MORPHOLOGIC IMPACTS OF HUNGRY WATER AT STREAM CONFLUENCES

The purpose of this poster is to present a heuristic model that explains interactions at the confluence between a tributary and trunk stream. The Confluence Effects Model (CEM) may be used to predict the resulting geomorphological impacts within a tributary stream's mouth with varying changes in trunk stream discharge and channel morphology. Currently, no model directly addresses the morphological response of a tributary stream's confluence downstream of a dam. A few models do exist that have been shown to effectively predict channel response downstream of a dam in a general qualitative way. However, these models do not directly address tributary responses, though they may indicate the trunk stream changes to which the tributary responds. In most models tributary responses to imposed trunk stream conditions are simply implied through the confluence-reach effects on the impounded trunk stream. Six possible cases that may occur within an alluvial system downstream of an impoundment are presented using the relationships of sediment load, stream capacity, and discharge. The six cases are used to qualitatively model confluence effects in downstream reaches of a dammed alluvial river with “hungry water”. This approach is similar to classification and qualitative predictive models of channel changes within trunk streams downstream of dams. The heuristic model offered here illustrates the numerous resulting cross-sectional and channel changes possible after impoundment. The six cases in the CEM were chosen because previous work on downstream dam effects indicated a lack of attention toward the affect of trunk stream morphometric changes on tributary stream morphometry.