The US Army Corps of Engineers, New York District, Passaic River Division (PRD) has been working on plans to reduce flooding in the Passaic River Basin since 1939, but none of those plans was authorized. Congress then authorized the Corps to conduct a new study of the basin for the state of New Jersey in the Water Resources Development Act of 1976. The Corps evaluated more than 150 plans, presented an array of plans to the state of New Jersey, and the state selected a dual-inlet water diversion tunnel system as the centerpiece of its comprehensive flood protection program for the basin. In November 1990, Congress authorized construction of the $1.2 billion Passaic River Flood Protection in the Water Resources Development Act of 1990; the project cost to the state is $310 million. The major elements of the project are two underground tunnels, a 20. l-milelong main tunnel about 40 ft in diameter and a 1.2-mile spur tunnel about 22 ft in diameter that convey central basin flood waters to an outlet in the vicinity of Kearny Point in Newark Bay. The proposed diversion tunnel and surface works are generally designed to ,protect against the 100-year flood event, during which it is anticipated that a flood volume equal to that of Newark Bay will be discharged over a two-day period. The Corps is studying the impact of discharging water from a diversion tunnel into Newark Bay and its tributaries, the Passaic and ~ackensack Rivers. While a diversion tunnel discharge itself would not cause significant flooding, it is the combination of a storm surge generated by hurricanes and northeasters coincident with the diversion tunnel operation that the Corps is evaluating. The main purpose of this study is to determine the stage-frequency curves for various locations and conditions throughout Newark Bay and the tidally influencedportion of the Passaic and Hackensack Rivers. These curves can be used to determine the heights of storms in the vicinity of Kearny Point. Another objective of this study is to examine the likelihood that a significant.diversion tunnel discharge could be coincident with a major storm surge, and to simulate such a combination, thereby determining the potential for additional flooding. During the 1970's and 19801s, a two-dimensional hurricane surge model was used for the Newark Bay/Passaic/Hackensack River system as boundary forcing for an interior Dynamic Estuary Model (DEM) to estimate flood frequencies. The current study builds on previous models and revalidates and uses a modified DEM to accurately simulate tidal elevations in the system using recent data on system bathyrnetry, river cross sections, topography, and historical hurricane, northeaster, and rain flow data through 1991, in combination with a refined grid. The revalidated DEM is a valuable engineering tool more accurately simulating tidal and river flows than previous studies. The coincidence analysis confirmed that large river flows are unlikely to coincide with large surges from New York Bight. Time history plots of several individual events show that there is a weak relationship between storm tides and river flows, and that the river flows lag the tides by several days; large storm tides with large Passaic River flows (lagged by 0-2 days) are extremely rare events. An increase in elevatiotis due to sea level rise has been accounted for in the stage-frequency distribution curves. The bootstrap method, a modification of the joint probability method, was used to generate stage-frequency distributions with 33 synthetic storms approximating the entire population of historical storms. Results of coincidence analysis show that large storm tides together with large river flows is an extremely unlikely combination, and they can be treated as essentially independent events. However, the analysis indicates that the likelihood of elevated river flows following storm tides (by 0-2 days) is quite strong. The effect of tunnel discharges to Newark Bay will have little effect (less than 0.1 foot) on tidal elevations in the lower Passaic River, Hackensack River, and Newark Bay where flood-prone areas are located. The inclusion of future project conditions, such as control levees in the vicinity of Kearny Point, changes the future unimproved stage-frequency distributions by less than 0.2 ft in the lower parts of the Passaic and Hackensack Rivers and in Newark Bay. However, the effect of tunnel diversion into Newark Bay will be to reduce river flooding in the upper tidal Passaic River by several feet.
Passaic River Basin Flood Protection Project Storm Surge Analysis
Technical Report ; CERC-92-10
1992
6845876
Report
Elektronische Ressource
Englisch
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