Throughout Human civilization, humans have tried to tame rivers to prevent flooding or provide water for drinking and irrigation. Unfortunately, for the past 100 years or so in the U.S., this modification to streams has only lead to increased flood risk. We will take a look at the success and failures of humans to manage streams and build lakes, as well as the impact of modern development on streams.
Humans have tried to modify streams in three ways:
- Flood Control:
- Channelization: Straightening out the meanders of a stream to for a straight line, or smoothing out the natural levee by replacing it with concrete flood walls.
- Artificial Levees: Artificially raising the height of a natural levee.
- Lakes: Placing a dam over a river.
- Urbanization: Building structures within the floodplain or on the banks/levee of the river.
Stream Management
With the coming of the industrial revolution, humans finally had an easy way to regulate the flow of streams. Using steam shovels and bulldozers, humans now had the ability to change the development and direction of streams. Two popular methods of management are channelization and levees construction. Although lake construction and urbanization are both technically forms of stream management, I’ll discuss lakes separately.
Channelization
Construction crews are replacing the concrete flood walls (already torn
out in this photo) along the White River at IUPUI with natural grassy
banks that slope down to the rive. r(On the left is an area that has already been restored).In the 1940s, to combat flooding in urbanizing areas, President Roosevelt’s Civilian Conservation Corps and the Army Corps of Engineers began channelization.Channelization involves engineering the shape of the stream channel by straightening the stream’s natural bends and curves with the goal of reducing flood risks or, in some cases, to make the stream “barge friendly,” reducing the number of miles river freight has to travel. Channelization can locally reduce flood risk by increasing the velocity of water traveling past an area, which in turn reduces the area (or size) of the river. The water essentially moves out of a specific area quickly, never allowing the water to pool on the surface and flooding.
The downside is this fast moving water increases flood risks downstream where no flood walls are present. The floodwalls also prevent the stream from eroding the river banks, which stops the meandering process. The textbook provides great detail on channelization construction and the pros and cons of channelization. All in all, channelization has resulted in urban areas acting like water slides: water moves very quickly through these areas but then communities downstream of the urban areas are often faced with more fast moving water, a recipe for more erosion and flooding.
Why more water? Well, remember that urban areas have many impervious surfaces which prevent water infiltration. So, not only does water move quickly out of these areas due to channelization, but there is just that much more water for downstream communities to deal with during periods of high precipitation.
The city of Indianapolis and IUPUI are currently involved in a project to do channel restoration on the White River. The city is removing concrete flood walls, while IUPUI’s Center for Earth and Environmental Science is replanting native trees. One reason Indianapolis is removing the floodwalls is because they’re ugly! A natural river bank has better visual appeal.