The Connecticut River basin project demonstrates (1) coordinating diverse stakeholders to assess the costs and benefits of re-operating more than 70 dams within in an interstate basin and (2) pursuing basin-wide environmental flow and water use objectives through collaborative simulation and optimization modeling.

This case study describes a major component of The Nature Conservancy’s Connecticut River Program to restore important river processes, thereby improving the health of declining native species and diverse habitats along the river and its tributaries. With 44 major tributaries, approximately 70 large dams, more than 2,600 smaller dams and 44,000 road-stream crossings spanning 4 states (Connecticut, Massachusetts, New Hampshire, and Vermont) within the 19,000-km² watershed, coordinated basin-scale planning and management clearly is needed. Currently, management of the 70 dams—including 14 owned and operated by the US Army Corps of Engineers (Corps)—is not integrated as a system.

The objective of Connecticut’s ecosystem flow restoration program is to modify management of dams and water supply systems to provide environmental benefits while continuing to supply water, reduce flood risk, and generate hydropower (Zimmerman et al. 2008).   It is collaboratively managed and funded by The U.S. Army Corps of Engineers and The Nature Conservancy.

Local, state, and federal stakeholders were convened on numerous occasions and in a variety of formats, beginning with a 2008 kick-off meeting. In 2009, the non-profit Consensus Building Institute interviewed all key stakeholders across the four states. One constituency that was crucial to the project’s success was the private large dam owners. A 2009 workshop and one-on-one onsite visits with dam owners over 1.5 years proved essential for understanding their operational constraints and for gaining their involvement in the process. A 2010 workshop introduced stakeholders to the modeling that was underway and a 2011 workshop made initial environmental flow recommendations for the basin.

The modeling team is building a hydrologic model and set of decision–support systems (DSS) for integrated water resource management. Water managers and stakeholders will be able to use the system to evaluate environmental and economic outcomes of various water management and climate change scenarios. The DSS also will be useful for upcoming Federal Energy Regulatory Commission (FERC) relicensing actions, for setting individual dam operations in their regional context.

The DSS includes two simulation models, a STELLA system-dynamics model to represent current reservoir operations and economic outcomes in sub-basins, and a more operationally detailed ResSim model that generates essentially identical output to the STELLA model. The STELLA model is more conducive to workshop settings, as it more readily incorporates stakeholders’ ideas, whereas ResSim is more comfortable to the engineers who will implement the resulting flow recommendations.  Both models use a hydrologic foundation of unregulated daily streamflow hydrographs accessed through the Connecticut River UnImpacted Streamflow Estimator (CRUISE) tool developed by U.S. Geological Survey (Archfield et al 2012).

The simulation models are linked to a multi-objective optimization model using the Lingo programming language. The optimization challenge was to find daily releases from 70 reservoirs that meet flood control, hydropower, water supply, recreation and ecosystem requirements over time periods ranging from one season to many years. HEC-RAS, a hydraulic model that calculates stage-discharge relations, will facilitate this conversation. Participants will be asked to refine their initial recommendations based on these results. 

Efforts to engage diverse stakeholders are paying off. Owners of one of the large dams plans to use the project models to support its Federal Energy Regulation Commission (FERC) relicensing request, and the National Atmospheric and Oceanographic Administration has already been using the CRUISE tool to support its participation in upcoming relicensing reviews. Having all stakeholders agree on a common scientific foundation is essential for integrating dam operations across the basin.