Dredging the Manasquan River Complex – Creating Capacity, Beneficial Use Through Beach Nourishment, and Enhancing the Greater Good of the Manasquan Inlet Area
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DREDGING SUMMIT & EXPO ’18 PROCEEDINGS DREDGING THE MANASQUAN RIVER COMPLEX – CREATING CAPACITY, BENEFICIAL USE THROUGH BEACH NOURISHMENT, AND ENHANCING THE GREATER GOOD OF THE MANASQUAN INLET AREA W.S. Douglas1 , W. Henderson2, M. Marano3, T.W. Chen4 and S. Flanigan5 ABSTRACT The Manasquan Inlet is one of New Jersey’s busiest recreational and commercial maritime complexes. This busy seaport is facilitated by a Federal channel (2.3 nautical miles (4.26 km)), 13 State channels (5.9 nautical miles (10.93 km)), and numerous local channels. Maintenance of this system is typically performed by hydraulic cutterhead pipeline dredge with placement in one of two confined disposal facilities (CDF’s) or on public beaches (coarse-grained material only). We will discuss the recently completed maintenance dredging of the Manasquan River Complex. This state-sponsored project provided direct relief for over fifty waterside businesses, over 180 private residences, multiple recreational access and bathing areas, and a critical United States Coast Guard (USCG) Search and Rescue Station. As part of the recovery effort following Superstorm Sandy, NJDOT performed a system wide condition survey of State channels. This survey determined that the Manasquan complex would require dredging of approximately 390,000 CY (298,180 CM) of sediment to return it to a state of good repair. Of this, over 41,500 CY (31,700 CM) of material could be directly attributed to the storm. While ample capacity for coarse grained material was available on several public beach areas, the two confined disposal areas did not have available capacity for the 60 percent of the material that was determined to be fine grained. It was determined that only the Gull Island CDF might be modified to accept dredged material. Gull Island CDF is a 9.36 acre (3.79 Ha.) facility on a 22 acre (8.90 Ha.) island, just west of the Inlet. Project timing precluded expanding the facility footprint and the existing berms were very steep and underlain by soft, organic soils, so raising the dike crest elevation was not a viable solution. Construction of a geotextile reinforced stockpile using the existing CDF material was proposed. The stockpile was designed to an elevation nearly fifteen feet (4.5 M) higher than the confining berms to create the needed capacity. A subsurface monitoring program was also proposed to detect any deep-seated movement of the existing berms that could eventually lead to failure. Project improvements include placing sand on one of New Jersey’s most popular bathing beaches consistent with a USACE beach fill program; the addition of Cooks Creek channel, home to the USCG Search and Rescue Station and charter and commercial fishing enterprises; and a mutually beneficial solution for Monmouth County by providing sand for a County beach. 1 Dredging Program Manager, New Jersey Department of Transportation Office of Maritime Resources, 1035 Parkway Avenue, Trenton, New Jersey 08625 USA T: 609-530-4770, Email [email protected]. 2 Resident Engineer, New Jersey Department of Transportation Office of Maritime Resources, 1035 Parkway Avenue, Trenton, New Jersey 08625 USA T: 609-530-4770, Email [email protected]. 3 Engineer of Record, WSP USA, Inc. 2000 Lenox Drive, Lawrenceville, New Jersey 08648 USA T: 609-512-3516, Email [email protected]. 4 Geotechnical Engineer, WSP USA, Inc. 2000 Lenox Drive, Lawrenceville, New Jersey 08648 USA T: 609-512- 3444, Email [email protected]. 5 Design Engineer, Gahagan & Bryant Associates, 9008 – O Yellow Brick Road, Baltimore, Maryland, 21237-5608 USA T: 410-682-5595, Email [email protected] 422 DREDGING SUMMIT & EXPO ’18 PROCEEDINGS Details of the construction and dredging sequence, monitoring program, and challenges met during the project will be discussed. Keywords: Dredged material management, maintenance dredging, beneficial use, beach replenishment, confined disposal facility INTRODUCTION Figure 1. Project Location Map – Manasquan Inlet – Ocean and Monmouth Counties, New Jersey The Manasquan River forms the border between Ocean and Monmouth Counties on the coast of central New Jersey, emptying into the Atlantic at the Manasquan Inlet; one of several Federally-maintained coastal inlets in the State and the initiation point for the NJ Intracoastal Waterway. Figure 1 shows the general project area located on the central New Jersey coastline. The Manasquan River and Inlet is one of New Jersey’s busiest recreational and commercial maritime complexes, home to 16 marinas, 50 water dependent commercial businesses, a commercial fishing fleet, a US Coast Guard search and rescue station, several heavily used bathing beaches and numerous ocean and riverside residences. Access is facilitated by a Federal channel (2.3 nautical miles 4.26 km)), 13 State channels (5.9 nautical miles (10.93 km)), and numerous local channels, lagoons and berths. Boaters can not only access the ocean via the Inlet, but they can also access Barnegat Bay via the Intracoastal Waterway which continues south through the Manasquan Canal, located approximately 2.7 miles (4.35 km) west of the Inlet. Dredging of one or more portions of the system is required nearly yearly, with material being placed on beaches or in one of two confined disposal facilities (CDFs) located at opposite ends of the 5.6 mile (9.01 km) long system. The larger (and more important) of the two CDFs is on Gull Island, a 22 acre (8.90 Ha.) island located in the middle of the River just inside the Inlet. In addition 423 DREDGING SUMMIT & EXPO ’18 PROCEEDINGS to being home to the 9.36 acre (3.79 Ha.) CDF, it is also a bird refuge, providing critical nesting and foraging habitat for a number of protected species including Osprey, American Oystercatcher and Least Tern. As part of the recovery effort following Superstorm Sandy, NJDOT performed a system-wide condition survey of State channels. This survey determined that the Manasquan complex would require dredging of approximately 390,000 CY (298,180 CM) of sediment to return it to a state of good repair (authorized depth). Of this, over 41,500 CY (31,700 CM) of material could be directly attributed to the storm. While ample capacity for coarse-grained material was available on several public beach areas, neither of the two confined disposal areas had any appreciable capacity remaining. This necessitated a prioritization in order to provide as much navigational relief as possible while minimizing cost and maximizing our use of the available capacity. Since the CDF at the far western end of the complex was the smallest, and held in private ownership, the focus naturally fell to the larger publicly-owned Gull Island CDF. DESIGN PARAMETERS AND PROJECT CONSTRAINTS State Channels Using the prioritization matrix shown as Table 1, below, five channels were initially selected to be dredged within the project area: Lower Manasquan River Channel, Crabtown Creek Channel, Kings Bridge Channel, Wills Hole Thorofare Channel, and Wills Hole West Channel. Table 1. Prioritization matrix for the State channels proposed to be dredged in the Manasquan River Complex, Ocean and Monmouth Counties, New Jersey. Channel Shoaling Usage Economic Logistical Volume Dredge Final Status Value Constraints - CY (CM) Material Rank Distance to the Composition CDF ft. (M) Upper Severe High Moderate 26,250 (8,000) 177,285 >75% fine Low Manasquan (135,500) River Lower Moderate High Moderate 18,000 (5,490) 35,694 Coarse with High Manasquan (27,290) some fine River Sawmill Severe High Low 21,750 (6,630) 42,706 >75% fine Low Creek (32,650) Glimmer Moderate Low Low Historic Bridge 10,508 >75% fine Low Glass (8,030) Watsons Moderate Moderate Low Historic Bridge 14,340 >75% fine Low Creek (11,000) Shermans Moderate Low Low Historic Bridge 5,138 >75% fine Low Creek (3,930) Crabtown Severe Moderate Low 4,750 (1,450) 10,763 >75% fine High Creek (8,230) Kings Moderate Low Low 3,250 (990) 8,681 >75% fine Mod Bridge (6,640) Channel Wills Hole Moderate Low High 2,750 (840) 45,899 Coarse with High Thorofare (35,100) some fine Wills Hole Moderate Low Low 7,500 (2,290) 12,827 >75% fine Mod West (9,800) Cooks Creek Minor Moderate High 2,750 (840) 1,676 >75% fine Low (1,280) 424 DREDGING SUMMIT & EXPO ’18 PROCEEDINGS Manasquan Severe Low Low 5,750 (1,750) 2,040 >75% fine Low Yacht Club (1,560) Clarkes Minor Moderate Moderate 9,250 (2,820) 3,372 >75% fine Low Landing (2,580) Gull Island Confined Disposal Facility Following an initial survey, it was determined that the Gull Island CDF had insufficient capacity for the channels targeted for priority dredging (approximately 26,000 CY (19,900 CM) of available air capacity in the pre-existing condition of the Gull Island CDF). Several reconstruction alternatives were investigated: excavating and raising the confining berms, expanding the existing CDF footprint, and reconstructing and restoring an existing bulkhead and area of historic fill on the east end of the island. Limited access for an in-depth geotechnical investigation, lack of as- built drawings and steep existing slopes (between 1.5 and 2:1, even steeper in some isolated areas) eliminated the alternative of raising the existing berms. Expanding the CDF footprint and/or restoring the existing bulkhead area would require a lengthy permitting and alternatives analysis process. Unfortunately, environmental windows for dredging in coastal NJ are very restrictive (typically 6-9 months), therefore an extensive permitting process could delay the project start for a year or more. Given the critical needs identified for this important resource, delays of this magnitude were not acceptable. From the engineering perspective, several issues were quickly identified. First, it had been previously determined that a very soft, organic soil layer was present about 10 ft.