Estimate the average,maximum day and peak hour demand for the communityof 60000 population.also find design capacity of water distribution system and water treatment plant
Answers
Answer:
Water Quantity Estimation
The quantity of water required for municipal uses for which the water supply scheme has to be designed requires following data:
Water consumption rate (Per Capita Demand in litres per day per head)
Population to be served.
Quantity= Per capita demand x Population
Water Consumption Rate
It is very difficult to precisely assess the quantity of water demanded by the public, since there are many variable factors affecting water consumption. The various types of water demands, which a city may have, may be broken into following classes:
Water Consumption for Various Purposes:
Types of Consumption
Normal Range (lit/capita/day)
Average
%
1
Domestic Consumption
65-300
160
35
2
Industrial and Commercial Demand
45-450
135
30
3
Public Uses including Fire Demand
20-90
45
10
4
Losses and Waste
45-150
62
25
Fire Fighting Demand:
The per capita fire demand is very less on an average basis but the rate at which the water is required is very large. The rate of fire demand is sometimes traeted as a function of population and is worked out from following empirical formulae:
Authority
Formulae (P in thousand)
Q for 1 lakh Population)
1
American Insurance Association
Q (L/min)=4637 ÖP (1-0.01 ÖP)
41760
2
Kuchling's Formula
Q (L/min)=3182 ÖP
31800
3
Freeman's Formula
Q (L/min)= 1136.5(P/5+10)
35050
4
Ministry of Urban Development Manual Formula
Q (kilo liters/d)=100 ÖP for P>50000
31623
Factors affecting per capita demand:
Size of the city: Per capita demand for big cities is generally large as compared to that for smaller towns as big cities have sewered houses.
Presence of industries.
Climatic conditions.
Habits of people and their economic status.
Quality of water: If water is aesthetically $ medically safe, the consumption will increase as people will not resort to private wells, etc.
Pressure in the distribution system.
Efficiency of water works administration: Leaks in water mains and services; and unauthorised use of water can be kept to a minimum by surveys.
Cost of water.
Policy of metering and charging method: Water tax is charged in two different ways: on the basis of meter reading and on the basis of certain fixed monthly rate.
Fluctuations in Rate of Demand
Average Daily Per Capita Demand
= Quantity Required in 12 Months/ (365 x Population)
If this average demand is supplied at all the times, it will not be sufficient to meet the fluctuations.
Seasonal variation: The demand peaks during summer. Firebreak outs are generally more in summer, increasing demand. So, there is seasonal variation .
Daily variation depends on the activity. People draw out more water on Sundays and Festival days, thus increasing demand on these days.
Hourly variations are very important as they have a wide range. During active household working hours i.e. from six to ten in the morning and four to eight in the evening, the bulk of the daily requirement is taken. During other hours the requirement is negligible. Moreover, if a fire breaks out, a huge quantity of water is required to be supplied during short duration, necessitating the need for a maximum rate of hourly supply.
So, an adequate quantity of water must be available to meet the peak demand. To meet all the fluctuations, the supply pipes, service reservoirs and distribution pipes must be properly proportioned. The water is supplied by pumping directly and the pumps and distribution system must be designed to meet the peak demand. The effect of monthly variation influences the design of storage reservoirs and the hourly variations influences the design of pumps and service reservoirs. As the population decreases, the fluctuation rate increases.
Maximum daily demand = 1.8 x average daily demand
Maximum hourly demand of maximum day i.e. Peak demand
= 1.5 x average hourly demand
= 1.5 x Maximum daily demand/24
= 1.5 x (1.8 x average daily demand)/24
= 2.7 x average daily demand/24
= 2.7 x annual average hourly demand
Design Periods & Population Forecast
This quantity should be worked out with due provision for the estimated requirements of the future . The future period for which a provision is made in the water supply scheme is known as the design period.
Design period is estimated based on the following:
Useful life of the component, considering obsolescence, wear, tear, etc.
Expandability aspect.
Anticipated rate of growth of population, including industrial, commercial developments & migration-immigration.
Available resources.
Performance of the system during initial period.
Population Forecasting Methods
The various methods adopted for estimating future populations are given below. The particular method to be adopted for a particular case or for a particular city depends largely on the factors discussed in the methods, and the selection is left to the discrection and intelligence of the designer.
Arithmetic Increase Method
Geometric Increase Method
Incremental Increase Method
Decreasing Rate of Growth Method
Simple Graphical Method
Comparative Graphical Method
Ratio Method
Logistic Curve Method
Worked-out Example