Water Exchange and Material Exchange through a Strait due to Tidal Flow

Abstract

The process of material transport through a strait due to tidal flow is modeled, and then the differences between various concepts of tidal exchange which have been usedhitherto are pointed out using this model. In particular, the exchange of water itself andthe exchange of material should be distinguished even in the case where the material ofinterest is carried by the water, i.e., the material and water move as one body. Further, the physical meaning of “tidal trapping” (Fischer et al., 1979) is discussed by using the modelin this paper. The relationship between the exchange ratio for the water itself (r) and thephase lag (δ) of material concentration to the tidal stream in a section of the strait, whichis an important factor in tidal trapping, is obtained as follows:
δ=tan^-1 (1/r-1).
Observational results at Lake Hamana (Shizuoka Pref.) and at Kabira Cove (Okinawa Pref.) support the validity of the above relationship.