A Lake drained

I am very tired now but I will post this.

This is the thread

I wanted to calculate how much energy was released during the draining of this lake.

Not being able to find out the volume (or even the name) of this lake I chose to figure it out on a lake only one meter deep at 5 hectors area.

The lake is in Santiago, and Google Earth gives an evevatation of 1220 meters.

5 hectares = 50,000 sq meters
125 hectares = 1,250,000 cubic meters
PE=mgh PE= potential energy (m=1,000kg g=9.8 h=1220m)
PE= 1000 x 9.8 x1220
PE= 11,956,000 J
Potential energy of one and a quarter million tonnes of water falling (almost) one and a quarter kilometres is all but twelve million Joules.

What does 12,000,000 Joules get you today?
Link
Well in oil terms one barrel = 35 gal, which equals 5,855,795 BTU
That’s 139,424 BTU per Gallon
1 BTU = 1060 Joules so... 1060 x 139,424 = 147,789,440 Joules / gallon
147,789,440 x 35 = 5,172,630,400 Joules / barrel

or/ 1 x 35 gal barrel makes 19.5 gal petrol (apx 73.9 litres)
A very good car well make 68.9 mpg so a barrel = (68.9*19.5)= 1343.55 miles (per barrel)
5,172,630,400 / 1343.65 = 3,849,685.856 Joules / mile

So now I got the energy of 1,250,000 cubic meters of water falling 1220 metres giving 11,956,000 Joules

I got the best car I can get, needing 3,849,685.856 Joules per mile.

11,956,000 / 3,849,685.856 = 3.105707958 miles

Please someone correct me if im wrong here. The way I've just worked it out one and a quarter million tonnes of water falling one thousand two hundred and twenty meters would give the same amount of energy required to drive an economical car three and a bit miles.

I must be wrong but in my tiredness I can't see how.




[edit on 21/6/2007 by Now_Then]