摘要: The purpose of this environmental assessment is to address the effects of newconstruction proposed as part of navigation channel maintenance. Navigation channel maintenance includes periodic repair of existing training works or re... 展开 The purpose of this environmental assessment is to address the effects of newconstruction proposed as part of navigation channel maintenance. Navigation channel maintenance includes periodic repair of existing training works or regulating structures, e.g., wing dams and closing dams, as well as modification of these structures. These actions generally involve large grade limestone rock placement. This document specifically addresses rock placement at two sites. One site is located at Lock and Dam (L/d) 16 between Rock Island County, Illinois and Muscatine County, Iowa. The site, referred to as Hog Island, is the location of the equipment storage yard for L/D 16. It lies between the gated portion and the overflow spillway portion of the dam, at approximate river mile (RM) 457.2. The other site is an existing notched closing dam between Huron Island and the Iowa bank at RM 425. The subject closing dam reduces flow to Huron Chute, thereby maintaining flow in the navigation channel. Recent increases in the frequency and amount of dredging required between RM 419 and 425 indicate the navigation channel flows may not be adequate to transport sediment through this river reach. Engineering consideration of the Huron Chute closing dam indicates that the notch may be contributing to this problem by allowing excess flow to pass down Huron Chute instead of the navigation channel. 收起