2007, according to the climate records at Texas A&M University, was a fairly wet year for Dallas. But when the Trinity River Audubon Center opened in 2008, there was a shift in the weather patterns caused by a strong La Nina event. Rainfall for Dallas was 78% of normal, and the pond named Great Blue Heron pond dried to a puddle. 2010's rainfall levels were 91% of normal, meaning that the DFW area started with the ground a bit less wet than usual, and the Texas State Climatologist says we're in the third worst drought since Texas began keeping records over 100 years ago: http://tamunews.tamu.edu/2011/06/07/texas-drought-continues-to-set-records-no-relief-in-sight/
Great Blue Heron pond is a new pond and, like Trailhead Pond, was apparently a location where the earth was so poisoned or damaged that the best solution was to dredge all the earth, put it in a landfill, stabilize the pit, and turn the pit into a pond. Earlier Google Earth images show an area with trees and then a bare landscape, scraped and gouged by bulldozers. By October, 2005, the pit was a pond and the shape was similar to what it is today. By the time they started building the center in 2007, vegetation (I suspect mostly Johnson grass and ragweed) had grown around the edges of the pond. In October 2008, after good rains, the pond was slightly larger than it is in the March 2011 Google Earth photo. There aren't available photos showing the pond shrinkage during 2008, so I can only make a guess at what happened and when it got to its lowest point.
This, of course, is an obvious opportunity for a nosy scientist to get out and get nosy. So I did.
On June 19, I borrowed some utility marker flags and trotted out to the pond and tagged the verge where the water met the soil to see what happened as the summer went along. What happened after that was that the area received five inches of rain (according to rainfall gauge #3055) late in June, and the water's edge moved over a foot beyond the original flag.
I'd like to get out and flag the northernmost edge of the water at Trailhead pond sometime this week. Again, the environment there has been modified by plants around the water's edge and we may see less evaporation because of this. And if they don't shrink down to tiny puddles during this very dry year, that would be a very good thing. The little arroyo we call Wood Duck Pond is mostly dry now. It dries up every summer in spite of it being shaded by trees -- or perhaps because trees line its bank.
I really need a "control" pond where someone's done Elegant Parkkeeping and has mowed the Bermuda grass and St. Augustine grass right down to the edge of the water. I suspect those will dry up faster unless water gets added.
I could be wrong. It would be interesting to see.