Water Stewardship Information Sources

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.
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
Aquifer #
Comments
Project status complete
Contact Name
Contact Email