SILT AND SEDIMENT FLOW OF THE MISSOURI RIVER The two thousand plus miles of the Missouri River have played host to a number of historical events over the last 250 years. Since the first arrival and written records of the Corps of Discovery expedition of 1804-1806, led by Lewis and Clark, the river itself has changed significantly. Even during their journey back home in 1806 Clark noted that: “… a great alteration in the [current] course and appearance of … the Missouri. In places where there was sandbars in the fall of 1804 at this time the main current passes, and where the current then passed is now a sandbar. Sandbars which were then naked are now covered with willow several feet high."(http://lewisandclarktrail.com/section2/ndcities/BismarckMandan/1806history1.htm) The Missouri River and its tributaries (drainage basin) encompasses 10 states, starting as far north and west as Montana just east of the Continental Divide. It terminates on the eastern border of its namesake where it enters the Mississippi River. Nicknamed ‘Big Muddy’ for the amount of silt and sediment it used to contribute to the Mississippi Delta, it is not so anymore. According to The Missouri River Ecosystem: Exploring the Prospects for Recovery by National Academies Press, http://www.nap.edu/catalog.php?record_id=10277 , the construction of over 75 dams have decreased silt and sediment drainage from 142 million tons to just 4 million tons. The Science Daily, http://www.sciencedaily.com/releases/2010/09/100928135049.htm , conveys that a system of dam bypasses and deconstruction could increase that sediment to 34 million tons a year. Floods naturally kept this silt moving south and east. June of 2011 brought record floods to the Missouri that are sure to increase silt in the down stream areas, a study that will take years before the full effects are realized. An over 200% snow pack in the Rockies (drainage basin) followed by record rainfall in the spring led to devastating flooding. A mile upriver from this point a levy breeched Sherman Army Airfield on Fort Leavenworth necessitating the closing of the facility for several months, but the town of Leavenworth remained largely unaffected. The initial intent of dams and dikes that line the Missouri was to claim valuable farmland for crops and create hydroelectricity. Unbeknownst to engineers of that time frame was the impact that those obstructions would have the ecological systems downstream. In the early 2000s, the US Fish and Wildlife agency began releasing silt to increase the sandbar habitats once again in order to try to reestablish some of the native species residing on those geological features. Residents now complained about the decreased quality of drinking water and the project was halted to be reexamined. As waters recede from the Missouri, you can expect the sandbars to once again appear and change the geological landscape of the river. Sandbars will form as the flow volume of the river tapers off and the river no longer has the energy to carry the silt. The silt will also deposit on the inside (or convex) curve of a river bank. It is not uncommon to find silt and sand on the inside (convex) bank while the outside bank will be eroded. Over the course of centuries this leads a river to meander, which in turn become oxbow lakes. Though, a large flood through the flood plain can again level the flood plain, if not contained by levies or dams. Standing at this point, answer the following questions:
1. What, if any, manmade features can you see that contributed to the flood of 2011?
2. What natural geological feature do you see upstream that you feel kept the town of Leavenworth safe and relatively flood free?
3. What kind of material do you find under your feet on this bank of the river?
4. Based on the answer to number 3 what side of the river (concave or convex) do you suppose you are on? Please send answers via messenger.
5. In accordance with revised GSA guidelines, I'm asking for a photo to be included to prevent "armchair" finds. Those without it after 31DEC23 will be deleted. Thank you.
And if you learned something or enjoyed it, please mark this as a favorite (ECs take quite a bit to put together and get approved).