Sunday, March 14, 2010

Flooding Minnesota

It is Sunday March 12 and the sky is lead gray and heavy with moisture. Here at the barn the ground is saturated from two days rain, and the melting snow combined with the rainwater is filling all the low spots.

The ground is still frozen and the water pools, then drains as best it can. Often the grade is shallow and the water has to rise to find an outlet from these little isolated and "perched" basins.

This water can be thought of as potential energy, energy awaiting release. In this case, as an elevated weight.

The water eventually rises in these pools. The rising water eventually crests the lowest spot in the basin's, ridge-line divide, that rings the drainage basin, and separates it from the neighboring basins.

In this way little puddles merge on the farm. They spread out as the volume of water increases. Lateral movement begins to become more apparent, water always flows downhill.

Little streams get organized and gently wend back and forth as they connect the low-spot "Dots" on the relatively flat terrain.

Eventually these streams reach a more dramatic drop and the water accelerates. The streams here are faster and more competent; and much straighter. Unlike the situation with a gentle slope, water is not meandering to drop an inch and is not bending, it is straight and fast.

Depending on the soil profile; this faster water, and the kinetic energy it releases in the drop, will scour the bed of the stream, and in so doing incise itself into the terrain.

Often the stream will hit a harder object than the base material it is embedded in. Like a large field stone in the dirt. A stream seeks its own level and also takes the course of least resistance.

A stream may come to a hard spot like our stone, and flow alongside it, removing more erodible material along its side as the stream continues its fall and flow.

In this way the water gathers, flows, falls and drains away. Eventually the rain stops, the sun shines.

The excess water is gone, the creek is back in its normal stream bed. The fields and pastures begin to show green grass shoots. The soft earth firms up and the young green grass grows fast.

Much like on the farm, Minnesota is experiencing the same thing. With unique situations and conditions to the many varied regions found in the great State of Minnesota, the same principles apply.

For example on the north west border, between Minnesota and North Dakota is the famous Red River of the North. It is located on the bottom of the glacial Lake Agassiz. It is flat, and experiences the same situations described above on the flat ground on the farm.

The Red is a gentle river, usually in a small trench meandering along the billiard-table flat ground of rich black loam. However, places like Grand Forks (fork = rivers joining) find themselves in trouble if the spring waters rise too fast. The water quickly fills the trench, overtops their natural levies and spreads out over the broad flat farmland.

The Red River also has another kicker. Because as it falls it flows north, it often melts in the southern headwaters, flows, and then meets an ice dam and frozen river downstream near the Canadian border.

This can really cause things to backup. History is full of examples of the Red River flooding and covering huge areas of flat land on both the Dakota and Minnesota side.

If the tributary streams had a little more control these high water events could be moderated. Also we wouldn't have the summer water shortages that lead to even-odd watering restrictions as we work on discarding sandbags from last springs flood.

"Wetlands", no matter what you may have been told, do not prevent flooding or erosion.

The State of Minnesota has a three continental divide. Water flows to Hudson Bay via the Red River.

The muddy Mississippi; father of waters, gathers tributary streams and flows to the Gulf of Mexico.

Along the North East or the Arrow-head region of Minnesota; from Duluth northward along the rugged lake Superior coastline, these spectacular creeks and rivers carve into the hard basalt and fall into the lake, eventually draining into the Atlantic ocean.

The namesake river of the state, the Minnesota, goes from west to east in a large gash across the southern third of the state and meets the Mississippi in Saint Paul.

It is very geologically unique. The Minnesota River is an under fit stream and drains about a quarter of the State. It meanders on the bottom of a large valley about two miles wide, flat bottomed and lying about 200 feet below the surrounding countryside. The Minnesota River's tributary streams fall from the high ground into this channel that the ancient glacial River Warren carved when Lake Agassiz was larger than all the Great Lakes and needed an outlet stream the size of the Amazon.

The many tributary streams are bedded in highly erodible glacial till and during high water events these lateral ravines are scoured. The sides also slump in great sand and gravel scallops, and these tributary river beds are incising into the soil with the energy of water dropping two hundred feet in less than a mile as it falls to meet the Minnesota on the bottom of the valley.

Minnesota means turbid or cloudy water. One Indian described the term Minnesota by putting some drops of milk into a glass of water.

You can learn more about the Minnesota River and more specifically the Glacial River Warren at the River Warren Research Committee website here. (I am an RWRC founding member and I wrote the newsletters found on the website, check them out.)

The Minnesota and its tributary is prone to wild fluctuations in elevation, from trickle to torrent. The Minnesota River is a sediment laden under fit stream.

Here too, some controls could be used for flood "flattening" as well as hydroelectric generation. The control of the wild energy would also secure the high ground from the growing threat of the inland devouring of the tributary streams.

You could also end up with some very nice fishing lakes and lots of happy farmers would retire with lakefront property.

And again, we could do away with the ridiculous water restrictions the land of lakes seems to experience every summer of late.

We could also use a bunch more water towers.

To experience a real good flood you need about five things.

One is a wet fall that fills the low spots and saturates the ground. Last fall was damp but not a total soaker.

Two is a hard deep freeze before deep snow. This locks the water in the ground and low spots and makes for a wet thawing with no ground saturation of spring rains. Our freeze came before the snow.

Number three is a lot of snow in the winter. We had a good snow this winter.

Four is a quick warm-up that melts the deep snowpack. We've had a four day period of 40+ degrees.

Fifth is a wet rainy period during the snow melt. We had two days of moderate rain during the warm weather.

Although they have been present in greater force in the past, these five conditions exist to some degree or another throughout Minnesota and we are expecting flooding along many of these rivers.

There are ways to prevent flooding, as well as ensuring we have a reliable source of freshwater for the benefit of all.

Setting aside so called "wetlands" is not one of them.

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