Rhodamine WT dye‐tracer injections in rivers of the Willamette Basin yield concentration‐time curves with characteristically long recession times suggestive of active transient storage processes. The scale of drainage areas contributing to the stream reaches studied in the Willamette Basin ranges from 10 to 12,000 km2. A transient storage assessment of the tracer studies has been completed using the U.S. Geological Survey's One‐dimensional Transport with Inflow and Storage (OTIS) model, which incorporates storage exchange and decay functions along with the traditional dispersion and advection transport equation. The analysis estimates solute transport of the dye. It identifies first‐order decay coefficients to be on the order of 10−5/sec for the nonconservative Rhodamine W.T. On an individual subreach basis, the first‐order decay is slower (typically by an order of magnitude) than the transient storage process, indicating that nonconservative tracers may be used to evaluate transient storage in rivers. In the transient storage analysis, a dimensionless parameter (As/A) expresses the spatial extent of storage zone area relative to stream cross section. In certain reaches of Willamette Basin pool‐and‐riffle, gravel‐bed rivers, this parameter was as large as 0.5. A measure of the storage exchange flux was calculated for each stream subreach in the simulation analysis. This storage exchange is shown subjectively to be higher at higher stream discharges. Hyporheic linkage between streams and subsurface flows is the probable physical mechanism contributing to a significant part of this inferred active transient storage. Hyporheic linkages are further suggested by detailed measurements of river discharge with an Acoustic Doppler Current Profiler system delineating zones in two large rivers where water alternately enters and leaves the surface channels through gravel‐and‐cobble riverbeds. Measurements show patterns of hyporheic exchange that are highly variable in time and space.
Exceedance probability.-Probability that a random event will exceed a specific magnitude in a given time period. For example, a flood with a 0.01 exceedance probability is a flood that has one chance in a hundred of being exceeded in any one year. This is a 100-year flood under the "recurrence-interval" terminology. In this report, the term "exceedance probability" is used in preference to the term llrecurrence interval." Both terms, however, are used in most of the tables, graphs, and illustrative problems. R-square.-The coefficient of determination. It is a measure of the variation explained by the regression equation. R-square x 100 yields the percent of variation explained. If R-square = 1, then 100 percent of the variation is explained by the equation; if R-square = 0.75, then 75 percent of the variation is explained by the equation. It is a "best-fit" test for the population scatter about a "I?" statistic.-A test that defines the iables. The larger the "Frl value, equation. Unless otherwise shown, 95-percent confidence limit. curve. significance of the independent varthe more significance it has in the all TF" statistics fall within the Standard error of estimate (SEE).-A statistical measure of accuracy based on population scatter about the curve only. It is the square root of the variance and is graphically defined as having two-thirds of the data points falling within its limits. Detention storage.-Storage of storm runoff from roofs, parking lots, and other impervious surfaces especially designed to reduce peak flows. Detention-storage areas normally have constricted outlets so that water will flood designated areas and flow out slowly, thereby reducing the effective flood peak. Effective impervious area (EIA).-The area, as a percentage of total drainage area, having a direct hydraulic link to the stream and impervious to the infiltration of rain. vii Typical rainfall-tunoff gage installation
At low lake elevations for Upper Klamath Lake (below 4,140 feet, Bureau of Reclamation datum), 75 percent or more of the areal extent of the lake can be affected by resuspension of bed sediment, under prevailing summer wind conditions when critical water quality conditions occur. At the minimum lake elevation of 4,137 feet, 90 percent of the lake can be affected.
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