Erosion at the Town of Clarksville, Indiana, shoreline near the town’s boat ramp, historic George Rogers Clark Park and Mill Creek Bridge has spurred the city managers and leaders to seek the Corp’s guidance to find a solution.
In July, the Louisville District Army Corps of Engineers representatives Brandon Brummett, outreach coordinator, and Tracey Keel, locks and dams operations manager, met with town officials and explained the Corps’ study process, how erosion and bank loss occur and the operations of McAlpine Locks and Dam, Louisville, Kentucky.
The Louisville District is conducting an initial assessment to document what has been done in the past and what resources are being threatened by the erosion. Currently, authorization and limited funding exists for the initial assessment, however additional funding is needed to perform a more detailed study. The Clarksville area across from the lower tainter gates of the dam is prone to erosion—as are many locations along the Ohio River—where natural river bends exist. Erosion occurs when the soil particles on the river bank are carried away by the forces of water. These forces increase as the water velocity and depth of flow increase. The forces are the highest in the outside bend of a channel. The location of the erosion is in the outside bend of the original channel.
Flooding and the rapid fall of the river is the main contributor to erosion which typically results in bank failure. Toe erosion from high velocity river flow is a secondary contributor. There has been a long history of bank failure and erosion along the riverfront, along Riverside Drive, and south along the Ohio River shoreline. Bank failures are basically small landslides. They occur when the driving forces of the bank slope are greater than the resisting soil strength and mass. Important factors are the height and angle of the slope, the sheer strength of the soil and groundwater levels.
Other possible contributing factors to riverbank saturation in general are very high groundwater levels due to saturation in flood events, poor drainage, erosion of the soil at the toe of the slope from the river and placement of fill and waste materials at the top of the slope. Significant flood events where high water and subsequent rise and falls occurred in recent years have contributed to an unstable slope and the sloughing off of the banks.
Erosion would occur naturally if the dam were not located adjacent to the McAlpine locks. Some flow conditions from the dam exacerbate a preexisting condition of natural river bends where erosion occurs. This is a key area for completion of the Ohio River Greenway Project, as well as a site that is rich in history and archaeology.
The Army Corps of Engineers has documented studies and work that has been done in this eroding area over a 30-year period, but any attempts to address the erosion have been temporary measures. Brummett said a full study would ultimately be needed to examine the forces causing the erosion in more detail, as well as to determine what potential solutions may be available to halt the erosion.