Hydraulic Design of a Lazy River

Lazy rivers are popular attractions at modern aquatic centers and water parks. These recreational water channels carry patrons on floating tubes around a meandering loop. The current is maintained by pumps that withdraw a small fraction of the flow from the channel through large bottom grates and return it to the channel in jets directed downstream. This paper presents the hydraulic relationships needed for lazy-river design. These relationships account for the propulsion of the flow by the water jets and the resistance to flow resulting from friction, bends and drag forces on standing persons. The total pump output power is minimized when the downstream component of the jet velocity equals twice the desired current speed. However, other practical considerations generally favor a higher jet speed. Field tests on three lazy rivers indicate that a Manning n value of 0.015 is sufficient to account for boundary friction, bend losses and other local losses. Persons standing in the flow cause added drag, which can reduce the current speed substantially. A design example illustrates the practical application of the relationships and experimental findings. The investigations presented in this paper were conducted for Water's Edge Aquatic Design LLC of Lenexa, Kansas. Water's Edge Aquatic Design is a leading design firm specializing in aquatic centers and water parks. The relationships in this paper have been applied successfully to numerous lazy-river design projects.