3 ms·

>until the energy costs of desalination are low enough. Really? You think desalination is the ultimate goal? I much prefer free, ecosystem-provided desalinatio

>until the energy costs of desalination are low enough. Really? You think desalination is the ultimate goal? I much prefer free, ecosystem-provided desalination (aka rooftop rain-water harvesting). As for agricultural water use, I highly suggest picking up a copy of P.A. Yeoman's classic Water For Every Farm. It details how proper runoff management, evaporation control, and correctly-scaled earthworks can provide reliable water availability with near-zero energy inputs [other than the sun, of course]. As for dams, it's not as simple as "all dams are bad". Oversized dams that are out of scale with the local hydrology are the problem. But, I guess some people would prefer to re-invent the Earth's water cycle!

ryan_j_naughton 13y ago
I agree that not all dams are bad. The real issue with dams is the scale. We are on track to dam the majority of the world's rivers over the next 50 years, and this will have significant effects on river and coastal ecosystems. >> I much prefer free, ecosystem-provided desalination (aka rooftop rain-water harvesting). I agree; however, this is not an infinite supply. Taking water from rivers is effectively a form of this and it is lower cost than many other "free, ecosystem-provided desalination" since the water has already been collected into a river due to gravity and land contours. As we remove water from these 'free' sources, we are depriving an ecosystem of that water. The worst case scenario is something like the Aral Sea http://en.wikipedia.org/wiki/Aral_Sea http://en.wikipedia.org/wiki/Aral_Sea
- schiffern 13y ago
  >The real issue with dams is the scale. I couldn't agree more. >I agree; however, this is not an infinite supply. Well no system can provide an infinite supply, but rainwater harvesting could support the current human population at a first-world standard of living (something our present system does not provide). Many areas famous for recent crippling droughts suffered from flooding only months before. This is a spectacular failure in water management. As to cost, I haven't seen any comparisons of the lifetime cost of rooftop rainwater harvesting vs centralized pumped underground pipe distribution. I know rainwater harvesting is much more common in Australia, so they might have more data. I suspect it's strongly dependent on the cost of energy. One thing I forgot to mention about desalination: current technology (specifically the Affordable Desalination Collaboration’s pilot plant) is at 30% of the thermodynamic limit. So we can expect a 3x improvement in performance, but no more. http://www.usbr.gov/research/AWT/energy_use.html http://www.usbr.gov/research/AWT/energy_use.html
InclinedPlane 13y ago
Whether you're desalinating or just doing runoff management you're mucking about with the Earth's water cycle either way. The bigger issue is actually just using waste water recycling, which is today a feasible proposition but for public perception.

ryan_j_naughton 13y ago

I agree that not all dams are bad. The real issue with dams is the scale. We are on track to dam the majority of the world's rivers over the next 50 years, and this will have significant effects on river and coastal ecosystems. >> I much prefer free, ecosystem-provided desalination (aka rooftop rain-water harvesting). I agree; however, this is not an infinite supply. Taking water from rivers is effectively a form of this and it is lower cost than many other "free, ecosystem-provided desalination" since the water has already been collected into a river due to gravity and land contours. As we remove water from these 'free' sources, we are depriving an ecosystem of that water. The worst case scenario is something like the Aral Sea http://en.wikipedia.org/wiki/Aral_Sea http://en.wikipedia.org/wiki/Aral_Sea

schiffern 13y ago
>The real issue with dams is the scale. I couldn't agree more. >I agree; however, this is not an infinite supply. Well no system can provide an infinite supply, but rainwater harvesting could support the current human population at a first-world standard of living (something our present system does not provide). Many areas famous for recent crippling droughts suffered from flooding only months before. This is a spectacular failure in water management. As to cost, I haven't seen any comparisons of the lifetime cost of rooftop rainwater harvesting vs centralized pumped underground pipe distribution. I know rainwater harvesting is much more common in Australia, so they might have more data. I suspect it's strongly dependent on the cost of energy. One thing I forgot to mention about desalination: current technology (specifically the Affordable Desalination Collaboration’s pilot plant) is at 30% of the thermodynamic limit. So we can expect a 3x improvement in performance, but no more. http://www.usbr.gov/research/AWT/energy_use.html http://www.usbr.gov/research/AWT/energy_use.html

InclinedPlane 13y ago

Whether you're desalinating or just doing runoff management you're mucking about with the Earth's water cycle either way. The bigger issue is actually just using waste water recycling, which is today a feasible proposition but for public perception.