Lecture Notes Oct. 4

Water Resources

•Water is, in theory, a renewable resource (via hydro-cycle), except groundwater may be depleted over time because aquifers can be slow to gain water via infiltration and percolation (discharge or use exceeds recharge). In one mentioned in the text, the Ogallala which underlies a large area of the Great Plains, the water is pumped for irrigation much faster than it recharges naturally and thus the Ogallala is being depleted.)

•Consumptive vs. non-consumptive uses: water use is generally classified as agricultural or municipal and industrial. Agricultural use is “consumptive in that only a small portion of the water put on crops (less than 20%) returns to lakes and streams or groundwater---most of it evaporates or is transpired by the plants (that is the goal of irrigation). Many municipal and industrial uses are non-consumptive in that maybe 80% or more of the water makes it back into lakes and streams or groundwater, often thru urban wastewater systems. The water has a lower quality, may be polluted, but it does make it back into the water bodies. The big exception here is landscape water use (lawn watering) which is just like agriculture—most of it is lost to the atmosphere.

•Water resources are under stress around the world due to rapid growth in use, 300% since 1950, associated with population growth, increased affluence, the spread of irrigated agriculture, and urbanization.

•We’ll talk about water quality in a couple of weeks.

•There are also growing tensions between Urban vs. agricultural uses---in many urbanizing areas, like Colorado, farmers are selling their water to cities.

•Finally, water is a source of political conflict: international rivers like Rio Grande, the Tigris-Euphrates, the Indus, and the Parana have been fought over by the nations that share their river basins. Even inter-state rivers like the Colorado and the Arkansas, cause conflict. For example, Kansas accused Colorado of letting its farmers pump too much water from the Arkansas River, which the two states share thru a river compact (like a treaty between the states). The suit went to the Kansas supreme court and arbitration between the states, and was decided in favor of the Kansas farmers. So now, by legal decree, Colorado farmers must pump less water and must pay Kansas for damages over the years in which they were taking more than their share.