INTERNATIONAL OSOYOOS LAKE BOARD OF CONTROL
Annual Report
for
CALENDAR YEAR 2001

1. ACTIVITIES OF THE BOARD
   In 2001, drought conditions were in effect from April 1 – October 31 as a result of the Similkameen River flow (forecast and actual) for April-July being less than 1.0 million acre-feet.  (The actual flow volume of 567,000 acre-feet ranked the lowest in 73 years of record.)  The Board informed the Washington State Department of Ecology of the drought declaration with a letter dated April 9, 2001.  A notice of the drought declaration (shown below) was published in local newspapers on both sides of the International Border and was posted on the Board’s public Web page.  The Board received no public complaints about the 2001 lake levels.
   
   
   
   
   On April 4, 2001, the Board participated in a video teleconference with the IJC.  The Board discussed 2001 drought conditions, the western power supply situation and potential implications for Osoyoos Lake (which were minimal at best), and an update on the Board’s actions in preparation for renewal of the Orders.
   
   A formal meeting of the Board was held on October 3, 2001, in Osoyoos, B.C.  At the public meeting following the Board meeting, presentations were made on Osoyoos Lake, Zosel Dam and the Orders of Approval, 2001 hydrologic conditions, and Zosel Dam operations. Attendance was 30, of which 10 were from the general public.
   
   
2. OPERATION AND MAINTENANCE OF ZOSEL DAM

   1.  Osoyoos Lake Elevations
      
      As shown by the blue area in appendix I, authorized normal operating elevations in Osoyoos Lake range from 911.0 to 911.5 feet from April 1 to October 31 and from 909.0 to 911.5 feet for the remainder of the year.  The gray area in appendix I shows the authorized range of elevations, 910.5 to 913.0 feet, that may be used to manage storage from April 1 to October 31 if drought conditions are declared by the Board in accordance with Condition 8 of the Orders of Approval.
      
      Condition 9 of the Orders of Approval recognizes that backwater from high flow in the Similkameen River and (or) excessive flow in the Okanagan River can cause Osoyoos Lake levels to rise above the authorized range.

      The level of Osoyoos Lake was within the levels authorized in the Order of Approval all year.
      
      The maximum instantaneous elevation of Osoyoos Lake occurred on June 1 and July 17 at 912.56 feet.

      The maximum daily mean elevation occurred on July 17 and 30 at 912.52 ft.

      The maximum instantaneous discharge of the Okanogan River at Oroville occurred on May 15  from 0900 to 1145 hours
      and was 1,260 cubic feet per second.
      
      Osoyoos Lake elevations for water years 1999-2001 are shown in appendix I.  Five days of record in October were not obtained due to a malfunction at the lake gage.
      
      Data on Osoyoos Lake levels and relevant river flows are summarized in appendix II and depicted in the hydrographs in appendix III.
      
      
      Osoyoos Lake  
      

   2. Zosel Dam
      
      In 2001, the Oroville-Tonasket Irrigation District operated Zosel Dam under authority from the State of Washington, Department of Ecology.
      
      

      
      Zosel Dam - 1970's

      
      New Zosel Dam
      
      

3. OKANOGAN RIVER CHANNEL CAPACITY
   
   Condition 4 of the IJC Order of Approval (December 9, 1982), and subsequently revised by the Supplementary Order of Approval (October 17, 1985), calls for the applicant (State of Washington Department of Ecology) to “...take all measures to ensure that the flow capacity of the Okanogan River, upstream and downstream from the control structure, enables the control structure to pass at least 2,500 cubic feet per second when the elevation of Osoyoos Lake is 913.0 feet USCGS and there is no appreciable backwater effect from the Similkameen River.
   
   The Board obtains confirmation from the State of Washington regarding the capacities of the Okanogan River Channel. Hydrologic conditions in 1997, 1998, and 1999 demonstrated that water is able to move out of the lake, through the outlet channel, and past the dam at a rate greater than 2,500 cubic feet per second with the lake at an elevation less than 913.0 feet and no appreciable backwater effect from the Similkameen River.
   
   Tonasket Creek enters a bypass reach of the outlet channel that was designed to accept the creek’s sediment load deposits. The Tonasket Creek alluvial fan has not impaired the capacity of the main outlet channel to perform according to requirements of Condition 4.
   
   
   Mouth of Tonasket Creek — looking south to Zosel Dam

APPENDIX II .—OSOYOOS LAKE LEVELS, INFLOWS, AND OUTFLOWS

APPENDIX III