High_Water_a_Natural_Process

Jeff Green | Apr 14, 2005

Feature article April 14, 2005

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by Gray Merriam

Recent heavy rains with the ground still partially frozen have given us maximum high water despite the lack of snowmelt. High water is viewed by many as an affront a challenge to the owners dominion over their property. Those who built thoughtlessly on a flood plain hate high water. Those with fixed-height docks think water level is supposed to be constant.

High water was here first and despite the beaver-like dam building by Canadians past and present, high water is still with us. We expend much effort trying to avoid high water as if it were a purely evil process. But it is not.

Beneficial effects of high water are seldom considered. Silt-fertilization is a really widespread benefit. One of the most effective ways of keeping up the productivity of a marsh or a low meadow or a hardwood swamp is to let the water flood over it in spring, carrying its load of silt. As the high water subsides, the silt is deposited on the flooded area. Silt carries a huge load of nutrients. Its fine texture attracts and holds nutrient ions all over the surfaces of the fine particles. Over the growing season, plants are able to pull the nutrients off the silt particles and use them to grow. When the High Aswan Dam put an end to flooding along the Nile in Egypt, the silt-fertilization that had made the land so rich was stopped. Consequently a large fraction of the power generated by the High Aswan dam had to be used to make nitrogen fertilizer to replace the nutrients that previously were delivered free by silt-fertilization during high water flooding of land along the river.

Other benefits of periodic high water are easier to see (or hear!). Shoreline or riverine marshes flooded in spring are major frog factories. Chorus frogs, spring peepers, leopard frogs, pickerel frogs, tree frogs and toads all use these temporarily flooded marshes and meadows for courtship, egg-laying and habitat for the hatchlings. Without the temporary high water, there would be many fewer amphibians.

Shallow waters filled with noisy frogs and toads attract connoisseurs of frogs legs (and other parts). Bitterns choose areas covered by high water for their nest sites and for the food around them. Great Blue Herons commute from their heronries of many nests, possibly a few kilometers distant, to marshes and meadows flooded by spring high water to get the food to raise their huge chicks. Local minks find good hunting here too. And many plant species require this temporary flooding followed by lower water and drier roots to get them through their life cycle. Constant flooding wont do because trees and shrubs, like Sweet Gale, Button Bush, native High Bush Cranberry, native Holly, Red Maple and others have no apparatus to let their roots breathe and they literally die of suffocation if high water persists too long. (Look at areas permanently flooded by highway construction to see the effect.) But temporary high water gives them life.

Herbaceous plants like the sedges thrive if their area has high water in spring and stays moist for the growing season. Many riverine meadows that flood at high water provide just what they need. Sedges contain unusually high amounts of protein (higher than hay) and so a sedge meadow is like a good crop field implanted in the bush; hungry grazers come to it from all around right through until the snow.

In some places, land that floods in spring and drains off later is called interval land. Interval land in the Maritimes is highly valued because, although it has a shorter growing season, it is very highly productive of both crops and wildlife. Our seasonally flooded land is in smaller strips and patches but also is highly productive and should be equally highly valued.

High water in rivers and creeks provides extra force that also can do vital work. During high water, the flow over rocks and logs pours down against the stream floor and will dig a deep hole unless it is bedrock. These holes are valuable habitat, particularly for cold water fish such as speckled trout. Most streambed and bank structuring is done by high water.

High water, variable water levels and seasonal change all are natural processes with beneficial effects. Constant water levels are artificial and are valued mainly as a convenience for us humans. Recognizing and putting more value on variations in water levels and the high water that results would be a more benevolent point of view.