There are a number of natural and artificially stabilized inlets in the world. Natural inlets maybe cut by natural forces such as a flooding of melting snow water, tsunami, and etc., then some of them naturally close and the rest of them keep an inlet mouth open. In addition, many inlets stabilized by single groin and double groins exist. These inlets are important geomorphological features as navigation channels and exchanging inner and outer water. Here, tidal prism data (P) and cross

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... l area (A) of inlet in Japan, China, U.S.A., New Zealand, Vietnam, and India are applied to study stability condition of natural and artificial inlets. Derived global A-P equation gives an overestimation (underestimation) of cross sectional area (A) of artificially stabilized inlets when tidal prism (P) is larger (smaller) than 2.383×10 7 (m 3 ). In addition, temporal change in A-P relation at Lake Hamana is examined.