Processes and Landscape Structure Underlying System Scale Hydrologic Transport: Theory, Experiment, and Modeling
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Date
2018-10-25
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Johns Hopkins University
Abstract
Time-variable transit time distributions (TTDs) and StorAge
Selection (SAS) functions have been widely used to model
system scale hydrologic transport. However, these functions,
TTD and SAS, are usually calibrated and not directly
observed in unsteady systems. Also, the forms of these
functions are not well explained. In this dissertation, I
discuss hydrologic processes and landscape structure
controls on these functions as a tool to better understand
and predict system scale hydrologic transport. Specifically,
and throughout the dissertation, I provide direct
experimental observations of these functions in unsteady
systems at two spatial scales (1 square meter sloping soil lysimeter
and 330 square meter hillslopes) and explain process controls on the
forms, time variabilities, and hysteresis of these
functions, with implications to the catchment scale
dynamics. I also present hillslope scale low-order
process-based theories that provide direct links between
these functions and landscape hydraulic as well as
geomorphic structures. The theory considers subsurface
dynamics under steady state. We used it to examine specific
structure controls on the SAS function such as sloping
impermeable layer, saturated hydraulic conductivity that declines
with depth, and geomorphic structure of the hillslope.
Subsequently, a theory to predict unsteady state SAS
function is developed that considers saturated zone dynamics
in a steep homogeneous hillslope. Finally, I present an
application of the developed low-order theory-based model to
a 6300 square meter till catchment that exemplifies a practical usage
and potential advantage of the theory.
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Keywords
Hydrologic Transport, Transit Time Distribution, StorAge Selection Function, Hillslope, Catchment