By Mollison.
The top drawing, a schematic of a dam, shows how to safely build a small dam. The “key” in the center acts in a similar way to a lego block, preventing water from seeping in between the new soil that makes the dam, and the original soil below it.
The dam is 3 times wider than it is high, which adds further strength. There are spillways and overflow drains built in so that you control exactly where the water goes when it overflows.
Building keypoint dams or any other type of dam of any size takes training to build properly. Large dams need engineers. I’m sharing some very basic information here, because it’s possible to use these principles, like spillways and thickness and shape of walls on smaller scale systems on an suburban lot for instance, and increase your success.
The illustration A-D shows clearly that when you place a dam in a keypoint, which tends to be a flatter place in the landscape, you capture a lot more water, with a lot less engineering needed than if you place a dam on a steeper slope.
Hands On Activity
Find a downslope near a tree or bush. Place two logs or several rocks in a V or circle formation on the downslope behind the tree. Observe over time if you are getting a build up of organic material or if the area stays moist, longer than surrounding areas. This could be a long term exercise done over weeks, months or even years. It’s an observation exercise that will give you a much deeper understanding of your land and how water relates to it. This is an example of where keeping a journal will come in handy.
Further Resources
How to build a one rock dam:
https://regenerativeskills.com/how-to-build-a-one-rock-dam-to-regenerate-an-erosion-area/
Article on successful methods for minimally invasive water catchment and erosion control:
https://www.researchgate.net/publication/325651474_Hand-Built_Structures_for_Restoring_Degraded_Meadows_in_Sagebrush_Rangelands_Examples_and_lessons_learned_from_the_