【摘要】 <正> 河口区域,上连淡水源(江河),下接咸水源(海洋)。上游的淡水既要通过这里输向海洋,下游的海水也将以这一种或那一种方式,进入本区(详见第一节)。咸、淡水既在这里交汇,它们之间便要发生混合交换。而在有潮河口区域内,则由于涨、落潮的作用,使海水周期性侵入这一区域,这不但加强了咸、淡水的交换作用,而且,其混合的过程也极为明显。因此,这类区域一向被认为是研究咸、淡水交换并了解其混合过程的一个理想区域。海洋学上,并特将有潮河口区域咸、淡水的交换过程,称之为“潮泛混合”(tidal flushing),或“潮混合”(tidal mixing)。更多还原

【Abstract】 Hangchow Bay (the estuary of the Chientang River) is the largest bay of the southeast China. It is well known for its world famous bore (the Chientang-kiang Bore). Recent observations revealed that tidal currents here are also considerably strong. It is therefore reasonable to expect that the tidal flushing here ought to be very strong, and thus this area affords an ideal location for studying the flushing problems (the exchange of fresh and salt waters, of dissolved and suspended materials, the distribution of planktons, etc.). This paper, however, only intends to deal with the exchange of fresh and salt waters in the upper part of the Bay, i.e. the upper estuary. It is the wish of these authors that this preliminary study may give some insight into the detailed mechanism involved in the tidal flushing of the whole Bay area. Such knowledge, particularly if combines with the knowledge of estuarine circulation, no doubt, will have great interests, both theoretically and practically.The main body of this article is divided into three parts. In the first section, theessential features of the three fundamental types of mixing in a tidal estuary--i.e. thenegligible mixing type, the moderate mixing type, the strong mixing type--are brieflyreviewed, and the general characteristics of salinity (or chlorinity) distributions of Hang-chow Bay are outlined. It is found that the distribution pattern of chlorinity in the upper estuary is rather simple--the vertical as well as lateral variations are small compared to the longitudinal variation--and, for a good first approximation, this area maybe regarded as an estuary of strong mixing type. On the contrary, the salinity distribution in the lower estuary is much more complicated, therefore, further studies should be made and those results will be reported later.In the second section, the existing theories of strong mixing type are critically reviewed and their applicabilities to the upper estuary of Hangchow Bay are discussed in full detail. Results show that the empirical theory of B. H. Ketchum cannot be applied to this area, though Ketchum claimed that his theory fitted remarkably well to the observed data of five estuaries of different nature in North America. It is these author’s opinion that the inapplicability of Ketchum’s theory in this area may partially be accounted for by the large fluctuation of the fresh water flow of the Chientang River, the lack of detailed informations on topography and tides of the investigated area, etc. The mixing length theory of tidal flushing advanced by A. B. Arons and H. Stommel for a model estuary (of constant depth, constant width, and equal tidal range) may, in principle, be extended to a real estuary through the introduction of a certain working formula. By so doing, however, the upper limit of salt water intrusion (which is the origin of the coordinate system in the fundamental equation of the mixing length theory) must be known. Owing to the lack of sufficient observations of chlorinity in this area, this upper limit cannot be ascertained. Under these circumstances, in order to examine whether the mixing length theory can actually be applied to this area or not, we must first determine location of this upper limit.In the third section of this paper, we first derived an empirical formula (in the form of logarithmic deformed hyperbolic curves) for expressing the longitudinal chlorinity distribution in the upper estuary of Hanchow Bay, by employment of available chlorinity data at shore stations (twelve months in total). By so doing, we are able to determine the approximate location of the upper limit of salt water intrusion of Hanchow Bay, by means of extrapolation.It can be shown that our empirical distribution of chlorinity is analogous to the analytical solution of Arons and Stommel’s mixing length theory for a model estuary. It is rather striking to find that with exception of a few points, all of our twelve calculated curves fit the observed data so well. It proves that Arons and Stommel’s mixing length theory for a model estuary is app更多还原