In order to further analyze the composition of downstream station flood, first we must understand the flood propagation characteristics of the Nen River, the second Songhua River and the main stream of Songhua River. After the Nen River flood running out of Ayanqian and into the plains, the water surface becomes very wide, generally up to several kilometers, the widest reach up to more than 10 kilometers. And there are many swamps and lowlands on both sides of the river. Therefore, the channel has a strong storage effect, significantly in flood regulating effect. And the slope is very small, the average ratio below Fulaerji dropped to 1.5U, causing the flood peak velocity to become very slow, and it takes 17 days from Kumo county to the mouth of Nen River.
In the second Songhua River basin, from Fengman dam to the mouth of Mushi River is a hilly area, and below the mouth of Mushi River is the plain. The river widens and with a varieties of ditches, river islands and bifurcation river roads, and Oxbow lakes, swamps and blisters. Therefore, the strong storage effect of the channel has a better effect in the middle reaches, and the transfer time is short in the middle reach.
The main stream of Songhua River basically belongs to the wide and shallow river plain, and is rich in river branches, sand beaches, and central beaches. The beaches of the two sides are wide, so the flood spreads slowly.
To sum up, it takes 23 days to transfer the flood from Kumo county of Nen River to Harbin station; it takes 15 days from Fengman station to Harbin station; it takes 4 days from Caijiagou station to Harbin; it takes 2 days from the west Hulan station to the mouth of Hulan station; and it takes 1 day from Changjiang county station to Yilan station.
It should be noted that the flood, the time for severe floods transferring is shorter, the time for small and medium-sized floods should be slightly longer.
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