Analysis and GIS

A Socio-economic Vulnerability(SOVI) and Ecosystems Adaptation approach to Coastal Flood Risk Assessment in Squamish British Columbia


 

Carter_TheSkwelilemSquamishEstuary,River

This analysis was undertaken as a final project in Advanced GIS studies in the department of geography at the University of British Columbia – Vancouver.

Introduction

Many historical and place-based factors influence the capacity of the Squamish environment, local government and residents to face coastal risk and disaster resilience. This section offers an overview of the Squamish setting including historically relevant flood information, environmental observation, social, geographic and institutional conditions which interact to produce vulnerability.

Major factors — belonging to major human, earth and constructed systems — present relevant historical and societal conditions. These inform the translation of knowledge into action in flood hazard planning. As these systems interact during hazard events, each system plays a unique role in increasing or reducing human loss and damage to property (Mileti, 1999). By understanding each aspect individually, their interaction and complex relationship can be understood and addressed strategically.

SOG_Squamish_Wide WatershedMap

Geographic Context

The total land area of the District of Squamish is 11,730 hectares (29,000 acres). At the head of Howe Sound, a steep fjord, Squamish is at sea level and terrain within the District boundaries rises to elevations of over 900 meters. At the confluence of major 6 mountain river systems (the Squamish, Mamquam, Cheakamus, Elaho, Ashlu and Stawamus), the Squamish Valley watershed is largest watershed originating in the Straight of Georgia region. The current Integrated Flood Hazard Management Plan  must create both riverine and coastal flood risk management solutions.

As human settlement in Squamish is prone to riverine flooding, coastal flooding, earthquakes, tsunami, liquefaction, landslide and debris flows, Squamish is often referred to as the “natural hazard capital” of Canada. The interaction between this geography of hazard and human exposure is tangible. In 2003, Squamish experienced riverine and intertidal flooding that cost approximately $40 million ($70 million in 2014 dollars) to properties and displacing 800 people, no fatalities were reported (Gardner, 2011).

The District faces probable and consequential coastal flood hazards. As 200-year flood events are the baseline for flood risk management planning and infrastructure design, recent KWL modeling of 1:50 year flood show considerable inundation (up to 3 m) to the largely unprotected down town. In December 2014, recordings of tidal gates noted that coastal waters were 0.1 meters of topping Loggers Lane during a storm surge (Kerr Wood Leidal, 20 15b.).

A majority of human settlement today sits on the valley on a river delta, an area subject to freshet flood events fed by heavy rain, mountain runoff and glaciers. While settlement in flood prone areas has decreased over the past 15 years, 7,440 residents today remain living on the flood plain, exposed to riverine and coastal flood hazard (Ebbwater, 2015; Journeay, M. J., 2011) . Smaller, lower-elevation watersheds create precipitation-based floods, while snowmelt and glacial runoff plays a more significant role for the larger, higher-elevation watersheds.All historical coastal inundation events to date have occurred during September to December period when some of the largest storm surges and when temperatures are warm enough that precipitation falls as rain throughout the elevation in the five watersheds. The Cheakamus and Mamquam rivers, mostly fed by snowmelt runoff are the largest of the 5 rivers draining an area 3700 km2.

The Squamish river system reaches a maximum discharge of 760 m3/s in the early summer.  The highest recorded peak flows in this watershed were 2100 m3/s.During these events river freshets due to early thaws have interacted with high tides to create major intertidal flood events, inundating the downtown area with 1.5 meters of water about every 16 years.  Driven by these major river flows from the Squamish watershed, the Howe Sound has an “estuarine-type” surface circulation, first creating an eddy at the mouth of Squamish river before making a major push south towards the Straight of Georgia, their rate greatly impacted by local diurnal and inlet wind currents (Department of Fisheries and Oceans, 2014).

Introduction and Problem Statement

First peoples, residents, business owners and the local government of Squamish, British Columbia face serious exposure to coastal and upland flood hazard. As the population of this coastal community is expected to double over the next twenty years, local planning must accommodate urban development while managing risk with citizens. Currently, the District, the Squamish First Nation, Provincial Agencies and community members are creating an Integrated Flood Hazard Management Plan (IFHMP) to meet these challenges. This plan will account for coastal flood risk for the first time in that community, identifying structural upgrades and non-structural approaches to guide safe development of human settlement on the river delta.

Under provincial Bill 27, local governments in British Columbia are mandated to do climate change mitigation planning through GHG target setting but coastal municipalities lag behind in adaptation planning. Connecting sound climate science with land use policy is difficult. Today it is unclear if local planning institutions operate using evidence-based policy making.

The District of Squamish is a coastal community with unique geography and extensive flood hazard. Located at the head of a fjord in the North Salish Sea of British Columbia, human settlement also rests at the foot of 6 mountain river systems. To date, the District has been equipped with an aging flood management plan, limited dyke infrastructure, little legislated risk-based land use guidelines and a lack of focus on the social and ecological determinants of flood risk vulnerability. To plan for disaster resilience, the District alongside the Squamish First Nation, civil society and businesses must meet risk complexity and new climate realities with innovative and collaborative solutions that effectively mitigate, prepare, respond to and recover from flood events.

In beginning of this analysis, the following hypotheses were made:

  1. Certain people in Squamish BC are disproportionately vulnerable to coastal flooding events.
  2. The District of Squamish accounts for current and future coastal flood hazards in its planning.
  3. The District of Squamish engages in evidence-based planning to reduce exposure of vulnerable people and lands.

To investigate these hypotheses, an analysis of social vulnerability to coastal flood risk spatially using a suite of vulnerability indicators and coastal flood modeling was undertaken.