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Water is a critically important nutrient for plants and animals.

The world's water supplies are extremely unevenly distributed - and many plants and animals are in a near-constant state of partial dehydration.

So, interventions that favourably alter the distribution of water on the planet's landmasses could have a large positive impact on most forms of land-based life.

The science and technology of managing this water is known as watershed management.

The world's landmasses are divided up into a series of drainage basins by drainage divides. This happens as a result of erosion that has been caused previously by running water.

To produce a more even water distribution over the available land, two areas need to be addressed.

• Management of the water within the drainage basins;
• Changing the distribution of water between those basins.

The some of the main technologies involved are:

• dam creation;
• barrier elimination;
• hole drilling and...
• syphon construction.

The areas of most interest are where running water faces a choice about the path it takes while flowing downhill. Erosion tends to create valleys surrounding flowing water - but there will be some places where running water faces a choice - and where relatively small interventions can make a big difference to the resulting flow.

This follows the principle of locating places where small actions can have large effects - and then applying your energy at those points.

Since humans have done only rather limited watershed management in the past, it is likely that there are still a considerable number of low-hanging fruit in this area.

Dams can be created by piling up matter. Barriers can be eliminated by shifting them. Earth can be moved by using conventional techniques - and rock can be moved by using explosives.

Imagine that you have a high ridge with water on one side, and a lack of water on the other - perhaps because rain clouds are forced up by the ridge itself - and so deposit their load of rain mostly on one side of it.

Then, cutting a channel through the ridge is not very practical.

However, fortunately, there are other options - using holes and syphons.

• Drilling a hole through the ridge allows water to be transferred across the boundary;
• Using a syphon is another way to transfer the water from one side to the other;
• Lastly if the top of the ridge is not of a uniform height, it is possible to transfer water from one side of the ridge to the other, simply by channeling it downhill to a point where the ridge happens to be relatively low.

Where water is diverted, ideally locks should be used - so the old flow can be restored periodically to service demand. One case when locks are useful is when a source is periodically used to top up a reservoir - but can also be used for other things.

Water flow has been controlled in and around cities for a long time. For example, in Bristol, the city where I currently live, there is a 5 km long engineered division of the river Avon, to provide a Floating harbour and the Bristol new cut - which insulates the harbour from tide and storm waters. The waters are diverted by using locks. This was all opened back in 1809. However much less effort has been expended in the areas outside cities.

To improve the planet's irrigation systems, I propose using publicly-available map information which identifies current water flows, and map elevation data to automatically calculate the cost-benefit ratio of various interventions which redistribute water so that it better irrigates the land. Then, the top projects around the world - those which provide the most benefit for the least cost - should be embarked upon.

Since water is so important to living things, improving irrigation via watershed management aimed at producing a more even distribution seems like an important area.

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