Mountain Top Inn Chittenden, VT Stormwater Management … · 2016-04-22 · Chittenden, VT...
Transcript of Mountain Top Inn Chittenden, VT Stormwater Management … · 2016-04-22 · Chittenden, VT...
Mountain Top Inn
Chittenden, VT
Stormwater Management System
Worksheets and Basis of Design
General Permit 3-9015
March 6, 2015
Revised April 22, 2016
Index
Pre & Post-Development Drainage Areas
Peak Flows
Water Quality Volume Worksheet - Subarea 1
Recharge Volume Worksheet - Subarea 1
Water Quality Volume Worksheet - Subarea 2
Recharge Volume Worksheet - Subarea 2
Water Quality Volume Worksheet - Subarea 3
Recharge Volume Worksheet - Subarea 3
Water Quality Volume Worksheet - Subarea 4A
Recharge Volume Worksheet - Subarea 4A
Water Quality Volume Worksheet - Subarea 4B
Recharge Volume Worksheet - Subarea 4B
5 Treatment Criteria Design - Subarea 1
5 Treatment Criteria Design - Subarea 2
5 Treatment Criteria Design - Subarea 3
5 Treatment Criteria Design - Subarea 4
Dry Swale Worksheet - Dry Swale 1
Dry Swale Worksheet - Dry Swale 2
Dry Swale Worksheet - Dry Swale 3
Dry Swale Worksheet - Dry Swale 4
Dry Pond Worksheet - Dry Swale 1
Dry Pond Worksheet - Dry Swale 2
Dry Pond Worksheet - Dry Swale 3
Dry Pond Worksheet - Dry Swale 4
Appendix A: HydroCAD Calculations
Page 1 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Pre & Post-Development Drainage Areas March 6, 2015
Revised: April 22, 2016
Pre-Development Areas
S/N 001
Areas
Subarea Soil Class sq. ft. sq. mi. ac.
1A Project Area C 31,886 0.0011 0.73
(Parking Imp Existing 17,123 0.0006 0.39
Lot) 49,009 0.0018 1.13
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 60 1786 1782 0.067
Areas
Subarea Soil Class sq. ft. sq. mi. ac.
1 Project Area C 57,767 0.0021 1.33
(East Imp Existing 8,354 0.0003 0.19
Meadow) 66,121 0.0024 1.52
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 100 1768 1756 0.120
Ditch 680 1756 1690 0.097
Channel Details (Roadside)
Bott. Width (ft) 1 Side (ft) 1.1
Top Width (ft) 2 P (ft) 3.2
Depth (ft) 1 A (sf) 1.5
Subarea Soil Class sq. ft. sq. mi. ac.
2 B 63,019 0.0023 1.45
C 13,597 0.0005 0.31
Imp Existing 2,441 0.0001 0.06
79,057 0.0028 1.81
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 100 1618 1614 0.040
Shallow 200 1614 1602 0.060
Note: Expanded western parking lot (constructed 2011) considered to be a pervious surface for pre-
development calculations.
Pre and Post Areas Page 2 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Pre & Post-Development Drainage Areas March 6, 2015
Revised: April 22, 2016
Areas
Subarea Soil Class sq. ft. sq. mi. ac.
3 Project Area B 24,362 0.0009 0.56
Imp Existing 961 0.0000 0.02
25,323 0.0009 0.58
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 50 1596 1590 0.120
Areas
Subarea Soil Class sq. ft. sq. mi. ac.
4A Project Area B 11,538 0.0004 0.26
C 81,547 0.0029 1.87
93,085 0.0033 2.14
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 120 1608 1600 0.067
Areas
Subarea Soil Class sq. ft. sq. mi. ac.
4B Project Area B 33,705 0.0012 0.77
C 17,575 0.0006 0.40
51,280 0.0018 1.18
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 70 1602 1594 0.114
Sheet 15 1594 1584 0.667
Pre and Post Areas Page 3 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Pre & Post-Development Drainage Areas March 6, 2015
Revised: April 22, 2016
Post-Development Areas
S/N 001
Areas
Subarea Soil Class sq. ft. sq. mi. ac.
1A Project Area C 16,034 0.0006 0.37
Imp Existing (1) 14,234 0.0005 0.33
Imp Existing (2) 2,889 0.0001 0.07
Imp Existing (3) 15,852 0.0006 0.36
Imp Proposed (4) 0 0.0000 0.00
49,009 0.0018 1.13
(1) Existing area to be treated, counting towards site balancing
(2) Existing area to be treated, NOT counting towards site balancing
(3) Expanded western parking lot area, constructed 2011
(4) Proposed impervious, Annex project
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 84 1790 1782 0.095
Ditch 250 1782 1778 0.016
18" Culvert 55 1778 1776 0.036
Areas
Subarea Soil Class sq. ft. sq. mi. ac.
1 Project Area C 52,239 0.0019 1.20
Imp Existing (1) 6,727 0.0002 0.15
Imp Existing (2) 1,627 0.0001 0.04
Imp Existing (3) 0 0.0000 0.00
Imp Proposed (4) 5,528 0.0002 0.13
66,121 0.0024 1.52
(1) Existing area to be treated, counting towards site balancing
(2) Existing area to be treated, NOT counting towards site balancing
(3) Expanded western parking lot area
(4) Proposed impervious, Annex project
Pre and Post Areas Page 4 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Pre & Post-Development Drainage Areas March 6, 2015
Revised: April 22, 2016
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 100 1762 1752 0.100
Channel 670 1752 1690 0.093
Dry Swale 130 1690 1685.5 0.035
Channel Details (Roadside)
Bott. Width (ft) 2 Side (ft) 4.5
Top Width (ft) 10 P (ft) 10.9
Depth (ft) 2 A (sf) 12
Channel Details (Dry Swale)
Bott. Width (ft) 4 Side (ft) 3.6
Top Width (ft) 10 P (ft) 11.2
Depth (ft) 2 A (sf) 14
2 Project Area B 62,029 0.0022 1.42
C 12,692 0.0005 0.29
Imp Existing (1) 2,441 0.0001 0.06
Imp Proposed 1,895 0.0001 0.04
79,057 0.0028 1.81
(1) Existing area to be treated, counting towards site balancing
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 80 1625 1621 0.020
Channel 360 1621 1602 0.053
Dry Swale 210 1602 1597.5 0.021
Channel Details (Roadside)
Bott. Width (ft) 2 Side (ft) 4.5
Top Width (ft) 10 P (ft) 10.9
Depth (ft) 2 A (sf) 12
Channel Details (Dry Swale)
Bott. Width (ft) 4 Side (ft) 3.6
Top Width (ft) 10 P (ft) 11.2
Depth (ft) 2 A (sf) 14
Pre and Post Areas Page 5 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Pre & Post-Development Drainage Areas March 6, 2015
Revised: April 22, 2016
3 Project Area B 15,858 0.0006 0.36
Imp Existing (1) 961 0.0000 0.02
Imp Proposed 8,504 0.0003 0.20
25,323 0.0009 0.58
(1) Existing area to be treated, counting towards site balancing
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 25 1596 1588 0.32
Channel 410 1588 1580 0.020
Channel Details
Bott. Width (ft) 2 Side (ft) 4.5
Top Width (ft) 10 P (ft) 10.9
Depth (ft) 2 A (sf) 12
4A Project Area B 8,632 0.0003 0.20
C 47,979 0.0017 1.10
Imp Proposed 36,474 0.0013 0.84
93,085 0.0033 2.14
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 130 1601 1598 0.020
Channel 1 158 1598 1596 0.013
Channel 2 150 1596 1590 0.040
Channel 3 51 1590 1588 0.039
18" Culvert 290 1588 1578 0.034
Channel Details (Dry Swale)
Bott. Width (ft) 2 Side (ft) 4.5
Top Width (ft) 10 P (ft) 10.9
Depth (ft) 2 A (sf) 12
Channel Details (Dry Swale)
Bott. Width (ft) 2 Side (ft) 4.5
Top Width (ft) 10 P (ft) 10.9
Depth (ft) 2 A (sf) 12
Channel Details
Bott. Width (ft) 4 Side (ft) 3.6
Top Width (ft) 10 P (ft) 11.2
Depth (ft) 2 A (sf) 14
Pre and Post Areas Page 6 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Pre & Post-Development Drainage Areas March 6, 2015
Revised: April 22, 2016
4B Project Area B 27,205 0.0010 0.62
C 17,575 0.0006 0.40
Imp Proposed 6,500 0.0002 0.15
1.18
Start End Slope
Watercourse Lengths & Slopes Length (ft) Elev (ft) Elev (ft) (ft/ft)
Sheet 45 1601 1600 0.022
40 1600 1580 0.500
Pre and Post Areas Page 7 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Peak Flows March 6, 2015
Revised: April 22, 2016
Subarea 1A
Pre-Development Post-Development
Storm Peak Flow t(c) Peak Flow t(c)
Event (cfs) (hrs) (cfs) (hrs)
1 1.7 0.01 2.9 0.01
10 4.1 0.01 5.6 0.01
100 8.2 0.01 9.8 0.01
Subarea 1
Pre-Development Post-Development
Storm Peak Flow t(c) Peak Flow t(c)
Event (cfs) (hrs) (cfs) (hrs)
1 1.2 0.11 1.6 0.09
10 3.6 0.11 4.2 0.09
100 8.1 0.11 9.0 0.09
Subareas 1A & 1
Pre-Development Post-Development Post-Detention
Storm Peak Flow t(c) Peak Flow t(c) Peak Flow t(c)
Event (cfs) (hrs) (cfs) (hrs) (cfs) (hrs)
1 2.9 --- 4.5 --- 0.09 ---
10 7.7 --- 9.8 --- 4.3 ---
100 16.3 --- 18.8 --- 15.8 ---
Subarea 2
Pre-Development Post-Development Post-Detention
Storm Peak Flow t(c) Peak Flow t(c) Peak Flow t(c)
Event (cfs) (hrs) (cfs) (hrs) (cfs) (hrs)
1 0.14 0.34 0.18 0.33 0.01 ---
10 1.3 0.34 1.4 0.33 0.6 ---
100 4.1 0.34 4.3 0.33 3.2 ---
Subarea 3
Pre-Development Post-Development Post-Detention
Storm Peak Flow t(c) Peak Flow t(c) Peak Flow t(c)
Event (cfs) (hrs) (cfs) (hrs) (cfs) (hrs)
1 0.04 0.11 1.10 0.02 0.05 ---
10 0.6 0.11 2.4 0.02 0.5 ---
100 1.9 0.11 4.5 0.02 3.6 ---
Subarea 4A
Pre-Development Post-Development
Storm Peak Flow t(c) Peak Flow t(c)
Event (cfs) (hrs) (cfs) (hrs)
1 1.19 0.02 7.26 0.03
10 4.5 0.02 14.6 0.03
100 11.3 0.02 26.3 0.03
Peak Flows Page 8 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Peak Flows March 6, 2015
Revised: April 22, 2016
Subarea 4B
Pre-Development Post-Development
Storm Peak Flow t(c) Peak Flow t(c)
Event (cfs) (hrs) (cfs) (hrs)
1 0.28 0.16 0.66 0.12
10 1.5 0.16 2.3 0.12
100 4.2 0.16 5.5 0.12
Subareas 4A & 4B
Pre-Development Total Post-Development Post-Detention
Storm Peak Flow t(c) Peak Flow t(c) Peak Flow t(c)
Event (cfs) (hrs) (cfs) (hrs) (cfs) (hrs)
1 1.5 --- 7.9 --- 0.16 ---
10 6.0 --- 16.9 --- 4.1 ---
100 15.5 --- 31.9 --- 24.2 ---
Peak Flows Page 9 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Water Quality Volume March 6, 2015
Revised: April 22, 2016
Page 1 of 2
Version: 9/06 For the area draining to*:
Located in drainage area for S/N: 001
WQ Volume and Modified Curve Number Calculation for Water Quality Treatment in Flow-Based Practice
Water Quality Volume Calculations
Line value/calculation units
1 Area draining to practice A= 2.64 acres
2 Impervious area 1.08 acres
3 Percent Impervious Area = [(line 2/line 1) * 100] = I = 40.70 % (whole #)
4 Precipitation P = 0.9 inches
5 Runoff coefficient calculation = (0.05 + (0.009*I)) Rv = 0.416
6 WQ Volume (in watershed inches) Calculation =( P * Rv) = 0.375 Qa (watershed inches, a.k.a. inches of runoff)
7 Minimum WQ Volume10.2 watershed inches
8 Enter the greater of line 6 or line 7 WQv = 0.375 watershed inches
9 WQ Volume Calculation = (line 8 *A)/12 = WQv = 0.083 ac. ft.
10 WQ Volume Calculation = (line 9 * 43560) = WQv = 3595 cu. ft.
Subarea 1 (Includes Subarea 1A)
Use this worksheet to calculate your WQv if you need to determine the Peak Q for the WQ storm (i.e. designing a grass channel, flow-splitter or other flow
based practice) and you are not using any of the site design credits in section 3 of the 2002 VSWMM. See page 2 for "Calculating Peak WQ Discharge
Rate (0.9" storm) using the Modified Curve Number." Please note that in the case of grass channels you must include any off-site area draining to the
practice as this will affect the peak discharge rate which will ultimately affect the hydraulics, and thus residence time, in your channel.
WQv Subarea 1 Page 10 of 48
Notes:
Page 2 of 2
Version: 9/06 For the area draining to*:
Located in drainage area for S/N: 001
Steps:
1. Transfer information from WQv calculation worksheets.
Enter the Qa ( line 8 from WQv sheet )
Qa = 0.375 inches
Enter the area (site +off-site draining to practice) used in calculating the percent impervious (I)
A = 2.6 acres
2. Use the following equation to calculate a corresponding curve number
where P = 0.9 inches
CN = 1000/(10 +(5*P)+(10*Qa) - (10*(Qa^2 + (1.25*Qa*P))^0.5))
CN = 93.0
Above, you should have calculated the WQv in watershed inches draining to the facility/practice for which you need to calculate the WQ-
peak discharge. As provided in the guidance listed on the grass channel worksheet, please remember that the WQv calculation should include
runoff from on-site as well as off-site area draining to the grass channel since this will have an impact on the channel hydraulics and thus the
velocity and residence time.
1: Sites with low impervious cover ( ~19%) but that do not employ a significant use of the stormwater design credits in Section 3 of the VSWMM are
required to treat the minimum water quality volume of 0.2 watershed inches. Sites that have a significant portion of their impervious cover addressed via
the stormwater credits (section 3 of the VSWMM) will be able to reduce this WQv and will only be required to treat the volume calculated on the "WQ
Volume (with credit reduction)" worksheet which will be less than the 0.2 watershed inches.
Subarea 1 (Includes Subarea 1A)
Calculating Peak WQ Peak Discharge Rate (0.9" storm) using the Modified Curve Number
Because NRCS methods underestimate the peak discharge for rainfall events of less than 2", simply plugging in 0.9" of rainfall into your
hydrologic model with the standard curve numbers will not produce the correct peak discharge during the WQv storm, nor will it produce a
volume of runoff equivalent to that which you have calculated using the WQv formula (WQv = P*Rv*A/12). In order to calculate the peak
discharge for the 0.9" storm, a modified curve number must be calculated. This modified curve number is based on the runoff (in inches)
calculated using the short cut method formula (WQv = P*Rv) that is also the basis of the familiar WQv calculations provided in the 2002
VSWMM (and on the WQv calculation worksheets). Essentially, the curve number that is calculated using the methods below is the curve
number that will generate the volume of runoff calculated using the WQv formula.
WQv Subarea 1 Page 11 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Recharge March 6, 2015
Revised: April 22, 2016
Version: 2/12 For the area draining to*:
Located in drainage area for S/N: 001
Site Information value/calculation units
Site Area (impervious + disturbed pervious) A= 2.64 acres
Impervious area 1.08 acres
Percent Impervious Area = [(line 2/line 1)] = I = 0.41 % (decimal percent)
Composite Recharge Factor Calculation
Enter site acreage of each HSG draining to POI or S/N value/calculation
HSG A acres
HSG B acres
HSG C 2.64 acres
HSG D acres
Total Site Area 2.643
Composite Recharge Factor 0.100
0.009 acre feet
390 cubic feet
0.108 acres
4,686 square feet
Subarea 1
Groundwater Recharge Treatment Standard - Calculation & Waiver Worksheet
The average annual groundwater recharge rate for the prevailing hydrologic soil group(s) (HSG) must be maintained in order to preserve existing water table elevations.
Recharge is determined as a function of annual predevelopment recharge for a given HSG, the average annual rainfall and the amount of impervious surface at the site. The
Groundwater Recharge Treatment Standard can be met by using one or both of the following methods: volume method and/or percent area method. See Table 2.2 in the
VSMM - Volume I for a list of acceptable STPs or credits that satisfy this requirement. Use NRCS's Web Soil Survey to obtain specific soil data at your site, available at:
http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm
ReV (Percent Volume Method)
The percent volume method is commonly used to meet recharge. Designers must demonstrate that a proposed STP
allows at least the Rev to enter the ground. The Rev is contained within the WQv. So, if a practice is infiltrating the
entire WQv, then Rev is automatically met. Please use the applicable STP worksheets to verify the Groundwater
Recharge Treatment Standard has been met. Note that not all STPs can be used to meet this standard.
ReA (Percent Area Method)
The percent area method is used when meeting recharge via nonstructural design credits(disconnection of
rooftop/non-rooftop surfaces, stream buffer, grass channel credit, or ESRD). In this case, the designer must
demonstrate that stormwater runoff from a portion of the new impervious area, equivalent to the area calculated
under the percent area method, drains into a nonstructural design credit practice.
Additional notes:
*Recharge is one of the unified sizing criteria that can be achieved site wide, rather than at each point of interest (POI) or discharge point (S/N), assuming the receiving water
is the same for each discharge point.
Re Subarea 1 Page 12 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Water Quality Volume March 6, 2015
Revised: April 22, 2016
Page 1 of 2
Version: 9/06 For the area draining to*:
Located in drainage area for S/N: 001
WQ Volume and Modified Curve Number Calculation for Water Quality Treatment in Flow-Based Practice
Water Quality Volume Calculations
Line value/calculation units
1 Area draining to practice A= 1.81 acres
2 Impervious area 0.10 acres
3 Percent Impervious Area = [(line 2/line 1) * 100] = I = 5.48 % (whole #)
4 Precipitation P = 0.9 inches
5 Runoff coefficient calculation = (0.05 + (0.009*I)) Rv = 0.099
6 WQ Volume (in watershed inches) Calculation =( P * Rv) = 0.089 Qa (watershed inches, a.k.a. inches of runoff)
7 Minimum WQ Volume10.2 watershed inches
8 Enter the greater of line 6 or line 7 WQv = 0.200 watershed inches
9 WQ Volume Calculation = (line 8 *A)/12 = WQv = 0.030 ac. ft.
10 WQ Volume Calculation = (line 9 * 43560) = WQv = 1318 cu. ft.
Subarea 2
Use this worksheet to calculate your WQv if you need to determine the Peak Q for the WQ storm (i.e. designing a grass channel, flow-splitter or other flow
based practice) and you are not using any of the site design credits in section 3 of the 2002 VSWMM. See page 2 for "Calculating Peak WQ Discharge
Rate (0.9" storm) using the Modified Curve Number." Please note that in the case of grass channels you must include any off-site area draining to the
practice as this will affect the peak discharge rate which will ultimately affect the hydraulics, and thus residence time, in your channel.
WQv Subarea 2 Page 13 of 48
Notes:
Page 2 of 2
Version: 9/06 For the area draining to*:
Located in drainage area for S/N: 001
Steps:
1. Transfer information from WQv calculation worksheets.
Enter the Qa ( line 8 from WQv sheet )
Qa = 0.200 inches
Enter the area (site +off-site draining to practice) used in calculating the percent impervious (I)
A = 1.8 acres
2. Use the following equation to calculate a corresponding curve number
where P = 0.9 inches
CN = 1000/(10 +(5*P)+(10*Qa) - (10*(Qa^2 + (1.25*Qa*P))^0.5))
CN = 88.1
Above, you should have calculated the WQv in watershed inches draining to the facility/practice for which you need to calculate the WQ-
peak discharge. As provided in the guidance listed on the grass channel worksheet, please remember that the WQv calculation should include
runoff from on-site as well as off-site area draining to the grass channel since this will have an impact on the channel hydraulics and thus the
velocity and residence time.
1: Sites with low impervious cover ( ~19%) but that do not employ a significant use of the stormwater design credits in Section 3 of the VSWMM are
required to treat the minimum water quality volume of 0.2 watershed inches. Sites that have a significant portion of their impervious cover addressed via
the stormwater credits (section 3 of the VSWMM) will be able to reduce this WQv and will only be required to treat the volume calculated on the "WQ
Volume (with credit reduction)" worksheet which will be less than the 0.2 watershed inches.
Subarea 2
Calculating Peak WQ Peak Discharge Rate (0.9" storm) using the Modified Curve Number
Because NRCS methods underestimate the peak discharge for rainfall events of less than 2", simply plugging in 0.9" of rainfall into your
hydrologic model with the standard curve numbers will not produce the correct peak discharge during the WQv storm, nor will it produce a
volume of runoff equivalent to that which you have calculated using the WQv formula (WQv = P*Rv*A/12). In order to calculate the peak
discharge for the 0.9" storm, a modified curve number must be calculated. This modified curve number is based on the runoff (in inches)
calculated using the short cut method formula (WQv = P*Rv) that is also the basis of the familiar WQv calculations provided in the 2002
VSWMM (and on the WQv calculation worksheets). Essentially, the curve number that is calculated using the methods below is the curve
number that will generate the volume of runoff calculated using the WQv formula.
WQv Subarea 2 Page 14 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Recharge March 6, 2015
Revised: April 22, 2016
Version: 2/12 For the area draining to*:
Located in drainage area for S/N: 001
Site Information value/calculation units
Site Area (impervious + disturbed pervious) A= 1.81 acres
Impervious area 0.10 acres
Percent Impervious Area = [(line 2/line 1)] = I = 0.05 % (decimal percent)
Composite Recharge Factor Calculation
Enter site acreage of each HSG draining to POI or S/N value/calculation
HSG A acres
HSG B 1.45 acres
HSG C 0.31 acres
HSG D acres
Total Site Area 1.759
Composite Recharge Factor 0.216
0.002 acre feet
78 cubic feet
0.022 acres
939 square feetReA (Percent Area Method)
The percent area method is used when meeting recharge via nonstructural design credits(disconnection of
rooftop/non-rooftop surfaces, stream buffer, grass channel credit, or ESRD). In this case, the designer must
demonstrate that stormwater runoff from a portion of the new impervious area, equivalent to the area calculated
under the percent area method, drains into a nonstructural design credit practice.
Additional notes:
*Recharge is one of the unified sizing criteria that can be achieved site wide, rather than at each point of interest (POI) or discharge point (S/N), assuming the receiving water
is the same for each discharge point.
Subarea 2
Groundwater Recharge Treatment Standard - Calculation & Waiver Worksheet
The average annual groundwater recharge rate for the prevailing hydrologic soil group(s) (HSG) must be maintained in order to preserve existing water table elevations.
Recharge is determined as a function of annual predevelopment recharge for a given HSG, the average annual rainfall and the amount of impervious surface at the site. The
Groundwater Recharge Treatment Standard can be met by using one or both of the following methods: volume method and/or percent area method. See Table 2.2 in the
VSMM - Volume I for a list of acceptable STPs or credits that satisfy this requirement. Use NRCS's Web Soil Survey to obtain specific soil data at your site, available at:
http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm
ReV (Percent Volume Method)
The percent volume method is commonly used to meet recharge. Designers must demonstrate that a proposed STP
allows at least the Rev to enter the ground. The Rev is contained within the WQv. So, if a practice is infiltrating the
entire WQv, then Rev is automatically met. Please use the applicable STP worksheets to verify the Groundwater
Recharge Treatment Standard has been met. Note that not all STPs can be used to meet this standard.
Re Subarea 2 Page 15 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Water Quality Volume March 6, 2015
Revised: April 22, 2016
Page 1 of 2
Version: 9/06 For the area draining to*:
Located in drainage area for S/N: 001
WQ Volume and Modified Curve Number Calculation for Water Quality Treatment in Flow-Based Practice
Water Quality Volume Calculations
Line value/calculation units
1 Area draining to practice A= 0.58 acres
2 Impervious area 0.22 acres
3 Percent Impervious Area = [(line 2/line 1) * 100] = I = 37.38 % (whole #)
4 Precipitation P = 0.9 inches
5 Runoff coefficient calculation = (0.05 + (0.009*I)) Rv = 0.386
6 WQ Volume (in watershed inches) Calculation =( P * Rv) = 0.348 Qa (watershed inches, a.k.a. inches of runoff)
7 Minimum WQ Volume10.2 watershed inches
8 Enter the greater of line 6 or line 7 WQv = 0.348 watershed inches
9 WQ Volume Calculation = (line 8 *A)/12 = WQv = 0.017 ac. ft.
10 WQ Volume Calculation = (line 9 * 43560) = WQv = 734 cu. ft.
Subarea 3
Use this worksheet to calculate your WQv if you need to determine the Peak Q for the WQ storm (i.e. designing a grass channel, flow-splitter or other flow
based practice) and you are not using any of the site design credits in section 3 of the 2002 VSWMM. See page 2 for "Calculating Peak WQ Discharge
Rate (0.9" storm) using the Modified Curve Number." Please note that in the case of grass channels you must include any off-site area draining to the
practice as this will affect the peak discharge rate which will ultimately affect the hydraulics, and thus residence time, in your channel.
WQv Subarea 3 Page 16 of 48
Notes:
Page 2 of 2
Version: 9/06 For the area draining to*:
Located in drainage area for S/N: 001
Steps:
1. Transfer information from WQv calculation worksheets.
Enter the Qa ( line 8 from WQv sheet )
Qa = 0.348 inches
Enter the area (site +off-site draining to practice) used in calculating the percent impervious (I)
A = 0.6 acres
2. Use the following equation to calculate a corresponding curve number
where P = 0.9 inches
CN = 1000/(10 +(5*P)+(10*Qa) - (10*(Qa^2 + (1.25*Qa*P))^0.5))
CN = 92.4
Above, you should have calculated the WQv in watershed inches draining to the facility/practice for which you need to calculate the WQ-
peak discharge. As provided in the guidance listed on the grass channel worksheet, please remember that the WQv calculation should include
runoff from on-site as well as off-site area draining to the grass channel since this will have an impact on the channel hydraulics and thus the
velocity and residence time.
1: Sites with low impervious cover ( ~19%) but that do not employ a significant use of the stormwater design credits in Section 3 of the VSWMM are
required to treat the minimum water quality volume of 0.2 watershed inches. Sites that have a significant portion of their impervious cover addressed via
the stormwater credits (section 3 of the VSWMM) will be able to reduce this WQv and will only be required to treat the volume calculated on the "WQ
Volume (with credit reduction)" worksheet which will be less than the 0.2 watershed inches.
Subarea 3
Calculating Peak WQ Peak Discharge Rate (0.9" storm) using the Modified Curve Number
Because NRCS methods underestimate the peak discharge for rainfall events of less than 2", simply plugging in 0.9" of rainfall into your
hydrologic model with the standard curve numbers will not produce the correct peak discharge during the WQv storm, nor will it produce a
volume of runoff equivalent to that which you have calculated using the WQv formula (WQv = P*Rv*A/12). In order to calculate the peak
discharge for the 0.9" storm, a modified curve number must be calculated. This modified curve number is based on the runoff (in inches)
calculated using the short cut method formula (WQv = P*Rv) that is also the basis of the familiar WQv calculations provided in the 2002
VSWMM (and on the WQv calculation worksheets). Essentially, the curve number that is calculated using the methods below is the curve
number that will generate the volume of runoff calculated using the WQv formula.
WQv Subarea 3 Page 17 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Recharge March 6, 2015
Revised: April 22, 2016
Version: 2/12 For the area draining to*:
Located in drainage area for S/N: 001
Site Information value/calculation units
Site Area (impervious + disturbed pervious) A= 0.58 acres
Impervious area 0.22 acres
Percent Impervious Area = [(line 2/line 1)] = I = 0.37 % (decimal percent)
Composite Recharge Factor Calculation
Enter site acreage of each HSG draining to POI or S/N value/calculation
HSG A acres
HSG B 0.58 acres
HSG C acres
HSG D acres
Total Site Area 0.581
Composite Recharge Factor 0.250
0.005 acre feet
197 cubic feet
0.054 acres
2366 square feet
Subarea 3
Groundwater Recharge Treatment Standard - Calculation & Waiver Worksheet
The average annual groundwater recharge rate for the prevailing hydrologic soil group(s) (HSG) must be maintained in order to preserve existing water table elevations.
Recharge is determined as a function of annual predevelopment recharge for a given HSG, the average annual rainfall and the amount of impervious surface at the site. The
Groundwater Recharge Treatment Standard can be met by using one or both of the following methods: volume method and/or percent area method. See Table 2.2 in the
VSMM - Volume I for a list of acceptable STPs or credits that satisfy this requirement. Use NRCS's Web Soil Survey to obtain specific soil data at your site, available at:
http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm
ReV (Percent Volume Method)
The percent volume method is commonly used to meet recharge. Designers must demonstrate that a proposed STP
allows at least the Rev to enter the ground. The Rev is contained within the WQv. So, if a practice is infiltrating the
entire WQv, then Rev is automatically met. Please use the applicable STP worksheets to verify the Groundwater
Recharge Treatment Standard has been met. Note that not all STPs can be used to meet this standard.
ReA (Percent Area Method)
The percent area method is used when meeting recharge via nonstructural design credits(disconnection of
rooftop/non-rooftop surfaces, stream buffer, grass channel credit, or ESRD). In this case, the designer must
demonstrate that stormwater runoff from a portion of the new impervious area, equivalent to the area calculated
under the percent area method, drains into a nonstructural design credit practice.
Additional notes:
*Recharge is one of the unified sizing criteria that can be achieved site wide, rather than at each point of interest (POI) or discharge point (S/N), assuming the receiving water
is the same for each discharge point.
Re Subarea 3 Page 18 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Water Quality Volume March 6, 2015
Revised: April 22, 2016
Page 1 of 2
Version: 9/06 For the area draining to*:
Located in drainage area for S/N: 001
WQ Volume and Modified Curve Number Calculation for Water Quality Treatment in Flow-Based Practice
Water Quality Volume Calculations
Line value/calculation units
1 Area draining to practice A= 2.14 acres
2 Impervious area 0.84 acres
3 Percent Impervious Area = [(line 2/line 1) * 100] = I = 39.18 % (whole #)
4 Precipitation P = 0.9 inches
5 Runoff coefficient calculation = (0.05 + (0.009*I)) Rv = 0.403
6 WQ Volume (in watershed inches) Calculation =( P * Rv) = 0.362 Qa (watershed inches, a.k.a. inches of runoff)
7 Minimum WQ Volume10.2 watershed inches
8 Enter the greater of line 6 or line 7 WQv = 0.362 watershed inches
9 WQ Volume Calculation = (line 8 *A)/12 = WQv = 0.065 ac. ft.
10 WQ Volume Calculation = (line 9 * 43560) = WQv = 2811 cu. ft.
Subarea 4A
Use this worksheet to calculate your WQv if you need to determine the Peak Q for the WQ storm (i.e. designing a grass channel, flow-splitter or other flow
based practice) and you are not using any of the site design credits in section 3 of the 2002 VSWMM. See page 2 for "Calculating Peak WQ Discharge
Rate (0.9" storm) using the Modified Curve Number." Please note that in the case of grass channels you must include any off-site area draining to the
practice as this will affect the peak discharge rate which will ultimately affect the hydraulics, and thus residence time, in your channel.
WQv Subarea 4A Page 19 of 48
Notes:
Page 2 of 2
Version: 9/06 For the area draining to*:
Located in drainage area for S/N: 001
Steps:
1. Transfer information from WQv calculation worksheets.
Enter the Qa ( line 8 from WQv sheet )
Qa = 0.362 inches
Enter the area (site +off-site draining to practice) used in calculating the percent impervious (I)
A = 2.1 acres
2. Use the following equation to calculate a corresponding curve number
where P = 0.9 inches
CN = 1000/(10 +(5*P)+(10*Qa) - (10*(Qa^2 + (1.25*Qa*P))^0.5))
CN = 92.7
Above, you should have calculated the WQv in watershed inches draining to the facility/practice for which you need to calculate the WQ-
peak discharge. As provided in the guidance listed on the grass channel worksheet, please remember that the WQv calculation should include
runoff from on-site as well as off-site area draining to the grass channel since this will have an impact on the channel hydraulics and thus the
velocity and residence time.
1: Sites with low impervious cover ( ~19%) but that do not employ a significant use of the stormwater design credits in Section 3 of the VSWMM are
required to treat the minimum water quality volume of 0.2 watershed inches. Sites that have a significant portion of their impervious cover addressed via
the stormwater credits (section 3 of the VSWMM) will be able to reduce this WQv and will only be required to treat the volume calculated on the "WQ
Volume (with credit reduction)" worksheet which will be less than the 0.2 watershed inches.
Subarea 4A
Calculating Peak WQ Peak Discharge Rate (0.9" storm) using the Modified Curve Number
Because NRCS methods underestimate the peak discharge for rainfall events of less than 2", simply plugging in 0.9" of rainfall into your
hydrologic model with the standard curve numbers will not produce the correct peak discharge during the WQv storm, nor will it produce a
volume of runoff equivalent to that which you have calculated using the WQv formula (WQv = P*Rv*A/12). In order to calculate the peak
discharge for the 0.9" storm, a modified curve number must be calculated. This modified curve number is based on the runoff (in inches)
calculated using the short cut method formula (WQv = P*Rv) that is also the basis of the familiar WQv calculations provided in the 2002
VSWMM (and on the WQv calculation worksheets). Essentially, the curve number that is calculated using the methods below is the curve
number that will generate the volume of runoff calculated using the WQv formula.
WQv Subarea 4A Page 20 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Recharge March 6, 2015
Revised: April 22, 2016
Version: 2/12 For the area draining to*:
Located in drainage area for S/N: 001
Site Information value/calculation units
Site Area (impervious + disturbed pervious) A= 2.14 acres
Impervious area 0.84 acres
Percent Impervious Area = [(line 2/line 1)] = I = 0.39 % (decimal percent)
Composite Recharge Factor Calculation
Enter site acreage of each HSG draining to POI or S/N value/calculation
HSG A acres
HSG B 0.26 acres
HSG C 1.87 acres
HSG D acres
Total Site Area 2.137
Composite Recharge Factor 0.119
0.008 acre feet
360 cubic feet
0.099 acres
4326 square feet
Subarea 4A
Groundwater Recharge Treatment Standard - Calculation & Waiver Worksheet
The average annual groundwater recharge rate for the prevailing hydrologic soil group(s) (HSG) must be maintained in order to preserve existing water table elevations.
Recharge is determined as a function of annual predevelopment recharge for a given HSG, the average annual rainfall and the amount of impervious surface at the site. The
Groundwater Recharge Treatment Standard can be met by using one or both of the following methods: volume method and/or percent area method. See Table 2.2 in the
VSMM - Volume I for a list of acceptable STPs or credits that satisfy this requirement. Use NRCS's Web Soil Survey to obtain specific soil data at your site, available at:
http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm
ReV (Percent Volume Method)
The percent volume method is commonly used to meet recharge. Designers must demonstrate that a proposed STP
allows at least the Rev to enter the ground. The Rev is contained within the WQv. So, if a practice is infiltrating the
entire WQv, then Rev is automatically met. Please use the applicable STP worksheets to verify the Groundwater
Recharge Treatment Standard has been met. Note that not all STPs can be used to meet this standard.
ReA (Percent Area Method)
The percent area method is used when meeting recharge via nonstructural design credits(disconnection of
rooftop/non-rooftop surfaces, stream buffer, grass channel credit, or ESRD). In this case, the designer must
demonstrate that stormwater runoff from a portion of the new impervious area, equivalent to the area calculated
under the percent area method, drains into a nonstructural design credit practice.
Additional notes:
*Recharge is one of the unified sizing criteria that can be achieved site wide, rather than at each point of interest (POI) or discharge point (S/N), assuming the receiving water
is the same for each discharge point.
Re Subarea 4A Page 21 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Water Quality Volume March 6, 2015
Revised: April 22, 2016
Version: 9/06 (calcs embedded) For the area draining to*:
Located in drainage area for S/N: 1
WQ Volume calculation (with credit reduction) for Volume Based Practice
Line Base values value/calculation units
1 Site Area (impervious + disturbed pervious) 1.18 acres note 1
2 Impervious area 0.15 acres
3 Precipitation P = 0.9 inches
Impervious Area Reductions
Rooftop disconnection
Completed credit sheet yes / no
4 Enter roof-top area disconnected 0.11 acres
Non-rooftop disconnection
Completed credit sheet yes/no
5 Enter non-rooftop area disconnected 0.04 acres
6 Total impervious area disconnected (line 4 + line 5) 0.15 acres
7 New impervious area total (line 2 - line 6) 0.00 acres
8 Percent Impervious = [(line 7 line 1) * 100] I = 0.00 %
Subarea 4B
Use this worksheet to calculate the water quality volume draining to your volume based (i.e. not a grass channel) STP if you are not using any of the site
design credits in section 3 of the 2002 VSWMM. Do not use this worksheet to calculate your WQv if you need to determine the Peak Q for the WQ storm
(i.e. designing a grass channel, flow-splitter or other flow based practice). See the worksheet "Water Quality Volume and Modified Curve Number Calculation
(with credit reduction) for Water Quality Treatment in Flow-Based Practice."
WQv Subarea 4B Page 22 of 48
Site Area Reductions
Stream Buffer Credit
Completed credit sheet yes / no
9 Enter area draining to a stream buffer acres note 2
Grass Channel Credit
Completed credit sheet yes / no
10 Enter site area draining to grass channels acres
Natural Area Conservation Credit
Completed credit sheet yes / no
11 Natural Area to be conserved (in the drainage to this S/N) acres
12 Total Site Area Reductions (line 9 + line 10 + line 11) 0.0 acres
13 New site area total ( line 1 - line 12) A = 1.2 acres
Runoff coefficient calculation = (0.05 + (0.009*I)) Rv = 0.050
14 Water Quality Volume Calculation = (P*Rv) WQv = 0.045 Qa (watershed inches or inches of runoff)
15 Water Quality Volume Calculation [(line 14* line 13)/12] WQv = 0.0000 ac. ft SEE BOLD NOTE BELOW
16 Water Quality Volume Calculation = line 15 *43560 WQv = 0 cu. ft.
Note 1: In most situations, site area = disturbed area (i.e. impervious + disturbed pervious for the project). If using the Natural Area Conservation Credit, the Site Area =
(disturbed area + area to be conserved).
Note 2: If using rooftop/ non-rooftop disconnection, credit can only be taken for the pervious area draining to the stream buffer
Addt'l notes: If all impervious has been disconnected and the percent impervious is thus zero (0 %) then WQv and Recharge are assumed to have been met and WQv = 0.
If significant use of site design credits has been employed, the designer may treat the reduced WQv and is not required to treat the minimum water quality volume of 0.2
watershed inches.
WQv Subarea 4B Page 23 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Recharge March 6, 2015
Revised: April 22, 2016
Version: 2/12 For the area draining to*:
Located in drainage area for S/N: 001
Site Information value/calculation units
Site Area (impervious + disturbed pervious) A= 1.18 acres
Impervious area 0.15 acres
Percent Impervious Area = [(line 2/line 1)] = I = 0.13 % (decimal percent)
Composite Recharge Factor Calculation
Enter site acreage of each HSG draining to POI or S/N value/calculation
HSG A acres
HSG B 0.77 acres
HSG C 0.40 acres
HSG D acres
Total Site Area 1.177
Composite Recharge Factor 0.199
0.002 acre feet
108 cubic feet
0.030 acres
1291 square feet
Subarea 4B
Groundwater Recharge Treatment Standard - Calculation & Waiver Worksheet
The average annual groundwater recharge rate for the prevailing hydrologic soil group(s) (HSG) must be maintained in order to preserve existing water table elevations.
Recharge is determined as a function of annual predevelopment recharge for a given HSG, the average annual rainfall and the amount of impervious surface at the site. The
Groundwater Recharge Treatment Standard can be met by using one or both of the following methods: volume method and/or percent area method. See Table 2.2 in the
VSMM - Volume I for a list of acceptable STPs or credits that satisfy this requirement. Use NRCS's Web Soil Survey to obtain specific soil data at your site, available at:
http://websoilsurvey.nrcs.usda.gov/app/HomePage.htm
ReV (Percent Volume Method)
The percent volume method is commonly used to meet recharge. Designers must demonstrate that a proposed STP
allows at least the Rev to enter the ground. The Rev is contained within the WQv. So, if a practice is infiltrating the
entire WQv, then Rev is automatically met. Please use the applicable STP worksheets to verify the Groundwater
Recharge Treatment Standard has been met. Note that not all STPs can be used to meet this standard.
ReA (Percent Area Method)
The percent area method is used when meeting recharge via nonstructural design credits(disconnection of
rooftop/non-rooftop surfaces, stream buffer, grass channel credit, or ESRD). In this case, the designer must
demonstrate that stormwater runoff from a portion of the new impervious area, equivalent to the area calculated
under the percent area method, drains into a nonstructural design credit practice.
Additional notes:
*Recharge is one of the unified sizing criteria that can be achieved site wide, rather than at each point of interest (POI) or discharge point (S/N), assuming the receiving water
is the same for each discharge point.
Re Subarea 4B Page 24 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 1 March 6, 2015
Revised: April 22, 2016
Five Sizing Criteria
Water Quality, WQ(v) See Below & WQv Worksheet
Recharge Volume, Re(v) See Below & Re Worksheet
Channel Protection, Cp(v) See Below
Overbank Flood, Qp(10) See Below
Extreme Flood, Qp(100) Waived Less than 10 acres of impervious surface
Water Quality Treatment
Subarea 1
WQ(v) treatment provided by Dry Swale 1
Wq(v) 3,595 cf
Compute minimum surface area of swale
A(f), surface area required = WQv*d(f)/[k*(h(f) +d(f))*t(f)]
d(f), filter bed depth 1 ft
k (permeability coefficient 3.5 (sand)
h(f), average height above filter bed 0.19 ft (from HydroCAD)
t(f), design drain time 1.67 days (40 hours)
WQ(v) 3,595 cf
A(f) 517 sf
Dry Swale width 4 ft
Minimum Dry Swale length 129
Swale Length provided 130
Dry Swale provides sufficient surface area.
Cp(v)
Calculated maximum velocity 3.3 fps
Maximum non-erosive velocity 5.0 fps (per Table D-5, VSMM)
Note: channel will be lined with tall fescue or Kentucky bluegrass
Qp(10)
Calculated flow depth 0.4 ft
Required freeboard 0.5 ft
Total depth required 0.9 ft
Channel depth provided 2.0 ft
Area 1 Five Treatment Criteria Page 25 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 1 March 6, 2015
Revised: April 22, 2016
Recharge Treatment
Subarea 1
Re(v) treatment provided by Dry Swale 1
Cp(v), Qp10 Treatment
Cp(v), Qp(10) treatment provided by Dry Pond 1
Basin Bottom Elevation 1683.5 ft
Cp(v) Elevation 1685.3 ft
Qp(10) Elevation 1685.8 ft
Qp(100) Elevation 1686.0 ft
Top of Embankment 1686.0 ft
Cp(v) Controlled Release
From HydroCAD Modeling
Cp(v) Provided 5,379 cf
Cp(v) Elevation 1685.3 ft
Cp(v), Predevelopment 2.9 cfs
Cp(v), Postdevelopment 4.5 cfs
Qp(v), Post Attenuation 0.09 cfs
0
500
1,000
1,500
2,000
2,500
3,000
3,500
4,000
4,500
5,000
1683.0 1684.0 1685.0 1686.0
Po
nd
Sto
rag
e (
cf)
Elevation (ft)
Dry Pond 1 Storage - Stage Curve
Area 1 Five Treatment Criteria Page 26 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 1 March 6, 2015
Revised: April 22, 2016
Qp(10) Controlled Release
From HydroCAD Modeling
Qp(10) Provided 7,375 cf
Qp(10) Elevation 1685.8 ft
Qp(10), Predevelopment 7.7 cfs
Qp(10), Postdevelopment 9.8 cfs
Qp(10), Post Attenuation 4.3 cfs
Area 1 Five Treatment Criteria Page 27 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 2 March 6, 2015
Revised: April 22, 2016
Five Sizing Criteria
Water Quality, WQ(v) See Below & WQv Worksheet
Recharge Volume, Re(v) See Below & Re Worksheet
Channel Protection, Cp(v) See Below
Overbank Flood, Qp(10) See Below
Extreme Flood, Qp(100) Waived Less than 10 acres of impervious surface
Water Quality Treatment
Subarea 2
WQ(v) treatment provided by Dry Swale 2
Wq(v) 1,318 cf
Compute minimum surface area of swale
A(f), surface area required = WQv*d(f)/[k*(h(f) +d(f))*t(f)
d(f), filter bed depth 1 ft
k (permeability coefficient 3.5 (sand)
h(f), average height above filter bed 0.07 ft (from HydroCAD)
t(f), design drain time 1.67 days (40 hours)
WQ(v) 1,318 cf
A(f) 211 sf
Dry Swale width 4 ft
Minimum Dry Swale length 53
Swale Length provided 210
Dry Swale provides sufficient surface area.
Cp(v)
Calculated maximum velocity 0.9 fps
Maximum non-erosive velocity 5.0 fps (per Table D-5, VSMM)
Note: channel will be lined with tall fescue or Kentucky bluegrass
Qp(10)
Calculated flow depth 0.16 ft
Required freeboard 0.5 ft
Total depth required 0.66 ft
Channel depth provided 2.0 ft
Area 2 Five Treatment Criteria Page 28 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 2 March 6, 2015
Revised: April 22, 2016
Recharge Treatment
Subarea 1
Re(v) treatment provided by Dry Swale 2
Cp(v), Qp10 Treatment
Cp(v), Qp(10) treatment provided by Dry Pond 1
Basin Bottom Elevation 1596.0 ft
Cp(v) Elevation 1596.2 ft
Qp(10) Elevation 1596.3 ft
Qp(100) Elevation 1596.7 ft
Top of Embankment 1598.0 ft
Cp(v) Controlled Release
From HydroCAD Modeling
Cp(v) Provided 774 cf
Cp(v) Elevation 1596.2 ft
Cp(v), Predevelopment 0.1 cfs
Cp(v), Postdevelopment 0.2 cfs
Qp(v), Post Attenuation 0.01 cfs
0
2,000
4,000
6,000
8,000
10,000
12,000
1596.0 1597.0 1598.0
Po
nd
Sto
rag
e (
cf)
Elevation (ft)
Dry Pond 2 Storage - Stage Curve
Area 2 Five Treatment Criteria Page 29 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 2 March 6, 2015
Revised: April 22, 2016
Qp(10) Controlled Release
From HydroCAD Modeling
Qp(10) Provided 1,397 cf
Qp(10) Elevation 1596.3 ft
Qp(10), Predevelopment 1.3 cfs
Qp(10), Postdevelopment 1.4 cfs
Qp(10), Post Attenuation 0.6 cfs
Area 2 Five Treatment Criteria Page 30 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 3 March 6, 2015
Revised: April 22, 2016
Five Sizing Criteria
Water Quality, WQ(v) See Below & WQv Worksheet
Recharge Volume, Re(v) See Below & Re Worksheet
Channel Protection, Cp(v) See Below
Overbank Flood, Qp(10) See Below
Extreme Flood, Qp(100) Waived Less than 10 acres of impervious surface
Water Quality Treatment
Subarea 3
WQ(v) treatment provided by Dry Swale 3
Wq(v) 734 cf
Compute minimum surface area of swale
A(f), surface area required = WQv*d(f)/[k*(h(f) +d(f))*t(f)
d(f), filter bed depth 1 ft
k (permeability coefficient 3.5 (sand)
h(f), average height above filter bed 0.1 ft (from HydroCAD)
t(f), design drain time 1.67 days (40 hours)
WQ(v) 734 cf
A(f) 114 sf
Dry Swale width 2 ft
Minimum Dry Swale length 57
Swale Length provided 200
Dry Swale provides sufficient surface area.
Cp(v)
Calculated maximum velocity 2.1 fps
Maximum non-erosive velocity 5.0 fps (per Table D-5, VSMM)
Note: channel will be lined with tall fescue or Kentucky bluegrass
Qp(10)
Calculated flow depth 0.31 ft
Required freeboard 0.5 ft
Total depth required 0.81 ft
Channel depth provided 2.0 ft
Area 3 Five Treatment Criteria Page 31 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 3 March 6, 2015
Revised: April 22, 2016
Recharge Treatment
Subareas 3
Re(v) treatment provided by Dry Swale 3
Cp(v), Qp10 Treatment
Cp(v), Qp(10) treatment provided by ponding in lower portion of Dry Swale 3
Basin Bottom Elevation 1580.0 ft
Cp(v) Elevation 1581.0 ft
Qp(10) Elevation 1581.6 ft
Qp(100) Elevation 1581.9 ft
Top of Embankment 1582.0 ft
Note: Refer to HydroCad modeling. Infiltration pond has no outfall for Cp(v), Qp(10) & Qp(100) rainfall events
Cp(v) Controlled Release
From HydroCAD Modeling
Cp(v) Provided 952 cf
Cp(v) Elevation 1581.0 ft
Cp(v), Predevelopment 0.04 cfs
Cp(v), Postdevelopment 1.1 cfs
Qp(v), Post Attenuation 0.05 cfs (Note: the minimum orifice size of 1" is used; can not reduce
orifice size to reduce flows any further)
0
500
1,000
1,500
2,000
2,500
3,000
3,500
1578.0 1579.0 1580.0 1581.0 1582.0
Po
nd
Sto
rag
e (
cf)
Elevation (ft)
Infiltration Pond Storage - Stage Curve
Area 3 Five Treatment Criteria Page 32 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 3 March 6, 2015
Revised: April 22, 2016
Qp(10) Controlled Release
From HydroCAD Modeling
Qp(10) Provided 1,757 cf
Qp(10) Elevation 1581.6 ft
Qp(10), Predevelopment 0.6 cfs
Qp(10), Postdevelopment 2.4 cfs
Qp(10), Post Attenuation 0.46 cfs (100% infiltration)
Area 3 Five Treatment Criteria Page 33 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 4 March 6, 2015
Revised: April 22, 2016
Five Sizing Criteria
Water Quality, WQ(v) See Below & WQv Worksheet
Recharge Volume, Re(v) See Below & Re Worksheet
Channel Protection, Cp(v) See Below
Overbank Flood, Qp(10) See Below
Extreme Flood, Qp(100) Waived Less than 10 acres of impervious surface
Water Quality Treatment
Subarea 4A
WQ(v) treatment provided by Dry Swale 4
Wq(v) 2,811 cf
Compute minimum surface area of swale
A(f), surface area required = WQv*d(f)/[k*(h(f) +d(f))*t(f)
d(f), filter bed depth 1 ft
k (permeability coefficient 3.5 (sand)
h(f), average height above filter bed 0.26 ft (from HydroCAD)
t(f), design drain time 1.67 days (40 hours)
WQ(v) 2,811 cf
A(f) 382 sf
Dry Swale width 2 ft
Minimum Dry Swale length 191
Swale Length provided 225
Dry Swale provides sufficient surface area.
Cp(v)
Calculated maximum velocity 4.9 fps (Upper Dry Swale)
Maximum non-erosive velocity 5.0 fps (per Table D-5, VSMM)
Note: channel will be lined with tall fescue or Kentucky bluegrass
Qp(10)
Calculated flow depth 0.94 ft (Upper Dry Swale)
Required freeboard 0.5 ft
Total depth required 1.44 ft
Channel depth provided 2.0 ft
Subarea 4B
WQ(v) treatment provided by Rooftop & Non-Rooftop Disconnections
Area 4 Five Treatment Criteria) Page 34 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 4 March 6, 2015
Revised: April 22, 2016
Recharge Treatment
Subarea 4A
Re(v) treatment provided by Dry Swale 4
Subarea 4A
Re(v) treatment provided by Rooftop & Non-Rooftop Disconnection
Cp(v), Qp10 Treatment
Cp(v), Qp(10) treatment provided by Dry Pond
Basin Bottom Elevation 1578.0 ft
Cp(v) Elevation 1579.1 ft
Qp(10) Elevation 1579.5 ft
Qp(100) Elevation 1580.0 ft
Top of Embankment 1580.0 ft
Note: Refer to HydroCad modeling. Infiltration pond has no outfall for Cp(v), Qp(10) & Qp(100) rainfall events
Cp(v) Controlled Release
From HydroCAD Modeling
Cp(v) Provided 9,668 cf
Cp(v) Elevation 1579.1 ft
Cp(v), Predevelopment 1.5 cfs
Cp(v), Postdevelopment 7.9 cfs
Qp(v), Post Attenuation 0.16 cfs
0
5,000
10,000
15,000
20,000
25,000
1578.0 1579.0 1580.0
Po
nd
Sto
rag
e (
cf)
Elevation (ft)
Dry Pond 4 Storage - Stage Curve
Area 4 Five Treatment Criteria) Page 35 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
5 Treatment Criteria Design - Subarea 4 March 6, 2015
Revised: April 22, 2016
Qp(10) Controlled Release
From HydroCAD Modeling
Qp(10) Provided 14,792 cf
Qp(10) Elevation 1579.5 ft
Qp(10), Predevelopment 6.0 cfs
Qp(10), Postdevelopment 16.9 cfs
Qp(10), Post Attenuation 4.1 cfs
Area 4 Five Treatment Criteria) Page 36 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Swale 1 March 6, 2015
Revised: April 22, 2016
Project Name:
Discharge Point:
Line
Indicate the treatment standards met for the site area draining to this practice:
1 WQv x
2 Rev x
3 Cpv
4 Qp10 Dry swales are not typically appropriate to provide Cpv, Qp10 or Qp100 except under ideal conditions.
5 Qp100
6
Response Attachment location
7 yes
Response Attachment location
8 yes See Basis of Design
9 yes See Basis of Design
10 yes See Basis of Design
11 yes See Basis of Design
Response Attachment location
12 yes
Channel Width (Feet)
13 4
Response Attachment location
14 yes See Basis of Design
15 yes See Basis of Design
16 yes See Basis of Design
17 yes See Basis of Design
18 yes See Basis of Design
19
Response Attachment location
20 yes Underdrain increased to 6" diam.
Page 2
2112 hours for cold water
24 hours for warm water
Response Attachment location
22 yes / no
Version: 4/10 The Annex at Mountain Top Inn
S/N 001
Dry Swale (O-1)
Dry Swale #1
Treatment Standards
This practice automatically meets Rev if you have met the WQv treatment standards
{
Water Quality Volume (WQv) WQv (Cubic Feet)
Provide the WQv for the site area draining to this swale (from WQv worksheets) 3595
Feasibility (2.7.5.A)
Is the maximum longitudinal slope of the swale 4% or less?
Conveyance (2.7.5.B)
Is the peak velocity for the 1-year storm non-erosive?
Are the design side slopes less than or equal to the 2:1 maximum?
Does the practice safely convey the 10-year storm with a minimum of 6 inches of freeboard?
Has the swale been designed with an underdrain system?
Pretreatment (2.7.5.C)
Has pre-treatment been provided for non-rooftop runoff?
Treatment (2.7.5.D)
What is the bottom width of the channel? (no greater than 8 feet, but no less than 2 feet)
Is the swale designed to accommodate a portion of the WQv through surface ponding?
Is the swale bottom designed to drain the WQv in less than 40 hours?
Does the swale design release the WQv over a minimum of 30 minutes?
Is the average head (height of water above the bottom of the swale) below 12 inches?
Does the soil media meet the open vegetated swale specifications?
What infiltration rate (if any) is used for exfiltration (in/hour)?
Cold Climate Design Considerations (2.7.5.G)
Have the potential impacts of Vermont's severe winter climate been addressed in your design?
Dry Swale: Cpv, Qp10 and Qp100 NOT APPLICABLE
Channel Protection Treatment Standard (Cpv) Response
Check which detention time standard must be used, based on the fisheries designation of the
receiving water:
Did you use the Storage Volume Estimation Method? If yes, skip to Line 26.*
Dry Swale 1 Page 37 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Swale 1 March 6, 2015
Revised: April 22, 2016
23
24
25
Response Attachment location
26 yes / no
Response Attachment location
27 yes / no
*Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not
appropriate if more than a one subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model
that accounts for pond routing is the preferred method.
What storage volume (cubic feet) necessary to meet the Channel Protection Standard?
What is the calculated average release rate (cfs)?
What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model?
Overbank Flood Protection Treatment Standard (Qp10)
Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?*
*Please include runoff and routing calculations of the 10-year storm event.
Extreme Flood Protection Treatment Standard (Qp100)
Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?*
*Please include runoff and routing calculations of the 100-year storm event.
A dry swale is a volume-based treatment channel. Check dams, weirs or coir logs are encouraged to promote ponding. Convey larger storms through
overflow weirs or outlet control structures. See VSMM-Vol. II, Appendix D7 for guidance about maintaining non-erosive conditions.
Attachment location: Please indicate the specific location (i.e. appendix, page, plan sheet) where the requisite support documentation has been provided within the application.
Dry Swale 1 Page 38 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Swale 2 March 6, 2015
Revised: April 22, 2016
Project Name:
Discharge Point:
Line
Indicate the treatment standards met for the site area draining to this practice:
1 WQv x
2 Rev x
3 Cpv
4 Qp10 Dry swales are not typically appropriate to provide Cpv, Qp10 or Qp100 except under ideal conditions.
5 Qp100
6
Response Attachment location
7 yes
Response Attachment location
8 yes See Basis of Design
9 yes See Basis of Design
10 yes See Basis of Design
11 yes See Basis of Design
Response Attachment location
12 yes
Channel Width (Feet)
13 4
Response Attachment location
14 yes See Basis of Design
15 yes See Basis of Design
16 yes See Basis of Design
17 yes See Basis of Design
18 yes See Basis of Design
19
Response Attachment location
20 yes Underdrain increased to 6" diam.
Page 2
2112 hours for cold water
24 hours for warm water
Response Attachment location
22 yes / noDid you use the Storage Volume Estimation Method? If yes, skip to Line 26.*
Channel Protection Treatment Standard (Cpv) Response
Check which detention time standard must be used, based on the fisheries designation of the
receiving water:
What infiltration rate (if any) is used for exfiltration (in/hour)?
Cold Climate Design Considerations (2.7.5.G)
Have the potential impacts of Vermont's severe winter climate been addressed in your design?
Dry Swale: Cpv, Qp10 and Qp100 NOT APPLICABLE
Is the swale designed to accommodate a portion of the WQv through surface ponding?
Is the swale bottom designed to drain the WQv in less than 40 hours?
Does the swale design release the WQv over a minimum of 30 minutes?
Is the average head (height of water above the bottom of the swale) below 12 inches?
Does the soil media meet the open vegetated swale specifications?
Pretreatment (2.7.5.C)
Has pre-treatment been provided for non-rooftop runoff?
Treatment (2.7.5.D)
What is the bottom width of the channel? (no greater than 8 feet, but no less than 2 feet)
Conveyance (2.7.5.B)
Is the peak velocity for the 1-year storm non-erosive?
Are the design side slopes less than or equal to the 2:1 maximum?
Does the practice safely convey the 10-year storm with a minimum of 6 inches of freeboard?
Has the swale been designed with an underdrain system?
Provide the WQv for the site area draining to this swale (from WQv worksheets) 1318
Feasibility (2.7.5.A)
Is the maximum longitudinal slope of the swale 4% or less?
Treatment Standards
This practice automatically meets Rev if you have met the WQv treatment standards
{
Water Quality Volume (WQv) WQv (Cubic Feet)
Version: 4/10 The Annex at Mountain Top Inn
S/N 001
Dry Swale (O-1)
Dry Swale #2
Dry Swale 2 Page 39 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Swale 2 March 6, 2015
Revised: April 22, 2016
23
24
25
Response Attachment location
26 yes / no
Response Attachment location
27 yes / no
Extreme Flood Protection Treatment Standard (Qp100)
Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?*
*Please include runoff and routing calculations of the 100-year storm event.
A dry swale is a volume-based treatment channel. Check dams, weirs or coir logs are encouraged to promote ponding. Convey larger storms through
overflow weirs or outlet control structures. See VSMM-Vol. II, Appendix D7 for guidance about maintaining non-erosive conditions.
Attachment location: Please indicate the specific location (i.e. appendix, page, plan sheet) where the requisite support documentation has been provided within the application.
What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model?
Overbank Flood Protection Treatment Standard (Qp10)
Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?*
*Please include runoff and routing calculations of the 10-year storm event.
*Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not
appropriate if more than a one subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model
that accounts for pond routing is the preferred method.
What storage volume (cubic feet) necessary to meet the Channel Protection Standard?
What is the calculated average release rate (cfs)?
Dry Swale 2 Page 40 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Swale 3 March 6, 2015
Revised: April 22, 2016
Project Name:
Discharge Point:
Line
Indicate the treatment standards met for the site area draining to this practice:
1 WQv x
2 Rev x
3 Cpv
4 Qp10 Dry swales are not typically appropriate to provide Cpv, Qp10 or Qp100 except under ideal conditions.
5 Qp100
6
Response Attachment location
7 yes
Response Attachment location
8 yes See Basis of Design
9 yes See Basis of Design
10 yes See Basis of Design
11 yes See Basis of Design
Response Attachment location
12 yes
Channel Width (Feet)
13 4
Response Attachment location
14 yes See Basis of Design
15 yes See Basis of Design
16 yes See Basis of Design
17 yes See Basis of Design
18 yes See Basis of Design
19
Response Attachment location
20 yes Underdrain increased to 6" diam.
Page 2
2112 hours for cold water
24 hours for warm water
Response Attachment location
22 yes / noDid you use the Storage Volume Estimation Method? If yes, skip to Line 26.*
Channel Protection Treatment Standard (Cpv) Response
Check which detention time standard must be used, based on the fisheries designation of the
receiving water:
What infiltration rate (if any) is used for exfiltration (in/hour)?
Cold Climate Design Considerations (2.7.5.G)
Have the potential impacts of Vermont's severe winter climate been addressed in your design?
Dry Swale: Cpv, Qp10 and Qp100 NOT APPLICABLE
Is the swale designed to accommodate a portion of the WQv through surface ponding?
Is the swale bottom designed to drain the WQv in less than 40 hours?
Does the swale design release the WQv over a minimum of 30 minutes?
Is the average head (height of water above the bottom of the swale) below 12 inches?
Does the soil media meet the open vegetated swale specifications?
Pretreatment (2.7.5.C)
Has pre-treatment been provided for non-rooftop runoff?
Treatment (2.7.5.D)
What is the bottom width of the channel? (no greater than 8 feet, but no less than 2 feet)
Conveyance (2.7.5.B)
Is the peak velocity for the 1-year storm non-erosive?
Are the design side slopes less than or equal to the 2:1 maximum?
Does the practice safely convey the 10-year storm with a minimum of 6 inches of freeboard?
Has the swale been designed with an underdrain system?
Provide the WQv for the site area draining to this swale (from WQv worksheets) 734
Feasibility (2.7.5.A)
Is the maximum longitudinal slope of the swale 4% or less?
Treatment Standards
This practice automatically meets Rev if you have met the WQv treatment standards
{
Water Quality Volume (WQv) WQv (Cubic Feet)
Version: 4/10 The Annex at Mountain Top Inn
S/N 001
Dry Swale (O-1)
Dry Swale #3
Dry Swale 3 Page 41 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Swale 3 March 6, 2015
Revised: April 22, 2016
23
24
25
Response Attachment location
26 yes / no
Response Attachment location
27 yes / no
Extreme Flood Protection Treatment Standard (Qp100)
Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?*
*Please include runoff and routing calculations of the 100-year storm event.
A dry swale is a volume-based treatment channel. Check dams, weirs or coir logs are encouraged to promote ponding. Convey larger storms through
overflow weirs or outlet control structures. See VSMM-Vol. II, Appendix D7 for guidance about maintaining non-erosive conditions.
Attachment location: Please indicate the specific location (i.e. appendix, page, plan sheet) where the requisite support documentation has been provided within the application.
What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model?
Overbank Flood Protection Treatment Standard (Qp10)
Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?*
*Please include runoff and routing calculations of the 10-year storm event.
*Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not
appropriate if more than a one subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model
that accounts for pond routing is the preferred method.
What storage volume (cubic feet) necessary to meet the Channel Protection Standard?
What is the calculated average release rate (cfs)?
Dry Swale 3 Page 42 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Swale 4 March 6, 2015
Revised: April 22, 2016
Project Name:
Discharge Point:
Line
Indicate the treatment standards met for the site area draining to this practice:
1 WQv x
2 Rev x
3 Cpv
4 Qp10 Dry swales are not typically appropriate to provide Cpv, Qp10 or Qp100 except under ideal conditions.
5 Qp100
6
Response Attachment location
7 yes
Response Attachment location
8 yes See Basis of Design
9 yes See Basis of Design
10 yes See Basis of Design
11 yes See Basis of Design
Response Attachment location
12 yes
Channel Width (Feet)
13 4
Response Attachment location
14 yes See Basis of Design
15 yes See Basis of Design
16 yes See Basis of Design
17 yes See Basis of Design
18 yes See Basis of Design
19
Response Attachment location
20 yes Underdrain increased to 6" diam.
Page 2
2112 hours for cold water
24 hours for warm water
Response Attachment location
22 yes / noDid you use the Storage Volume Estimation Method? If yes, skip to Line 26.*
Channel Protection Treatment Standard (Cpv) Response
Check which detention time standard must be used, based on the fisheries designation of the
receiving water:
What infiltration rate (if any) is used for exfiltration (in/hour)?
Cold Climate Design Considerations (2.7.5.G)
Have the potential impacts of Vermont's severe winter climate been addressed in your design?
Dry Swale: Cpv, Qp10 and Qp100 NOT APPLICABLE
Is the swale designed to accommodate a portion of the WQv through surface ponding?
Is the swale bottom designed to drain the WQv in less than 40 hours?
Does the swale design release the WQv over a minimum of 30 minutes?
Is the average head (height of water above the bottom of the swale) below 12 inches?
Does the soil media meet the open vegetated swale specifications?
Pretreatment (2.7.5.C)
Has pre-treatment been provided for non-rooftop runoff?
Treatment (2.7.5.D)
What is the bottom width of the channel? (no greater than 8 feet, but no less than 2 feet)
Conveyance (2.7.5.B)
Is the peak velocity for the 1-year storm non-erosive?
Are the design side slopes less than or equal to the 2:1 maximum?
Does the practice safely convey the 10-year storm with a minimum of 6 inches of freeboard?
Has the swale been designed with an underdrain system?
Provide the WQv for the site area draining to this swale (from WQv worksheets) 2811
Feasibility (2.7.5.A)
Is the maximum longitudinal slope of the swale 4% or less?
Treatment Standards
This practice automatically meets Rev if you have met the WQv treatment standards
{
Water Quality Volume (WQv) WQv (Cubic Feet)
Version: 4/10 The Annex at Mountain Top Inn
S/N 001
Dry Swale (O-1)
Dry Swale #4
Dry Swale 4 Page 43 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Swale 4 March 6, 2015
Revised: April 22, 2016
23
24
25
Response Attachment location
26 yes / no
Response Attachment location
27 yes / no
Extreme Flood Protection Treatment Standard (Qp100)
Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?*
*Please include runoff and routing calculations of the 100-year storm event.
A dry swale is a volume-based treatment channel. Check dams, weirs or coir logs are encouraged to promote ponding. Convey larger storms through
overflow weirs or outlet control structures. See VSMM-Vol. II, Appendix D7 for guidance about maintaining non-erosive conditions.
Attachment location: Please indicate the specific location (i.e. appendix, page, plan sheet) where the requisite support documentation has been provided within the application.
What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model?
Overbank Flood Protection Treatment Standard (Qp10)
Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?*
*Please include runoff and routing calculations of the 10-year storm event.
*Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not
appropriate if more than a one subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model
that accounts for pond routing is the preferred method.
What storage volume (cubic feet) necessary to meet the Channel Protection Standard?
What is the calculated average release rate (cfs)?
Dry Swale 4 Page 44 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Pond 1 March 6, 2015
Revised: April 22, 2016
Project Name:
Discharge Point:
Line
1 Cpv x
2 Qp10 x
3 Qp100 Not Applicable - Qp100 Waived
Response
4 Yes
5 Yes
6 Yes
8 Yes
9 Yes
10 Yes
11 Yes
12 Yes
13
Response
14 no
15
16
17
18
Response
19 Yes
Response
Yes
Version: 4/10 The Annex at Mountain Top Inn
S/N 001
Dry Detention Pond (LA-1)
Dry Detention Pond #1
Indicate the treatment standards met for the site area draining to this practice:
Attachment location
Have you performed a site evaluation to establish the Hazard Classification of the pond? n/a - site visit
Have you determined depth to bedrock and soil properties using geotechnical investigations? n/a - site visit
Have the outfalls been designed/protected to avoid erosive velocities? See Plans
Is the principal spillway accessible from land and equipped with a removable trash rack? See Plans
Have all low flow orifices been designed or sized to ensure no clogging occurs? See Plans
Have the potential impacts of frozen culverts and deicers on vegetation been addressed in the design? See Plans
Does the application include oultet elevation and size information for the basin?. See Plans
Has the peak storage volume and elevation information for the 1, 10 and 100-year storms been included? See Plans
Channel Protection Treatment Standard (Cpv) Response
Check which detention time must be used, based on the fisheries designation of the receiving water: x12 hours for cold water
24 hours for warm water
Attachment location
Did you use the Storage Volume Estimation Method? If yes, skip to Line 19.*
*Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not appropriate if more than a one
subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model that accounts for pond routing is the preferred method.
What storage volume (cubic feet) necessary to meet the Channel Protection Standard? 5,379
What orifice size (inches) is necessary to meet the required detention time? 1.60
What is the calculated average release rate (cfs)? (Divide the Vs by detention time) 0.09
What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model? 0.09
Overbank Flood Protection Treatment Standard (Qp10) Attachment location
Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?* See Peak Flow Summary
*Please include runoff and routing calculations of the 100-year storm event.
Please see VSMM-Vol. II, Appendix D7 for guidance about maintaining non-erosive conditions. Ensure that appropriate overflow outlets are designed to safely release all off-site water
that may also be entering the pond. Visit VSMM-Vol.II, Appendix B for dam safety design specifications.
Attachment location: Indicate the specific location (i.e. appendices, pages, plan sheets) where the requisite support documentation has been provided within the application.
*Please include runoff and routing calculations of the 10-year storm event.
Extreme Flood Protection Treatment Standard (Qp100) Attachment location
Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?* See Peak Flow Summary
Dry Pond 1 Page 45 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Pond 2 March 6, 2015
Revised: April 22, 2016
Project Name:
Discharge Point:
Line
1 Cpv x
2 Qp10 x
3 Qp100 Not Applicable - Qp100 Waived
Response
4 Yes
5 Yes
6 Yes
8 Yes
9 Yes
10 Yes
11 Yes
12 Yes
13
Response
14 no
15
16
17
18
Response
19 Yes
Response
Yes*Please include runoff and routing calculations of the 100-year storm event.
Please see VSMM-Vol. II, Appendix D7 for guidance about maintaining non-erosive conditions. Ensure that appropriate overflow outlets are designed to safely release all off-site water
that may also be entering the pond. Visit VSMM-Vol.II, Appendix B for dam safety design specifications.
Attachment location: Indicate the specific location (i.e. appendices, pages, plan sheets) where the requisite support documentation has been provided within the application.
*Please include runoff and routing calculations of the 10-year storm event.
Extreme Flood Protection Treatment Standard (Qp100) Attachment location
Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?* See Peak Flow Summary
What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model? 0.01
Overbank Flood Protection Treatment Standard (Qp10) Attachment location
Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?* See Peak Flow Summary
*Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not appropriate if more than a one
subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model that accounts for pond routing is the preferred method.
What storage volume (cubic feet) necessary to meet the Channel Protection Standard? 774
What orifice size (inches) is necessary to meet the required detention time? 1.10
What is the calculated average release rate (cfs)? (Divide the Vs by detention time) 0.01
24 hours for warm water
Attachment location
Did you use the Storage Volume Estimation Method? If yes, skip to Line 19.*
Has the peak storage volume and elevation information for the 1, 10 and 100-year storms been included? See Plans
Channel Protection Treatment Standard (Cpv) Response
Check which detention time must be used, based on the fisheries designation of the receiving water: x12 hours for cold water
Have all low flow orifices been designed or sized to ensure no clogging occurs? See Plans
Have the potential impacts of frozen culverts and deicers on vegetation been addressed in the design? See Plans
Does the application include oultet elevation and size information for the basin?. See Plans
Have you determined depth to bedrock and soil properties using geotechnical investigations? n/a - site visit
Have the outfalls been designed/protected to avoid erosive velocities? See Plans
Is the principal spillway accessible from land and equipped with a removable trash rack? See Plans
Indicate the treatment standards met for the site area draining to this practice:
Attachment location
Have you performed a site evaluation to establish the Hazard Classification of the pond? n/a - site visit
Version: 4/10 The Annex at Mountain Top Inn
S/N 001
Dry Detention Pond (LA-1)
Dry Detention Pond #2
Dry Pond 2 Page 46 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Pond 3 March 6, 2015
Revised: April 22, 2016
Project Name:
Discharge Point:
Line
1 Cpv x
2 Qp10 x
3 Qp100 Not Applicable - Qp100 Waived
Response
4 Yes
5 Yes
6 Yes
8 Yes
9 Yes
10 Yes
11 Yes
12 Yes
13
Response
14 no
15
16
17
18
Response
19 Yes
Response
n/a*Please include runoff and routing calculations of the 100-year storm event.
Please see VSMM-Vol. II, Appendix D7 for guidance about maintaining non-erosive conditions. Ensure that appropriate overflow outlets are designed to safely release all off-site water
that may also be entering the pond. Visit VSMM-Vol.II, Appendix B for dam safety design specifications.
Attachment location: Indicate the specific location (i.e. appendices, pages, plan sheets) where the requisite support documentation has been provided within the application.
*Please include runoff and routing calculations of the 10-year storm event.
Extreme Flood Protection Treatment Standard (Qp100) Attachment location
Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?* Not Required
What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model? 0.05
Overbank Flood Protection Treatment Standard (Qp10) Attachment location
Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?* See Peak Flow Summary
*Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not appropriate if more than a one
subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model that accounts for pond routing is the preferred method.
What storage volume (cubic feet) necessary to meet the Channel Protection Standard? 952
What orifice size (inches) is necessary to meet the required detention time? 1.00
What is the calculated average release rate (cfs)? (Divide the Vs by detention time) 0.05
24 hours for warm water
Attachment location
Did you use the Storage Volume Estimation Method? If yes, skip to Line 19.*
Has the peak storage volume and elevation information for the 1, 10 and 100-year storms been included? See Plans
Channel Protection Treatment Standard (Cpv) Response
Check which detention time must be used, based on the fisheries designation of the receiving water: x12 hours for cold water
Have all low flow orifices been designed or sized to ensure no clogging occurs? See Plans
Have the potential impacts of frozen culverts and deicers on vegetation been addressed in the design? See Plans
Does the application include oultet elevation and size information for the basin?. See Plans
Have you determined depth to bedrock and soil properties using geotechnical investigations? n/a - site visit
Have the outfalls been designed/protected to avoid erosive velocities? See Plans
Is the principal spillway accessible from land and equipped with a removable trash rack? See Plans
Indicate the treatment standards met for the site area draining to this practice:
Attachment location
Have you performed a site evaluation to establish the Hazard Classification of the pond? n/a - site visit
Version: 4/10 The Annex at Mountain Top Inn
S/N 001
Dry Detention Pond (LA-1)
Dry Detention Pond #3
Dry Pond 3 Page 47 of 48
The Annex Long Trail Engineering, P.C.
Mountain Top Inn Job No. 0807.2
Chittenden, VT Copyright 2016
Dry Pond 4 March 6, 2015
Revised: April 22, 2016
Project Name:
Discharge Point:
Line
1 Cpv x
2 Qp10 x
3 Qp100 Not Applicable - Qp100 Waived
Response
4 Yes
5 Yes
6 Yes
8 Yes
9 Yes
10 Yes
11 Yes
12 Yes
13
Response
14 no
15
16
17
18
Response
19 Yes
Response
n/a*Please include runoff and routing calculations of the 100-year storm event.
Please see VSMM-Vol. II, Appendix D7 for guidance about maintaining non-erosive conditions. Ensure that appropriate overflow outlets are designed to safely release all off-site water
that may also be entering the pond. Visit VSMM-Vol.II, Appendix B for dam safety design specifications.
Attachment location: Indicate the specific location (i.e. appendices, pages, plan sheets) where the requisite support documentation has been provided within the application.
*Please include runoff and routing calculations of the 10-year storm event.
Extreme Flood Protection Treatment Standard (Qp100) Attachment location
Have you demonstrated that Qp100 post is less than or equal to Qp100 pre at the discharge point?* Not Required
What is the controlled peak release rate (cfs) during the 1-year storm as indicated by the model? 0.16
Overbank Flood Protection Treatment Standard (Qp10) Attachment location
Have you demonstrated that Qp10 post is less than or equal to Qp10 pre at the discharge point?* See Peak Flow Summary
*Please review the guidance sheet "Channel Protection Storage Volume Estimation" and attach the specified information. This method is not appropriate if more than a one
subwatershed drains to the practice. Using the center of mass detention time calculated by a hydrologic model that accounts for pond routing is the preferred method.
What storage volume (cubic feet) necessary to meet the Channel Protection Standard? 9,668
What orifice size (inches) is necessary to meet the required detention time? 2.40
What is the calculated average release rate (cfs)? (Divide the Vs by detention time) 0.16
24 hours for warm water
Attachment location
Did you use the Storage Volume Estimation Method? If yes, skip to Line 19.*
Has the peak storage volume and elevation information for the 1, 10 and 100-year storms been included? See Plans
Channel Protection Treatment Standard (Cpv) Response
Check which detention time must be used, based on the fisheries designation of the receiving water: x12 hours for cold water
Have all low flow orifices been designed or sized to ensure no clogging occurs? See Plans
Have the potential impacts of frozen culverts and deicers on vegetation been addressed in the design? See Plans
Does the application include oultet elevation and size information for the basin?. See Plans
Have you determined depth to bedrock and soil properties using geotechnical investigations? n/a - site visit
Have the outfalls been designed/protected to avoid erosive velocities? See Plans
Is the principal spillway accessible from land and equipped with a removable trash rack? See Plans
Indicate the treatment standards met for the site area draining to this practice:
Attachment location
Have you performed a site evaluation to establish the Hazard Classification of the pond? n/a - site visit
Version: 4/10 The Annex at Mountain Top Inn
S/N 001
Dry Detention Pond (LA-1)
Dry Detention Pond #4
Dry Pond 4 Page 48 of 48