Colin Gutcher, Jason Krompart, & Peter Nowell
| The output of the USLE model, or the contaminant
mobilisation potential, can be seen in Figure
The results were grouped into 4 categories, no risk of
mobilisation, low risk, medium risk, and high risk. In
waterways and urban areas were removed from the analysis as
of this study was on contaminants from agricultural sources
total of 49% of the Fairchild Creek Watershed was classified
risk for contaminant mobilisation with only 8% of the total
classified as being at high risk, a further 13% consisted of
classified as medium risk. The areas of high risk are
around zones with high slope length-gradient values or where
dominant soil exhibited high erodibility, such as with fine
silty soils. A total of 30% of the land, excluding surface
urban areas, had no potential to mobilise contaminants and
forested land, urban areas, or wetlands. The spatial
areas of high risk of contaminant mobilisation is
headwaters of the Fairchild Creek Watershed are mostly
low risk for contaminant mobilisation while the area north
has a relatively high density of high risk land. The high
are concentrated between lower order streams within valley
with higher slopes. The central portion of the Fairchild
Watershed, as well as the outlet area southwest of
exhibited a greater concentration of high risk land.
After running the USLE model the contaminant transport factor was added to account for the movement of contaminants to nearby surface waters. The area ranked as high potential to contaminate surface water in the USLETrans output comprised 6% of the Fairchild Creek Watershed with 4% of the watershed having a medium risk and 60% having a low risk. Again the remaining 30% of the watershed consisted of non-agricultural land that posed no risk for surface water contamination. The output of the USLE model combined with the transport factor (USLETrans) can be seen in Figure 8, because areas located closer to surface water were assigned a higher value than those farther away one can see that high risk areas are located closer to streams than those which are farther away. Again the headwaters of the watershed are classified as generally being at low risk for contributing to surface water contamination while the central part of the watershed as well as the land to the northeast and southwest of Brantford having a greater concentration of areas classified as high risk.
Due to the nature of the DRASTIC model the output classified the entire watershed as either at high, medium, or low risk and did not only account for the agricultural land, thus, the results of the DRASTIC model (Figure 9) identified 92% of the watershed as being at medium risk to contaminate aquifers directly below the surface, with only 4% of the watershed at high risk and another 4% at low risk. Areas at low risk were generally located around urban areas or adjacent to streams. Conversely, locations exhibiting a high risk to contaminate groundwater were almost exclusively found adjacent to streams with wide floodplains. Because most of the underlying material found in the Fairchild Creek Watershed is fairly uniform, only differing substantially in the soil type and aquifer material in some locations, it was expected that groundwater vulnerability would not differ significantly over the watershed. The majority of the high risk area is underlain by sandy loam soils although the small patch of gravel loam located near the headwaters also exhibited high groundwater vulnerability. Gravels and sands had a higher DRASTIC value than almost all other soil classes within the DRASTIC model and would explain why areas underlain by these soils contributed to a higher groundwater vulnerability. Areas of high risk to contaminate aquifers below are also correlated with not only the soil texture but also the depth to groundwater. Areas with a low depth to the water table generally have a higher risk than areas with a high depth to water table such as the area just north of Brantford as well as the western most edge of the watershed.
The final MCE results, as seen in Figure 10, classify the agricultural land within the watershed at risk of contaminating surface or groundwater into low, medium, and high categories. Out of the entire watershed only 5% of the land was classified as having a high risk of contaminating surface or groundwater, while 11% was classified as having a medium risk and 54% as having a low risk. The remaining 30% was not located within an agricultural area and thus was not of interest for this study. Areas of low contamination potential occur away from streams or in areas with relatively impermeable subsurface materials. Areas of high risk occur closer to streams or in areas with sandy soils and permeable surficial geology. Again the spatial distribution of the MCE output is not uniform and generally follows the spatial patterns present seen within the USLETrans output. Because the DRASTIC output classified much of the Fairchild Creek Watershed as medium risk it can be seen that more of the MCE output was classified as medium risk compared to the USLETrans due to the influence of the DRASTIC layer.
Following an analysis of the findings of the MCE model four general locations were identified as having a high risk of contaminating surface or groundwater. The first area (Figure 11) is located on at the south-east corner of the watershed where the outlet point flows into the Grand River. The area is typified by meandering streams and wide floodplains with areas of high contaminant potential located adjacent to tributaries of the main channel. Location two (Figure 12) is located centrally on the western edge of the watershed. The area is primarily agricultural with numerous streams running primarily southeast. The third location (Figure 13) is found in the middle of the watershed. Although there is a significant amount of area that is not classified as agricultural there is also a large portion of arable land classified as high risk, principally located adjacent to streams. The final location (Figure 14) is located just north of Brantford and contains a portion of urban area. However, within the agricultural land there exists significant high risk areas that pose dangers to the quality of both surface and groundwater. The position of this last location is especially pertinent when one considers that a high concentration of individuals live within less than 2 km of high risk land. These four areas have been highlighted as potential areas for mitigation efforts due to the relatively high concentration of land classified as high risk.
Figure 11 (Click to enlarge) Figure 12 (Click to enlarge) Figure 13 (Click to enlarge) Figure 14 (Click to enlarge)
Risk can be mitigated in these areas through policy initiatives or by preventative measures undertaken by landowners. Landowners can employ conservation practices, such as mulch tillage or contour farming, which greatly mitigate the risk to surface water at little to no cost to the landowner . Furthermore, policy makers can employ programs which encourage landowners to make use of more conservative practices on high or medium risk areas. These programs may consist of incentives for building permanent erosion reduction structures such as grassed waterways or riparian buffer zones. Most importantly the results presented here could be used in public information packages to ensure landowners are aware of the potential impacts on groundwater and surface waters that come about from agricultural operations.