Storm Water Calcs 9-17-04
PRELIMINARY STORM WATER
RUNOFF CALCULATIONS
CITY OF CHANHASSEN
RECEIVED
Pinehurst
SEP 1 7 2004
Chanhassen, MN
CHANHASSEN PLANNING DEPT
Prepared for:
Plowshares Development, LLC
1851 Lake Drive West
Chanhassen, MN 55317
Prepared by:
Westwood Professional Services, Inc.
7599 Anagram Drive
Eden Prairie, MN 55344
Phone (952)937-5150, Fax (952) 937-5822
September 17, 2004
Project # 20041064
SUMMARY
The attached storm water runoff and ponding calculations are based on Nationwide Urban Runoff
Program (NURP) and The Soil Conservation Service Synthetic Unit Hydrograph Method incorporated into
the software program Hydraflow by Intelisolve, version 7.0.0.19.
Two interconnected ponds were incorporated into the project for both rate control and quality control. The
goal for rate control on this project was not to exceed existing discharge rates for the 2, 10 and 100-year
events.
SITE CONDITIONS
The site consists of Type "B" soils, and curve numbers were obtained from "Technical Release 55: Urban
Hydrology for Small Watersheds." A curve number of 55 was used for the existing condition of woods, 70
for residential, 69 for grassland and 65 for woods and grass area mixed. For the proposed conditions a
curve number of 70 was used for residential single-family development. Refer to attachments for existing
and proposed drainage areas.
ROUTING
Under existing conditions, 27.82 acres drains to an existing ravine located at the southwest corner of the
site. Another 7.09 acres drains to an existing swale in the Wood Ridge Heights development, 3.48 acres
drains to an existing catch basin on the Wood Ridge Heights development and the remaining 4.93 acres
drains to an Existing Pond located at the intersection of Lake Lucy Road and County Road 117. Under
post-development conditions, 22.84 acres of drainage is routed through the development to the existing
ravine located on the southwest corner of the site, 0.64 acres drains to the Wood Ridge Heights swale,
1.06 acres drains to the existing catch basin, 2.10 acres drains to the existing pond and the remaining
16.69 acres of development is routed to the proposed ponds prior to being discharged to a storm sewer
stub located in Manchester Drive. The capacity of the existing stub is 9.5 ds per the City of Chanhassen.
The storm water is then routed to the existing storm water pond located at the intersection of Lake Lucy
Road and County Road 117.
RATE CONTROL
An evaluation was made for both the pre-development and post-development peak runoff rates for the
entire site. By using a 15" culvert the peak runoff rates were within rate control requirements. The
following is a table summarizing pre-development and post-development peak runoff rates for the 2-year,
10-year, and 100-year storms:
PEAK RUNOFF RATES
Pre-Development Post-Development
Drainage 2 yr 10 yr 1 00 yr 2 yr 10 yr 1 00 yr
(ds) (ds) (ds) ( cfs ) ( cfs ) ( ds )
Ravine 3.42 15.43 36.89 2.81 12.67 30.29
*Existinq Swale 2.23 8.74 19.05 0.31 1.07 2.24
*Existing Catch Basin 1.10 4.29 9.35 0.51 1.77 3.71
*Existing Pond 1.55 6.08 13.24 1.01 3.51 7.34
*Existinq Stub 0.00 0.00 0.00 1.69 5.21 8.41
Totals 8.30 34.54 78.53 6.33 24.23 51.99
*Ultimately the flows to the existing catch basin, existing stub and existing swale are conveyed to the
existing Pond. The flows were subdivided for comparison purposes.
The capacity of the existing stub is 9.5 cfs per the City of Chanhassen.
· WESTWOOD PROFESSIONAL SERVICES, INC. (952) 937-5150
SUMMARY
Following is a table summarizing the rate control pond system:
Pond
NWL
(feet)
Dead
Storage
(acre-feet)
1.09
Live
Storage
( acre-feet)
3.80
100-yr
Discharge
(cfs
8.41
Pond A & B
WATER QUALITY
The PONDNET model was used to determine the phosphorus removal efficiency of the proposed pond.
The removal efficiency of the pond is 62%
I hereby certify that this report was prepared by me or under my direct supervision and that I am a duly
Licensed Professional Engineer under the laws of the State of Minnesota.
//) / / /Z/)
~.1f / :;:./
C ns Moehrl,·P. . ~
Reg. No. 40853
q //7/o?!
Date ' I
~~~
urtis Neft, EIT
7/17/0¿¡
Date
· WESTWOOD PROFESSIONAL SERVICES, INC. (952) 937-5150
Hydrograph Summary Report Page 1
--_.~.- -_.__._~ ---~-~-----
Hyd. Hydrograph Peak Time Time to Volume Inflow Maximum Maximum Hydrograph
No. type flow interval peak hyd(s) elevation storage description
(origin) (cfs) (min) (min) (acft) (ft) (acft)
-- ---------- -- -~.-.._-_._~~-
SCS Runoff 3.42 3 750 0.782 DA-1
2 SCS Runoff 2.23 3 726 0.242 DA-2
3 SCS Runoff 1.10 3 726 0.119 DA-3
4 SCS Runoff 1.55 3 726 0.168 DA-4
5 SCS Runoff 2.81 3 750 0.642 DA-5
6 SCS Runoff 0.31 3 720 0.020 DA-6
7 SCS Runoff 0.51 3 720 0.033 DA-7
8 SCS Runoff 1.01 3 720 0.065 DA-8
9 SCS Runoff 8.07 3 729 0.786 DA-9
11 Reservoir 1.69 3 765 0.786 9 1024.63 0.263 NURP PONDS
I
\
i
I
I
r Proj. file 04-09-10-DAP01g¿ Retu~;"~od: 2 yr
_._._-~_._--- ------------ --_._--~--"._..__._--~-----_._---_._._-
---"---
Run date: 09-16-2004
Hydraflow Hydrographs by Intelisolve
Hydrograph Summary Report Page 1
---,._._------._~ ------ .------- ----_._~---- -."..---.--....- --- --------,
Hyd. Hydrograph Peak Time Time to Volume Inflow Maximum Maximum Hydrograph
No. type flow interval peak hyd(s) elevation storage description
(origin) (cts) (min) (min) (acft) (ft) (acft)
._-_._~- -- ---.- ----.--_.._-_.~_._--_.
SCS Runoff 15-43 3 744 2.414 DA-1
2 SCS Runoff 8.74 3 726 0.699 DA-2
3 SCS Runoff 4.29 3 726 0.343 DA-3
4 SCS Runoff 6.08 3 726 0.486 DA-4
5 SCS Runoff 12.67 3 744 1.982 DA-5
6 SCS Runoff 1.07 3 720 0.057 DA-6
7 SCS Runoff 1.77 3 720 0.095 DA-7
8 SCS Runoff 3.51 3 720 0.188 DA-8
9 SCS Runoff 23.50 3 729 1.986 DA-9
11 Reservoir 5.21 3 753 1.986 9 1025.82 0.758 NURP PONDS
Proj. file: 04-09-10-DAP01.~~~eturn peri;d:-1_--_-_~-y;-
_____ _____~___ _____ .._~___J~______________ ___
Run date: 09-16-2004
._-~
Hydraflow Hydrographs by Intelisolve
Hydrograph Summary Report
-
Hyd. Hydrograph Peak Time
No. type flow interval
(origin) (cts) (min)
"---~-
1 SCS Runoff 3689 3
2 SCS Runoff 19.05 3
3 SCS Runoff 9.35 3
4 SCS Runoff 13.24 3
5 SCS Runoff 30.29 3
6 SCS Runoff 2.24 3
7 SCS Runoff 3.71 3
8 SCS Runoff 7.34 3
9 SCS Runoff 46.67 3
11 Reservoir 8.41 3
___L-. _ --
Proj. file: 04-09-10-DAP01.g
----------._- -.., u______ --~~-_.-
Page 1
------ ___n________
Time to Volume Inflow Maximum Maximum Hydrograph
peak hyd(s) elevation storage description
(min) (acft) (ft) (acft)
---'-'-~--'-- . - -- -------- -------------- -~---_.--~-_.-
744 5.109 DA-1
726 1.433 DA-2
726 0.703 DA-3
726 0.996 DA-4
744 4.194 DA-5
717 0.118 DA-6
717 0.195 DA-7
717 0.386 DA-8
726 3.804 DA-9
756 3.804 9 1027.52 1.642 NURP PONDS
pw
Return Period: 100 yr
Run date: 09-16-2004
- --~-- -
Hydraflow Hydrographs by Intelisolve
Hydrograph Report
Page 1
Hyd. No. 1
DA-1
Hydrograph type
Storm frequency
Drainage area
Basin Slope
T c method
Total precip.
Storm duration
Hydraflow Hydrographs by Intelisolve
= SCS Runoff
= 100 yrs
= 27.82 ae
= 3.6 °10
= LAG
= 6.00 in
= 24 hrs
Peak discharge = 36.89 cfs
Time interval = 3 min
Curve number = 63
Hydraulic length = 1950 ft
Time of conc. (Te) = 45.9 min
Distribution = Type II
Shape factor = 484
----~-,- ~--
Hydrograph Discharge Table
Hydrograph Volume = 5.109 adt
Time -- Outflow
(hrs cfs)
12.40 36.89 «
...End
Hydrograph Report
Page 1
Hydraflow Hydrographs by In!elisolve
Hyd. No. 2
DA-2
Hydrograph type == SCS Runoff Peak discharge == 19.05 cfs
Storm frequency == 100 yrs Time interval == 3 min
Drainage area == 7.09 ac Curve number == 65
Basin Slope == 6.5 % Hydraulic length == 850 ft
T c method == LAG Time of cone. (Tc) == 16.7 min
Total precip. == 6.00 in Distribution == Type II
Storm duration == 24 hrs Shape factor == 484
_.-.-----
-._-~---_._-----~-
.---------,--._----- --------.---~--
Hydrograph Volume = 1.433 act!
Hydrograph Discharge Table
Time -- Outflow
(hrs cfs)
12.10 19.05«
...End
Hydrograph Report
Page 1
Hydraflow Hydrographs by Intelisolve
Hyd. No. 3
DA-3
Hydrograph type = SCS Runoff
Storm frequency = 100 yrs
Drainage area = 3.48 ac
Basin Slope = 5.9 %
T c method = LAG
Total precip. = 6.00 in
Storm duration = 24 hrs
Peak discharge = 9.35 cfs
Time interval = 3 min
Curve number = 65
Hydraulic length = 860 ft
Time of cone. (Tc) = 17.6 min
Distribution = Type II
Shape factor = 484
_._----~..._._------_._-_.__..._. ---- -~-~~..-._------
~._---~_.._---- .__...~---_.._-
Hydrograph Volume = 0.703 act!
Hydrograph Discharge Table
Time -- Outflow
(hrs cfs)
12.10 9.35«
...End
Hydrograph Report
Page 1
Hydraflow Hydrographs by Intelisolve
Hyd. No. 4
DA-4
Hydrograph type = SCS Runoff Peak discharge = 13.24 cfs
Storm frequency = 100 yrs Time interval = 3 min
Drainage area = 4.93 ac Curve number = 65
Basin Slope = 5.3 % Hydraulic length = 880 ft
T c method = LAG Time of conc. (Tc) = 19 min
Total precíp. = 6.00 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
--~--
---~_.,- -_._-------_._-------~----------_._---------.
".__.._------~._~_.-._--
Hydrograph Volume = 0.996 act!
Hydrograph Discharge Table
Time -- Outflow
(hrs cfs)
12.10 13.24«
...End
Hydrograph Report
Page 1
Hydraflow Hydrographs by Intelisolve
Hyd. No. 5
DA-5
Hydrograph type = SCS Runoff
Storm frequency = 1 00 yrs
Drainage area = 22.84 ac
Basin Slope = 3.6%
T c method = LAG
Total precip. = 6.00 in
Storm duration = 24 hrs
Peak discharge = 30.29 cfs
Time interval = 3 min
Curve number = 63
Hydraulic length = 1950 ft
Time of conc. (Tc) = 45.9 min
Distribution = Type II
Shape factor = 484
----..--------
---_._----_.._-_._-~----
------- -~ ~~-------_._- ------~_.-
Hydrograph Volume = 4.194 act!
Hydrograph Discharge Table
Time -- Outflow
(hrs cfs)
12.40 30.29 «
...End
Hydrograph Report
Page 1
Hydraflow Hydrographs by In!elisolve
Hyd. No. 6
DA-6
Hydrograph type = SCS Runoff
Storm frequency = 100 yrs
Drainage area = 0.64 ac
Basin Slope = 0.0%
T c method = USER
Total precip. = 6.00 in
Storm duration = 24 hrs
Peak discharge = 2.24 cfs
Time interval = 3 min
Curve number = 65
Hydraulic length = Oft
Time of conc. (T c) = 7 min
Distribution = Type II
Shape factor = 484
---..._._-_._--_.~._~~-~--
---.._--------- ---_..~._---_._..._..~-----_.._--------
Hydrograph Volume = 0.118 ad!
Hydrograph Discharge Table
Time -- Outflow
(hrs cfs)
11.95 2.24 «
...End
Hydrograph Report
Page 1
Hydraflow Hydrographs by Intelisolve
Hyd. No. 7
DA-7
Hydrograph type = SCS Runoff Peak discharge = 3.71 cfs
Storm frequency = 1 00 yrs Time interval = 3 min
Drainage area = 1.06 ac Curve number = 65
Basin Slope = 0.0 % Hydraulic length = Oft
T c method = USER Time of conc. (Tc) = 7 min
Total precip. = 6.00 in Distribution = Type II
Storm duration = 24 hrs Shape factor = 484
--~_.,_._-'-------'--------- ---"--'~------~'-'---- -- ---------
Hydrograph Volume = 0.195 acft
Hydrograph Discharge Table
Time -- Outflow
(hrs cfs)
11.95 3.71«
...End
Hydrograph Report
Page 1
Hydraflow Hydrographs by Intelisolve
Hyd. No. 8
DA-8
Hydrograph type = SCS Runoff Peak discharge = 7.34 cfs
Storm frequency = 1 00 yrs Time interval = 3 min
Drainage area = 2.10 ac Curve number = 65
Basin Slope = 0.0% Hydraulic length = Oft
T c method = USER Time of conc. (T c) = 7 min
Total precip. = 6.00 in Distribution = Type 1/
Storm duration = 24 hrs Shape factor = 484
.-----------..-.---...... .._------~
- ---_._--------_._-
-- --------
------- --~-~--- - -- ~
Hydrograph Volume = 0.386 acft
Hydrograph Discharge Table
Time -- Outflow
(hrs cfs)
11.95 7.34 «
...End
Hydrograph Report
Page 1
Hydraflow Hydrographs by Intelisolve
Hyd. No. 9
DA-9
Hydrograph type = SCS Runoff
Storm frequency = 100 yrs
Drainage area = 16.69 ac
Basin Slope = 0.0 %
T c method = USER
Total precip. = 6.00 in
Storm duration = 24 hrs
Peak discharge = 46.67 cfs
Time interval = 3 min
Curve number = 70
Hydraulic length = 0 ft
Time of conc. (T c) = 20 min
Distribution = Type II
Shape factor = 484
~--_._------_._.._-_._---~~-----_._---- ----------
Hydrograph Volume = 3.804 acft
Hydrograph Discharge Table
Time -- Outflow
(hrs cfs)
12.10 46.67«
...End
Hydrograph Report
Page 1
Hydratlow Hydrographs by Intelisolve
Hyd. No. 11
NURP PONDS
Hydrograph type
Storm frequency
Inflow hyd. No.
Max. Elevation
= Reservoir
= 1 00 yrs
= 9
= 1027.52 ft
Peak discharge
Time interval
Reservoir name
Max. Storage
= 8.41 cfs
= 3 min
= NURP PONDS
= 1.642 acft
.~------_.--_._- ---~--_..-- ----..----
-----_._--,.._--~_.. - -- --- -- ~-- -
Storage Indication method used_
Outflow hydrograph volume = 3_804 acft
Hydrograph Discharge Table
Time Inflow Elevation Clv A Clv B ClvC Clv D WrA WrB WrC WrD Exfil Outflow
(hrs) cfs ft cfs cfs cfs cfs cfs cfs cfs cfs cfs cfs
12.60 8.66 1027.52 « 8.41 8.41 «
...End
Reservoir Report
Page 1
Hydraflow Hydrographs by Intelisolve
Reservoir No. 1 - NURP PONDS
Pond Data
Pond storage is based on known contour areas. Average end area method used.
Stage I Storage Table
Stage (ft) Elevation (ft)
Contour area (sqft) Incr. Storage (acft)
Total storage (acft)
0.00
2.00
4.00
1024.00
1026.00
1028.00
15,755
20,585
25.605
- -------------------
Culvert I Orifice Structures
[A] [B] [C] [D]
Rise in 15.0 0.0 0.0 0.0
Span in 15.0 0.0 0.0 0.0
No. Barrels 1 0 0 0
Invert EI. ft 1024.00 0.00 000 0.00
Length ft 100.0 0.0 0.0 0.0
Slope % 0.50 000 0.00 0.00
N-Value .013 .000 .000 .000
Orif. Coeff. 0.60 0.00 0.00 0.00
Multi-Stage n/a No No No
Stage I Storage I Discharge Table
Stage Storage Elevation Clv A
ft acft ft cfs
Clv B
cfs
0.00
2.00
4.00
0.000
0.834
1.895
1024.00
1026.00
1028.00
0.00
5.65
9.10
-- - --------.------
0.000
0.834
1.060
0000
0.834
1.895
-~ _.' ._~--- ---------.------..-
_._-------_._-~._------_._---_.---
Weir Structures
[A] [B] [C] [D]
Crest Len ft 0.00 0.00 0.00 0.00
Crest EI. ft 0.00 0.00 0.00 0.00
Weir Coeff. 0.00 0.00 0.00 0.00
Weir Type
Multi-Stage No No No No
Exfiltration Rate = 0.00 in/hr/sqft Tailwater Elev. = 0.00 ft
---',------._----,-..
_._---
Note: All outflows have been analyzed under inlet and outlet control.
Clv C
cfs
Clv D
cfs
WrA
cfs
WrB
cfs
WrC
cfs
WrD
cfs
Exfil
cfs
Total
cfs
0.00
5.65
9.10
PROJECT TITLE:
PROJECT NO.:
DESIGNED BY:
DESIGNED DATE:
Pinehurst
2004-1064
Curtis N eft
09/17/04
Sediment Pond
Station Distance Sq. Ft. Ac. Ac-ft Cumm.
Contour Feet Area Area Stora2e Stora2e
1014 347.00 0.00797
2 0.039878 0.039878
1016 1,530.00 0.03512
2 O. 10 1973 0.141851
1018 2,993.00 0.06871
2 0.180175 0.322026
1020 4,936.00 0.11331
2 0.286412 0.608438
1022 7,638.00 0.17534
1 0.193252 0.801690
1023 9,223.00 0.21173
1 0.283382 1.085072
1024 15,755.00 0.36169
2 0.831784 1.916856
1026 20,585.00 0.47257
2 1.058283 2.975139
1028 25,605.00 0.58781
TOTAL 2.97514
PONDSIZ - Version 2.1 - W. Walker
INPUT VARIABLE UNITS
case title --------------->
watershed area acres
pervious curve number -
impervious fraction
design storm inches
antecedent moisture condo
pond maximum depth feet
bench width bc feet
bench slope bc fUft
side slope ab fUft
pond shape factor
length/width ratio
top length c feet
OUTPUT VARIABLE
target volume
design volume
UNITS
acre-ft
acre-ft
VALUES NOTES
Pond E
16.69
61 from SCS tables, for AMC=2
0.25
2.5 VLAWMO criterion = 2.5 inches
2 (1 ,2,or 3), VLAWMO criterion = 2
4 <=10ft
o >= 10ft
4 >= 10ft horiz / ft vertical
4 >= 3 ft horiz / ft vertical
3 1 =triangle,2=rectangle,3=ellipse
2 >= 3
140.00 adjust to achieve target volume
VALUE
1.07 = design storm runoff volume
1.08 should be >= target volume
PONDNET 2.1
W. Walker March 1989
INPUT VARIABLES....
case labels
watershed area
runoff coefficient
pond surface area
pond mean depth
upstream pond p load
upstream pond outflow
TITLE-->
UNITS
acres
acres
feet
Ibs/yr
ac-ftIyr
OUTPUT VARIABLES........
outflow p load Ibs/yr
outflow volume ac-ftIyr
outflow p conc ppb
pond removal %
total removal %
Pond A
16.69
0.25
0.36
3
o
o
9.230223
13.90833
244.1674
62.43778
62.43579
ASSUMED EXPORT FACTORS.............
period length yrs
period precipitation inches
runoff total p ppb
runoff ortho p/total p
relative decay rate
unit runoff
unit export
in/yr
Ibs/ac-y
0.5
20
650
0.3
1
10
1.472328
POND WATER BUDGETS......................
runoff ac-ftIyr 13.90833
upstream pond ac-ftIyr 0
total inflow ac-ftIyr 13.90833
outflow ac-ftIyr 13.90833
POND PHOSPHORUS BUDGETS...................
runoff Ibs/yr 24.57315
upstream pond Ibs/yr 0
total inflow Ibs/yr 24.57315
net sedimentation Ibs/yr 15.34293
outflow Ibs/yr 9.230223
HYDRAULIC PARAMETERS............
pond volume acre-ft
vlawmo pond volume acre-ft
relative volume inches
residence time years
residence time days
overflow rate ftIyr
inflow phos conc ppb
outflow phos conc ppb
p reaction rate
1-rp
1.08
0.869271
3.106052
0.077651
28.34272
38.63426
650.0344
244.1674
4.425322
0.375622