The concave bank, called "anti-bow water" in ancient geomantic omen, is worthless and not suitable for turning into residential land.

Ancient humans had poor ability to transform nature and resist natural disasters, so they could only choose their residence depending on the established natural environment. Settlements generally require close to water sources, stable foundations and guaranteed foundations. However, the concave bank of the river is an erosion bank, and the water erosion is strong, and the bank is steep, which is not conducive to water intake. The river is easy to divert or break its banks in flood season, which is far less stable and convenient than the convex bank (river accumulation bank), so the concave bank is not conducive to the location of ancient settlements.

Shanghai, London and other big cities were originally developed from port cities, mainly considering traffic factors and using natural conditions to establish good ports. Most of the river depressions are natural harbors: the banks are steep, the water depth is deep, it is not easy to deposit, and the river surface is open and sheltered from the wind, which is conducive to shipping and berthing. At the same time, with the development of modern science and technology, the problem of running water erosion is weakened, the flood resistance of river banks is enhanced, and the safety is guaranteed.

concave bank, which is the concave bank of the coastline of the river bend. The concave bank is usually scoured by the main slide, and the water depth and velocity are large. From the shore, the convex bank is convex, and the concave bank is concave. Usually, the surface water flows from convex to concave, while the lower water flows from concave to convex. Sediment is easy to deposit on the convex bank. From the perspective of geostrophic force, the right bank of rivers in the northern hemisphere is easy to be eroded and become a concave bank, while the left bank of rivers in the southern hemisphere is easy to be eroded and become a concave bank. If the original valley has existed in the form of concave bank and convex bank in advance because of the initial topographic fluctuation and trend, then no matter which hemisphere the river is located in, the river will scour the concave bank because it keeps inertia, making the river bend out more. The Jingjiang reach of the Yangtze River in China is called the nine-bend ileum, and there are concave banks on the left and right banks of the river. This is because the curvature of the river increases and the flow rate slows down, and the geostrophic bias will not play any role.