Dealing with stormwater, by definition, means dealing with surface waters: the lakes, rivers, wetlands, and estuaries that receive runoff. But a great deal of stormwater infiltrates and becomes groundwater instead. Many cities, in fact, are actively trying to increase the rate at which that happens, through the widespread use of green infrastructure, but from a stormwater perspective we still tend to think of infiltration mostly in terms of getting that water out of the way—off the surface where we’ll have to deal with it—rather than in terms of replenishing the aquifers.
About 30% of the world’s liquid freshwater—that is, the portion that’s not frozen in glaciers or ice caps—is groundwater. We tap into our aquifers, especially in times of drought; in most parts of the US we’re depleting groundwater much faster than it’s being replenished. We know, for instance, that for the Ogallala aquifer in the central US—believed to be one of the largest in the world—annual recharge is only about 10% of annual withdrawal. The uneasy fact is, though, that in many cases we don’t really have a clear picture of where all of the groundwater is, or how much there is. (For a good perspective on research that’s being done in this area, see our reader profile in this issue on Lenny Konikow, a hydrogeologist who has spent decades studying groundwater flows and is developing models to show, among other things, the interaction between ground- and surface waters.)
My counterpart here at Forester, Laura Sanchez, the editor of Water Efficiency magazine, recently posted a thought-provoking blog on the issue of transboundary aquifers. (You can find it, and other content from that magazine, here.) She points out that although states and countries are usually pretty good at cooperatively managing shared surface waters like rivers—we might wrangle over water rights or pollutant loads, but at least we know what it is we’re arguing about—aquifers are mostly overlooked. Often we don’t even know their boundaries or how, exactly, water is moving through them. Yet so many things we do on the surface—pumping groundwater for drinking water or irrigation, letting pollutants seep in—affect our shared aquifers.
An article from Circle of Blue explains how complex the issue is, pointing out, for example, that some researchers believe the US and Mexico have eight shared aquifers, while others say there might be as many as 36. “It does not help that there is no internationally recognized standard for defining aquifer boundaries,” the article notes.
It also states, “Despite more than a decade of technical and political attention at the highest international level, countries have made little progress in developing agreements to coordinate the oversight of groundwater resources that cross political borders…. Worse, experts say that scientific understanding of the roughly 600 transboundary aquifers and groundwater bodies—which underlie nearly every country—is so poor that even identifying the basins most vulnerable to conflict, contamination, or depletion is comes down to an educated guess.”
How aware are people in your area—elected officials included—of the groundwater situation? If your water table is high, or if the aquifer is a major source of drinking water, you might have strict regulations about pretreatment for stormwater that will be infiltrated. If you’re in a drought-affected area like California, you might be hearing a lot about restrictions on pumping and groundwater withdrawals. And if you’re near an international border, perhaps you’ve even been involved with some of the ongoing studies of our shared aquifers. Tell us your perspective in the comments, or e-mail [email protected].
