River makes a shortcut

A RIVER RUNS THROUGH IT would be an excellent definition for floodplain lands close to the Hardin/Marshall County line. Over many years, the river at high water flows kept eating away at the outside curves of its banks. Soil material cut from outside bends upstream get sorted by flowing water and deposited downstream on the inside of curves. People see these as sand bars.

This is a typical ages old geologic process, always on-going, silently changing the flow line and pathway of a river channel. It is by this action that river bends sometimes make big loops that seem to snake along the lowlands. When erosion of the river banks brings adjacent loops closer and closer, there comes a time when the separation distance of the land itself gets too thin to resist. Especially at high water flows either at full bank capacity of when floods overtop all of the floodplain, saturated soils at these thin spots will quickly cave-in. Now with a mini-shortcut in place, water pressure will be unrelenting in its cutting action to remove obstacles to its flow. The opening will widen until it is about the same width as the river above the break. The result is a channel change, one likely to remain for many decades into the future.

The other inevitable change is the old river channel left behind. It only gets water during high flow events. But because these waters flow slower now compared to the new main channel, silts and sands in suspension will fall out sooner and accumulate quicker in the old oxbow. Over time, nature will attempt to fill the oxbow each time another high water event happens. All the new vegetation of willows, cottonwoods or some grasses helps catch more silt.

Canoeists and kayakers may not even be aware of a channel change. They must paddle where the water is, skirting old log jams and looking for dark colored water deep enough to float the hull of the watercraft. Sometimes an old river channel will show its location to observant paddlers who know what they are looking at. A bit of water may still exist to temp them to paddle into this quiet backwater. And if a paddler does make the effort, around the next bend they are likely to run into a blockage without a water outlet back to the river’s main channel. When that happens, its time for a short portage.

Examination of aerial photos from the Soil and Water Conservation District office can show many oxbows of former river courses, cutoffs from the main channel. One may elect to compare photos of the same parcel of land over a time frame of a decade or two to see the slow but unstoppable relocation of the river’s main channel. This scribe did just that a long time ago when I was working at the Marshall County Conservation Board. The assignment was to develop a canoeing brochure for public use. The publication would map out put-in boat launching points and take-out ramps, tell how many river miles it was between these places, and estimate paddle times for weekend recreationists so they could plan a river float with family or friends. This brochure, when completed, featured the Iowa River from the upper portion of Hardin County all the way to the eastern edges of Marshall County near the Tama County line.

The old aerial photos were very interesting. The dates on these images was 1939, only about two decades since the floating dredge, the Mary Ann, set about its duties to straighten the Iowa River from the Hardin County line to the Iowa Soldier’s Home. The images clearly showed the main river channel as it was in 1939, however, many old oxbows locations were easily identified due to the texture of early successional vegetation. I carefully plotted the length of the river channel in Marshall County as it existed in the 1980s, and compared it to the river’s length prior to any dredging operations. The result was astonishing. About 8.2 miles of river bed had been eliminated!

One must also be reminded that the elevation of the land at the Hardin County line did not change much, nor did it at the Soldier’s Home. But the slope of the river bed was increased after the dredge left its mark of a straightened channel. Thus, river water flowed faster even at normal times. Faster yet at flood times. Faster water has more power to cut and hold in suspension silts, sand and clay particles. Faster water would and did cut away at both river banks to widen the channel. But when all that force of high water or flood water reached the city of Marshalltown, it ran into resistance.

Downstream from the Soldier’s Home, the river remained in a natural curving pathway. This was the resistance to a fast escape of flood water. There was no option for the river at such times but to spread out over the floodplain, a natural physical reality for dispersal of energy. In hindsight, the 1918-21 dredging of the Iowa River between Liscomb and the Soldier’s Home that took away 8.2 miles of river bed, helped make flood situations worse for the city of Marshalltown forever. We are still paying the price and are reminded of our human errors each time the Iowa River breaks a new record flood level.

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CANOE, KAYAK and COOK is a river exploration program coming up soon. Registration is required for the Saturday, Sept. 12 event from 10 a.m. until 2 p.m. The Marshall County Conservation Board is now taking names for those who want to paddle the river that day. The cost is $5 per person. Canoes or kayaks will launch at Furrow Access on East Main Street and float to Three Bridges County Park. At Three Bridges, an outdoor cooking demonstration will take place. Pre-registration in advance should be completed on or before Sept. 4 so that arrangements for food can be made. Do call 752-5490 for details and to register. Those wishing to float the river must arrange for their own watercraft and life jackets, plus reusable table service. The food will be furnished.

The river mileage from Furrow Access to Three Bridges is a bit over four miles. At an average paddle speed of two miles per hour, it may only take a couple of hours to reach the destination. But on the way there will be a lot of river to watch, wildlife to see, tree snags to avoid and old oxbow river channels to entice the brave to explore. Remember that a portage may be required for those that attempt to do this.

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RABBIT and SQUIRREL seasons open next weekend, Sept. 5. Cottontail rabbit survey data shows a 50 percent increase over the average of the last 10 years. Rabbit populations are strong everywhere with best numbers in southeast Iowa. Squirrel populations tend to follow the success of acorn crops from oak trees. Since the production of mast from oaks was very good in 2014, the bushy tailed critters also have good numbers. Both species can be inexpensive and fun to hunt. A .22 rifle, a soft place to sit and wait and watch in a forest with lots of oak trees, and in time one will be rewarded. Squirrel season is Sept. 5 through Jan. 31, 2016. Cottontail rabbit season is Sept. 5 through Feb. 28, 2016.

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DUCK HUNTERS will be asked to cooperate with avian influenza sampling this fall. Since the epidemic in northwest Iowa this summer on turkey farms, researchers want to know if wild ducks or other waterfowl are carriers of the disease without being affected themselves. Samples taken from waterfowl will be screened to determine if any disease vectors are present. The study will focus on dabbling ducks – teal, gadwall, widgeon, and mallards.

“Biologists hope to get enough samples on the opening day of the regular duck season” says Orrin Jones, waterfowl biologist with the Iowa DNR. Watersheds selected for the study include the Upper Mississippi, Iowa, Skunk and Wapsipinicon rivers. It will only take a few minutes to collect the samples. No hunter information is taken. Hunters can be notified if they desire on the results of the ducks they took. Hunters from all parts of Iowa are encouraged to report any sick or already dead waterfowl they may come upon.

Another aspect of waterfowl hunting is recovery of a duck or goose with a leg band. Only a very small percentage of waterfowl are captured and banded. Even a smaller segment will be taken by hunters. Only when the bird is down will the excitement note the aluminum bracelet on the leg. Each band is inscribed with a unique eight or nine digit number, and the last number on the prefix indicated the band size. Of course large bands fit goose legs, medium bands for mallards and so on. On average about 350,000 waterfowl are banded each year. Somewhere around 85,000 are recovered and reported. Leg bands can be reported by calling 1-800-327-BAND. Hunters that do this receive a certificate with information about where and when the bird was banded, who marked it, and its age and sex. And you get to keep the band as a token of your contribution.

An early objective of waterfowl leg banding was to determine migration routes by noting banding locations and points of harvest. When this was done nationwide, four different flyways were mapped. Band recovery shows biologists how the harvest is distributed through out states, flyways or the continent. Bands are also helpful to estimate age, sex and species to species survival. This is part of the data collection requirements to help manages set hunting seasons, bag limits and start/end dates. A few waterfowl, very few actually, are fitted with GPS radio tracking devices to find then anytime, anywhere around the globe. And another tracking scheme involves PIT tags. PIT stands for passive integrated transponder as geolocators. When placed on ducks or geese, lots of new information is gathered by these devices. A wealth of information improves biologist’s understanding and management options.


Garry Brandenburg is a graduate of Iowa State University with BS degree in Fish & Wildlife Biology. He is the retired director of the Marshall County Conservation Board. Contact him at P.O. Box 96, Albion, Iowa 50005