cordilleran geoscience/gcdz/rogues gallery 2 of 11 · relative elevations were determined by...

Cordilleran Geoscience/GCDZ/Rogues Gallery 1 of 11

May 31, 2004

Anders OuramClimbers Access Society of British ColumbiaVancouver, BC

Re: Garibaldi Civil Defence Zone and conflicts with climber’s access to Rogues Gallery.

IntroductionThe Climbers Access Society of British Columbia (CASBC) has asked me to prepare anoutline of the issues pertaining to recreation in the Garibaldi Civil Defence Zone,specifically with respect to climber’s parking and access to the Rogues Gallery climbingarea located at the south end of the GCDZ (Figure 1). They desire a list ofrecommendations consistent with the intent of the GCDZ that, if followed, would allowcontinued access to this popular climbing area. This report is based on a review of theGaribaldi Civil Defence Zone Land Use Plan and its appendices, published literature onthe Barrier landslide, and on a field review of sites discussed in the text. Observation siteswere located using a handheld Garmin GPS unit with a stated accuracy of ±10 m.Relative elevations were determined by Thommen altimeter accurate to ±5 m. River anddebris terrace heights were measured. Of importance to the Approving Officer reviewingthis report are the qualifications of the person making recommendations, and thereforemy CV is attached.

The Garibaldi Civil Defence Zone (GCDZ) was established in 1980 by Order in Council(OIC 1185/80). The intent of the GCDZ was stated in land use policy 1.01 contained inOIC 1409: the GCDZ is designated “to minimize the loss of life in the Garibaldi Hazardarea in the event of a slide” from the Barrier. The details of the Garibaldi Civil DefenceZone, including the scientific basis, its history and administration, etc. are reviewed in theGaribaldi Civil Defence Zone Land Use Management Plan (Gryphus-Thurber 2001) andwill not be repeated herein. This report specifically addresses the intent and managementof the GCDZ as it bears on recreation at Rogues Gallery.

Since 1992 climbers have pulled off Highway 99 into a low flat area on the east side ofthe highway located at UTM E488040, 5532243 (NAD 83), and then walked upslope to agroup of crags referred to informally as Rogues Gallery (Figure 2). Presently this is arelatively popular area with consistent use on weekends and many weekdays as soon asthe area is snow free, and any time the rock is dry and the weather warm - a periodextending from mid March to late September.


In the GCDZ land use plan, Kevin McLane, the author of the climbing guidebook for thearea and a representative of the CASBC was listed as a contact on the distribution list forthe recreation questionnaire (Appendix 3, Gryphus-Thurber 2001). This implies thatrockclimbers had some input into the planning document, however, no mention ofRogues Gallery appears in the questionnaire results, and Mr. McLane does not recall everseeing or responding to the questionnaire. Thus, it is not clear if access to Rogues Gallerywas ever considered during the development of the land use plan. Recently, parking at thetrailhead to Rogues Gallery has been discouraged by the Ministry of Transport. CASBCbelieves, and the argument is made herein, that conditional approval for parking andaccess is consistent with the intent of the Garibaldi Civil Defence Zone.

GCDZ: Configuration and PurposeIn the Cheakamus River valley bottom, beyond the mouth of Rubble Creek, the boundaryof the Garibaldi Civil Defence Zone is defined by the 400 m contour elevation (Figure 1).At the upstream end this boundary is naturally closed, but at the downstream end theboundary is artificially terminated near the upstream end of the Cheakamus Rivercanyon. As stated by OIC 1409, this cutoff is drawn east/west from the SE corner of Lot3669, Group 1, New Westminster District, and corresponds approximately with UTMnorthing 5531250 (NAD 27) on NTS map 92G/14. This line is roughly coincident withthe rockfall that blocked Highway 99 for a week in 1997. In all the GCDZ extends about11.5 km along the valley axis.

The intent of the GCDZ is derived from the Garibaldi Advisory Panel report (1978),which was conducted in response to the Berger (1973) decision. The wording of theadvisory panel recommendation (section 8.5.1, pg 70) is reiterated below:

“The extent of the area of limited development should include both sides ofCheakamus Valley to a distance of 3 km downstream from Cheakamus dammeasured along the river and should extend 20 m in elevation above the limits ofthe previous deposits of slide debris and debris flow deposits.”

In the subsequent delineation of the GCDZ, the arbitrary designation of the 400 m levelfor the boundary resulted in the inclusion of “excess relief” on the order of 80 m on theeast side of Cheakamus River near Rogues Gallery. Cognizant of the Advisory Panel’srecommendation, Thurber (2001) has divided the GCDZ into different hazard typesshown on Figure 1.


The Rogues Gallery Climbing Area: Location and HazardsRogues Gallery (Figure 2) is located on the east side of the Cheakamus River, in thesouthern part of the GCDZ about 3.1 km south of Rubble Creek and 800 m north of thesouthern boundary. According to 1:20 000 TRIM mapping, the valley bottom at thislocation is about 300 m elevation, or 100 m below the arbitrary 400 m level of theGCDZ. In this area Thurber Engineering (2001, DWG 19-3490-0-1) has divided theGCDZ into two hazard classes:

1. A debris flow hazard zone confined to the valley bottom, and delineated, given thelimits of the map scale, roughly 20 m above the valley bottom level; and

2. A mountain slope hazard area found above the debris flow hazard zone.

Highway 99, the climbers parking for Rogues Gallery and the lowermost climbing wallinformally named “Road Warrior” are located in the debris flow hazard zone (Figure 1).In the river channel along the west bank buried trees are being exhumed by theCheakamus River (Figure 1, site 7; Figure 3b). We conducted a survey of these trees.Stems exhumed during the October 17-19, 2004 flood still support bark andremnant caps of the forest litter layer thatgrew on the enclosing debris flowsurface. Species mix was similar to themodern day mix of mature Douglas firand pole cedar. Two mature fir stemshave been exhumed to the roots anddirect measurement of 1855 debris flowthickness was possible. At thisdownstream location, the debris flow was4-5 m thick, consisting of a material witha matrix of massive, clast-supportedsandy gravel, with angular clasts topebble size, supporting a coarse fractionof subangular to subrounded, cobble tomedium boulders. D90 clast size is about1.5 m diameter. Lithology is volcanic.There are no fluvial materials capping thedebris. Assuming that a similar debrisflow hazard exists, a future event couldlikely inundate the existing floodplain in5 m of debris.

Rogues Gallery itself (Figure 2) consists of a series of predominantly west and southwestfacing cliffs developed along a structural lineation that extends 2 km southeast of theparking area. Most of the climbing occurs on the cliffs directly upslope of the parkingarea and up to 500 m distance to the southeast. The cliffs range up to 50 m in height andare underlain by granodiorite. Aside from the “Road Warrior” wall, the Rogues Galleryclimbing area is above the mapped DF hazard area and within the MSH area of the


GCDZ (Figure 1). Mountain slope hazards include a variety of hazards normal to steepmountainous terrain in southern British Columbia. At Rogues Gallery these would consistof small rockfall events.

GCDZ: Management Authority and Land-use GuidelinesSince the access and majority of the cliffs at Rogues Gallery are located within theGCDZ, climbing at the site falls under the jurisdiction of the GCDZ. According to OIC1409 administration of the GCDZ is under the authority of the Provincial ApprovingOfficer (AO) of British Columbia, presently Mr. Howard Hunter, Ministry of Transport,Burnaby, BC. The approving officer is responsible for receiving and evaluatingapplications for activities proposed to take place within the GCDZ. Further, approval isrequired for any form of construction, dredging, excavation or filling of land. Thedecisions of the AO are guided by a series of land-use policies as stated in OIC 1409.Those that are relevant to Rogues Gallery are paraphrased below:

2.01 Human ActivityHuman activity in the hazard area shall be kept to a minimum.

2.02 RecreationPublic use of recreation facilities should be discouraged, and facilities should be removedand access roads barricaded.

2.07 SigningAppropriate signs informing the public of the nature of the danger to life in the hazardarea shall be posted.

GCDZ: Existing Management PracticesWith respect to guideline 2.02 the specific recommendations have not been followed byBC Parks. Parks recognized that the Rubble Creek trail into Garibaldi Park was animportant access point that would likely continue to be used illegally (Vicki Haberl, perscom. 2004). Preventing road access to the existing trailhead would only forcerecreationists to walk to the trailhead and spend more time in the rock avalanche hazardarea. Therefore, the solution that has been adopted is one of minimizing the risk,consistent with guideline 2.01, by allowing vehicle access to the trailhead, butencouraging people to limit their time in the hazard area through the use of signage.

GCDZ: Land Use Plan RecommendationsRecommendations of the GCDZ land use management plan (Gryphus-Thurber 2001)pertinent to this review are listed below:


In Section 4.1.4, with respect to the traveling public it is recommended that all roadswithin the CDZ be posted with signs warning of the landslide hazard and prohibitingparking in inappropriate areas.

Also in Section 4.1.4, with respect to recreationists it is recommended that interpretivesigns displaying information about the Barrier landslide hazard be erected at trailheads orother appropriate locations.

In Section 4.2.4, although intended for day use areas indicated on Figure 11 in the GCDZland use plan, it is recommended that where boundaries of day use areas are proposedthey should be checked by a professional geologist and/or geotechnical engineer withtraining and experience in geological hazard and risk assessment and mapped utilizingbase mapping with 2-m contour intervals.

Recommendations included in the Garibaldi Civil Defence Zone Land Use ManagementPlan must be approved by Cabinet. To our knowledge this has not occurred.

Risk EvaluationIn the GCDZ the risk to life varies for each hazard zone, and these levels have beenassigned qualitative values relative to one another, as shown in the legend on Figure 1.The debris flow hazard zone is assigned a very high risk to human life, while themountain slope hazard zone has a moderate to low risk to human life.

Here we present a quantitative risk analysis for risk to life, or the “probability of death bydebris flow” resulting from the activity of climbing at Rogues Gallery. It must be stressedthat the risk calculation is conducted from the point of view of the administrator in thatthe assigned probabilities PE:H and PL:E consider the presence of any climber at the site.From an individual’s perspective these assigned probabilities would be much lower, andtherefore the resultant would be PDI very low. The risk analysis follows equation 1:

[1] PDI = PH x PE:H x PL:E x PD:L

where PDI is the probability of death to any individual, PH is the annual probability ofhazard occurrence, PE:H is the probability of an individual’s recreation period coincidingwith the hazard, PL:E is the probability of being in a location affected by the hazard, andPD:L is the probability of death of the individual in the area affected by the hazard.

Below each element of the risk equation is quantified:

PH

Hazard probabilities for different event types in different parts of the GCDZ arediscussed by Graham (1990) and summarized by Thurber (2001). Thurber (2001)indicates a 1:600-1:2500 (mean 1:1800) annual return for large rockslides and 1:400 –1:750 (mean 1:550) annual return for debris flows affecting the Rubble Creek valley andreaching the extent of the modern fan. However, no probabilities were given for


Cheakamus River below Rubble Creek. We suggest that only large rockslides have thevolume on reaching the Cheakamus River to continue as debris flows for an additional 3km to Rogues Gallery. Since there are no hydrothermally altered volcanic rocks in theBarrier headscarp, the volcanic debris is not clay-rich, it dilutes readily, and long-runoutlahars characteristic of hydrothermally altered volcanoes are not expected from smallervolume debris flows on Rubble Creek fan. Therefore, we take the probability ofrockslides on Rubble Creek fan as a proximate estimate for debris flows alongCheakamus River below Rubble Creek.

PE:H

The probability of a climber being at Rogues Gallery is the estimated proportion of siteuse in a year. The climbing season at Rogues Gallery is up to 200 days per year,generally on dry days. We have compiled climate normals for Upper Squamish climate(Table 1) located at a lower elevation (46 m) but in a similar valley setting to RoguesGallery. The estimated number of climbing days are based on the combination of warmtemperatures (> 10 °C) and number of days with precipitation <5 mm. On average thetotal number of possible climbing days is estimated as 185 days/year. We assume thatclimbers may be at the site 12 hours per/day, or about 50% of each day. Thus, theprobability of being at Rogues Gallery on any given day in any year is 1:2 x 185:365,which is 1:4.

Table 1: Selected climate normals for Upper Squamish used to estimate climbingdays at Rogues Gallery.

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov DecTemperature:Daily Average (°C) 0.2 2.3 5.7 9.0 12.5 15.2 17.7 17.8 14.6 9.1 3.5 0.1Precipitation:Rainfall (mm) 265.7 235.3 188.9 159.2 105.8 85.8 61.1 59.6 88.2 279.0 357.5 245.2Snowfall (cm) 71.7 47.6 22.5 2.5 0.0 0.0 0.0 0.0 0.0 0.6 21.4 69.1Precipitation (mm) 337.4 283.0 211.4 161.7 105.8 85.8 61.1 59.6 88.2 279.6 378.9 314.3Days with Maximum Temperature:> 10 °C 0.20 2.7 14.9 23.7 30.3 30.0 31.0 31.0 30.0 24.2 3.0 0.13Days with Precipitation:>= 5 mm 13.9 11.1 11.0 8.9 6.2 5.1 3.5 3.1 4.5 10.3 14.6 12.8Climbing days 0 0 20 20 25 25 25 25 25 20 0 0

PL:E

The probability of someone being in the location affected by the debris flow hazard is theproportion of time during any climbing day that someone is at the parking area and/orRoad Warrior. Road Warrior is a popular mid-grade (5.10) climb, and we assume thatsomeone will always be on it. Therefore, this factor reduces to 1:1.


PD:L

The probability of death if caught in a debris flow is 1:1.

PDIThree estimates of the probability of death to an individual at Rogues Gallery arecalculated in Table 2 using the range of rock avalanche hazard probabilities reported byThurber (2001). These are conservative estimates, in that we probably over estimate thetime that people are at Rogues Gallery, and we assume that someone will always be inthe debris flow hazard area, which might not be the case. It is important to note that theseestimates are for existing conditions, and would be significantly lowered by riskmanagement. Again, the risk is estimated from the administrator’s perspective: from anindividual’s personal perspective the PDI values would be significantly lower.

Table 2: Estimates of probability of deathto an individual (PDI) by debris flow at Rogues GalleryPH PE:H PL:E PD:L PDI1:600 1:2 * 185/365 1 1 1:2 5001:1800 1:2 * 185/365 1 1 1:10 0001:2500 1:2 * 185/365 1 1 1:20 000

Thurber (2001), after Morgan (1990) and other researchers, indicates that when the PDIis less than 1:10 000 it is considered acceptable risk. The estimated annual probability ofdeath by debris flow to someone climbing at Rogues Gallery, under existing conditions is1:2 500 – 1:20 000. Except for the highest hazard probability, these values are within theacceptable risk area. We would discount the highest value because the site is 3 kmdownstream from the Rubble Creek fan, and only the largest, most infrequent rockslideswould evolve to debris flows and reach this far downstream. We consider that 1:600annual frequency is an overestimate of this hazard.

The parking lot is on the floodplain level about 3 m above low water level. The base ofthe climb “Road Warrior” is about 5 m above the parking level. Thus, the parking levelwould be inundated by a debris flow of similar thickness to the 1855 event, while thebase of Road Warrior would be just at the edge. Both sites are within the level of an eventof twice the thickness, but this would be an exceedingly rare event, within tolerable risk.

Rogues Gallery: Barrier Debris Flow Hazard and Risk ManagementBased on the observed thickness of the 1855 debris flow deposit on the floodplain acrossfrom Rogues Gallery, and on the risk calculation above, to mitigate the risk of death bydebris flow we suggest the following measures are appropriate:

1. Filling the proposed parking area with rock spoil derived from highway constructionor nearby talus rock to a level at least 5 m higher than the present parking area.

2. Placing signage at the parking area that educates climbers about the debris flowhazard and encourages them to “gear up” quickly and get climbing.


Conclusions1. The intent of the GCDZ is to minimize the loss of life in the event of a landslide

from the Barrier.2. Management of the GCDZ is the authority of the Provincial Approving Officer, who

is guided by land use guidelines found in OIC 1409.3. Although recreation is formally discouraged within the GCDZ, the precedent set by

BC Parks is risk management consistent with guideline 2.01 which states that humanactivity should be kept to a minimum, and 2.07 which calls for the display ofeducational signage encouraging people to move out of the hazard zone as quickly aspossible.

4. Rogues Gallery is a popular climbing area at the south end of the GCDZ. Withrespect to Barrier slope hazards, the site is subject to debris flow and flood wavehazards only. Moreover, only the parking area and one climbing wall referred to as“Road Warrior” are subject to the Barrier hazard. The remaining climbing walls arelocated above the designated 20-m high buffer zone.

5. At the parking area for Rogues Gallery, the Barrier debris flow hazard zoneencompasses the valley floor with a vertical buffer of 20-m, but the exact limits areonly generally mapped at 1:20 000 scale.

6. Based on our detailed field observations, the 1855 debris flow inundated the nearbypre-event floodplain in 5 m of gravelly to bouldery debris.

7. Note that although the GCDZ extends to the 400 m elevation, in the area nearRogues Gallery the GCDZ includes additional terrain subject to normal mountainslope hazards, not Barrier landslide hazards. These areas are arbitrarily included inthe GCDZ, although it was never the intent to protect the public from these.

8. Under existing conditions, risk of death by debris flow at Rogues Gallery isinherently low (i.e., ≤1/10,000).

9. Any mitigative action (e.g., filling, educational signage) will serve to further reducethe inherent risk to life posed by barrier hazards to climbers at Rogues Gallery.

10. The recommendations provided below do not require legislative changes to theGCDZ, and therefore do not need to be considered at Cabinet level, only by theApproving Officer.

RecommendationsTo mitigate the risk of death by debris flow at Rogues Gallery we recommend that

1. A parking area be established at least 5-m above the existing floodplain level, andthat the parking area be configured so that it is not possible for cars to park at lowerlevels. The parking area could be established at the present location, or in the vicinityof the old “Salt shed” location.

2. Signage be designed and erected that educates climbers about the debris flow hazardand directs them to leave the debris flow hazard area as quickly as possible.

3. If the project is approved in principle, then a formal management plan should bedeveloped in conjunction with a qualified geoscientist or geotechnical engineer, and asite plan with 2-m contour intervals be prepared for the site.

4. Details of access and egress for the parking area should be negotiated with Ministryof Transport.


If you have any questions regarding this matter please contact Cordilleran Geoscience

Pierre A. Friele

ReferencesBerger, J., 1973. The Law and Mr. Planner. Supreme court of British Columbia. Action

X4042/1973. Reasons for Judgment of the Hon. Mr. Justice Berger dated August23, at Vancouver, BC.

Garibaldi Advisory Panel, 1978. Report to the BC Department of Highways.Gryphus land-use planning corp. and Thurber Engineering Ltd. 2001. Garibaldi Civil

Defence Zone Land Management Plan. For Provincial Emergency Program,Ministry of the Attorney General, British Columbia.

Morgan, G.M., 1990. Rubble Creek slide area risk assessment. Report to the Ministry ofMunicipal Affairs and Culture.

Thurber Engineering Ltd. 2001. GCDZ land use plan: overview of geological hazard andrisk assessment, dated October 31, 2001. Appendix 2 in Garibaldi Civil DefenceZone Land Management Plan.

Moore, D.P., and Mathews, W.H. 1978. The Rubble Creek landslide, southwesternBritish Columbia. Canadian Journal of Earth Sciences, 15:1039-1052.

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