The purpose of this Environmental Assessment (EA) is to address the effects of new construction 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. Modification may include the raising, lowering, or notching of these structures to optimize their performance in flow control and sediment transport. Also, navigation dams and appurtenant structures require periodic rock placement for repair or improvement of batik protection. This document specifically addresses rock placement at seven sites. All seven sites are in Pool 18, River Miles (RMs) 420.2 to 421.6, Mississippi River, Des Moines, County, Iowa. All of the structures are existing wing dams (plate 1). These structures direct flow away from the shoreline and into the main navigation channel. Basically, these structures constrict the river flows into a more narrow cross section. This reduced cross section causes the water velocity to increase and subsequently to transport more sediment. As a result, the need for channel maintenance, i.e., dredging and dredged material placement, should be reduced in this area. Alternatives to the proposed actions are limited. They include the no Federal action alternative or other configurations and quantities of rock. The project is expected to help maintain the navigation channel, with no significant impacts to natural, cultural, economic, or social resources. For this reason, an Environmental Impact Statement (EIS) will not be prepared for this action. Because the proposed action is subject to the provisions of the Clean Water Act, a Section 404(b)(1) Evaluation has been prepared for the project (appendix B). Section 401 compliance has been sought through coordination with the State of Iowa. A Public Notice has been prepared and distributed concurrently with this document. Copies of correspondence relative to this action are included in Appendix A-Pertinent Correspondence. EA-1 II. PROJECT DESCRIPTION The proposed work addressed in this document involves improving seven wing dams from RM 420.2 to RM 421.6. Each proposed action is described as follows: A. Wing Dam No. 2. This structure is located at RM 420.3 (plate 2). Its elevation will be raised from 522.7 to 525.0, approximately 3 feet below flat pool. The length of the wing dam will be brought back to original design of 1,400 feet. Wing Dam No. 2 will have a total of 200 feet of bankline protection added upstream and downstream along the bank.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.