First, we must calculate how rapidly limestone is being removed from the floor of the valley. Most of the limestone leaving the valley is dissolved in Spring Creek. Later, we will discuss chunks of limestone being rolled, bounced or otherwise carried out of the valley by Spring Creek, although these are rare. There is almost no loss or gain of limestone in the wind, and meteorite falls are VERY rare and can be ignored.
About 1 m (just over 3 feet) of rain per year falls on Happy Valley. About two-thirds of this is used by trees and evaporated, and one-third leaves the valley in Spring Creek. That water which leaves in Spring Creek, called runoff, contains a lot of dissolved limestone, which is picked up from the ground. Spring Creek water averages about 0.33 kilograms (0.33 kg) of limestone for each cubic meter (1 m3) of water. (1 kg is 2.2 pounds, and 1 m3 is a cube just over 3 feet on a side), so the limestone in the water weighs 0.33 kg/m3.
If Spring Creek collects a layer of water 0.3 m thick from all of Happy Valley each year (0.3 m3 from each square meter or m2), and each cubic meter of Spring Creek water contains 0.32 kg of limestone, then how much limestone is lost from each square meter of Happy Valley each year, on average? (Note that the units are included and calculated properly for you here, but you should understand what was done, and why.) 0.3 m3/m2/yr x 0.32 kg/m3 = __________ kg/m2/yr.
