Essay: Measurement Folio Task – Rainwater Harvesting

Introduction:
In today’s world, the scarcity of water due to global warming and climate changes is a major problem. This cannot be reduced just by introducing water restrictions, it is necessary to collect and store water in order to use them during droughts and situations where the supply of water is limited. For this purpose, many cities have decided to build rainwater harvesting tanks in order to collect and store rainwater for future use.
Rainwater can be used in various ways including watering gardens, toilet flushes, household chores etc. Though, it is not advisable to drink rainwater, it can still be used for cooking after being boiled or cleansed.
This report will include investigating several things such as the sizes of the tanks required for a certain volume of water, the volume of water that should be used during different times of the year and so on.
Through this task, common questions like-
What is the capacity of rainfall that my roof can catch?
How often does rainfall occur? / What is the average rainfall in my area?
What dimensions of the tank would I need, to save a certain amount of water?
How much water would I need for a certain period of time? Would be answered
Answers
To prove: 1mm of rain that falls on 1m2 of surface = 1 litre of water in the tank.
L.H.S= 1 mm of rain on 1m2 of surface
Volume/ Capacity = h*A
= 1mm * 1m2
= 0.001m * 1m2 (Since 1mm= 0.001m)
= 0.001m3
1m3 = 1000 litre
∴ 0.001m3 = 1 litre.
R.H.S= 1 litre of tank
∴ L.H.S= R.H.S
This implies that the statement of the salesman: “Every millimetre of rain that falls on each square metre of your roof equals 1 litre of water in your tank” is TRUE.
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Calculated amount of water collected by a 100m2 roof when 8mm of rain falls over it is as follows.
Surface area of roof= 100m2
Rainfall= 8mm
∴ Amount of water collected over night
= V= A*h
= 100m2 * 8mm
=100m2 * 0.008m (Since 1mm = 0.001m)
= 0.8m3
1m3 = 1000 litres= 1kl.
∴ 0.8m3 = 800 litres= 0.8l
This implies that 800 litres of water would be collected by a roof of 100m2 when the rainfall is 8mm.
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The capacity of water collected by a 100m2 roof in the month of September when the
Average rainfall= 59.2mm is as follows.
Given:
Average rainfall of Adelaide in September 2013: 59.2mm
The surface area of the roof collecting rain water= 100m2
http://www.australia.com/en/facts/weather/adelaide-weather.html
Amount of water collected
by a roof with surface area of 100m2 = Surface Area x The average rainfall
= 100m2 * 59.2mm
= 100m2 * 0.0592m (Since 1mm = 0.001m)
= 5.92m3
1m3= 1000 litres= 1kl
∴ 5.92m3= 5920 litres= 5.92kl.
∴ The amount of water expected to be collected in September by a roof with 100m2 surface are = 5920 Litres.
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Given is the capacity of a tank with a roof of 80m2 is 5000 litres/5kl, the millimetres of rainfall required to fill the tank is as follows.
Given:
The capacity of the tank = 5000 litres.
The surface area of the roof collecting rain water= 80m2
The millimetres of rainfall= xmm
It is known that
V= A * h
= The capacity of the tank= surface area of roof * the millimetres of the rainfall
= 5000= 80m2 * xmm
= 5m3 = 80m2 * x (Since 1m3 = 1000litres)
= x = 0.0625m
∴the millimetres of rainfall
= x= 0.0625m = 62.5mm
∴ The millimetres of rainfall required to fill a 5000 litres tank with a surface area of 80m2 is 62.5mm.
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http://www.australia.com/en/facts/weather/adelaide-weather.html
The range of water levels saved each month from a roof of 80m2 in 2013
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A family of 5 with a roof of 80m2 potentially saves around 43584 litres (Sum of water saved each month from Q5) in a year.
The family is not advised to buy a tank big enough to hold all this water, because it is practically not possible and safe to install a tank with a capacity of over 40,000litres in a residential area. Moreover, the capacity of the water would be reduced with time as the family would be using the water for daily needs, therefore, a tank with such a large capacity is
not advisable.
Q6 (continued)
a) The daily average of water that should be used over the year 2013 is as follows:
Known to us:
Total volume of rainfall over the year= 43584 litres
Number of days in a year= 365
∴ The daily average that the family should use= Volume of rainfall over the year / 365 = 43584/365
= 119.41 litres.
∴ The daily average of water that should be used by the family in the year 2013= 119.41 litres.
b)
The daily average of water that should be used in the wettest month June of 2013 is as follows:
Given:
The wettest month of 2013= June
The volume of rainfall in June= 6352 litres
No.of days in June= 30
∴ The daily average for the wettest month
= Volume of rain in wettest month/ No.of days in wettest month= 6352/30
= 211.73 litres
∴ The daily average of water that should be used for the wettest month June= 211.73 litres
C)
The daily average of water that should be used in the driest month February of 2013 is as follows:
Given:
The driest month of 2013= February
The volume of rainfall= 1080 litres
No.of days in February= 28
∴ The daily average for the driest month
= Volume of rain in the driest month/ No.of days in the driest month= 1080/28
38.57 litres.
∴ The daily average of water that should be used for the driest month February= 38.57litres
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– Yes, I think that there would be times when the tanks are empty. It is assumed that the tanks would be empty in times of drought or when excessive water is being used, but there is no rainfall.
I wouldn’t think that the tank would ever be flowing because, water would constantly be used for daily requirements. But, in a situation where the capacity of the tank is lower than the volume of the rain, there are chances of the tank overflowing.
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Conclusion
Investigating this report found that every mm of rain that falls on a square metre of surface is equal to 1 litre of water. It was concluded that a family of 5 could potentially save an approximate of 43kl of water every year, yet they are not advised to install a tank with such a large capacity. The daily average of water that should be used by a family of 2 adults and 3 children during different times of the year was also calculated. Therefore, we can conclude that through this report we have learned that different volumes of rainwater require tanks with different capacities.
Bibliography:
http://www.australia.com/en/facts/weather/adelaide-weather.html