# Waste Water Engineering Questions and Answers – Dry Weather Flow & Variations in Rate of Sewage

This set of Waste Water Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Dry Weather Flow & Variations in Rate of Sewage”.

1. What is the wastewater flow in a sewer system during the periods of dry weather with minimum infiltration called?
a) Wet weather flow
b) Dry weather flow
c) Wet flow
d) Dry flow

Explanation: Summers are usually dry. Hence the rainfall is minimum and is called as dry weather flow in sewers. During the rainy season or periods of high rainfall or storm, the sewers will be full and are called wet weather flow.

2. In order to determine the section of the sewer, it is essential to know the total quantity of the sewage that would flow through the sewer.
a) True
b) False

Explanation: The quantity of sewage that would flow in dry weather is different from the quantity of the sewer that would flow in the wet weather. Hence peak conditions must be considered and sewer size should be determined.

3. The dry weather flow is also called as sanitary sewage.
a) True
b) False

Explanation: Dry weather flow mainly consists of domestic sewage and industrial wastewater as the rainfall or storm is absent or less in the times of summer of dry weather. Hence dry weather flow is also called as sanitary sewage.

4. Which of the following factors does the dry weather does not depend on?
a) Rate of water supply
b) Population growth
c) Infiltration of groundwater
d) Design of sewer system

Explanation: Dry weather flow depends on the type of area served, rate of water supply, population growth, infiltration of groundwater. Design of sewer system is to determine the size of a sewer system in peak conditions. It has nothing to do with the factors responsible for dry weather flow.

5. Which of the following common unit is used to express the rate of water supply to a city or town?
a) Litres/capita/second
b) Litres/capita/day
c) Millilitres/capita/day
d) Millilitres/capita/hour

Explanation: The common unit used to express the rate of water supply to a city or town is in terms of litres per person for a day. Capita refers to each person or an individual. Hence the unit is litres/capita/day.
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6. The quantity of sanitary sewage entering the sewers would be ___________ the total quantity of water supplied.
a) Less than
b) Equal to
c) More than
d) Greater than

Explanation: The quantity of sanitary sewerage entering the sewers would be less than the total quantity of water supplied because the water is lost in domestic consumption, evaporation, lawn sprinkling, fire fighting and industrial consumption.

7. The quantity of sanitary sewage directly depends on ______
a) Rate of water supply
b) Area
c) Population
d) Precipitation

Explanation: As the population increases the rate of water consumption also increases which leads to the direct increase in sanitary sewage. This also increases water demand. Hence the quantity of sanitary sewage directly depends on the population.

8. The quantity of water supply is equal to the rate of supply multiplied by the ______
a) Population
b) Quantity of sewage
c) Area
d) Net usage

Explanation: The rate of usage of water varies from individual to individual and different sectors. Hence the total quantity of water supplied is equal to the rate of supply multiplied by population.

9. Wet weather flow is _________ than the dry weather flow.
a) Lower
b) Higher
c) Equal to
d) Not equal to

Explanation: Wet weather flow is higher than the dry weather flow because of the inflow and infiltration in the sewer system. Wet weather flow is the combination of stormwater and sanitary sewage but dry weather flow consists of only sanitary sewage.

10. Dry weather flow+ storm water=_________
a) Dry weather flow
b) Stormwater
c) Wet weather flow
d) Sanitary sewage

Explanation: Dry weather flow is the wastewater flow in sewers during dry weather. Dry weather flow in combination with stormwater is called as wet weather flow.

11. Sewage flow rates vary by source and with a time of the day, the season of the year and weather conditions.
a) True
b) False

Explanation: The rate of usage of water depends on the population of a city of a country. Sewage generation in terms depends on water usage. Different cities use the quantity of water based on their needs. Hence the sewage flow rates vary by source and with a time of the day, season of the year and so on.

12. A proper assessment should be made before sewers are sized or treatment plant capacities are set.
a) True
b) False

Explanation: Different treatment plants produce different quantities of wastewater depending upon the water needs and usage within the industry. The quantity of wastewater in sewer depends upon the population in that area and water usage. Hence proper assessment should be made considering both peak and normal conditions.

13. What is the lowest wastewater flow in hospitals?
a) 50 gpcd
b) 700 lpcd
c) 900 lpcd
d) 40 lpcd

Explanation: The unit lpcd stands for litres per capita per day and gpcd stands for gallons per capita per day. 40 lpcd indicates the minimum water usage for places like kids play home and schools. 700 lpcd is for hospitals.

14. __________ in residential areas resemble water usage patterns in those areas.
a) Hydrographs
b) Sewage flow patterns
c) Dry period patterns
d) Daily flow

Explanation: The water usage depends upon the population, number oh houses and the type of water usage in that area. Sewage flow in turn depends upon these activities. Hence sewage flow patterns in residential areas resemble water usage patterns in those areas.

15. A graph showing discharge versus time past a specific point in a conduit carrying flow is called?
a) Water flow graph
b) Precipitation graph
c) Hydrograph
d) Variation graph

Explanation: A graph showing discharge versus time at a specific point in a conduit carrying flow or river is called ‘hydrograph’. Hydrograph helps in understanding the flow characteristics of water at different time intervals.

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