A landscape formed by floods

The entirety of the Missisissip Aluvial Valley (MAV) was formed by the ebb and flow of flooding events, and the meandering of ancient channels of the Mississippi, Ohio, and other rivers lost to the sands of time.  The recent story of the Sunken Lands is one of man's desire to tame the floods, and "reclaim" flood prone areas for agriculture.  Historic floods in the region were recorded in 1858, 1862, 1867, 1882, 1884, and 1890.  The St. Francis Levee District was formed in 1893 to begin an organized battle against the unchecked waters.  The Swamp Land Act of 1850 had deeded the majority of flood prone areas to the States to sell, and use the proceeds to fund flood control projects.  Floods continued to affect the area, with notable events in 1903, 1912, 1913, 1915, and 1916.  The 1912 flood in particular was the first to garner significant federal attention, and a colorful recollection of the event by a supervisor of a section of the levee was published by the Arkansas Historical Quarterly in 1947, https://www-jstor-org.ezproxy.lib.vt.edu/stable/pdf/40027473.pdf.

Flooding in the Sunken Lands comes from two directions. Headwater flooding flowing from the headwaters in the mountains of Missouri, and backwater flooding pushing up from the mouth at the Mississippi river.  Two federally funded projects have focused on reducing the impacts of these sources.  Lake Wappapello is situated along the St Francis River channel at the edge of the MAV, and was authorized as a flood management project to hold water and slow the flooding downstream into the Sunken Lands and adjacent agricultural areas.

Near the mouth of the St. Francis River at Marianna Arkansas, the Huxtable Pumping Station and dam was created to restrict the backwater flooding off the main channel of the Mississippi River, but still allow for the flow of water from the St. Francis into the Mississippi.  When the Mississippi reaches 177 feet above sea level, or exceeds the height of the St. Francis, the gates are closed, and the world's largest freshwater storm runoff pumps are turned on to pump the entire flow of the St. Francis River into the Mississippi.

 https://www.mvm.usace.army.mil/Media/Images/igphoto/2000757605/

Flooding continues to be a significant part of the lifecycle of the watershed.  Even with over 120 years of projects and engineering, mother nature has still shown her might with recent major flood events in 2011, 2017, and the longest period of flooding in history in the first half of 2019.  Recent floods have come with significantly less loss of life and property than those of years past, due to the extensive flood control structures that are in place, but I find myself torn.  When I consider the massive loss of habitat that has occurred in the last 200 years, weighed against the production of those lands and the benefits to humans, both locally and worldwide through food production, I often wonder if it was worth the cost. 

A Unique Remnant

Prior to Western settlement, the vast majority of the of the Mississippi River Alluvial Valley (MAV) was criss-crossed with numerous winding, braided channel sloughs, larger meandering secondary rivers (like the St. Francis), and a smattering of abandoned channels and oxbow lakes.  The dominant land cover was bottomland hardwood forests of oaks and other mast producing trees that were adapted to seasonal flooding.  Within the wetter areas were cypress-tupelo swamps with standing water most months of the year.  As permanent European settlers moved west across the Mississippi river, this area was recognized as a having high agricultural potential.  The prevailing view of swamps was very different than today's understanding of the habitat and ecological services they provide, as is summed up well in this article from the Brick and Clay Record printed in January of 1912.  The brick and clay industry was invested in the installation of drain tiles (subterranean clay pipes to drain agricultural lands).  The article is titled WAR DECLARED ON SWAMPLANDS, and here is an excerpt mentioning the St. Francis watershed.

This assault on the natural hydrology and native forests of the region has been the largest threat to the natural habitat in eastern Arkansas and south east Missouri.  Both water and tree were something to be conquered, to be "reclaimed" from a "worthless" state.  The widening and subsidence of the natural channel caused by the New Madrid Earthquakes in 1811-1812 that created the Sunken Lands proved too difficult to completely tame, and the area was instead walled in with massive levees.  This abandonment preserved a remnant of the bottomland hardwood forests and terraces that were once common.

Often when we look at hazards to a watershed, we look uphill.  Although there are no shortage of issues upstream in the watershed that put its future health at risk, this area is unique in that some risks lay downstream.  The construction of the floodway that is mentioned above in the early 1910's diverted a portion of the natural course of the river out of the Sunken Lands into an artificial channel.  A short earthen dam was constructed at the head of the new floodway, essentially creating a reservoir that contained the Sunken Lands above Marked Tree, Arkansas.  In 1926 water control structures were installed at the floodway outfall, and a lock and sluice way were installed at the outfall into the natural channel.  The old channel of the St. Francis was not completely abandoned so it could continue to collect water that fell on the surrounding area outside of the levees, and support commercial boat traffic.  In times of high flow, the majority of the downstream flow was directed down the floodway to prevent flooding along the old channel.  This created two outfall locations that had to be managed in conjunction to maintain water levels within the Sunken Lands.

The soils of the area are silt, clays, and fine sands deposited from alluvial activity of the St. Francis, and historically the Mississippi and Ohio rivers as they meandered through the area in pre-history.  These native soils were used to build the levees, starting as far back as 1893 when the St. Francis Levee District was created.  These soils are not the most stable when saturated, and the combination of two outfalls, and multiple structures, has proven a consistent threat to the maintenance of the water level in the Sunken Lands.  In the 1930's, the original sluice way and lock on south east side of the Sunken lands sustained damage in several successive floods, and was deemed damaged beyond repair during a flood in 1938 that washed out 90 feet of levee.  To the consternation of upstream inhabitants, that relied on an average of 750 lockings per month through the levee, the US Army Corp of Engineers (USACE) determined there was no way to design a robust water control structure that would allow boat traffic through the levee.  An innovative solution to lift the entire flow of the river over, instead of through, the levee was designed by the Memphis District of the USACE.  Three nine-foot diameter pipes were installed to siphon water from the Sunken Lands into the naturally channel of the St. Francis downstream.  These structures are still in use today, and are a highly regarded engineering solution to a specific problem, with no pumping costs, and minimal maintenance.

The dam across the floodway, and the outfalls through it, have not had the same longevity.  The dam has been subject to scouring and overtopping damage multiple times, and the outfalls have gone through several different designs, most recently reducing two floodway water control structures into one in the late 1970's.  The Arkansas Game and Fish Commission (AGFC) currently operates the outfall at the St. Francis Floodway, while the USACE still operates the siphons.  The two agencies have an operating agreement according to the Wildlife Management Area (WMA) Master Plan to maintain the water level in the Sunken Lands at 210 feet above sea level between February and October, and 212 feet above sea level during the waterfowl hunting season of November through January.  This plan approximates the natural cycles of water flow with a focus on creating additional wintering habitat for migrating waterfowl.  The surface area of the lake at the summer pool is approximately 3,122 acres, increasing to 5,474 acres at 212 foot elevation.  Efforts are made in the current management plan to keep the water level below 214 feet to prevent driving whitetail deer and wild turkey out of the WMA.  The lack of higher ground for retreat in flooding events is thought to be a significant hindrance to the management of these two species in particular, especially turkey, as these higher water levels often occur during the spring nesting season.

The most recent levee breach initially formed in 2008, and can be seen to the east of the outfall structure in this aerial image above. The repairs to this area were started several times between 2008 and 2017, each time ending in failure due to additional flooding events and shoddy workmanship.  The overflow structure was left open for more than two years starting in 2015 to prevent additional damage to the earthen dam.  During the summers, this left the lake area nothing more than a dry river bed with several shallow, braided channels.  In the winter, the water level could jump up as much as 10 feet after storm event, only to drop back out to a mudflat several days later.  The Google Earth before and after below shows the unmanaged water levels. After almost 10 years of ineffective repairs to the dam, the AGFC reached out the the USACE for assistance in closing the scour, and the dam collapse was finally closed in 2017.

Hopefully this last repair will last, but the modifications to the areas ability to hold water that resembles the pre-settlement condition have historically been a major threat to the continued health of this remnant sliver of habitat.

Additional threats to the habitat quality within the Sunken Lands are increased sedimentation from agriculture runoff that is slowly filling in the lake, invasive woody species (Callery pear Pyrus calleryana), and invasive animals (feral hogs and unwanted beaver activity).  Management of the areas is additionally challenged by mulitple private inholdings.  Over 100 private landowners still hold a smattering of properties within the Sunken Lands, preventing cohesive habitat management, and have generated numerous legal battles associated with the public access for recreation, navigability, and water level maintenance.   

The headwaters of the St. Francis start in the Ozark and St. Francois Mountains of south eastern Missouri.  The highest peak in the state, Taum Sauk, at 1759 feet above sea level, is located on the western boundary of the watershed.  The river winds through National Forest Service land through much of its stretch in the mountains, and provides two high class whitewater rafting recreational areas, dropping as quickly as 60 feet per mile.  Right before the river drops out of the mountains into the flatter Mississippi River Alluvial Valley, it travels through the 34 sq km Lake Wappapello and the Wappepello dam, that was constructed in 1941 to help control headwater flooding along the river downstream.

After exiting Wappepello dam, the surround landscape switches from forested mountains to agricultural fields (mostly corn, cotton, rice, and soybeans), as well as some remnant bottomland hardwood forests.  The river forms the western boundary of the Missouri bootheel, serving as the boundary between Missouri and Arkansas.  As the course continues into Arkansas, Crowley's Ridge, an elongated ridge formed by windblown, glacial sediment, rises as the western boundary of the watershed. The next 30 or so miles are the portion of the watershed that I will focus my research on.  The seismic events of the early 19th century created an area of subsidence along the former river channel, deepening and widening the existing channel into an area that earned local names of the St. Francis Lake, and the Sunken Lands.  This area was resistant to over 150 years of "reclamation" of lands into agricultural uses, and has preserved a unique piece of the original bottomland hardwood and cypress swamp habitats that would have been prevalent across the entire Mississippi River valley in Missouri, Arkansas, Tennessee, Mississippi, and Louisiana.

Nearly the entire lower end of the watershed has been surrounded by a levee, separating the majority of the major tributaries from their original flow into the Sunken Land, and not meeting up with the rest of the river until many miles south.  At the southern end of my watershed, near Marked Tree, Arkansas, the majority of the flow of the river has been diverted into an artificial floodway to contain excess flows during high water events, and hold water that floods upstream from the Mississippi River that eventually collects all the rainfall from this area.

When this floodway was created, there was still a desire for a controlled amount of flow to continue down the original St Francis river.  This has created two outfalls from the Sunken Lands, one that sends water down the artificial channel, and one through the original channel, at approximately 210 feet above sea level.  After several engineering challenges with traditional water control structures on the outfall into the natural channel, a truely unique solution was install that lifts the entire flow of the river up and over the levee through a set of three siphons.  There will be more to come on the issues of two outfalls, and the control of the water level in the lake above them.

The entire watershed of the St Francis above the Sunken Lands contains fourteen 10-digit Hydrologic Water Code (HUC) watersheds from the US Geological Survey. This covers an area of approximately 2.5 million acres (the green polygon in the map.)

The focused study area for my blog will be the northern half of the Saint Francis River Floodway - Saint Francis River (HUC 802020309), bounded my the dam/levee that bisects the watershed.  This  is an area of 62,831 acres (the blue polygon in the map.)  The majority of the land in the study area is part of the St Francis Sunken Lands Wildlife Management Area that is owned by the Arkansas Game and Fish Commission, with several notable private in holdings that I will expand on later.

Take a look at the map I have created below, I have also included a link on the left hand nav to a larger version.  The menu buttons on the top right will allow you to toggle different layers on and off, as well as examine different base maps.