Saturday, 15 August 2015


Hydroelectric dam that spans the Yangtze River by the town of Sandouping, located in Yiling
District, Yichang, Hubei province, China. The Three Gorges Dam is the world’s largest power station in terms of installed capacity (22,500 MW) but is second to Itaipu Dam with regard to the generation of electricity annually.

General Quick Facts:
Type: Concrete Gravity Dam
Cost: Official cost $25bn - actual cost believed to be much higher
Work began: 1993
Due for completion: 2009
Power generation: 26 turbines on left and right sides of dam. Six underground turbines planned for
Power output: 49 billion kilowatt-
Reservoir: 660km long, submerging 632 sq km of land. When fully
flooded, water will be 175m above sea level
Navigation: Two-way lock system became operational in 2004. One- step ship elevator due to open in 2009.
Land submerged: 13 cities, 140 towns, 1352 villages, 657 factories & 30,000 hectares of cultivated land
Relocation of People: 1.3 million to
located in 3 stages in 1997, 2003 &2009 Stretching
Excavation: 102.6 million cubic meters of earth and stone (134 million cubic yards).
Concrete: 27.2 million cubic meters (35.5 million cubic yards).
Steel reinforcing bars: 354,000 tons.
Dam height: 185 meters (607 feet).
Dam length : 2,309 meters (1.4 miles) divided into three parts. In the center will be a 484-meter spillway section with 23 bottom outlets and 22 sluice gates. On the left and right of the spillway will be two giant power stations.

Rain Water Harvesting System.

What is Rain Water harvesting?

Rain Water Harvesting is an act of accumulating and storing rainwater for reuse. As we know rainwater is the purest form of water, we can utilize this water for various purposes after necessary purification process as per required. This system can be a boon in regions where there is shortage of water. This problem is common in today’s big cities. Hence rainwater harvesting can be very effective in these areas.
Broadly rainwater can be harvested for two purposes:
1. Storing rainwater for ready use in
containers above or below ground.
2. Charged into the soil for withdrawal later (groundwater recharging).
Importance of Rain Water harvesting Technique These techniques can serve the following
1)Provide drinking water
2)Provide irrigation water
3)Groundwater recharge
4)Reduce storm water discharges, urban flood.
5)overloading of sewage treatment plants
6)Reduce seawater ingress in coastal areas.

*Rain Water harvesting Methods*
Rainwater harvesting can be harvested using different methods. It may follow surface harvesting methods or rain water collection methods which are explained below:
In this method, rooftops are used for collecting the water. If buildings with impervious roofs are already in place, the catchment area is effectively available free of charge and they provide a supply at the point of consumption. Paved and unpaved areas i.e., landscapes, open fields, parks, storm water drains, roads and pavements and other open areas can be effectively used to harvest the runoff. The main advantage in using ground as collecting surface is that water can be collected from a larger area. This is particularly advantageous in areas of lo rainfall.
The potential of lakes, tanks and ponds to store rainwater is immense. The harvested rainwater can not only be used to meet water requirements of the city, it also recharges groundwater aquifers.
Storm-water drains: Most of the r colonies have proper network of storm water drains. If maintained neatly, these offer a simple and cost effective means for harvesting rainwater.

*Whether to store rainwater or use it for recharge?
The decision whether to store or recharge water depends on the rainfall pattern and the potential
to do so, in a particular region. The sub-surface geology also plays an important role in making this decision.
For example,
Delhi, Rajasthan and Gujarat where
the total annual rainfall occurs during 3 or 4 months, are examples of places wheregroundwater recharge is usually practiced. In places like Kerala, Mizoram, Tamil Nadu and Bangalore where rain falls throughout the year barring a few dry periods, one can depend on a small sized tank for storing rainwater, since the period between two spells of rain is short.
Wherever sub-strata is impermeable recharging will not be feasible. Hence, it would be ideal to
opt for storage. In places where the groundwater is saline or not of potable standards, the alternate
system could be that of storing rainwater. Beyond generalisations, it is the requirement that governs the choice of water harvesting technique
For example,
in Ahemadabad, which has limited
number of rainy days as that of Delhi, traditional rainwater harvesting tanks, known as tankas, are used to store rainwater even today in residential areas, temples and hotels.
How much rainwater can be harvested? The total amount of water that is received in the form of rainfall over an area is called the rainwater endowment of the area. Out of this, the amount that can be effectively harvested is called the water harvesting potential.
Water harvesting potential =
Rainfall (mm) xCollection efficiency.