I need some help with a calculation (and "informed guesses" based on experience also welcome), that I believe is essential for specing a pump (or pumps) for my pool. So far everything I've been able to find is very anecdotal and I would appreciate a better understanding of the "background math", if possible. This is a new area for me so please let me know if I am even approaching this the correct way and asking the right questions?

Here's the situation. I am building a perimeter negative edge pool (see http://www.troublefreepool.com/diy-p...es-t28572.html for initial posting although planned shape and size changed radically due to recently passed by-laws on "water containment vessels" and associated permit fees and property tax assessments). The Hydraulics 101 thread and a few others have been helpful in calculating flow rates (GPM) for pool turnover/filtration and in calculating volumes/dimensions for the catchment basin (pending other information from this post). The flow rate for pool turnover however is based on simply the volume of the pool with zero flow over the perimeter edge.

A few observations from other posts in TFP and some other web sites and then some details about my pool. The posted discussions usually deal with one wall or a small segment that is a negative edge. Out of curiosity, and perhaps essential in my case, are flow rates for spillage over a negative edge dependent only on the number of linear feet of negative edge or is there some "factor" included as part of the calculation for water having to spill over the entire perimeter as opposed to (for example) only one of four walls? One TFP post mentions "projects with over 100` of edge powered by a half HP pump" (but gives no further details). An article in Watershapes (ezine, August 2005) mentions "wetting" over 160 ft of perimeter negative edge using only a 3/4 HP pump with flows of 65-75 GPM (original spec was a 3HP pump). It is this latter example that interests me the most and if there is a calculation that can be done for the depth of flow over the edge (from "wetting" or, more precisely, "X" inches), the GPM entering the pool required for a depth of flow of "X" inches, and the appropriate pump to deliver it.

Pool details:

In-ground Pool: 24x13x4 (on average) = 9400 gal.

Surface area: 325 sq ft (exact)

Catchment Basin: 16x2x2.5=600 gal.

Estimated GPM for 8 hour pool/basin turnover = 21

Max GPM for Pentair CC50 filter = 50 (as an example only)

No heater

Suction vacuum cleaner

***AND***

Water feature:

- perimeter negative edge, 75 linear feet (approx.)

- water spills into perimeter gutter system about 4-6" below edge.

- "sheeting/cascading" water NOT part of the design plan.

- assume a dead level edge tolerance (not beyond my capabilities or others on the build).

The flow of water into an open topped container would equal the flow of water over its' edges given no other outlet. Even 1 GPM would overflow the edges. As would 50 and 100 GPM; but at what depth? Here's where I'm stuck and need some help. How do you calculate the flow rate entering the pool required to rise the level of water so that it flows evenly over the entire perimeter edge at a given depth? I suspect (but don't really know at this point) that 1/4" flowing over the edge would be a good starting point. What flow into the pool would support this? I'd also like to know the calculation/requirement for a flow of 1/8" and 1/2".

Look forward to hearing from you or if you can point me in a direction to find out more. Thanks for stopping by and reading the post.