Morphodynamics of Coevolving Fluvial and Hyperpycnal Valleys

• Main Authors: Steven Yueh-Jen Lai, 賴悅仁
• Other Authors: Herve Capart
• Format: Others
• Language: en_US
• Published: 2010
• Online Access: http://ndltd.ncl.edu.tw/handle/99939684135112364126

博士 === 國立臺灣大學 === 土木工程學研究所 === 98 === The aim of this dissertation is to examine the morphodynamics of coevolving fluvial and hyperpycnal valleys. The dissertation consists of two parts: (i) morphodynamics of constrained valleys, and (ii) morphodynamics of free valleys. In the first part, we consider the morphodynamics in constrained valleys. Deltas and submarine breaching are the two selected subtopics for further examination. For deltas, we use microscale experiments to explore delta formations over bedrock, responding to the condition of inflow density, bed inclination and sediment influx. Similarity exact analytical solutions with two internal moving boundaries are then used to predict the delta formation over bedrock. The theory compared to those experiments in either microscale or Froude scale results in good agreement, confirming that our study is scale independent. For submarine breaching, microscale experiments and relative mechanic theory are also provided for examining the morphodynamics in submarine constrained valleys. The theory catches the trend of horizontal breaching speed and provides an insight into the velocity profile in the breaching layer. Submarine breaching with hyperpycnal flows is used to end the first part of this dissertation, and the experimental results motivate us to study the second part of this dissertation. In the second part, we look at morphodynamics in free valleys. We use microscale experiments to characterize the formation of coevolving terrestrial and submarine dynamic landscapes with a constant rainfall and uplift rate. To link these two different sedimentary environments, hyperpycnal flows are used as a physical transporter to study the sediment source-to-sink processes. During the experimental processes, hyperpycnal flows are simulated using saline water spurting out from two sprinklers above the experimental sedimentary basin, and the uplift force is modeled by a step base level falling device. With above conditions, it yields autogenic terrestrial and submarine valley-ridge systems. During the autogenic processes, the terrestrial system is forced to coalesce with the submarine system. After the completion of this coalescence, the entire landscape reaches a steady-state and coevolving phase. Through imaging measurements of the entire landscape, a series of high quality DTM are acquired and compared qualitatively with field landscapes. The preliminary comparisons are in good agreement and may help to interpret the evolution of terrestrial and submarine landscapes in the field. In conclusion, a summary gives an overview of the works and syntheses integrate the entire dissertation. Finally, possible future works are provided to end this dissertation.