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Seasonal freezing and thawing influence the hydrological regimes of winter streamflow in northeast China where abrupt increases of 1.3° C and 2.8° C in the annual and winter air temperatures have occurred since the 1990s. Correlation between winter discharge and soil freezing is based upon hydrometeorological and geocryological data for the last 40 years. A mountainous watershed is used. The active‐layer temperature is estimated by a statistical model derived from annual air temperature, its annual range and the maximum depth of snow cover in January. Results indicate an asymptotic curve between winter streamflow and both thickness of the active layer and winter temperature. They imply that winter streamflow increases with a thickening of the active layer and a decrease in the depth of seasonal frost penetration in winter. Copyright © 2003 John Wiley & Sons, Ltd.

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The efficiency of an inverted internal hydraulic jump as a mixing and dispersion mechanism in an aquatic environment was examined. The flow considered was a two‐dimensional buoyant flow from a shallow channel over a sloping bottom into a deep reservoir. It could be seen that a rapidly varied flow associated with violent turbulent mixing occurred near the point of discharge if specific discharge conditions and downstream controls were met. Downstream from the mixing zone the flow was stably stratified. The main object of the study was to find the conditions under which a turbulent mixing zone occurred and the rate of turbulent entrainment. Energy loss and length of the mixing zone were also investigated. The independent variables were the outlet densimetric Froude number, the density differential between outfall water and receiving water, the relative depths of the upper and lower layers in the stratified flow portion, the total depth, and the slope of the transition. Theoretical calculations had to be confined to a step increase in depth, but experiments in a laboratory flume showed that results obtained with slopes of 23° and 90° were quite similar. Both theory and experiments showed, for example, that dilution (entrainment rates) up to 2:1 (2 parts heated water to one part cold water) can be achieved at very little energy expense and with downstream depths approximately 8 times the outlet depth. Theoretically, any amount of dilution can be obtained, but large depths may be required. Experimental results also indicate that the length of the mixing zone was frequently ten times the value of the outlet densimetric Froude number.

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