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During the summer of 2005, the United States Geological Survey (USGS) Nebraska and Iowa Water Science Centers (WSC) began conducting hydrographic surveys and measurements of river discharge and velocity at several Missouri River bend sites. The purpose of the survey, as requested by the Omaha office of the U.S. Army Corps of Engineers, was to assess the effects that the habitat improvement structures placed by the Corps were making within the river channel. The USGS Nebraska and Iowa WSC’s specialize in many water resource-related projects. Through cooperative programs they work closely with more than 25 different federal, state, and local agencies to collect data, map, and monitor one of our nation’s most valuable natural resources and the environment associated with water.
The Missouri River is one of our largest and longest rivers, beginning in the Rocky Mountains of Montana and flowing south and east as it makes its way to St. Louis, Missouri, where it joins the Mississippi River. Although the Native Americans and early French traders made use of it as a natural passageway to the Northwest, it did not gain widespread recognition until Lewis and Clark traversed it between 1804 and 1806.
One of the obstacles faced by these early explorers and river travelers were the Missouri’s many bends and loops that greatly slowed their travel. Some bends were so large that they required a full day of travel only to end up almost exactly across from where the bend started. The Missouri was also laden with submerged trees called "snags," which are estimated to have sunk some 400 loaded steamboats and hundreds of smaller vessels. These unseen dangers could rip apart the hull and quickly sink any unsuspecting boat that ran into them. The Corps had begun sending snag boats up the Missouri as early as 1838 in an effort to eradicate the dangerous snags, but the need for a safe passageway only increased as westward expansion continued.
Another obstacle was the ever-shifting channel that at times was so spread out that the depth of the thalweg only measured a few feet. Early historians often claimed that the wandering Missouri River could be found sleeping in a different bed every night. The Missouri was unquestionably scheduled to play a vital role in American expansion. As an artery for the transport of supplies to a rapidly growing nation, the issues of making it a safe and reliable passageway had to be addressed. Environmental issues concerning the taming of a major river were virtually non-existent and easily gave way to commercial interests.
The Missouri, which claimed paths that varied across an 18-mile-wide swath in some places, was reigned in section by section. Great bends and meanders of the wild river were cut off and eventually nearly 130 miles of shoreline deemed "unnecessary" was eliminated. Thousands of acres of natural habitat were converted to agriculture, and displaced wildlife became confined to the banks of an unnatural channel designed for deep-draft barge traffic. An entire ecosystem of deep pools, marshes, sloughs, sandbars, and oxbows was almost entirely eliminated from the Missouri River basin.
Even with channelization, the Missouri was still subject to uncontrolled flooding in the spring and low water levels in the summer, so major dams were built further upstream in the Dakotas to control the flow. These dams that alleviated the occasional flooding downstream, however, permanently inundated vast areas behind them, thus removing even more natural habitat. To many in the basin, the Missouri River was deemed an enemy to civilization, and harnessing it was the only way to make it predictable for a society that desired order. Thousands of wing dams were built by the Corps to shift the river into one main channel, and millions of tons of quarried rock were placed along the banks for further stabilization. By the mid to later twentieth century, the river below Sioux City was almost completely reformed into a man-made entity that had virtually no resemblance to its original state. The memorable floods of 1993 provided the Missouri a brief opportunity to escape its confines and roam across land that it had previously known as home. This flood and the devastation that it caused, however, was seen differently than those that preceded it. It provided data on the river that has caused a new direction of thinking about controlling the water during heavy rains. Deep channelization and levees had caused the river to rise higher and run faster until something finally had to give, often with disastrous effects further downstream. The recreation of natural floodplains is now being seen as greatly aiding in dispersing and slowing down the river after heavy rains.
The effect of straightening the river has been met with mixed results. It helped to solve the boundary problems between neighboring states whose borders were fixed beneath the ever-shifting waters. The GLO surveys of the 1850s provided the first true representation of the exact location of the river and the definitive boundary lines between Nebraska with Iowa and Missouri. Words like accretion, avulsion, reliction and riparian rights in litigation became all too familiar between the states that shared the common boundary of the Missouri.
The Missouri River Commission was formed in the 1880s and provided the first large-scale detailed mapping of the Missouri River. This agency was highly organized and it established the first permanent triangulation stations and bench marks in this area. A series of boundary compacts between the neighboring states finally decided the legal boundary of the river that was largely based upon the geographical center of the design channel established by the Corps. In several areas each adjoining state has legal ownership to land that actually lies across the river–such as Carter Lake, Iowa, that is almost surrounded by the city of Omaha, Nebraska, Nebraska’s Desoto National Wildlife Refuge that lies on the east side of the river, and McKissick Island in Missouri that has had several legal issues between the two states.
Channelization also enabled land owners along the river to have some sense of security that they could farm and live upon the fertile land that stretched for miles between the bluffs without yearly fears of flooding. Farmers needed a predictable assurance that they would be harvesting corn and not catfish upon their valuable crop land. The confined channel also provided for the intended barge traffic below Sioux City, Iowa. This latter benefit was really the primary objective of the Corps, as they sought to protect commerce and navigation through channelization. Unfortunately, barge traffic on the river peaked in 1977 and has been on the decline ever since. The benefits to the farmers and cities of alleviating flooding and helping to establish defined state boundaries were an added result of a confined channel.
As barge traffic continues to decrease and a keener sense of protecting our environment has increased, the role that the Missouri River should be playing is being reexamined. The Corps did exactly with the Missouri River what it was originally commissioned to do, but it now has to broaden its scope to include environmental concerns.
To help restore habitat, the Corps has begun installing structures, such as chevron-shaped water diverters, and has begun notching existing wing dikes on hydraulic flow patterns in an attempt to create a more natural river for endangered species such as the Least Tern, Piping Plover and the Pallid Sturgeon. These measures would create disturbance and sediment buildup on the back side of the structures and hopefully create new habitat. Side channels are being dredged to create areas that would imitate historic natural channels. The data collection by the USGS surveyors will determine if these structures are working as planned. Other agencies have begun collecting fish samples in the affected areas. It is an engineering challenge to increase habitat and at the same time maintain the integrity of the channel for navigation purposes.
Fieldwork by the USGS includes bathymetry and topography of the river in straight line cross-sections from highbank to high-bank perpendicular to the flow of the river. Sections are spaced at 50-foot intervals approximately one mile upstream and downstream from the bend apex at each site. Acoustic Doppler Current Profilers (ADCP) are used to show a depth to the bottom tied to the water surface. The ADCP data also shows the speed of the water and amount of discharge.
The establishment of the survey base control as well as the processing of the data is being done by Sonja K. Sebree, Brenda K. Woodward and Michaela R. Johnson, who established the permanent ground control points with static GPS using Ashtech/Thales equipment. Solutions for the control points are processed through the National Geodetic Survey’s Online Positional User Service (OPUS). The horizontal coordinate system is based upon NAD83 and converted to UTM Zone 15 (1983). The vertical control is based upon NAVD29. Since the Missouri River has had a long surveyed history, the continued use of the NAVD29 vertical datum will enable the Corps to compare the recent data with their historical data.
Two boats doing the bathymetry work were guided by Mike Andersen and Tim Boyle from the NWSC and Joe Gorman and Scott Thul from the IWSC. Aboard each boat the ADCP measures water currents using a principal of sound waves by transmitting a succession of acoustic "pings" of sound at a constant frequency along four beams. As the sound waves travel through the water they reflect off the particles, such as silt, that are suspended in the moving water and return to the ADCP. The velocity is determined based on the assumption that the particles in the water are flowing at the same speed as the water current that suspends them. The region of the Missouri River involved in the study areas was so turbid that the ADCP returned excellent results. A collection of acoustic pings work to create an ensemble that is used to determine the absolute speed of the water current, the direction of flow, and the depth in the water column to the river bottom, thus giving an almost complete picture from the surface to bottom of the river. There are, however, four areas of the water column that are not measured. The first is the top portion from the water surface down to approximately 30cm below the ADCP face called the blanking-distance. The second is the bottom of the riverbed up to approximately 6% of the total depth which is called the side-lobe interference. The final two areas are the edges of the river due to the fact that the boat can only get so close to shore. To gain estimations of these four areas the data is extrapolated from the measured portions into the unmeasured portions. The velocity data will often vary at different depths at the same location since the vertical distribution of the river velocity in turbulent water can be very complex despite what is happening at the surface. Up to 450 different ensembles can be created across the 650-foot-wide cross-section from the water edges in real time. On a good day, each boat crew can maneuver across 100 different cross-sections, thus creating cross-sectional profiles and velocity data to an accuracy and degree that was previously unobtainable before using ADCP.
Prior to entering the river and collecting data, the onboard computers are configured to know exactly where the cross-sections are to be placed by using HYPACK marine surveying software. Since the sections are spaced only 50 feet apart, it leaves very little interpretation as to what the river is doing. The HYPACK software also provides the collection and processing of the collected data in real time. The boats were guided to the cross-section lines with Trimble boat-mounted GPS antennas that used OmniSTAR real time differential GPS service. WinRiver software allowed the crew to see exactly where the boat was located in relation to the configured line. The boats then moved along each line by monitoring the screen which showed the position of the boat left or right of the configured line as it moved across the river. In a sense it is similar to working a video game as the pilot moves the steering wheel of the boat to keep it closely on line. The USGS crews did extremely well and rarely exceeded a few feet from the configured line unless adverse conditions such as wind provided a more challenging situation.
Those working on the land portions were Rick Wilson, PE, and Kellan Strauch from Nebraska, and Clint Van Schepen and Damian Brochey from Iowa. Because the tree cover along the banks often made RTK GPS unusable to obtain the desired accuracy, the crews used Sokkia and Topcon total stations with data collectors to obtain the data from the edge of the water, the bankfull line and then up to the actual high-bank. Guidance along the banks to match the same cross-sections that the boats were collecting data was done by using RTK mounted to a backpack.
Although the surveying being done along the Missouri River by the USGS is time consuming, the amount of time spent pales in comparison to the methods once used by surveyors in the past to collect the same data. Cross-sections were obtained by having to stretch a cable across a river and then take soundings at selected intervals along the cable with weights attached to ropes to get the depths. The work was dangerous and laborious and required more people for less data. The accuracy and frequency of the data being collected today by using GPS, ADCP, and total stations provides a clearer picture that leaves much less interpretation as to what the river is actually doing below the surface.
The Corps of Engineers is now coming to the forefront of a changing role that keeps them doing what historically they have done best while also being more sensitive to the environment. The United States Geological Survey continues its role as they have successfully done since 1879 to provide the nation with reliable and impartial information to better describe and understand our earth.
Jerry Penry is a licensed land surveyor employed by Lancaster County Engineering in Lincoln, Nebraska. He was invited by USGS to observe its mapping process of the Missouri River.
A 3.473Mb PDF of this article as it appeared in the magazine complete with images is available by clicking HERE