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STORMWATER MANAGEMENT PLAN
RIDGEMONT AVENUE LOT SPLIT
FOR
JOHN MAHONEY CONSTRUCTION, INC.
July 2, 1990
Prepared by
VALLEY ENGINEERING CO., INC.
16670 Franklin Trail SE - suite l20C
Prior Lake, MN 55372
STORMWATER MANAGEMENT PLAN
RIDGEMONT AVENUE LOT SPLIT
FOR
JOHN MAHONEY CONSTRUCTION, INC.
JULY 2, 1990
I hereby certify that this report was prepared by me or under
my direct supervision and that I am a duly Registered Engineer
under the Laws of the State of "nnesota.
tJ;!r
2-,19'0
I
Reg. No. 11052
Date:
SUMMARY AND CONCLUSIONS:
John Mahoney Construction Inc. proposes to build two single-family homes on
Ridgemont Avenue in Hannan 2nd Addition. Because the proposal requires a lot-
split the stormwater runoff is subject to Prior Lake's Subdivision Standards.
Accordingly the proposed housing development must not increase the rate of runoff
from the present condition. On-site ponding is needed for this condition to be met.
Calculation of the stormwater runoff is in accordance with the "TR-55" Method.
The difference in runoff before and after development is 0.57 inches for the 100
year event. It should be noted that much of the wooded area on the property must
be cleared in order to construct the on-site ponds. The 100 year peak rate of
runoff would increase from 1 cfs to 2 cfs without ponding.
TWo retention ponds are proposed as shown in the Grading and Drainage Plan.
These ponds are designed to retain the runoff from a 6 inch 100 year storm.
The storage volume required is 0.57 inches X 0.87 acres z 1800 cubic feet. The
storage available ,in,-Uie '.two ,ponds is 1815 cubic feet. With ponding the 100 year
peak runoff from the site will be 1 cfs, the same as the present condition rate.
TR-55 CURVE NUMBER COMPUTATION
VERSION 1.11
Project :
County
Subtitle:
Subarea :
LOT SPLIT HANNAN 2ND ADD'N.
SCOTT State: MN
JOHN MAHONEY CONSTRUCTION PROPOSAL
EXIST
User:
Checked:
sdh
Date:
Date:
06-26-90
----------------------------------~--------------------------------------------
COVER DESCRIPTION
A
Hydrologic Soil Group
BCD
Acres (CN)
-------------------------------------------------------------------------------
FULLY DEVELOPED URBAN AREAS (Veg Estab.)
Open space (Lawns,parks etc.)
Good condition; grass cover> 75%
0.04(61)
OTHER AGRICULTURAL LANDS
Woods
good
0.83(55)
Total Area (by Hydrologic Soil Group)
.87
-------------------------------------------------------------------------------
SUBAREA: EXIST TOTAL DRAINAGE AREA: .87 Acres
WEIGHTED CURVE NUMBER:55
-------------------------------------------------------------------------------
Project :
County
Subtitle:
Subarea ;
TR-SS CURVE NUMBER COMPUTATION
LOT SPLIT HANNAN 2ND ADD'N.
SCOTT State: MN
JOHN MAHONEY CONSTRUCTION PROPOSAL
DEVEL
COVER DESCRIPTION
FULLY DEVELOPED URBAN AREAS (Veg Estab.)
Open space (Lawns,parks etc.)
Good condition; grass cover> 75%
Impervious Areas
Paved parking lots, roofs, driveways
OTHER AGRICULTURAL LANDS
Woods
good
Total Area (by Hydrologic Soil Group)
VERSION 1.11
User:
Checked:
sdh
Date: 06-26-90
Date:
A
Hydrologic Soil Group
BCD
Acres (CN)
0.42(61)
0.16(98)
0.29(55)
.87
c:::::=
SUBAREA: DEVEL TOTAL DRAINAGE AREA: .87 Acres
WEIGHTED CURVE NUMBER:66
TR-55 Tc and Tt THRU SUBAREA COMPUTATION
Project: LOT SPLIT HANNAN 2ND ADD'N.
County SCOTT State: MN
Subtitle: JOHN MAHONEY CONSTRUCTION PROPOSAL
------------------------------ Subarea *1 - EXIST
Flow Type 2 year Length Slope Surface n
rain (ft) (ft/ft) code
Sheet
2.8
160
.15
I
0.433
Time of Concentration = 0.43*
------------------------------ Subarea *2 - DEVEL
Flow Type 2 year Length Slope Surface n
rain (ft) (ft/ft) code
Sheet
2.8
250
--- Sheet Flow Surface
A Smooth Surface
B Fallow (No Res.)
C Cultivated < 20 % Res.
D Cultivated> 20 % Res.
E Grass-Range, Short
.0593
F
0.343
Time of Concentration = 0.34*
Codes ---
F Grass, Dense
G Grass, Burmuda
H Woods, Light
I Woods, Dense
* - Generated for use by TABULAR method
User: sdh
Checked:
Area
(sq/ft)
Area
(sq/ft)
Wp
(ft)
Wp
(ft)
VERSION 1.11
Date: 06-26-90
Date:
Velocity
(ft/sec)
Velocity
(ft/sec)
Shallow Concentrated
Surface Codes
P Paved
U Unpaved
Time
(h r )
=-====
Time
(h r )
=====
TR-55 TABULAR DISCHARGE METHOD
VERSION 1.11
Project: LOT SPLIT HANNAN 2ND ADD'N.
County SCOTT State: MN
Subtitle: JOHN MAHONEY CONSTRUCTION PROPOSAL
User: sdh
Checked:
Date: 06-26-90
Date:
Total watershed area: 0.002 sq mi Rainfall type: II Frequency: 100 years
-------------------------- Subareas --------------------------
Area(sq mi)
Rainfall(in)
Curve number
Runoff(in)
Tc (hrs)
(Used)
TimeToOutlet
Ia/P
Time
(hr)
Total
Flow
11.0 0
11.3 0
11.6 0
11.9 0
12.0 1
12.1 1
12.2 2
12.3 3P
12.4 3
12.5 2
12.6 1
12.7 1
12.8 0
13.0 0
13.2 0
13.4 0
13.6 0
13.8 0
14.0 0
14.3 0
14.6 0
15.0 0
15.5 0
16.0 0
16.5 0
17.0 0
17.5 0
18.0 0
19.0 0
20.0 0
22.0 0
26.0 0
P - Peak Flow
EXIST
0.00
6.0
55*
1. 52
0.43*
0.40
0.00
0.27
DEVEL
0.00*
6.0
66*
2.44
0.34*
0.30
0.00
0.17
Subarea Contribution to Total Flow (cfs) ------------
EXIST OEVEL
0 0
0 0
0 0
0 0
0 1
0 1
0 2P
1P 2
1 2
1 1
0 1
0 1
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
0 0
* - value(s)
provided from TR-55 system routines
TR-55 CURVE NUMBER COMPUTATION
VERSION 1.11
Project :
County
Subtitle:
Subarea :
LOT SPLIT HANNAN 2ND ADDITION
SCOTT State: MN
UPPER POND
UPPER
User:
Checked:
sdh
Date: 06-28-90
Date:
COVER DESCRIPTION
A
Hydrologic Soil Group
BCD
Acres (CN)
FULLY DEVELOPED URBAN AREAS (Veg Estab.)
Open space (Lawns,parks etc.)
Good condition; grass cover) 75%
.20(61)
Impervious Areas
Paved parking lots, roofs, driveways
.07(98)
OTHER AGRICULTURAL LANDS
Woods
good
.05(55)
Total Area (by Hydrologic Soil Group)
.32
SUBAREA: UPPER TOTAL DRAINAGE AREA: .32 Acres
WEIGHTED CURVE NUMBER:68*
* - Generated for use by GRAPHIC method
TR-55 Tc and Tt THRU SUBAREA COMPUTATION
Project : LOT SPLIT HANNAN 2ND ADDITION
County SCOTT State: MN
Subtitle: UPPER POND
Flow Type
Length
(ft)
2 year
rain
Sheet
Sheet
2.8
50
10
--- Sheet Flow Surface
A Smooth Surface
B Fallow (No Res.)
C Cultivated < 20 % Res.
D Cultivated> 20 % Res.
E Grass-Range, Short
Slope
(ft/ft)
Surface
code
.15
.40
I
F
Codes ---
F Grass, Dense
G Grass, Burmuda
H Woods. Light
I Woods. Dense
* - Generated for use by GRAPHIC method
VERSION 1.11
User: sdh
Checked:
Date: 06-28-90
Date:
n
Area
(sq/ft)
Velocity
(ft/sec)
Wp
(ft)
Time
(hr)
0.171
0.012
Time of Concentration = 0.18*
Shallow Concentrated
Surface Codes
P Paved
U Unpaved
==z:==
TR-55 GRAPHICAL DISCHARGE METHOD
Project : LOT SPLIT HANNAN 2ND ADDITION
County SCOTT State: MN
Subtitle: UPPER POND
Data: Drainage Area
Runoff Curve Number
Time of Concentration:
Rainfall Type
Pond and Swamp Area
.32 * Acres
68 *
0.18 * Hours
II
NONE
=========a===================================
Storm Number I 1 1 2 I 3 I
----------------------1------1------1------1
Frequency (yrs) I 2 I 10 I 100 I
I I I I
24-Hr Rainfall (in) I 2.8 1 4.2 I 6 I
I I 1 I
Ia/P Ratio I 0.34 I 0.22 I 0.16 I
I I I I
Runoff (in) I 0.53 I 1.33 I 2.62 I
I I I I
Unit Peak Discharge 11.078 11.203 11.256 I
(cfs/acre/in) I I I I
I I 1 I
Pond and Swamp Factorl 1.00 1 1.00 I 1.00 I
0.0% Ponds Used I I I I
----------------------1------1------1------1
Peak Discharge (cfs) I 0 I 1 I 1 I
=============================================
* - Value(s) provided from TR-55 system routines
User: sdh
Checked:
VERSION 1.11
Date: 06-28-90
Date:
TR-55 STORAGE VOLUME FOR DETENTION BASINS
VERSION 1.11
Project : LOT SPLIT HANNAN 2ND ADDITION
County SCOTT State: MN
Subtitle: UPPER POND
User: sdh
Checked:
Date: 06-28-90
Date:
Drainage Area: .32
Rainfall-Type: II
Runoff: 2.6 inches
Peak Inflow: 1.053299
Detention Basin Storage
Peak Outflow: 1 cfs
Acres
Rainfall Frequency: 100 years
cfs
Volume:
.019 acre-feet
TR-SS CURVE NUMBER COMPUTATION
VERS ION 1. 11
Project:
County
Subtitle:
Subarea :
LOT SPLIT
SCOTT
UPPER AND
UPPER
HANNAN 2ND ADD'N
State: MN
LOWER POND AREAS CO~BINED
User:
Checked:
sdh
Date: 06-28-90
Date:
-------------------------------------------------------------------------------
COVER DESCRIPTION
A
Hydrologic Soil Group
BCD
Acres (CN)
-------------------------------------------------------------------------------
FULLV DEVELOPED URBAN AREAS (Veg Estab.)
Open space (Lawns.parks etc.)
Good condition; grass cover> 75%
.20(61)
Impervious Areas
Paved parking lots, roofs, driveways
.07(98)
OTHER AGRICULTURAL LANDS
Woods
good
.05(55)
Total Area (by Hydrologic Soil Group)
.32
=:-===
-------------------------------------------------------------------------------
SUBAREA: UPPER TOTAL DRAINAGE AREA: .32 Acres
WEIGHTED CURVE NUMBER:68
-------------------------------------------------------------------------------
Project :
County
Subtitle:
Subarea :
LOT SPLIT
SCOTT
UPPER AND
LOWER
TR-SS CURVE NUMBER COMPUTATION
HANNAN 2ND ADD'N
State: MN
LOWER POND AREAS COMBINED
COVER DESCRIPTION
FULLY DEVELOPED URBAN AREAS (Veg Estab.)
Open space (Lawns,parks etc.)
Good condition; grass cover> 75%
Impervious Areas
Paved parking lots, roofs. driveways
Total Area (by Hydrologic Soil Group)
VERSION 1.11
User: sdh
Checked:
Date: 06-28-90
Date:
A
Hydrologic Soil Group
BCD
Acres (CN)
.12(61)
.07(98)
.19
--:::=:
SUBAREA: LOWER TOTAL DRAINAGE AREA: .19 Acres
WEIGHTED CURVE NUMBER:75
TR-55 Tc and Tt THRU SUBAREA COMPUTATION
VERSION 1.11
Date: 06-28-90
Date:
Project: LOT SPLIT HANNAN 2ND ADD'N User: sdh
County SCOTT state: MN Checked:
Subtitle: UPPER AND LOWER POND AREAS COMBINED
Flow Type
2 year
rain
Length
(ft)
______________________________ Subarea 11 - UPPER
Slope Surface n
(ft/ft) code
-----------------------------
Area
(sq/ft)
Wp
(ft)
Velocity
(ft/sec)
Time
(hr)
-------------------------------------------------------------------------------
Sheet
Sheet
2.8
50
10
.15
.40
I
F
0.171
0.012
Time of Conce.ntration lit 0.18*
______________________________ Subarea *2 - LOWER
Flow Type 2 year Length Slope Surface n
rain (ft) (ft/ft) code
=-===
-----------------------------
Area
(sq/ft)
Wp
(ft)
Velocity
(ft/sec)
Time
(hr)
Sheet
Sheet
2.8
-------------------------------------------------------------------------------
50
10
--- Sheet Flow Surface
A Smooth Surface
B Fallow (No Res.)
C Cultivated < 20 % Res.
D Cultivated) 20 % Res.
E Grass-Range, Short
.15
.40
I
F
Codes ---
F Grass, Dense
G Grass, Burmuda
H Woods, Light
I Woods, Dense
* - Generated for use by TABULAR method
0.171
0.012
Time of Concentration - 0.18*
Shallow Concentrated
Surface Codes
P Paved
U Unpaved
==--==
TR-55 TABULAR DISCHARGE METHOD
VERSION 1.11
Project: LOT SPLIT HANNAN 2ND ADD'N
County SCOTT State: MN
Subtitle: UPPER AND LOWER POND AREAS COMBINED
User: sdh
Checked:
Date: 06-28-90
Date:
Total watershed area: 0.001 sq mi Rainfall type: II Frequency: 100 years
-------------------------- Subareas --------------------------
UPPER LOWER
Area(sq mi) 0.00* 0.00
Rainfall(in) 6.0 6.0
Curve number 68* 75*
Runoff(in) 2.62 3.28
Tc (hrs) 0.18* 0.18*
(Used) 0.20 0.20
TimeToOutlet 0.00 0.00
Ia/P 0.16 0.11
Time Total -------------
(hr) Flow UPPER LOWER
11. 0 0 0 0
11.3 0 0 0
11.6 0 0 0
11.9 0 0 0
12.0 0 0 0
12.1 2P 1P 1P
12.2 2 1 1
12.3 1 1 0
Subarea Contribution to Total Flow (cfs) ------------
12.4 0 0 0
12.5 0 0 0
12.6 0 0 0
12.7 0 0 0
12.8 0 0 0
13.0 0 0 0
13.2 0 0 0
13.4 0 0 0
13.6 0 0 0
13.8 0 0 0
14.0 0 0 0
14.3 0 0 0
14.6 0 0 0
15.0 0 0 0
15.5 0 0 0
16.0 0 0 0
16.5 0 0 0
17.0 0 0 0
17.5 0 0 0
18.0 0 0 0
19.0 0 0 0
20.0 0 0 0
22.0 0 0 0
26.0 0 0 0
p - Peak Flow * - value(s) provided from TR-55 system routines
TR-55 STORAGE VOLUME FOR DETENTION BASINS
Project: LOT SPLIT HANNAN 2ND ADD'N
County SCOTT State: MN
Subtitle: UPPER AND LOWER POND AREAS COMBINED
User:
Checked:
sdh
VERSION 1.11
Date: 06-28-90
Date:
Drainage Area: .51 Acres Rainfall Frequency: 100 years
Rainfall-Type: II
24-Hour Rainfall: 6 inches Runoff Curve Number: 71
Peak Inflow: 2 cfs
Detention Basin Storage Volume: 1.17 inches
Runoff Volume: 2.9 inches
Peak Outflow: 1 cfs
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