Stave River Water Use Plan - BC Hydro

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Stave River Water Use Plan Monitoring Terms of Reference June 13, 2005 (Bauersfeld 1978, and Chapman et al. 1986), and the other in New Zealand (Hawke 1978). These studies however, were only concerned with Chinook salmon. Whether these results could be extended to other pacific salmonids was unknown. For WUP purposes however, it was assumed that this was the case and the concept of ‘partial peaking’ was adopted as part of the Combo 6 WUP operating strategy recommended by the CC, provided that a monitor was carried out to verify results. 1.2 Management Questions The key management question addressed by this monitor is whether the limited block loading strategy adopted in the WUP is as successful in minimising redd stranding as was the pre-WUP ‘full’ block loading strategy. Given that the escapement of chum to the Stave system appears to have reached full capacity (Baily 2002), an increase in average escapement is not expected, largely because of the limiting effects of redd super-imposition. As a result, a more likely indicator of success would be that average escapement does not drop over time. If successful, the question then arises as to whether the range of partial peaking can be extended by lowering the base flow from the 100 m 3 s -1 without impacting reproductive success (measured here in terms of escapement). Increasing the range of daily flow fluctuation would increase operational flexibility and thus potentially increase power revenue. Conversely, if the trial is found to negatively impact escapement numbers, the question would be whether the concept of limited block loading should be continued, or whether some modification should be made to lessen the impact, such as impose an upper boundary to the daily fluctuations. Though the present monitor is not necessarily designed to answer these questions, data should be collected in such a manner that it would give insight during the next WUP process. Success should not be solely defined by changes in escapement numbers. There are risks associated with daily fluctuations in water level, and one of the most important is the loss or persistent relocation of quality spawning habitat. With changes in flow come changes in local water depth and velocity. Though chum salmon are capable of spawning over a wide range of depths and velocities (particularly in crowded conditions), there are limits to what they can tolerate and they will avoid unsuitable hydraulic conditions if they persist. In considering the limited block load strategy, the CC assumed that within the range of daily fluctuation, hydraulic conditions in mid-channel spawning grounds and key gravel bars would remain within tolerance limits. This however, must be verified, as it was based primarily on anecdotal information. If found not to be the case, the expected benefits for spawning chum salmon may not be fully realised. In fact, if the impact is severe, it may affect the spawning capacity of the reach. Conversely, if the quality and quantity of spawning habitat is found to be stable over the range of flows, it may be beneficial for future WUPs to explore spawning habitat quality and quantity at lower flows. As alluded to above, this will provide the information needed to explore opportunities to expand the range of daily flow fluctuation. BC Hydro Page 50
Stave River Water Use Plan Monitoring Terms of Reference June 13, 2005 It should be noted that there are two other risks associated with daily flow fluctuations. The first of these is that the limited daily flow fluctuations could potentially strand adult fish that have yet to spawn and the other is that partial block loading could strand early emergent fry during the latter part of the incubation period. Both of these issues are beyond the scope of the present study and are dealt separately in monitors 5 and 6. 1.3 Summary of Impact Hypotheses The management questions above lead to the following set of null hypotheses that can be grouped into two categories; those that deal with aspects associated with a successful deterrence response in areas with stranding risk, and those that pertain to the availability and persistence of spawning habitat in non-stranding areas. Collectively, these hypotheses form a means of testing the success of the limited block loading strategy through a weight of evidence approach. In the first group, the null hypotheses are; H01: Redd density above the 100 m 3 s -1 watermark is the same or greater than below the 100 m 3 s -1 watermark. This is a one-tailed test of the redd density hypothesis that requires several years of data and will take into account annual variability in escapement. H02: Over several years of testing, there is no correlation between the average discharge during the spawning period and redd density above the 100 m 3 s -1 watermark. The ability to cycle water flows during the spawning period will depend on the hydrology of the system, which can vary considerably form year to year. During low water years, the ability to cycle flows, or even maintain a 100 m 3 s -1 base, flow may be limited. The ability to cycle flows may also be limited during high water years. In moderate water years, the duration of daily high flow periods may vary considerably from day to day. All of the hydrological condition will be reflected in the measures of average discharge during the spawning period. This variability in the duration of daily high flows will have an impact on the ability of the limited block load strategy to deter spawning activity and provides a unique opportunity to test its effectiveness from year to year. H03: The average size of each redd above the 100 m 3 s -1 watermark is the same or greater than below the 100 m 3 s -1 watermark. This a one-tailed test of the redd size hypothesis which takes into account that redds excavated because of test digging would be smaller than those where egg pockets have been deposited. H04: Redds located above the 100 m 3 s -1 watermark increase in size over successive daily cycles in water level. BC Hydro Page 51
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Stave River Water Use Plan - BC Hydro

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