This case study demonstrates the development of statewide regulations to protect environmental flows, including a process to establish condition goal classes for every river and stream in the state and the development of reservoir release rules that apply statewide. These reservoir release rules feature several innovative approaches to mimic natural conditions, to ensure water reliability for communities, and to be flexible during drought events.
In 1971, the Connecticut legislature passed a law requiring the protection of environmental flows for the “stocked streams” of Connecticut—that is, those rivers and streams stocked with fish by the Division of Wildlife. In 2005, at the request of environmental advocates and with the concurrence of water users, the legislature updated this statute to require the Department of Environmental Protection (DEP) to develop environmental flow regulations for all rivers and streams in the state while also providing for the other uses of water.
The statute requires that these regulations be developed with the participation of an advisory group representing a broad range of stakeholders. The DEP Commissioner subsequently established three advisory groups—a technical advisory committee, a policy advisory committee, and a Commissioner’s advisory committee—to inform the process. These groups met and negotiated for six years until final regulations were agreed to in November 2011. This process included a formal public comment process and high-visibility advocacy campaigns, both for and against the new regulations. In addition, in Connecticut all final regulations must be reviewed by the Regulations Review Committee of the legislature to ensure they comply with the legislative intent. The first of these committee reviews sent the initial regulations back for further negotiation and narrowing of the scope before the final regulations were produced. In the end, all sides advocated for approval of the regulations as something they could “live with.”
The 2011 regulations  contain three primary components: (1) a set of narrative streamflow standards that apply to all streams; (2) a goal classification process through which every stream segment is being associated with one of four environmental flow standards; and (3) a detailed set of flow release requirements for reservoirs and impoundments.
The streamflow regulations provide for four stream condition classes, essentially 1) unaltered,  2) minimally altered, 3) moderately altered, and  4) streams that are allowed substantial alteration of flow conditions to meet human water needs.  Condition classification considers the presence of sensitive species, the presence of existing water withdrawals, existing and planned development upstream of the reach, and other factors.  Additionally, the regulations provide for a process by which a stream’s condition class can be reviewed and changed in the future—based either on new information that may become available or based on future needs that cannot be anticipated.
Detailed release requirements are stipulated for reservoirs, based on existing studies of flow-response relationships for fluvial-dependent species, as studied in Georgia (Freeman and Marcinek 2006) and subsequently confirmed for the northeastern United States (Vokoun and Kanno 2009, 2010; Armstrong et al. 2010, 2011). Building upon these and other environmental flow studies, the technical committee used a “weighted evidence” approach (Norris et al. 2012) to recommend that dams on class 1 streams cannot actively manipulate the storage of a reservoir (in effect making these dams “run of river”) and dams on class 2 streams must release at least 75% of their reservoir inflows at all times. Class 3 release rules vary by season according to biological need and by antecedent conditions according to inflows measured during the previous two weeks.  The rules are expressed in terms of seasonal flow exceedance probabilities derived from model-calculated daily flow data (Archfield et al. 2010).
Negotiations of release requirements were substantially aided by the use of the Stockholm Environment Institute's Safe Yield Wizard tool (Vogel et al.2007). This tool calculates changes in the amount of water consistently available for human use, which would result from different environmental flow release requirements. Water suppliers and aquatic ecologists used the tool iteratively to design release requirements that would not unacceptably impact the amount of water available for supply.   Nonetheless, various exemptions and exceptions also resulted from the protracted negotiations.
Read more about Connecticut Statewide Environmental Flow Regulations in A Practical Guide to Environmental Flows for Policy and Planning.