Downspouts and vertical planters.

[ramblescramble]

If I only wanted a certain amount of water to enter a downspout from my roof (going to a planter) at any given time, and any extra would be diverted to a secondary downspout (going to the storm drain, or yard) how would that be possible?

I was thinking that the more water flowing along a horizontal pipe, the greater its kinetic energy, the more likely some of the water would run over a lip down into the overflow pipe, with a portion of it still going down the planter pipe. If the flow rate was at or under what I needed, the water's kinetic energy wouldn't be enough to run over the lip.

Am I overthinking it? Should I just have the water collect in a small cistern, have the overflow pipe set higher than the planter pipe, and call it a day?

 

[Danger]

Hi, RS.
How about just building a box of your preferred volume with a flapper type diverter valve on top and a dumper valve on the bottom? You can set it with a weight sensor to trip the dumper when the box is full and reposition the diverter to allow a refill.

 

[ramblescramble]

I"m more concerned with heavy rains versus light rains. If there's a massive downpour where I live, I don't want the full volume of water sheeting off my roof going into my planter where it can wreck the soil.

A box that dumps automatically doesn't really solve my problem that I can see.

 

[Danger]

Ahh... understood.
I'm not in a position right now to fully think about this, so I'm just going to brainstorm a tad. Maybe a trough with a set of holes over your garden drilled in the "top" end, but angled downward to sluice the rain away. If you have it on a pivot and spring loaded to a slight opposite tilt, medium rain would fall through on the way down, light rain would accumulate over the holes and fall down, but heavy rain would tilt it downward and drain most of it off.
That's just off the top of my head. I have other things to attend to, but I'll give it some more thought later.