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3.2 Incorporating environmental flows

Environmental flows overview

In order to counteract dam's alteration of the natural flow regime, environmental flows have been incorporated into many dams' operations plans, particularly in some western countries (e.g. US, Australia, Canada). Environmental flows manage the quantity, timing and quality of water flows below a dam, with the objective of sustaining ecosystem functions and riverine species. The objective of environmental flows is not reproduce a natural flow regime in whole, but rather to achieve a flow regime that maintains the essential processes required to support healthy river ecosystems. For example, it not usually desirable to reproduce large flood events that can harm people and damage property, but it may still be possible to introduce smaller flood events that achieve the objective of transporting sediment and wood to create essential habitat features. While some dam operations plans included environmental flows from the outset of their operations, including Folsom Dam, in most cases, environmental flows have been retroactively introduced into operations plans.Watch the video from the Natural Heritage Institute on the Global Dam Reoptimization Initiative for more information on the impacts of dams and how redesigning operations can help restore ecosystems and provide climate change mitigation opportunities.

Environmental flows at Folsom (historical)

In addition to the primary operating objectives of flood control, water supply, and hydropower production, other purposes in the initial plans at Folsom dam included fish and wildlife preservation and recreation. Historically, environmental flow regulations focused on minimum flow requirements. For Folsom these included a minimum flow at the mouth of the American River of 250 cfs from January through mid-September and a minimum of 500 cfs required between September 15 and December 31.

Updating Folsom's environmental requirements (present)

Biological, socioeconomic, legal, and institutional conditions have changed substantially since the initial minimum flows at Folsom Dam were adopted in 1958. Many diverse stakeholders involved in various American River actions have agreed that the current regulations are not sufficient to protect the fishery resources within the lower American River. The bullet points below reflect a partial list of some more recent recommendations for an updated flow management standard on the Lower American River. 

Recommendations for lower American River flow management standard (SWRI 2004)

  • Required Flows equal to 2,250 cfs
    • 250 cfs step increases from 1,500 cfs on October 1 to 2,250 cfs on November 9
    • Oct 1 to Oct 24 1,500 cfs
    • Oct 25 to Oct 31 1,750 cfs
    • Nov 1 to Nov 8 2,000 cfs
    • Nov 9 to Dec 31 2,250 cfs
  • Required Flows between 2,250 cfs and 1,500 cfs
    • Incremental step increases from 1,500 cfs on October 1 to Required Flows on November 9
    • Oct 1 to Oct 15 Required Flows = 1,500 cfs
    • Oct 16 to Oct 31 Required Flows -500 cfs, or 1,500 cfs, whichever is greater
    • Nov 1 to Nov 8 Required Flows -250 cfs, or 1,500 cfs, whichever is greater
    • Nov 9 to Dec 31 Required Flows
  • Required Flows less than or equal to 1,500 cfs
    • Implemented on October 1
    • Continue at same level through December 31



During what time of year do the above recommendations apply?
from ____ to ____ (please type full month name)

Display "Correct, the recommendations above only apply during the fall months from Oct-Dec. As such, the recommendations do not address the dam's impact on the natural flow regime for the other 3/4 of the year. Importantly, none of the recommendations attempt to reintroduce controlled high flows or floods into the system, a significant component of the natural flow regime and one with important implications for native fish species."

What dam objectives would be impacted by implementing the recommendations above?

Flood control ____ Hydropower ____ Both ____




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