International Lake Ontario-St. Lawrence River Study

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Technical Working Groups

Spill at Long Sault Dam

Performance Indicator Summary

Performance indicator: Spill at Long Sault Dam

Technical Workgroup: Hydropower TWG

Research by: Hydropower TWG

Modeled by: The SVM should indicate when flows are in excess of the plant capacity at Moses-Saunders. Spill during the season from April 1 to mid June should be avoided to avoid fish spawning.

Activity represented by this indicator: This PI refers to spilling water through Long Sault Dam when river flows exceed the capacity of the generating units at the Moses-Saunders station.

Link to water levels: High water levels on Lake Ontario dictate high outflows.

Importance: Since the facility became operational, spills at Long Sault Dam into the South Channel have occurred infrequently and in varied amounts. As a result, a warm water aquatic habitat has developed in what is essentially a backwater habitat in the St. Lawrence River. During spill events in early spring and early summer, the potential exists for cooler river water to spill into the warmer, shallow-water habitats of the upper end of the South Channel, causing concern for the propagation and survival of warm-water species immediately downstream of the dam that use this area preferentially as spawning and nursery habitat.

Economically, hydropower generation that is spilled is forever lost. This is addressed in the PI above that seeks to maximize the value of hydropower generation.

Performance Indicator Metrics: The combined capacity of the Moses-Saunders station is approximately 10,000 cms (353,000 cfs) when all 32 generators are in service. Total maximum discharge per unit is approximately 315 cms (11,000 cfs).

Temporal Validity: This PI is critical during the spring months. Fish spawning occurs during the period from mid-April through the end of June in the South Channel. This is a warm water environment relative to the rest of the river. Spillage introduces cold water which is thought to be harmful to fish spawning during this period. This is addressed in further detail in the contextual narrative and in NYPA's FERC license.

Spatial Validity: South Channel immediately downstream of Long Sault Dam.

Links with hydrology used to create the PI algorithm: The upper bound of the four foot range on Lake Ontario is 75.37 meters (247.3 ft). When levels exceed 75.37 m (247.3 ft) the regulation plan seeks to drive down the level with high outflows.

Algorithm: Outflows in excess of 10,000 cms (353,000 cfs) will normally cause spill at Long Sault Dam.

Validation: Unit rating tables

Documentation and References: As a result of resource agency concerns in re-licensing, FERC has required monitoring and reporting of South Channel water temperatures and dissolved gases during the spring. Documentation regarding NYPA's license and environmental assessments have been made part of the public record and provided to the Study Board.

Risk and uncertainty assessment: Spill at Long Sault dam is infrequent. There is uncertainty regarding the impact on fish species during spill. Water temperature monitoring and dissolved gases monitoring will take place when spill is required to try to determine the impact on the fish habitat.

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