The City of Bridgeport has implemented a stormwater management program to meet NPDES (National Pollutant Discharge Elimination System) requirements for the discharge of stormwater into the City’s CSO (Combined Storm/Sewer Overflow) system and receiving waters. Measures required under the City’s NPDES permit include stormwater management during construction and stormwater management on the developed site after construction.
Stormwater management is an integral part of Bridgeport’s approach to CSO management. United States Environmental Protection Agency’s (USEPA) CSO Control Policy, published in 1994, promotes effective stormwater management on a watershed basis. Proper stormwater management also enables the City of Bridgeport to comply with EPA Clean Water Act regulations, and state of Connecticut Department of Energy & Environmental Protection stormwater standards.
Property owners must submit a site-specific stormwater management plan before any development activity can occur. Also part of this plan, post-construction stormwater management practices, should seek to utilize pervious areas for storm water treatment and to infiltrate storm water runoff from driveways, sidewalks, rooftops, parking lots, and landscaped areas to the maximum extent practical to provide treatment for both water quality and quantity.
Bridgeport Zoning & Subdivision Regulations
Section 4-13 - Stormwater Management Regulations
a. Purpose: The intent of the City of Bridgeport’s comprehensive stormwater management program is to fulfill relevant state statutes, reduce soil erosion and sediment deposition resulting in water pollution and damage to land and resources, reduce damage from stormwater runoff; protect Long Island Sound’s resources, ecosystems and habitats, minimize sediment pollution resulting from land development activities, and reduce pollutants from, detain, and/or retain, and provide a destination for stormwater to best preserve or mimic the natural hydrologic cycle, to accomplish the goals of reducing and controlling stormwater runoff, or to fit within the capacity of existing infrastructure.
b. Authority: Activities with the potential for stormwater impacts shall be controlled by the City of Bridgeport’s official Stormwater Management Manual, as updated from time to time. The manual is issued by the City Engineering Department, with the assistance of the Water Pollution Control Authority. These agencies are responsible for reviewing and approving the stormwater management component of applications before the Planning and Zoning Commission, or any other reviewing and approving body. The Planning and Zoning Commission, or other approval body, shall not issue an application approval until and unless the City Engineering Department and/or the Water Pollution Control Authority has granted final approval for the stormwater management component. The Planning and Zoning Commission, or other approval body, is not authorized to grant a waiver to the manual’s requirements.
c. Reference: The City of Bridgeport’s official Stormwater Management Manual, as updated from time to time, is incorporated into these regulations by reference.
Bridgeport Stormwater Management Manual
All projects which generate earth disturbance of 20,000 square feet or more (5,000 sq ft or more in flood prone areas) must comply to the greatest extent practical with the requirements of the Storm Water Management Regulations. There are four major elements to the Bridgeport Storm Water Regulations: Water Quality, Water Quantity, Channel Protection, and Flood Control Requirements.
The flood insurance study for the City of Bridgeport has designated areas as Zone A, areas inundated by a 100-year flood and Zone V, areas of 100-year coastal flood with velocity (wave action).
Water Quality Requirements
The Water Quality Requirement concerns the first one inch of precipitation over Directly Connected Impervious Areas from each storm and is established to: (1) recharge the groundwater table and increase stream base flows; and (2) reduce contaminated runoff from sites as well as to improve water quality discharge into Long Island Sound.
1) The management technique required is infiltration unless infiltration is determined to be physically impossible (due to contamination, high groundwater table, shallow bed rock, poor infiltration rates) or where it can be shown that doing so would cause property or environmental damage.
2) Where infiltration is not feasible for the entire inch, any remaining portion of the initial inch of precipitation from a storm that cannot be infiltrated must be treated for water quality using the secondary treatment practices found in the CTDEPSWQM.
6. WATER QUALITY CONTROLS
All storm water management practices shall be designed to capture and treat storm water runoff according to the specifications outlined in the CTDEP 2004 Connecticut Storm Water Quality Manual. These specifications will designate the water quantity and quality treatment criteria that apply to an approved storm water management practice. All storm water management practices shall be designed to convey storm water but allow for the maximum removal of pollutants and reduction in flow velocities. This shall include, but not be limited to:
- Maximizing length of flow paths from inflow points to outflow points of basins, pools and ponds.
- Protection of inlet and outfall structures.
- Elimination of erosive flow velocities.
- Provision of underdrain systems, where applicable.
All storm water management practices must have a landscaping plan detailing the vegetation to be planted after construction is finished.
The use of non-structural best management practices is encouraged in order to minimize the reliance on structural practices.
A. The Changing Regulatory Environment
Flow control is intended to protect downstream properties, infrastructure, and natural resources from the increases in storm water runoff peak flow rates and volumes resulting from development. Storm water runoff from almost all the developed areas of the City, whether served by separate storm water sewers or combined sewers, is causing impairment to the aquatic and riparian habitats of streams and rivers in Bridgeport. These water bodies are suffering from streambank and channel erosion resulting in the exposure of sewer infrastructure and decreased stream baseflow due to reduced groundwater recharge. The streams do not support healthy aquatic communities, do not meet uses designated by the State, do not serve as amenities to the community, and occasionally cause property damage due to flooding.
The City’s policy is to ensure that runoff leaving the post-development site:
- Does not exceed the capacity of the receiving conveyance facility or water body.
- Does not increase the potential for stream bank and stream channel erosion.
- Does not add significant volume to an existing closed depression, such as Lake Forest or other similar geologic features found throughout the City.
- Does not create or increase any upstream or downstream flooding problems.
- Does not create or increase the occurrence of CSOs or basement sewer backups.
The basic design concept for flow control (detention and retention) is simple: water from developed areas is managed with a variety of flow control techniques and released to downstream conveyance systems at a slower rate (detention) and lower volume (retention). Managing flows in this way attempts to mimic the site’s natural rainfall runoff response prior to development
B. NPDES Combined Sewer Permits and Regulations
Storm sewers discharging to surface waters in Bridgeport are regulated under the NPDES. Measures required under NPDES storm water permits include storm water management during construction and storm water management on the developed site after construction.
Sections of Bridgeport’s land area is served by sewers that carry sanitary sewage and storm water in a single pipe. During dry weather, all this flow is treated at water pollution control plants before discharge to receiving waters. During wet weather, total flow exceeds the capacity of the sewer system and a portion of the flow (combined sewer overflow) is discharged untreated to receiving waters.
Storm water management is an integral part of Bridgeport’s approach to CSO management. United States Environmental Protection Agency’s (USEPA) CSO Control Policy, published in 1994, promotes effective storm water management on a watershed basis.
All site designs shall establish storm water management practices to control the peak flow rates of storm water discharge associated with specified design storms and reduce the generation of storm water. The most effective practices increase infiltration and evaporation at the site level and reduce the amount of wet weather flow in the sewer system. These practices should seek to utilize pervious areas for storm water treatment and to infiltrate storm water runoff from driveways, sidewalks, rooftops, parking lots, and landscaped areas to the maximum extent practical to provide treatment for both water quality and quantity. Other practices detain storm water and release it to the sewer system at a slower rate, taking advantage of sewer system capacity over a longer period of time. These techniques are most effective during small storms. Techniques designed to limit streambank erosion and flood damage during large storms work equally well in areas of combined sewers and separate storm sewers.
Dry Detention Basins (CTDOTDM Chapter 10)
Dry detention basins are utilized for the detention of storm water to reduce the peak discharge and release the stored water at an acceptable and controlled rate. Dry detention basins shall be designed to drain completely within 72 hours.
Detention structures can be categorized as dry basins, underground storage facilities, and multi-use storage areas such as parking lots, roadway shoulder, and other shallow holding areas. Structures for detention of storm water may be considered together since the major control structures functions the same for each. The maximum depth of storm water allowed at any location in a parking lot shall be six (6) inches.
Control structure release rates shall approximate pre-developed peak runoff rates for the two (2), ten (10), and twenty five (25) year storms, with emergency overflow capable of handling the 100-year discharge. Measures should be employed to prevent the clogging of the outlet structure.
A minimum freeboard of one (1) foot above the 100-year water surface elevation shall be provided for all impoundments. The 100-year event shall be routed through the facility to ensure that the embankment will not be damaged or fail during the passage of that storm.
Relief may be granted from the one hundred (100) year storm design requirements for existing sites with the approval of the City Engineer and provided that:
- The physical constraints of site will not allow for construction of a basin for the one hundred (100) year storm event.
- Any possible increase in runoff will not adversely impact adjacent properties and area upstream and down stream from the project.
Fencing may be required around the detention basin for public safety. An access gate shall be provided for maintenance purposes. The maintenance of all detention basins, which are required, will be the responsibility of the private property owner(s).
Detention basins shall be constructed as part of the first phase work and incorporate sedimentation and erosion controls to minimize the impacts of construction on adjacent watercourses. Detention basin embankments shall have a minimum top width of eight (8) feet along the access side of the basin. The bottom of the facility shall slope at 0.5% minimum toward the outlet.
The calculations for the detention pond shall provide information on the impacts of the outflow hydrograph from the detention basin on the existing drainage systems and/or watercourse. Detention basins that discharge to combined sewers may only discharge 90% of the peak rate of the 10-year predevelopment flow. Storage outflows greater than that rate (i.e. 25-, 50-, 100-year) must be detained longer onsite to ensure that the basin discharge does not overload the combined sewer.