Chapter 7 Future Model Development

This report has presented the development and application of the New York Bight Ecological Model (NYBEM, “nigh-bem”). The models currently apply an index-based modeling framework (i.e., a habitat-suitability-style, quantity-quality approach) to assess patch-scale effects for six ecosystem types (e.g., estuarine intertidal zones). This report documents technical details, use, and relevant information for USACE model certification (EC 1105-2-412, PB 2013-02). In all applications, models represent incomplete abstractions of reality, and opportunities exist for future development of this toolkit. Specifically, the following items were identified as important topics for potential expansion:

• Improvements to Sub-Models: Six major habitat types were examined in the NYBEM, and important model extensions and knowledge gaps were noted as each model was presented (Sections 4.2-4.7). These habitat types could also be further divided into sub-types such as low marsh, high marsh, and tidal flats, and the model domain could be expanded to other habitat types (e.g., non-tidal freshwaters or riparian systems).

• Model Evaluation: Habitat zones and quality should be compared to existing habitat maps for the region. For instance, the National Wetlands Inventory and analogous state data sets could provide important source of model verification data for the estuarine intertidal zone. Similarly, submerged aquatic vegetation and shellfish data sets may provide important tools for verification of estuarine subtidal models. Appendix B has presented a preliminary version of these verification analyses, and additional analyses will be summarized in peer-reviewed journal articles (Mahan et al. forthcoming; Cordero et al. forthcoming). Furthermore, models could be compared with field-based approaches such as the Evaluation of Planned Wetlands (Bartoldus 1994), the New England Marsh Models (McKinney, Charpentier, and Wigand (2009a), McKinney, Charpentier, and Wigand (2009b)), or the Marsh Resilience to Sea-level rise model (Raposa et al. 2016).

• Spatial Scaling: The NYBEM is being applied in a spatially explicit format at a large regional scale. The spatial extent and grain of these analyses provide a unique opportunity to examine scaling issues and understand the effects of model assumptions (e.g., grid size) on observations about the system (e.g., overall habitat quality). Analyses are underway to understand these issues in the context of NYBEM (Saltus et al. forthcoming).

• System connectivity: As described in Chapter 3, NYBEM was conceived as a suite of models including habitat-type effects (presented here) as well as connectivity for migratory organisms. To date, connectivity models have not been developed to address impacts of storm surge barriers on migratory organisms. These models could draw from existing approaches in freshwater systems (e.g., S. K. McKay et al. (2017)) as well as experiences in other estaurine systems with storm surge barriers (NOAA-Sponsored Workshop).

• Taxa-Specific Outcomes: NYBEM was designed as a tool for examining broad-scale effects of proposed coastal infrastructure on regional ecosystems. This model intends to provide a relative accounting of ecological outcomes at a regional scale with highly divergent management actions (e.g., Are the effects of Barrier-A 5% or 50% different than Barrier-B?). The model will be used to compare management alternatives to inform feasibility scale planning in the USACE and identify key regions where effects are anticipated. From these analyses, additional models may be required to examine imperiled species at a particular location.

• Effects of Barrier Closures: NYBEM is designed generally to respond to changes in hydrodynamics as a result of storm surge barriers. Clearly the operational patterns of these features would affect model outcomes (e.g., frequency or duration of gate closure). The strategy for model application would proceed through a series of increasingly detailed considerations of operations. First, a “gates open” scenario would be used to examine the effects of barrier structures on general hydrodynamic conditions, which would occur the majority of time. Second, a worst case scenario could be designed to study the effects of a complete closure on estuarine circulation and habitats. Third, more nuance closure scenarios could be studied using more representative closure frequencies, duration, and timing.

As described in Chapter 1, the U.S. Army Corps of Engineers (USACE) is using the NYBEM in the context of two large-scale coastal storm risk management feasibility studies in the New York Bight ecosystem, specifically: the New Jersey Back Bays (NJBB) and the New York-New Jersey Harbor & Tributaries Study (HATS). In these studies, the USACE is considering a diversity of measures for mitigating flood risks, including structural actions (e.g., levees, floodwalls, storm surge barriers), non-structural measures (e.g., buy-outs, elevation of structures, flood-proofing), and natural and nature-based features (e.g., wetland creation, reefs for breakwaters). Environmental outcomes and acceptability are important constraints on plan selection, and the studies are applying a “tiered” approach to compliance with the National Environmental Policy Act. The NYBEM was developed to partially inform the impact assessment process and is being used in conjunction with other information (e.g., contaminant mapping, cultural and historical resources, etc.) to inform decisions. The models intend to provide a broad general view of the effects of proposed actions on coastal ecosystems, and this document summarizes model development and provides access to the underlying numerical code and other information summarized in this report.