California County Drainage

Area Percentage

This map shows the drainage area percentage for each California county. This percentage is defined here as the total drainage area feeding all dams in the county, divided by the total area of the county. The drainage area feeding a dam is defined as the the total area of all watersheds which feed the river feeding the dam, up to the point of the dam.

Of interest here is the fact that the dams of many California counties capture water from areas much greater than the total area of the county in which they reside; in some cases, dams capture water from up to fourteen times the area of their county. For California as a whole, the total drainage area feeding its dams is approximately 135% of its total land area. This gives a qualitative impression for the significant displacement of water resources occurring in the state, and the use of water from other states. However, it must be noted that some of this effect is probably due to the fact that water is dammed repeatedly by multiple dams as it makes its way to the Pacific.