HomeMy WebLinkAboutCC - Drainage Report and Calcs DRAINAGE CALCULATIONS
FOR
BRUNDAGE ESTATES
SUBDIVISION NO. 2
ADA COUNTY, IDAHO
July 22, 2025
ENGINEERING SOLUTIONS, LLP
1029 N. Rosario Street, Suite 100
Meridian, Idaho 83642
(208) 938 -0980
�\C ENS
60
OFP
M.
Job Number: 250522
Brundage Estates Subdivision No. 2
Drainage Calculations Report
Brundage Estates Subdivision No. 2 is the second phase of a multi-phase
residential development. The project is generally located in Section 25, T.3N.,
R.1 W., B.M., Meridian, Ada County, Idaho. It is located on the east side of
Brundage Estates Sub. No. 1 and north of the Calkins Lateral and is comprised of
36 residential lots and 10 common lots on approximately 12.6+/- acres. The storm
drainage from this project will be intercepted by drop inlets, will flow through sand
and grease traps and then into seepage beds located within common lots.
Assumptions used for this drainage report are as follows:
1. Rational Equation used to estimate storm runoff(Q = CIA)
2. SCS: TR-55 Method used to determine Time of Concentration (Tc)
3. Coefficient of Runoff used is C = 0.50 this is from ACHD Section 8011.2.1
Coefficients of Runoff. Residential Single Family 0.35-0.50. I used
maximum.
4. ACHD Policy allows one half of the entire lot area to be included in the
runoff calculations unless a specific lot grading plan is developed.
The rational method was used to determine the peak discharge. This method uses
a "C" value (0.50 in this case), Time of Concentration (Tc) calculated by SCS TR-
55 methods and rainfall Intensity Duration Frequency (IDF) curves for the Boise
Front from the ACHD Storm Water Design Manual. The rainfall intensity is
determined from the IDF curve where "I" is selected at the calculated Tc and the
100-year return.
I used the latest ACHD spreadsheet Version 10.5, November 2018.
Brundage Estates Subdivision No. 2 is divided into ten runoff collection zones.
The contributing areas are depicted on the attached drainage map. Six of the
drainage areas flow to existing storm drain systems constructed as a part of
Brundage Estates Subdivision No. 1. The remaining four flow to two new
drainage systems/seepage beds.
The assumption is made that the front half is the only contributing portion of the
lot. This is based on the assumption that the rear portion of the lot is self-
contained and/or is delayed long after the peak discharge has passed.
The peak discharge is used to determine the capacity of the pipes and drop inlet. A
minimum value of 10 minutes is used to select the "I" in the peak discharge
calculations. Per ACHD policy, the volume calculations are determined using Tc
of 60 minutes, therefore; I=0.96". I have used the ACHD worksheets Version 10.5
dated November 2018 to determine the peak discharge, and volumes of the
storms.
Proposed Drainage
The proposed drainage system improvements consist of drop inlets, a storm pipe
network, sand and grease traps and seepage beds.
Seepage Bed No. 2.1
Areas 2.1 and 2.2 will be picked up in drop inlets and piped to two 1000-gallon
sand and grease traps. From the sand and grease traps an 18" pipe goes 5' into the
seepage bed, then an 18" top only perforated pipe extends through the seepage
bed. The bottom of the bed is in free draining soils and has 3' separation from
groundwater.
Seepage Bed No. 2.2
Areas 2.3 and 2.4 will be picked up in drop inlets and piped to a 1000-gallon sand
and grease trap. From the sand and grease trap an 18" pipe goes 5' into the
seepage bed, then an 18" top only perforated pipe extends through the seepage
bed. The bottom of the bed is in free draining soils and has 3' separation from
groundwater.
Areas 1 and 2 flow to existing Seepage Bed 1.1, areas 3 and 4 flow to existing
Seepage Bed 1.2 and Areas 5 and 6 flow to existing Seepage Bed 1.3; all
constructed as a part of Brundage Estates Subdivision No. 1.
Seepage Beds
All seepage bed systems are sized for the 100-year storm using the ACHD
spreadsheets. The seepage beds use clean drain rock wrapped in filter fabric to
facilitate drainage, an 18" pipe perforated on the top only and 1.5' of sand
underneath the clean drain rock. The seepage beds also contain a monitoring well
inside the bed and one outside of the bed. The seepage beds were sized using a
percolation rate of 1" per hour which is less than the recommended percolation rate
from the soils engineer. The beds were designed to have 3' of separation from
high groundwater based on the groundwater monitoring report that was provided.
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ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.1-Area 2.1
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max)
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 Subbasin 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) Acres 0.70
Acres 0.70
6 Determine the Weighted Runoff Coefficient(C) 0.50
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg1 0.50
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min to Min. Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"i
Business
Downtown areas 0.70-0.95
Hydraulic Urban neighborhoods 0.50-0.70
Radius Flow Residential
Intercept A/Wet Velocity V Flow Time single Family 0.35-0.50
ID Pipe Size(in) Slope(ft/ft) Coeff. Length Manning n Perm (fps) (min) Multi-family 0.60-0.75Residential(rural) 0.25-0.40
Segment 1:Pipe Flow Apartment Dwelling Areas 0.70
a Industrial and Commercial
Light areas 0.80
Heavy areas 0.90
Segment 2:Gutter Shallow Concentrated Flow
Parks,Cemeteries 0.1010-0.25
b 0.005 0.619 366 1.4 4.5 Playgrounds 0.20-0.35
Railroad yard areas 0.20-0.40
Segment 3:Overland Sheet Flow By TR-55,<300-ft
c 0.020 40 0.240 3.6 11.1
Computed Tc= 15.6
User-Entered Tc= 15.6
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 2.18 in r
y Calculate the Post-Development peak discharge(QPeak) Qpe k 0.76 cfs
10 Calculate total runoff vol(V)(for sizing primary storage) V 1,210 ft
V=Ci(Tc=60)Ax3600
it Calculate Volume of Runoff Reduction Vrr
Enter Percentile Storm I(95th percentile=0.60 in) 95th 0.60 in
Enter Runoff Reduction Vol(95th Percentile=0.60-in x Area x C) Vrr 756 ft'
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) cfs
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin Streets
Basin Forebay V 121 ft' Asphalt 0.95
Concrete 0.95
Primary Treatment/Storage Basin V 1,089 ft' Brick 0.95
Subsurface Storage Roofs 0.95
' Gravel 0.75
Volume Without Sediment Factor(See BMP 20 Tab) V 1,210 ft Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
K:\Data From PC\2025\250522-Brundage Estates No.2\Calculations\ACHD_SD_CALCS_Area 2.1.xlsm 7/16/2025,11:05 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
t
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.2-Area 2.2
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max)
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 Subbasin 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) Acres 3.40
Acres 3.40
6 Determine the Weighted Runoff Coefficient(C) 0.50
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg1 0.50
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min 10 Min. Estimated Runoff Coefficients for Various Surfav
Type of Surface Runoff Coefficients
Business
Downtown areas 0.70-0.95
Hydraulic Urban neighborhoods 0.50-0.70
Radius FlowLFlowTime
Residential
Intercept A/Wet Velocity V single Family 0.35-0.50
Multi-family 0.60-0.75
ID Pipe Size(in) Slope(ft/ft) Coeff. Length Manning n Perm (fps) Residential(rural) 0.25-0.40
Segment 1:Pipe Flow Apartment Dwelling Areas 0.70
a Industrial and Commercial
Light areas 0.90
Heavy areas 0.90
Segment 2:Gutter Shallow Concentrated Flow
Parks,Cemeteries 0.1010-0.25
b 0.006 0.619 866 1.6 9.2 Playgrounds 0.20-0.35
Railroad yard areas 0.20-0.40
Segment 3:Overland Sheet Flow By TR-55,<300-ft
c 0.020 27 0.240 3.3 8.2
Computed Tc= 17.4
User-Entered Tc= 17.4
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 2.18 in r
y Calculate the Post-Development peak discharge(QPeak) Qpeak 3.71 cfs
10 Calculate total runoff vol(V)(for sizing primary storage) V 5,875 ft
V=Ci(Tc=60)Ax3600
11 Calculate Volume of Runoff Reduction Vrr
Enter Percentile Storm I(95th percentile=0.60 in) 95th 0.60 in
Enter Runoff Reduction Vol(95th Percentile=0.60-in x Area x C) Vrr 3,672 ftJ
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) cfs
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin streets
Basin Forebay V 588 fe Asphalt 0.95
Concrete 0.95
Primary Treatment/Storage Basin V 5,288 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 5,875 ft' Gravel Fields:Sandy soil Soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
K:\Data From PC\2025\250522-Brundage Estates No.2\Calculations\ACHD_SD_CALCS_Area 2.2.xlsm 7/16/2025,11:05 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
tfor Peak
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.2-Areas 2.1 and 2.2
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max)
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 Subbasin 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) Acres 0.70 3.40
Acres 4.10
6 Determine the Weighted Runoff Coefficient(C) 0.50 0.50
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg1 0.50
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 Luser Calculate
min 10 Min. Estimated Runoff Coefficients for Various Surfao
Type of Surface Runoff Coefficients"t
Business
Downtown areas 0.70-0.95
Hydraulic Urban neighborhoods 0.50-0.70
Radius Flow Residential
Intercept A/Wet Velocity V Flow Time Single Family 0.35-0.50
ID Pipe Size(in) Slope(ft/ft) Coeff. Length Manning n Perm (fps) (min) Multi-family 0.60-0.75
Residential(rural) 0.25-0.40
Segment 1:Pipe Flow Apartment Dwelling Areas 0.70
a Industrial and Commercial
Light areas 0.80
Segment 2:Gutter Shallow Concentrated Flow Heavy areas 0.
90 Parks,Cemeteries 0.1010-0.25
b 0.006 0.619 866 1.6 9.2 Playgrounds 0.20-0.35
Railroad yard areas 0.20-0.40
Segment 3:Overland Sheet Flow By TR-55,<300-ft
c 0.020 27 0.240 3.3 8.2
Computed Tc= 17.4
User-Entered Tc= 17.4
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 2.18 in hr
y Calculate the Post-Development peak discharge(QPeak) Qpeak 4.47 cfs
10 Calculate total runoff vol(V)(for sizing primary storage) V 7,085 ft
V=Ci(Tc=60)Ax3600
11 Calculate Volume of Runoff Reduction Vrr
Enter Percentile Storm I(9Sth percentile=0.60 in) 95th 0.60 in
Enter Runoff Reduction Vol(95th Percentile=0.60-in x Area x C) Vrr 4,428 ft'
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) cfs
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin Streets
Basin Forebay V 708 ft Asphalt 0.95
Concrete 0.95
Primary Treatment/Storage Basin V 6,376 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 7,085 ft' Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
K:\Data From PC\2025\250522-Brundage Estates No.2\Calculations\ACHD_SD_CALCS_Areas 2.1 and 2.2.xIsm 7/16/2025,11:06 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Sand/Grease Traps
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the
Engineer's calculation methodology. These calculations shall establish a minimum requirement.The Engineer's methodology must
result in facilities that meet or exceed these calculations in order to be accepted.
Steps for Sand/Grease Trap Velocity Calculation
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.2-Areas 2.1 and 2.2
2 Enter number of Sand/Grease Traps(25 max) 1
Number of Peak Flow Baffle Throat Velocity Is the
S/G Traps Q-cfs
Vault Size Spacing width Area(ft2) 0.5 fps Velocity
inch inch max. ok?
1000 G 2 4.47 20 48 13.33 0.34
Reference for Throat widths(inch)
Boise ADS
Vault Lar-ken WQU,
BMP 16
1000 G 48.0 50.5 n/a
1500 G 60.0 61.5 n/a
WQU1000 n/a n/a 60
WQU1500 n/a n/a 60
K:\Data From PC\2025\250522- Brundage Estates No. 2\Calculations\ACHD_SD_CALCS_Areas 2.1 and 2.2.xIsm 7/16/2025, 11:06 AM
Version 10.0, May 2018
ACHD Calculation Sheet for Sizing Seepage Bed With Optional Chambers
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the
Engineer's calculation methodology. These calculations shall establish a minimum requirement.The Engineer's methodology must result in
facilities that meet or exceed these calculations in order to be accepted.
Note this spreadsheet pulls information from the"Peak Q,V"tab
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.2-Areas 2.1 and 2.2
2 Enter number of Seepage Beds(25 max) 1
3 Design Storm 100
4 Weighted Runoff Coefficient C 0.50 Link to: LQ,v
QV TR55
5 Area A(Acres) 4.10 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? Yes V 7,085 ft3 0%Sediment
8 Set Total Design Width of All Drain Rock W 6.0 ft
9 Set Total Design Depth of All Drain Rock D 9.0 ft
Rock Only,Do Not Include Filter Sand Depth or Cover
10 Void Ratio of Drain Rock Voids 0.4
0.4 for 1.5"-2"drain rock and 3/4"Chips
11 Design Infiltration Rate(8 in/hr max) Perc 1.00 in/hr
12 Size of WQ Perf Pipe(Perf 180°) Dia pipe 18 in
13 Size of Overflow Perf Pipe(Perfs 3600),READ if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf 22.3 ft3/ft
15 Calculate Design Length L 318 320 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 320 ft
17 Variable Infiltration Window W SWW 6.0 ft
18 Time to Drain 39.9 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 320 314 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxd(2xgxH)
Optional Storage Chambers
Note:This assumes chambers are organized in a rectangular layout.
1-StormTech,
1 Type of Chambers SC740
2 Volume to Store V 0 ft3
3 Installed Chamber Width Cw 4.25 ft
Installed Chamber Depth Cd 2.50 ft
Installed Chamber Height Ch 7.12 ft
4 Chamber Void Factor
5 Chamber Storage Volume,Without Rock,Per Manuf 45.90 ft3/Unit
6 Chamber Storage Volume,With Rock,Per Manuf 74.90 ft'/Unit
7 Total Number of Units Required 0 ea
8 Area of Infiltration Aperc ft2
9 Volume Infiltration Vperc 0 ft3/hr
10 Time to Drain hours
90%volume in 48-hours minimum
K:\Data From PC\2025\250522-Brundage Estates No.2\Calculations\ACHD_SD_CALCS_Areas 2.1 and 2.2.xIsm 7/16/2025,11:06 AM
Version 10.0,May 2018
ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.2-Area 2.3
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max)
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 Subbasin 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) Acres 2.10
Acres 2.10
6 Determine the Weighted Runoff Coefficient(C) 0.50
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avgl 0.50
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min 10 Min. Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"1
Business
Downtown areas 0.70-0.95
Hydraulic Urban neighborhoods 0.50-0.70
Radius Flow Residential
Intercept A/Wet Velocity V Flow Time single Family 0.35-0.50
ID Pipe Size(in) Slope(ft/ft) Coeff. Length Manning n Perm (fps) (min) Multi-family 0.60-0.75Residential(rural) 0.25-0.40
Segment 1:Pipe Flow Apartment Dwelling Areas 0.70
a Industrial and Commercial
Light areas 0.80
Heavy areas 0.90
Segment 2:Gutter Shallow Concentrated Flow
Parks,Cemeteries 0.1010
-0.25
b 0.009 0.619 1,097 1.9 9.6 Playgrounds 0.20-0.35
Railroad yard areas 0.20-0.40
Segment 3:Overland Sheet Flow By TR-55,<300-ft
c 0.020 70 0.240 4.0 17.4
Computed Tc= 27.0
User-Entered Tc= 27.0
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 1.58 in r
y Calculate the Post-Development peak discharge(QPeak) Qpeak 1.66 cfs
10 Calculate total runoff vol(V)(for sizing primary storage) V 3,629 ft
V=Ci(Tc=60)Ax3600
11 Calculate Volume of Runoff Reduction Vrr
Enter Percentile Storm I(9Sth percentile=0.60 in) 95th 0.60 in
Enter Runoff Reduction Vol(9Sth Percentile=0.60-in x Area x C) Vrr 2,268 ft'
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) cfs
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin streets
Basin Forebay V 363 ft Asphalt 0.95
Concrete 0.95
Primary Treatment/StorageBasin V 3,266 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 3,629 ft' Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
K:\Data From PC\2025\250522-Brundage Estates No.2\Calculations\ACHD_SD_CALCS_Area 2.3.xlsm 7/16/2025,11:07 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.2-Area 2.4
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max)
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 Subbasin 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) Acres 1.50
Acres 1.50
6 Determine the Weighted Runoff Coefficient(C) 0.50
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avg1 0.50
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min 10 Min. Estimated Runoff Coefficients for Various Surfao
Type of Surface Runoff Coefficients
Business
Downtown areas 0.70-0.95
Hydraulic Urban neighborhoods 0.50-0.70
Radius Flow Residential
Intercept A/Wet Velocity V Flow Time Single Family 0.35-0.50
ID Pipe Size(in) Slope(ft/ft) Coeff. Length Manning n Perm (fps) (min) Multi-family 0.60-0.75
Residential(rural) 0.25-0.40
Segment 1:Pipe Flow
Apartment Dwelling Areas 0.70
a Industrial and Commercial
Light areas 0.80
Segment 2:Gutter Shallow Concentrated Flow Heavy areas 0.90
Parks,Cemeteries 0.10-0.25
b 0.005 0.619 446 1.4 5.2 Playgrounds 0.20-0.35
Railroad yard areas 0.20-0.40
Segment 3:Overland Sheet Flow By TR-55,<300-ft
c 0.020 75 0.240 4.0 18.4
Computed Tc= 23.6
User-Entered Tc= 23.6
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 1.81 in r
y Calculate the Post-Development peak discharge(QPeak) Qpeak 1.36 cfs
10 Calculate total runoff vol(V)(for sizing primary storage) V 2,592 ft
V=Ci(Tc=60)Ax3600
it Calculate Volume of Runoff Reduction Vrr
Enter Percentile Storm I(95th percentile=0.60 in) 95th 0.60 in
Enter Runoff Reduction Vol(9Sth Percentile=0.60-in x Area x C) Vr, 1,620 ft'
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) cfs
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin Streets
Basin Forebay V 259 W Asphalt 0.95
Concrete 0.95
Primary Treatment/Storage Basin V 2,333 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 2,592 ft Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
K:\Data From PC\2025\250522-Brundage Estates No.2\Calculations\ACHD_SD_CALCS_Area 2.4.xlsm 7/16/2025,11:07 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Finding Peak Discharge/Volume-Rational Method
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the Engineer's calculation methodology.These
calculations shall establish a minimum requirement.The Engineer's methodology must result in facilities that meet or exceed these calculations in order to be accepted.
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.2-Areas 2.3 and 2.4
2 Is area drainage basin map provided? YES
(map must be included with stormwater calculations)
3 Enter Design Storm(100-Year or 25-Year With 100-Year Flood Route) 100
4 Enter number of storage facilities(25 max)
Click to Show More Subbasins ❑
Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin Subbasin
1 Subbasin 2 3 4 5 Subbasin 6 7 8 9 10
5 Area of Drainage Subbasin(SF or Acres) Acres 2.10 1.50
Acres 3.60
6 Determine the Weighted Runoff Coefficient(C) 0.50 0.50
C=[(C1xA1)+(C2xA2)+(CnxAn)]/A Weighted Avgl 0.50
7 Calculate Overland Flow Time of Concentration in Minutes(Tc)or use default 10 User Calculate
min 10 Min. Estimated Runoff Coefficients for Various Surface
Type of Surface Runoff Coefficients"I
Business
Downtown areas 0.70-0.95
Hydraulic Urban neighborhoods 0.50-0.70
Radius FlowLFlowTime
Residential
Intercept A/Wet Velocity V single Family 0.35-0.50
Multi-family 0.60-0.75
ID Pipe Size(in) Slope(ft/ft) Coeff. Length Manning n Perm (fps) Residential(rural) 0.25-0.40
Segment 1:Pipe Flow Apartment Dwelling Areas 0.70
a Industrial and Commercial
Light areas 0.80
Heavy areas 0.90
Segment 2:Gutter Shallow Concentrated Flow Parks,Cemeteries 0,10-0.25
b 0.009 0.619 1,097 1.9 9.6 Playgrounds 0.20-0.35
Railroad yard areas 0.20-0.40
Segment 3:Overland Sheet Flow By TR-55,<300-ft
c 0.020 70 0.240 4.0 17.4
Computed Tc= 27.0
User-Entered Tc= 27.0
8 Determine the average rainfall intensity(i)from IDF Curve based on Tc i 1.58 in r
y Calculate the Post-Development peak discharge(QPeak) Qpeak 2.84 cfs
10 Calculate total runoff vol(V)(for sizing primary storage) V 6,221 ft
V=Ci(Tc=60)Ax3600
11 Calculate Volume of Runoff Reduction Vrr
Enter Percentile Storm I(95th percentile=0.60 in) 95th 0.60 in
Enter Runoff Reduction Vol(95th Percentile=0.60-in x Area x C) Vrr 3,888 ft,
12 Detention:Approved Discharge Rate to Surface Waters(if applicable) cfs
13 Volume Summary Unimproved areas 0.10-0.30
Surface Storage:Basin streets
Basin Forebay V 622 ft Asphalt 0.95
Concrete 0.95
Primary Treatment/Storage Basin V 5,599 ft' Brick 0.95
Subsurface Storage Roofs 0.95
Volume Without Sediment Factor(See BMP 20 Tab) V 6,221 ft' Gravel 0.75
Fields:Sandy soil Soil Type
Slope A B C D
Flat:0-2% 0.04 0.07 0.11 0.
Average:2-6% 0.09 0.12 0.15 0.
Steep:>6% 0.13 0.18 0.23 0.
Adapted from ASCE
K:\Data From PC\2025\250522-Brundage Estates No.2\Calculations\ACHD_SD_CALCS_Areas 2.3 and 2.4.xlsm 7/16/2025,11:08 AM
Version 10.5,November 2018
ACHD Calculation Sheet for Sand/Grease Traps
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the
Engineer's calculation methodology. These calculations shall establish a minimum requirement.The Engineer's methodology must
result in facilities that meet or exceed these calculations in order to be accepted.
Steps for Sand/Grease Trap Velocity Calculation
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.2-Areas 2.3 and 2.4
2 Enter number of Sand/Grease Traps(25 max) 1
Number of Peak Flow Baffle Throat Velocity Is the
[71000G
Spacing width Area(ft2) 0.5 fps Velocity
S/G Traps Q-cfs inch inch max. ok?
1 2.84 20 48 6.67 0.43
Reference for Throat widths(inch)
ADS
Boise Lar-ken WQU,
Vault BMP 16
1000 G 48.0 50.5 n/a
1500 G 60.0 61.5 n/a
WQU1000 n/a n/a 60
WQU1500 n/a n/a 60
K:\Data From PC\2025\250522- Brundage Estates No. 2\Calculations\ACHD_SD_CALCS_Areas 2.3 and 2.4.xlsm 7/16/2025, 11:08 AM
Version 10.0, May 2018
ACHD Calculation Sheet for Sizing Seepage Bed With Optional Chambers
NOTE:This worksheet is intended to be a guideline to standardize ACHD checking of drainage calculations and shall not replace the
Engineer's calculation methodology. These calculations shall establish a minimum requirement.The Engineer's methodology must result in
facilities that meet or exceed these calculations in order to be accepted.
Note this spreadsheet pulls information from the"Peak QV"tab
Calculate Post-Development Flows(for pre-development flows,increase number of storage facilities to create new tab)
User input in yellow cells.
1 Project Name Brundage Estates Subdivision No.2-Areas 2.3 and 2.4
2 Enter number of Seepage Beds(25 max) 1
3 Design Storm 100
4 Weighted Runoff Coefficient C 0.50 Link to: LQY
QV TR55
5 Area A(Acres) 3.60 acres
6 Approved discharge rate(if applicable) 0.00 cfs
7 Is Seepage Bed in Common Lot? No V 7,776 ft3 25%Sediment
8 Set Total Design Width of All Drain Rock W 15.0 ft
9 Set Total Design Depth of All Drain Rock D 9.0 ft
Rock Only,Do Not Include Filter Sand Depth or Cover
10 Void Ratio of Drain Rock Voids 0.4
0.4 for 1.5"-2"drain rock and 3/4"Chips
11 Design Infiltration Rate(8 in/hr max) Perc 1.00 in/hr
12 Size of WQ Perf Pipe(Pert 180°) Dia pipe 18 in
13 Size of Overflow Perf Pipe(Perfs 360%READ if Q100>3.3 cfs in
14 Calculate Total Storage per Foot Spf 55.4 ft3/ft
15 Calculate Design Length L 140 ft
Override Value Required for Chambers
16 Variable Infiltration Window L SWL 140 ft
17 Variable Infiltration Window W SWW 15.0 ft
18 Time to Drain 39.9 hours
90%volume in 48-hours minimum
19 Length of WQ&Overflow Perf Pipes 140 134 ft
20 Perf Pipe Checks.Qperf>=Qpeak;
where Qperf=CdxAxV(2xgxH)
Optional Storage Chambers
Note:This assumes chambers are organized in a rectangular layout.
1-StormTech,
1 Type of Chambers SC740
2 Volume to Store V 0 ft 3
3 Installed Chamber Width Cw 4.25 ft
Installed Chamber Depth Cd 2.50 ft
Installed Chamber Height Ch 7.12 ft
4 Chamber Void Factor
5 Chamber Storage Volume,Without Rock,Per Manuf 45.90 ft3/Unit
6 Chamber Storage Volume,With Rock,Per Manuf 74.90 ft'/Unit
7 Total Number of Units Required 0 ea
8 Area of Infiltration Aperc ft2
9 Volume Infiltration Vperc 0 ft3/hr
10 Time to Drain hours
90%volume in 48-hours minimum
K:\Data From PC\2025\250522-Brundage Estates No.2\Calculations\ACHD_SD_CALCS_Areas 2.3 and 2.4.xlsm 7/16/2025,11:08 AM
Version 10.0,May 2018
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Test Pit Log
Project: Brundage Estates Subdivision Page 1 of 1
Client: Lee Centers
Project No.: 24006 Test Pit: TP-3
Excavation Company: Schmidt Construction Excavation Date: 5/30/2025
Excavation Equipment: DEERE 350D Logged By: A. Mascorro
Excavator Bucket Width: 5 feet Test Pit Location (Latitude, Longitude):
Equipment Operator: David 43.5683020, -116.4095610
Laboratory Tests
_71Q Notes / Remarks
USCS Soil Description Atterber
g
M Limits Depth to Groundwater: N/A
Y U)
Ground Elevation =2706.3 ft N I 2E LL PL PI BGS = Below Ground Surface
0
Fat CLAY with Sand (Native): brown, very Approximately 6 inches of
1 U stiff to stiff, moist surficial topsoil and roots.
Sandy silt contained cemented
2 _J Sandy SILT: orange-tan, m. dense to dense, moist �%
-�r���. particles
3fy
x SILT-STONE (hardpan): tan, hard to very'hard
dA
4 Silty SAND with 1/" to 8" diameter cemented
particles (caliche): orange-tan, dense, moist
5
W
6
[1,
7
x SILT-STONE (hardpan): orange-tan, very hard
ro r�l S
8
Silty SAND with 1/2" to 8" diameter cemented
9 particles (caliche): orange-tan, dense to
medium dense, moist
10
11
12 ...... Variable weakly cemented zones
W observed from 10 to 15 feet
13
14
15
Field seepage test
16 performed at 17 feet.
Seepage rate 3 in/hr.
17 Test pit terminated at 17 feet BGS.
18 PVC pipe installed to 17 feet BGS.
19
Test Pit Log
Project: Brundage Estates Subdivision Page 1 of 1
Client: Lee Centers
Project No.: 24006 Test Pit: TP-4
Excavation Company: Schmidt Construction Excavation Date: 5/30/2025
Excavation Equipment: DEERE 350D Logged By: A. Mascorro
Excavator Bucket Width: 5 feet Test Pit Location (Latitude, Longitude):
Equipment Operator: David 43.5683080, -116.4079560
Laboratory Tests
Notes / Remarks
$ U' USCS Soil Description � `. Atterberg
� U � ..c
Limits Depth to Groundwater: N/A
Ground Elevation =2706.7 ft o 2 LL PL PI JBGS = Below Ground Surface
0
Fat CLAY with Sand (Native): brown, very Approximately 6 inches of
= stiff to stiff, moist surficial topsoil and roots.
1 U
2 -7 0 Sandy silt contained cemented
J Sandy SILT: orange-tan, m. dense tp dense moist particles
3 SILT-STONE (hardpan): tan, hard to very
x hard
4 Q�
Silty SAND with 1/� to 8 diameter cemented
6 particles (caliche): orange-tan, dense, moist
7 �
s
x SILT-STONE (hardpan): orange-tan, very
9 L hard
10 Silty SAND with 1/2" to 8" diameter cemented
particles (caliche): orange-tan, dense, moist
11 U)
12
SILT-STONE (hardpan): orange-tan, very
13 x hard
14
Silty SAND with 1/2" to 8" diameter cemented
15 particles (caliche): orange-tan, dense to
medium dense, moist
16 2
U)
17 Field seepage test
performed at 18.25 feet.
18 * sy Seepage rate 4 in/hr.
Test pit terminated at 18.25 feet BGS.
19 PVC pipe installed to 18.25 feet BGS.
20