Geoscience Reference
In-Depth Information
Integrated Experimental and Computational
Hydraulic Science in a Unique Natural
Laboratory
J.R. Manson, B.O.L. Demars, and S.G. Wallis
1
Introduction
This chapter is concerned with the initial stage of investigations into stream
metabolism, which can be studied by quantifying the fate and transport of dissolved
oxygen. In this, for a given stream reach we would perform an oxygen mass balance
to determine the rate of endogenous oxygen production (photosynthesis) and
consumption (respiration). Before undertaking the oxygen mass balance, however,
we need to determine the flow and transport characteristics of the stream, such as
discharge, lateral inflow, velocity, surface gas exchange, mixing rates, relative
volumes of flowing versus stagnant stream water, etc. Some of these quantities
are required in order to perform the oxygen mass balance; others are determined
because we hypothesise that they directly influence stream metabolism and there-
fore will be useful correlates. Most of these characterising parameters may be found
through the analysis of tracer experiments. In such experiments, we release a
discrete (known) mass of tracer and then measure tracer concentration-time profiles
at locations downstream of the tracer release site. In this study, we obtain these
parameters by fitting a computational stream transport model to the tracer data. This
requires an efficient and accurate numerical solution of the advection-dispersion-
transient storage equation and a reliable optimisation approach. The aim of this
chapter is to describe our integrated experimental and computational approach and
to present the findings for the study site in question. Because we performed these
experiments twice (in early spring and in late summer), we are able to discuss
