TEMPORAL AND SPATIAL CHANGES IN BRAIDING INDEX OF ALLUVIAL RIVERS IN JAPAN AND THEIR REASONS

日本Meiji时代的全能河流的渠道形式，I.e.，1870 - 1910年代，假定在接近自然条件的情况下，因为没有大型水坝在Meiji时代之前和期间被构造。在1870年代以来不同年份中，34条适用河流在过去100年中使用1/50，000个主题地图出版了重复四个或九个时间的天气和空间变化。这些结果按以下顺序汇总。（1）在Meiji时代，一个河流趋势的最大值出现在通道梯度的1×10 -3通道梯度D1中，I.e.在风扇边缘的河流粒度的平均水平下降从梯度到沙子。2）在目前情况下，与Meiji时代的数据相比较，被掩盖的指数的最大值在信道梯度中的粉丝和观众中增加了3×10 -3 YieD 1中的粉丝。在任何地方，最大值都被降级为由球迷、平均平面和三角洲组成的大型平面，但它出现在同一地区，就像在Meiji时代一样。（3）在织物的构造之后，被掩盖的指数在球迷上游渠道中增加，但在平均平面上，织物对被掩盖的外表有很小的影响。4） The maximum value of sinuosity tends to appear in the channel span of 1×10イD1-3イD1 ~ 1×10イD1-4イD1 in channel gradient。这个临界点比密西西比河上的那个大。这些渠道欺诈和模糊性中的临时和空间变化可能是从1960年代以来的河流改善和水坝建设中得到的。

Channel forms of alluvial rivers in the Meiji Era of Japan, I.e. 1870〜1910's, is assumed to be under the nearly natural condition, because no large dams were constructed before and during the Meiji Era. The temporal and spatial changes in channel braiding and sinuosity of 34 alluvial river during the past about 100 years were examined with morphometry using 1/50,000 topographic maps published repeatedly four or nine times in the different years since 1870's. The results are summarized as follows. 1) in the Meiji Era, the maximum value of braided index of a river tends to appear in the channed span of 1×10ィイD1-3ィエD1 in channel gradient, I.e. at the fan margin where the mean grain size of river sediment decreases from gravel to sand. 2) In the present, as compared with the data for the Meiji Era, the maximum value of braided index has increased markedly in the fan and appears at the mid-fan of 3×10ィイD1-3ィエD1 in channel gradient. Whereas the maximum value has decreased markedly in the large plains composed of fan, meander plains and delta, but it appears at the same area as that in the Meiji Era. 3) After the construction of weirs, the braided index increase in the upstream channel of the weirs in fan, but a little effect of weirs on the braiding appears in the meander plains. 4) The maximum value of sinuosity tends to appear in the channel span of 1×10ィイD1-3ィエD1〜1×10ィイD1-4ィエD1 in channel gradient. This threshold gradient is larger than those in the Mississippi River. These temporal and spatial changes in channel braiding and sinuosity is considered to be resulted from the river improvement and dam construction since the 1960's in particular.