Existing Condition and Other "Local" Project Alternatives
The existing condition presently involves about million a year in dredging on average,
bypassing to the chronically eroding Gilgo Beach, the threat of erosion along Oak Beach,
occasional back passing of sand to Fire Island Beaches to the east and, a nearly unstable inlet and
navigation channel. Based on an informal estimate of 0 million dollars to relocate the inlet,
including construction of the dual jetties, and reduced cost of maintenance and bypassing at the
new entrance of 0,000 annually (same order of magnitude as for other south shore inlets),
cost savings for the relocated inlet would begin to accrue sometime after 20 years, given the
increased cost of future dollars and that bypassing would likely not be necessary at the relocated
inlet for a number of years. The need for back passing would be minimal because of the
impoundment functioning of the new east jetty. Therefore, an order-of-magnitude cost estimate
indicates the hypothetical relocation alternative is cost effective and justified. Societal,
environmental, and other physical process issues remain, some of which are discussed below.
"Local" or project-specific alternatives for reducing costs and providing a more reliable
channel have been identified by MNE (2000), compiled based upon deliberations by a technical
committee with members drawn from state and federal agencies as well as a local university.
Among project-specific alternatives are those that (1) extend the existing jetty, (2) reconfigure
the training dike, and (3) optimize (if possible) the channel and deposition basin configurations.
The project-specific alternatives do not addresses regional sediment considerations and have
limitations in being short-term and in bringing relatively small incremental improvement. It is
noted that the MNE (2000) compilation includes inlet relocation as discussed here, but gives it a
low rating due primarily to judged high risk of creating a new inlet.
Selected Regional Sediment Issues Associated with Inlet Relocation
In this section, selected regional sediment management issues are identified, and the possible
performance of two alternatives are examined and compared. The two alternatives are
(1) maintaining the existing condition (or implementing some small modification of the existing
condition), and (2) relocating the inlet and constructing dual jetties as described above. The
selected issues and comparison are summarized in Table 1.
Navigation Reliability. Navigation reliability (safe navigation for greatest possible sea state for
the given design vessel) is expected to be better for the relocated inlet. Vessels can exit heading
into the incident waves, and they will be protected by the jetties while crossing the surf zone
under mild to moderate (navigable) wave conditions.
Cost of Channel Maintenance Dredging. The relocated inlet is expected to have maintenance
requirements similar to the other five federally maintained channels on the south shore of Long
Island, meaning 1/5 to 1/10 the dredging cost of the existing inlet. Less channel sediment
shoaling during storms is expected, meaning less potential for costly emergency dredging.
Sediment Sharing with Adjacent Beaches (Bypassing and Backpassing). Collapse of the ebb
shoal at the existing inlet will provide sand to the downdrift (western beaches), including Gilgo
Beach, for 50-100 years after inlet relocation. The beaches will widen and increase in volume,
reducing or completely eliminating the erosion threat to infrastructure. Bypassed material
associated with maintenance dredging of the relocated inlet will enter the littoral stream to reach
the downdrift beaches. Consideration would need to be given for gradual removal of the old
jetty to allow Democrat Point to realign with beaches to the west, eliminating a sharp, cape-like