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Case Study: “Dead pool” Scotts Flat Reservoir

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Water supply impacts under a flow-only approach become even more significant when evaluated by impacted facility.  For example, NID’s Scott’s Flat Reservoir is highly reliant on diverted Sierra water supplies given its own small watershed.

Yet, Scotts Flat is essential to District operations insofar as it supplies the water for Nevada County and is the primary source of drinking water supply for NID customers. 

In the graph below, April 30 is used to show typical reservoir highpoint as the season transitions into the high-water use summer months.  Under the proposed plan amendments, Scotts Flatt Reservoir is effectively at dead pool in many of the drier year types.  This term describes the occurrence when the amount of water stored in a reservoir is so low, water can no longer flow downstream. 

This means there is effectively no water supply for Nevada County before the high-demand summer and fall water seasons

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Even in above normal and below normal year types, there are huge water supply impacts of 20,000 to 30,000 acre-feet per year (an acre-foot is the amount of water that would cover a football field in one foot of water). 

A supply reduction of this magnitude would result in the rationing of water supply throughout NID’s service area:

  • Domestic supply would take service priority, thereby leaving the irrigation system with little to no supply and dry irrigation canals
  • The loss of irrigation water would be catastrophic to the community from agriculture and fire suppression perspectives
  • Loss of supply would have a detrimental effect to the environment with small streams and tributaries suffering from the lack of tail waters of NID’s canals.
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