GLG 110: Dangerous World

Part 2: Aquifer Recharge See slides 24-25 of the lecture given on October 28th for reference. One of the resource issues related to aquifers is that humans are using the water faster than it can be replaced through natural processes. This causes the aquifer to dry up. The following questions will give you an idea of these timescales. The numbers are based on data about the Ogallala aquifer, which underlies most of the western Great Plains and is a crucial water source for agriculture in the region. The Ogallala aquifer underlies a surface area of 450,000 km2. On average, it is found at a depth of 15 to 90 meters (a thickness of 75 meters). Its average recharge rate is 21.59 mm/year. A few decades ago during the peak of human pumping, the average rate of withdrawal was as high as 1 meter/year (1000 mm/year). These rates mean that the thickness of the aquifer increases or decreases by those distances every year. For the purposes of this assignment, we assume that these rates affect the aquifer uniformly. This is not actually the case- pumping varies from region to region, but these averages give us a basic idea of the processes involved. 7) At the peak rate of pumping, what was the annual rate of overdraft of the aquifer? (Overdraft is the rate by which the withdrawal exceeds the recharge). Watch your units! Give your answer in mm/year. Show your work and put a box around your answer. 8) At this rate, how many years would it take for human actions to drain the aquifer? Show your work and put a box around your answer. 9) Recently, conservation efforts have reduced overdraft of the aquifer to only 55.86 mm/year. At this rate, how many years will it take for human actions to drain the aquifer? Show your work and put a box around your answer. 10) If the aquifer is completely depleted, how long will it take to refill? Show your work and put a box around your answer.