Drainage Meaning: Definition and Importance in Construction

Cross Drainage Works is a structure that takes away a discharge from a natural stream across a canal obstructing the stream. This helps to prevent the drain water from mixing with the canal water. This is a costly construction and should be avoided as well.

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There are two ways to keep away from cross drainage works:

Diverting the stream to another
Changing the canal alignment crosses below the junction of two streams.

In irrigation projects, the canals pass water from the headwords to crop fields and may need to cross a few drainage systems such as rivers. To cross these natural systems, there is a need for a structure to help with the passing of the canal water. Where drainages and canals meet, the bed levels may not be at the same level; hence different structures are constructed and designated with varied names.

Types of cross drainage works

There are three types of cross drainage works.

Cross drainage works carrying a canal over a drain

Structures that fall into this category are aqueducts and siphon aqueducts.

Cross drainage works carrying drainage over a canal

Structures falling into this category are super passage and canal siphon.

Cross drainage works admitting canal water into the canal

Structures falling into this category are level crossing and canal inlets.

Aqueducts are an example of canals over drainage; thus, the canal has to be constructed over the drainage. A canal trough is constructed in which the water flows upstream to downstream. The trough rests on piers. Aqueducts are similar to bridges that carry water, and the drainage water flows below that.
In a siphon aqueduct, canal water is over the drainage, and the drainage water flows through via a syphonic action. There is no natural pressure on the drain. Siphonic aqueducts are more often constructed compared to normal aqueducts.
A super passage cross drainage work carries the drainage over the canal as the canal bed level is below the drainage level. The drainage trough is constructed at road level, and the water flows from upstream to downstream. For the canal, water flows through the piers, and the complete water supply is below the drainage. This is a reverse aqueduct structure.
In a canal siphon, the water in the canal flows via a syphonic action. A super passage drainage works system is preferred over a siphon canal as any minerals cannot be removed.
The drainage water is mixed with the canal for drainages admitted into the canal. A level crossing is constructed when the canal bed and drainage bed are at the same level.
In a canal inlet construction, very less drainage water is admitted into the canal. The drainage is taken through the banks of the canal in an inlet. This drainage and canal mixed water travels a certain length, after which an outlet creates a suction pressure to remove all dirt from the drainage and transfer it to a watershed nearby.

Classification of an Aqueduct and Siphon Aqueduct

Aqueducts and Siphon Aqueducts may be classified under three headings depending on their sides:

Type 1:

The sides of an aqueduct in earthen banks with earthen slopes.

Type 2:

The sides of an aqueduct in earthen banks with other slopes supported by a wall.

Type 3:

The sides of the aqueduct are made of concrete or masonry.

Factors influencing the selection of cross drainage works

The following factors influence the selection of a particular cross drainage work:

Relative bed level:

The bed levels of the canal and drainage will affect the choice.

Foundation:

To implement cross-drainage works, a suitable foundation is required.

Relative water level

The water level at the canal and drainage also affect the choice.

Cost:

A canal system outweighs the cost of installing a hydraulic system.

Discharge:

The flow of the drainage may be more at times; thus, the hydraulic system installed should withstand weathering conditions.

Canal alignment:

The canal alignment is sometimes changed to achieve better cross-drainage works.

Provision of road:

An aqueduct is preferred over a super passage cross drainage works because an aqueduct allows for the construction of a road bridge along with it.

Availability:

The required construction materials should be available in the area.

Selection of site for cross drainage works

When selecting a site for cross drainage works, the following points should be considered.

At the site, the drainage should cross the canal at the right angles. This keeps the cost of the structure at a minimum.
The stream at the selected site should be stable.
A firm sub-stratum should exist below the drainage.
The site should be such that the high and long approaches of the canals are not required.
The water table should not be high
The site should be selected downstream at the drainage and canal to avoid the construction of multiple structures.
This work should be combined with a bridge if possible so that the bridge can be shifted as cross drainage works when required.

Importance of cross drainage works

Watershed canals may pass drainage areas, so there is a need for cross drainage works for irrigation purposes. At the crossing point, the water of the canal and drainages get mixed. For the smooth functioning of the canal with its discharge design, there is a need for cross-drainage works. The area of the site condition may be such that without a structure, there may be no diversion of the canal water and drainage water. A cross drainage work is a must to help direct the water at natural flow.

Cross drainage works are structures constructed for the crossing of canal water over or another drainage water. The structure carries the discharge from the natural stream across the canal that is intercepting the stream. It is an expensive construction and hence should be avoided as much as possible.

What is drainage and why is it important in construction?

Water can cause a great deal of damage to any building in case no prior planning is done for its proper drainage. While mold, discoloration, cracking etc. happen to be the small issues caused by water leakage, the problem has the potential to cause building-life threatening issues like foundation issues, erosion, sinkholes, etc.

FAQs

What is the need for cross drainage works?

When water is required for irrigation purposes, and there is a natural drainage system in between, such as a river or stream, a structure of cross-drainage work is required. It helps with the smooth running of water and avoids the intermixing of water.

What canal type is suitable to avoid cross drainage works?

A side slope canal is suitable in that it runs beside the natural drainage flow and does not intercept the drainage.

Why is cross drainage works required?

Cross drainage works help with irrigation purposes. For the smooth running of canal water to its designated discharge area, cross drainage works are a must.

Which type of canal requires the maximum amount of cross drainage works?

A contour canal requires the maximum amount of cross-drainage work. A contour canal aligns with the natural contour of the country. It only allows irrigation through one side.

One way to avoid cross drainage works construction?

One way is to divert the drainage stream.

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