Erosion Control

Turf Reinforcement Matrix Shear Stress & Channel Velocity Limits

Mats are rated in shear, not velocity — and the same velocity can sit either side of the limit depending on how deep the water is.

Channel Hydraulics Design flow
m
m/m
m
Mat & Roughness Lining
n

Vegetated mats run higher than bare mats; use the design condition.

Pa

Manufacturer rating for the vegetated or unvegetated case being checked.

Applied Boundary Shear

— Pa

Shear the design flow imposes on the channel lining

Capacity Check

Mean Flow Velocity
— m/s
Factor of Safety
— ×
Maximum Flow Depth
— m
Unit Discharge
— m²/s
Channel Discharge
— m³/s

Hydraulic radius is taken as flow depth, which holds for wide shallow channels and overstates capacity in narrow ones — use the true hydraulic radius where width is less than about ten times depth. Permissible shear for a vegetated mat depends on the stand of grass actually established, so the unvegetated rating governs the first season and after any repair. Shear at bends and at the toe of a drop runs well above the uniform-flow value computed here.

Turf Reinforcement Matrix Shear Stress & Channel Velocity Limits — free, with the formula and a worked example, at Textile School.