Here's a doctored screen shot from NFPA #20.
If you haven't done this sort of thing before what is going to surprise you most is how large the area of the intake screens will be. With a 3,000 gpm pump they are going to be huge!
How big? You will find your answer in NFPA #20 Section 2-9.8.
2-9.8* Suction Screening.
Where the water supply is obtained from an open source such as a pond or wet pit, the passage of materials that could clog the pump shall be obstructed. Double removable intake screens shall be provided at the suction intake. Below minimum water level these screens shall have an effective net area of openings of 1 in.2 (645 mm2) for each gpm (3.785 L/min) at 150 percent of rated pump capacity. Screens shall be so arranged that they can be cleaned or repaired without disturbing the suction pipe. A brass, copper, monel, stainless steel, or other equivalent corrosion-resistant metallic material wire screen of 1/2-in. (12.7-mm) mesh and No. 10 Brown & Sharpe (B. & S.) gauge wire shall be secured to a metal frame sliding vertically at the entrance to the intake. The overall area of this particular screen shall be 1.6 times the net screen opening area. (See screen details in Figure A-4-2.2.2.)
We need an effective open area of 1 sq. in. per gpm at 150% of rated pump capacity. For a 3,000 gpm pump we need 4,500 sq. inches.
If we use the No. 10 Brown & Sharpe (B. & S.) wire mesh we have to multiply the 4,500 sq. in. by 1.6 and we end up with 7,200 sq. in. or 50 sq. ft.
This 50 sq. ft. should be available at the ponds lowest pumping level not when it is filled.
The screen can be any shape... we can have 4'-0 wide by 12'-6” high or we can square it up to 7'-0” x 7'-0” (I know, only 49 sq. ft. but close enough) and in any event it's going to be bigger then most would expect.
Here's a preliminary drawing of a pump house I did for a customer last September.
This is for a baby pump compared to the Colorado big boy. 32 sq. ft. of screen for 20 sq. ft. of opening.
2,880 sq. in. this pump was going to be 2,000 gpm but I used a different stainless steel screen and that was all I needed to get my area.
How do you figure the lowest level of water? I never thought it being the bottom of the pond because some ponds, like Lake Superior, can get pretty large. If NFPA #13 (or whatever) required a 2 hour supply I figured the where that level would be with the pump operating at 150% after two hours but you are going to want to be conservative remembering those hot summer days when pond levels can drop from evaporation and lack of rain.
On this drawing you will also notice I placed the pump close to the side of the wet well. Try to get the pump bowl a couple inches away from the side of the shaft it breaks up vortices.
Here's a pump house showing the intake screens for a 2,000 GPM diesel engine driven vertical turbine fire pump.
Here's the same pump house with the pump being installed through the roof hatch.
Another angle at the intake screens.
Here's the inside of the pump house taken during installation.
Here's a different pump I think it is a 3,000 gpm pump. This is what you would have in Colorado.
During installation here's an I-Beam base. When it came to steel I never designed it as it was beyond my capability. Turned that part of the job over to a PE so weights and thrusts would be his problem. These pumps weigh a lot.
Here's a shot looking down at the screen. It's 4'-0” wide.
A shot of the non-exciting side. Use double doors so you can remove items easily and if you opt to go with a diesel engine driven pump make sure the doors are aligned with the engine so it can be removed with a fork lift.
This is how an intake should not look. Sad to say this house had two 2,000 gpm pumps one diesel the other an electric. This intake should have been designed for 6,000 gpm and looks to me like you could barely get a jockey pump to work. Sad, sad, sad.
Ponds do take a little care and algae killer helps a lot but taken care of you can have the best fishing hole in the county.
This was one of my designs from 1982.
Here is the same installation showing what algae can do to the intake screens.
And finally the same pond a few weeks later after a much needed algae treatment.
Oh, and StoneCold , one more thing.
What about elevation? I didn't think about it before, being in the Tidewater area of southeast Georgia where everything is flat, but what is the elevation difference between where the pressure was measured and your proposed installation? Perhaps this was already calculated? Ten feet can make a big difference with 20 feet being a disaster if your site is higher then the waterline.
Night all!
