Hydrology Water Use and Conservation Flows for Kokanee Salmon and Rainbow Trout in the Okanagan Lake Basin


Northwest Hydraulic Consultants . (2001). Hydrology Water Use and Conservation Flows for Kokanee Salmon and Rainbow Trout in the Okanagan Lake Basin. North Vancouver: BC Fisheries.

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The purpose of this study was to express the habitat sensitivity of twenty-one tributaries to Okanagan Lake, through various indices that are calculated from natural flows, water use, land use and physiography in their watersheds. The study streams support spawning runs of either rainbow trout (Oncorhynchus mykiss) or Kokanee salmon (Oncorhynchus nerka).

Re-construction or estimation of the natural hydrologic regime was one of the most important tasks. The study also calculated potential licenced demands on surface waters, assessed potential effects of land use on hydrology, described fish periodicity, and provided preliminary conservation flows. Sensitivity indices calculated from the natural flows, water demands, and land use were used to rank the tributaries for meeting conservation flows, water withdrawals, low flows, peak flows, forest harvesting and urbanization. The most sensitive streams included those that were most affected by human activity and those that, because of their hydrologic regime, have the least ability to resist human impacts.

All the tributaries, except Prairie Valley Creek and Thompson Brook, have licences for irrigation, waterworks, domestic, or industrial extractions. In the large and mediums-sized watersheds, withdrawals are often supported by storage development and the net licenced demand on summer and winter low flows is theoretically small. The greatest demands on low flows seem to occur in small tributaries, particularly Naramata, Eneas, McDougall and Naswhito Creeks. Large demands, in excess of storage, also appear on tributaries near Vernon, such as B.X., Deep and Vernon Creeks and on Trepanier and Powers Creek near Peachland. Groundwater is extracted from many aquifers around Okanagan Lake. These extractions may reduce low flows in some tributaries but the actual effect on surface waters has not been studied.

A number of the tributaries have no stream gauging records or only occasional miscellaneous measurements. Continuous stream flow measurements to supplement existing programs, combined with measurements of storage, diversions and extractions, would assist in reconstructing natural hydrographs for small tributaries and better defining conservation flows.

Storage fills during the snowmelt freshet, potentially reducing the magnitude and duration of the mean annual flood in downstream reaches. The consequences may be less frequent movement of bed material, aggradation, fining of the bed material, and sedimentation of instream gravel. Unusually low peak flows, relative to mean annual flow, occur in Peachland, Kelowna, Vernon, B.X. and Deep Creeks. Trepanier, Lambly and Bellevue Creeks have the greatest mean annual floods (as a percentage of mean annual flow). Scour of bed material frequent transport of bed material, and channel erosion are expected. Forest harvesting is thought to play a role in increasing peak flows in Lambly and Bellevue Creeks.

The lower reaches of several of the tributaries are aggrading. Naramata and particularly Mission Creek have had gravel removal as part of flood control and channel management. Detailed studies of the sources of the coarse material and potential source management programs have not been undertaken. Such programs would greatly assist management of these streams.

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