B09_Amd2_Report_0002.pdf

Hydrodynamic Modeling to Support Natural Tidal Exchange in Watersheds along Northeast Corridor Amtrak Line (Cooperating Agreement, F23AC02109-01) Contributed by: Peter Bacopoulos1, Matthew V. Bilskie2 and L. Casey Jones1 1 Louisiana State University, Coastal Ecosystem Design Studio 2 University of Georgia, College of Engineering

4/30/2026

Executive summary: This report documents the numerical modeling and analysis completed for evaluating hydrodynamics in design scenarios to support natural tidal exchange in three watersheds along the northeast corridor of Amtrak: 1) East River (ER); 2) Stewart B. McKinney NWR (SBM); and 3) Wequetequock Cove (WQK). The design scenarios evaluated concerned different cases of channel width based on realistic redesigns of the bridge span. The objective metrics included velocities through the channel, associated bed stress, tidal prism and up-estuary water levels. The evidence provided by the model and reported herein is meaningful towards the potential for (or alternatives to) constructing a redesign of the bridge spans at the Amtrak line crossings. The information provided in this report is relevant to 1) redesign and construction via our evaluation of channel velocities and bed stresses, and 2) environmental management via our evaluation of tidal prism and up-estuary water levels. The modeling conducted is rigorous in its scientific basis and real-world application. The modeling and analysis results are interpreted in terms of local impacts at the waterway opening and broader impacts in the upper estuary.

Primary findings: The results connote a dual benefit with a wider channel through reduced bottom shear stresses acting upon the bed and increased tidal prism and the improved flushing capacity of the estuary. The reduced bottom shear stresses and increased tidal prism are physically manifested by diminished tidal velocities due to a larger cross-sectional area and the more efficient flow throughput with a wider channel. Designing the channel with a wider/larger opening would not have an adverse impact up-estuary with tidal amplification and overly flooded marsh while it would beneficially reduce the tidal choking effect induced by the channel opening and mitigate existing headwater effect, enhancing estuary flushing.

Deliverables: The products delivered by this project include:

• Final report o Model data of velocities, bed stresses, tidal prism and up-estuary water levels for

ER, SBM and WQK across different design scenarios (channel width)

• Model file repository: https://doi.org/10.5281/zenodo.19445848 o Finite-element meshes of ER, SBM and WQK, including working input files for hydrodynamic (ADCIRC) simulations o Animations of velocity vectors and overland tidal flooding

• Web map interface: https://proteus.cee.lsu.edu/usfws/ o Interactive web interface containing maps of all model inputs and outputs https://doi.org/10.5281/zenodo.19445848 https://proteus.cee.lsu.edu/usfws/

Introduction: Hydrodynamics were modeled using the advanced circulation (ADCIRC) model (Bunya et al., 2010). The governing equations are solved for water levels and depth-integrated velocities, which are suitable for longwave motions like astronomic tides, river flows and storm surge. The numerical solution utilizes an unstructured finite-element mesh that permits flexible element sizes to describe more complex (i.e., complicated) features with finer resolution and less intricate (i.e., smooth) features with coarser features. Figure 1 shows the boundary definition of the local ADCIRC meshes for East River, Stewart B. McKinney NWR and Wequetequock Cove, with overlays of roadways and the Amtrak line. Attributes of the meshes are listed in Table 1.

Mesh resolution is generally 10 ± 5 m (mean ± standard deviation). Figure 2 shows the mesh detail zoomed into the area of the Amtrak line crossing for each of the three domains.

The physical attributes of the three model domains are listed in Table 2. Stewart B. McKinney is the smallest estuary of the three domains in terms of length, surface area and volume. East River is 50–100% larger than Stewart B. McKinney. Wequetequock Cove is the shortest estuary by length and the largest estuary by surface area. We approximate the offshore tidal amplitude as 70 cm based on tide gauge data.

Model scenarios for the three domains of East River, Stewart B. McKinney NWR and Wequetequock Cove were based on different channel widths associated with the existing condition and redesigns of Amtrak line bridge pass (Figure 2). Redesign scenarios involved a case of a narrowed opening relative to the existing condition, two cases of an expanded opening and a case of approximating a natural opening in the absence of an Amtrak line crossing (Table 3). Changes in the channel widths correspond to changes in cross-sectional areas by non-negligible amounts measured on a percentage basis.

The model scenarios were controlled by the mesh definition of the waterway opening (Figure 2) and all other simulation settings were held constant, so that the channel width was an isolated factor in the evaluation of hydrodynamic effects.

Modeling approach: The offshore arc of each model mesh boundary (Figure 1) is where time series of water levels are prescribed as boundary conditions. The boundary conditions are derived from a large-scale model that encompasses the western North Atlantic Ocean (Hagen et al., 2006) with locally fine resolution of the coastline, including Long Island Sound (Figure 3).

Large-scale modeling: To confirm the quality of the boundary conditions driving the local model meshes, water levels simulated by the large-scale model (Figure 3a) were validated against observed data from five NOAA stations in Long Island Sound (Figure 3b). Figure 4 displays time series of observed and modeled tides over 14.7-day spring-neap tidal cycle. Amplitude and phase of the tidal signal are well-replicated by the model, including capturing the variable tidal amplitude across the five stations. This level of validation (>95% R2) corroborates the large-scale model as providing quality boundary conditions to the local-scale model meshes.

Figure 1. Overview of the hydrodynamic modeling and analysis for scenario testing of different channel-opening widths for (a) East River, (b) Stewart B. McKinney NWR and (c) Wequetequock Cove.

Table 1. Attributes of the finite-element meshes for the three model domains.

Element sizes (m) Nodes Elements Min P25 Median Mean P75 Max East River 36,669 69,746 3.4 7.3 10.3 12.9 14.3 78.5 Stewart B. McKinney 10,284 16,835 1.7 4.8 7.0 7.9 10.3 46.3 Wequetequock Cove 16,473 29,995 1.4 9.9 31.7 32.4 57.5 99.1

Figure 2. Mesh detail zoomed into the area of the Amtrak line crossing for (a) East River, (b) Stewart B. McKinney NWR and (c) Wequetequock Cove. The color variation of the mesh triangulation connotes the respective modeling scenarios.

Table 2. Physical attributes of the three model domains. Below and above the structure refers to downstream and upstream of the structure, respectively.

East

River Stewart B.

McKinney

Wequetequock Cove

Estuary length (km) Total 5.94 3.77 2.58 Below structure 2.82 1.66 0.84 Above structure 3.12 2.11 1.74

Estuary surface area (km2) Total 0.376 0.292 0.691 Below structure 0.227 0.170 0.421 Above structure 0.149 0.122 0.270

Estuary volume (106 m3) Total 1.248 0.513 0.777 Below structure 0.764 0.287 0.527 Above structure 0.484 0.226 0.250

Local-scale model configuration: ADCIRC simulations were run using five input files (Table 4).

The finite element mesh (*.14) is a spatial characterization of the domain bathymetry (z). Nodal attributes (*.13) involved four uniform, standardized settings: 1) Manning’s roughness (= 0.020);

2) sea surface height above geoid (= 0); 3) primitive weighting in continuity equation (= 0.03);

and 4) elemental slope limiter (= 0.05). Input parameters were specified in the *.15 file, which includes numerical settings like the time step (= 0.05 seconds), physical settings like advection (enabled) and output settings like harmonic analysis (23 constituents) and time series (water levels and velocities). Boundary conditions are contained in the *.19 file as unsteady water levels and *.20 file as unsteady inflows, which are imposed as time-series forcings on the open-ocean and upstream boundaries of the local model mesh, respectively. The input files used for running the ADCIRC model for tide simulation of East River, Stewart B. McKinney and Wequetequock Cove are contained in a public repository (Bacopoulos and Bilskie, 2026).

Local-scale model validation: The models of the three domains were validated against observations of water levels and/or velocities. We summarized the model-data fit in terms of coefficients of determination (R2). An R2 value of 1 implies the model perfectly replicates the data, and an R2 value of 0 implies the model replicates none of the variability in the data. We present the coefficients of determination as percentages (Table 5), showing that R2 is no less than 85% for any of the model-data comparisons. Water levels modeled in East River replicate the data with R2 ≥ 90%, while velocities are replicated with R2 of 85% for speeds and 92% for directions. Appendix A provides plots of time-series water levels and velocities (model versus data) for the 2020 and 2025 deployments. Water levels modeled in Stewart B. McKinney NWR replicate the data with R2 of 88% and 89% for the bridge and marsh sites (see Appendix B for time-series plots). Water levels modeled in Wequetequock Cove replicate the data with R2 of 85–87% for the four sites (see Appendix C for time-series plots). This level of validation (≥85% R2) corroborates the local-scale models as providing quality hydrodynamic information for the analysis of redesign impacts. Importantly, the model captures the tidal oscillations and its subtle modulation by astronomical forcing but also excursions from the regular tidal signal in the form of meteorologically driven pulses of water-level setup or setdown.

Table 3. Five scenarios of waterway openings for the three domains of East River, Stewart B.

McKinney NWR and Wequetequock Cove. The associated cross-sectional area of flow at mean sea level is listed with the percentage difference (Δ) relative to the existing condition.

East River Channel width (m)

Cross section area, Ω (m2)

Δ(Ω)

Constrict 13.0 78 –39 Existing condition 21.5 129 0 Widen ×1 26.2 150 17 Widen ×2 31.2 172 33 Widen full 50.0 230 78 Stewart B. McKinney Channel width

(m) Cross section area, Ω

(m2) Δ(Ω)

Constrict 6.9 26 –18 Existing condition 8.7 32 0 Widen ×1 10.6 37 17 Widen ×2 12.6 48 51 Widen full 19.2 69 117 Wequetequock Covea Channel width

(m) Cross section area, Ω

(m2) Δ(Ω)

Existing condition 19.3 93 –25 Widen ×1 25.3 124 0 Widen ×2 29.2 136 10 Widen ×3 32.1 148 19 Widen full 91.3 132b 6 a No constricted case was evaluated for Wequetequock Cove and only widen cases were evaluated b Depths were adjusted in the fully widened case to account for infilling in a natural state

Figure 3. (a) Large-scale, finite-element mesh encompassing the western North Atlantic Ocean and telescoping into (b) Long Island Sound. Water levels simulated by the large-scale model provide the boundary conditions for the local model meshes of East River, Stewart B. McKinney NWR and Wequetequock Cove. To confirm the quality of the boundary conditions driving the local model meshes, water levels simulated by the large-scale model were validated against observed data from five NOAA stations in Long Island Sound.

Figure 4. Time series of observed and modeled tides over 14.7-day spring-neap tidal cycle for five NOAA stations in Long Island Sound.

Table 4. Input files used for running the ADCIRC model for tide simulation of East River, Stewart B. McKinney and Wequetequock Cove. BC stands for boundary conditions.

File description File extension Finite element mesh *.14 Mesh attributes *.13 Input parameters *.15 Unsteady water levels (BC) *.19 Unsteady inflows (BC) *.20

Table 5. Coefficients of determination (R2) associated with the validation of the model results against measured hydrodynamics for the three model domains.

Variable R2 (%) East River 2020 water levels 98 2020 velocity speed 85 2020 velocity direction 92 2025 water levels (ESTR1, brackish) 91 2025 water levels (ESTR1, saline) 91 2025 water levels (ESTR2) 90 2025 water levels (ESTR3) 93 Stewart B. McKinney NWR 2023-24 water levels (bridge) 89 2023-24 water levels (marsh) 88 Wequetequock Cove 2024 water levels (WQK1) 87 2024 water levels (WQK2) 87 2024 water levels (WQK3) 85 2024 water levels (WQK4v2) 86

Analytics: Six metrics provide analytics derived from the model results (Table 6). The first two metrics evaluate the amplitude and phase of the M2 water level. The second set of metrics evaluate the amplitude and phase of the M2 velocity. We focused on the M2 tidal constituent because it is the dominant tidal frequency of hydrodynamics. The amplitude tells of the low- and high-water heights (and ebb and flood velocities) associated with the sinusoid of specific frequency (e.g., M2) while the phase tells of the timing of the waveform.

Table 6. Six metrics provide analytics derived from the model results.

Acronym Units M2 water level amplitude M2 ζamp m M2 water level phase M2 ζpha deg M2 velocity amplitude M2 Vamp cm s–1 M2 velocity phase M2 Vpha deg Bottom shear stress τbed Pa Tidal prism P 106 m3

The next metric evaluates bottom shear stresses from time series of velocities, reporting the median and 90th percentile values from the distribution of time-series bottom shear stresses.

Bottom shear stresses were calculated as:

𝜏𝜏bed = 𝜌𝜌𝑤𝑤𝐶𝐶𝐷𝐷𝑉𝑉bed 2 (1) where ρw is the density of seawater, CD is the drag coefficient and Vbed is the water velocity at the bed. The drag coefficient is defined as:

𝐶𝐶𝐷𝐷 =

𝑔𝑔𝑛𝑛2

𝐻𝐻1 3⁄ (2)

where g is gravity, n is the Manning’s roughness coefficient and H is the depth of the water column. The water velocity at the bed is approximated from the simulated depth-integrated velocity as (Lewis et al., 2017):

𝑉𝑉bed = 𝑉𝑉DI � 𝑧𝑧bed 𝛽𝛽𝛽𝛽� 1 𝛼𝛼⁄

(3) where β (= 0.32) and α (= 7) are coefficients of the power-law relationship and zbed is a depth taken just above the bed (= 10 cm).

The last metric evaluates tidal prism from time series of water levels and velocities, reporting the average tidal prism associated with a half tidal cycle (i.e., ebb or flood tide).

Theory of tidal prism: Tidal prism is defined as the total volume of water that flows through an inlet during half of the tidal cycle (Petti et al., 2023). The tidal prism is founded upon morphological and hydrodynamic empirical relationships between the cross-sectional area of an inlet and the tidal prism of the back-barrier embayment. The tidal prism can be approximated by means of the hydrodynamic relationship:

𝑃𝑃 = 2𝑎𝑎𝑡𝑡𝐴𝐴 (4)

where P is the tidal prism, at is the tidal amplitude and A is the basin area of the back-barrier embayment. The empirical relationship between inlet cross-sectional area and tidal prism is (O’Brien, 1931; Jarrett, 1976):

Ω = 𝑘𝑘𝑃𝑃𝛼𝛼 (5)

where Ω is the inlet cross-sectional area, P is the tidal prism, k is a proportionality constant and α is a scaling coefficient that typically lies in the range of 0.85–1.10. The k constant ranges from O(–4) to O(–6), where the O(n) notation refers to the order of magnitude, i.e., 10n. We applied a coefficient value of k = 0.656×10–4 and an exponent value, α, near equal to 1 following the O’Brien empiricism (Petti et al., 2021).

The model results of water levels and depth-integrated velocities were analyzed for tidal prism by assessing the volume of water that discharges through the opening on a tidal flood/ebb cycle (Wu et al., 2023):

𝑇𝑇𝑝𝑝 = � 𝑄𝑄Γ𝑑𝑑𝑑𝑑

𝑡𝑡2 𝑡𝑡1 (6) where QΓ is the normal flux through a specified boundary section, and t1 and t2 are the start and end times of the high or low tide cycle, respectively. It must be noted that our definition of tidal prism differs slightly from the conventional definition. Conventionally, the tidal prism is defined for inlet-bay systems where tides cycle from the sea to the bay through an inlet (O’Brien, 1931;

Jarrett, 1976). Here, tidal prisms for a channel constriction located midway through the estuary are analyzed, and it is important to recognize the disparity in the physical interpretation between theoretically derived values of tidal prism and those computed from the numerical model results.

Local-scale model results: We present the model results for each domain separately in the subsequent subsections; however, summary findings are common across the three domains. We make the following summary observations relating to the hydrodynamic impacts of modifying the existing waterway openings associated with the Amtrak line crossings for the three domains.

1. Modifying the channel width generates negligible effects on the amplitude and phase of tidal water levels and the phase of tidal velocities (Figure 5a–c)

2. Modifying the channel width generates appreciable effects on the amplitude of tidal velocities (Figure 5d)

a. A more constrictive channel elevates the amplitude of tidal velocities

b. A more open channel diminishes the amplitude of tidal velocities

3. The effects of channel width on tidal velocity amplitude translate directly to impacts on bottom shear stresses (Figure 5e) and tidal prism (Figure 5f)

a. Bottom shear stresses diminish with a wider channel

b. Tidal prism increases with a wider channel

4. Designing the channel with a wider/larger opening would not have an adverse impact up-estuary with tidal amplification and overly flooded marsh while it would beneficially reduce the tidal choking effect induced by the channel opening and mitigate existing headwater effect, enhancing estuary flushing

Figure 5. Top row shows hydrodynamic variables with negligible influence by modifying the channel width across five discrete cases for the three domains: (a) M2 tidal water-level amplitudes; (b) M2 tidal water-level phases; and (c) M2 tidal velocity phases.

Bottom row shows variables appreciably influenced by channel width: (d) M2 tidal velocity amplitudes; (e) median values of bottom shear stresses; and (f) tidal prism.

The results connote a dual benefit with a wider channel through reduced bottom shear stresses acting upon the bed and increased tidal prism and the improved flushing capacity of the estuary.

The reduced bottom shear stresses and increased tidal prism are physically manifested by diminished tidal velocities due to a larger cross-sectional area and the more efficient flow throughput with a wider channel (Figure 6).

Figure 6. Hydrodynamic variables appreciably influenced by the cross-sectional area associated with five discrete cases of different channel widths for the three domains: (a) M2 tidal velocity amplitudes; (b) median values of bottom shear stresses; and (c) tidal prism.

East River Figure 7 displays geometric and hydrodynamic measures across the dimension of discrete cases of waterway opening (Table 3). Cross-sectional area increases relatively linearly with a wider channel. M2 water-level amplitude is ~58 cm regardless of the channel width. M2 water-level phase is similarly uninfluenced by the channel width, ranging from 91 to 92 degrees. M2 velocity amplitude is strongly influenced by the channel width, ranging between 35 and 68 cm s–

1. M2 velocity phase is relatively uninfluenced by the channel width, ranging from 101 to 102 degrees.

Bottom shear stress reduces with a wider channel; however, there are diminishing returns with the curves approaching an asymptote at the extreme end. For the existing situation, bottom shear stress less than ~0.33 Pa half of the time and greater than ~0.6 Pa ten percent of the time. The potential to mobilize heavier sediments off the bed reduces with a wider channel, inferred from the model results compared to the critical shear stresses of silt and silty sand. The model results suggest that fine sediments (mud particles) will be mobilized under any redesign scenario, considering a critical shear stress of 0.1 Pa required to mobilize mud.

Figure 7. Geometric and hydrodynamic measures across the dimension of discrete cases of waterway opening for East River. (a) Channel width and (b) associated cross-sectional area. (c) Amplitude and (d) phase of M2 water levels. (e) Amplitude and (f) phase of M2 velocities. (g) The median and 90th percentile of time-series bottom shear stress derived from simulated velocities, with dashed lines denoting the critical shear stresses of silt and silty sand. (h) Average tidal prism derived from time series of simulated water levels and velocities, with theoretical values based on inlet-bay relationships (α = 1).

Tidal prism increases with a wider channel, which follows with the theory that a more open inlet enables a greater volumetric exchange of water within the embayment (Eq. 5). Tidal prism for the existing situation is ~0.23 106 m3, comparing favorably with the theoretical value based on tidal amplitude and the basin area of the back-barrier embayment (Eq. 4) which we take as 70 cm and the surface area of the estuary above the structure (Table 2), respectively.

Figure 8 displays water surface profiles for the thalweg of East River based on the five different waterway openings (Table 3). The channel constriction at the Amtrak crossing induces a choking effect on the tide, with a slight water-level setup (1–2 cm, depending on the opening size) updrift of the ebbing or flooding tide. The choking effect is greatest during the maximum flows of ebb and flood tide, and the updrift water-level setup is most exhibited with the smallest opening size.

A larger opening size reduces the choking and setup effects, with the fully widened case inducing almost no effect.

Stewart B. McKinney NWR: Salt Meadow Unit Figure 9 displays geometric and hydrodynamic measures across the dimension of discrete cases of waterway opening (Table 3). Cross-sectional area increases relatively linearly with a wider channel. M2 water-level amplitude is ~76 cm regardless of the channel width. M2 water-level phase is similarly uninfluenced by the channel width, ranging from 27 to 28 degrees. M2 velocity amplitude is strongly influenced by the channel width, ranging between 31 and 49 cm s–

1. M2 velocity phase is relatively uninfluenced by the channel width, ranging from 245 to 246 degrees.

Bottom shear stress reduces with a wider channel; however, there are diminishing returns with the curves approaching an asymptote at the extreme end. For the existing situation, bottom shear stress less than ~0.2 Pa half of the time and greater than ~0.45 Pa ten percent of the time. The potential to mobilize heavier sediments off the bed reduces with a wider channel, inferred from the model results compared to the critical shear stresses of silt. The model results suggest that fine sediments (mud particles) will be mobilized under any redesign scenario, considering a critical shear stress of 0.1 Pa required to mobilize mud.

Tidal prism increases with a wider channel, which follows with the theory that a more open inlet enables a greater volumetric exchange of water within the embayment (Eq. 5). Tidal prism for the existing situation is ~0.1 106 m3, comparing favorably with the theoretical value based on tidal amplitude and the basin area of the back-barrier embayment (Eq. 4) which we take as 70 cm and the surface area of the estuary above the structure (Table 2), respectively.

Figure 8. Water surface profiles along East River shown every hour during (a–e) the falling tide cycle and (f–j) the rising tide cycle for the five different waterway openings. (k) Water surface profiles for the five different waterway openings, consolidated on the same plot, for the hour when ebb flow is maximum. (l) Water surface profiles for the hour when flood flow is maximum.

Figure 9. Geometric and hydrodynamic measures across the dimension of discrete cases of waterway opening for Stewart B. McKinney NWR. (a) Channel width and (b) associated cross-sectional area. (c) Amplitude and (d) phase of M2 water levels. (e) Amplitude and (f) phase of M2 velocities. (g) The median and 90th percentile of time-series bottom shear stress derived from simulated velocities, with dashed line denoting the critical shear stress of silt. (h) Average tidal prism derived from time series of simulated water levels and velocities, with theoretical values based on inlet-bay relationships (α = 0.95).

Figure 10 displays water surface profiles for the thalweg of Stewart B. McKinney NWR based on the five different waterway openings (Table 3). The channel constriction at the Amtrak crossing induces a choking effect on the tide, with a slight water-level setup (2–3 cm, depending on the opening size) updrift of the ebbing or flooding tide. The channel constriction at Route 1, downstream of the Amtrak crossing, causes a similar choking effect. The choking effect is greatest during the maximum flows of ebb and flood tide, and the updrift water-level setup is most exhibited with the smallest opening size. A larger opening size reduces the choking and setup effects, with the fully widened case inducing almost no effect.

Wequetequock Cove Figure 11 displays geometric and hydrodynamic measures across the dimension of discrete cases of waterway opening (Table 3). Cross-sectional area increases relatively linearly with a wider channel. M2 water-level amplitude is ~40 cm regardless of the channel width. M2 water-level phase is similarly uninfluenced by the channel width, at 320 degrees. M2 velocity amplitude is strongly influenced by the channel width, ranging between 8 and 15 cm s–1. M2 velocity phase is relatively uninfluenced by the channel width, ranging from 232 to 237 degrees.

Bottom shear stress reduces with a wider channel; however, there are diminishing returns with the curves approaching an asymptote at the extreme end. For the existing situation, bottom shear stress less than ~0.01 Pa half of the time and greater than ~0.05 Pa ten percent of the time. The potential to mobilize sediments off the bed reduces with a wider channel; however, the magnitudes for any of the scenarios suggest that only the finest of sediments will be mobilized, considering a critical shear stress of 0.1 Pa required to mobilize mud particles.

Tidal prism increases with a wider channel, which follows with the theory that a more open inlet enables a greater volumetric exchange of water within the embayment (Eq. 5). Tidal prism for the existing situation is ~0.21 106 m3, comparing favorably with the theoretical value based on tidal amplitude and the basin area of the back-barrier embayment (Eq. 4) which we take as 40 cm and the surface area of the estuary above the structure (Table 2), respectively.

Figure 12 displays water surface profiles for the thalweg of Wequetequock Cove based on the five different waterway openings (Table 3). The channel constriction at the Amtrak crossing induces a choking effect on the tide, with a slight water-level setup (<1 cm, depending on the opening size) updrift of the ebbing or flooding tide. The choking effect is greatest during the maximum flows of ebb and flood tide, and the updrift water-level setup is most exhibited with the smallest opening size. A larger opening size reduces the choking and setup effects, with the fully widened case inducing almost no effect.

Figure 10. Water surface profiles along Stewart B. McKinney NWR shown every hour during

(a–e) the falling tide cycle and (f–j) the rising tide cycle for the five different waterway openings. (k) Water surface profiles for the five different waterway openings, consolidated on the same plot, for the hour when ebb flow is maximum. (l) Water surface profiles for the hour when flood flow is maximum.

Figure 11. Geometric and hydrodynamic measures across the dimension of discrete cases of waterway opening for Wequetequock Cove. (a) Channel width and (b) associated cross-sectional area. (c) Amplitude and (d) phase of M2 water levels. (e) Amplitude and (f) phase of M2 velocities. (g) The median and 90th percentile of time-series bottom shear stress derived from simulated velocities. (h) Average tidal prism derived from time series of simulated water levels and velocities, with theoretical values based on inlet-bay relationships (α = 1).

Interactive web map interface: An application was developed to allow for exploration of all modeling scenarios evaluated for the three domains (East River, Stewart B. McKinney NWR and Wequetequock Cove) with Amtrak crossing along the Connecticut coastline. The application includes an overview map showing the three model domains and close-up maps for each of the three focus areas. To view model results, select one of the domain names from the side panel.

From the domain page, you can then select between the scenarios. Each scenario map has an interactive legend for viewing and comparing outputs for a variety of metrics. The ellipsis icon to the right of the layer in the legend allows for user control of transparency, zoom or other tools.

An option to change the base map can be found in the top left corner of the map window. You can return to the homepage from any domain page by clicking “Return to Home” at the bottom of the side panel. A splash screen automatically displays in the viewer space upon launching the application to explain the content and navigation.

The web application can be broken down into the three primary components (Figure 13), including overview map, results pages and interactive legend.

Overview map: The web application was created to allow for exploration of the model results with geospatial context. The home screen displays an overview map showing the locations and extents of the three model domains. It also includes key transportation infrastructure and drainage areas. The basemap can be changed to satellite imagery at any time using the windowpane icon in the top left corner of the map, allowing viewers to see the underlying existing landscape. The collapsible panel to the right describes the project background and provides links to explore the results pages for each domain.

Results pages: After a domain is selected, the user will be brought to the results page with the model outputs of water levels, velocities, bathymetry, etc. The results pages include a short site summary and list of scenarios tested. The scenario and domain being viewed can be selected using the buttons in the panel to the right and the legend will populate automatically. The “Return to Home” button at the bottom of the panel will bring the user back to the overview map from any of the results pages.

Interactive legend: The interactive legend allows for exploration of each of the model output metrics of interest. Each of the layers can be turned on/off using the check box to the left of the layer name. Domain boundaries for all channel-width scenarios are included in each map so that the currently viewed domain extent can be compared to the others tested. Which boundaries are visible can be selected using the dropdown arrow to the left of the visibility control. The ellipsis to the right of each layer gives the option to change the transparency of each layer if multiple layers are being viewed at a time. Selecting the “zoom to layer” option for the “Crossing of Interest” or “Domain Boundaries” layers allows the user to view the same extent across maps and aid in comparison.

Figure 12. Water surface profiles along Wequetequock Cove shown every hour during (a–e) the falling tide cycle and (f–j) the rising tide cycle for the five different waterway openings. (k) Water surface profiles for the five different waterway openings, consolidated on the same plot, for the hour when ebb flow is maximum. (l) Water surface profiles for the hour when flood flow is maximum.

Figure 13. Snapshots taken from the interactive web map at different levels showing the overview map, results pages (using East River as an example) and interactive legend (using Stewart B. McKinney NWR as an example).

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https://doi.org/10.5281/zenodo.19445848

Appendix A: Validation for East River: Figure A1 displays time-series water levels and velocities (model versus data) for the 2020 deployment in East River. To better illustrate the tidal velocities, we display modeled versus measured velocity vectors as time series for the 2020 deployment (Figure A2). Figure A3 displays time-series water levels (model versus data) across four measurement sites for the 2025 deployment.

Figure A1. Time-series (a) water levels and velocity (b) speeds and (c) directions (model versus data) for the 2020 deployment in East River.

Figure A2. Time-series vector plot of modeled versus measured tidal velocities for the 2020 deployment in East River.

Figure A3. Time-series water levels (model versus data) for the 2025 deployment across four measurement sites in East River: (a) ESTR1 brackish; (b) ESTR1 saline; (c) ESTR2;

and (d) ESTR3.

Appendix B: Validation for Stewart B. McKinney NWR: Figures B1 and B2 display time-series water levels (model versus data) at a bridge site and a marsh site in Stewart B. McKinney NWR, respectively. It is important to note that the gauge bottomed out for the measurements at the marsh site, where the many of the low tides were not captured by the sensor.

Figure B1. Monthly plots (2023-24) of time-series water levels (model versus data) for the bridge site in Stewart B. McKinney NWR.

Figure B2. Monthly plots (2023-24) of time-series water levels (model versus data) for the marsh site in Stewart B. McKinney NWR.

Appendix C: Validation for Wequetequock Cove: Figure C1 displays time-series water levels (model versus data) across four measurement sites in Wequetequock Cove.

Figure C1. Time-series water levels (model versus data) for the 2024 deployment across four measurement sites in Wequetequock Cove: (a) WQK1; (b) WQK2; (c) WQK3; and

(d) WQK4.