lowland area has faced many water problems such as flood, drainage, water pollution, saltwater intrusion, etc. Generally, an integrated water management system is needed to solve these problems in the lowland area, both in terms of water quantity and quality. The main objective of this study is to develop the integrated water management system for Saga lowland. A comparative study between the water management systems in the Netherlands and Saga lowland is carried out. The Policy Analysis of Water Management for the Netherlands (PAWNp roject) is reviewed to clear the concept of integrated water management in lowland. The water system in Saga area is evaluated from the view point of flood control and drainage by using a computer model. Main conclusions of this study are as follow;1) New concept for water management/control system should be developed in Japan.2) Drainage system planning in Saga lowland has been limited by flood control system of the main river, in terms of design period and capacity.3) Open channel network with some facilities such as storage ponds, pumping stations, etc. are an efficient water system in lowland.4) Policy analysis of water management especially for lowland should be conducted to develop the integrated water management.
The hydrological problem of Saga area is governed by the fact that almost the area is below the Ariake sea level with the highest tide in Japan. Another problem is difficulty of supplying huge quantity of water for agriculture because of less water resources in Saga area. Therefore, open channel network system, Saga creeks, have been developed in this area. In this paper, an old system of water management on Saga creeks is described. The water management was a kind of integrated system by making use of function of Saga creeks such as drainage, storage. On the other hand, the main objective of modern and general water management is to protect flood damage caused by main river. The paper describes that, according to the modern concept, there has been many problems on drainage system in lowland especially in Saga area. Also, it is described that many factors to be cleared such as the drainage characteristic, time constant of design rainfall and the storage effect of channel network are examined. Finally, it is pointed out that the integrated water management system should be developed especially in lowland such as Saga area.
Hydrological and environmental characteristics in lowland areas are considerably different from other regions. Flood protection, drainage and irrigation works are very important for lowland development. In Japan, the main purpose of water control has been to protect flood damage caused by main rivers. On the other hand, lowland such as Saga area has been faced with many problems viz, drainage, flood control, development of water resources, etc. The main objective of this study is to develop a concept of water system in lowlands. The water system for drainage in the Saga area is evaluated by using a computer model. In this paper, the following conclusions are provided.1) The unsteady flow analysis should be applied for planning flood and drainage control of a tidal river.2) An open channel network has a function of reducing and retarding the peak discharge.3) The water system for lowlands should be constituted by open channel network with some facilities such as storage ponds, pumping stations, etc.
