Variation of flow pattern in waterways due to degradation and aggradation

Abstract

The cross section and profile of waterways are constantly subjected to alteration due to changes in flow volume and velocity. Banks and beds of waterways could experience excessive scouring especially at locations with sharp bents. At these locations, the soil constituting the cross section of the waterway could be subjected to considerable degradation, which could significantly alter the flow pattern at these locations. With severe degradation, the volume of sediment transport increases and may exceed the water carrying capacity resulting in the phenomenon known as aggradation. Contrary to degradation, aggradation results from the deposition of carried aggregate transport, which can hinder water flow in the waterway and obstruct its path. As degradation and aggradation take hold at some location along the waterway, their effect gets compounded over time which exacerbates the problem and make it difficult for the waterway to recover. Geographic Information Systems (GIS) is used to study the effect of degradation and aggradation along the Schoharie Creek, which is one of the major tributaries of the Mohawk River in upstate New York. The change in the selected locations will be examined over time to show the gradual alteration that a given section experiences and its effect on flow pattern and waterway profile. The analysis will also include a Digital Elevation Model (DEM) study of bank slopes based on the creation of a contour map. The August and September 2011 Tropical Storms Irene and Lee, respectively, left in their wake tremendous change to the waterway due to excessive degradation and aggradation. This effect was sensed due to the severe brunt it brought on the area landscape and its infrastructure. This study will identify the areas most in need for buffering and most susceptible to the impact of these natural phenomena. This will help implement proper protection methods, and in case of a damage, it will help plan for effective restoration systems.