|Is that an efficient curve?|
Besides letting water flow where it wants, humans can work with natural flows by using check dams or other means of slowing water so that it infiltrates into the soil. In urban areas, we can use permeable surface covering to keep water on land instead of forcing it into flood/drainage channels. This latter move -- so common in the Netherlands where flooding can turn nasty -- has the additional advantage of reducing CSO (combined sewer overflow) events.
Bottom Line: Nature has managed water for billions of years. We should take advantage of those lessons to maximize the value we get from water.
* These thoughts are the flipside of my increasing interest in removing dams to improve BOTH human and environmental benefits from water. For more on the benefits of removing dams AND a very good cap and trade scheme to do so efficiently, read this article [PDF] by Jamie Workman.