Washburn Libe, McClure Kurt A, Jones Burton H, Bay Steven M
ICESS and Department of Geography, University of California, Santa Barbara, CA 93106-3060, USA.
Mar Environ Res. 2003 Jul-Aug;56(1-2):103-25. doi: 10.1016/S0141-1136(02)00327-6.
Rainfall during winter storms produces extensive turbid, freshwater plumes in the coastal waters of the Southern California Bight. When the plumes result from urban runoff they contain toxic pollutants along with pathogenic bacteria and viruses, often resulting in closure of public beaches. We examined the spatial structure and evolution of stormwater plumes in Santa Monica Bay in 1996. The plumes resulted from freshwater discharge from the Ballona Creek and Malibu Creek watersheds which supply approximately 60% of the freshwater runoff to Santa Monica Bay. The spatial scales of the plumes were determined using shipboard measurements of water properties obtained from towyo transects and surface underway sampling. Salinity maps showed that the plumes typically extended 4-7 km offshore, consistent with scaling by the internal Rossby radius of deformation. Plumes extended along shore 10 km or more. Generally the plumes occupied the upper 10 m of the water column. The persistence time of a plume offshore of Ballona Creek was about three days based on a sequence of surveys in March 1996 following rainfall of about 21 mm. Limited comparison of plumes from Ballona Creek, which drains a developed watershed, and Malibu Creek, which drains a rural watershed, suggested that Malibu Creek required greater rainfall to produce an offshore plume. A stormwater plume offshore of Malibu Creek was observed on both sides of the creek mouth, possibly due to freshwater discharge from smaller surrounding watersheds or advection of freshwater discharges from the east and south. Plumes offshore of Ballona Creek mainly resulted from the creek itself and usually extended northward from the creek mouth, consistent with the wind forcing and the Coriolis acceleration.
冬季风暴带来的降雨在南加州湾的沿海水域形成了广泛的浑浊淡水羽状流。当这些羽状流源于城市径流时，它们会携带有毒污染物以及致病细菌和病毒，常常导致公共海滩关闭。我们在1996年研究了圣莫尼卡湾雨水羽状流的空间结构和演变。这些羽状流是由巴洛纳溪和马里布溪流域的淡水排放形成的，这两条溪为圣莫尼卡湾提供了约60%的淡水径流。羽状流的空间尺度是通过对从拖曳剖面和水面航次采样获得的水体特性进行船上测量来确定的。盐度图显示，羽状流通常向近海延伸4 - 7千米，这与根据内罗斯比变形半径进行的尺度分析结果一致。羽状流沿岸延伸10千米或更长。一般来说，羽状流占据水柱上部10米。根据1996年3月在约21毫米降雨后进行的一系列调查，巴洛纳溪近海羽状流的持续时间约为三天。对来自已开发流域的巴洛纳溪和来自乡村流域的马里布溪的羽状流进行的有限比较表明，马里布溪需要更大的降雨量才能产生近海羽状流。在马里布溪河口两侧都观测到了近海雨水羽状流，这可能是由于周边较小流域的淡水排放，或者是来自东部和南部的淡水排放的平流作用。巴洛纳溪近海的羽状流主要源于该溪流本身，通常从溪口向北延伸，这与风力强迫和科里奥利加速度一致。
