Experimental analysis on the change of groundwater in tidal river zone and studies on the optimum estimation ・ control

本研究的目的是对退耕还林还草过程中的几个问题进行研究。调查区域为新开、南国朝、米亚扎基。调查内容如下。排水沟中的水流状态。2.排水沟深度与海平面的关系。3.排水渠糙率系数。4.地下水位的变化。5.地下水的流动状态。6.地下水含盐量的变化。7.海水入侵情况。8.土壤调查。9.泵出水的仿真。1)小潮时排水沟水深变化大于大潮时；2)小潮时海水入侵距离大于大潮时。这种海水入侵提高了海水的盐度稠度，这是造成作物盐害的原因之一。3)排水沟糙率系数为0.025~0.055。该实验值与开挖渠道糙率系数标准值吻合较好。4)地下水对排水渠道周边的含盐性有很大提高。5)地下水的流动随着降雨、灌溉和干旱天气的出现而呈现出自己的特点。6)排水渠道(开挖工程)中的土壤清除成为地下水下降和土壤淡化的一种非常有用的方法。

The purpose of the present investigation is study about a few problems in the connection with the conversion of field into multipurpose one. The area of investigation is the SHINKAI,NANGO-cHo,MIYAZAKI.The contents of the investigation are as follows.1. the state of the flow in drainage channel. 2. The relationship of the depth in drainage channel and sea level. 3. The coeffecient of the roughness of drainage channel. 4. The change of ground-water table. 5. The state of the flow on groundwater. 6. The change of the salinity consistency of groundwater. 7. The state of the sea-water intrusion. 8. The investigation of the soil. 9. the simulation of the pump out water. 10. the runoff analysis.The results of the experiment are summarized as follows.1) The change of depth in drainage channel at the neap tide time is larger than the spring tide time.2) The sea-water intrusion distance at the neap tide time is longer than the spring tide time. this sea-water intrution raise the salinity consistency of the sea-water and this phenomenon is one of the cause for the salt injury to the crops.3) The coefficient of roughness on drainage channel is the value of 0.025-0.055. This experimental values agree well with a standard values of the coefficient of roughness on the excavation channel.4) The salinity consistency of groundwater to the circumference of drainage channel if very raise. but, as reduse in the distatnce from drainage channel have a tendency to become low.5) The flow of groundwater shows its own characteristics with the rainfall,irrigation and dry weather period.6) The removal of the soil in drainage channel (the excavation works) becomes a very useful method for the drop of the groundwater and the desalinization of soil.