Geotech Hazard Assessment Report - Amended Draft - Executive Summary

Apr 27, 2011: EBA considers the property can be safely developed for proposed residential and equestrian uses...

April 27, 2011

EBA Engineering Consultants Ltd.

ISSUED FOR REVIEW – REV F

GEOTECHNICAL HAZARD ASSESSMENT

PARADISE TRAILS

SQUAMISH

EXECUTIVE SUMMARY

EBA has been retained by Timeline Project Management to assess potential geohazards that may exist at its proposed Paradise Trails Development, just north of Squamish, BC. The development is situated along the east bank of the Cheakamus River within the Paradise Valley.

We were asked to assess whether the following ongoing apparent potential geohazards will or have impacted the subject property:

· Direct and indirect impacts from a significant rockslide at the Barrier.

· Localized slope stability / rockfall on the slope above the property.

· Out-break floods on the Cheakamus River due to blockages from Culliton Creek events or localized slope hazards.

· Determination of a bulking factor to apply to clear-water floods on the Cheakamus River.

We were also asked to determine whether mitigation would be required to make the site safe for intended use in accordance with generally accepted international guidelines.

The assessment methodology included air photo interpretation, site reconnaissance, testpit investigation, and a helicopter overview of the watershed.

Based on a review of historical air photos, it appears that the construction of the Cheakamus Dam, which led to the formation of Daisy Lake, has altered the flow regime in the Cheakamus River, resulting in down cutting by the stream channel.

This down cutting has resulted in the existing river channel being about 2 to 3 m (to be verified by survey) below the average subject property elevation. River levels would have to rise over 2 to 3 m before the water and debris would start to inundate the Property.

The helicopter and air photo reviews indicated that active flood channels exist to the west of the existing main river channel, away from the property. As the river level rises; due to floods or debris floods, a portion of the flow would be expected to flow through the existing flood channels within its active flood channel prior to overtopping the riverbank along and onto the property.

Based on our assessment and discussions with other parties (BC Hydro), we have concluded that:

· “a breach of Daisy Lake Dam (Cheakamus Dam) would be a hazard to your site, but the probability of such an event is so extremely small, it won’t normally be considered in a development plan” (BC Hydro).

· There is no evidence that any of the geohazards noted above, that in the past have had a direct impact on the subject property, despite the evidence of geohazards in the upper Cheakamus watershed. This is likely due to a combination of mitigating factors, including river channel down cutting, a relatively wide, active channel, and high banks adjacent to the property.

· Among the geohazards that were the subject of our assessment, we have concluded that the hazard most likely to occur would be a sediment laden out-break flood on the Cheakamus River.

· There is very much less than a 0.002 chance per annum (10% in 50 years) probability of the subject property being directly impacted by geohazards.

EBA considers the property can be safely developed for proposed residential and equestrian uses, however, given the uncertainty in the magnitude and frequency of geohazards in general and the existence of other hazards, such as flooding, we recommend mitigation measures be designed and implemented.

EBA will be working with a hydrological engineering specialist to provide input into a water surface profile model, including landslide dambreak modeling. The results of the modeling will be used to determine the required geometry, height, and alignment mitigation measures.