Erosion and Sediment Pollution Control Program Manual.pdf

FLOW TRANSITION MAT - Transition mats may be used to prevent scour below pipe outfalls where
the anticipated flow depth of the tailwater is less than or equal to 1/3 the pipe diameter (D). The mats
should be placed at the pipe outlet, preferably in contact with the pipe and centered laterally with the
pipe (see Figure 9.5).
ScourStop
The surface on which the mats are to be placed should be smooth and uniform. If a thick uniform sod
is not present, a Turf Reinforcement Mat (TRM) or High Performance TRM (HPTRM) should be
installed as an underlayment for the mats. The TRM (or HPTRM) should be capable of withstanding a
velocity of at least 5.5 fps in the unvegetated condition.
Since transition mats do not dissipate energy, the receiving channel should be capable of handling the
design discharge without accelerated erosion. Wherever this is not the case, additional energy
dissipation should be provided. Transition mats may also be used for other applications
(e.g. streambank stabilization) if manufacturer’s recommendations are followed.
363-2134-008 / March 31, 2012 / Page 242