Rivers course always on the move
The IOWA RIVER is a force we humans must adapt to. Its gentle flow most of the time leads us into a lack-luster attitude about its potential strength. Only when a large rainfall event falls within the watershed do we get concerned. If flooding is predicted from huge amounts of runoff, then we suddenly become alert (again)and take notice. If the river is slated to rise to new high levels authorities grow increasingly concerned about roadways, bridges and the negative impact a flood event can and does cause to the economy. Nature speaks and we need to listen.
One excellent method to compare a river’s changes is by examining aerial photography. This scribe was able to obtain copies of the site near what is now Sand Lake dated from the 1930s. The next map is dated 1950s followed by another from 1960s, 70s, 80s, 90s, 2002, 2006, 2008 and lastly 2013. I chose to make today’s photo using the contrast between 1970s and 2013. The location of the river channel obviously moved. The move was mostly gradual during the intervening 40 years. But it always accelerates during high water flow events and floods. Saturated soils along the adjacent river banks becomes unstable. They slide away and become a mixture of muddy contents in high water.
Geologists title the cutting and filling of meandering river courses as one of the natural process of changes to the landscape. In our long term earth history past, glacial ice over the land was one huge force of change. After glaciers began their retreat, strong winds unlike anything we typically know today added scouring effects to exposed surface materials. Storms added water that had to runoff somewhere and in doing so, created the initial outlines for many river systems within North America. Since the above processes took tens of thousands of years to happen, it is the rock record and study of ancient sediments that give clues to geologists of past climates and major landscape shaping events. Since glaciers are not a factor at this point in time, the only real geologic force remaining to reshape the land and river courses is water flow. And this happens primarily at high water and flood events.
The Iowa River has a long history of long calm periods and many episodes of flooding. One year ago we witnessed the power of running water after prolonged heavy rains. The water was an unstoppable force. And under the surface of the flooded land, river bank soils were saturated and easy to move. Another chapter was being written of stream flow eroding on the outside bend of the river where current speeds are fastest, and the deposition of sands and gravels downstream at the next inside bend where current speeds are slower. Just imagine this scenario from the head waters of the Iowa River in Hancock County all the way to its juncture with the Mississippi, a distance of over 300 miles. Now extrapolate similar cut and fill stream course changes in every creek, stream and river in the Midwest. That is a huge amount of silty soils removed from the landscape, all on its way to the Mississippi and the Gulf of Mexico.
Locally the Iowa River has several places within or close to Marshall County where the river took a short cut at a narrow place between river bends. At the Hardin/Marshall County line the river made a shortcut that caused the abandonment of a big loop in the river. Another one that happened less than 10 years ago is in near North Center Street just upstream from the river bridge. A big bend in the river is now a backwater area where silt deposits accelerate during high water times. At normal flow rates this backwater area is mostly dry. Downstream between Marshalltown and Furrow Access, other river bends have had short cuts develop in the recent past. And this year a new opening took place not too far away from Le Grand, but just inside the Tama County line. It is upstream from McCoy landing, where the river made another shortcut leaving at least one-half mile of old river bed as a backwater.
Hopefully you can picture a typical floodplain scene and the river within it like this: Take your garden hose and lay it out on the lawn in big sweeping loops back and forth between any two points. Now walk along the hose and give one of the loops a slight tap with your toe to move it a couple of inches. Do the same at the next loop and the next. Repeat this process tomorrow and the next day and the next. Keep doing this for a month or two or three. Well, you get the picture. Every old course line in the grass is still evident by the matted grasses. But the layout of the garden hose is completely different than what it was initially. That is how cut and fill river stream bank erosion works. It is a natural process. Mankind has done some adverse things to add to the problem and many good things to slow the process. There is always a tradeoff. Learning how to adapt is a good long term strategy.
A check of the DECORAH eaglets shows that they are growing fast. The all dark fully feathered eaglets do not resemble the little white fluff balls of only a few weeks ago. The website shows a total of over 296,000,000 visits from about 80 countries around the world. Amazing stuff. And a big credit and thank your to the raptor center for installing the camera to make it all visible as we tune in on the egg laying, hatching and growth of three new bald eagles. Locally one eagle nest has two eaglets inside. The three or four other eagle nests in Marshall County likely have an equal outcome.
This scribe has to give a big salute to several television programs related to natural history. The first that comes to mind is Nature series on Iowa Public Television. These shows are always terrific and host some of the best video of wild things in wild places. A few weeks ago the subject was “swarms,” large concentrations caught on video on Monarch butterflies in Mexico, followed by illustrations of Australian parakeets, sardine fishes of the coast of Africa, Emperor penguins, mayfly hatches along the Mississippi, bats from caves in Texas, bees, Army ants and lastly wildebeests and zebra migrations in East Africa. This is just plain terrific great stuff to watch.
Also on this scribe’s must watch list is the COSMOS series hosted by Neil deGrasse Tyson. The science of astrophysics is awesome. Tyson’s ability to illustrate our place in the universe is awesome. When placed in proper perspective, we learn that our very tiny earth in just one part of one segment of many spiral arms of the Milky Way. Telescopes of increasingly higher power and observation at super low or high frequency wave lengths allows scientists to deduce more and more marvelous workings of the universe. Natural history is being opened up as if we were reading the pages of a huge book about the cosmos. I like to think about these things when observing the dark sky at night.
This is the month of June, a mid-point in earth’s pathway orbit of the sun. Two weeks from now, the day length will be maxed out. From that point on days will get shorter, and nights will bet longer. I thought you’d want to know what you already know. Have fun this summer outside.
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 PO Box 96, Albion, IA 50005.