We had a client who wanted to create a new dam around a small existing dam – and he asked if that was a good idea.
Long story short, the answer is no – because dams need separation from each other and ignoring this demand is one of the most common dam-building mistakes.
So how Joining Dams contradicts physics laws?
The reason being, in hydrology physics and the study of morphology (form & structure) of dam wall design, you need a wet side and a dry side.
This is because of the real world environmental concepts of transpiration & evapotranspiration. In dam wall design, we use the concept of bio-mimickery to successfully replicate these two processes to ensure dam wall stability
Transpiration is the process of water movement through a dam wall from the wet side to the dry side.
Evapotranspiration is the sum of transpiration plus evaporation
These concepts are relevant because water saturation is necessary for dam wall stability & structural integrity – but it needs constant slow movement through the dam wall to avoid settling.
A wet wall and a dry wall achieves this by drawing the water through the wall (transpiration) and disposing of it at the end of its journey as it exits the dry side (evapotranspiration)
When you have two wet sides and that’s what happens when you are joining dams, the water does not egress, and the wall will be subject to static saturation – and will eventually slump and collapse, so joining dams can turn into a complete disaster.
The most practical analogy is to imagine a swamp.
You will never see a hill or a mound in a swamp because the soil material in that swamp lacks integrity due to constant static saturation. Everything in a swamp reduces to the level of least integrity – which is the water level
What does all this mean?
It just means that you should put a swale system (growing area) between the two dams
This growing area will not only take advantage of the overflow, but it will also allow separation between the dams
Then healthy transpiration will take place, and your dam wall will be internally saturated and stable. It will also not suffer summer surface cracking due to the internal moisture contained in the wall