I was recently pondering my obsessive interest in water and had a BGO (Blinding Glimpse of the Obvious)!
>Some 70% of the Earth's surface is covered by the oceans i.e. salt water.
>Nature provides us with the most wonderful re-cycling system whereby warmth over our oceans causes evaporation and cloud formation, winds moves the cloud around and as it cools (condensation) it falls as beautiful fresh water.
>There is no shortage of total water, but there are often shortages of fresh water.
>From earliest days, man has stored fresh water to deal with these shortages. We don't lie in the rain with our mouths open to meet our drinking needs-rather we store fresh water when it is available to cover for our future drinking needs.
>Storage methods for our drinking and washing requirements need to be "efficient". That mostly means avoiding evaporation. There is plenty of salt water in the oceans to meet cloud formation needs.
>Exactly these same principles apply to storing water for irrigation (food and fibre production)needs. Only the scale is different. We need to store and to store "efficiently".
>This is particularly the case in Australia where we have the most variable rainfall on Earth. Our predecessors did a great job in building water storages-dams.
>We need more, but they need to be deep (valleys)to minimise surface area and thus evaporation and have good catchments.
>Storages also need to be flexible so as to allow flows from smaller events to pass and to take "the top" off the bigger events, both for flood mitigation and storage for future needs.