Water volume needed for rock wall feature

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  #1  
Old 02-05-11, 04:44 PM
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Water volume needed for rock wall feature

Hi everyone. I am trying to construct a 'water feature' wall. My intention is to have water overflow a channel at the top of a wall, and flow/tumble gently down the vertical, rock faced, surface. The wall is to be 20 ft long and 8 feet high. The reservoir/pool at the bottom will be hidden. My problem is trying to find out the size of pump I will need in order to keep the entire face of the wall wet at all times ie: what size of pump do I need. The pumping elevation is 8 ft and the horizontal travel is virtually nil. What gpm or gph do I need?

Thanks Mark
 
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  #2  
Old 02-06-11, 04:43 AM
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Keeping the entire rock wall wet at all times will depend quite a bit on how the rock wall is made. Can you post a picture of the wall? A rough rock texture will take considerably more water than a smooth face.

You will need about 100 gallons per minute for every 1/8" of water thickness going over the edge of your weir.
 
  #3  
Old 02-06-11, 05:26 PM
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Thanks, Pilot Dave.

No photos available right now as wall is under construction, in Mexico, as we speak. I am currently in the US and will purchase a pump to take back with me next week. The rock used for suface is reasonably smooth in texture. There will be, however, spaces, both vertical and horizontal, between the facing rocks. The rock is natural, somewhat slate like in form, and the pieces will vary considerably in size dimensions. There will be no mortar showing on the finished surfaces, but rather crevices will show.

I am guessing that the vertical spaces will allow the water to fall more quickly than the water running on a smooth rock surface, but at the same time the rocks will form little dams and thus slow the fall considerably, as will the horizontal spaces. I am also guessing that on start up, it will take a couple of minutes for the wall to retain the water, and thus the flow required would appear less than needed, but once the water has filled the crevices, I am figuring the flow rate would settle out.

I won't be able to 'try' a pump and go back for a larger or smaller one, if needed, so I would prefer to buy over sized than undersized. I plan on installing an exhaust/escape T in line to the weir (with the vertical leg of the T having a tap in it to be able to adjust the water escaping back into the tank). In this way if I am over sized I can regulate the water supply to the weir while allowing the pump the run smoothly/normally without 'back pressure' being created by restricting the flow to the weir.

Any more or new info/advice will be appreciated.
 
  #4  
Old 02-06-11, 06:37 PM
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I am assuming I've not said anything you don't already know but it's a tough call. Slight irregularities in the surface can wreak havoc on a smooth even flow. You are correct thinking go big with the pump and throttle it down as needed. What's the biggest pump you can fit in your checked luggage?
 
  #5  
Old 02-06-11, 07:55 PM
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Not sure, but could probably get even a 5 horse or something similarly goofy. Am going to drive the pump suppliers crazy this week with my questions, but once I decide, probably around a 1 hp ( somewhere around 100 to 150 gpm) , I'll let you know.
 
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