The International Osoyoos Lake Board of Control was established on February 12, 1986, by the International Joint Commission to carry out the provisions of the Commission's Order of Approval dated December 9, 1982, and the Supplementary Order of Approval dated October 17, 1985.

ACTIVITIES OF THE BOARD

The Washington State Department of Ecology provided the Board with Y2K compliance certifications for Zosel Dam in March.  These certifications were forwarded to the International Joint Commission upon receipt.  The Board has received no reports of problems concerning operation of Zosel Dam since January 1, 2000.

The Board received several inquiries concerning the high snow pack and the potential for spring flooding.  A special statement was developed concerning this situation and was posted on the Osoyoos Lake Board of Control’s web site from May 12 to October 21.  The statement is included in appendix IV.

On April 7, 1999, the Board advised Mr. Keith Phillips of the Washington State Department of Ecology by letter that current forecasts indicated drought conditions would not be met this year.  The Northwest River Forecast Center’s April to July volume forecast was for 1.91 million acre feet of runoff for the Similkameen River.  The Canadian River Forecast Centre’s forecast for the Okanagan River and for Okanagan Lake levels was well above drought criteria.

A formal meeting of the Board was held on October 7, 1999, in Osoyoos, B.C.  A public meeting followed the meeting of the Board on the same date.

1.      OPERATION AND MAINTENANCE OF ZOSEL DAM

1. Osoyoos Lake Elevations
   

The authorized range of normal operating elevations, 909.0 to 911.5 feet, is shown by the blue area in appendix I. 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 conditions 7 and 8.

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 except for the period from April 23 to June 10 and June 15-22. 

During these periods, lake levels were influenced by Similkameen River backwater and (or) high Okanagan River flows. Okanogan River flows, as measured at the Okanogan River at Oroville gaging station, first exceeded 2,500 cubic feet per second on April 26.  Backwater from the Similkameen River restricted flow at the Okanogan River at Oroville gaging station from May 23 to July 23.  The gates of the Zosel Dam were removed from the water from April 19 to June 11 and June 17-28.

The maximum instantaneous elevation on Osoyoos Lake occurred on May 29 at 912.56 feet.

The maximum daily mean elevation occurred on May 29 at 912.53 ft.

The maximum instantaneous discharge of the Okanogan River at Oroville occurred on May 20 and was 2,700 cubic feet per second.

Recorded lake elevations for water years 1997-99 are shown in appendix I.

Data on Osoyoos Lake levels and relevant river flows are summarized in appendix II and depicted in the hydrographs in appendix III.

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

2.      IMPROVEMENTS TO THE OKANOGAN RIVER CHANNEL

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 obtained 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 be moved 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.

3.      PUBLIC MEETING COMMENTS

A public meeting was held in Osoyoos, B.C., on October 7, 1999. Presentations were made on Osoyoos Lake, Zosel Dam and the Orders of Approval, 1999 hydrologic conditions, and Zosel Dam operations. Attendance was 25, of which 9 were from the general public.

Comments from those in attendance included a question of the validity of the terms of the drought conditions, an inquiry about the current lake level, and one person expressed concern that septic tanks may leak sewerage to the lake when lake levels reach 913 feet.

During the period of open discussion with the public, one person expressed concern that the level of the lake is kept too high in late April and early May prior to the spring freshet.  Another person stated that residents on and near Osoyoos Lake feel that they are being sacrificed for Okanagan Lake residents.  A member of the public stated that Okanogan County has set a minimum elevation for construction around the lake at 918 feet but in Canada it is at 921 feet.  Mr. Christopher Fisher (Colville Confederated Tribes) asked what benefits were derived from straightening the river channel north of Osoyoos, and if the Oxbows could be replaced.  He also asked if the system could be manipulated to improve the thermal barrier to fish passage.

A.     International gaging stations in operation throughout the year:

(1)     For Stage Records

Osoyoos Lake near Oroville, Washington
Okanogan River at Oroville, Washington (auxiliary gage)

(2)     For Discharge Records

Okanagan River near Oliver, British Columbia
Okanogan River near Oroville, Washington (base gage)
Similkameen River near Nighthawk, Washington

(3)     Reports

Monthly summary reports of stage and discharge data were forwarded to the International Joint Commission and to the Board of Control members.

B.      Compliance with the lake levels specified in the Orders of Approval is measured at the station Osoyoos Lake near Oroville, where elevations are expressed in terms of USCGS datum.

C.     Osoyoos Lake

Maximum daily mean elevation                                                       278.139 meters - May 29
                                                                                                   (912.53 feet)
Maximum instantaneous elevation                                                   278.148 meters - May 29
                                                                                                   (912.56 feet)
Minimum instantaneous elevation                                                    277.252 meters - January 6 and 8
                                                                                                   (909.62 feet)

         Lake elevation at time of peak flow for Okanogan River at Oroville   277.978 meters May 20

                                                                                                            (912.00 feet)

D.     Okanogan River at Oroville

Maximum instantaneous discharge                                                 76.5 cms - May 20
                                                                                                   (2,700 cfs)
Maximum daily mean discharge                                                     75.6 cms - May 20 and 21
                                                                                                   (2,670cfs)
Annual mean discharge                                                                 31.0 cms
                                                                                                   (1,095 cfs)

The annual mean discharge was 156 percent of the 57-year average of 704 cfs.

E.      Similkameen River near Nighthawk

Maximum instantaneous discharge                                                 544 cms - June 17
                                                                                                   (19,200 cfs)
Maximum daily mean discharge                                                     544 cms - June 17
                                                                                                   (19,200 cfs)

High river discharges and stages created backwater conditions for the Okanogan River at Oroville gaging station from May 23 to July 23.

APPENDIX IV.—

***Special Statement about Spring 1999 Lake Levels***

The International Osoyoos Lake Board of Control has received a number of inquiries this spring about potential high Osoyoos Lake levels this year due to melting of the abundant snowpack in the upper Okanagan and Similkameen River Basins. This statement explains the International Joint Commission's orders for regulation of Osoyoos Lake levels and the unique hydrologic and hydraulic circumstances that cause high water levels on this lake.

Zosel Dam is owned by the Washington State Department of Ecology (WSDOE) and operated by an agreement with the Oroville-Tonasket Irrigation District, subject to the Orders of the International Joint Commission (IJC) and oversight from the International Osoyoos Lake Board of Control (IOLBOC). The IJC Orders of 1982 and 1985 specify how the lake level is to be controlled, to the extent possible, and provide for the appointment of the IOLBOC.

The IJC Orders require that Washington State Department of Ecology operate Zosel Dam to maintain Osoyoos Lake levels between 911.0 and 911.5 feet (USCGS) between April 1 to October 31 as much as possible.

During high flows, as expected this spring, the level of Osoyoos Lake is controlled by the flows in the Similkameen River and from Okanagan Lake. The Similkameen is an uncontrolled river with a mean annual flow three times that of the Okanagan River, and a peak (flood) flow ten times that of the Okanagan River. When Similkameen floods, the Zosel Dam has little or no effect on Osoyoos Lake levels.

When the Similkameen River floods, the water south of the Zosel dam and Osoyoos Lake can become as high as 916 or 917 feet. If Osoyoos Lake is low, the Similkameen River flow can block the flow in the Okanagan River, and in the worst case, water flows northward to fill Osoyoos Lake until the level of the lake is the same as that in the Similkameen River south of the lake. This blockage begins to occur when Silmilkameen River flow rises above about 9,000 cubic feet per second. Because the flow in the Similkameen River is uncontrolled, and is very much larger than the flow in the Okanagan River, there is nothing that can be done to prevent this.

On May 9, 1999, the United States National Weather Service estimated that the most likely range for peak spring flood on the Similkameen River will be 20,400 to 30,400 cubic feet per second. These magnitudes are in the range that could result in backing up water in Osoyoos Lake above 915 feet.

Releases from Okanagan Lake can be adjusted but this has little impact when the Similkameen River is high for any length of time.

On average, Osoyoos Lake can be expected to exceed 913 feet every other year, 915 feet every 12 years, and 917 feet every 50 years.

Observed Osoyoos Lake elevations and Similkameen River streamflow data are available on the internet at the following site:

http://wa.water.usgs.gov/IJC/

All gates at the Zosel dam have been fully out of the water since April 19, 1999. When the water level at the dam exceeds 913 feet, the water will flow over the overflow portion of the dam.

If you have further questions about this information, please contact Mr. Larry Adamache, Secretary to the Canadian Section of the IOLBOC at 604-664-4004, or Mr. Thomas Zembrzuski, Secretary to the United States Section at 253-428-3600; ext. 2608. If you have questions about hydrologic conditions or the upper Okanagan system operations, please contact Mr. Brian Symonds with the B.C. Ministry of Environment, Lands and Parks in Penticton at 250-490-8255. If you have questions about Zosel Dam operations, please contact Mr. Ray Newkirk with the Washington Department of Ecology at 360-407-6630.