HARVESTING SYSTEM"
By: Kennedy Mlay (Active KMK co. ltd)
A rainwater harvesting system comprises components of various stages from catchment, Guttering, Transporting rainwater through pipes or drains, filtration, and storage in tanks for reuse or recharge.
1.
Catchments: The catchment of a
water harvesting system is the surface which directly receives the rainfall and
provides water to the system. It can be a paved area like a terrace or
courtyard of a building, or an unpaved area like a lawn or open ground. A roof
made of reinforced cement concrete (RCC), galvanised iron or corrugated sheets
can also be used for water harvesting.
2. Gutters:
Channels all around the edge of a sloping roof to collect and transport rainwater to the storage tank. Gutters can be semi-circular or rectangular and could be made using:
- Locally available material such as plain galvanized iron sheet (20 to 22 gauge), folded to required shapes.
- Semi-circular gutters of PVC material can be readily prepared by cutting those pipes into two equal semi-circular channels.
- Bamboo or betel trunks cut vertically in half.
Conduits are pipelines or drains that carry rainwater from the catchment or rooftop area to the harvesting system. Conduits can be of any material like polyvinyl chloride (PVC) or galvanized iron (GI), materials that are commonly available.
Diameter Of pipe (mm)
|
Average rate of rainfall in mm/h
|
|||||
50
|
75
|
100
|
125
|
150
|
200
|
|
50
|
13.4
|
8.9
|
6.6
|
5.3
|
4.4
|
3.3
|
65
|
24.1
|
16.0
|
12.0
|
9.6
|
8.0
|
6.0
|
75
|
40.8
|
27.0
|
20.4
|
16.3
|
13.6
|
10.2
|
100
|
85.4
|
57.0
|
42.7
|
34.2
|
28.5
|
21.3
|
125
|
-
|
-
|
80.5
|
64.3
|
53.5
|
40.0
|
150
|
-
|
-
|
-
|
-
|
83.6
|
62.7
|
The size of the gutter should be according to
the flow during the highest intensity rain. It is advisable to make them 10 to
15 per cent oversize.
Gutters need to be supported so they do not
sag or fall off when loaded with water. The way in which gutters are fixed
depends on the construction of the house; it is possible to fix iron or timber
brackets into the walls, but for houses having wider eaves, some method of
attachment to the rafters is necessary.
The following table gives an idea about the
diameter of pipe required for draining out rainwater based on rainfall
intensity and roof area:
Sizing of rainwater pipe for roof drainage
(mm/ h - millimeters per hour; m)
A first flush device is a valve that ensures that runoff from the first spell of rain is flushed out and does not enter the system. This needs to be done since the first spell of rain carries a relatively larger amount of pollutants from the air and catchment surface.
6. Storage Containers
Any container, (masonry or concrete
underground tanks, old unused tanks, pre-fabricated PVC or ferrocement tanks)
with adequate capacity of storage can be used as a settlement tank.
Sizing of Rainwater Storage Tanks
The most appropriately sized rainwater storage can be chosen by quantitatively assessing the performance of various sized storage capacities. By assessing the performance of various sized storage capacities, it is possible to make an informed decision as to what would be the most suitably sized storage capacity for the given application. The input for the assessment is historical rainfall pattern, and the number of people that the system will be saving.
Contact Tel: 0754 363238, Kennedy Mlay
0754 42 8243 Mr. Kahigwa
I Read your article. Thanks for sharing such beautiful information, and I hope you will share some more info about Rainwater Harvesting. You wrote really very well, I really like your blog and information provided by you. I appreciate your work.
ReplyDeleteThanks