Appendix 1. Geotechnical Report - Ryzuk Geotechnical

Appendix 1. Geotechnical Report

Original Date: March 25, 2022 Revised: March 28, 2023 File No: 9693-1

Leanne Howes 297 View Royal Avenue View Royal, BC V9B 1B3 (By E-mail: leanne.howes@telus.net)

Re: Proposed Foreshore Stabilization Works

297 View Royal Avenue – View Royal, BC

As requested, we attended the referenced waterfront property to complete a visual geotechnical assessment as such relates to the stability of the seaward facing slope above the foreshore area. The site is located within the Environmental Protection & Natural Hazard Development Permit Area, in accordance with the View Royal Official Community Plan. Our associated observations, comments, and recommendations in this regard are summarized herein. Our work has been carried out in accordance with, and is subject to, the previously accepted Terms of Engagement.

The site is a roughly wedge-shaped waterfront lot, which is bounded by View Royal Avenue to the northeast, neighbouring residential properties to the northwest and southeast, and the marine foreshore of Limekiln Cove (Esquimalt Harbour) to the southwest. See attached Site Plan by McIlvaney Riley Land Surveying Inc.

Grade over the northeastern third of the property is relatively flat and at/near that of View Royal Avenue. This part of the property is occupied by the existing dwelling. Beyond to the southwest, the property slopes down to the foreshore area at around 20° or so (locally steeper in places) with overall vertical relief of around 9 m. The slope has been landscaped and incorporates low height landscaping walls of various types and a switchback beach access path. A 1 m high near vertical scarp of very stiff brown silty clay mineral soil is present at the base of the slope. The beach consists of finer sediments as well as gravel/cobbles with outcropping bedrock observed in the intertidal zone. Historical cast in place concrete seawalls armour the base of the slope on both neighbouring properties. We noted the soil scarp on the subject property was set back approximately 1.2 m from the face of the adjacent concrete seawalls and likely defines the Present Natural Boundary (PNB), see attached Site Photograph. The frontage of the slope as measured between the adjacent concrete seawalls is approximately 10 m. Seepage was emanating from the base of the slope, possibly from perched surface water migrating down through the surficial organic soils atop the less permeable native clays. Vegetation consists of sporadic property line tree presence and low height ground cover, including ornamental shrubbery, horsetail, and English ivy. On the basis of our observations, it appears that the slope is largely stable under static conditions. This would be expected given the relatively benign grading of the slope and our experience in the area (including our site observations), which indicate that materials within the slope comprise of a very stiff/hard brown silty clay atop an intermittent veneer of glacial till then bedrock.

We observed indication of minor creep within the surficial soils of the slope and erosion at the toe of the slope. Soil creep on sloping terrain is commonplace and describes the gradual downslope movement of the surface soils. The rate of creep can be influenced by a number of factors. In this case, we expect that perched surface water migrating downslope to the foreshore likely contributes to creep.

At the toe of the slope, above the foreshore area, both the current position of the slope toe relative to armouring on adjacent properties as well as the exposed mineral soils are indicative of ongoing erosion. We expect that upslope seepage and periodic wave action during high tide storm events likely contribute to the toe erosion. Limekiln Cove appears well protected from extreme weather events. That being said, in the long term we would expect that toe erosion would continue, the rate of such possibly increasing due to anticipated sea level rise that would result in more frequent wave wash at the slope toe. On going toe erosion will result in episodic small scale soil slumps and gradual regression of the slope crest.

From our discussions and review of the Landscape Plan, produced by Imagine Garden Design, dated May 18, 2022, we understand that it is desired to redo the landscaping/vegetation on the slope using soft shore/green shore stabilization techniques. This will include placing a gabion basket (rock filled) wall at the toe of the slope to mitigate future erosion and constructing a series of tiered low height (≤ 1.2 m) landscape retaining walls throughout the slope, including additional gabion baskets, Flex MSE® (soil filled bags), and stone veneer walls. Existing trees will be retained where possible. The proposed works should balance cuts and fills and avoid substantial additional loading on the existing slope. This would avoid accelerating the rate of shallow creep and unduly influencing slope stability.

We consider the proposed stabilization techniques to be feasible given the anticipated low energy erosional regime experienced in Limekiln Cove. The gabion basket wall is a suitable option for protecting the slope toe from wave erosion, as it will provide surface roughness similar to the existing bedrock beach outcrop (rather than the smooth/hard finish of concrete block or cast in place), allow vegetative growth in interstices, and is relatively simple and economical to construct. The various landscape retaining wall options noted above are suitable for the intended slope stabilization as such are considered to be capable of accommodating minor movement without unsightly cracking that can occur with concrete, masonry, or modular blocks.

The proposed tiered landscaping walls would need to be located such that each tier is set back behind a minimum 2H to 1V (Horizontal to Vertical) plane extending up from the base of the lower wall, so as not to induce a surcharge on the lower wall. Additionally, the 2H to 1V setback is a requirement of unreinforced retaining walls stipulated in Town of View Royal’s Zoning Bylaw No. 900. As per the Professional Practice Guidelines for Retaining Wall Design – Version 1.1, published in February 2020 by Engineers and Geoscientists of BC (EGBC), retaining walls with a maximum height of 1.2 m and whose failure would not impact a habitable structure or human life, are considered landscaping retaining walls and do not require engineering design. The various walls noted above are intended as landscaping walls only and have not been designed to accommodate support of any structure. However, we should attend site at the early stages of wall construction to ensure the locations, setbacks, and heights are in accordance with the noted slope requirements. Further details regarding such are included in the attached Proposed Foreshore Stabilization drawing set.

The gabion basket wall that will armor the slope toe should be founded on suitable bearing soils (likely native clay) below the mobile beach deposit. We recommend at least 450 mm of basket embedment to key-in and mitigate concerns relating to future wave wash undermining the baskets. The gabion basket wall should extend at least 1 m above the beach to offer protection to the exposed soil scarp. We recommend placement of a medium weight non-woven filter fabric against the back of the baskets to prevent tidal action/wave wash from pulling out finer granular backfill through the baskets. Backfill between the scarp and baskets should consist of a well graded free draining granular fill such as a 19 mm minus crushed rock. The baskets will extend laterally to contact the neighbouring concrete walls and be positioned at/near the current alignment of the slope toe (PNB). We consider incorporation of the proposed stairs into the basket arrangement to be feasible/acceptable.