base with at least 20% void
space over soil
Area of Cobbles less than 12 inches deep and over soil
Area of Cobbles less than 12 inches deep and over soil
Area of Reinforced Grass Pavement on less than 12 inches of base with at least 20%
void space over soil
Area of Reinforced Grass Pavement on at least 12 inches of base with at least 20%
void space over soil
Area of Porous Gravel Pavement on less than 12 inches of base with at least 20%
void space over soil
Area of Porous Gravel Pavement on at least 12 inches of base with at least 20% void
space over soil
Area of Poured Porous Concrete or Asphalt Pavement with less than 4 inches of
gravel base (washed stone)
Area of Poured Porous Concrete or Asphalt Pavement with 4 to 8 inches of gravel
base (washed stone)
Area of Poured Porous Concrete or Asphalt Pavement with 8 to 12 inches of gravel
base (washed stone)
Area of Poured Porous Concrete or Asphalt Pavement with 12 or more inches of
gravel base (washed stone)
Tree Planting Credit Worksheet
Please fill out a tree canopy credit worksheet for each project sub-watershed.
Tree Canopy Credit Criteria
Number of proposed evergreen trees (credit = number of trees x 0.005)
Number of proposed deciduous trees (credit = number of trees x 0.0025)
Number of existing trees that will remain that are less than 6 in diameter (credit = number of trees x 0.125
Number of existing trees that will remain that are at least 6 in diameter (credit = number of trees x 0.25)
Please describe below how the project will ensure that these trees will be maintained.
Rain Barrel/Cistern Credit Worksheet
Please fill out a rain barrel/cistern worksheet for each project sub-watershed.
Rain Barrel/Cistern Credit Criteria
Total capacity rain barrel(s)/cistern(s) (in gallons)
Total capacity rain barrel(s)/cistern(s) (in cu ft) 1
1
accounts for 10% loss
Fill in either Acres or SqFt
Runoff Reduction* In SqFt. In Acres Equivalent Acres
0.45 0.00
0.90 0.00
0.30 0.00
0.60 0.00
0.45 0.00
0.90 0.00
0.38 0.00
0.75 0.00
0.40 0.00
0.60 0.00
0.80 0.00
1.00 0.00
*=1-Rv** Return to Calculator
**Using Site Design Techniques to meet Development Standards for Stormwater Quality (BASMAA 2003)
**NCDENR Stormwater BMP Manual (2007)
Number of
Trees
Planted Area Credit (acres)
0
0
dit = number of trees x 0.125) 0
t = number of trees x 0.25) 0
ntained.
Return to Calculator
.
Response
0
Return to Calculator
Impervious Area Disconnection Credit Worksheet
Please fill out an impervious area disconnection credit worksheet for each project sub-watershed. If you
yes to all questions, you may subtract all impervious surface draining to each discharge location. Disconn
impervious area is entered in Volume Calculator Worksheet.
Non-Rooftop Disconnection Credit Criteria
The maximum contributing impervious flow path length is 75 feet.
The length of the disconnection is equal to or greater than the contributing length. A
storage device (e.g. French drain, bioretention area, gravel trench) may need to be
implemented to achieve the required disconnection length.
The impervious area to any one discharge location does not exceed 5,000 square feet.
Percentage of existing 0.00 Acres non-rooftop surface area disconnected
Percentage of the
proposed 0.00 Acres non-rooftop surface area disconnected
ject sub-watershed. If you answer
discharge location. Disconnected
Response
Yes No
Yes No
Yes No
Return to Calculator
Downspout Disconnection Credit Worksheet
Please fill out a downspout disconnection credit worksheet for each project subwatershed. If you
answer yes to all questions, all rooftop area draining to each downspout will be subtracted from
your total Impervious surface area. Rooftop area is entered Volume Calculator Worksheet.
Downspout Disconnection Credit Criteria
Downspouts and any extensions extend at least six feet from a basement and two feet from a crawl
space or concrete slab.
The contributing area of rooftop to each disconnected downspout is 500 square feet or less.
All roof runoff drains as sheet flow to a planter box or landscaped area.
All roof runoff drains onto turf as sheet flow and allowed to spread out over an area large enough to
contain the 85th percentile 24 hour rain event.
of rooftop surface has disconnected
Percentage of existing 0.00 Acres downspouts
of rooftop surface has disconnected
Percentage of the proposed 0.00 Acres downspouts
each project subwatershed. If you
downspout will be subtracted from
Volume Calculator Worksheet.
dit Criteria
a basement and two feet from a crawl Yes No
Yes No
pout is 500 square feet or less.
Yes No
ped area.
read out over an area large enough to Yes No
p surface has disconnected
outs
p surface has disconnected
outs
Return to Calculator
Greenroof Credit Worksheet
Please fill out a greenroof credit worksheet for each project sub-watershed. If you answer yes to all ques
greenroof area will be subtracted from your total impervious area.
Green Roof Credit Criteria
Is the roof slop less than 15% or does it have a grid to hold the substrate in place until it forms a
thick vegetation mat?
Has a professional engineer assessed the necessary load reserves and designed a roof
structure that meets state and local codes?
If supplemental irrigation is needed to sustain the green roof during extended dry periods, is the
source from recycled, reclaimed, or reused water?
Acre
Percentage of existing 0.00 s rooftop surface area in greenroof
Percentage of the Acre
proposed 0.00 s rooftop surface area in greenroof
ach project sub-watershed. If you answer yes to all questions, 70% of the
otal impervious area.
Credit Criteria Response
grid to hold the substrate in place until it forms a
Yes No
ssary load reserves and designed a roof
Yes No
e green roof during extended dry periods, is the
r? Yes No
surface area in greenroof
surface area in greenroof
Return to Calculator
Stream Buffer Credit Worksheet
Please fill out a stream buffer credit worksheet for each project sub-watershed. If you answer yes to all q
subtract all impervious surface draining to each stream buffer. Impervious area draining to a stream buff
Volume Calculator Worksheet.
Stream Buffer Credit Criteria
Runoff enters the floodprone width or within 500 feet (whichever is larger) of a stream channel as
sheet flow. The maximum contributing length shall be 150 feet for pervious areas and 75 feet for
impervious areas?
The contributing overland slope is 5% or less, or a level spreader shall be used?
Buffer area is protected from vehicle or other traffic barriers to reduce compaction?
Stream Buffer will be maintained in a natural state set back from development or other structure?
Acre
Percentage of existing 0.00 s impervious surface area draining into a stream buffer:
Percentage of the Acre impervious surface area that will drain into a stream
proposed 0.00 s buffer:
Please describe below how the project will ensure that the buffer areas will remain in ungraded
and uncompacted condition, and that the overstory and understory vegetation will be maintained
in a natural condition.
or each project sub-watershed. If you answer yes to all questions, you may
stream buffer. Impervious area draining to a stream buffer is entered in
Credit Criteria Response
feet (whichever is larger) of a stream channel as
all be 150 feet for pervious areas and 75 feet for Yes No
a level spreader shall be used? Yes No
ffic barriers to reduce compaction? Yes No
te set back from development or other structure? Yes No
ous surface area draining into a stream buffer:
ous surface area that will drain into a stream
re that the buffer areas will remain in ungraded
ory and understory vegetation will be maintained
Return to Calculator
Vegetated Swale Credit Worksheet
Please fill out a vegetated swale worksheet for each project subwatershed. If you answer yes to
all questions, you may subtract all impervious surface draining to each vegetated swale.
Impervious area draining to vegetated swales is entered in the Volume Calculator Worksheet.
Vegetated Swale Credit Criteria
All vegetated swales are designed in accordance with Treatment Control BMP 30 (TC-30 -
Vegetated Swale) from the California Stormwater BMP Handbook, New Development and
Redevelopment (available at www.cabmphandbooks.com).
The maximum flow velocity for runoff for the 85th percentile rainfall event is less than or equal to
1.0 foot per second.
Percentage of existing 0.00 Acres of impervious area draining to a vegetated swale
Percentage of the proposed 0.00 Acres of impervious area draining to a vegetated swale
ect subwatershed. If you answer yes to
aining to each vegetated swale.
n the Volume Calculator Worksheet.
t Criteria
eatment Control BMP 30 (TC-30 -
andbook, New Development and Yes No
m).
tile rainfall event is less than or equal to Yes No
vious area draining to a vegetated swale
vious area draining to a vegetated swale
Return to Calculator
Soil Quality Credit Worksheet
Please fill out a soil quality worksheet for each project sub-watershed.
Will the soils used for landscaping meet the ideal bulk densities listed in Table 1? 1
If you answered yes to the question above, and you know the area-weighted bulk density within
the top 12 inches for soils used for landscaping (in g/cm 3)* fill in the cell to the left and skip to
cell G10. If not select from the drop-down menu in G9.
If you answered yes to the question above, but you do not know the exact bulk density, which of
the soil types in the drop down menu to the right best describes the top 12 inches for soils used
for landscaping (in g/cm 3).
What is the average depth of your landscaped soil media meeting the above criteria (inches)?
What is the total length of the landscaped areas meeting the above criteria (in feet)?
What is the average width of the landscaped area meeting the above criteria (in feet)?
Table 1
Sands, loamy sands <1.6 Porosity (%) for
Sandy loams, loams <1.4
Sandy clay loams, loams, clay loams <1.4
Silts, silt loams <1.3
Silt loams, silty clay loams <1.1
Sandy clays, silty clays, some clay
loams (35-45% clay) <1.1
Clays (>45% clay) <1.1
1
USDA NRCS. "Soil Quality Urban Technical Note
No.2-Urban Soil Compaction". March 2000.
http://soils.usda.gov/sqi/management/files/sq_utn_2.pdf
* To determine how to calculate density see:
http://www.globe.gov/tctg/bulkden.pdf?sectionID=94
Response
Yes No
Soil Type
Return to Calculator
Soil Type
Mineral grains in many soils are mainly quartz and
feldspar, so 2.65 a good average for particle
density. To determine percent porosity we use the
formula: Porosity (%) = (1-Bulk Density/2.65) X
100
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