Water way

Waterway

The waterway may be defined as the area of opening, under the bridge which should be sufficient for the maximum flood discharge that would ever pass under the bridge without increasing the velocity of flow beyond permissible limit.

 For determining waterway following should be known

1. Maximum expected flood discharge which will pass under the bridge 

2 Maximum Permissible velocity, generally maximum velocity should not be allowed more than 3 m/s

3. Linear waterway in alluvial soils can be obtained from Lacey's equation

W = C√Q

W = Regime width of waterway 

C =  constant, whole average value is taken as 4.75

 Q = Design flood discharge in m/sec

Waterway for Small Bridges

For small bridges and culverts following 

empirical formula may be used to calculate the minimum waterway in terms of area of catchment:

1. For areas as that of Bombay or' North Gujarat province.

(a) Area of catchment upto 40 hectares, waterway W =0.029 A 

(b) Catchment area between 40 to 280 hectares W = 1.63+0.555A

2 For South Indian rivers

W = 1.63 x 0.05 A, A = Catchment area in hectares whers Depth of scouring when Linear waterway is less than regime width:

In this case scouring depth under the bridge can be obtained by following equation

d = d1(W/L) power .61

W - Regime width of stream

L = Linear waterway provided under the bridge 

d= Normal scour depth,when L=W

d1= Normal scour depth when L< W