Citation | P Slaney Aquatic Science Ltd. 2008. Brohm River: A productive at-risk salmonid habitat system supporting Squamish-Cheakamus fisheries. Prepared for BC Conservation Foundation. |
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Organization | BC Conservation Foundation |
URL | http://www.livingrivers.ca/gbvi/dox/Brohm%20River%20at%20risk%20BCCF%20report%20BRO-2008a%20by%20PSlaney.pdf |
Abstract/Description or Keywords | The purpose of this report is to summarize past fisheries-related inventories and assessments of Brohm River; assess existing fish habitat conditions, limitations and disturbance risks; document habitat conditions as a monitoring benchmark; and identify sensitive habitat-riparian reserves and other protective measures that would reduce potential land-use risks and sustain Brohm River fish resource values. • Historically, the Brohm River was an unusually productive steelhead stream, which flows for 2.5 km via Cheekye River into the Cheakamus River. Unusually high phosphorus concentrations, similar to a nutrient-rich Interior stream, apparently originated from Mt Garibaldi’s glaciovolcanogenic eruption some 15,000 years ago. The Brohm watershed’s fish, wildlife and vegetation have continued to be well used by Squamish Nation peoples for sustenance, materials and medicines, and for several thousands years before the arrival of European settlers. Historically, a major fishery developed in the Cheakamus River, targeting steelhead and salmon stocks, with Brohm River as the key steelhead nursery tributary. • An intensive fish habitat assessment in late winter of 2008 demonstrated that salmonid habitats remain impaired as a result of past land use impacts, with several sites at risk of further degradation, yet the river is currently on a recovery vector/trend. Dominance of steep bouldery steelhead habitats in the mainstem of Brohm River have provided resistance of the past highway encroachments and storm-related logging land-use impacts. Regardless, steelhead and coho habitats have been degraded to the degree that Brohm coho salmon, although in low historical abundance compared to steelhead, are probably functionally extirpated. • Three aquatic-sensitive land areas would be of value as expanded riparian reserve buffers, as there are very few riparian settings that would protect the Brohm system habitats from future land developments. At river km 1.0 to km 1.5, a relic flood channel within the east floodplain would be an effective riparian reserve, using the steep terrain 80 m east of the river as an effective demarcation. This 4 ha area is a natural flood zone which has potential for habitat rehabilitation to offset past river encroachment by the Sea-to-Sky Highway. Secondly, at the east tributary (river km 2.35), an expanded reserve would be beneficial in the fan zone where three subdrainages combine, 300 m upstream from the Brohm River. The alluvial fan of the tributary was destabilized by a past debris flow, and thus an expanded riparian reserve on the lower reach of this tributary would reduce the risk of further fan and channel destabilization. Thirdly, a 2-3 ha east-side pond on the east tributary is also a sensitive aquatic area. It has potential for application of “low impact development” (LID) measures as a settling basin to isolate Brohm River from any future land-use in the east tributary sub-drainage. A proposal for an expansive ski and resort development by Garibaldi Resorts at Brohm Ridge (“Garibaldi at Squamish”) was submitted initially to government in 1996/97, and updated as a 2003 Province of BC Environmental Assessment Office (EAO) submission, coordinated by Enkon Environmental (2003). The proposal targets recreational use by 5,000-12,000 users per day in a developed area of 1,850 ha of 4,900 ha in the Brohm River watershed. The development is projected to extend over 15 to 25 years for completion, and includes 22,850 bed units of accommodations, hotel/resort services and two 18-hole golf courses with residential dwellings and chalets similar to other large ski-resorts. The development is estimated to result in an average production of 2,200 m3 of sewage per day (to a maximum of 5,060 m3 •sec-1). It is currently proposed that sewage will be treated on-site and discharged into the Cheekye River with partial Brohm land disposal for irrigation of the golf courses. Domestic and commercial water use have been estimated at 800,000 m3 per year, plus an additional 500,000 m3 for snow making and 300,000 m3 for golf course irrigation, or a total of 1.6 million m3 per year. This may be reduced via water conservation measures to 1,315,000 m3 per year (G. Stewart, Enkon Environmental, per comm. 2008). Brohm watershed is proposed as the preferred year-round surface source of water. A 2008 revision of the water-use projection incorporates storage of Brohm River water in five small headwater reservoirs, two of which are for potable water. Fisheries resource values, historical habitat impacts and habitat risks associated with the proposed development were reviewed/examined. Aquatic risks from existing and proposed hillslope roads and gullies were not considered because of existing winter snow cover. Several fisheries-related risks are an outcome of this aquatic assessment: • The proposed ski area and resort footprints encompass a substantial portion of the Brohm River watershed and therefore the development has the potential to alter the hydrology/stream flows, geomorphology, water quality and trophic productivity of the Brohm River system, historically a regionally significant steelhead trout and salmon nursery stream for the Cheakamus River within the Squamish system. • At significant risk from the Brohm resort development are excessive water withdrawals during peak seasonal daily use in late-winter and particularly during mid- to late-summer. Significant river flow withdrawal for the Garibaldi at Squamish project would result in deficient steelhead rearing and spawning flows as development of the resort phases upwards. Assuming a peak daily water withdrawal of 2-3 times the average annual withdrawal, and insufficient storage in reservoirs and no external water source, mid- to late-summer flows of Brohm River could be reduced 22- 34% to 42-62% (the former based on adopting water conservation similar to that of Sun Peaks resort near Kamloops). Under conditions of a global warming trend, minimum-flow risks are exacerbated. Storage of excess water in five small steep-terrain reservoirs (including two for potable water) for withdrawal during these low flow periods is planned and would reduce, but not eliminate seasonal risks to fish habitat. More recently, project developers are considering the potential for water supplementation from Cheakamus River groundwater (G. Stewart, Enkon Environmental, per comm., July 15, 2008). Selection of pumped external water source would be a best-management-decision for both the Brohm fish resource and the proposed resort, as results-based monitoring could only detect a postimpact water-supply crisis. • A second significant risk is excessive eutrophication of an extraordinary phosphorus-rich river system that is currently productive and nitrogen limited. Unless moderated, nitrogen run-off from fertilized residential lands and golf courses, as well as from erosion of disturbed volcanic-enriched soils, has the potential to over-enrich Brohm River, potentially degrading salmonid habitats as organic matter accumulates over time. Proposed use of treated liquid waste as fertilizer for golf courses or other land sites would elevate this risk substantially. Currently, periphyton and grazing benthic insects are in healthy equilibrium, sustaining a diverse community, which is very highly dominated by mayflies, stoneflies and caddis flies at base of the salmonid food chain. • There is also broad-scale risk from hillslope land clearing, road construction, and multiple stream/gulley crossings, resulting in significant transport of fine sediments and other road-source pollutants, unless systematically and intensively managed using “low impact development” (LID) measures as outlined by Hinman (2005). Development and management of settling basin ponds on key tributaries, and small-scale expansion of selected mainstem and tributary riparian reserves would be beneficial to the Brohm aquatic ecosystem in the short and long-term development of the proposed resort project. |
Information Type | report |
Regional Watershed | Howe Sound & Sunshine Coast |
Sub-watershed if known | Brohm River |
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Comments | |
Project status | complete |
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