Thursday, June 24, 2010

An Ogallala Groundwater Concept Rarely Discussed

Much has been and is being written about the Ogallala Aquifer and its groundwater situation.  Most articles do several things that I always want to question.  First, they tend to discuss a specific part of the Ogallala, but attach a headline that applies to the entire aquifer.
Take for example a recent Twitter post:  "Decline of the Ogallala Aquifer - a classic common pool resource problem."  When you follow the link and read the article, it's solely about the High Plains Texas portion of the aquifer, and moreover, the situtation (problem) is attributed almost exclusively to that states' groundwater management scheme - the Rule of Capture.  Yet, anyone skimming headlines only will come away thinking the entire Ogallala is a classic common pool resource problem - even though there are 8 different management approaches to the entire aquifer and only Texas uses the Rule of Capture.  I have probably 4 times over the past 6 months left comments to this effect on blogs and replied to twitter posts.  This will be a hard practice to correct, I'm afraid.

Secondly, a lot of the articles couch the problem of declines in a constant time frame - and predict a future-certain "plane crash".  For example, they say something to the effect that the water table is declining at 1.5 feet per year, and at this rate, 50% of the aquifer will be gone in 40 years and the aquifer will be dry in 80 years.  What is not commonly understood is that while a constant decline rate will predict the future, there will NOT be a constant decline rate because the wells producing the water and causing the decline will NOT be able to maintain a constant rate of production as the water table continues to drop. 

In fact, even if you are aware enough to know that reductions in saturated thickness will result in reduced pumping rates, most consider these reduced production rates as linear, and therefore predictable over time.  Not true.  A well's production rate decreases ever-faster as the saturated thickness dwindles.  In other words if you find a 10% reduction in your well yield with the last 20 feet of decline, the next 20 feet of decline will reduce your well yield significantly more than 10%, and so on.  The exact relationship is dictated by the aquifer characteristics so they vary from place to place - even within the same aquifer, but the relationship is a geometric one rather than arithmetic.

What this means is that the economic end of pumping will be closer than most think, AND the predicted future water level elevation of the aquifer will be higher than predicted as a result, AND an aquifer (in the sense it is being used in the article) will never be pumped dry.  Said another way, our "plane" will land softer than everyone is predicting.  However, of course, the core issue remains - any overdrafting will eventually see the plane land, while most would prefer that it keep flying forever (sustainability).  This, however, is an issue for a later blog.   


  1. Interesting post—I'll Wave you a question or two about it at some point (hopefully this afternoon).