Planning & Zoning Commission - 1235 (03/10/2026)

January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT   
i 
 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
STORMWATER MANAGEMENT REPORT 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike 
Waterford, Connecticut 06385 
 
Prepared for 
 
 
TABLE OF CONTENTS 
1.0 
Narrative ........................................................................................................................................... 1 
2.0 
Existing Conditions ........................................................................................................................... 1 
3.0 
Post Development Conditions ........................................................................................................... 7 
4.0 
Analysis............................................................................................................................................. 8 
5.0 
CT DEEP 2024 Stormwater Quality Manual Compliance ............................................................. 12 
5.1  
Standard 1 – Runoff Volume and Pollutant Retention .................................................................... 12 
5.2  
Standard 2 – Stormwater Runoff Quantity Control ........................................................................ 17 
5.3  
Standard 3 – Construction Soil Erosion and Sediment Control ...................................................... 17 
5.4  
Standard 4 – Post Construction Operation and Maintenance .......................................................... 17 
5.5 
Standard 5 – Stormwater Management Plan ................................................................................... 19 
 
LIST OF FIGURES 
Figure 1:  
Location Map (USGS) 
Figure 2: 
Watershed Map: Existing Condition 
Figure 3: 
Watershed Map: Post Development 
Figure 4: 
Watershed Map: Hydrodynamic Separators 
 
CALCULATIONS 
Hydrograph Reports - 2, 10, 25, 50, and 100-Year Frequencies 
 
APPENDICES 
Appendix A: 
Support Data 
Appendix B: 
Soil Resource Report 
Appendix C: 
Stormwater Sample Lab Reports 
Appendix D: 
Hydrodynamic Separator Information 
 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
1 
1.0 
Narrative 
 
The proposed project is the adaptive reuse of the former Crytal Mall (Mall) complex located at 850 Hartford 
Turnpike (CT Route 85), Waterford, Connecticut for use by the Electric Boat Corporation.  The Location 
of the property in reference to the USGS Quad Map is attached as Figure 1.  A location map is included on 
the Site Improvement Plans (Plans).  
 
The Electric Boat adaptive reuse of the property includes the conversion of the existing retail mall building 
for office, work force development, and research and development use.  The existing restaurant pad sites 
(currently Olive Garden and Longhorn Steakhouse) located along the Hartford Turnpike (CT Route 85) 
frontage will remain.    
 
Proposed modifications to the site are depicted on the Plans.  The existing bituminous concrete parking lots 
will be reconfigured and rehabilitated to accommodate the parking necessary for Electric Boats adaptive 
reuse of the facility.  The entirety of the parking lots and parking spaces are necessary for Electric Boat’s 
employee operations and the reuse of the property.  
 
Stormwater management improvements have been proposed to the maximum extent practicable.  The 
improvements have been proposed to meet the goals of the Waterford Zoning Regulations Section 25, and 
the 2024 CTDEEP Connecticut Stormwater Quality Manual (SQM).   
 
 
2.0 
Existing Conditions 
 
The existing property is approximately 77.8 acres in total along the southwest side of Hartford Turnpike 
(CT Route 85) as shown on Figure 1 and the location map included on the Plans.  The Crystal Mall was 
constructed on the property circa 1983-1984.  The property is comprised primarily of commercially 
developed land containing the Crystal Mall Building, two restaurant pad sites, and approximately 46 acres 
of paved parking lots.  The total impervious area on the site is 54.6 acres.  The western portion of the 
property is approximately 22 acres of undeveloped woodland that includes a detention basin (referred to as 
the stormwater management basin herein) for the facility and the surrounding area.  The property is 
bordered by Hartford Turnpike (CT Route 85) to the northeast, additional commercial development to the 
southeast (currently Home Depot) and northwest (currently Target), and undeveloped woodland to the 
southwest.  An aerial view of the existing property and surrounding area as they currently exist is included 
in the Plans.   
 
The existing topography of the site generally runs from the high points along Hartford Turnpike 
southwesterly toward the low point along the undeveloped woodlands.  The elevations range between 196 
along Hartford Turnpike and 78 along the southwest property line.    
 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
2 
The site soils are generally comprised of Urban Land (307).  Rock outcrops are present along the eastern 
side of the property along the CT Route 85 frontage.  A USDA Soil Resource Report is included in 
Appendix B.  Inland wetlands are present at the stormwater management basin and along the western edge 
of the site. 
 
Stormwater from the facility is collected in a standard catch basin and culvert system.  Inlets are typically 
cast iron 2’ diameter or 2’x2’ grates located throughout the parking areas as depicted on the Plans.  The 
culverts are primarily reinforced concrete pipe (RCP) ranging in size from 12” through 72” diameter.  It 
appears that the stormwater infrastructure was constructed with the Mall in the 1983-1984 era.  Spot repairs 
and grate replacements have been performed as needed. 
 
The stormwater discharge is to a vegetated stormwater management (detention) basin located at the 
southwest corner of the property, sometimes referred to as Trading Cove Pond on public mapping.  The 
basin is located on a separate parcel under the same ownership.  The basin location is shown on the Plans.  
This basin is sometimes referred to as the detention basin in previous applications; it is referred to as the 
stormwater management basin herein.  The basin collects runoff from the mall property, the adjacent Home 
Depot property, and the State of CT Route 85 drainage system (Nevins Brook).  It appears that the basin 
was constructed with the development of the Mall around 1983-1984.  It was modified to its current 
configuration with the development of the adjacent Home Depot around 1995.  Our understanding is that 
the intent of this detention basin was to mitigate peak stormwater runoff from the commercial developments 
at that time.   
 
Nevins Brook 
The stormwater management basin was constructed over Nevins Brook.  Nevins Brook traverses the site in 
a closed catch basin and culvert system.  The headwater of the brook appears to be a wetland system located 
northeast of the property; to the south of Dayton Road and flows behind the former Cohanzie School.  The 
brook is collected at a 30” RCP inlet near the Dayton Place and Hartford Turnpike intersection and is 
conveyed across Hartford Turnpike in the State of Connecticut drainage system.  At the time of the Mall 
construction a drainage manhole was constructed over the cross-culvert discharge and the flow was 
conveyed through the developed portion of the property by RCP culvert.  Several catch basin inlets are 
located along the routing that collect stormwater runoff from CT Route 85.  Stormwater from the Mall 
property is collected separately in a segregated collection system onsite.  There is a portion of the Mall 
property in the Longhorn Steakhouse area that is collected in a drainage system and combines with the 
Nevins Brook system offsite in the Home Depot Parking lot.  The brook discharges into the existing 
stormwater management basin where it combines with other discharge from the Mall and the Home Depot.  
The stormwater management basin is depicted on the Plans and in Picture 1. 
 





 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
7 
3.0 
Post Development Conditions 
 
The proposed project is the adaptive reuse of the existing Crystal Mall Building.  The existing Mall building 
will remain in place as it currently exists.  The reuse includes the interior conversion of the building for 
office, work force development, and research and development.  The existing restaurant pad sites (currently 
Olive Garden and Longhorn Steakhouse) located along the Hartford Turnpike (CT Route 85) frontage will 
remain.    
 
Proposed modifications to the site are depicted on the Plans.  The existing bituminous concrete parking lots 
will be reconfigured and rehabilitated to accommodate the parking necessary for Electric Boats adaptive 
reuse of the facility.  The entirety of the parking lots and parking spaces are necessary for Electric Boat’s 
employee operations and reuse of the property.  
 
The reconfigured parking lot has reduced the amount of impervious surface onsite by approximately 1.2 
Acres. 
 
The existing stormwater infrastructure will remain in place.  Existing tops, frames, and grates will be 
replaced with new structures.   Due to the parking lot reconfiguration and landscape island relocations, 
additional stormwater infrastructure will be added to supplement the existing system.  The new 
infrastructure was located to capture runoff and direct it to the existing system to prevent excessive gutter 
flow and ponding within the parking lots and generally includes the following improvements. 
- 
All new drainage structures will be constructed with a 2-foot deep sump. 
- 
All new drainage structures will include a hood on the discharge pipe. 
- 
Permanent inlet filters are proposed within existing catch basin tops at strategic locations to filter 
runoff prior to entering the system. 
- 
Four hydrodynamic separators are proposed where new piping runs are proposed to further cleanse 
the stormwater in the drainage system.  
 
Zoning Considerations 
The proposed project is considered a redevelopment project based on the Waterford Zoning Regulation and 
the CTDEEP 2024 Stormwater Quality Manual (SQM).  Section 25.6.8 of the Waterford Zoning 
Regulations requires the redevelopment project comply with one of three objectives 
1. Reduce the total impervious cover by 40% from the existing conditions; or 
2. Where site conditions prevent a reduction in impervious cover, implement stormwater controls for 
at least 40% of the site’s impervious cover; or 
3. Implement a combination of impervious cover reduction and area treated with stormwater controls 
that shall equal or exceed 40% of the site’s impervious cover. 
 
The reduction in impervious cover to meet the 40% is not practical due to Electric Boat’s need to utilize all 
of the available parking for their employees and visitors.  Therefore, an approach to implement a 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
8 
combination of impervious cover reduction and area treated with stormwater controls that shall equal or 
exceed 40% of the site’s impervious cover has been proposed. 
 
The entire existing impervious area onsite is 54.6 acres.  Implementing impervious coverage reduction and 
stormwater controls for at least 40% of that area requires providing improvement and treatment for at least 
22.4 acres of the site. 
 
With the new parking lot reconfiguration, the impervious surface was reduced by approximately 1.2 Acres 
and is the maximum achievable due to the need for employee parking.   
 
The structural stormwater management improvements have been proposed to the maximum extent 
achievable and generally include the following: 
1. Four hydrodynamic separators have been proposed within the new stormwater infrastructure.  The 
combined total watershed for these separators is 8.75 Acres. 
2. Permanent catch basin inlet filter pretreatment has been proposed at strategic locations within the 
parking lots.  The combined total watershed for these inlet filters is 22 Acres. 
 
The proposed additional pervious surface and structural stormwater management improvements total 31.95 
Acres.  This equates to 58.5% of the existing impervious area, meeting the Zoning Regulation requirements.   
Additionally, a large portion of the remaining impervious surface (approximately 12 Acres) is the building 
roofs that have limited potential for pollutant loading to the stormwater runoff.  
 
In addition to the structural stormwater management improvements, maintenance and operations 
improvements have also been proposed that generally include the following: 
1. Snow storage will be primarily focused to the landscape areas, with limited storage in the parking 
areas.  Due to the need for employee parking, excess snow will be trucked offsite to a separate 
facility as needed.  This will reduce the amount of deicing materials within the stormwater runoff 
from the site. 
2. Implement inspection and maintenance procedures for the facility as outlined in this document and 
the Plans. 
 
 
4.0 
Analysis 
 
The overall site stormwater analysis was performed for the 2-year, 10-year, 25-year, 50-year, and 100-year 
frequency storms using the USDA/NRCS TR-55 method to determine the peak flow rates from the existing 
and post development site.  Precipitation data and rainfall were acquired from NOAA Atlas 14, Volume 
10, Version 3 for the site, and are included in Appendix A.  NRCS Type D regional rainfall distribution 
was used in accordance with the 2024 CTDEEP Connecticut Stormwater Quality Manual.  The soils within 
the analyzed watersheds generally fall into the hydrologic soil group D due to the current level of 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
9 
development.  A copy of the soil mapping is included in Appendix B.  The runoff curve numbers for the 
site are based on the ground cover and hydrologic soil group and are included in Table 1. 
 
Table 1 – Curve Numbers 
Runoff curve numbers for the existing and post development conditions were compiled from Table 2-2 of 
the USDA/NRCS TR-55 manual a portion is included in Appendix A.  The following curve numbers were 
used for the calculations: 
 
Existing Conditions 
Watershed EX 1 
 
 
 
 
 
 
 
CN 
Area 
Impervious (roofs, pavement, rock outcrop, etc.)  
 
 
98 
55.35 
Open space (lawns), HSG D, Good Condition 
 
 
 
80 
5.75 
 
Watershed EX 2 
 
 
 
 
 
 
 
CN 
Area 
Impervious (roofs, pavement, rock outcrop, etc.)  
 
 
98 
3.35 
Open space (lawns), HSG D, Good Condition 
 
 
 
80 
0.75 
 
Watershed  EX 3 
 
 
 
 
 
 
 
CN 
Area 
Impervious (roofs, pavement, rock outcrop, etc.)  
 
 
98 
0.05 
Open space (lawns), HSG D, Good Condition 
 
 
 
80 
0.08 
 
Watershed  EX 4 
 
 
 
 
 
 
 
CN 
Area 
Impervious (roofs, pavement, rock outcrop, etc.)  
 
 
98 
0.32 
Open space (lawns), HSG D, Good Condition 
 
 
 
80 
0.23 
 
Post Development Conditions 
Watershed PD 1 
 
 
 
 
 
 
 
CN 
Area 
Impervious (roofs, pavement, rock outcrop, etc.)  
 
 
98 
54.05 
Open space (lawns), HSG D, Good Condition 
 
 
 
80 
6.80 
Pervious Surface w/ Silva Cell Subsurface Storage 
 
 
60 
0.25 
 
Watershed PD 2 
 
 
 
 
 
 
 
CN 
Area 
Impervious (roofs, pavement, rock outcrop, etc.)  
 
 
98 
3.35 
Open space (lawns), HSG D, Good Condition 
 
 
 
80 
0.75 
 
Watershed  PD 3 
 
 
 
 
 
 
 
CN 
Area 
Impervious (roofs, pavement, rock outcrop, etc.)  
 
 
98 
0.05 
Open space (lawns), HSG D, Good Condition 
 
 
 
80 
0.08 
 
Watershed  PD 4 
 
 
 
 
 
 
 
CN 
Area 
Impervious (roofs, pavement, rock outcrop, etc.)  
 
 
98 
0.32 
Open space (lawns), HSG D, Good Condition 
 
 
 
80 
0.23 
 
 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
10 
Watershed Descriptions 
The existing and post development watersheds are depicted on Figures 2 and 3.  The following is a general 
description of each watershed.   
 
EX1/PD1 
This is the major watershed on the property.  The watershed surrounds the mall building 
and includes the majority of the parking lots and mall roof.  It is generally contained within 
the parking lot curb line with sheet flow from a portion of CT Route 85 contributing.  Is 
approximately 61.1 Ac.  Discharge is to Analysis Point 1 (AP 1) which is a 72” culvert 
located within the existing Stormwater Management Basin. 
EX2/PD2 
This watershed generally surrounds the current Longhorn Steakhouse. It includes the 
parking lot surrounding the building, a portion of the southern driveway and sheet flow 
from a portion of CT Route 85.  Discharge is to Analysis Point 2 (AP 2) which is a drainage 
manhole located at the property boundary with Home Depot.  The final discharge is into 
the Stormwater Management Basin after passing through the Home Depot property. 
EX3/PD3 
This is an isolated watershed at the middle driveway near Olive Garden.  A portion of the 
vegetated property frontage and CT Route 85 flow to an 18” RCP culvert inlet. 
EX4/PD4 
This watershed includes the CT Route 85 frontage along the Olive Garden development.  
It includes a portion of the front parking area, vegetated frontage and a portion of the 
northern entrance drive.  Stormwater is collected in catch basins and discharges to the north 
through a 36” RCP culvert in a concrete wingwall. 
 
Peak Flow Rates and Volumes 
Peak stormwater flow rates and runoff volume for the existing conditions and post development conditions 
are summarized in Tables 2 and 3 respectively.  Supporting calculations are included in the Calculations 
section.   
 
The post development peak flow rates and runoff volume match the existing conditions.  Stormwater 
improvements for water quality and impervious surface reduction have been made onsite as outlined herein.  
However, due to the order of magnitude of the existing watersheds and the impervious surfaces they contain, 
the proposed improvements did not impact the weighted curve numbers used in the calculations. 
 
Table 3 – Peak Flow Rates 
 
WATERSHED 1 (AP 1) 
Peak Flow Rate (CFS) 
2-Year 
10-Year 
25-Year 
50-Year 
100-Year 
Existing Condition: EX 1 (Hyd. #1) : 
199.840 
303.000 
367.040 
414.480 
464.880 
Post Development: PD 1 (Hyd. #6) : 
199.840 
303.000 
367.040 
414.480 
464.880 
Change : 
0.000 
0.000 
0.000 
0.000 
0.000 
 
 
 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
11 
WATERSHED 2 (AP 2) 
Peak Flow Rate (CFS) 
2-Year 
10-Year 
25-Year 
50-Year 
100-Year 
Existing Condition: EX 2 (Hyd. #2) : 
13.480 
20.620 
25.050 
28.320 
31.800 
Post Development: PD 1 (Hyd. #7) : 
13.480 
20.620 
25.050 
28.320 
31.800 
Change : 
0.000 
0.000 
0.000 
0.000 
0.000 
 
WATERSHED 3 (AP 3) 
Peak Flow Rate (CFS) 
2-Year 
10-Year 
25-Year 
50-Year 
100-Year 
Existing Condition: EX 3 (Hyd. #3) : 
0.332 
0.560 
0.702 
0.807 
0.918 
Post Development: PD 1 (Hyd. #8) : 
0.332 
0.560 
0.702 
0.807 
0.918 
Change : 
0.000 
0.000 
0.000 
0.000 
0.000 
 
WATERSHED 4 (AP 4) 
Peak Flow Rate (CFS) 
2-Year 
10-Year 
25-Year 
50-Year 
100-Year 
Existing Condition: EX 4 (Hyd. #4) : 
1.552 
2.512 
3.106 
3.545 
4.011 
Post Development: PD 1 (Hyd. #8) : 
1.552 
2.512 
3.106 
3.545 
4.011 
Change : 
0.000 
0.000 
0.000 
0.000 
0.000 
 
Table 4 – Runoff Volumes 
 
WATERSHED 1 (AP 1) 
Runoff Volume (CF) 
2-Year 
10-Year 
25-Year 
50-Year 
100-Year 
Existing Condition: EX 1 (Hyd. #1) : 685,232 1,066,260 1,305,249 1,483,001 1,672,285 
Post Development: PD 1 (Hyd. #6) : 685,232 1,066,260 1,305,249 1,483,001 1,672,285 
Change : 
0 
0 
0 
0 
0 
 
WATERSHED 2 (AP 2) 
Runoff Volume (CF) 
2-Year 
10-Year 
25-Year 
50-Year 
100-Year 
Existing Condition: EX 2 (Hyd. #2) : 
45,438 
71,511 
87,894 
100,088 
113,078 
Post Development: PD 1 (Hyd. #7) : 
45,438 
71,511 
87,894 
100,088 
113,078 
Change : 
0 
0 
0 
0 
0 
 
WATERSHED 3 (AP 3) 
Runoff Volume (CF) 
2-Year 
10-Year 
25-Year 
50-Year 
100-Year 
Existing Condition: EX 3 (Hyd. #3) : 
1,040 
1,796 
2,282 
2,648 
3,039 
Post Development: PD 1 (Hyd. #8) : 
1,040 
1,796 
2,282 
2,648 
3,039 
Change : 
0 
0 
0 
0 
0 
 
WATERSHED 4 (AP 4) 
Runoff Volume (CF) 
2-Year 
10-Year 
25-Year 
50-Year 
100-Year 
Existing Condition: EX 4 (Hyd. #4) : 
4,944 
8,239 
10,338 
11,909 
13,586 
Post Development: PD 1 (Hyd. #8) : 
4,944 
8,239 
10,338 
11,909 
13,586 
Change : 
0 
0 
0 
0 
0 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
12 
 
 
Conclusion: 
In our opinion, the proposed redevelopment will have no negative impact to the peak stormwater runoff 
rates and volumes leaving the site.   Stormwater quality improvements and a reduction in impervious surface 
on the site have been proposed that benefit the watersheds and the receiving Stormwater Management 
Basin.  As such, in our opinion, the proposed development will have no negative impact on the adjacent 
State of CT infrastructure, Nevins Brook, or properties downstream of the site. 
 
 
5.0 
CT DEEP 2024 Stormwater Quality Manual Compliance 
 
The proposed development meets the five performance standards of the Connecticut DEEP 2024 
Stormwater Quality Manual to the Maximum Extent Achievable (MEA).  The project is a redevelopment 
of an existing facility; as such stormwater improvement have been incorporated into the proposed 
improvements as much as possible given the site parameters and necessary use of the site.  Low impact 
development features have been incorporated into the site development plans including the addition of 
impervious landscape surfaces, subsurface infiltration by way of Silva Cell underground storage, catch 
basin inlet filters, and hydrodynamic separators.   Low impact development features have been designed in 
accordance with the 2024 Connecticut Stormwater Quality Manual to treat the proposed stormwater runoff.   
 
 
5.1  
Standard 1 – Runoff Volume and Pollutant Retention 
 
The primary discharge form the site is to the Stormwater Management Basin.  Stormwater runoff pollutant 
renovation is provided in this basin as a byproduct of the detention basin storage, stormwater flow path 
through the basin, and vegetation.  As previously outlined under the Existing Conditions narrative herein, 
the existing discharge from Stormwater Management Basin removes pollutants to levels meeting a CT 
DEEP standards and Stormwater Quality Manual standards.    
 
As an improvement to the existing site and watershed additional pervious surface has been incorporated 
into the design amounting to approximately 1.2 Acres.  Catch basin inlet filters have also been proposed to 
pre-treat approximately 22 Acres of the site.  Four hydrodynamic separators are proposed that will further 
renovate the stormwater runoff.  Hydrodynamic separator sizing is based on the water quality flow (WQF) 
as required in the SQM. 
 
 
 





 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
17 
5.2  
Standard 2 – Stormwater Runoff Quantity Control 
As outlined under the Analysis section of this report the peak flow rates and volume leaving the site match 
the existing conditions.   Stormwater improvements by impervious surface reduction and addition of 
subsurface storage have been made onsite to the maximum extent achievable as outlined herein.  However, 
due to the order of magnitude of the existing watersheds and the impervious surfaces they contain, the 
proposed improvements did not impact the weighted curve numbers used in the calculations or the 
calculated peak flow rates and runoff volumes. 
 
 
 
 
5.3  
Standard 3 – Construction Soil Erosion and Sediment Control 
The erosion and sedimentation control plan was designed in accordance with the 2024 Connecticut DEEP 
Guidelines for Soil Erosion & Sediment Control.  Erosion and sedimentation control measures are depicted 
on the site development plans.  Plans, construction details, and a narrative are included in the plan set. 
 
 
 
5.4  
Standard 4 – Post Construction Operation and Maintenance 
The following is a general operations and maintenance schedule for the stormwater infrastructure and 
project site.  These provisions are also included on the project Plans. 
 
 
Maintenance Schedule for Existing Stormwater Management Basins 
Activity 
Schedule 
• 
Inspect for damage, undercut, or eroded area 
Monitor for sediment accumulation 
Semi-Annual inspection 
 
• 
Repair undercut or eroded areas. 
As needed maintenance 
• 
Clean and remove debris & sediment from inlet and outlet 
structures  
• 
Inspect and clean debris & sediment in the basin 
• 
Clean and remove debris from inlets 
 
 
Semi-annual 
 
 
Maintenance Schedule for Catch Basins 
Activity 
Schedule 
• 
Clean out sediment from catch basin 
 
• 
Between November 
15th and December 
15th (after leaf fall) 
• 
During April (after 
snow melt) 
 
 
 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
18 
 
Maintenance Schedule for Catch Basin Inlet Filters 
Activity 
Schedule 
• 
Inspect inlet filters for accumulated sediment 
• 
Inspect oil skimmer pouches for solidification and color 
• 
Inspect the filter bag for punctures, tears, or other damage 
Quarterly 
 
• 
Remove sediment when accumulation reaches ½ of the filter 
volume. Use industrial vacuum or replace the filter bags 
• 
Replace oil skimmer pads when they have solidified or turned black 
• 
Replace damaged filter bags 
As needed maintenance 
As observed at quarterly 
inspections 
 
Maintenance Schedule for Hydrodynamic Separators 
Activity 
Schedule 
• 
Inspect sump for accumulated sediment 
• 
Inspect oil skimmer pouches for solidification and color 
• 
Inspect the filter bag for punctures, tears, or other damage 
Semi-annual 
 
• 
Remove sediment when accumulation reaches 50% of the 
maximum storage volume. Use industrial vacuum / Vac-all. 
• 
Replace oil skimmer pads when they have solidified or turned black 
• 
Replace damaged filter bags 
As needed maintenance 
As observed at semi-
annual inspections 
 
Maintenance Schedule for Parking Areas 
Activity 
Schedule 
• 
Sweep parking lots & impervious areas  
• 
Between November 
15th and December 
15th (after leaf fall) 
• 
During April (after 
snow melt) 
 
• 
Remove and dispose of trash and debris onsite 
Daily - As needed 
maintenance 
 
 
 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
19 
5.5 
Standard 5 – Stormwater Management Plan 
 
During Construction 
The stormwater pollution prevention plan and all erosion and sedimentation control measures have been 
designed in accordance with the 2024 Connecticut DEEP Guidelines for Soil Erosion & Sediment Control. 
 
The location of temporary erosion and sedimentation control measures for the proposed development are 
included in the site development plan set.  Construction details and an erosion and sedimentation control 
narrative are also included in the plan set.  The narrative and construction details outline the requirements 
for stabilization of disturbed areas, slope stabilization requirements, and maintenance requirements.   
 
Stormwater Management & Pollution Prevention: 
Provisions for stormwater management and pollution prevention are outlined on the plans and are as 
follows: 
 
1. Pollution Prevention Team: 
The General Contractor shall be responsible for carrying out the provisions of the plan. 
2. Sweeping:  
Parking lots, sidewalks, and other impervious surfaces beyond the work site shall be swept 
clean of sand, silt, and litter daily at the end of the work day. 
3. Outside Storage: 
Accessories or equipment stored outside shall be covered or maintained to minimize the 
possibility of these materials or their residue passing to stormwater. 
4. Washing: 
 
No washing of vehicles, accessories, equipment, or appliances in the work site. 
5. Maintenance and Inspection: 
a. The Contractor shall inspect, repair, and/or replace erosion control measures every 7 
days and immediately following any significant rainfall or snow melt. 
b. Sediment deposits must be removed when deposits reach approximately one-half the 
height of the barrier. 
c. Daily dust control using water or approved equal shall be provided for all earth 
stockpiles, earth piled along excavations, surfaces of backfilled trenches and gravel 
surfaces. 
6. Spills or Accidental Discharges: 
a. Comply with State and Federal regulations to contain and clean up any spill or 
discharge and dispose of materials at an approved facility. 
b. Contact Connecticut DEEP oil and chemical spill response division 860-424-3338. 
c. The following steps should be performed as soon as possible  
- 
Stop the source of the spill 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
20 
- 
Contain the spill 
- 
Cover the spill with absorbent material such as kitty litter, saw dust, or oil 
absorbent pads.  Do not use straw. 
- 
Dispose of absorber in accordance with Local and State regulations. 
 
Post Construction 
Stormwater Management & Pollution Prevention: 
Provisions for stormwater management and pollution prevention are outlined on the plans and are as 
follows: 
 
1. Pollution Prevention Team: 
 
The Owner shall be responsible for carrying out the provisions of the plan. 
2. Sweeping:  
Parking lots, sidewalks, and other impervious surfaces shall be swept clean of sand and 
litter and any other pollutants at least twice per year 
a. Between November 15th and December 15th (after leaf fall) 
b. During April (after snow melt) 
3. Outside Storage: 
Accessories or equipment stored outside shall be covered or maintained to minimize the 
possibility of these materials or their residue passing to stormwater. 
4. Washing: 
 
No washing of vehicles, accessories, equipment, or appliances onsite. 
5. Maintenance and Inspection: 
a. Inspect stormwater structures and outfalls twice per year. 
b. Clean sediment and debris from structures at least once per year during April. 
c. Stormwater Management Basin 
- 
Remove accumulated sediment, leaf litter, and trash from the inlets twice yearly.  
Between November 15th and December 15th (after leaf fall) and During April 
(after snow melt). 
- 
Perform yearly inspection for embankment erosion and restore as needed. 
- 
Review yearly for invasive species. 
6. Spills or Accidental Discharges: 
d. Comply with State and Federal regulations to contain and clean up any spill or 
discharge and dispose of materials at an approved facility. 
e. Contact Connecticut DEEP oil and chemical spill response division 860-424-3338. 
f. The following steps should be performed as soon as possible  
- 
Stop the source of the spill 
- 
Contain the spill 

 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
January 26, 2026 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
21 
- 
Cover the spill with absorbent material such as kitty litter, saw dust, or oil 
absorbent pads.  Do not use straw.  
- 
Dispose of absorber in accordance with Local and State regulations 
 

 
 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
 
 
 
 
 
 
 
 
 
FIGURES 
 
 





 
 
 
 
 
Stormwater Management Report 
 
Crystal Mall Adaptive Reuse 
850 Hartford Turnpike, Waterford, CT 
 
CLA Engineers, Inc. 
 
    Civil · Structural · Survey 
 
 
 
 
 
 
 
 
CALCULATIONS: 
 
Hydrograph Reports 
2, 10, 25, 50, and 100-Year Frequencies 
 
 

Hydraflow Table of Contents
8185.gpw
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Watershed Model Schematic...................................................................................... 1
Hydrograph Return Period Recap............................................................................. 2
2 - Year
Summary Report......................................................................................................................... 3
Hydrograph Reports................................................................................................................... 4
Hydrograph No. 1, SCS Runoff, EX1....................................................................................... 4
Hydrograph No. 2, SCS Runoff, EX2....................................................................................... 5
Hydrograph No. 3, SCS Runoff, EX3....................................................................................... 6
Hydrograph No. 4, SCS Runoff, EX4....................................................................................... 7
Hydrograph No. 6, SCS Runoff, PD1....................................................................................... 8
Hydrograph No. 7, SCS Runoff, PD2....................................................................................... 9
Hydrograph No. 8, SCS Runoff, PD3..................................................................................... 10
Hydrograph No. 9, SCS Runoff, PD4..................................................................................... 11
10 - Year
Summary Report....................................................................................................................... 12
Hydrograph Reports................................................................................................................. 13
Hydrograph No. 1, SCS Runoff, EX1..................................................................................... 13
Hydrograph No. 2, SCS Runoff, EX2..................................................................................... 14
Hydrograph No. 3, SCS Runoff, EX3..................................................................................... 15
Hydrograph No. 4, SCS Runoff, EX4..................................................................................... 16
Hydrograph No. 6, SCS Runoff, PD1..................................................................................... 17
Hydrograph No. 7, SCS Runoff, PD2..................................................................................... 18
Hydrograph No. 8, SCS Runoff, PD3..................................................................................... 19
Hydrograph No. 9, SCS Runoff, PD4..................................................................................... 20
25 - Year
Summary Report....................................................................................................................... 21
Hydrograph Reports................................................................................................................. 22
Hydrograph No. 1, SCS Runoff, EX1..................................................................................... 22
Hydrograph No. 2, SCS Runoff, EX2..................................................................................... 23
Hydrograph No. 3, SCS Runoff, EX3..................................................................................... 24
Hydrograph No. 4, SCS Runoff, EX4..................................................................................... 25
Hydrograph No. 6, SCS Runoff, PD1..................................................................................... 26
Hydrograph No. 7, SCS Runoff, PD2..................................................................................... 27
Hydrograph No. 8, SCS Runoff, PD3..................................................................................... 28
Hydrograph No. 9, SCS Runoff, PD4..................................................................................... 29
50 - Year
Summary Report....................................................................................................................... 30
Hydrograph Reports................................................................................................................. 31
Hydrograph No. 1, SCS Runoff, EX1..................................................................................... 31
Hydrograph No. 2, SCS Runoff, EX2..................................................................................... 32
Hydrograph No. 3, SCS Runoff, EX3..................................................................................... 33
Hydrograph No. 4, SCS Runoff, EX4..................................................................................... 34
Hydrograph No. 6, SCS Runoff, PD1..................................................................................... 35

Contents continued...
8185.gpw
Hydrograph No. 7, SCS Runoff, PD2..................................................................................... 36
Hydrograph No. 8, SCS Runoff, PD3..................................................................................... 37
Hydrograph No. 9, SCS Runoff, PD4..................................................................................... 38
100 - Year
Summary Report....................................................................................................................... 39
Hydrograph Reports................................................................................................................. 40
Hydrograph No. 1, SCS Runoff, EX1..................................................................................... 40
Hydrograph No. 2, SCS Runoff, EX2..................................................................................... 41
Hydrograph No. 3, SCS Runoff, EX3..................................................................................... 42
Hydrograph No. 4, SCS Runoff, EX4..................................................................................... 43
Hydrograph No. 6, SCS Runoff, PD1..................................................................................... 44
Hydrograph No. 7, SCS Runoff, PD2..................................................................................... 45
Hydrograph No. 8, SCS Runoff, PD3..................................................................................... 46
Hydrograph No. 9, SCS Runoff, PD4..................................................................................... 47

1
2
3
4
6
7
8
9
1
Watershed Model Schematic
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Project: 8185.gpw
Sunday, 01 / 25 / 2026
Hyd. Origin
Description
Legend
1
SCS Runoff
EX1
2
SCS Runoff
EX2
3
SCS Runoff
EX3
4
SCS Runoff
EX4
6
SCS Runoff
PD1
7
SCS Runoff
PD2
8
SCS Runoff
PD3
9
SCS Runoff
PD4

Hydrograph Return Period Recap
2
Hyd.
Hydrograph
Inflow
Peak Outflow (cfs)
Hydrograph
No.
type
hyd(s)
Description
(origin)
1-yr
2-yr
3-yr
5-yr
10-yr
25-yr
50-yr
100-yr
1
SCS Runoff
------
-------
199.84
-------
-------
303.00
367.04
414.48
464.88
EX1
2
SCS Runoff
------
-------
13.48
-------
-------
20.62
25.05
28.32
31.80
EX2
3
SCS Runoff
------
-------
0.332
-------
-------
0.560
0.702
0.807
0.918
EX3
4
SCS Runoff
------
-------
1.552
-------
-------
2.512
3.106
3.545
4.011
EX4
6
SCS Runoff
------
-------
199.84
-------
-------
303.00
367.04
414.48
464.88
PD1
7
SCS Runoff
------
-------
13.48
-------
-------
20.62
25.05
28.32
31.80
PD2
8
SCS Runoff
------
-------
0.332
-------
-------
0.560
0.702
0.807
0.918
PD3
9
SCS Runoff
------
-------
1.552
-------
-------
2.512
3.106
3.545
4.011
PD4
Proj. file: 8185.gpw
Sunday, 01 / 25 / 2026
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026

Hydrograph Summary Report
3
Hyd.
Hydrograph
Peak
Time
Time to
Hyd.
Inflow
Maximum
Total
Hydrograph
No.
type
flow
interval
Peak
volume
hyd(s)
elevation
strge used
Description
(origin)
(cfs)
(min)
(min)
(cuft)
(ft)
(cuft)
1
SCS Runoff
199.84
1
727
685,232
------
------
------
EX1
2
SCS Runoff
13.48
1
727
45,438
------
------
------
EX2
3
SCS Runoff
0.332
1
727
1,040
------
------
------
EX3
4
SCS Runoff
1.552
1
727
4,944
------
------
------
EX4
6
SCS Runoff
199.84
1
727
685,232
------
------
------
PD1
7
SCS Runoff
13.48
1
727
45,438
------
------
------
PD2
8
SCS Runoff
0.332
1
727
1,040
------
------
------
PD3
9
SCS Runoff
1.552
1
727
4,944
------
------
------
PD4
8185.gpw
Return Period: 2 Year
Sunday, 01 / 25 / 2026
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Hyd. No. 1
EX1
Hydrograph type
=  SCS Runoff
Peak discharge
=  199.84 cfs
Storm frequency
=  2 yrs
Time to peak
=  727 min
Time interval
=  1 min
Hyd. volume
=  685,232 cuft
Drainage area
=  61.100 ac
Curve number
=  96*
Basin Slope
=  0.0 %
Hydraulic length
=  0 ft
Tc method
=  User
Time of conc. (Tc)
=  6.00 min
Total precip.
=  3.45 in
Distribution
=  Custom
Storm duration
=  M:\NOAA Type D Distribution 1 min.cds
Shape factor
=  484
* Composite (Area/CN) = [(55.350 x 98) + (5.750 x 80)] / 61.100
4
0
120
240
360
480
600
720
840
960
1080
1200
1320
1440
1560
Q (cfs)
0.00
0.00
30.00
30.00
60.00
60.00
90.00
90.00
120.00
120.00
150.00
150.00
180.00
180.00
210.00
210.00
Q (cfs)
Time (min)
EX1
Hyd. No. 1 -- 2 Year
Hyd No. 1

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Hyd. No. 2
EX2
Hydrograph type
=  SCS Runoff
Peak discharge
=  13.48 cfs
Storm frequency
=  2 yrs
Time to peak
=  727 min
Time interval
=  1 min
Hyd. volume
=  45,438 cuft
Drainage area
=  4.200 ac
Curve number
=  95*
Basin Slope
=  0.0 %
Hydraulic length
=  0 ft
Tc method
=  User
Time of conc. (Tc)
=  6.00 min
Total precip.
=  3.45 in
Distribution
=  Custom
Storm duration
=  M:\NOAA Type D Distribution 1 min.cds
Shape factor
=  484
* Composite (Area/CN) = [(3.450 x 98) + (0.750 x 80)] / 4.200
5
0
120
240
360
480
600
720
840
960
1080
1200
1320
1440
1560
Q (cfs)
0.00
0.00
2.00
2.00
4.00
4.00
6.00
6.00
8.00
8.00
10.00
10.00
12.00
12.00
14.00
14.00
Q (cfs)
Time (min)
EX2
Hyd. No. 2 -- 2 Year
Hyd No. 2

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Hyd. No. 3
EX3
Hydrograph type
=  SCS Runoff
Peak discharge
=  0.332 cfs
Storm frequency
=  2 yrs
Time to peak
=  727 min
Time interval
=  1 min
Hyd. volume
=  1,040 cuft
Drainage area
=  0.130 ac
Curve number
=  87*
Basin Slope
=  0.0 %
Hydraulic length
=  0 ft
Tc method
=  User
Time of conc. (Tc)
=  6.00 min
Total precip.
=  3.45 in
Distribution
=  Custom
Storm duration
=  M:\NOAA Type D Distribution 1 min.cds
Shape factor
=  484
* Composite (Area/CN) = [(0.050 x 98) + (0.080 x 80)] / 0.130
6
0
120
240
360
480
600
720
840
960
1080
1200
1320
1440
1560
Q (cfs)
0.00
0.00
0.05
0.05
0.10
0.10
0.15
0.15
0.20
0.20
0.25
0.25
0.30
0.30
0.35
0.35
0.40
0.40
0.45
0.45
0.50
0.50
Q (cfs)
Time (min)
EX3
Hyd. No. 3 -- 2 Year
Hyd No. 3

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Hyd. No. 4
EX4
Hydrograph type
=  SCS Runoff
Peak discharge
=  1.552 cfs
Storm frequency
=  2 yrs
Time to peak
=  727 min
Time interval
=  1 min
Hyd. volume
=  4,944 cuft
Drainage area
=  0.550 ac
Curve number
=  90*
Basin Slope
=  0.0 %
Hydraulic length
=  0 ft
Tc method
=  User
Time of conc. (Tc)
=  6.00 min
Total precip.
=  3.45 in
Distribution
=  Custom
Storm duration
=  M:\NOAA Type D Distribution 1 min.cds
Shape factor
=  484
* Composite (Area/CN) = [(0.320 x 98) + (0.230 x 80)] / 0.550
7
0
120
240
360
480
600
720
840
960
1080
1200
1320
1440
1560
Q (cfs)
0.00
0.00
1.00
1.00
2.00
2.00
Q (cfs)
Time (min)
EX4
Hyd. No. 4 -- 2 Year
Hyd No. 4

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Hyd. No. 6
PD1
Hydrograph type
=  SCS Runoff
Peak discharge
=  199.84 cfs
Storm frequency
=  2 yrs
Time to peak
=  727 min
Time interval
=  1 min
Hyd. volume
=  685,232 cuft
Drainage area
=  61.100 ac
Curve number
=  96*
Basin Slope
=  0.0 %
Hydraulic length
=  0 ft
Tc method
=  User
Time of conc. (Tc)
=  6.00 min
Total precip.
=  3.45 in
Distribution
=  Custom
Storm duration
=  M:\NOAA Type D Distribution 1 min.cds
Shape factor
=  484
* Composite (Area/CN) = [(54.050 x 98) + (6.800 x 80) + (0.250 x 60)] / 61.100
8
0
120
240
360
480
600
720
840
960
1080
1200
1320
1440
1560
Q (cfs)
0.00
0.00
30.00
30.00
60.00
60.00
90.00
90.00
120.00
120.00
150.00
150.00
180.00
180.00
210.00
210.00
Q (cfs)
Time (min)
PD1
Hyd. No. 6 -- 2 Year
Hyd No. 6

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Hyd. No. 7
PD2
Hydrograph type
=  SCS Runoff
Peak discharge
=  13.48 cfs
Storm frequency
=  2 yrs
Time to peak
=  727 min
Time interval
=  1 min
Hyd. volume
=  45,438 cuft
Drainage area
=  4.200 ac
Curve number
=  95*
Basin Slope
=  0.0 %
Hydraulic length
=  0 ft
Tc method
=  User
Time of conc. (Tc)
=  6.00 min
Total precip.
=  3.45 in
Distribution
=  Custom
Storm duration
=  M:\NOAA Type D Distribution 1 min.cds
Shape factor
=  484
* Composite (Area/CN) = [(3.450 x 98) + (0.750 x 80)] / 4.200
9
0
120
240
360
480
600
720
840
960
1080
1200
1320
1440
1560
Q (cfs)
0.00
0.00
2.00
2.00
4.00
4.00
6.00
6.00
8.00
8.00
10.00
10.00
12.00
12.00
14.00
14.00
Q (cfs)
Time (min)
PD2
Hyd. No. 7 -- 2 Year
Hyd No. 7

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Hyd. No. 8
PD3
Hydrograph type
=  SCS Runoff
Peak discharge
=  0.332 cfs
Storm frequency
=  2 yrs
Time to peak
=  727 min
Time interval
=  1 min
Hyd. volume
=  1,040 cuft
Drainage area
=  0.130 ac
Curve number
=  87*
Basin Slope
=  0.0 %
Hydraulic length
=  0 ft
Tc method
=  User
Time of conc. (Tc)
=  6.00 min
Total precip.
=  3.45 in
Distribution
=  Custom
Storm duration
=  M:\NOAA Type D Distribution 1 min.cds
Shape factor
=  484
* Composite (Area/CN) = [(0.050 x 98) + (0.080 x 80)] / 0.130
10
0
120
240
360
480
600
720
840
960
1080
1200
1320
1440
1560
Q (cfs)
0.00
0.00
0.05
0.05
0.10
0.10
0.15
0.15
0.20
0.20
0.25
0.25
0.30
0.30
0.35
0.35
0.40
0.40
0.45
0.45
0.50
0.50
Q (cfs)
Time (min)
PD3
Hyd. No. 8 -- 2 Year
Hyd No. 8

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Hyd. No. 9
PD4
Hydrograph type
=  SCS Runoff
Peak discharge
=  1.552 cfs
Storm frequency
=  2 yrs
Time to peak
=  727 min
Time interval
=  1 min
Hyd. volume
=  4,944 cuft
Drainage area
=  0.550 ac
Curve number
=  90*
Basin Slope
=  0.0 %
Hydraulic length
=  0 ft
Tc method
=  User
Time of conc. (Tc)
=  6.00 min
Total precip.
=  3.45 in
Distribution
=  Custom
Storm duration
=  M:\NOAA Type D Distribution 1 min.cds
Shape factor
=  484
* Composite (Area/CN) = [(0.320 x 98) + (0.230 x 80)] / 0.550
11
0
120
240
360
480
600
720
840
960
1080
1200
1320
1440
1560
Q (cfs)
0.00
0.00
1.00
1.00
2.00
2.00
Q (cfs)
Time (min)
PD4
Hyd. No. 9 -- 2 Year
Hyd No. 9

Hydrograph Summary Report
12
Hyd.
Hydrograph
Peak
Time
Time to
Hyd.
Inflow
Maximum
Total
Hydrograph
No.
type
flow
interval
Peak
volume
hyd(s)
elevation
strge used
Description
(origin)
(cfs)
(min)
(min)
(cuft)
(ft)
(cuft)
1
SCS Runoff
303.00
1
727
1,066,260
------
------
------
EX1
2
SCS Runoff
20.62
1
727
71,511
------
------
------
EX2
3
SCS Runoff
0.560
1
727
1,796
------
------
------
EX3
4
SCS Runoff
2.512
1
727
8,239
------
------
------
EX4
6
SCS Runoff
303.00
1
727
1,066,260
------
------
------
PD1
7
SCS Runoff
20.62
1
727
71,511
------
------
------
PD2
8
SCS Runoff
0.560
1
727
1,796
------
------
------
PD3
9
SCS Runoff
2.512
1
727
8,239
------
------
------
PD4
8185.gpw
Return Period: 10 Year
Sunday, 01 / 25 / 2026
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026

Hydrograph Report
Hydraflow Hydrographs Extension for Autodesk® Civil 3D® by Autodesk, Inc. v2026
Sunday, 01 / 25 / 2026
Hyd. No. 1
EX1
Hydrograph type
=  SCS Runoff
Peak discharge
=  303.00 cfs
Storm frequency
=  10 yrs
Time to peak
=  727 min
Time interval
=  1 min
Hyd. volume
=  1,066,260 cuft
Drainage area
=  61.100 ac
Curve number
=  96*
Basin Slope
=  0.0 %
Hydraulic length
=  0 ft
Tc method
=  User
Time of conc. (Tc)
=  6.00 min
Total precip.
=  5.13 in
Distribution
=  Custom
Storm duration
=  M:\NOAA Type D Distribution 1 min.cds
Shape factor
=  484
* Composite (Area/CN) = [(55.350 x 98) + (5.750 x 80)] / 61.100
13
0
120
240
360
480
600
720
840
960
1080
1200
1320
1440
1560
Q (cfs)
0.00
0.00
40.00
40.00
80.00
80.00
120.00
120.00
160.00
160.00
200.00
200.00
240.00
240.00
280.00
280.00
320.00
320.00
Q (cfs)
Tim