Take That, Dry Earth!
We’ve got you covered… literally. For the sake of brevity, we are talking about shaping land so simply, it has been done in most places around the Earth, by nature herself.
Look at any river on a map, and you will see carved out of valleys the undulating, curved shape of rivers. Most of them have dry times now, and some are flowing year-around. To make them flow as they were intended by nature, we have a solution that is not decades, not centuries, but millennia old.
Let’s take the many shapes of swales, or ditches dug along slopes, steep ones and lesser slopes. They can follow the hill or mountain for a few miles, and that has been done in many places starting many centuries ago. Many of those are still being used by nature. Some swales are shorter ones to serve an immediate place, or individual property. Some are so short they simply serve one tree.
All these ditches with accompanying berms of soil from the ditch forming a rim to slow down water are doing their best to slow that water so it permeates the soil and stays there rather than going away and possibly just evaporating. This can be done wherever you are, no matter what the terrain is.
What are you waiting for?