Case Study: How Ecological Design Can Mitigate Life, Financial and Infrastructure Risk
Identifying the Formative System
The consultancy that I performed was in Central Alberta on the Red Deer River, which delineates the badlands from the grasslands. You can see in the photo that the erosion in the coulees is very angular indicating an arid environment that likely has a short but extreme rainy season with high erosion and sediment conveyance. In addition, the farmers above are growing a combination of hay and grains. The hay is beneficial as it is perennial and likely reducing runoff, while the grain is likely leading to runoff and high sediment loading. Rain in this region of Alberta is transported via convective weather systems, typically thunder clouds. All of this equates to large volumes of rain in short periods of time which can lead to enormous sediment conveyance. The property is located on the flood plain of the Red Deer River and within the property there are two alluvial fans. We will refer to these Alluvial Fans as South Fan and North Fan. But before we move on, lets look at the formative system.
The formative system for this property:
Arid, continental climate. Extreme high and low temperatures. Grass fires are likely at the end of the season.
Short rainy season with extreme rain events from thunderstorms. 50mm – 100 mm per hour
Located on a river delta, highly silt soils, high water table
Flash flood and drought prone
Located at the bottom of the sub water shed, high nutrient availability, prone to river channel migration, prone to mud slides
After walking the property and looking at it on Google Earth, it is easy to determine where the fans lie based on the cone-like deposition pattern. When the water hits the fan, it dissipates in a radial fashion taking the shape of the fan or cone. However, as new material is deposited onto the cone, water can take a new path to the left or right of the cone moving like a window wiper on a car. Because the fan is constantly changing shape through erosion and deposition and because there is such a high flood risk, building on them is not a good idea. The risk ranges from damp shoes during the rainy season all the way to loss of buildings, real estate and death if the flash flood is large enough. The Cougar Creek disaster that occurred in Canmore in June 2013 is a great example of how much energy these systems can convey.
The property has two alluvial fans and is currently managing massive amounts of water via a 36” culvert on the south part of the property and via an erosion gully on the north. This has formed two alluvial fans, South Fan and North Fan one of which has a significant amount of development on it. Luckily, it is all portable infrastructure so it can be moved. The client wanted advice on how to harvest the water, and how to proceed with the placement of permanent buildings. Initially the client wanted to place dams on the property, however due to the high sediment loads in the water, it is likely that dams will silt up fairly rapidly.
Southern Alluvial Fan
The southern fan is a result of the catchment that is being directed to a 36” culvert underneath the highway that travels along the western edge of the property. Without a contour map, it is hard to determine the size of the catchment but it is safe to say that it is very large. The 36” culvert currently discharges on to bare ground and there is a massive head cut forming under the culvert which needs to be addressed to halt its progress under the culvert and compromising it. In large rain events, it is not uncommon for the culvert to be flowing at full capacity.
When the client first moved to the property the culvert would fan water to where their homes (currently fifth wheel trailers) are located. In order to mitigate this they dug a ditch from the culvert straight through the middle of the fan in order to prevent the water from fanning and thus dissipating. This ditch has progressively incised deeper and deeper and the walls of the ditch are undercutting and will eventually fall into the ditch. Just before I had gotten to the site there had been a 75mm rainfall and it was clear to see that erosion from high in the catchment had conveyed a massive amount of sediment and careful observation of the site showed indication that the fan was starting to rebuild. Overtime it is likely that sediment will fill the ditch and will go back to fanning back and forth, eventually flooding out where the client currently has their trailers set up.
Northern Alluvial Fan
The northern Alluvial Fan is a naturally occurring fan that is leaving massive deposition on the client’s pasture. The main issue with this fan is a deer fence that is acting as a gabion holding back the sediment and redirecting the fan further to the north. As the sediment builds behind the fence, the pressure on the fence will build and eventually fail catastrophically which will likely cause a torrent of water across their field, potentially causing massive erosion and a series of head cuts. There is currently no major infrastructure in the path of this fan in threat of being hit by seasonal flood. However, because the soils are highly silty and the rainfall patterns are extreme, there is a risk of mudslide in this area which is why it is not wise to build permanent infrastructure on this pasture.
After walking the land, here are my design recommendations.
Move all of the permanent infrastructure (homes, barns, orchards, parking) away from the fans and use the fans for food production. Homes should be moved to the red triangle which is the zone least likely to flood from the river or the fans and unlikely to be subject to mudslide.
Food production should be limited to types that are portable: grazing of chickens, cows, horses. It should be portable so that the systems can be moved in the wet season when the property is prone to flood to protect the animals and the pasture from being hurt/damaged.
Grazing should be done using fast rotational grazing methodologies to ensure healthy ground cover and diversity which will hold the soil together and minimize erosion during large events.
For the Southern fan coming from the culvert, the first step is to move infrastructure that is within the fan. Once relocated, manage the massive inflow of water from the 36” culvert with a series of plunge pools to de-power the water and a series of media luna (fan shaped one rock dams, see the Erosion Control Field Guide for more details) which fan water out in the same radius as the existing fan. Fill in the ditch that is currently being used to convey the water down the hill.
For the northern fan, take out the bottom of the deer fence which is currently acting like a gabion and level the sediment out.
Get permission from the neighbours and set up a series of media luna to spread the flow evenly in the shape of the cone so that the majority of it infiltrates.
If required, we could keyline plow the property to encourage infiltration and break up any hard pan from poor grazing practices. Tree belts can be established using a keyline pattern leaving pasture between tree belts providing shade and windbreaks for animals.
Through careful analysis, it is clear where the opportunities and liabilities are on this property. The majority of present day human development does not take this into account because this knowledge is not common within our culture. After witnessing the destruction that occurred in Calgary, Canmore and High River, it is clear that a thorough understanding of the formative system and how water interplays within it can eliminate or, at the very least reduce, these types of disasters. Not because we stop nature from expressing her power but because we respect how she expresses her power and we build within her constraints. Ignoring this represents a threat to human life, infrastructure, and livelihood. These all represent massive financial consequences that can be avoided using an understanding of how we best fit within the ecological system. Best of all, if we get this piece right, we can actually change our relationship with nature from one that is adversarial to one that is positive. Ecological designers can play this role which has an unlimited amount of value to our clients and future generations.