Large dam renewals and removals—Part 1: Building a science framework to support a decision‐making process

Abstract

Altered rivers and managed flows are a hallmark of civilization and dams are a principal agent of alteration. Peak dam construction occurred at the turn of the last century in Western countries, and many of the largest dams are reaching the end of their service life. As a result, dam operators are increasingly facing a complex renewal/ removal decision-making process in a large part because the economic and social values of dams have changed. The Mactaquac Hydroelectric Generating Station (New Brunswick, Canada), operated by NB Power Corporation (NB Power), is Canada's 25th largest dam and it is reaching the end of its service life. A decision is required for the dam's future state and three options were originally proposed: renew, rebuild, or remove. An overarching science framework was developed with

Replicate DNA metabarcoding can discriminate seasonal and spatial abundance shifts in river macroinvertebrate assemblages

“…Although the costs of replication could limit application at large scales, as discussed, metabarcoding is likely to improve the needs of most monitoring schemes. Instead, inferences from MSAMs based on detection frequency are likely to be most suited to applications at local scales (e.g., environmental impact assessment monitoring: Curry et al, 2020), situations where quantitative information would accelerate our understanding of ecological responses prior to exclusion (e.g., pollution sensitivity; Liess & Ohe, 2005), or studies to understand how function scales with dominance (Dangles & Malmqvist, 2004). Importantly, consistent identification using DNA metabarcoding will allow quantitative information developed locally to readily inform interpretation of monitoring across all scales.…”

Quantitative modelling of fish habitat in a large regulated river in a changing climate

“…At the MGS, river discharge averages ~1,100 m 3 s −1 with river widths and depths averaging 750 and 2 m, respectively (Kidd et al, 2011). The boundary on the focused impact reach was the ~20 km reach downstream of MGS to the city of Fredericton where the river widens, and the tidal influence intensifies (Figure 1; R.A. Curry et al, 2020). The hydroelectric facility is operated using a run‐of‐the‐river approach, allowing for relatively natural extreme high flows, whereas minimum low flows are higher than historical natural flows to maintain attraction flow for fish trapping (Monk et al, 2017) and due to logistical constraints when generating power with large 112 MW generator units without spilling.…”

“…The Mactaquac Hydroelectric Generating Station (MGS, New Brunswick, Canada), located on the WolastoqjSaint John River (SJR), is Canada's 25th largest dam, and it is reaching the end of its service life. An elaborate review process has been developed, weighing options to rebuild, renew or remove the facility (R.A. Curry et al, 2020). Each of these alternative future management options would result, in combination with climate induced changes, in a new normal with regard to the lower SJR's flow regime.…”

Developing environmental flow targets for benthic macroinvertebrates in large rivers using hydraulic habitat associations and taxa thresholds

“…There are three hydropower generating stations along the mainstem of the W|SJR with additional barriers on some of the major tributaries. The Mactaquac Generating Station (MGS) is the largest dam in the catchment and is approaching a premature end of its service life (Curry et al, 2020). Operating as a run-of-the-river system at MGS, the downstream hydrograph mostly reflects the seasonal patterns in flow.…”