Cowanesque Lake Environmental Assessment

Published June 27, 2013

Notice of Availability
Draft Environmental Assessment
Cowanesque Lake Water Supply Releases to Cowanesque, Tioga,
Chemung, and Susquehanna Rivers, Pennsylvania and New York

ALL INTERESTED PARTIES: In accordance with the National Environmental Policy Act (NEPA) of 1969, as amended, the U.S. Army Corps of Engineers, Baltimore District (USACE), has prepared a draft Finding of No Significant Impact (FONSI) and Environmental Assessment (EA) for a proposed revised plan of operation for the water supply storage owned by the Susquehanna River Basin Commission (SRBC) at Cowanesque Lake, located in Tioga County, PA (Enclosure). USACE operates Cowanesque Lake as a multi-purpose project. USACE makes infrequent water supply releases to compensate for downstream consumptive use during dry years when Q7-10[1] low flow water levels are observed on the Susquehanna River at either the Wilkes-Barre or Harrisburg, PA, stream flow gages.

SRBC requested USACE to modify the water supply release operation plan for SRBC-owned water from Cowanesque Lake. SRBC has proposed alternative plan WBH95, which is founded on a trigger flow of monthly P95[2] at the Wilkes-Barre and/or Harrisburg, PA stream gages. Modified water supply releases could occur during the months of July through November when low flow events in the Susquehanna River typically occur. The water supply releases would be made through existing gates, and no physical construction would occur. Alternative plan WBH95 is consistent with both the critical low flow recommendations of The Nature Conservancy (TNC) for mainstem rivers and the passby flow/conservation release values for low flow protection in large rivers in SRBC’s Low Flow Protection Policy.

Under the current plan, the lake has approximately a 36 percent chance each year of being drawn down by more than one foot. There is approximately a 31 percent chance each year that drawdowns greater than one foot would occur during the May through September recreation season. Under the proposed WBH95 alternative, there would be approximately a 44 percent chance each year that drawdowns greater than 1 foot would occur resulting from increased water supply releases. There would be approximately a 35 percent chance each year that those drawdowns would occur during the recreation season. In comparing the current operational plan with the WBH95 alternative, there is an eight percent increase in chance each year of Cowanesque Lake being drawn down by more than one foot and a four percent increase in chance each year of drawn downs greater than one foot occur during the May through September recreation season.

Consequences would range from negligible to minor to Cowanesque Lake. No adverse in-lake water quality effects would be produced. During most drawdown events, minor and temporary adverse impacts to lake submerged aquatic vegetation (SAV) would occur. During severe drought events, there may be moderate impacts to SAV, and SAV would recover in several years. During drawdown events, there would be minor adverse impacts to in-lake wetlands. Lake wetland water quality improvement functions would be lessened in the increased drawdown years and some woody vegetation encroachment may occur. During event years, there would be minor adverse effects to fish from loss of established shallow water habitat. No effects to terrestrial vegetation, wildlife, or rare species at the lake would occur. During the additional drawdown events that would occur during the recreation season, there would be reduced opportunities for lake swimming and boating. Alternative plan WBH95 would have no effect on Cowanesque Lake’s flood risk reduction or water quality management purposes.

Water supply releases during low flow conditions would improve habitat for aquatic life downstream in the Cowanesque, Tioga, Chemung, and Susquehanna Rivers. These water supply releases would reduce detrimental impacts from consumptive uses and benefit a wide range of downstream plant, invertebrate, fish, and wildlife species. While the proposed Cowanesque Lake water supply releases would help downstream flow conditions, they would not maintain flows during a prolonged low flow event but merely offset consumptive uses.

The draft FONSI and EA find that there will be no significant detrimental impacts to the natural or human environment. The plan would provide low flow augmentation to offset consumptive use in the Susquehanna River Basin and support TNC ecosystem flow recommendations while minimizing effects of environmental conditions and recreational opportunities in Cowanesque Lake. The revised water supply release plan, in combination with other instream flow protection requirements and measures, represent an integrated approach to protecting the aquatic ecosystems of the Cowanesque, Tioga, Chemung, and Susquehanna Rivers. USACE has determined that the proposed action complies with all applicable environmental and social regulations. No permits would be needed for the proposed action.

Individuals wishing to obtain a copy of, or wanting more information about, the draft FONSI and EA, may write to the U.S. Army Corps of Engineers, Baltimore District, ATTN: CENAB-PL-P, P.O. Box 1715, Baltimore, Maryland 21203-1715 or by electronic mail to or by telephone at (410) 962-4900. The draft FONSI and EA are available at the USACE website: The documents have also been provided to following public libraries for review: Elkland Area Community, Southeast Steuben County, West Elmira Branch Chemung County, Waverly Free – Central, Osterhout Free, and Harrisburg Downtown.

Any person who has an interest in the project may make comments within 30 days of the date of publication of this notice. Comments must clearly set forth the interest that may be adversely affected by this proposed action and the manner in which the interest may be adversely affected.


[1] The Q7-10 flow is the 7-day average low flow expected to occur at a 1-in-10-year frequency and has a 10 percent chance of occurring in any year.

[2] P95 represents the flow that is exceeded 95 percent of the time.