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Corps Fails to Assess Flooding Impacts from Dredging

Corps Fails to Assess Flooding Impacts from Dredging

The following are comments submitted to the Army Corps of Engineers by Lisa Rinaman, the St. Johns Riverkeeper, on December 29, 2017, regarding the Corps' failure to fully assess potential flooding impacts from the propsed dredging of the St. Johns River:

"On behalf of our members, St. Johns Riverkeeper (SJRK) submits the following comments regarding the December 2017 Draft Supplemental Environmental Assessment – Review of Recent Storm Events and Flooding (DSEA) released on December 14, 2017.

SJRK has continually voiced opposition to the proposed Jacksonville Harbor Channel Deepening Project due to faulty, incomplete information and analyses presented by the U.S. Army Corps of Engineers (USACE) regarding environmental, as well as economic impacts. The Corps has also failed to provide a beneficial mitigation plan to offset harm to the St. Johns, its tributaries and adjacent properties.

Following Hurricane Irma, it is paramount that any increase in future flood damage potentially resulting from the proposed deepening project must be fully understood by the Corps, the City of Jacksonville leadership and the general public. Of specific interest is the probable increase in nuisance flooding which will occur in the downtown, San Marco, Riverside and Ortega neighborhoods due to a predicted increase in the elevation of tidal waters – after the deep dredge.

The Army Corps DSEA fails to acknowledge or consider relatively irrefutable adverse consequences that will occur on a high frequency (i.e. annual) basis. In contrast, the federal predictions of project “impact” have been limited to scenarios associated with low frequency (i.e. 50 and 100 year) storm events in combination with a 50 to 100 year horizon of sea level rise. Although of scientific value, these federal predictions do not portray the project’s immediate impacts that must be dealt with on an annual basis by a portion of the City of Jacksonville, including waterfront development far removed from the area of river deepening.

Hurricane Irma well demonstrated the extreme vulnerability to flood damage that exists along the riverfront within downtown, as well as the San Marco, Riverside and Ortega waterfront areas of Jacksonville. The latter occurred as a combination of hurricane related storm surge, rainfall, preceding super-elevated river water level conditions, saturated uplands, and a significant duration wind field originating from southerly sectors (blowing directly up the river).

Of specific interest is the fact that the 2017 resultant historical water levels recorded in the downtown urban core, San Marco, Riverside and Ortega were not the result of a statistical “50 or 100-Year Storm” as addressed by the USACE study. Actually, measured sustained wind speeds at the Jacksonville Naval Air Station on the St. Johns River never even reached hurricane force during Hurricane Irma.

Adding to the cumulative water levels experienced were the seasonal astronomical tides which during each hurricane season are predictably the highest of the year. For example, in September, October and November of 2017, the highest monthly astronomical tide levels predicted were .35 ft., .45 ft., and .5 feet above the elevation of mean high water, respectively, at the Acosta Bridge tidal station. These water levels combined with nor’easter effects which cause additional super-elevation of the upper reaches of the St. Johns River in the fall months, typically cause annual nuisance flooding in the San Marco, Riverside and Ortega riverfront areas – in the complete absence of the added effects of any tropical or extra-tropical storm events. A major contributory factor to nuisance flood events is the inability of the developed uplands to drain when the river is “high”. Accordingly, the assessment of risks of the proposed deep dredge to businesses and homeowners should be considered to be a “game of inches” – due to the present day vulnerability of downtown neighborhoods. Any additional water level increases during those May–November months when water levels are already higher than average can cause significant property damage and loss of physical access to both businesses and residences. To-date this type of impact analysis has not been presented to either COJ elected officials or the general public.

In contrast, the types of USACE analyses associated with deep dredge effects avoid addressing high-frequency, “baseline” type impacts that consider today’s existing conditions. That is, by design and tradition the USACE analyses consider the effect of a project based upon a low-frequency, 50- or 100-year hurricane storm in the future – a storm that doesn’t necessarily reflect the reality of today’s frequent nuisance flooding conditions.  Hence, the numerical simulation and accounting for the above described documented hydrological effects argues for a significantly different analysis than the type of storm surge modeling performed to predict 50- and 100-year water levels associated with the Jacksonville harbor deepening project, and in particular where those analyses seek to likewise factor into their predictions 50 years-worth of sea level rise.

The federal predictions are based upon numerical models for the simulation of open coast surge based upon techniques similar to those utilized for purposes of the federal flood insurance mapping of low frequency events. For example, predicted 50- and 100- year open coast surge levels were propagated from the ocean – through the project area – up the St. Johns River for purposes of providing water level hydrographs throughout the “Jacksonville Harbor Vicinity,” which by definition extended through downtown Jacksonville and beyond. Various calibrations of the federal model were attempted based upon simulations of Hurricanes Frances and Dora. The latter was the historical hurricane of record for Duval County which occurred in 1964. Hurricane Dora entered the State of Florida in the vicinity of St. Augustine and South Ponte Vedra Beach. Accordingly, its trajectory bore little resemblance to Hurricane Irma which generally moved up the western center of the State as it impacted Duval County.

The prescribed numerical modeling approach employed by the USACE for purposes of evaluating pre- and post-channel deepening water elevations within the area of channel deepening are in all probability realistic for that limited area of interest – only. Conversely, what the federal modeling strategically avoids is the reliable prediction of present day high-frequency storm impacts in the downtown urban core and adjacent developed waterfronts of San Marco, Riverside and Ortega – in combination with increases in tide range which are acknowledged to result from the proposed channel deepening. As noted above, the timing of these high frequency storms, tides and accompanying nuisance flooding – such as during annual nor’easter events – are synonymous with each annual hurricane season.

Executive Order EO11988, Floodplain Management requires federal agencies to avoid to the extent possible the long and short-term adverse impacts associated with the occupancy and modification of floodplains. To comply with EO11988, impacts of the proposed Jacksonville Harbor Deepening Project were to be identified.

The USACE was required to:
1. Estimate the potential impacts of the proposed federal project on water levels within the St. Johns River
2. Determine if the potential impacts are significant enough to affect the flood hazard zones designated by FEMA

Without providing any analysis regarding the quantification of floodplain impacts, the USACE study simply states that “This project would have no adverse impacts to floodplain management” (GRR/FEIS ref. pg. 289). At face value, this conclusion is hard to accept when the Corps’ own modeling exercises indicate increases of water elevations of an additional 0.5 to 0.7 feet in the developed areas bordering the deepening project – for a 100-year storm with sea level rise. This includes the entirety of the Mill Cove shoreline. The damages and loss of homes, contents and businesses throughout the San Marco, Riverside and Ortega areas bordering the St. Johns River during Hurricane Irma are clear evidence that any level of floodplain increase resulting from the federal project represents significant potential financial losses and endangerment of the citizens of Jacksonville. To that end, the USACE can be considered to be noncompliant with respect to the requirements of EO11988.

It would appear that the DSEA issued by the Corps in late December 2017 is an effort to assure City of Jacksonville leadership and the general public that the occurrence of Hurricane Irma in no way invalidated the findings of the initial federal study. More specifically, the document concludes that “The Corps modeled events comparable to, or more severe than Hurricane Irma,” and that “recent storm events and flooding in the vicinity of the Jacksonville Harbor Navigation Project do not constitute new circumstances or information relevant to environmental concerns bearing on the project or its impacts.” Again, the Corps completely discounts or inadvertently misses the significance of the probability of high frequency flooding events in the City core due to continued deepening of the St. Johns River channel. It likewise fails to discuss additional flooding potential in developed areas directly abutting or in the vicinity of the project channel improvements.

The Corps’ modelling fails to analyze water levels and the project’s effect upon flooding in the weeks after a hurricane – during which the river levels remain anomalously high and lead to continued flooding. In fact, for the one or two days that are included in the model’s calibration after the peak storm has passed, the Corps’ model consistently and significantly under-predicts the actual water levels that were observed in the downtown and upriver areas that were included in the model.

That is, the model fails to accurately predict the elevated river levels that consistently occur in the fall, during which nuisance flooding is observed and sensitivities to increased water levels are greatest.

The December 2017 DSEA document re-explains the federal modeling approach by which it predicted potential future effects to the City of Jacksonville downtown urban and residential core. However, the federal analysis and discussion seek to portray the impacts of the project solely in combination with low frequency (50- and 100-year) storm events and future sea level projections. Since the latter occur over a long period of time (say 50 years or more into the future), such a comparison fails to relate or address in any meaningful way the present day probability of exacerbated higher-frequency flooding which will occur annually after channel deepening and which should be the greatest concern to the City of Jacksonville given the documented flooding caused by Hurricane Irma.

Any increase in the severity of high frequency seasonal flooding in the San Marco, Riverside and Ortega areas (even if only a few inches) can be highly impactful to private and public properties and infrastructure, as well as physical access to residences and businesses alike. The USACE acknowledges a predicted increase in the elevation of high tide of at least 0.2 feet in the San Marco and Ortega areas after channel deepening. That should be of significant concern to both the citizens of Jacksonville and their elected leaders in the impact evaluation of any proposed channel deepening project. Attempting to dilute that acknowledged increase in water level by comparing it to surge levels from a 50- or 100-year storm in the ocean and 50+ years of sea level rise does a disservice to those desiring a meaningful analysis of project impacts.

It is an undeniable fact that decades of federally sponsored deepening and channelization of the St. Johns River has “invited the ocean downtown.” As such, dredging has incrementally exposed the City’s riverfront interior to increased fluctuations in ocean water level, by making the downtown river more tidal. At the same time, the downtown urban core and adjacent waterfronts are 120+ years old – developed at a time when the sea level was at least 1 foot lower than present. As sea level continues to increase, and storm water drainage problems intensify, and the surge and tides of the ocean can more readily reach upriver, it is evident that every inch of water level rise is important when expressed in the context of the low-elevation areas of the St. Johns River waterfront that are already subject to high frequency flooding.

Accordingly, increases in river water levels caused by further river deepening cannot be dismissed as trivial in the context of urban flooding.

It is the responsibility of USACE to provide the public a thorough and honest assessment of the potential benefits, impacts, risks and costs of the proposed deepening of the Jacksonville Harbor and a transparent and open decision-making process. Anything less, fails to meet the minimum thresholds set by Federal Law.

USACE fails to adequately assess the environmental impacts, fails to provide a beneficial mitigation plan to offset harm to the St. Johns and its tributaries, and fails to articulate the need for this project.

The USACE release of this important yet inadequate assessment on December 14, 2017 with comments due on December 30, 2017 is a further disservice to the citizens of Jacksonville.

We request a 30-day extension for public comment period to allow citizens and the City of Jacksonville time to assess and discuss this critical issue. A sixteen day comment period over the holidays is simply inadequate.

We also request a USACE public meeting with City of Jacksonville officials to discuss flood risks resulting from the deep dredge prior to completion of the DSEA.

We cannot afford to roll the dice with the future health of our river or the surrounding riverfront communities until the flood risk has been fully vetted."

Click here to download the comments. 
 

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