Although maps and charts of the Jamaica Bay landscape extend back to the 17th century (Sanderson, 2016), the first thorough bathymetric and topographic maps were made by the US Coast Survey between the 1840s and 1870s. The first tidal measurements also date from this period (e.g., Talke and Jay, 2013). Because the 1870s time period predates most channel deepening, this period constitutes a good proxy for conditions prior to major 20th century anthropogenic modifications.

To develop numerical models of the “present-day” and 1870s conditions, we first created digital elevation models and land cover maps at 30 m resolution. The domain extends eastward and northward to land up to 6 m NAVD88 elevation and extends westward past Coney Island. The landscape reconstruction from the 1870s forms a waypoint between the pre-European landscape of ca. 1609 and modern conditions (Sanderson, 2016). Since no bathymetric data are available from before the 19th century, comparisons between the 1600s and 1800s are qualitative (see Sect. 4.3).

A hydrodynamic model was applied to the historical and modern “landscapes” (land surface elevation and roughness) and used to simulate an ensemble of storm tide events described in Sect. 2.3. The Stevens Estuarine and Coastal Ocean Model (sECOM) is a free-surface, hydrostatic, primitive equation model with terrain-following (sigma) vertical coordinates set on an orthogonal, curvilinear Arakawa C-grid (Georgas and Blumberg, 2010; Blumberg et al., 1999). The model has been further developed with regard to wind stress formulations (Orton et al., 2012), coupled wave modeling (Georgas et al., 2007), and land wetting and drying (Blumberg et al., 2015). It has been used to provide validated and accurate ensemble 3D storm tide predictions as part of the NY Harbor Observation and Prediction System (NYHOPS; Georgas and Blumberg, 2010) and the Stevens Flood Advisory System (Jordi et al., 2018). Typical errors in hindcasts of extreme storm tides (e.g., Hurricane Sandy) are 0.15–0.20 m (Orton et al. 2016b).

The Jamaica Bay model grid was a 30m×30m square-cell grid (Orton et al., 2015). This grid was doubly nested inside two larger model domains that represent (1) the regional coastal ocean and estuaries from Maryland to Cape Cod and (2) the Atlantic Ocean from Cape Hatteras to Nova Scotia (Orton et al., 2016b). Storm meteorological forcing for the regional and large-scale grids was spatially and temporally variable and is described in Orton et al. (2016b) and the next section.

Simplifying assumptions are used for the model simulations on the Jamaica Bay grid for computational efficiency in simulating a large number of storms. While the regional coastal and estuary modeling used 3D simulations, the model's 2D mode was used for Jamaica Bay (e.g., Orton et al., 2015). This is a common practice in estuary storm tide modeling (Familkhalili and Talke, 2016; Kennedy et al., 2011). While stratification can have a small influence on storm tides in stratified estuaries (Orton et al., 2012), Jamaica Bay has limited freshwater input and weak stratification (Marsooli et al., 2018). For computational efficiency and because our focus here is on storm tides and “still-water” elevations, a wave model is not coupled with the local Jamaica Bay grid. The broad shallow continental shelf at the apex of the New York Bight leads to relatively small impacts of waves on estuary storm tide temporal maxima (e.g., due to wave setup; Marsooli and Lin, 2018; Lin et al., 2012). Lastly, the time-varying meteorological forcing was assumed spatially constant on the Jamaica Bay grid because the bay is only ∼10 km wide.

The gridded land elevation and land cover type datasets for the 1870s and present day were interpolated onto the model grid to create land elevation and Manning's n roughness model input files. The 30 m resolution modeling does not resolve fine-scale features such as elevated seawalls, though they are rare in this area. In 2D tide and storm surge modeling studies, a common simplified approach (Irish et al., 2014; Mattocks and Forbes, 2008; Szpilka et al., 2016) to representing the effects of wetlands and other natural features is to treat them as enhanced landscape roughness features through a variable called Manning's n. Reasonable estimates for Manning's n values are 0.045 for intertidal wetlands and eelgrass (Zostera marina) beds, 0.020 for unvegetated continental shelf and estuary substrate, and 0.10 and 0.13 for medium- and high-intensity developed land, respectively (Mattocks and Forbes, 2008). This approach has previously been applied to Jamaica Bay (Orton et al., 2015).

Depending on the purpose, different mean sea levels were used in the study. To determine habitat and tidal datum changes, we run tide-only simulations using the mean sea level that existed for a given landscape year. Storm simulations for both the modern and historic (1870s) period use 2015 mean sea level to quantify the effect of landscape change on flood hazard and isolate this process from the effect of sea level change. Mean sea level for the 1870s was -0.28 m (Kemp and Horton, 2013), and in 2015 it was +0.09 m (based on smoothed recent trends), both relative to the 1983–2001 mean sea level datum at the Battery (NOAA station 8518750). These values are -0.37 and 0.00 m NAVD88, respectively, based on conversions for the Jamaica Bay Inwood tide gauge (USGS station 01311850). An elevated (or reduced) mean sea level was imposed as a constant offset to a given simulation's offshore elevation boundary conditions at the edge of the Jamaica Bay grid. This is a reasonable simplification here because recent work showed virtually no change to tides at nearby Sandy Hook (NOAA station 8531680) when there is sea level rise (below a 1 % change to tide range per meter of sea level rise; Kemp et al., 2017).

Tide-only simulations for 1878 were run for a 40 d period that overlapped with water level observations made from 13 August through 21 September 1878 at a pier on the north side of the Rockaway Peninsula (Fig. 1). The tide simulation for the present day covers a 35 d period from 1 August through 5 September 2015. Since wind forcing during the late summer is typically weak, these tide-only simulations are useful for direct validation of the model.

Model validations were performed for the 1870s era model, and the present-day model was previously validated (Orton et al., 2015). The prior storm validation of the present-day model for Hurricane Sandy showed a time series RMSE of 20 cm and high water mark RMSE of 19 cm (Orton et al. 2015). The tidal validations here use summertime periods without strong wind influences, and modeled time series were compared to observations for both 1878 and 2015 using RMSE and the Willmott skill (e.g., Warner et al., 2005). The 2015 period included 7920 samples taken at 6 min intervals over a 33 d period at the Inwood USGS gauge station. The 1878 period included only daytime measurements, with 2438 samples taken at 10 min intervals over a 37 d period at the Holland House pier on the north side of Rockaway Peninsula. The mean error is subtracted before computing statistics to account for possible remote sea level anomalies or steric sea level variations and because the 1878 tide staff datum is poorly known. The results for the tide modeling time series validation for 1878 were 0.09 m RMSE and 0.991 skill, while the results for the 2015 period were 0.09 m RMSE and 0.989 skill.

Historic and modern tidal datums, tidally wetted area, and intertidal zones were assessed by the following methodology. First, simulated water levels after a 2 d spin-up period were harmonically analyzed (Pawlowicz et al., 2002) at historic gauge locations. A year-long synthetic tide time series was then produced using appropriate nodal corrections, and once- and twice-daily water level minima and maxima were compiled and averaged to compute tidal datums such as mean lower low water (MLLW) and mean higher high water (MHHW). The tidally wetted area was then defined as the area wetted at high tide in Jamaica Bay after MHHW conditions at Rockaway Inlet. The intertidal area is similarly defined as the difference between the tidally wetted area and the area flooded at the low tide occurring after a predicted MLLW tide at Rockaway Inlet.

A probabilistic flood hazard assessment was used to quantify the annual probabilities of exceedance (or inversely, the return periods) for any given storm tide. We applied the storm set and statistical framework utilized by Orton et al. (2016b), which employed a joint probability method of flood hazard assessment that is an ensemble simulation of a diverse set of possible storms (the storm climatology) including both synthetic tropical cyclones (TCs; e.g., hurricanes) and historical extratropical cyclones (ETCs; e.g., nor'easters). The synthetic TCs spanned all combinations of a complete range of intensities (6 bins), sizes (3 bins), speeds (3 bins), landfall locations (5 bins), and angles (3 bins), and each simulated TC had an estimated annual frequency of occurrence based on an extensive simulation with a statistical–stochastic TC model (Hall and Yonekura, 2013). The wind and pressure meteorological forcing for ETCs came from historical reanalysis data from Oceanweather, Inc., whereas the forcing for TCs came from simplified parametric TC models. The assessment methods were validated by comparison to historical data at multiple levels of the study, demonstrating unbiased storm tide simulations and storm tide hazard estimates (versus return period) relative to historical events (Orton et al., 2016b). Additional details of the assessment, including historical data, validations, storm climatology development, statistical analysis, and uncertainty quantification, are given in Orton et al. (2016b). The storm tide modeling results from the larger-scale model grids in this prior study were applied as offshore boundary conditions to the Jamaica Bay domain simulations for the present study.

Some simplifications of the application of the Orton et al. (2016b) flood hazard assessment to our Jamaica Bay submodels are noted here. The prior flood hazard assessment included 1516 storm simulations (606 TCs and 961 ETCs), but we use an abbreviated storm set to reduce the computational expense. The abbreviated set of 80 ETCs includes all the same storm events but fewer random tide permutations for each storm. Instead of 50 simulations for the top 19 historical ETC storm tide events, there were 5 or 10 simulations each for the 11 highest ETC storm tides that are most relevant for the 5-year and higher return periods. The abbreviated set of 64 TCs includes a range of storm tide events from low to high magnitude (1.5 to 6.0 m). Model results for simulated TC events at a given magnitude are then used as a proxy for all the events at that magnitude, thus representing all 606 storms. A statistical comparison of the abbreviated versus full storm set showed minor differences of less than 5 % across 5- to 500-year storm return periods, validating our approach. The historic and modern model landscapes are subjected to the same set of storms, and therefore any differences in storm tide hazard reflect geomorphic changes rather than artifacts of the simplified hazard assessment.

Simple “leverage experiments” were then used to isolate the effects of specific historical landscape changes on the simulated water levels during a fast-moving, Category 3 hurricane that approximates an event from 1821 (Orton et al., 2015). The storm surge from this hurricane (3.4±0.4 m) likely exceeded the surge in Hurricane Sandy (2.76 m) and produced water levels of ∼3 m above the 1821 mean sea level despite occurring near low tide (Orton et al., 2016b). Meteorological forcing for the simulations was created from parametric models (Orton et al., 2015). The following experiments were performed using modifications to the modern-day landscape to mimic the historical landscape's main features one by one:

tapered shallowing of the channel depth from offshore (8 m) into the inlet (5 m) and into the innermost areas of the bay (1 m depth);

The surface areas of many habitat types have changed dramatically since the 1870s in spite of an only 23 % reduction in interior bay area wetted by average daily high tides (Table 1). The reduction in total area is caused by the reclamation of fringing floodplain and marshlands but is partially offset by a growth of the bay westward due to an increase in inlet length.

Total marsh area has declined by 76 %, eelgrass area by 100 %, intertidal unvegetated area by 72 %, and total intertidal area by 73 %. The deepwater area (>4 m) has increased by 314 % (or alternatively, the 1870s had 76 % less deepwater area than the present). The estimates for wetland area and loss are nearly identical to the prior estimate of a loss of 75 %, from 64 to 16 km2 (NYC-DEP, 2007), but here we provide greater context of changes to other habitat types. The habitat type changes are computed within the differing bay interiors for the 1870s and present day, as enclosed by inlet boundaries (red lines) shown in the top panels of Fig. 5.

The flood hazard assessment shows similar basic features as found in the prior study of New York Harbor form which methods and offshore model boundary conditions were taken (Orton et al., 2016b). The estimated storm tide for return periods below 30 years is determined predominantly by the relatively frequent extratropical cyclones, and the curve (Fig. 6) has a relatively small slope of storm tide with increasing return period. For return periods above 30 years, tropical cyclones become increasingly important, and the slope abruptly increases at about the 70-year return period.

The results reveal that storm tides are markedly larger on the present-day landscape than the historical landscape across a wide range of return periods (Fig. 6; Table 2). Holding sea level constant at 2015 levels, the modern 10- and 100-year storm tides of 2.02 and 2.66 m are larger than historical simulations by 0.20 and 0.28 m, respectively, at the eastern end of the bay (Inwood). By contrast, sea level rise effects are small; when we simulate storms in the 1870s landscape with the 1870s sea level, the 100-year storm tide difference increases by 0.02 m, from 0.28 to 0.30 m. The increase in storm tides is attributable to decreased frictional effects, which scale as 1/H (e.g., Friedrichs and Aubrey, 1994). Because the ∼3 m increase in average depth caused by landscape changes is much larger than the ∼0.37 m increase in sea level, landscape changes dominate long-term changes to flood hazard.

Storm tides for the 1870s landscape are seen to clearly decrease with distance into the bay, with the 100-year flood elevation declining from 2.54 m outside the inlet to 2.42 m in the eastern part of the bay (Fig. 7). By contrast, present-day storm tides (and tides) amplify within the bay, and therefore the 100-year flood hazard increases from 2.56 (outside the inlet) to 2.70 m (eastern bay).

Increases in storm tide magnitudes in the bay do not necessarily lead to increases in flooding extent. While Fig. 6 shows that storm tides are increased substantially by the landscape changes from the 1870s to present, Fig. 7 demonstrates that the flooded area has substantially decreased for the 100-year flood. Table 2 shows that the 100-year flood area decrease is 41 km2, and the 10-year flood area decrease is 53 km2 across the model domain (both including the Coney Island and Jamaica Bay areas). The simple explanation for this is that fringing marshes across the region that were -0.25 to 0.50 m NAVD88 elevation in the 1870s were converted using landfill into elevated neighborhoods and airports at 1.5–3.0 m NAVD88 and thus are above this extra 0.20–0.28 m of storm tide. Similarly, for the United Kingdom the frequency of extreme sea level events increased over the last 100 years, yet coastal flooding has not increased (Haigh and Nicholls, 2017) because of improvements in forecasting and warning as well as flood defenses.

It was previously established that the bay's tide ranges have grown substantially (Swanson and Wilson, 2008), and we find similar results. Averaging high and low waters for daytime minima and maxima in 1878 over 37 d gives an observed tide range of 1.35 m, while observations for the entire year 2015 show a tide range of 1.73 m. This increase of 28 % is smaller than the prior estimate of the tide range change from 1899 to 2000 from Swanson and Wilson (2008), which was 1.16 to 1.64 m, or 41 %. However, the 1878 measurements are for a location at midbay (Holland House), whereas the 1899 measurements are for the easternmost end of the bay (Inwood or Norton Point), where tide attenuation (e.g., due to narrow, shallow channels and wetlands) was likely more pronounced.

Three of the leverage experiments led to large reductions in hurricane storm tide. The tapered shallowing leads to a change in the peak hurricane storm tide of -56 cm, or -23 % (Fig. 8a and b). The inlet narrowing leads to a change of -19 cm, or -8 % (Fig. 8c and d). Bay perimeter floodplain and wetland restoration results in a change of 31 cm, or -13 % (Fig. 8e and f). All the other landscape changes showed smaller impacts, indicating that they likely play little role in the long-term changes to storm tides. For example, extensive wetland restoration in the center of the bay (not the fringing wetlands) leads to a change in peak storm tide of only -2 % . A small rise in Manning's n across the entire bay's seabed from 0.020 to 0.025 (mimicking bay-wide lost eelgrass, sand bedforms, or shells) changed the peak by -3 %.

The 1870s landscape mitigates storm tide elevations (Fig. 6) and damps them as they propagate into the bay (Fig. 7) by several mechanisms identified in the leverage experiments (Fig. 8). First, the natural floodplain and its wetlands act as a storage reservoir, allowing a given volume of water to spread over a larger area but rise to a lesser vertical extent than a confined (modern) system (Fig. 8e and f). Second, as also pointed out in Orton et al. (2015), the shallower historical channels produce a more frictional environment that damped long waves such as tides and storm surge (Fig. 8a and b). Third, the narrower (Fig. 8c and d) and shallower inlet alter the impedance of the storm surge entering the estuary.

As has been shown previously, extensive wetland restoration in the center of the bay (not the fringing wetlands) leads to a change in peak storm tide of only -2 % because deep shipping channels around the wetlands are the primary conduit for flood waters (Orton et al., 2015; Marsooli et al., 2016). These results are also consistent with prior studies that showed that the influence of lagoonal wetland loss on water levels is different when it comes to lateral erosion versus landfill reclamation. Reductions in the tidally wetted area through wetland reclamation increase storm tides, while wetland retreat due to lateral erosion has the opposite effect (e.g., Donatelli et al., 2018; Picado et al., 2010).

Scaling suggests that the conveyance of long waves (e.g., storm surges, tides) through an inlet into a lagoonal estuary depends on the inlet choking number P=gb2H3T2CdLηAe21/2, i.e., on the drag coefficient (Cd), inlet width (b), length (L), and depth (H) as well as tide or surge amplitude (η), the long-wave period (T), and estuary surface area (Ae; e.g., MacMahan et al., 2014; Stigebrandt, 1980). For decreasing values of P, the inlet is increasingly “choked”, meaning that long-wave amplitudes strongly decrease entering the lagoon. For low values of P (below 5), choking becomes important, and for high P (above 10), the inlet geometry is unimportant (Stigebrandt, 1980). The dependence of P on H3/2 conveys a strong sensitivity to water depth, and dependencies on b and Ae convey modest sensitivities to inlet width and estuary area.

Our landscape reconstruction and numerical results suggest that the choking of long waves at Rockaway Inlet has been strongly reduced. For typical tides, we estimate that P increased from 4.5 in the 1870s to 13 at present. For a large-amplitude, short-timescale storm surge such as the 1821 hurricane, P has changed from 0.69 to 2.0. These changes are driven by a 41 % increase in the inlet's average depth (from 6.0 to 8.5 m), a 50 % increase in average width (from 1000 to 1500 m), and a 23 % reduction in bay area. A lengthening of the inlet (from 6600 to 9900 m) due to the growth of Rockaway Peninsula slightly counteracts these effects on choking number, however. Measured at its minimum along-inlet location, there is an 85 % increase in the cross-sectional area of the inlet, from 4800 to 8900 m2. Reflection and possibly resonance likely play a role in the amplification of tides in the present-day estuary, whereas the shallow water depths and frictional effects of fringing wetlands would also reduce these effects in the 1870s system.

The dependence of the inlet choking number on both geometric properties and long-wave characteristics helps interpret numerical results. Changes to inlet geometry and channel depth have most strongly changed the large-amplitude, high-impact storm surges caused by TCs such as the 1821 event. Smaller-amplitude events (e.g., ETCs) are less likely to be affected by inlet geometry; this is one of the reasons that there is a lesser change in the 5-year storm tide than the 100-year storm tide (Fig. 6). The difference between the 500-year storm tide for 1877 and present-day landscapes is not larger than that of the 100-year storm tide. This may arise because overtopping of Rockaway Peninsula becomes important, circumventing the inlet and invalidating the above scaling arguments.

Similarly, the tide or surge timescale (wave period) T impacts the conveyance of surge or tide into estuaries and back bays (Aretxabaleta et al., 2017; Kennedy et al., 2011) as well as the damping that occurs within them (Orton et al., 2015). Slow surge events such as Hurricane Sandy (e.g., those building to a peak over more than 18 h) are less affected by hydrodynamic drag (due to smaller flow velocity), potentially producing more severe estuarine floods (Familkhalili and Talke, 2016; Orton et al., 2015). These considerations suggest that modeling flood hazard or designing infrastructure using a representative “storm of record” can produce bias; instead, using an ensemble approach (such as that used here) with both small- and large-timescale events produces better results.

The primary reasons for increased storm tides – the floodplain (bay area) reduction, inlet width and depth increases, and bay channel depth increases (Fig. 8) – were all imposed by human activities such as landfilling, dredging, inlet stabilization (e.g., with the jetties), and shoreline hardening. Moreover, sea level rise of 37 cm since the 1870s raised total water levels during storms but only changed the storm tide by 2 cm. Because the ∼3 m increase in average depth caused by landscape changes is much larger than this increase in mean sea level, landscape changes dominate the long-term changes to flood hazard. Therefore, we conclude that the amplification in storm tides is primarily of anthropogenic origin.

The present-day landscape of Jamaica Bay supports a highly eutrophic but in many ways healthy estuarine ecosystem, with oxygen levels slowly rising over recent decades (Walsh et al., 2018; NYC-DEP, 2018). However, the abundance of various indicator species, particularly those that depend on intertidal habitats (e.g., diamondback terrapin), has continued to decline (Walsh et al., 2018). Here, we note some likely ecological influences of the landscape and habitat changes summarized in Figs. 4 and 5 and Table 1.

Our landscape reconstruction confirms that the bay's eelgrass beds have disappeared completely, and wetland area has declined dramatically since the 1800s. The wetland decline may be stopped with marsh island restoration and reconstruction activities, which have been occurring over the past decade (Seavitt et al., 2015). Eelgrass beds provide many similar ecological services in estuaries, including nursery and refuge for a diverse and dense faunal community, trapping of sediment, and erosion prevention (Orth et al., 2006). They are known to decline in eutrophic conditions due to the reduced sunlight that results from increased turbidity (Vaudrey et al., 2010; Orth et al., 2006). Salt marshes are widely known for their ecological importance, including many of the same roles as eelgrass beds but also including intertidal habitat. At Jamaica Bay, this habitat serves diamondback terrapin and birds such as the sharp-tailed sparrow, egrets, herons, and geese.

Our landscape reconstruction shows that unvegetated intertidal area has decreased by 12.7 km2, a loss of 74 %. This change is of equal magnitude in square kilometers to the loss of eelgrass beds (Table 1). Mudflats, sandbars, oyster and mussel reefs, and other unvegetated intertidal areas are forms of “shallows” and provide important habitats for benthic invertebrates like polychaetes, snails, clams, crabs, and blue mussels as well as birds that feed on them such as the oystercatcher and willet. They are also used by terrapins for feeding and by horseshoe crabs for reproduction.

The center of the bay (inside the channels that circle the bay today) has not only lost marsh islands, it has had its land elevation drop substantially, most areas by about 1 m since the 1800s (Fig. 5). What were once large expanses of intertidal unvegetated area have shifted to being subtidal. This drop may reduce the sediment supply to the remaining marsh islands' substrate during storms (Wang et al., 2017). Furthermore, an increased depth in front of the marsh can increase wave energy and promote lateral erosion (Fagherazzi et al., 2006). As a result, the loss of intertidal zones and associated increased water depths may be detrimental to the sustainability of the remaining marsh islands and their critical habitat.

The increase from 7 to 28 km2 of deep habitat areas (Table 1) may attract more large fish such as striped bass due to increased swimming space, the reduction in thermal variability caused by a deep water column, or stratified deep water's lower temperature in summertime. It is unknown whether there were more or fewer striped bass in Jamaica Bay in the 1800s, but their presence today has the benefit of supporting a small fleet of fishing charter boats. However, there are several square kilometers of poorly flushed deepwater regions, predominantly in Grassy Bay, immediately southwest of JFK Airport, that are prone to hypoxia and even anoxia in late summer, providing compromised habitat areas for many organisms (NYC-DEP, 2018).

Our landscape reconstruction and modeling suggest that the residence time of water within the bay has more than doubled between the 1870s and today, with potential adverse ecological implications. The residence time of water in an estuary that receives large wastewater-derived nutrient inputs like Jamaica Bay is an important control on hypoxia, with longer residence times often leading to worsened hypoxia (e.g., Sanford et al., 1992). A simple model of the residence time of a lagoonal-type estuary system is the volume of the bay divided by the tidal flux rate, the latter of which is the tide prism (volume of water between mean high water and mean low water) over the tide period (12.42 h; e.g., Sanford et al., 1992). For the 1870s landscape and sea level, the average modeled tidal prism of the bay was 8.0×107 m3, and the volume was 9.7×107 m3, leading to a residence time of 0.63 d. For the 2015 landscape and sea level, the average modeled tidal prism of the bay was 1.02×108 m3, and the volume was 2.9×108 m3, leading to a computed residence time of 1.5 d. This simple model was shown for the modern landscape to underestimate residence times (relative to modeled tracer releases) but nevertheless shows that the changes in bay morphology lead to a substantial increase in residence time by a factor of 2–3 mainly due to the much greater volume of the present-day bay. More detailed analyses of water quality and residence time have been performed in other recent studies, and these results are being reported on in separate papers but generally support this interpretation (Marsooli et al., 2018; Fischbach et al., 2018).

The 1870s landscape of Jamaica Bay was already influenced by humans. Prior to European colonization, Jamaica Bay was likely more open to the ocean, with an actively migrating inlet located further to the east, a barrier island system, and extensive fringing marshlands but far fewer marsh islands than in the 1870s (Black, 1981; Sanderson, 2016). A less well-constrained model for the pre-European landscape was also produced for this study, and modeling suggests storm tide reductions (from offshore into the bay) were caused by the landscape of the 17th century (Orton et al., 2016a). The model was based on 17th- and 18th-century maps that showed coastlines and major features, such as an inlet which was in the center of today's Rockaway Peninsula and a general absence of marsh islands in the bay, calling the bay “Jamaica Sound”. However, the maps did not show bathymetry measurements, and therefore the actual hydrodynamic behavior of the system is highly uncertain relative to the 1870s and present-day landscape (Orton et al., 2016a). Ongoing research is helping improve our understanding of the landscape of the 1600s and long-term evolution through analyses of sediment cores from the west central area and eastern ends of the bay (Peteet et al., 2018). That study showed that European settlement led to increases in inorganic sediment delivered to the bay, likely due to forest clearance for agriculture and subsequent erosion, which may explain the increase in marsh island area in the 1700s and 1800s. These considerations suggest that, on century timescales, hard-to-quantify factors such as the anthropogenically mediated sediment supply may also exert an important influence on long-term system evolution.

Remarkably, despite the visions of the Jamaica Bay Improvement Commission (1907) and the River and Harbor Acts of 1910 and 1925, the present-day commercial shipping activity through this largely man-made, 1 km wide, 8–16 m deep shipping channel (measured at Floyd Bennett Field, the narrowest part) is limited to an average of three one-way trips per day servicing gravel and sand companies, sewage treatment plants, and bulk fuel companies (USACE, 2016). Our results show that maintaining these shipping channels leads to higher storm tides in the bay even though the economic activity that justified their construction is largely absent.

Globally, common development approaches such as dredging for port development and landfilling for neighborhood development can have major economic benefits but can also raise vulnerability as they did for Jamaica Bay (Talke and Jay, 2020). The movement towards “New-Panamax” and larger ships is leading major harbors to dredge wider channels and depths of approximately 16 m (Briggs et al., 2015). Other dredged estuaries have been shown to cause enhanced inland propagation of storm tides, such as with the Cape Fear estuary (Familkhalili and Talke, 2016). The Mississippi River–Gulf Outlet Canal was originally created through dredging and was recently deauthorized and blocked in part because of a debate over whether it increased storm surge penetration inland (Shaffer et al., 2009). Within the St. Johns River, in Florida, channel deepening to a controlling depth of >14 m is continuing despite model results that showed increases in tide range and storm surge of 0.1–0.2 m in some locations (USACE, 2014).

The results presented here suggest that evaluating changes to flood hazard should be part of the cost–benefit analysis of any environmental impact study or restoration study, particularly projects that propose altering inlet geometry or channel depth. Our results can help inform debates about whether to continue maintaining underused ports since allowing inlets and channel depths to return to predevelopment geometry is potentially a way to mitigate against future sea level rise effects. Given adequate sediment supply, many systems quickly return to predevelopment depths; for example, the lower Passaic River in New Jersey has accumulated as much as 5 m of sediment after maintenance dredging ceased in the early 1980s (Chant et al., 2011).