Nobuhiro Yotsukura

Field Techniques for Reaeration Measurements in Rivers

Dissolved oxygen is an important measure of water quality in rivers, and surface reaeration is an important source of dissolved oxygen. In conducting reaeration experiments, it is important to consider transport and mixing to determine whether one- or two-dimensional distributions are likely to exist. The three primary methods that have been used for reaeration measurements are based on oxygen balances, disturbed equilibrium, and tracer gases. The oxygen balance approach is not widely used now because of the potentially large errors associated with the many sources and sinks of oxygen which must be evaluated. If temporal variations of dissolved oxygen exist, the disturbed equilibrium method suffers from the conflicting requirements of a short travel time for estimation of natural dissolved oxygen concentrations and long travel time for error considerations. Although all questions concerning tracer gas techniques have not been addressed, these techniques seem to hold the greatest promise for reliable gas transfer measurements under field conditions. For each of the methods, it is possible to analyze the propagation of random measurement errors to estimate the error bounds on gas transfer coefficients.

A Tracer Simulation of Waste Transport in the Muddy Creek-Rhode River Estuary, Maryland

A small quantity of Rhodamine WT dye was injected at the headwater of the Muddy Creek estuary and concentration of the dispersed dye was measured with a uniform time interval at a number of fixed locations in the lower portion of the estuary. By the use of the superposition principle of a linear system, the built-up concentration of the dye is found to range from 8 ppb at 1,900 feet downstream from the confluence of the north and south forks of Muddy Creek to 2 ppb near the Smithsonian Institutions pier in the Rhode River, provided that the dye is continuously injected at the headwaters at the rate of one pound per two tidal cycles.