Critical Water Velocity for Snail Habitats in Canals

A design velocity was determined to prevent disease-bearing snails from inhabiting irrigation canals. In tropical irrigation systems many people in the argicultural community are infected with a parasitic disease spread by aquatic snails living in the canals and reservoirs. The disease, bilharzia (schistosomiasis) can have a serious impact on agricultural productivity as well as being a general health problem, thus it is of concern to engineers and agricultural planners. High flow velocities have been suggested as a means of eliminating snails from canals, thus data from existing canals were collected to verify predictions made from hydrodynamic considerations. A study of the Patillas Irrigation Canal in Puerto Rico showed that populations of the local bilharzia snail Biomphalaria glabrata, would be overpowered by mean water velocities greater than 2 ft/s (0.6 m/s), the velocity at which the compulsive forward motion of the snail against the current was halted. This confirmed theoretical calculations for the canals of this size.