Design of Crossdrainage Structures

DESIGN OF CROSSDRAINAGE STRUCTURES

Before undertaking detailed designs of any important crossdrainage structure, collect relevant field data is required. Basides, a note regarding the several alternative alight surveyed and reasons for final selection of a particular crossing site is also necessary. A lo map of the site along with the results of subsurface explorations of the site, and stream sections at different locations around the site should also be prepared. The following sp hydraulic data regarding the canal and stream should be made available.

i) Canal

a)    Discharge, depth of flow, and water level at full supply,

b)    Bed width,

c)     Canal bed slope and the water surface slope,

d)   Levels of canal bed and the top of canal banks,

e)     Channel crosssection,

f)      Characteristics of material of the bed and sides of the channel, and

g)    Width of roadway and type and class of IRC loading.

ii) Stream

a)    Extent and nature of stream and its catchment,

b)    Detailed records of rainfall in the catchment,

c)     Maximum observed discharge,

d)   Maximum flood level and water surface slope as observed under the highest fl condition at the proposed site.

e)     Site plan of the proposed crossing including contours,

f)      Log of borehole or trial pit data.

g)    Information about the sediment load,

h)  Characteristics of the  bed  material   including   Manning’s

i)      Longitudinal section of the stream for suitable distance upstream and downstre of the chosen site for crossdrainage structure depending upon the site condition

j)       Crosssection of the stream for about 100 to 300 m upstream and downstream the site at intervals of 10 to 50 m,

k)    Waterways provided in road/railway bridges or other hydraulic structures of the area,

l)      Spring water levels at the crossing site.

Any crossdrainage structure should preferably be located in a straight reach of tb stream crossing the canal at right angle as far as possible. The alignment of the canal should also be such that it results in minimum lengths of embankments (for aqueduct and siph aqueduct structures). If required, the site of the structure may even be shifted away from the existing stream channel, when it is possible to divert the channel and also keep it there b construction will be carried out in dry conditions.