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Methods

Identifying Suitable Land for Building

The first step in determining ideal ALR land for development requires the isolation of areas that are suitable to build upon. This requires the removal of unrelated and inapt land such as those outside of the land reserves, parcels most crucial to the ALR, marshland, parks and national reserves, and areas that are too steep to act as a foundation. Listed below are the data layers used to isolate suitable land in Abbotsford's Agricultural Land Reserve with a description of how each layer was used. All layers were reprojected to a NAD_1983_Albers projection.

Distance from Wetlands, Lakes and Rivers

As water is a valuable resource that is important to every community for natural beauty as well as recreational opportunities, careful management is undertaken around waterbodies to minimize negative impacts on water resources. The BC Ministry of Environment (2011) insists that a 30 meter Riparian Area Assessment zone be created from the high water mark of a waterbody and its proposed development adjacent to it - this area regulation is used throughout BC to evaluate all land development in riparian areas. To honour these guidelines, we have buffered 30 meters around wetlands, lakes and rivers. This area was erased from the study area along with the wetlands, rivers and lakes themselves (as building is not possible where they exist).

Distance from Highways and Railroads

Ideally, housing should be situated a specific distance away from highways and railroads to avoid noise pollution. Highway traffic noise generally ranges 70-80 decibels from the source (Corbisier, 2003), and can be dissipated with the appropriate placement of sound barriers between roads and residences. According to several transportation departments, sound barriers are most effective 61 meters away from highways (Maryland Department of Transportation, 2011). Using this information, while assuming relatively flat ground and the implementation of these barriers, we have buffered a distance of 60 meters around highways and erased such area from our analysis. Noise generated from trains are assumed to be louder, although not as frequent, and have been given an arbritrary buffer distance of 80 meters (the shortest distance from existing houses and the Canadian Pacific Railway in Abbotsford was measured to be as close as 72 meters). This buffered zone, along with the highways and railroads themselves, were also removed.

Avoiding National Parks and Native Reserves

Areas within National Parks and Native Reserves have been removed, using the erase tool, to avoid further complications to our study. In general, development is forbidden in such areas.

Avoiding Steep Terrain

Building on steep ground can be extremely difficult, and so slopes steeper than 34 degrees have been removed from the analysis via a "NoData" reclassification (explained further in the MCE procedure in the following section). This threshold value was chosen because 34 degrees is the maximum slope angle recommended for the use of cut and fill methods for levelling a surface (Nichols and Day, 2005). Any slope value beyond this threshold is dangerous and too costly to manage.

Ranking Suitable Land - A Multi-Criteria Approach

After identifying suitable land to build on, the next step is to rank ALR parcels in order of the most to least ideal for urban development. Parcels that are considered to be good for development are those with lower agricultural capability, sizes typical for the development of residential complexes, those located closer to existing urban land and away from area associated with industrial or resource conservation practices, and lastly, those on flatter, stable ground. This was done using a multi-critera evaluation (MCE) with a total of 5 variables, each representing the aforementioned land characteristics. In order to combine and spatially analyze all these factors using GIS, we converted all layers to a raster format under a uniform resolution and projection. Raster resolution was set to 77.09 meters by 77.09 meters and the projection used was NAD_1983_Albers. The raster resolution was defined by the Elevation layer which had the lowest, and thus limiting, resolution.

Agriculture Capability

Firstly, agriculture capability classes were attributed to each ALR parcel fabric by inputting values referenced from the City of Abbotsford's agricultural growth maps. Because the focus of this study is aimed towards expanding urban uses into the ALR while conserving the most agriculturally capable land for farming purposes, land with higher agriculture potential was weighted to be less favourable for urban development. According to the Provincial Agricultural Land Commission (2011), ALR parcels with agriculture capability classes 1 and 2 are capable of producing the widest range of crops and are optimal for agriculture. These areas should be preserved for the ALR and have therefore been removed from our study via "NoData" reclassification. Area within the remaining agriculture capability classes - from land that is capable of producing a restricted amount of crops, to land that has minimal capability for soil bound agriculture - were reclassified according to the break values found in the table below.

Appropriate Parcel Size

Developers require land that is large enough to build on, however, in this particular case, not too large of an area - an oversized parcel would lead to unnecessary use of additional ALR land. The value of 4046 square meters (one acre) was chosen as the lower threshold parcel size because we personally believe that this size of land is sufficient for the building of a typical, small residential complex. The average townhouse, for example, is usually anywhere from 120-180 squared meters (Sutton, 2011). Taking into account the space needed for roads, parking and green space, we assume that one acre of land will be able to sustain a residential complex with approximately 15-20 dwelling units. Any land smaller than this is impractical, and any land much larger, unpreferred. Break values for parcel size are found in the table below.

Proximity to Urban Center

Generally, the closer residential land is to the city's center, the better - goods and services are easier to access and living in close proximity to the urban core is convenient socially, as well. Thus, new housing should be built as close as possible to the city center to promote accessibility and communication. Distance from the city center was weighted in intervals of 800 meters, which were created using the buffer tool. The interval of 800 meters was chosen as it is a comfortable 10 minute walking distance and is a simple measure to use (Fairfax County, 1999).

Edge Contrast

When considering community developments, it is also important to measure the harshness of land use change between adjacent lands. Harshness between two land types - edge contrast - is representative of an unfavorable, sharp land use change (for example, an abrupt change from agricultural to industrial land). At the patch level, the edge contrast index (ECON) metric quantifies the degree of interference between a patch and its immediate neighborhood. We assigned arbitrary values to the interaction of bordering land uses. An "Ftable" was generated using the Edge Contrast Index formula below to assign patch class IDs with our weighted scores contingent on the conflicts between urban operations. In order to analyze contrast both inside and out, the patches of the ALR boundary was buffered out 130 meters away from the agricultural zone. A value of 130 meter s was chosen because the Agricultural Land Commission Edge Planning Guide enforces that urban land uses must be within 130 of agriculture to mitigate ecological disturbance (City of Abbotsford, 2008). We distinguished that industrial land was the most unsuitable land use to build an adjacent residential community; therefore, industrial zones were given the highest weight when blended on the edges of residential neighbourhoods.

Stable Slope

To generate a slope raster surface, the slope spatial analyst tool on the British Columbia DEM was used and cells with slopes greater than 34 degrees were removed by reclassifying them as "NoData". The remaining values were reclassified according to the break values found in the table below, given that flatter ground is preferred for building purposes.

Multi-Criteria Evaluation (MCE)

FInally, we performed a multi-criteria evaluation of parcel size, distance to city center, agriculture capability, edge contrast index and slope to determine the most ideal locations for urban growth into the Abbotsford ALR. The weighted sum tool (under Spatial Analysis Tools: Overlay) was used to set weights to each criteria dependant on their relative importance during the selection - taking into account building fundamentals and the goal of preserving the ALR as much as possible. Weighted values were assigned as followed: