Round bottoms are better than angular bottoms (see picure 1). Especially where soils are concerned. By round we mean the soil particles (see Picture 2). Angularity in soil particles is due to compaction and mechanical intervention to break up soil into smaller particles, however this creates very small surface area as particles themselves are large. Roundness of soil particles is related to biological action by soil organism as in worm action. The fact that worms ingest soils and extract nutrients like carbohydrates, amino acids, fats etc. from the soil. Makes the soil, coming out of their derriere increase its biological active surface area. The action of their digestive system has been shown to make elements like Phosphorus up to 9 times more available to the plant. On top of increased nutrient availability. Worms due to their burrowing action, creating worm Holes and Channels, which will increase the Water and Air infiltration rate. This helps the soil to breathe and take more water. Both of which are essential for good crop growth and preventing drought as well as flooding caused by excessive rainfall and runoff. It is not uncommon for really active worm riddled soils to have the ability to absorb over 8″ of water per hour.
Hence these soils have the capacity to prevent flooding when managed properly, as well as providing aeration and increased nutrient availability.
Hence next time you look at your soil. Check for worm casts on top and the structure of the soil further down.