The value of permissible velocity
of airflow and humidity Working Permissible velocity
Permissible humidity [%] class of airflow [[ms.sup-1]] Warm season Cold season Warm season Cold season 1a [less than or [less than or 30-70 30-70 equal to] 0,25 equal to] 0,20 1b [less than or [less than or 30-70 30-70 equal to] 0,30 equal to] 0,25 1c [less than or [less than or 30-70 30-70 equal to] 0,30 equal to] 0,30 2 0,1-0,3 [less than or 30-70 30-70 equal to] 0,30 3 4 The value does not determine Tab.
In these waterways, the channel should be designed to carry the runoff at a permissible velocity under conditions of minimum retardance (short vegetation) that may be encountered during the runoff season, and the design then adjusted to ensure adequate capacity under conditions of maximum retardance (tall vegetation).
The permissible velocity in the channel is dependent on the type, condition, and density of vegetation and the erosive characteristics of the soil.
From Table 8-3, the permissible velocity for grass mixtures on erosion resistant soils with a slope between 0 and 5 percent slopes is 1.5 m/s.
The bottom width is determined by the permissible velocity under the mowed condition of minimum retardance, and the depth is determined by the need to provide capacity under conditions of maximum retardance and to allow for freeboard.