On the nature and mechanics of floodplain response and stability in the semi-arid environment of southern California
Date
2009
Authors
Dust, David Walter, author
Bledsoe, Brian P., advisor
Grigg, Neil S., committee member
Watson, Chester C., committee member
Wohl, Ellen E., 1962-, committee member
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Abstract
The core research questions motivating this dissertation are: (1) How can we assess the existing stability state of a floodplain? ; and (2) How can we estimate the trend and magnitude of the change in floodplain geometry due to urbanization? Field investigations conducted early in this research indicated that it was essential to build a basic framework of understanding for the fluvial systems in the semi-arid environment of southern California, prior to addressing the core research questions. To build this framework, various classification systems and conceptual models have been developed to characterize the nature and form of floodplains at multiple spatial scales. A reach-scale classification system and conceptual model were created to synthesize the observed floodplain forms into three basic floodplain continuums (armored, non-armored, and active-regional alluvial fan), where each of these continuums are comprised of three to five alluvial floodplain forms (cascade, step-pool, plane-coarse-bed, plane-mixed-bed, plane-fine-bed, pool-riffle, braided, and dune-ripple). A catchment-scale conceptual model was created to describe the interrelationship between the three basic floodplain continuums in terms of climatic and geologic metrics. This conceptual model provided the basis to develop a practical GIS-based technique for predicting the floodplain continuum type within a catchment. For the non-armored and armored floodplain continuums, floodplain state plots have been generated to quantitatively describe the natural downstream progression of floodplain forms, using specific stream power and the width-to-depth ratio as the state and shape metrics. These floodplain state plots provided the bases to create conceptual models for intra-catchment processes and to develop techniques for assessing the stability state of a floodplain. Using the series of conceptual models as a framework, regime-type modeling tools have been developed for estimating the trend and magnitude of the change in floodplain geometry due to changes in water and sediment supply. At the core of these tools are the basic flow relationships of continuity, flow resistance, and sediment transport for floodplains with trapezoidal geometry. To factor in bank erosional resistance and stability characteristics, the basic flow relationships are coupled with floodplain response and stability constraints developed from the conceptual models for intra-catchment processes.
Description
Department Head: Luis A. Garcia.