Chapter 1 - 5

05 Environmental Science

Artificial Flood Controls

In earlier eras, humans were forced to adjust their living patterns according to seasonal changes each year.

For people that settled in river valleys, these adjustments were especially pronounced.

Over the course of the winter months, snow accumulates in mountainous regions.

With the onest of spring summer, the snow melts and collects into streams and rivers.

In other regions, heavy rains fall during late summer, forcing rivers over their normal boundaries.

As a result, ancient people that settled near rivers often experienced yearly floods.

In the modern era, however, people have altered their environment to avoid the hassle and destruction that accompany annual river valley flooding.

These methods involve manipulating the river or the environment surrounding the river to minimize the impact of flooding, a process that has both advantages and disadvantages.

Artificial levees are the most straightforward flood control device.

Levees are large earthen containment structures that are built along the banks of a river.

During flood season, the river still rises, but the levees contain the rising waters.

As a result, the land surrounding the river can be used without the hassle of annual flooding.

More recently, levees have been reinforced using various methods to make them more structurally sound, but the principle remains the same.

While levees do work, they are by no means foolproof.

Unusually large amounts of flood waters can compromise the integrity of a levee.

Furthermore, levees have to be strengthened regularly to remain functional.

Floodwaters typically carry large amounts of sendiment, which will be deposited along the riverbed.

Without levees, the sendiment carried by rivers is distributed across the floodplain.

Rivers controlled with levees, however, can only deposit sendiment along the riverbed.

Over time, large amounts of sendiment settle along the riverbed, taking up a large amount of the river channel.

As such, the height of levees has to be increased to avoid flooding.

Dams are another method whereby the effects of flooding can be mitigated.

Flood-control dams can be built in strategic areas along the course of the river to collect the water in a reservoir.

The impact of flooding can be controlled by releasing the collected water from the dam slowly.

There are a number of drawbacks to damming a river, however.

It is expensive and sometimes difficult to dam a river.

Moreover, the area behind the dam–the reservoir–will be filled with water, covering valuable riverfront land and scenic valleys.

Sendiment also tends to collect heavily in the reservoir area of a dam, requiring the reservoir to be drained and the soil removed.

On top of the high costs of building dams, they are also expensive to maintain.

Channelizetion is yet another method to control the impact of flooding.

The process of channelisation involves manipulating the river channel.

In many cases, the riverbed may simply be dredged, a process whereby the materials collected in the riverbed are removed.

By removing excess material in the riverbed, more water can flow through it without flowing over the river’s banks.

A more dramatic from of channelisation involves creating new routes for the river.

By removing bends and curves in the river, the water flows more rapidly.

With a streamlined river channel, floodwater flows more quickly and, hopefully, the river remains within its banks.

Dredging itself is a costly and time-consuming process, but is minor in comparison to the cost and effort involved in cutting new river channels.

Furthermore, channelizetion is not always reliable.

As is the case with levees and dams, unusually large amounts of flood water can cause the system of fail.

The dramatic alterations in a river’s behavior that flood controls require can have a negative impact on the environment.

The sediment carried by rivers is usually rich in nutrients and can replenish the topsoil of nearby land.

By preventing floods, many of these restorative nutrients are lost.

Furthermore, regulating flood cycles is expensive and labor-intensive.

Reliance on artificial flood controls has also led to disaster.

With the aid of these controls, people settle in areas vulnerable of flooding.

When levees, dams, or channelizetion fail, the resulting flood can be devastating and costly.

Many scietists and engineers have begun advocating more practical and less intrusive approaches to managing floodwater.

These new methods allow natural flooding to occur modifying land use around rivers.

By controlling the construction of roads and structures within the floodplain and managing the buildup of debris in where flooding occurs, we can adapt to the normal behavior of rather than flight them.