Page 41 - การระบายน้ำ

4-3

ี
่
ตารางท 4.1 Values for Manning’s and maximum permissible velocities of flow in open channels

Ditch Lining Manning’s n V (fps)
max
1. Natural earth:
a. Rock: smooth and uniform 0.038 20

jagged and irregular 0.043 18
b. soils: GW 0.023 7

GP 0.025 8
GMd 0.024 5

Gmu, MH 0.023 4
GC 0.025 7
SW, SP 0.023 2

Smd, SMu 0.022 3
SC, ML 0.024 4

CL, CH, OL, OH, PT 0.023 3
2. Paved surfaces:
a. Concrete (all surfaces) 0.014 20

b. Concrete bootom w/sides of--
dressed stone in mortar 0.016 20

random stone in mortar 0.018 19
dressed stone or smooth

concrete rubble (riprap) 0.023 15
rubble or random stone 0.027 15

c. Gravel bootom, w/sides of--
formed concrete 0.018 10
random stone in mortar 0.022 10

random stone or rubble 0.028 10
d. Brick 0.016 10

e. Asphalf 0.015 20
NOTE : To calculate V assumed , take V , and subtract 1. For example, V assumed for a GP soll
max
is 8 - 1 or 7 fps.