On the Mechanism of Hydrological Cycle in Reclaimed Upland Fields

填海造地工程不仅改变了流域的地理特征，而且改变了流域的水循环结构。这些变化导致了径流特性的变化。为了验证这一点，在京都北部的Tango国家复垦项目区设置了三个小型径流试验区(其中两个是复垦旱地，其余是林区)，并在这些试验区进行了土壤和径流试验。复垦和非复垦样地的土壤试验结果如下：1.由于围垦后土壤A0和/或A1层的去除和土壤固相比例的增加，土壤持水能力降低。由于使用大型施工机械进行各种围垦工程，土壤的渗透性也降低了。河道和农家路的修建也导致了复垦地块的允许流量和持水能力的下降。研究结果如下：1.复垦后的洪峰流量明显增加。这反映了上述土壤物理性质的变化所导致的浓缩时间缩短和峰值流量系数增大。由于调查期间缺乏水文记录，枯水性质的变化尚不清楚，但已发现流量退缩常数的微小变化。在复垦地下游建造沉淀池，在干旱地区防治旱灾和补充低水都是非常有效的。

Not only geographical features but also structures of water cycle of river catchments change due to the land reclamation works. And these changes lead the change in runoff properties. To examine this, three small runoff test plots (two of them are reclaimed upland fields and the rest is forestry area) were set in the Tango national reclamation project area in northern part of Kyoto prefecture, and soil and runoff experiments were conducted in these plots.The results of soil tests in both the reclaimed and the non-reclaimed plots are as follows;1. Water holding capacity has been lowered due to the removal of A0 and/or A1 horizons and the increase of the solid-phase percentage of soil after the reclamation.2. Soil permiability has been also lowered due to the various reclamation works with the large construction machinery.3. Construction of water channels and farm roads have also led to the decrease of permiability and water holding capacity of reclaimed plots.The results of investigations for the runoff properties are as follows;1. Peak discharge increased much due to the reclamation. Thiswas a reflection of the decrease of concentration time and the increase of coefficient of peak discharge which were led by the change in soil physical properties described above.2. Though change in low water properties has not been clarified yet because of the shortage of hydrological records during the investigating periods, a slight change in the recession constant of discharge have been recognized.3. Settling basins constructed in the downstream of reclaimed plots have been much efficient both for fllog control and for low-water supplement in drought seacon.