Instream Flow Needs Analysis - Okanagan Basin Water Board

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FINALOkanagan Basin Instream Flow NeedsThe 1996-2006 period of record included several years with exceptionally high annual streamflow yields.As a result, the BCIFN analysis resulted in higher average minimum instream flow thresholds and highermaximum diversion rates for 1996-2006 than for 1970/71–2006, for both catchments. Aggregating dailydata to weekly data resulted in increased average minimum instream flow thresholds for Vaseux Creekbut decreases for Whiteman Creek. Aggregating to weekly data resulted in increased maximum diversionrates for Whiteman Creek for both periods of record, and for the 1971–2006 period for Vaseux Creek;whereas, the maximum diversion rate for Vaseux Creek decreased slightly for the 1996–2006 period.Higher maximum diversion rates generated by use of the 1996–2006 weekly record would hypotheticallyallow greater diversions in high flow years like 1999, whereas, higher average minimum instream flowthresholds with the 1996–2006 weekly record would have restricted diversions more in low flow yearslike 2001. For example, using the 1996–2006 period of record with weekly data would have resulted in anincrease in the volume diverted for both Vaseux and Whiteman Creeks in 1999 (a high flow year) by 11%and 1%, respectively, compared to using the 1970/71-2006 record with daily data. In contrast, the volumeof water diverted in 2001 (a low flow year) would have decreased in Vaseux and Whiteman Creeks by23% and 57%, respectively. An overall comparison (see Figure 2.8 and Figure 2.9) of the minimuminstream flow thresholds from 1970/71–2006 daily data vs. 1996–2006 weekly data shows that using theshorter and less frequent 1996–2006 weekly records would have resulted in higher thresholds during highflow periods but similar thresholds during low flow periods compared to the more complete record(1970/71–2006 daily).Figure 2.8. Vaseux Creek above Solco Creek (WSC #08NM171). Minimum instream flow thresholds for the1971–2006 vs. 1996–2006 periods of record and for daily vs. weekly discharge data.ESSA Technologies Ltd. & 28Solander Ecological Research
FINALOkanagan Basin Instream Flow NeedsFigure 2.9. Whiteman Creek above Bouleau Creek (WSC #08NM174). Minimum instream flow thresholds for the1971–2006 vs. 1996–2006 periods of record and for daily vs. weekly discharge data.2.6 Method 3: Flow guidelines from site specific studiesIFNs to meet fisheries objectives in main-stem river and lake segments in the Okanagan Valley bottomhave been specified in several previous reports (Anonymous 1973, Okanagan Basin Agreement (OBA)1974, Bull 1999) and are reflected in an advanced decision support system (Alexander et al. 2008) thatresource managers now use to satisfy competing objectives of managing water supplies to balanceobjectives such as ensuring fish friendly flows, adequate levels of flood protection and adequate water tomeet dry-period irrigation needs. IFNs and “ecosystem integrity” indicators for some Okanagan tributarystreams have also been explored (NHC 2001). Finally, considerable work has been completed on TroutCreek and is currently underway on Mission Creek to identify flow requirements and Water Use Plans(WUP) that address fish conservation and production goals. Rainbow trout, kokanee or sockeye salmonhave been used as the indicator species for assessing flow/habitat impacts and benefits for these studiesbased on their high level of sensitivity to water quality, water quantity and physical habitat conditions(from OBWB 2008).2.6.1 Okanagan River mainstem – Fish/Water Management Tools guidelinesBecause Okanagan Lake Dam at Penticton controls the flow in the mainstem Okanagan River, both socioeconomicand fish flow requirements have been the subject of a number of intensive investigations (seeCanada-British Columbia Okanagan Basin Agreement 1974a,b,c; Alexander and Hyatt 2008; Alexanderet al. 2008). In the case of Okanagan Lake and River, water levels and flows are managed to provide abalance between flooding, agriculture, fisheries, urban water supply and other interests. However, naturalvariation in seasonal inflows, scientific uncertainty, competing objectives and multi-agencycommunication barriers (often related to staff turnover) have historically been significant challenges facedby resource managers responsible for deciding how to allocate limited and variable water supplies in thebasin. As with most water management decisions, value differences often come into play, with widevariations in weight placed on flood control vs. other considerations such as water for ecological needs.29 ESSA Technologies Ltd. &Solander Ecological Research
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