Environmental Engg. 3(2+1)

Lesson-15 Types of sewers

Sewers are generally circular in shape.  The advantages of circular sewers are:

• The perimeter of circular sewer is the least with respect to the sewer of other shape.

• The inner surface is smooth hence the flow of sewage is uniform and there is no chance of deposition of suspended particles.

• The circular sewers are easy to construct.

However non-circular shaped sewers are also adopted for the following reasons:

• They can be construct in such a convenient shape and size so that a man can enter the sewer for cleaning, maintenance, etc.

• The process of construction is easy.

• The structural strength is more.

• Cost of construction is low.

The following are the non-circular shaped sewers that are more commonly adopted

Standard Egg-shaped sewer

These types of sewers are generally used in combined sewers.  These sewers can generate self cleansing velocity during dry weather flow.

 

New egg-shaped sewer

 

 

Horse shoe shaped sewer

This type of sewer is constructed for carrying heavy discharge.  This is like a tunnel and resembles a horse-shoe.  The size is so large that the maintenance works within the sewer are very easy.

Parabolic shaped sewer

The upper surface of the sewer is of the shape of a parabola and the invert is in the form of an ellipse.  This type of sewer is suitable for carrying small discharges.

Semi-elliptical section

 

 Rectangular shape section

This type of sewer can be easily constructed.  These are suitable for large sewers to carry heavy discharge of sewage.  The maintenance works are easy in this section

U-shaped section

The shape of sewer resembles the letter ‘U’.  The sewer is suitable for carrying heavy discharges. Maintenance works are very easy in this type of sewers.

Semi-circular shaped sewer

Basket handled shape sewer

In this type of sewer, the outer surface is circular.  The inner surface is divided into two portions.  The upper portion resembles a basket-handle and the lower portion is like a channel.  During dry season, the sewage flows through the lower portion and during monsoon, the combined sewage flows through the full section.