For ease of construction and hydraulic
performance, swales are typically designed
with trapezoidal cross-sections . Cross-section
design fits size and depth to accommodate
peak discharge using hydraulic design
charts . A bottom width and depth of flow
are selected to handle the discharge from a
two year rainfall without reaching erosive
velocity [1 .2 to 1 .5 m/s (4 .0 to 5 .0 ft/sec)
maximum] . Additional depth is added to
accommodate the discharge from a ten year
rainfall without eroding [2 .1 m/s (7 .0 ft/sec)
maximum] .