Cross Drainage works: types, selection of suitable type, various types, design considerations for cross drainage works

1. Presented by:
MOOD NARESH
ASST.PROF
PETW

2. Cross Drainage
works:
types,
selection of suitable type,
various types,
design considerations for cross drainage
works

3. Whenever an irrigation channel intercepts a natural
drainage, which may be small stream or river, a
masonry work has to be constructed to pass one
above the other or to pass at the same level. Such
masonry works are known as cross drainage works.
Canals are mostly run at ridges, and hence there
should not be any necessity of such works.

4.  Soil of good quality should be available so that safe
foundations may be laid on it.
 2.The natural banks should be high and stable, otherwise
large cost is required for making good bank connections.
 3.The canal and drainage, should cross each other at right
angles.There should be straight reaches in both on the
U/S and D/S sides.
 4.The section of the drainage should he uniform.The bed
of the drainage should be even and the flow should be free
from turbulences.

5. The factors which affect the selection of suitable type of cross drainage works are:
Relative bed levels and water levels of canal and drainage
Size of the canal and drainage.
The following considerations are important
When the bed level of the canal is much above the HFL of the drainage, an aqueduct is the obvious choice.
When the bed level of the drain is well above FSL of canal, super passage is provided.
The necessary headway between the canal bed level and the drainage HFL can be increased by shifting the
crossing to the downstream of drainage. If, however, it is not possible to change the canal alignment, a
siphon aqueduct may be provided.
When canal bed level is much lower, but the FSL of canal is higher than the bed level of drainage, a canal
siphon is preferred.
When the drainage and canal cross each other practically at same level, a level crossing may be preferred.
This type of work is avoided as far as possible.

7. A Factors which influence the Selection of Cross DrainageWorks
The considerations which govern the choice between aqueduct and
siphon aqueduct are:
1.Suitable canal alignment
2.Suitable soil available for bank connections
3.Nature of available foundations
4.Permissible head loss in canal
5.Availability of funds
6.Compared to an aqueduct a super passage is inferior and should be
avoided whenever possible. Siphon aqueduct is preferred over siphon
unless large drop in drainage bed is required.

8. Cross drainage works can be grouped
under following three heads:
I. Cross drainage works when canal
crosses over the drainage.
II. Cross drainage works when drainage
crosses over the canal.
III.. Cross drainage works when drainage
and canal waters are allowed to
intermix.

9. Cross Drainage Works when Canal Passes over the Drainage:
In this case, irrigation canal passes over the drain.
The cross drainage works connected with this particular
condition are the following:
(i) Aqueduct:
(ii) Siphon Aqueduct:
Cross Drainage Works when Drainage Passes over the Canal:
In this case, drainage is carried over the canal.This is found
suitable when bed level of the canal lies below the bed level of
the channel.
Cross drainage works of this category are:
(i) Super passage and,
(ii) Canal Syphon.

10. Cross Drainage Works when Drainage and Canal Waters
are Allowed to Intermix:
Inlet:
Outlet:
Pipe Aqueduct: