Riverwatch Daily – Garrison and Oahe

Update #12

OMAHA, Neb. ‐‐The situation in the basin continues to deteriorate due to heavy rain in eastern and western , necessitating higher releases from Garrison in Riverdale, N.D. and near Pierre, S.D. to evacuate stored waters.

In expectation of continued high runoff, the U.S. Army Corps of Engineers will release a daily bulletin detailing releases and levels for both dams. Conditions in the Missouri River basin are changing rapidly, so forecasted releases shown below are subject to change with little notice. Below are the May 24, 2011 statistics for the two dams.

Daily Information Update

Garrison Dam and :

 Midnight level – 1850.4 feet mean sea level

 Yesterday’s Reservoir Inflow – 113,000 cubic feet per second (cfs)

 Current Reservoir Release – 70,000 cfs, increasing to 60,000 cfs Monday afternoon.

 Annual and multiple use zone – El. 1,837.5 to 1,850 msl

 Exclusive flood control zone‐ El. 1,850‐1,854 msl

 Top of spillway gates ‐ 1,854 feet msl

 6 a.m. River Stage at Bismarck‐14.5 feet (Flood stage at Bismarck‐16.0 feet)

 Planned scheduled releases, subject to change based on changing reservoir and river conditions:

o Wednesday May 25: Increase to 75,000 cfs at 8 a.m.

o Thursday, May 26: Hold 75,000 cfs

o Friday May 27 Increase to 80,000 cfs at 8 a.m.

o Saturday, May 28 and Sunday May 29: Hold 80,000 cfs

o Monday, May 30: Increase to 85,000 cfs at 8 a.m.

Oahe Dam and Lake:

 Midnight reservoir level – 1617.6 feet msl

 Yesterday’s Reservoir Inflow – 94,000 cfs

 Current Reservoir Release – 65,000 cfs

 6 am river stage at Pierre 12.5 feet (Flood stage 15.0)  Annual Flood control and multiple use zone – El. 1607.5 to 1617.0 feet msl

 Exclusive flood control zone – El. 1617.0 to 1620.0 feet msl

 Top of spillway gates: ‐ 1620.0 feet msl

 Planned scheduled releases, subject to change based on changing reservoir and river conditions:

o Wednesday, May 25: Increase to 70,000 cfs

o Thursday, May 26: Increase to 75,000 cfs

o Friday, May 27: Increase to 80,000 cfs

o Saturday, May 28: Increase to 85,000 cfs

o Sunday, May 29: Hold at 85,000 cfs

Garrison Dam is a 210‐foot high rolled earth embankment. Discharges are normally passed through five power tunnels having a combined discharge capacity of 41,000 cfs, and three flood tunnels having a combined discharge capacity of 98,000 cfs. They may also be passed through the spillway when necessary. The spillway is equipped with 28 tainter gates and has a maximum discharge capacity of 660,000 cfs at the top of its flood control zone. NOTE: The Corps has never previously used the spillway for releases. The Corps anticipates that all releases this year will go through the power plant and regulating tunnels.

Oahe Dam is a 245‐foot high rolled earth embankment. Discharges are normally passed through seven power tunnels having a combined discharge capacity of 56,000 cfs, and six flood tunnels having a combined discharge capacity of 111,000 cfs. They may also be passed through the spillway when necessary. The spillway is equipped with eight tainter gates and has a maximum discharge capacity of 80,000 cfs at the top of its flood control zone. NOTE: The Corps has never previously used the spillway for releases. The Corps anticipates that all releases this year will be made through the power plant and outlet tunnels.

Daily bulletin updates are available from the Corps’ website: http://www.nwo.usace.army.mil/

Northwestern Division’s water management website for the most up to date information: http://www.nwd‐mr.usace.army.mil/rcc/index.html

U.S. Army Corps of Engineers Contact: Jody Farhat, Chief, Missouri River Basin Water Management 402‐996‐ 3840