Portal de Periódicos da CAPES

ON WATER UTILIZATION OF IRRIGATION RESERVOIRS (II)

1975; Association of Japanese Geographers; Volume: 48; Issue: 2 Linguagem: Inglês

10.4157/grj.48.98

2185-1735

Kiyoshi Fukuda,

Energy, Environment, Agriculture Analysis

A field investigation has been underway since April 1960 of the adequacy of supplies of irrigation water from the Manno Reservoir. Using daily water level for 15 years (June 1958 to May 1973) of the reservoir, a time series analysis of water storage variation was made. A storage ratio p=Q/QU was introduced to show the variation in reservoir water storage with time, where Q is the initial water storage plus inflow minus irrigation usage for a 10-day period and QU is the total storage capacity of the reservoir for irrigation water use. Results were as follows : 1) Values of p for the reservoir ranged from 0.056 to 1.008 during the 15 years. 2) Values of p> 1.0 occurred during seventeen 10-day periods in the non-irrigation season. Out of the 15 years, 5 years had the p-value greater than 1.0 at the beginning of the irrigation season, or the first decade in June. Thus, it is evident that there was excess water which was discharged from the reservoir unused. From the standpoint of conserving water resources, a larger reservoir would be needed. However, this would require a larger dam and would involve considerable expense. 3) On the other hand, p was as low as 0.056 to 0.074 from the second decade in September to the second decade in November, in 2 out of the 15 years. Although the reservoir was nearly empty during these periods, there was no serious shortage of irrigation water, because it was at the end of the irrigation season. 4) The term p355 was defined as the minimum water storage occurring during the 355 day in an irrigation year. It is apparent that the larger the p355 value, the securer the water supplies for irrigation. The values of p355 varied from 0.08 to 0.72, with an average of 0.15 for the 15 years. 5) when water storage in the reservoir decreases below 350.0 × 104m3, water is no longer distributed to all of the irrigated areas. Most of the reduced flow goes to a small irrigated area nearest to the reservoir. Water storage used in such a manner is called “Shomonsui”. A p-value of 0.23 corresponds to the upper limit of the Shomonsui. Values of p _??_ 0.23 occurred in twenty three 10-day periods from the second period in August to the first period in April for 5 out of the 15 years. However, during the June to September irrigation period, p_??_0.23 occurred in only two 10-day periods (the second and third decade in September) for 7 out of the 15 years. From these results it is concluded that the Shomonsui having 350.0 × 104m3 in water storage is an adequate capacity for the reservoir.