Table – Maximum Permissible Velocities Material
Feet per Second (FPS)
Meters per Second (MPS)
Fine Sand (Noncolloidal)
2.5 2.5 3.0 3.5 5.0
0.8 0.8 0.9 1.1 1.5
Sandy Loam (Noncolloidal)
Silt Loam (Noncolloidal)
Ordinary Firm Loam
Fine Gravel
Stiff Clay (Very Colloidal) Graded, Loam to Cobbles (Noncolloidal) Graded, Silt to Cobbles (Colloidal)
5.0
1.5
5.0
1.5
5.5
1.7
Alluvial Silts (Noncolloidal)
3.5 5.0 6.0 5.5 6.0
1.1 1.5 1.8
Alluvial Silts (Colloidal)
Coarse Gravel (Noncolloidal)
Cobbles & Shingles Shales & Hard Pans
1.7
1.8 Source - Adapted from recommendations by Special Committee on Irrigation Research, American Society of Civil Engineers, 1926, for channels with straight alignment. For sinuous channels, multiply allowable velocity by 0.95 for slightly sinuous, by 0.9 for moderately sinuous channels, and by 0.8 for highly sinuous channels. C. Acceptable Management Measures . Measures applied alone or in combination to satisfy the intent of this Section are acceptable if there are no objectionable secondary consequences. The Town recognizes that the management of stormwater runoff to minimize or control downstream channel and bank erosion is a developing technology. Innovative techniques and ideas will be considered and may be used when shown to have the potential to produce successful results. Some alternatives, while not exhaustive, are to:
i. Avoid increases in surface runoff volume and velocity by including measures to promote infiltration to compensate for increased runoff from areas rendered impervious;
ii. Avoid increases in stormwater discharge velocities by using vegetated or roughened swales and waterways in place of closed drains and high velocity paved sections:
iii. Provide energy dissipaters at outlets of storm drainage system to reduce flow velocities to the point of discharge;
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