1. What size pump do I need? It would run about 40 feet, including about 10 feet of total rise (somewhere on the internets I came across this wording: "The general rule on pond pumps is 10 feet of horizontal length reduces water flow as much a 1 foot of height from the pump does."). I'd prefer a medium-to-fast flow.
Pump flow will be 100% dependent on the style of waterfall you want coming down the tiers but a bare minimum recommendation is 100gph ... 150gph avg ... 200gph high. So if at any given point you're expecting a 5' wide solid sheet of water, then you're immediately looking at 9000 to 12000 & that's AFTER you've overcome all the friction loss. You're right, generally, 10' of horizontal run = 1' of vertical rise. Keep in mind each & every 90deg elbow will slap on another 1' of rise. Add those to the actual 10' of vertical rise. With such flows, oftentimes 2 pumps will be more energy efficient than 1 large pump. Another option is to consider a variable speed pump ... reason for this is that projects start w/lofty intentions, then the sound of water & resonance in the backyard can actually get too distracting (sometimes even obnoxious) for you or your neighbors. It's fun to have a variable speed pump so you can dial it down for a calm evening or dial it up for a big hoopla-of-a-dinner party!
2. What tube type/diameter do I need to bring the water from the pump to the source?
Once the pump(s) is determined, the pipe/tubing size can be ascertained.
- 1.5" will allow a max flow of 3000gph
- 2" will allow a max flow of 4800gph
- 3" will allow a max flow of 9000gph
- 4" will allow a max flow of 12000gph
Sometimes it costs LESS $ using qty (3) 2" pipes to get you to 14000+ gph (in terms of pipe costs as well as escalated pricing on fitting costs!) the price of fittings jump DRAMATICALLY when you go from 2" to 3" or 4"!
3. Would there be a problem with splitting the pipe three ways so the water would flow into three separate streams (as seen in the diagram)?
No not at all ... ball valve controls needed for all 3 but that's it. Limit the amount of 90deg elbows ... if you want to (or need to) reduce the amount of friction loss, use two 45deg elbows or long sweep elbows versus your standard 90deg elbow.
4. How deep does my basin need to be?
My recommendation for all pondless projects is that the basin should comfortably hold 3x the volume of water of everything up stream! This includes the volume of water in your pipe -- even if you use a check valve assembly.
5. Are Water matrix blocks really needed, or would milk crates or plastic pipes be enough?
Personally, I say yes. Although all plastics can crack, there's two MAJOR manufacturers of matrix-style boxes & both are tested w/enormous compaction strength. The units are carried over from industrial drainage & water applications & are often used underneath drives & parking applications. The LAX airport uses them over where utility vehicles drive. The danger in milk crates is the grade of plastic degrades quickly & can crack -- major child/adult/pet safety issue if people walk around the basin that has milk crates w/hundreds of pounds of river rocks & cobbles over the top.
An alternative is to fill the entire basin w/rocks & gravel but that alone is a back breaking NIGHTMARE! 1cu foot of river rock holds approximately 2.2gal of water ... whereas 1cu foot of matrix blocks holds 7.4gal. This means using a matrix you can get away w/a smaller basin foot-print.
Also a lot less prone for clogging over time.
6. I read some of the horror stories on here of people who didn't reinforce their sides. Would that be necessary in the Texas limestone, for a pondless construction? My gut says no (it's solid rock under the ground here, I had to rent a jackhammer to dig out what I've dug so far) but I wanted to see if anyone's had a problem.
Doesn't sound like reinforcing will be an issue considering #1, the nature of your soil & #2, the void will be filled w/matrix blocks w/ a top dressing layer of river rocks & cobbles?