A draft environmental assessment for bank repairs to Dry Creek, a left-bank tributary of the Big Sioux River, near Hawarden in Sioux County, Iowa is currently available for public review.
The draft EA evaluates the environmental impacts of repairing bank erosion along a portion of Dry Creek and filling a scour hole caused by high flows in the Big Sioux River in June 2014.
Repairs include reshaping the left and right banks of a portion of Dry Creek near Hawarden and placing riprap to stabilize the banks and stone/gravel material to fill the scour hole.
Bank and scour hole repairs will be completed under the Corps’ PL 84-99 Emergency Levee Rehabilitation Program.
In June 2014, record rainfall in South Dakota, Minnesota, and northwestern Iowa caused unprecedented flooding along the Big Sioux River. High flows from the Big Sioux River increased flow velocities in Dry Creek that caused erosion of its left and right bank and created a scour hole in the channel invert downstream of a sheet pile control structure in the creek.
Dry Creek is protected by a right and left bank levee unit. The right bank levee provides protection to the city of Hawarden to the north and the left bank levee protects agricultural land to the south.
Over time, the bank erosion and scour hole could cut into both left and right bank levees and impair their effectiveness during future flood events.