The isolating property of enclosed bays, which cuts off the connection with the open sea by the topographical constriction at the bay mouth, affects strongly the cultural environment in the bay not only positively but also negatively. In order to prevent the retrogradation of culture farm and to maintain the sound cultural environment, it needs to understand quantitatively the physical processes in enclosed bays. In this paper, the observational results in Yamada Bay of Sanriku Coast are introduced as one of examples of oyster culture farm developed in many enclosed bays. The steady process and the transitory process in the onclosed bay play respectively important roles in formation and change of the cultural environment. The tide is weak in the enclosed bay, but steadily acts to form the cultural environment over a long term. On the other hand, the actions such as an intemal Seiche (an intemal standing wave) and the Kyucho (a stomy current) tend to be overlooked because of transitory event, but their energies disturb suddenly the cultural environment which has been formed by the steady process. Further the interaction between the steady process and the transitory process is also important to form the cultural environment in enclosed bays.
