Bathymetry.xls
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Abstract
Surface transient storage (STS) and hyporheic transient storage (HTS) have
functional significance in stream ecology and hydrology. Both provide refugia for aquatic
communities and their longer mean residence times (compared to the main flow) increase
the potential for biogeochemical reactions that can improve water quality. As STS and
HTS have different storage and mass exchange mechanisms, hydrologists have proposed
quantitatively separating STS from HTS to better predict solute fate and transport in
streams. In addition, more accurate estimates of mass exchange parameters, such as mean residence times, are needed for STS and HTS. At present, effective solute transport
parameters are estimated either from empirical relationships or by parameterizing
effective transport metrics in solute transport models, resulting in empirical and nontransferrable parameters and an approximate equifinality in optimized numerical
solutions. Through the development of relationships using field-measureable hydraulic
and morphologic parameters, transient storage mass exchange parameters can be better
constrained in solute transport models. To develop mass exchange relationships for
transient storage, this dissertation focuses on the study of a prevalent and widelyrecognized
type of STS termed lateral cavities. Lateral cavities have flow fields characterized by a recirculation region comprised of one or more gyres and a shear layer that spans the entire entrance.
The goals of this dissertation are: (1) to develop a classification scheme that
categorizes different types of STS in fluvial systems in order to quantitatively separate
STS from HTS; and (2) to develop accurate estimates of mass exchange parameters (i.e.,
mean residence times) for lateral cavities in order to better understand and quantify solute
transport and dispersion in fluvial systems.
There are six major contributions of this work to the hydrology community. First,
to quantitatively separate STS from HTS, a fluid-mechanics-based classification scheme
is presented that identifies and categorizes different types of STS based on their
characteristic mean flow structure. The classification scheme will allow for the
systematic study of different STS types and development of predictive mean residence
time relationships. Second, the best estimate of lateral cavity mean residence time, which
represents the mean residence time of the primary gyre, is the first characteristic time of
exponential decay. Third, a cavity shape factor--ratio of the square root of cavity width
and depth to the cavity length--represents the degree of cavity equidimensionality and
best quantifies the effect of cavity shape on mean residence time. Fourth, two roughness
factors have good correlations with normalized mean residence time when computed
using the median grain diameter of sediments measured in the shear layer: ratio of
median grain diameter to channel depth and ratio of shear velocity to mean channel
velocity. Fifth, mean residence time relationships are derived for lateral cavities in open
channel flows with hydraulically smooth beds and for lateral cavities in gravel-bed rivers
and streams. The mean residence time relationships are applicable for lateral cavities over
a range of geometry, shape, roughness, and flow conditions. Sixth, cavity configuration
(e.g., series or parallel) has a greater influence on breakthrough curve shape and transport
parameters than the number of lateral cavities present. Therefore, the configuration and
interaction of transient storage zones must be considered to accurately quantify stream
solute transport and is a missing component in current solute transport theory