04 Mar Assessment of Lake Levels on Kokanee Recruitment in the West Arm of Kootenay Lake
This report provides an examination of the hydrograph of the West Arm of Kootenay Lake in relation to the shore spawning kokanee. The hydrograph has been altered significantly following a series of hydroelectric developments over the last century. Upstream and downstream impoundment and the subsequent alteration of the natural hydrograph have had a profound ecological impact upon Kootenay Lake. Shore spawning kokanee at specific sites in the West Arm are affected due to dewatering of redds as the hydrograph declines over the fall, winter and early spring months. Analysis of the hydrograph prior to major impacts revealed that dewatered redds increased from approximately 12% on average during the 1928-1932 period to an estimated average of 70% during the last decade based on redd depth data from the 2009 and 2010 field seasons. The hydrograph is considerably more variable in the 2000-2011 period than in the 1928-1931 period with the current system configuration of dams and operational directives. The variability results in a delay in spring flood to meet flood control requirements thus leaving the West Arm littoral areas exposed with more frequent and extended periods of low water into late spring.