Barrier prioritization in the tributaries of the Hudson-Raritan Estuary

Abstract

One study outcome was the development of a Comprehensive Restoration Plan (CRP) that serves as a master plan and blueprint for future restoration in the HRE. The CRP's goal is to develop a mosaic of habitats that provide the public with renewed and increased benefits from the estuary. In addition, the CRP provides the framework for an estuary-wide ecological restoration program by utilizing restoration targets-Target Ecosystem Characteristics (TECs)-developed by the region's stakeholders. One TEC focuses on restoring tributary environments and reconnecting rivers to coastal environments that benefit impacted or imperiled migratory fishes (e.g., Alewife, blueback herring, Striped bass, American shad, and American eel). This technical note describes a procedure developed to prioritize removal of major migratory barriers, specifically dams. These methods are demonstrated in one of eight planning regions, the Harlem River, East River, and Western Long Island Sound Planning Region, where they were applied to prioritize potential barriers for removal over a range of costs. The prioritization scheme is based on four primary components: habitat quantity upstream of a dam, habitat quality upstream of a dam, the effects of multiple dams in sequence in the context of diadromous fish (i.e., if a fish cannot pass the most downstream dam, then upstream dam removal provides no benefits), and a rapid, screening-level relative cost estimate. This technique is then applied to examine 49 potential dam removal sites. A combinatorial algorithm was applied to develop plans with more than 489,000 combinations of removal sites (e.g., remove barrier-A, barrier-B, neither, or both). From this analysis, 49 proposed sites were screened and refined to a recommended plan containing 12 sites, which provides 66% of the total potential habitat gain at 19% of the relative cost. The advantages and challenges of barrier prioritization are then discussed more broadly with an emphasis on efficiencies that can arise as a result of spatial prioritization methods.

A comparison of approaches for prioritizing removal and repair of barriers to stream connectivity

“…More often, actions are prioritized on a more local scale, where one or more stakeholders selects among a modest set of potential projects under tight funding constraints. For instance, an interagency collaboration used optimization to identify barrier priorities in the Hudson‐Raritan estuary (Northeastern USA), where 12 of 49 barriers were identified as providing more than 60% of total possible connectivity gain at less than 20% of the cost of pursuing all projects (McKay, Reif, Conyngham, & Kohtio, 2017). The modest scale of such analyses makes them much easier to implement analytically, as well as making the results more accessible by intuition.…”