Building Hydraulic Structures to Analyze Flow and Sediment Transport Characteristics in the Entrance of Sunset Marina

Abstract

The Sunset Marina in the City of Rock Island, Illinois is located at River Mile (RM) 479.8 of the Mississippi River, approximately three miles downstream from the Lock and Dam 15. This harbor was constructed on the left bank of the Mississippi River, and completed in 1956. Since that, the problem of sediment deposition at the entrance to Sunset Marina has existed. For maintaining access to the marina, maintenance dredging has been required frequently. To reduce the costs of dredging and keep the marina operable and functioning, an investigation searching for alternatives is needed. This study modeled the area near the Sunset Marina from RM 477 to RM 482 in the Mississippi River using the ADaptive Hydraulics (ADH) Modeling System. Alternatives, including with and without hydraulic structures, for various flow conditions were compared to analyze any kind of changes on flow and sediment transport characteristics in the vicinity of the Sunset Marina as well as in the entrance to the harbor. This study showed that (1) hydraulic structures, such as a dike with a length of 1,460 feet or 870 feet, does change the flow and sediment transport characteristics; (2) the change for a dike with a short length (870 feet) is more significant than that for a dike with a long length (1,460 feet); and (3) the change is occurred only for the low flow conditions, such as 2-year flow, and no change is found for the high flow conditions, such as 5-year flow. BACKGROUND OF SUNSET MARINA The Sunset Marina in the City of Rock Island, Illinois is located at River Mile (RM) 479.8 of the Mississippi River, which is approximately three miles downstream from the Lock and Dam 15. This harbor was constructed on the left bank of the Mississippi River, and completed in 1956 (USACE - U.S. Army Corps of Engineers, 1996). Since that, the problem of sediment deposition at the entrance to Sunset Marina has existed. A tendency for bottom currents and sediment to move toward the entrance results in a tendency for shoaling. Shoaling in harbor entrance is usually located along the upstream shoreline. The amount of shoaling will depend on the amount of sediment carried by the river, size of the entrance, and the location of the entrance with respect to the alignment of the river channel. Shoaling in the entrance could also be affected by the rate of rise and fall of river stages which cause flow toward and away from the harbor. Because of shoaling, maintenance dredging has been required frequently to maintain access to the marina. To reduce the costs of dredging and keep the marina operable and functioning, an investigation searching for alternatives is needed. This study modeled the area near the Sunset Marina from RM 476 to RM 482 in the Mississippi River using the ADaptive Hydraulics (ADH) Modeling System. The ADH model provides a quantitative estimate of velocity and depth that can be used