Predicting Landslides at Point Grey UBC: Interrelationship Between Vegetation and Slope Stability (Best Overall Research Project Award Winner)

Abstract

British Columbia is prone to landslides, which are the most common natural disaster (Strouth & McDougall, 2021). According to UBC/Pacific Spirit Park Cliff Erosion Management Planning (2000), the cliffs are eroding because of a variety of reasons, and this erosion has multiple effects, including affecting the nearby lands, UBC facilities, and the beach. One of the main causes of a steepening slope is erosion, which plants can greatly reduce (Ip, 2011). Throughout our study’s first objective, we investigated and recorded the factors affecting the slope stability of the Point Grey Cliffs include: the sedimentary makeup, steepness of the slopes, density and age of dominant vegetation present, presence of dead vegetation, unvegetated exposed sand faces caused by past landslides, and heavy precipitation effects between Trail 4 and Trail 6, and then demonstrated the destabilizing effects of heavy rainfall on the slope stability in light of the absence of root systems within the nature of the study area as a hypothesis. It was discovered that the impact of plant roots can minimize the effects of precipitation and provide a stabilizing effect on the resistance of soils to erosion. Suggesting a strong correlation between vegetation and slope stability. Then the results of our findings in response to the study’s second objective are summarized in a proposed Terrain Stability Map that predicts where the likelihood of slope failure may occur along with the cliffs of the study area between Trail 4 and Trail 6, thus answering the study's question. At the same time, our advocacy includes the use of long-lived trees at point Grey Cliffs as well as removing dead vegetation as a means of enhancing slope stability.

Terrain Stability Map

Figure 1. Terrain Stability Map - Point Grey Cliffs between Trail 4 and Trail 6. Accessed through Google Earth.

The classification of slope stability is from I to V and indicates the likelihood that the slope will fail along with the cliffs between Trail 4 and Trail 6 (I indicates a very low likelihood, whereas V indicates a high likelihood). Table 1 summarizes these ranking factors and their associated stability factors.

Terrain Stability Class	Interpretation
I	No significant stability problems exist. - Little or no slope (<52%)
II (see Example 1)	Low likelihood of slope failure. - Gentle or moderate slope (<52%) - Mature forest - Dense undergrowth
III (see Example 2)	Minor stability problems with moderate likelihood of slope failure. - Moderate to steep slope (>52%) - Less dense forest or populated by young trees - Less dense undergrowth - Presence of dead vegetation
IV (see Example 3)	Larger stability problems with a moderate likelihood of slope failure. - Steep to very steep slope (>65%) - Sparse forest of young trees - Sparse undergrowth - Presence of dead vegetation - Unvegetated exposed sand faces
V (see Example 4)	High likelihood of slope failure. - Very steep slope (>80%) - Little to no trees - Little to no undergrowth - Presence of dead vegetation - Unvegetated exposed sand faces - Landslide scars are visible on air-photographs

Table 1. Terrain stability classification

Examples:

1. Example of Class (II). June 28, 2022

2. Example of Class (III). June 14, 2022

3. Example of Class (IV). June 14, 2022

4. Example of Class (V). March 23, 2022 + Screenshot from Google Earth

Biographies

Aladdin Obaid is a first-year undergraduate student in the Vantage One science program from Yemen. He has always been interested in science and continues to educate himself. Aladdin enjoys nature and appreciates rain and thunder.

Jafar Alhasan is a first-year undergraduate student in the Vantage One science program from Kuwait. He is interested in some aspects of arts. His main goal is to pursue a career in dentistry. He is planning to get the magic Lamp from Aladdin and become sultan.