1. 1 of 7
Post-Development
Memo
Empire Engineering, Inc.
555 Five St.
Over there, Florida 77777
Phone: (407) 555-5555
To: Larry Wray, P.E.
Jeremy Morton, P.E.
CC:
From: Empire Engineering, Inc.
Date: 6/16/2015
RE: POST-DEVELOPMENT STORMWATER REPORT
Capstone Senior Design
1. Post-Development Basin Map
a. Basin Divide Lines and Names
i. The basins were divided up based on the two dry retention ponds placed
on our site. Basin 1 flows into pond 1 which is our larger pond by
volume located at the south east portion of our property while basin 2
flows to pond 2 which is located on the north portion of our property by
the apartment complex.

2. 2 of 7
b. Node Names
i. Each of the basins led to a node which was a pond. Basin 1 leads to pond 1
and basin 2 leads to pond 2. Each pond then leads to its boundary node with
Pond 1 going to OBT 1 and Pond 2 going to OBT 2.

3. 3 of 7
c. Tc Paths
i. For the Tc paths we just had the flow of rainfall to drain towards our ponds
split at the basin divide line.
*Flow example for pond 1

4. 4 of 7
2. Nodal Diagram
a. A nodal diagram was generated in Microsoft paint to help visualize the basin
and node paths and this also was helpful as a reference for developing nodes and
basins in the ICPR program.

5. 5 of 7
3. Basin Composite CN Calculation Tables
a. We had to calculate the DCIA% and change our composite curve number using
developed area curve numbers and good soil for open space for what we called
our “pre-post” development. This means the property had impervious and
changed basin divides all in order to size our pond correctly. As stated in table
2-2a of the TR-55 for open space and an A hydrologic soil group in good
condition there were 3 different curve numbers that were applicable. We
chose good under the assumption that most of the property was grass and that
had a curve # of 39 (this included the pond area because we chose dry retention
ponds) and our developed area (impervious) had a curve number of 98.
Area IA DCIA %DCIA Sq. Ft Acres
Basin 1 40.27 13.75 10.04 24.9 Apt. 19224.14 0.441
Basin 2 21.05 10.57 3.65 17.3 Office 39025 0.896
retail 45796 1.05
Pond 1 262934.8 3.21
Pond 2 76000 1.41
Basin 1 Basin 2
Open Space Impervious Non-DCIA Open
Space
Impervious Non-
DCIA
CN 39 98 98 CN 39 98 98
Acres 26.52 13.75 3.71 Acres 10.48 10.57 6.92
CN-Acre 1034.28 363.58 CN-
Acre
408.72 678.16
Composite CN 46.24 Composite CN 62.46
4. Time of Concentration Calculations
a. The Tc calculations (time of concentration) were assumed to be 10 minutes
for a developed area.

6. 6 of 7
5. Water Quality Calculations
a. SJRWMD Applicant’s Handbook Requirement
i. Based off the applicant’s handbook for the St. John’s River Water
Management District the treatment volume is retention of the first
one-half inch of runoff or 1.25 inches of runoff from the
impervious area, whichever is greater for an offline system and
additional one half inch of runoff from the drainage area over that
volume specified for off-line treatment for an online system which
is what we have.
Basin 1
Treatment Volume 1" of runoff over drainage area = 3.36 acre-ft
1.25" runoff over impervious area = 1.43 acre-ft
Basin 2
Treatment Volume 1" of runoff over drainage area = 1.75 acre-ft
1.25" runoff over impervious area = 1.10 acre-ft
b. Pond Stage, Area and Volume
i. For each pond we ran an ICPR report known as “pre-post” before
the ponds were “developed” to get a flow to size our ponds to a
correct depth.
ii. It was then decided that 40% of our runoff would be retained
with the rest being sent to the boundary and this was to help stage
the pond and set the peak warning stage.
40% Runoff Retention
Runoff (in) Area (acre) V (acre-ft)
Basin 1 1.4548 40.27 4.88
Basin 2 1.8676 21.05 3.28
This gave us a way to set a proper stage for each pond using a 4:1 sloping ratio in each basin
and allowed us to see if our depth would be allowable given the bore samples water table
levels.
Runoff (in) Area (acre) V (acre-ft)
Basin 1 3.637 40.27 12.21
Basin 2 4.669 21.05 8.19

7. 7 of 7
Pond 1
Stage (ft) Length (ft) Width (ft)
Area (sq
ft)
Volume (per 1
ft h)
Cumulative
Volume (cubic
ft)
Cumulative
Volume (Acre-
ft)
94 350 200 70000 67832 297720 6.835
93 342 192 65664 63560 229888 5.278
92 334 184 61456 59416 166328 3.818
91 326 176 57376 55400 106912 2.454
90 318 168 53424 51512 51512 1.183
89 310 160 49600 0 0 0.000
Peak Stage (WQV is provided here)
92.73 4.88
Pond 2
Stage (ft) Length (ft) Width (ft)
Area (sq
ft)
Volume (per 1
ft h)
Cumulative
Volume (cubic
ft)
Cumulative
Volume (Acre-ft)
126 350 250 87500 85132 380220 8.729
125 342 242 82764 80460 295088 6.774
124 334 234 78156 75916 214628 4.927
123 326 226 73676 71500 138712 3.184
122 318 218 69324 67212 67212 1.543
121 310 210 65100 0 0 0.000
Peak Stage (WQV is provided here)
123.11 3.28

8. 6. Pond Design

9. 7. Stormwater Pipe Network Design(2 pipes and 2 inlets)
Pipe Sizing Calculations
Inlet 1)
𝑄 = 𝑐𝑖𝐴
𝑄1 = (0.9)(8.5
𝑖𝑛
ℎ𝑟
)(0.551 𝑎𝑐) = 4.22 𝑐𝑓𝑠
Inlet 2)
𝑄 = (0.9)(8.5
𝑖𝑛
ℎ𝑟
)(0.574 𝑎𝑐) = 4.39 𝑐𝑓𝑠
𝑄2 = 4.22 + 4.39 = 8.61 𝑐𝑓𝑠
Pipe 1)
𝑄 =
1.49
𝑛
𝐴𝑅
2
3 √𝑆
4.22 = (
1.49
0.013
)(
𝜋𝑑2
4
)(
𝑑
4
)
2
3
√0.02
𝑑1 = 0.94 𝑓𝑡 = 11.2 𝑖𝑛
Use 12” RCP
Pipe 2)
8.61 = (
1.49
0.013
)(
𝜋𝑑2
4
)(
𝑑
4
)
2
3
√0.02
𝑑2 = 1.22 𝑓𝑡 = 14.7 𝑖𝑛
Use 15” RCP

10. 8. ICPR Input Report
==========================================================================================
==== Basins ==============================================================================
==========================================================================================
Name: Basin 1 Node: Pond 1 Status: Onsite
Group: BASE Type: SCS Unit Hydrograph CN
Unit Hydrograph: Uh256 Peaking Factor: 256.0
Rainfall File: Storm Duration(hrs): 0.00
Rainfall Amount(in): 0.000 Time of Conc(min): 10.00
Area(ac): 40.270 Time Shift(hrs): 0.00
Curve Number: 46.24 Max Allowable Q(cfs): 999999.000
DCIA(%): 25.00
----------------------------------------------------------------------------------------------------
Name: Basin 2 Node: Pond 2 Status: Onsite
Group: BASE Type: SCS Unit Hydrograph CN
Unit Hydrograph: Uh256 Peaking Factor: 256.0
Rainfall File: Storm Duration(hrs): 0.00
Rainfall Amount(in): 0.000 Time of Conc(min): 10.00
Area(ac): 21.050 Time Shift(hrs): 0.00
Curve Number: 62.50 Max Allowable Q(cfs): 999999.000
DCIA(%): 17.00
==========================================================================================
==== Nodes ===============================================================================
==========================================================================================
Name: OBT 1 Base Flow(cfs): 0.000 Init Stage(ft): 89.000
Group: BASE Warn Stage(ft): 104.000
Type: Time/Stage
Time(hrs) Stage(ft)
--------------- ---------------
0.00 89.000
12.00 89.700
24.00 89.400
------------------------------------------------------------------------------------------
Name: OBT 2 Base Flow(cfs): 0.000 Init Stage(ft): 89.000

11. Group: BASE Warn Stage(ft): 104.000
Type: Time/Stage
Time(hrs) Stage(ft)
--------------- ---------------
0.00 89.000
12.00 89.700
24.00 89.400
------------------------------------------------------------------------------------------
Name: Pond 1 Base Flow(cfs): 0.000 Init Stage(ft): 89.000
Group: BASE Warn Stage(ft): 93.000
Type: Stage/Area
Stage(ft) Area(ac)
--------------- ---------------
89.000 1.1400
90.000 1.2300
91.000 1.3200
92.000 1.4100
93.000 1.5100
94.000 1.6100
------------------------------------------------------------------------------------------
Name: Pond 2 Base Flow(cfs): 0.000 Init Stage(ft): 121.000
Group: BASE Warn Stage(ft): 125.000
Type: Stage/Area
Stage(ft) Area(ac)
--------------- ---------------
121.000 1.4900
122.000 1.5900
123.000 1.6900
124.000 1.7900
125.000 1.9000
126.000 2.0100
==========================================================================================
==== Drop Structures =====================================================================
==========================================================================================
Name: Drop 1 From Node: Pond 1 Length(ft): 160.00
Group: BASE To Node: OBT 1 Count: 1

12. UPSTREAM DOWNSTREAM Friction Equation: Automatic
Geometry: Circular Circular Solution Algorithm: Most Restrictive
Span(in): 24.00 24.00 Flow: Both
Rise(in): 24.00 24.00 Entrance Loss Coef: 0.000
Invert(ft): 92.730 88.000 Exit Loss Coef: 1.000
Manning's N: 0.013000 0.013000 Outlet Ctrl Spec: Use dc or tw
Top Clip(in): 0.000 0.000 Inlet Ctrl Spec: Use dc
Bot Clip(in): 0.000 0.000 Solution Incs: 10
Upstream FHWA Inlet Edge Description:
Circular Concrete: Square edge w/ headwall
Downstream FHWA Inlet Edge Description:
Circular Concrete: Square edge w/ headwall
*** Weir 1 of 2 for Drop Structure Drop 1 ***
TABLE
Count: 1 Bottom Clip(in): 0.000
Type: Vertical: Mavis Top Clip(in): 0.000
Flow: Both Weir Disc Coef: 3.200
Geometry: Rectangular Orifice Disc Coef: 0.600
Span(in): 10.00 Invert(ft): 92.730
Rise(in): 12.00 Control Elev(ft): 92.730
*** Weir 2 of 2 for Drop Structure Drop 1 ***
TABLE
Count: 1 Bottom Clip(in): 0.000
Type: Horizontal Top Clip(in): 0.000
Flow: Both Weir Disc Coef: 3.200
Geometry: Rectangular Orifice Disc Coef: 0.600
Span(in): 24.00 Invert(ft): 93.730
Rise(in): 36.00 Control Elev(ft): 93.730
----------------------------------------------------------------------------------------------------
Name: Drop 2 From Node: Pond 2 Length(ft): 400.00
Group: BASE To Node: OBT 2 Count: 1
UPSTREAM DOWNSTREAM Friction Equation: Automatic
Geometry: Circular Circular Solution Algorithm: Most Restrictive
Span(in): 24.00 24.00 Flow: Both
Rise(in): 24.00 24.00 Entrance Loss Coef: 0.000
Invert(ft): 124.040 122.000 Exit Loss Coef: 1.000
Manning's N: 0.013000 0.013000 Outlet Ctrl Spec: Use dc or tw
Top Clip(in): 0.000 0.000 Inlet Ctrl Spec: Use dc
Bot Clip(in): 0.000 0.000 Solution Incs: 10

13. Upstream FHWA Inlet Edge Description:
Circular Concrete: Square edge w/ headwall
Downstream FHWA Inlet Edge Description:
Circular Concrete: Square edge w/ headwall
*** Weir 1 of 2 for Drop Structure Drop 2 ***
TABLE
Count: 1 Bottom Clip(in): 0.000
Type: Vertical: Mavis Top Clip(in): 0.000
Flow: Both Weir Disc Coef: 3.200
Geometry: Rectangular Orifice Disc Coef: 0.600
Span(in): 10.00 Invert(ft): 124.040
Rise(in): 12.00 Control Elev(ft): 124.040
*** Weir 2 of 2 for Drop Structure Drop 2 ***
TABLE
Count: 1 Bottom Clip(in): 0.000
Type: Horizontal Top Clip(in): 0.000
Flow: Both Weir Disc Coef: 3.200
Geometry: Rectangular Orifice Disc Coef: 0.600
Span(in): 24.00 Invert(ft): 125.040
Rise(in): 36.00 Control Elev(ft): 125.040
==========================================================================================
==== Hydrology Simulations ===============================================================
==========================================================================================
Name: 2.3yr24hrFLMOD
Filename: D:Icpr post2.3yr24hrFLMOD.R32
Override Defaults: Yes
Storm Duration(hrs): 24.00
Rainfall File: Flmod
Rainfall Amount(in): 4.55
Time(hrs) Print Inc(min)
--------------- ---------------
24.000 5.00
----------------------------------------------------------------------------------------------------
Name: 25yr24hrFLMOD
Filename: D:Icpr post25yr24hrFLMOD.R32

14. Override Defaults: Yes
Storm Duration(hrs): 24.00
Rainfall File: Flmod
Rainfall Amount(in): 8.40
Time(hrs) Print Inc(min)
--------------- ---------------
24.000 5.00
----------------------------------------------------------------------------------------------------
Name: 25yr24hrOrange
Filename: D:Icpr post25yr24hrOrange.R32
Override Defaults: Yes
Storm Duration(hrs): 24.00
Rainfall File: Orange
Rainfall Amount(in): 8.40
Time(hrs) Print Inc(min)
--------------- ---------------
24.000 5.00
==========================================================================================
==== Routing Simulations =================================================================
======================================================================================== ==
Name: 2.3yr24hrFLMOD Hydrology Sim: 2.3yr24hrFLMOD
Filename: D:Icpr post2.3yr24hrFLMOD.I32
Execute: Yes Restart: No Patch: No
Alternative: No
Max Delta Z(ft): 1.00 Delta Z Factor: 0.00500
Time Step Optimizer: 10.000
Start Time(hrs): 0.000 End Time(hrs): 24.00
Min Calc Time(sec): 0.5000 Max Calc Time(sec): 60.0000
Boundary Stages: Boundary Flows:
Time(hrs) Print Inc(min)
--------------- ---------------
999.000 15.000
Group Run
--------------- -----
BASE Yes
----------------------------------------------------------------------------------------------------

15. Name: 25yr24hrFLMOD Hydrology Sim: 25yr24hrFLMOD
Filename: D:Icpr post25yr24hrFLMOD.I32
Execute: Yes Restart: No Patch: No
Alternative: No
Max Delta Z(ft): 1.00 Delta Z Factor: 0.00500
Time Step Optimizer: 10.000
Start Time(hrs): 0.000 End Time(hrs): 24.00
Min Calc Time(sec): 0.5000 Max Calc Time(sec): 60.0000
Boundary Stages: Boundary Flows:
Time(hrs) Print Inc(min)
--------------- ---------------
999.000 15.000
Group Run
--------------- -----
BASE Yes
----------------------------------------------------------------------------------------------------
Name: 25yr24hrOrange Hydrology Sim: 25yr24hrOrange
Filename: D:Icpr post25yr24hrOrange.I32
Execute: Yes Restart: No Patch: No
Alternative: No
Max Delta Z(ft): 1.00 Delta Z Factor: 0.00500
Time Step Optimizer: 10.000
Start Time(hrs): 0.000 End Time(hrs): 24.00
Min Calc Time(sec): 0.5000 Max Calc Time(sec): 60.0000
Boundary Stages: Boundary Flows:
Time(hrs) Print Inc(min)
--------------- ---------------
999.000 15.000
Group Run
--------------- -----
BASE Yes
9. ICPR Hydrology Basin Summary Report
Basin Name: Basin 1
Group Name: BASE

16. Simulation: 2.3yr24hrFLMOD
Node Name: Pond 1
Basin Type: SCS Unit Hydrograph
Unit Hydrograph: Uh256
Peaking Fator: 256.0
Spec Time Inc (min): 1.33
Comp Time Inc (min): 1.33
Rainfall File: Flmod
Rainfall Amount (in): 4.550
Storm Duration (hrs): 24.00
Status: Onsite
Time of Conc (min): 10.00
Time Shift (hrs): 0.00
Area (ac):40.270
Vol of Unit Hyd (in): 1.000
Curve Number: 46.240
DCIA (%):25.000
Time Max (hrs): 12.04
Flow Max (cfs): 29.08
Runoff Volume (in): 1.380
Runoff Volume (ft3): 201733
--------------------------------------------------------------------------------
Basin Name: Basin 2
Group Name: BASE
Simulation: 2.3yr24hrFLMOD
Node Name: Pond 2
Basin Type: SCS Unit Hydrograph
Unit Hydrograph: Uh256
Peaking Fator: 256.0
Spec Time Inc (min): 1.33
Comp Time Inc (min): 1.33
Rainfall File: Flmod
Rainfall Amount (in): 4.550
Storm Duration (hrs): 24.00
Status: Onsite
Time of Conc (min): 10.00
Time Shift (hrs): 0.00
Area (ac):21.050
Vol of Unit Hyd (in): 1.000
Curve Number: 62.500

17. DCIA (%):17.000
Time Max (hrs): 12.07
Flow Max (cfs): 22.80
Runoff Volume (in): 1.752
Runoff Volume (ft3): 133882
--------------------------------------------------------------------------------
Basin Name: Basin 1
Group Name: BASE
Simulation: 25yr24hrFLMOD
Node Name: Pond 1
Basin Type: SCS Unit Hydrograph
Unit Hydrograph: Uh256
Peaking Fator: 256.0
Spec Time Inc (min): 1.33
Comp Time Inc (min): 1.33
Rainfall File: Flmod
Rainfall Amount (in): 8.400
Storm Duration (hrs): 24.00
Status: Onsite
Time of Conc (min): 10.00
Time Shift (hrs): 0.00
Area (ac):40.270
Vol of Unit Hyd (in): 1.000
Curve Number: 46.240
DCIA (%):25.000
Time Max (hrs): 12.07
Flow Max (cfs): 88.76
Runoff Volume (in): 3.637
Runoff Volume (ft3): 531706
--------------------------------------------------------------------------------
Basin Name: Basin 2
Group Name: BASE
Simulation: 25yr24hrFLMOD
Node Name: Pond 2
Basin Type: SCS Unit Hydrograph
Unit Hydrograph: Uh256

18. Peaking Fator: 256.0
Spec Time Inc (min): 1.33
Comp Time Inc (min): 1.33
Rainfall File: Flmod
Rainfall Amount (in): 8.400
Storm Duration (hrs): 24.00
Status: Onsite
Time of Conc (min): 10.00
Time Shift (hrs): 0.00
Area (ac):21.050
Vol of Unit Hyd (in): 1.000
Curve Number: 62.500
DCIA (%):17.000
Time Max (hrs): 12.04
Flow Max (cfs): 66.01
Runoff Volume (in): 4.669
Runoff Volume (ft3): 356769
--------------------------------------------------------------------------------
Basin Name: Basin 1
Group Name: BASE
Simulation: 25yr24hrOrange
Node Name: Pond 1
Basin Type: SCS Unit Hydrograph
Unit Hydrograph: Uh256
Peaking Fator: 256.0
Spec Time Inc (min): 1.33
Comp Time Inc (min): 1.33
Rainfall File: Orange
Rainfall Amount (in): 8.400
Storm Duration (hrs): 24.00
Status: Onsite
Time of Conc (min): 10.00
Time Shift (hrs): 0.00
Area (ac):40.270
Vol of Unit Hyd (in): 1.000
Curve Number: 46.240
DCIA (%):25.000
Time Max (hrs): 9.02
Flow Max (cfs): 32.81
Runoff Volume (in): 3.637

19. Runoff Volume (ft3): 531710
--------------------------------------------------------------------------------
Basin Name: Basin 2
Group Name: BASE
Simulation: 25yr24hrOrange
Node Name: Pond 2
Basin Type: SCS Unit Hydrograph
Unit Hydrograph: Uh256
Peaking Fator: 256.0
Spec Time Inc (min): 1.33
Comp Time Inc (min): 1.33
Rainfall File: Orange
Rainfall Amount (in): 8.400
Storm Duration (hrs): 24.00
Status: Onsite
Time of Conc (min): 10.00
Time Shift (hrs): 0.00
Area (ac):21.050
Vol of Unit Hyd (in): 1.000
Curve Number: 62.500
DCIA (%):17.000
Time Max (hrs): 9.02
Flow Max (cfs): 23.91
Runoff Volume (in): 4.669
Runoff Volume (ft3): 356772
10. ICPR Nodes Max/Min Report
11. Pre-Development vs Post-Development
Pre Development Post Development

20. Node
Name
Hydrology
Simulation
Max Inflow
(Cfs)
Node
Name
Hydrology
Simulation
Max Inflow
(Cfs)
OBT 1 2.3yr24hrFLMOD 1.05 OBT 1 2.3yr24hrFLMOD 0.00
OBT 2 2.3yr24hrFLMOD 0.21 OBT 2 2.3yr24hrFLMOD 0.00
OBT 1 25yr24hrFLMOD 18.12 OBT 1 25yr24hrFLMOD 9.19
OBT 2 25yr24hrFLMOD 3.62 OBT 2 25yr24hrFLMOD 1.95
OBT 1 25yr24hrOrange 12.58 OBT 1 25yr24hrOrange 10.21
OBT 2 25yr24hrOrange 3.71 OBT 2 25yr24hrOrange 2.25
All post values are less than or equal to pre values