{"id":3745,"date":"2024-09-11T11:55:17","date_gmt":"2024-09-11T06:25:17","guid":{"rendered":"https:\/\/study.madeeasy.in\/?p=3745"},"modified":"2025-08-11T16:17:21","modified_gmt":"2025-08-11T10:47:21","slug":"sewage-discharge","status":"publish","type":"post","link":"https:\/\/www.madeeasy.in\/study\/ce\/sewage-discharge","title":{"rendered":"Sewage Discharge"},"content":{"rendered":"

ESTIMATION OF SEWAGE DISCHARGE<\/h2>\n

The sewage discharge which has to pass through a sewer must be estimated as correctly as possible. Otherwise, the sewers may either prove to be inadequate, resulting in the overflow, or may prove to be of too much of size, resulting in unnecessary investments or uneconomical.<\/p>\n

The quantity of sewage through a sewer (Q\u2032) at end of its design period can be computed by multiplying per capita production of sewage (q \u2032) by expected population at end of design period.<\/p>\n

The per capita sewage which is produced (q \u2032) in a community can be estimated by assuming it as 75 to 85 percent of per capita water supplied (q). The per capita demand of water (q) and corresponding per capita sewage production (q \u2032) is based upon annual flows, and therefore are defined as annual average daily flow per person. Although this average value is useful but it not sufficient for designing of various components of a sewerage scheme, because there are wide variations in actual flows that takes place through sewers at any given time.<\/p>\n

Although the flow in sanitary sewers fluctuate seasonally, monthly, daily as well as hourly with water consumption, yet they are sometimes delayed and less pronounced as they are damped because of storage space in sewers and time required for sewage to reach the gauging<\/a> point.\"Water<\/p>\n

It can be seen in figure that peak for sewerage flow are dampened because it requires considerable sewage to fill the sewers to high flow point and high flows from various sections will reach the gauging point after different time of flows. Thus, the time when peak flow occurs will depend upon flow time in sewers. If the sewage is gauged near its origin, peak flow will be more pronounced whereas if the sewage has to travel a long distance before gauged, the peak will be dampened. Hence, peak flows (expressed as number of times of their average values) will be much greater for small lateral sewers, as compared to these for large trunk sewers.<\/p>\n

For areas of moderate sizes, such as for branched sewers, maximum daily or hourly sewage flows can be expressed as<\/p>\n

Maximum daily flow = 2 times the average daily flow
\nMaximum hourly flow = 1.5 times the maximum daily flow = 3 times the average daily flow<\/p>\n

The estimation of maximum hourly flows for different types of sewers is given in the table below.<\/p>\n\n\n\n\n\n
<\/th>\nHourly variations in sewage flow<\/th>\n<\/tr>\n
S. No.<\/strong><\/th>\nType of sewer<\/strong><\/th>\nRatio of maximum flow\u00a0<\/strong>to average flow<\/strong><\/th>\n<\/tr>\n
\n

1.<\/p>\n

2.<\/p>\n

3.<\/p>\n

4.<\/p>\n<\/td>\n

Trunk mains above 1.25 m in dia.<\/p>\n

Mains up to 1 m in dia.<\/p>\n

Branches up to 0.5 m in dia.<\/p>\n

Laterals and small sewers upto\u00a00.25 m in dia.<\/td>\n

\n

1.5<\/p>\n

20.<\/p>\n

3.0<\/p>\n

4.0<\/p>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

The minimum flow passing through a sewer is an important factor in design of sewer, because if the flow is very low, then the velocity will be low and hence silting will take place. Hence, the slope at which the sewer is to be laid has to be decided in accordance with requirement of minimum permissible velocity at minimum flow.<\/p>\n

For moderate areas, for designing of branch sewers, the following minimum flow may be assumed.<\/p>\n

Minimum daily flow = 2\/3 x Average daily flow<\/p>\n

Minimum hourly flow = 1\/2 x Minimum daily flow<\/p>\n

Minimum hourly flow = 1\/3 x Average daily flow<\/p>\n

The sewers, must therefore be checked minimum velocities at their minimum hourly flows.<\/p>\n

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