METHODOLOGY


Base Map

TRIM data obtained included vector data related to transportation systems (roads), water systems (coastline, rivers, lakes), elevation (DEM points), as well as cultural point and arc data (including buildings, parks, schools, marinas, and other infrastructure).  Several layers and shapefiles were created as a basemap for the Ucluelet region.  The road network was developed to establish the areas of settlement and neighbourhoods, as well as exhibiting the main evacuation routes in the case of a disaster.   The data were also clipped to include only data for the Ucluelet region.

 Ucluelet base map

Elevation Model

The Digital Elevation Model (DEM) points provided in the TRIM data were used to create an elevation model of the Ucluelet area.  A Triangulated Irregular Network (TIN) was created from the DEM points, using auxiliary data such as lakes, roads and coastline to define the elevation.   A graduated symbology was used to indicate safe and hazardous zones in the case of a tsunami.   The District of Ucluelet has determined that elevations of 20m and higher would be safe zones for the worst-case-scenario tsunami.  This estimate is based on geological data that has identified marine sediment deposits from the 1700 tsunami at points as high as 20m elevations on the Ucluelet Peninsula.  The elevation map, therefore, was symbolized with the safe zone (20m+) as green, while the danger zone is represented in red, orange and yellow. 

Elevation model

This elevation model was used to create the basis of the flood analysis, therefore, a contour of 20m was created to establish the flood zone. The contour map was then used to create polygons of the flooded zone by forming a polygon of the peninsula defined by the coast.  The overlay tool, erase, in the analysis toolbar was then used to subtract the ‘safe’ 20+ metre zone in order to create a floodzone polygon.  

Floodzone

Damage zones were also created using the erase tool, defining separate regions of damage/destruction at elevations less than 18 m, elevations less than 17 m, and elevations less than 15 m.    These damage areas will be used to define where different types of homes will be completely destroyed or just damaged. 

Damage zones

 

Infrastructure 

“Cultural” points and arcs are included in the TRIM data which denote such items as buildings, parks, schools, marinas and other designated areas such as trailer parks.  However, for the District of Ucluelet, the buildings are described with the feature code BR90000110, which simply indicates “building.”  Therefore, it is impossible to know what each specific building point or arc is used for: commercial, residential or other.  Therefore, this uncertainty in the data was acknowledged and the residential and commercial buildings were initially assumed to be random, then adjusted using orthophoto interpretation and geocoding of a random sample of residential and commercial addresses.  

Orthophoto, Ucluelet, BC

 

2001 Census data was used to determine the population at risk from the tsunami.  The census coverage for the District of Ucluelet is made up of three dissemination areas (DAs):  59230015, 59230016 and 59230017, as shown in the base map.  For simplicity, these dissemination areas will be denoted DA15, DA16, and DA17 for the context of this project.  The data used was obtained from a DMTI census table relaying the “Profile of Marital Status, Common-law Status, Families, Dwellings and Households, for Canada, Provinces, Territories, Census Divisions, Census Subdivisions and Dissemination Areas, 2001.” 

 

 Table 1:  DMTI Census Data Table

Profile of Marital Status, Common-law Status, Families, Dwellings and Households, for Canada, Provinces, Territories, Census Divisions, Census Subdivisions and Dissemination Areas, 2001

OID

System Object Id

1

Total population 15 years and over by legal marital status - 100% Data

69

Total number of occupied private dwellings by structural type of dwelling - 100% Data

70

    Single-detached house

71

    Semi-detached house

72

    Row house

73

    Apartment, detached duplex

74

    Apartment, building that has five or more storeys

75

    Apartment, building that has fewer than five storeys

76

    Other single-attached house

77

    Movable dwelling

78

Total number of private households by household size - 100% Data

79

    1 person

80

    2 persons

81

    3 persons

82

    4-5 persons

83

    6 or more persons

DAUID

DA Unique Identifier (use to join to boundary layer)

 











 











 

According to the 2001 Census, the District of Ucluelet has a population of 1560 persons and 650 private households according to the 2001 Canadian Census.  This population is distributed between the three dissemination areas.  However, only DA15 and DA16 are used in this analysis due to discrepancies in the timing of the data.   The TRIM data is outdated compared to the 2001 Census data and therefore does not include a new settlement in DA17 which has an attributed population in the census data. 

Ucluelet population, 2001
 

The census data was used to create a probability mass function (pmf) to describe the population distribution with regards to household sizes and dwelling types, as well as cumulative probability distribution functions (cdf). 

 Population distributions

 

The cumulative probability functions were employed to randomly apply a type and occupancy to the building points and arcs in the TRIM data using a random number generator.  Fields were added to the attribute tables of the buildings (points and arcs) to denote a type of building and occupancy for each residential building.  The options for building type were single-detached home, duplex (2 dwellings per building), row home (5 dwellings per building), moveable home and apartment building (average of 10 dwellings per building).   The total population for each DA was conserved. Moveable homes were applied to the building data within the trailer park boundary then the distributions were applied randomly to the remaining buildings to create a community population distribution. 

 

In order to determine the infrastructure damage, the dwelling types were grouped according to structure type:  single detached homes, duplexes and row homes were grouped together as typical family houses (ie. most likely timber construction) as these types of dwellings were assumed to react the in a similar way to the flood wave; moveable homes were categorized to be the least resistant to a flood wave while apartment buildings were assumed to withstand water and protect occupants the most from the flood wave. 

Residential Buildings

 

The damage zones were based on these assumptions:  moveable homes would be destroyed if the flood wave was greater than 2 meters above the groud, typical family homes would be destroyed if the flood wave was greater than 3 meters and apartment buildings would be destroyed if the floodwaters were higher than 5 meters.  It was assumed that if the building is destroyed by the floodwaters, the persons inside would perish.  This type of analysis represents the scenario of the tsunami occurring at “3 am” while everyone is asleep in bed and receives no warning to evacuate.  This is assumed to represent the worst case scenario for a loss of life estimate. 

 

Once the residential buildings were established with a specific type and occupancy, the damage zone polygons were used as boundaries to select and identify the destroyed structures.  These destroyed structures were then exported as a separate shapefile to represent the infrastructure destroyed by a 20 meter tsunami wave.  The sum of the occupancies of the destroyed homes provides the estimated lives lost due to the flooding.