Abstract
Irrigation water takes the greater part of utilization and consumption of water resources in this country, and moreover, the irrigation water use has been supported by the conventional water right for a longtime.
Recently, owing to the rapid increase of demand for municipal water and irrigation water with the new development of city industry and agriculture, there has been built many new dams in the upper parts of rivers and the utilization facilities in lakes in the lower reaches of rivers as the countermeasures to meet the above increase.
Even though such measures has already been adopted, there seems to be great necessity to promote rationalization in the agricultural water use by the new method such as repeated use of irrigation water.
The author, therefore, wants to grasp feasible quantity in the repeated use of irrigation water in connection with quantity of water consumption in irrigation.
The area of about 8, 000 ha.(mainly paddy fields and partly upland fields) in the upper stream of the Naka River in Saitama Prefecture was chosen as the object area of the investigation in this purpose, and the fundamental factors such as quantity of rainfall, evaporation, intake flow, drainage discharge, groundwater flow and land area by kinds were clarified in detail. In addition to the above measurement the quantity of evaporation from the rice plants in the paddy fields was observed by a new equipment named “Chamber”.
The results of the examination by statistics clarified the actual proof as follows: It is possible to utilize the formula of water balance for planning irrigation projects, if 5-day period is adapted as a unit for calculation of water balance, since the variation of stored water on the surface of paddy fields in the period is negligible.
The application of the calculation formula of water balance for irrigation plannings was also examined by the studies concerning the variation of stored water on the surface of paddy fields after rainfalls or continuous drought days.
