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Iowa River at low flow rate

PHOTOS BY GARRY BRANDENBURG The Iowa River is at a very low flow rate at present time. This is understandable due to drought conditions this past summer. Yet water still enters the river system or there would be no flow at all. Water is maintained in the river from what geologists call base flow. A slow seepage of ground water from adjacent soil layers weeps slowly into the river channel. Right now the flow rate is only 106 cubic feet per second. Today’s aerial image was made over Sand Lake looking downstream. Those large sinuous river curves are typical on flat floodplain lands. The other image was made at Stanley Mill river bridge looking upstream where the water is very shallow from bank to bank with lots of exposed sand bars in this man-made channelized river course.

The IOWA RIVER is running low on water. Will it ever run dry? The answer is no. Base flow is a constant seepage of water out of adjacent flood plain soil layers. A good science lab experiment involves placing a line of water filled sponges along either side of the center line of a slightly downward curved long layer of sheet metal. At first, the water saturated sponges will leak profusely with the moisture seeking by gravity its low point, in this case a channel at the lowest elevation of this experimental river. One can collect the water off the low end into a container and subsequently measure the volume of runoff per unit of time.

Step two involves doing the collecting every hour on the hour, then plot runoff volume on a graph. Step three is to see what happens overnight while you sleep. Next morning there will be water to collect, but a lot less volume. The sponges will not be saturated any more. In fact they may feel dry to the touch on top but remain only slightly damp on their undersides. Never the less, those damp sponge bottoms represent base flow supplying water to your experimental river.

Real rivers and all of its tributary streams large and small contribute water to a river. Each stream also collects water from base flow within its watershed. All that water, what there is of it, is what you and I see when crossing a bridge over the channel or wading in its shallow depths.

If people try to paddle a kayak or canoe at river levels as low as they are right now, they will do a lot of walking. If people try to sit in the kayak or canoe they may find the watercraft’s bottom sliding over very shallow sand way too often, especially in portions of the river upstream from the Iowa Veterans Home to the Hardin County line.

This is the segment of Marshall County’s river that was deliberately dug out by a dredge between the years 1918 and 1921, on purpose, to straighten the channel. That operations was a classical ecological mistake not based on science but on politics at the time. Floodplain lands are notorious for being wet, staying wet and being not especially friendly to conventional farming practices. For the landowners along the river in 1918 and prior years, it was a frustrating problem. They thought the ‘cure’ was to channelize the river, take out all those sinuous back and forth loops of the river in favor a big ditch.

After the river channelization ended, with a fire destroying the dredge while it was parked near the north side of the Iowa Soldiers Home, (as it was called then), the dredge had displaced 8.2 miles of river….or think of it as the river between the Hardin County line and the Soldiers Home was now 8.2 miles shorter. That also meant the gradient was steeper. Steeper gradients means that the water in the ditch will flow faster, especially during flood events. Faster flowing river water erodes bank soils more quickly. Faster water holds more and larger soil particle sizes in suspension for a longer period of time and deposits those eroded soils far downstream or as thick deposits of silt on any overflowed floodplain lands.

Marshalltown has paid that price repeatedly over the last century as flood event waters come roaring down the channel and then began backing up behind bridges and meandering river loops downstream from Marshalltown. The natural impediments to flood flows of a meandering river channel slowed the water and dropped bigger loads of silt for others to deal with.

In fact, the plat books of Marshall County label the straightened channel as “drainage ditch number one.” To pay for the channelization costs, property owners affected by the dredging were assessed an additional tax on property. Some could pay and many could not. Some lost the ability to continue farming floodplain lands due to financial concerns. In other words, Mother Nature rules and her rules are going to win every time. If people think they can outsmart her, beware and be ready to be reminded the next time the Iowa River runs high and flooding occurs over its banks.

A BIT OF HISTORY regarding our segment of the Iowa River is in order. The Corps of Engineers maintains a river gauge near the Highway 14 bridge on the north side of Marshalltown. Readings are sent to the offices to compile a record every hour of every day of how the river is flowing, during low times and at flood events. Right now the river flow is creeping along at 106 cubic feet per second and the water elevation is about 862 feet above sea level.

On July 2, 2014, a flood maximum new record happened for us in Marshall County and Marshalltown. On that date the river crested at a stage reading of 22.25 feet or about 875.28 feet above sea level. Roadways were closed at so many points that Marshalltown was cut off from the north. So was Le Grand. So was Albion or any city lying north of the river channel. That flood created a major disruption to the economy that only time could cure. And it takes a lot of time for flood waters to recede enough to expose once closed roadways. Costly roadway and road shoulder repairs must take place before traffic can be allowed access.

The difference in elevation from flood maximum to drought time low flow rates is about 13.3 feet. To help visualize that much water in the river, go to the river now and place a long pole 13.3 feet tall vertically at the low flow water level. The top of the pole represents where maximum flood waters were on July 2, 2014. Flow rates at that flood event exceeded 20,000 cubic feet per second. Mother Nature rules and her rules win every time.

PHEASANT SEASON for youth begins Oct. 24 and Oct. 25. Then on Oct. 31, the regular pheasant season begins for the general hunting public. I have observed several, not a lot, but a good number of rooster pheasants and heard the cackling calls drifting upon the airwaves. A daily limit of three roosters is allowed.

Other birds on my witness list include a good number of wild turkeys. They are sneaky and silent and stealthy. So I count myself lucky to observe this largest game bird. I have one fall wild turkey license in my pocket just in case the opportunity is provided while perched in a tree stand.

Another neat little bird observed was a White-throated Sparrow. It was obvious with its white throat patch, black eye line, and flitting behavior as it hopped from branch to branch. Lots of this species call Canada home for the summer. Summer is ending quickly in Canada so this bird will make its way south. In Iowa, people can count on seeing them at feeding stations this winter. Nests for this critter are usually on the ground neatly hidden inside grasses and leaves.

OCTOBER WEATHER is here. Nice and warm one day and nice and cool the next. I like fall weather and I like cool fall weather even better. Enjoy any and every day since each is a gift. Mother Nature rules. So people might as well adjust to her standards since she always wins.

Garry Brandenburg is the retired director of the Marshall County Conservation Board. He is a graduate of Iowa State University with a BS degree in Fish & Wildlife Biology.

Contact him at:

P.O. Box 96

Albion, IA 50005

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