Melting snow sometimes forms a turbulent rush of water that washes soil from slopes and hills, and floods the lowlands. Torrential rains often rip gaping gullies in farmlands, and fill city homes with silt-laden water. Uncontrolled water is one of nature's most destructive forces. Water erosion is not always so spectacular as wind erosion or soil drifting. Sheet and rill erosion may take place almost unnoticed, yet result in great damage. For example, in an experiment conducted at Ottawa, 66.1 tons of valuable topsoil were eroded from one acre in 60 minutes by a flash rain of 2.9 inches on June 17, 1946. It is true that there is little or no danger of erosion in many parts of Canada during five or more winter months, frozen soil is not susceptible to the ravages of flowing water. Furthermore, neither monthly nor yearly precipitation totals are as great in Canada as in some other countries. It must not be taken for granted, however, that water erosion cannot be extremely damaging in this country.