narrow middle的意思|示意

Or you could just draw a line connecting the middle and narrow edge points and extend it to the wide side to get the same thing.

或者你可以只画一条线连接，中间窄边缘点，并将其扩展到广泛的一面得到同样的事情。

In late Holocene, climate is dryer and cooler than that in middle Holocene, the precipitation of drainage area decreases. So runoff deceases, the width of riverbed becomes narrow.

进入全新世晚期，由于气候相对于全新世中期变得较为干燥，也较为温凉，流域来水减少，故流量减小，河床宽度变小。