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Little Mill Creek Flood Risk Management

Status 

On September, 30, 2013, the U.S. Army Corps of Engineers' Philadelphia District awarded a contract to RC&D, Inc. of Pawtucket, RI to construct the lower portion of the Little Mill Creek Flood Risk Management Project for $2.7 million. Work was completed in November of 2015. 

Work involved widening of only the right bank (facing downstream) from approximately 381 feet downstream of the Maryland Avenue Bridge (DE State Route 4) downstream for a length of approximately 500 feet. This segment did not include any deepening of the channel or widening along the left bank. Riprap was placed along the right bank toe for toe protection and extends up the right bank slope to approximately 6 feet above the channel bottom. Channel modification resumed further downstream where the channel was widened to 30 feet and deepened by 3 feet, which included the clearing and widening of both channel banks for a length of approximately 1,670 feet (approximately 100 ft. upstream of the Amtrak railroad bridge). Channel widening was variable with a maximum widening of the channel by about 17 feet with an average channel bottom width of 39 feet (existing average width is 36 ft.). At the upstream end of this segment, riprap was placed from the toes of both banks to 6-feet above the channel bottom for a distance of approximately 100 feet.

Background

Little Mill Creek, which is located in the northern portion of New Castle County, Delaware, has seen recurrent flooding events over the past 100 years.  These flooding events, specifically September 1971, January 1978, and July 1989, resulted in several Federal and Private watershed studies of the areas surrounding Little Mill Creek. 

The most recent Federal study, a Section 205 Flood Control Feasibility Study, was completed by the United States Army Corps of Engineers (USACE) in 1995.  This study proposed significant channel improvements for two separate portions of Little Mill Creek.  The channel improvements for the upper portion, which extended from the Kirkwood Highway Bridge to the CSX Wilsmere Railroad Yard Bridge, were completed in 2007. The lower portion investigated within the 1995 USACE Feasibility Study extends from approximately the Maryland Avenue (Route 4) Bridge to the Amtrak Railroad Bridge.  

The project for the lower Little Mill Creek is a flood risk management project utilizing channel modification to reduce flood stages in Little Mill Creek.

The majority of the flood damage potential can be attributed to heavy development on the flood plain. New commercial development in the lower portion has also encroached on the flood plain. In addition, numerous bridges and culverts obstruct flood flows. These structures are prone to clogging with debris, and often cause backwater due to their inability to pass the flood flows. As a result, flood waters pond upstream of these structures and overflow the streambanks. Flood damages in the lower portion occur extensively to the many commercial establishments and few residences that line the creek in these reaches.