The State of New Jersey has adopted "Smart Growth" initiatives to ensure that development within the state's watersheds occurs in a way that is environmentally sustainable.  A primary objective of these initiatives is to protect the state's water resources.  They encourage future growth within areas that are already substantially developed and discourage development within the more rural, environmentally sensitive areas.  

Two metropolitan areas targeted for future development and growth were Berlin Borough and Berlin Township, where the New Jersey Department of Transportation (NJDOT) planned several improvements that will:      

Berlin is located at the headwaters of the Great Egg Harbor River, a high-quality and high-value stream that is designated by the National Park Service as a Wild and Scenic River.  (Rivers receive such a designation as a result of their high water quality, fish and wildlife habitat, and/or recreation and aesthetic values.)  Consequently, NJDOT's project offered an ideal opportunity to merge the goals of watershed protection with those of smart growth.  PB is serving as the prime consultant.

Project Overview

Berlin Borough and Berlin Township are at the crossroads of several major roadways (Figures 1 and 2).  Included is the functionally obsolete Berlin Circle, which is a major cause of congestion and accidents.  Under this project:

• The Berlin Circle will be eliminated      
• Traffic operations and safety along Route 73 and several local and county roads that connect to the Berlin Circle will be improved:      
• There will be major roadway widenings
• New interchanges and new connectors will be designed and constructed.

The project also addresses highway drainage problems that have long been experienced throughout the project area. The solutions include combinations of:

• New drainage systems      
• A bypass trunk line
• A regional flood control basin      
• Roadway culvert replacements
• Raised roadway profiles.

Environmental Constraints and Design Objectives

The project area is subject to numerous environmental constraints and regulatory requirements.  In summary, to obtain the necessary approvals from regulatory agencies, we had to include provisions to address:      

• Wetland mitigation
• Flood control      
• Runoff water quality.

Wetlands.  The roadway improvements associated with eliminating Berlin Circle result in the loss of more than 0.4 ha (1 acre) of freshwater wetlands/state open waters.  Therefore, more than 0.76 ha (1.87 acres) of wetland mitigation had to be provided to comply with the applicable permitting requirements.  Finding a suitable site for this mitigation was a key to the project obtaining the approvals needed from New Jersey Department of Environmental Protection (NJDEP).

Flood Control.  The project site is located at the headwaters of the Great Egg Harbor River in an area that is now subject to frequent flooding.  The upstream watershed has been developed almost entirely for large residential communities since Route 73 was constructed in the 1940s, with commercial and industrial development along the roadway corridors.  For the most part, this development did not include measures for stormwater management.  The increased stormwater runoff has greatly increased flood flows in stream corridors to the point where the roadway culverts can no longer convey the flows.  This runoff has, in turn, resulted in frequent flooding of roadways and nearby properties. 

An additional factor contributing to the area's flooding problem is the railroad line that bisects the community (Conrail, shown on both figures) and is on a raised embankment. The culvert that conveys the stream under the railroad is not large enough to handle the increased flood flows, so the embankment acts as a dam that blocks the floodwater and inundates a large area upstream, including residential and commercial areas.

In accordance with the requirements of the New Jersey Flood Hazard Area Control Act Rules, we had to incorporate measures to ensure that the project would not worsen the existing flooding.  However, a major objective of the client was to alleviate the existing flooding problems to the maximum extent possible and not merely to maintain the status quo. 

Water Quality.  The quality of stormwater runoff from the project area was a significant concern because Great Egg Harbor River is considered a high-quality and high-value stream.  The NJDEP Stormwater Management Rules provide specific design and performance standards for water quality that must be satisfied.  If these standards cannot be met using measures within the project area, then additional measures located elsewhere in the watershed must be provided for stormwater runoff quality "mitigation." 

Multi-purpose Regional Best Management Practice:  The Concept

Instead of sacrificing valuable commercial property fronting a state highway within a designated growth area for on-site stormwater management, we pursued a regional watershed-based approach.  In addition, we wanted to find a site that could accommodate a multi-purpose design that addressed all three needs: wetland mitigation, flood control, and water quality.  The site that was chosen is located north of Zulker Avenue between Haddon Avenue and Walker Avenue (Figure 2).  This 4.5 ha (11-acre) site is immediately adjacent to the stream that forms the headwater of the Great Egg Harbor River.  As a result, it provided an opportunity to treat the runoff from a large, urbanized watershed.

Wetland Mitigation.  A 1.9-ha (4.7-acre) wetland will be created.  This area is well above the required 0.76 ha (1.87 acres), so it also provides a "mitigation bank" for future NJDOT projects within the same watershed. 

Flood Control.  Taunton Branch, a tributary branch of the Great Egg Harbor River, passes through the project area south of Berlin Circle (Figure 1).  The drainage area contributing to Taunton Branch east of Route 73 is completely developed such that runoff is collected through storm sewer systems, piped under Route 73, and discharged to an existing ditch along the railroad line.  Route 73 will be widened in this area, resulting in an increase in stormwater runoff to Taunton Branch.  To address this increase and protect the commercial properties along the railroad ditch, a diversion structure will be provided to divert the excess runoff toward a new bypass trunk line. 

This new bypass trunk line will be constructed along Berlin-Cross Keys Road.  It will pass through the community, convey flood flows under the railroad line, and finally discharge to the Great Egg Harbor River downstream of the community (Figure 2). 

The intended lowering of flood elevations in the project area will reduce the capacity of the floodplain to attenuate, or reduce the flood flows to downstream areas; however, the Zulker Avenue site will supply the required flood storage to address the flood mitigation objectives in the project area.  A regional detention basin upstream of the railroad line will ensure that downstream properties are protected.  This basin will offset the effect of lowering the floodplain elevations.

Water Quality.  The diversion structure mentioned above provided flood protection but did not address the requirement to provide water quality treatment for Taunton Branch.  Providing typical best management practices (BMPs), such as basins, required sacrificing commercial property along Route 73, but that was contrary to the goals of the project. 

On the other hand, because the Zulker Avenue site is immediately adjacent to the stream that forms the headwater of the Great Egg Harbor River, the regional basin located there provides an opportunity to treat the runoff from a 90-ha (220-acre) portion of an urbanized watershed.  This is such a large portion of the upstream watershed that it easily compensates for the lack of treatment on the Taunton Branch.  Thus, the project provides water quality treatment as required by regulations, and it does so in a way that is consistent with the goals of smart growth.

Multi-Purpose Regional BMP:  The Technical Challenges

The goal of addressing wetland mitigation, flood control, and water quality concerns in one location was complicated by the fact that each of these issues has numerous and sometimes conflicting technical requirements. 

Wetlands and Water Quality.  One of the most important technical requirements is NJDEP's policy that wetland mitigation areas not be used for water quality treatment of stormwater runoff resulting from the New Jersey Water Quality Design Storm, which is defined as a 2-hour storm with a rainfall depth of 32 mm (1.25 inches).  (The rainfall distribution is provided in the NJ BMP Manual and is similar in shape to the National Resource Conservation Service Type III Storm.)  Wetlands that have been created for mitigation purposes may be used for flood control if doing so does not impair wetland values or functions, but stormwater runoff from the project area must be treated before it is discharged to the wetlands.

This policy is addressed by providing a .85-ha (2.1)-acre wet pond adjacent to the created freshwater wetland system to receive stormwater inflows from the project area.  Wet ponds are a type of stormwater BMP specifically recognized by NJDEP, and the wet pond at Zulker Avenue was designed in accordance with the criteria provided in New Jersey Stormwater Best Management Practices Manual (NJ BMP Manual), 2004). 

The amount of total suspended solids (TSS) removal that is credited to the wet pond depends on the amount of:      

• Volume retained by the permanent pool
• Temporary storage of runoff provided above the permanent pool. 

For the Zulker Avenue wet pond, the permanent pool volume is slightly more than the total runoff volume from a 2-hour storm with a rainfall depth of 32 mm (1.25 inches).  Based on the volume of the permanent pool, the amount of TSS removal credit is only 50 percent. No additional TSS removal credit was obtained for temporary storage of runoff above the permanent pool since the retention time is less than the minimum required. 

Although 50 percent TSS removal efficiency is rather low, the contributing drainage area is large and urbanized, so a significant amount of TSS will be removed by the wet pond.  Since runoff from the project area will first enter the wet pond and then overflow into the mitigation area, functional separation of water quality and wetland mitigation is achieved. 

Water quality treatment of runoff is only required for the New Jersey Water Quality Design Storm, as defined above.  For larger and less frequent storm events, untreated runoff may overflow into the mitigation area.  Therefore, the regional facility has been designed so that for large storm events, the wet pond and the wetland mitigation area will become inundated and act together as a single, large flood control facility.  As discussed previously, the design criteria for the flood control aspect of this regional basin is that it must provide adequate floodplain storage such that neither the flood elevations in the project area nor the flood flows downstream are increased. 

Extensive hydraulic modeling of the watershed was performed to verify that these criteria would be met by the regional basin, bypass trunk line, and other drainage infrastructure improvements.  The modeling was performed using the USDA Natural Resources Conservation Service (NRCS) methodology as described in Section 4 of the National Engineering Handbook (NRCS, 2002) for both runoff hydrograph generation and reservoir routing calculations.  In locations where interconnected storage areas were encountered and the "storage indication" method could not be used, special routing techniques available through Pondpack(r) software by Haestad Methods, Inc. (Haestad, 2003) were used. 

We found that:      

• Significant flood relief would be provided in the form of reduced flood elevations and, therefore, reduced flood frequencies in the project area.
• The downstream impacts would be minimal, with peak discharges to the Great Egg Harbor River increasing slightly. 

It was judged that the substantial flood control benefits achieved upstream justified the increased flood hazard downstream, since all of the downstream impacts occurred in an area that was entirely contained within an undeveloped and environmentally constrained County Park. 

The approach we took was to use the hydraulic models discussed above to determine the depth and duration of flooding that would occur under existing conditions for the wetlands in the immediate area, and to use the results as the baseline against which to evaluate conditions after the project is built (build conditions).  We reasoned that if the depth and duration of flooding under build conditions was similar to those under existing conditions, then the effect on the wetland hydrology would not be adverse.  Flood depths and durations for existing and build conditions were determined for the 1, 2, and 5-year storm events. 

We found that for the build condition, flood depths were slightly reduced and flood durations were slightly increased, as illustrated in Figure 3, which compares depth and duration for the 1-year storm.  Similar results were obtained for the 2- and 5-year storms.  This replication of existing conditions was achieved primarily through a trial-and-error process in the design of the hydraulic control structures. 

The primary outlet from the regional facility will be a simple weir discharging to a relocated section of stream.  However, the critical hydraulic design element is an overflow structure discharging to a culvert under Zulker Avenue.  This overflow will permit flood flows from larger storm events to cross under Zulker Avenue rather than over it as currently happens.  This was a necessary design consideration to ensure that drainage patterns will be maintained. 

Conclusion

Public works projects almost always involve impacts to natural resources, and must also address an ever-growing list of regulatory requirements to minimize these impacts and provide mitigating measures.  These mitigating measures usually require some amount of space to implement them, but this increasing need for space for natural resource protection is in conflict with the objectives of smart growth when a project is located in an area targeted for development and growth.  In such areas, available land that is suitable for development or redevelopment is scarce and must be reserved for such development as much as possible if the goals of smart growth are to be achieved. 

Addressing the regulatory requirements for natural resource protection individually and on a project-by-project basis is short-sighted and will result in an inefficient use of land that is becoming an increasingly precious resource itself.  An alternative strategy is the use of multi-purpose regional facilities such as the one described in this article. 

In addition to meeting the regulatory requirements, it is hoped that the excess water quality treatment and freshwater wetland mitigation provided by the regional basin at Zulker Avenue will ease the regulatory burden on future transportation infrastructure projects in the region.  The objectives of smart growth, specifically the accommodation of future development in the Berlin area, are enabled through this BMP because it reduces the loss of commercial property within the project area and may also reduce the loss of property that might occur otherwise as part of future projects.