Rain Chen

mosaic

A group studio final project, my partners and I focused on the vegetation, water, and bathymetry of the Point Grey cliffs to address the mitigation of its erosion.

  1. This is our existing slope, largely populated by trees such as Douglas Firs and Red Alder, as well as low-lying shrubs such as swordfern and salmonberry.
  2. Because our intervention has no focus on anthropocentric usage, our first action was to implement a retaining wall to restrict pedestrian access. This also reduces runoff from Marine Drive.
  3. Following that, we installed a detached breakwater to prevent longshore drift from removing eroded sediment at the toe of the slope.
  4. The trees on site were removed to ensure they wouldn’t destroy the modular planters when the slope begins its gentle failure.
  5. The construction of the modular planters will proceed in a series of 4 phases. Each phase will begin with drilling in the 30-meter poles for the planters. Once the planter poles are in place, the modular planters themselves will be installed.
  6. By the beginning of the 3rd phase, the 1st phase of planters will have have reached early establishment through shorebird population and vegetative growth. This progression will proceed all the way until the slope has reached its resting profile, by which the entire installation of modular planters will be complete and thriving. The biodegradable retention reservoirs will progressively degrade, opening up natural skylights to aid slope regrowth, which will largely consist of shade-tolerant plants.

We began our analysis by investigating the vegetation on the slope, namely which ones were erosion-inducing and which ones were erosion-reducing.

Next, we examined the water table of our site and looked into the factors that were perpetuating the erosion, such as pore pressure, seepage points, and long-shore drift.

Third, soil formation and tectonic forces were considered as we identified the soil quality and types within the stratification and how glacial rebound destabilized the layers.

The intense erosion is mostly due to hydrological conditions such as infiltration, which leads to seepage. It has fostered a repetitive failure cycle.

Our group decided to mitigate and slow down the damage of the erosion by desaturating the top layer of quadra sand above the water table, effectively preventing it from failing catastrophically.

Instead, it allows a more gradual mass movement, ultimately arriving at a stable resting profile. This was achieved by our designed steps of impermeable ‘modular planters’, meant to intercept rainfall and harness the water to nurture an elevated habitat for existing shorebirds above the failure slope.

Because we were creating a gradient of habitat types, from songbird habitat at the top of the slope to shorebird habitat at the bottom, we needed to have different types of planters to accommodate the different plant needs. All planters had the same 4 meter by 4 meter footprint, but they had variable depths.

 

The planters at the top of the slope were the deepest (½ meter in depth) to allow for larger shrubs and ferns which are the preferred habitats of local songbirds. The lowest section of the slope had planters that were a mere 20cm deep allowing for plenty of drainage to support the grasses and rushes that make up shorebirds prefered habitat. 

The middle, transitional zone had planters that were 35cm deep, allowing for a mix of plants from both habitat types. Our final planter type had only a water tray and was made to be fully biodegradable.

Although the existing vegetation was projected to be severely disturbed by the mass movements, the man-made habitat on our modular planters would thrive and provide enhanced cover and protection while the slope reached its final stages and was naturally re-vegetated. The re-vegetation was to be further accelerated as some of our modules decompose to become natural skylights.

 

These plans also show the path of water through the planters as well as their overall spill point and groundwater seepage. Notice that the biodegradable modules were always at the beginning of a path to prevent large concentrations of water from being deposited on the slope once the modules collapse.

  1. The first detail site is at the top of our slope, highlighting the difference between our permanent planters and our biodegradable ones, which don’t have planter boxes and are instead just water retention reservoirs. Theses modules are fully biodegradable and will collapse after the slope has stabilized, creating skylights that allow in light and water.
  2. The second one is midway through the slope, showing the changes from the existing profile, to when the modular planter habitats begin to thrive, to when the slope undergoes natural regrowth after it reaches its resting profile.
  3. The third one is of our shoreline, showing the detached breakwater obstructing the longshore drift and becoming a habitat feature for shorebirds, such a cormorants, which can use the blocks as a fishing spot.