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On the banks of the North Saskatchewan River there are a large number of outfalls. An outfall is a drainage facility that conveys stormwater into a natural receiving water body (ex. creek, river, etc…). There city has a map online of all the outfall locations and, well, there are quite a few of them. The other day, as I was walking along the southern shore of the North Saskatchewan River I spotted Outfall 23 across the river. I noticed that the water coming out of the culvert was foaming and getting stuck along the shore as it drifted down stream. Foamy water in itself does not necessarily mean that the water is contaminated (see my previous post number 131 on foam lines). This time, however, it was clear that the foam originated from the outfall culvert. Outfalls convey stormwater that has been collect from runoff from impervious surfaces (e.g., roofs and roads) typically from entire neighbourhoods. This means that pollutants from roadways, lawns and roofs are essentially concentrated and discharged at a single point making the outfall a point source for pollution. The water quality in the North Saskatchewan River changes throughout the seasons with high runoff seasons such as spring resulting in more silty and polluted water. A 1994 study found that discharge of stormwater during summer rain storms does affect water quality in the North Saskatchewan River, including increasing levels of heavy metals and fecal coliform bacteria. The same study also found that the composition of invertebrate animals are dramatically affected downstream from Edmonton due to the change in water chemistry as it flows through the city. One of the effects is an increase in the nutrient levels in the river (think lawn fertilizers) which on one hand can augment the food base for the invertebrates but it can also wreck havoc with the levels of disolved oxygen, similarly to lake suffering from eutrophication (nutrient enrichment).
May the curiosity be with you. This is from “The Birds are Calling” blog (www.thebirdsarecalling.com). Copyright Mario Pineda.