Current Channels / Lazy Rivers

In lazy rivers or current channels that are not a closed loop, a nozzle should be placed immediately after that opening to try and prevent “dead-spots”. Main drains should be designed at the end of the river.  Nozzles should be placed after the main drains, not before.

Skimmers or weirs should be used around the perimeter of the river. Do not design a gutter or single trench drain if it can be avoided.

River nozzles should be placed along the inside of the river wherever possible to avoid the gutter. If the nozzles need to be along the outside of the river, the upper nozzle should be lowered 6”.  CH’s detail shows the centerline of the top nozzle 12” below the waterline.  If this dimension is lowered to 18”, there should be 2” cover between the top of the pipe and the bottom of a 12” deep gutter.

The river nozzles will be installed at an angle of 15 to 30 degrees from the pool wall. The 15° to 30° angle results in piping that exits the back of the wall between 29” and 14” behind the nozzle opening.  A greater angle will result is less propulsion, and a lesser angle will create difficulties with installation/conflicts with rebar inside the wall.

Minimum wall thickness for a river/channel should be 18”. This wall thickness should provide sufficient room to install the supply piping for the river nozzles.

The primary controlling factor in providing propulsion to the river is kinetic energy (KE = ½ mv2) of which V is the controlling factor.  In this case V is the velocity coming out of the 3" pipe and currently that is 10.8 ft/sec.  Changing the pipe diameter to 2-1/2" would increase velocity to 15.5ft/sec.  The difference in the squares of these two numbers doubles the kinetic energy put into the river.

The ASTM standard on maximum jet pressure is 20 ft/sec. This standard originated from the water sprayground industry and kids putting their eye in front of jets.

  • Propulsion inlet velocity is critical. This needs to be between 15-20 ft/sec.  Using 1750 GPM as a design point is helpful because inlet diameters of 2”, 2-1/2” or 3” works well with this pump size.
    • 1750 GPM – ten 2” nozzles @ 175 GPM each – 17.9 ft/sec
    • 1750 GPM – six 2-1/2” nozzles @ 292 GPM each – 19.1 ft/sec
    • 1750 GPM – four 3” nozzles @ 438 GPM each – 19.9 ft/sec


River flow is always a subjective issue to the owner only confirmed upon startup of the river system.  One can always throttle back the propulsion pumps to slow the river down, but to speed it up requires a lot more work (plugging nozzles, changing impellors, adding pumps and piping), may have significant cost, and one is always subject to the subjective satisfaction of the owner of the project and once a subjective issue is deemed not acceptable it is extremely hard to make the owner satisfied.

Target velocities should be between 3.0 and 4.0 ft/sec for 6 feet wide current channels, and between 2.5 and 3.5 ft/sec for lazy rivers that are 8 or 10 feet in width.

Nozzles should be designed in the wall and not the floor. When the pipe is cut off at the floor (Marke), winterizing/plugging becomes an issue.

Channels and rivers should not be designed with nozzles on directly across from one another.

A positive flow is required when the feature is off. Therefore, wall inlets are required.  Consider utilizing an inter-connect with the river main drains and the pool main drains.

On a roll-out gutter or deck level gutter, the GPM must be reduced or the surge tank must be enlarged to allow for splash out. We had to reduce velocity (i.e. pump size) at Ballwin and Santa Fe.  Gutters on rivers are not the preferred design option.

The normal height for overhead bridge clearance is 7’-0”. For a current channel like Baldwin with no floatable, it is measured from the bottom of the river, i.e. 3’6” for water and 3’6” for clearance.  For rivers with floatables, 4’-0” from the water level to the underside of the bridge is recommended.  Consult local regulations for varying clearance requirements.

The use of VFDs on propulsion pumps is preferred for optimum control and energy efficiency.

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