this is not the first time recently i've heard about how part of the solution is slowing water to return some to the aquifer but it's essential to understand that changing the rate of flow of water also changes sediment deposition rates, which can have enormous impacts on ecosystems, power production, agriculture, and a bunch of other things. It isn't a dial you get to just arbitrarily tweak.
The best example of “slowing down water” would be what beavers do. The results are not so straightforward, even with taking deposition as an outcome. Beavers following their instincts result in complex yet resilient landscapes that supports woodlands.
I think the pattern of simplification you are talking about is thoroughly explored in James C Scott’s Seeing Like a State, where complex systems are too complex for the governing body, and made legible through oversimplification. Actions are undertaken on the basis of the oversimplication. The results are disastrous. There are many historical examples. I was not talking about “slowing down water” in that way, though I get people might take it that way.
In areas with poor soil, increased deposition is a desirable thing in many cases. Extreme cases like wasteland and erosion that exposes bare bedrock, you need all the deposition you can get (until the land can support an ecosystem again)
More importantly, the design patterns I am thinking of involves the accumulation of organic material. The overall goal and metrics isn’t just slowing down water, but rather, restoring soil health to support an ecosystem, which in turn, helps regulate water.
You wouldn’t necessarily slow down the river. You start with slowing things down onsite where the land receives rainfall. And you definitely want to avoid having soil wash away to be deposited downstream.
Every site is different, and requires intense observation and unique designs using working principles — that’s design principle #1 of permaculture design, “observe and interact”.
It's crazy visiting China and southeast Asia, seeing entire hill ranges terraced (in the same way that farm fields would be divided in the UK or US), and realizing just how old those terraces are.
Makes you appreciate how old of a technology farming is.
Andrew Millison has a great video about designing with slope. This includes a brief discussion about the steep slope found in the rice terraces of Southern China
