Urban Flooding: We don’t need to live near the rivers anymore.
It’s hard to make sense of what is happening with weather events and their aftermath. It appears, by watching and listening to the media and government, that they’ve increased in number and severity. They haven’t! It’s an illusion created by exploitation by environmentalists to promote their political agenda and amplified by a compliant and sensationalist driven media, and a government controlled by politically motivated bureaucrats. In this age of environmental hysteria, it is the practice to take normal events and present them as if they are abnormal.
The illusion is partly driven by a phenomenon we all experience. You are introduced to a person and after that, they are there every time you turn around. They were always there. They were just not part of your awareness. The media have decided weather events, and climate are a frontpage stories so now you hear about every event with all the exaggeration they can generate. It creates the illusion that they are new, with the implication it is due to human activity. Sadly, these claims drive demands for action, which results in distorted policies, that often make things worse.
Recent flooding in the US is reminiscent of flooding in Alberta a couple of years ago, and that provides a good illustration of the problem from my experience. Flooding on rivers is basically the same everywhere. Flooding on Prairie rivers is not unusual, and recent events are not outside the historical record. However, they are exaggerated by the failure of short-term political involvement to recognize the long-term geographic realities. I was involved in water issues across the Prairies for decades. I learned that the pattern is wet and dry cycles. I also realized the government never caught up and never properly understood or resolved the problems. Governments are always on a political cycle that rarely matches the climate cycles.
People being allowed to live in dangerous places enhance the problems of the flooding. They are encouraged by governments who take care of people who get into problems and also by insurance coverage. Insurance generally encourages bad practices and behavior. It is called a flood plain for a reason! Why are people allowed to live in these regions without being forced to accept full responsibility for their actions? I learned a long time ago while flying Search and Rescue with the Air Force that I am my brother’s keeper, but I should not be required to be my stupid brother’s keeper.
Here are some of the issues related to flooding exemplified by the pattern of extremes on the Prairies. Wet cycles bring demands for more drainage, stormwater storage, dykes, and dams. Dry cycles create demands for storage dams, water distribution systems, canals, and diversions. By the time construction for dry problems begin a wet cycle has arrived. The mistake is in designing structures for only one purpose, most can serve to reduce or retain water. The major challenge after that is knowing the pattern and levels of wet and dry. The secondary issue is to understand the mechanisms of flooding and drought and how they change over time.
I became aware of all these problems after teaching a course in Water Resources and serving on Commissions and Boards related to water issues and conflicts across the Prairies. I learned most problems are old and understood but political for resolution doesn’t exist. Commissions to resolve problems are only created to take the heat off politicians, create the illusion they’ve taken the politics out of the issue and defer things until they are out of office.
The first commission I served on was conflict over a lake. The politicians and bureaucrats set up an inquiry but controlled the process by very restrictive terms of reference. They even limited the amount of data and the areas we could investigate. I told the Chair of the commission that unless we received all information, I would tell the media the government was trying to predetermine the outcome. Once we got the information, I discovered that someone identified the problem over 100 years earlier and solutions proposed. They did nothing, so the problem recurred. In fact, there were three more commissions of inquiry before the one I was on. We learned during the inquiry that the top bureaucrat responsible for the region had never been in the region.
Geography and history are considered two different subjects. They’re studied separately, which is a major problem. The reality is that geography is the stage and history the play acted out on that stage. You don’t understand history unless it is in the context of the geography. Equally, you are not going to understand or make better policy.
In the early days living near water was a necessity. It provided essential water supply, but also provided food (fish) and transportation. There is only one major Canadian city, Regina, not built on a river or lake and it suffered from water quality problems for decades. These benefits generally overcame the risk of flooding, but that is no longer true. One of the best (worst) examples was the location of Winnipeg at the junction of the Assiniboine and Red Rivers. These rivers are called ‘underfit’ streams because the rivers did not create the valley they occupy over most of their length. They located Winnipeg close to the bottom of Glacial Lake Agassiz, reputedly the largest fresh water lake that ever existed. As a result, it is on a very flat plain that floods easily and does so virtually every spring with snowmelt. You get an idea of the size of Agassiz (Figure 1) when you know Lake Winnipeg, which is just a remnant of the 13th largest lake in the world by area.
Figure 1: Glacial Lake Agassiz
The floods within Calgary were in urban areas and exacerbated by the increased discharge and reduced lag time. I also agree that in the larger basin the effect of urbanization is not significant. Indeed, we found in the Assiniboine and the larger Red River basin the effects of changed urban drainage and, surprisingly, extensive agricultural drainage had no measurable impact. I say surprisingly because the Red River flood plain is reputedly the largest most densely drained agricultural region in the world. It is an unsolved hydrological conundrum
This was a big issue because the Assiniboine is the major tributary of the Red River of the North, which has consistent urban flooding problem at Minot, Fargo and then Winnipeg. The City of Winnipeg has a massive diversion channel called the floodway that takes water out of the River south of the city and returns it north of the city. It effectively doubles the river capacity over the length of the diversion channel. When they built the diversion, they used the modern record of flooding, particularly the famous 1950 event. This event was considered a one-in -100-year flood, which is what hydrologists call the recurrence frequency. It is based on a probability, but because of the wet and dry cycles, two floods of this magnitude could occur within two years. The precipitation pattern changes much more frequently and widely than any 100-year record could accommodate. They ignored the historical evidence of the 1826 flood that was three times larger and reports of an even bigger flood in 1776, which coincides with cold events of that time. The 1826 flood was approximately a one-in-400-year event. Another flood of this magnitude occurred in 1996, and the floodway alleviated to some extent, but it forced expansion of the floodway.
Most rivers flood. The channel they create is designed for average flow, but if precipitation increases the channel will fill. The first stage is “bank full” when water reaches the top of the banks. Once water flows over the bank, it is in “first flood stage” and covers an area called the first flood plain.
Figure 2: Thalweg is the deepest part of a channel. Levees form when silt deposited during flooding.
Nobody should be allowed to build in that floodplain. Dikes to contain the river should not be allowed either because when breached catastrophic flooding occurs. Also, they prolong the flood because they prevent water from returning to the river. Both these situations occurred in New Orleans with hurricane Katrina.
There is a reason why in the US is the government provides flood insurance. Private insurance companies won’t get involved because living in flood-prone areas is asking for trouble, a self-inflicted wound, and government actions often aggravate the problem. Flooding in Calgary was likely a victim of government actions or more precisely inappropriate actions.
The greatest surface changes are in the centre of the city where only a few trees exist, usually in very small squares. An area called the Central Business District (CBD) has almost 100% solid surface which is impervious to water. Even the suburbs are at least 50 percent impervious surface. Figure 3 shows an average suburban lot and impervious surfaces.
Figure 3: Average suburban lot and impervious surfaces
As a result, extensive drainage systems are designed to carry water away quickly. In the country, this water lies around and evaporates slowly or is used by plants and expired by them. Both processes create cooling. This is part of why urban areas are warmer than the countryside.
Figure 4. Rates of Runoff Urban/Rural
Figure 4 shows how these changes alter the peak at which the water reaches the river channel. Notice that even removal of trees in a rural area causes changes to the rate and timing of runoff.
Canadian social commentator Marshall McLuhan correctly said we live in a global village. He was right, but the comment requires elaboration. People live in a village and think they know what is going on when they don’t. More important the most destructive people in a village are the gossips. They create and spread false stories that force inappropriate responses and behaviour. The media are the gossips in the global village. They distort, sensationalize and force incorrect and inappropriate actions. So we lurch from wet to dry and back to wet never dealing with the problem properly for the period beyond the political cycle. Primarily, this includes recognizing that people don’t need to live by rivers anymore.