Instream Flow Needs Analysis - Okanagan Basin Water Board

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FINALOkanagan Basin Instream Flow NeedsFrequently Asked Questions (FAQs)Q1: What is the major difference between BCIFN minimum risk and optimal fish flow metaanalysis(Hatfield and Bruce 2000) guidelines? Do they target the same ecological objectives?”A: No, they don’t target the same ecological objectives nor do they use the same assumptions. TheProvinces’ Phase II Instream Flow Guidelines For Fish (BCIFN) provide a set of seasonallyadjusted(monthly) recommended thresholds for minimum risk flows and allowable waterdiversion based on a natural flow regime approach. Maintaining these recommended minimumrisk flows and allowable diversions is expected to result in low risk to fish, fish habitat, andoverall productive capacity. These flows are not to be interpreted as minimum flows required to“adequately” protect aquatic biota. As one proceeds below these thresholds the likelihood offlow-related constraints on aquatic productivity increases. The BCIFN thresholds are intendedto be risk-averse because of general uncertainties in fish-flow relationships, but also becausethey are to be used in situations where there is little or no site-specific information. Anotherway of coming to terms with these guidelines is through the notion of “burden of proof”. TheBCIFN guidelines place the burden to prove that there are no unacceptable deleteriousconsequences on water extraction activities on proponents of such activities. Doing so in acredible fashion will almost always require site-specific assessments of impacts.The available evidence indicates that there is not a simple 1 to 1 relationship between risk to thefish resource and amount of water used. At times water levels can be severely limiting for fish;in other instances large changes in flow appear to have little effect on fish production. Thismeans that the “right balance” between water use and fish protection is difficult to predict, andmay be different for each stream. It is expected that flow criteria may be adjusted on a sitespecificbasis to reflect the local environment, provided appropriate data are collected (Hatfieldet al. 2003).Alternatively, the Hatfield and Bruce (2000) meta-analysis approach identifies the particularinstream flows that are considered optimal (i.e., maximizes the PHABSIM index for streammicrohabitat) for different salmonid species at different stages of their life-cycle. These flowslikewise are thus not minimum flows required to “adequately” protect aquatic biota. The maindifference from BCIFN guidelines are that the meta-analysis approach focuses on optimal flowsfor specific salmonid species’ life stages at different times of the year. BCIFN guidelines moregenerally identify minimum instream flows required in general to maintain healthy, functioningstreams for multiple species.Q2: Isn’t it true that fish could do just fine without all this water? In 2003 (as in the 1930s) therewas much less water than shown by the BCIFN/meta-analysis values, and the fish still survivedand persist today. So aren’t you over-exaggerating fish needs?”A: It is true that fish populations have evolved to withstand environmental perturbations. If theyhad not they would have long since gone extinct. The flows described herein are based on awide range of studies across North America with multiple peer reviews; the IFN values are an“unexaggerated’ best estimate of the needs of fish and other organisms in order that they faceminimum stress. Readers need to appreciate that there is a major difference between just“hanging on” and recommendations for instream flows that provide a high likelihood ofmaintaining highly productive fish populations and resilient ecosystems.ESSA Technologies Ltd. &Solander Ecological Researchx
FINALOkanagan Basin Instream Flow NeedsA key concept worth keeping in mind when considering this question is resilience – thecapacity of an ecosystem to tolerate disturbances without collapsing into a qualitativelydifferent state that is controlled by a different set of processes. A resilient ecosystem canwithstand shocks and rebuild itself when necessary. As human development and waterextraction activities spread and become more homogeneous throughout the Okanagan basin,more and more pressures are exerted on fish populations. Land-use development that removesaccess to pristine productive habitats with BCIFN-like flows eliminates the refuge habitats thatfish populations would have historically inhabited when waiting out drought. Ultimately, thechoice of instream flows depends on: (i) ecological objectives (e.g., maintaining diverse,resilient communities vs. allowing sensitive species to be extirpated in favour of the hardiestorganisms, and accepting lower local diversity); (ii) personal value systems and (iii) the largerspatial strategic environmental management framework in place for fish protection in theOkanagan. For instance, one could choose to protect a number of representative, productive,pristine sub-basins as ecological reserves where human development and water extraction wereforbidden or highly constrained, and allow intensive development elsewhere. Were this thepresent situation in the Okanagan Basin (it is not) it might be possible for moreenvironmentalists to answer “yes” to this question.Q3: In the summer dry period, meta-analysis flows look like they’re actually enhancement flows,right?”A: Yes. If there were more water available during these periods, we would expect rearing salmonidspecies to benefit (i.e., achieve closer to optimal production at these times). Extraction activitieswill only further exacerbate the natural stresses to these populations. Our analysis shows thatfor a number of sub-basins, fish populations are already under stress due to the semi-aridclimate regime and hydrology in the Okanagan Basin.Q4: During the winter/summer dry weeks of the year, it looks like there’s no water at all left toallocate in fish bearing streams. From a fish standpoint, is this true? Doesn’t this mean we haveto add new storage in order to consider allowing further water allocations in these streams?”A: Our analysis shows that for a number of sub-basin systems, a variety of fish populations arealready under stress due to the semi-arid climate regime and hydrology in the Okanagan Basin.Therefore, yes, in many cases further water extraction activities will further exacerbate stress tothese populations. As one proceeds below these thresholds the likelihood of flow-relatedconstraints on aquatic productivity increases. The BCIFN minimum risk thresholds indicatewhen it is inadvisable (from a fish perspective) to remove flow but also indicate the times andamounts of flow that can be safely diverted when water is plentiful. Adding new water storageis one possible response to enable water extraction and meet instream flow needs, so long as therule-curves and operating procedures for these reservoirs do in fact explicitly take instreamflow needs into account. This includes the spawning period when reservoir releases may tend tobe lower than natural flows. The flow thresholds herein may help increase priority for studyeffort toward the collection of relevant data to resolve conflicts between proposed water usesand instream flows for fish (e.g., site-specific detailed assessments).Q5: Why does the BCIFN minimum risk method move in monthly time-steps when thefundamental time-step of the Okanagan water supply/demand study is weekly?”A: The BCFIN method is designed to develop recommended monthly (not weekly) flow thresholdsbased on variable percentiles of flow for each month based on daily flow data collected over a20+ year time period. For the Okanagan study we are limited to estimates of naturalized weeklyflows (some with considerable uncertainty) over a shorter 11 year period. Althoughconceptually the BCIFN approach could be adapted to be expressed as a weekly value an 11-yrxiESSA Technologies Ltd. &Solander Ecological Research
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