青岛沙子口近岸海域海水稀释扩散的经验模式

AN EMPIRICAL MODEL FOR THE DILUTION AND DIFFUSION BY SEAWATER IN THE NEAR SHORE AREA OF SHAZIKOU, QINGDAO

利用水中荧光计、航空摄影和陆地定位立体观测手段,于1984年和1985年在青岛沙子口近岸海域进行了数次现场示踪试验。研究了示踪剂在海水中的时空分布,计算了稀释因子、扩散方差和扩散系数及其变化规律。得到半经验、半理论的稀释扩散模式,推算出污染物的污染时间和范围。

A series of in-situ tracer experiments were made in Shazikou near-shore area in 1984 and 1985 using a towed-fluorometry, aerial-photography and land-based locating technique. Pollutants were discharged in various ways in the experiments, including instantaneous and continuous discharges with high (10-7g/ml) and low(10-9g/ml) concentrations to the near-shore as well as the offshore. In the case of instantaneous discharge, irregular elliptical patches appeared with fast diffusion along the tidal current (longitudinal direction) and slow diffusion in the direction perpendicular to the current (lateral).The patch translated with the current with an average velocity of about 40 cm/s, the horizontal diffusion coefficient ranged from 8.71 × 10-3 to 2.92×10m2/s, while that in the vertical direction was about 10-3m2/s, two orders of magnitude less than the former. The horizontal diffusion coefficient for the near-shore discharge was one order of magnitude greater than that for the offshore discharge. For the continuous discharge with high concentration (10-3g/ml), a slim plume with a width of about 100-300 meters appeared and came into equilibrium when the plume became 4 kilometers long. The concentration in the lateral section is normal with a maximum of about 10-8 g/ml at the center of the plume. For the continuous discharge with low concentration, no plume was formed and no trace of the pollutant could be found 300 meters away from the source. Therefore, this is a safe method for discharging pollutant.The concentration at the center of the patch decreased with the time raised to a negative power of 2.76. The variance for the longitudinal diffusion increased with the time raised to a positive power of 2.55. The diffusion coefficient increased with the diffusion scale raised to the power of 2.66.At No. 2 station in the offshore area where the water depth was a little more than 20 meters, a stronger thermocline existed at the layer of 5-10 meters, which obstructed as a barrier the vertical diffusion of the pollutant. An empirical model for the diffusion by the near-shore seawater was finally obtained and the duration of the pollution as well as its scope were estimated in this paper.