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COLUMN: Nature’s Flood Control

The recent tragic flooding in Houston has shocked people with both the amount of water and how fast it accumulated.

While this flood was caused by unprecedented amount of rain falling in a short period of time the fact that natural flood control options were limited in this situation added to the problem.

Like in many urban areas around the world, wetlands have been filled in, paved over and natural brooks and streams diverted into a pipe or culvert. This contrasts with natural systems where wetlands serve as an important buffer during flood conditions.

Wetlands come in a variety of forms and the Nova Scotia Department of Natural Resources recognizes eight types of wetlands in their land classification system. They are: bog, shrub swamp, wooded swamp, deep marsh, shallow marsh, meadows, seasonal flooded flats and open waters. While most of us are familiar with swamps and bogs, which tend to remain wet all the time, seasonal wetlands that may only be wet during part of the year are also critical for water storage and wildlife.

Swamps, and other forms of wetlands, are an important component of a healthy aquatic ecosystem. These wetlands are especially important habitat for frogs, salamanders and toads, particularly because they do not allow fish, which prey on them, to live there.

In some areas half the population of amphibians depends on these seasonal wetlands for breeding sites and for nursery areas for their offspring. These seasonal wetlands, known as vernal pools, also provide a place to store water during high water events.

Most of our brooks, rivers and lakes depend on a system of wetlands to provide them with water throughout the year. This is in the form of either surface water or through groundwater. Groundwater is especially important to trout and salmon because it is cooler.

Altering wetlands through human activity usually results in a negative impact. Changes in vegetation by removing trees and shrubs, paving the ground and draining wetlands reduce the amount of rainfall, snowmelt and runoff the earth can absorb. As a result more water is forced to run off into brooks and rivers. This increased volume damages stream banks, disrupting spawning beds for fish and altering stream flow patterns which promotes more flooding in the future.

These altered channels now have increased flows in flood conditions and none in the summer. This results in less water downstream for lakes and rivers and reduced water quality.

Wetlands are especially important to fish for their role in water storage and filtration. They act as a sponge, soaking up flood water during the spring, releasing it slowly throughout the summer. They also help purify water by naturally filtering water running off fields, streets and parking lots. By trapping sediments and silt they also protect trout and salmon eggs which hatch in the spring and are susceptible to being smothered by mud and silt.

In the past we have not valued wetlands but there is growing awareness of their importance in the water cycle, especially during flood conditions, and as habitat for fish, amphibians and insects. All of which combine to create healthy aquatic habitat for all of us, and better trout fishing.

Don MacLean is an outdoor writer and biologist who lives in Pictou County.

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