slowing down seasonal streams on the wet side?

One rock dams and such come up a lot when discussing greening the desert. I haven't seen or heard of anyone slowing down intermittent or seasonal streams on the wet side of the cascades but I'd love to know if anyone has any experience with this or thoughts (yes, I know it's probably illegal, this is for hypothetical purposes only). If anyone has feelings of why this shouldn't be done for ecological reasons, I'd love to hear about that too. thanks! zZz

I dont quite understand what you are describing.

I have done some research and realise what you are talking about.
Nothing is illegal about it and there are no ecological downsides to it.
In fact it is used very widely by man in degraded areas and occurs naturally in nature.
The way its used depends on the topography, so I will deal with 2 easy ones, slopes and flat country.
IN FLAT COUNTRY WHERE OVERGRAZING AND WIND HAS DESTROYED AND BLOWN EVERYTHING AWAY, a single row of rocks garnered from THE degraded land
can catch dust, organic matter, seeds and water to just improve the small area upstream of the rocks.
Over time things get better. If many of these 'walls' are established the area can improve.
If a plant like vivtar is added later, its very deep rooted and resilient and will improve the catching ability of the system.
In some areas, small hat sized holes will also be dug to catch and hold water, dust and organic material that enables food to be grown over time.
SLOWLY and Slowly the area will improve.
ON SLOPES FAST MOVING WATER IS THE PROBLEM
Once water gets to about 4 feet per second velocity it can pick up or roll soil particles and thus erosion starts.
By building walls of any type, the water can be slowed down, sediment will stop eroding and drop in to the water course.
As the wall is added to the process slowly improves the water table and the soil quality.
This Video shows some of the techniques I am speaking of.

Here on the wet side we also have a dry season of 3 to 4 months.  Before modern clear cutting and agriculture intervened trees would fall and rock or land slides would occur or beavers would build dams and slow winter streams creating deeper soils.  My farm has a flat clay field that was an ancient lake bottom, it had a natural zig zag swale pattern but for plowing purposes it was diched for rapid drainage and spring plowing resulting in it drying out during early summer by blocking or filling the ditches the natural flow leaves shallow ponds that remain into July and the field may remain green into August or even until the rain returns in September.
On another property a year round spring ran to the salt water.  We would regularly block the flow with rocks or logs to divert it to different gardens and orchards down the slope. The water would soak into the sandy soil and travel along the impervious layer until it came out near the beach.  So with observation and design the natural prosses can be enhanced for greater productivity and sustainability.

There is absolutely precedence for slowing down creeks on the east and west sides of the state. The book Eager (I would really encourage it), is a book about Beavers and the geomorphology of waterways. The emphasis though is on the impact of slowing water down on the ecosystem. Working with local fisheries agencies I was able to get a grant to rebuild the watershed here on my land Basalt Blossom, which includes creating significant natural barriers using logs and boulders.

*In late spring I will be posting some workshop opportunities on building natural barriers and beaver damn analogues.

Scotty-

Since you already know about rock dams her is some information on brush dams and check dams that you or others might find interesting:

https://permies.com/t/51421/Creek-repair-brush-dams

https://permies.com/t/142672/slow-storm-water-flow-culvert#1155272

https://permies.com/t/45355/Geoff-Lawton-Check-Dams-Video