Positive Studies on the　Formation of Surplus Water Reguirement (Part 3 ) : On the Variable Characteristic of Net Water Requiremen

ln this paper, the variable characteristic of net water requirement was explained by means of case study and theoretical study. In chap. 1, problem and method of the study were descrived. In chap.2, three elements which make up net water reguirement (paddy field area, repeating use of water and water requirement in depth) were explained. Water requirement in depth was especially discussed in connection with urbanization. In chap. 3, qualitative analysis of the variable characteristic of net water requirement was tried in case studies of the SHINAN water use district, OSAKA pref. and the KAMEDAGO water use district. NIIGATA Pref.. In chap. 4, a basic theory of the variable characterristic was proposed.Then, quantity of discharge was estimated with net water requirement. In chap.5, this basic theory was applied to the case of the JUGOKA water district. AICHI Pref.. Brief contents of this paper area as follows ; 1. In districts where repeated use of water is done, decrease of paddy field area is not always combined with los in quantity of net water requirement. 2. The net water requirment possibly increases under reduction of repeated use. Then, new water demand occurs. 3. In the phase of decreasing net water requirement, obligatory quantity of discharge sets limits to form the surplus water requirement. In the case of exsitence of obligatory, the efficiency of occurrence of surplus water requirement decreases. 4. Thus, the occurrence of surplus water requirement is controled by three elements; paddy field area, repeated use of water and obligatory quantity of discharge. The variation of water requirement in depth makes the variable curves of net water requirement and discharge to rise or fall