Borrego Sun - Since 1949

Borrego Springs - WATER! Part II

 

Last updated 1/15/2016 at 1pm

In the Nov. 19 issue of the hard copy, we took a look at some of the findings of the U.S. Geological Survey (USGS) Report on the Borrego Valley groundwater situation. In short, there is currently a huge yearly imbalance between the approximately 20,000 acre-feet of water being extracted, or discharged from our aquifer system, compared to the 5,700 acre-feet naturally recharged from stream flow and underground sources.

An example here might shed some light on what we're up against. One must go to our biggest user of aquifer water (70 percent Agriculture) to find meaningful savings, and the biggest single user is 'citrus trees' (see previous issue for graphic). According to Jerry Rolwing, General Manager at the Borrego Water District (BWD), and USGS Report numbers, there are about 2,000 acres of citrus trees in northern Borrego Valley, and they consume about 8,600 acre-feet (43 percent) of all the groundwater pumped out of our aquifer system. Citrus trees currently consume almost 50 percent of our water, and they do it on less than fifteen percent of the land in active use among the three sectors.

The first question is, can a single citrus tree get by with ten percent less water? Twenty percent less? Thirty percent less? We live in a desert, and on top of that we've been in a Drought condition for five years. How much is too much water to take away from a citrus tree?

Let's make the assumption that the average citrus tree could, with improvements in watering efficiencies (already very high), use thirty percent less water and still produce the same quantity and quality of fruit. But thirty percent of 8,600 acre-feet per year is a savings of slightly more than 2,500 acre-feet of water per year, not even twenty percent of the 14,000+ acre-feet per year deficit we now face.

Reducing golf course water by the same thirty percent (another questionably viable option) unless non-grassy periferal areas are removed from watering, gives us an additional 1,200 acre-feet per year in savings; and a thirty percent reduction in municipal water use gives us only an extra 600 acre-feet. When you add them all up – 4,300 acre-feet per year in, "overdraft protection," it's still only thirty-one percent of the total percentage reduction needed for long-term groundwater/upper aquifer sustainability.

So, if significant savings (and thirty percent across the board would seem to be significant, at least at first glance) do not get us even close to the Promised Land of long-term sustainability (5,700 acre-feet per year discharge and recharge), what will?

The specific recommendations by our Borrego Water Coalition go a long way toward addressing that very question, including the options of fallowing agricultural land and/or obtaining some form of water credits purchased from, or sold to, other users to meet their individual water reduction goals. Penalties for non-compliance are in the mix, as well. We'll cover that subject in later issues.

But in summary, the Water Coalition recommends starting off with a twenty percent overall reduction in water use from all sectors, from not-yet-adopted baseline numbers, between 2020-2025, and then higher reductions in five-year increments out to the year 2040. In a later issue, we'll compare these recommendations with the six 'scenarios' presented in the USGS Report.

The USGS Report takes a comprehensive look at the geography, geology, hydrology (groundwater flow patterns), and historical land and water use patterns of Borrego Valley in our three aquifers – upper, middle, and lower.

The derived data from local wells and other historical sources allowed the USGS to produce a computer model – the Borrego Valley Hydrologic Model (BVHM) – that simulates both past and future conditions and interactions.

In the chart, we see the extent of the Upper Aquifer, and the cross section to the right shows all three layers of our aquifer system. The color-coded graphic shows the various depths to bedrock around Borrego Valley, again computer-simulated.

The three charts together provide a quick 3-dimensional visualization, a lay of the land, so to speak. There are some who argue that Rams Hill sits on a separate upper aquifer, but we'll go into that in another issue.

I've added reference points and numbers to all three charts for quick reference. The take-away for me in the modeling results was the finding that the upper aquifer is thinner than previously thought. But just how good are the underlying USGS Report data that will define, quantitatively, the scope and limits on our water future? Hopefully it's not a garbage-in/garbage-out situation! The histogram gives a rough idea in one example of how accurate or 'predictive' the model is for simulating actual aquifer conditions.

As in most of life, there is the actual and the ideal. Or in this case, measured vs. simulated. In the histogram, the ideal is for the simulated numbers on the water level at various depths generated by the computer model (using pretty sophisticated math) to match perfectly with the actual ones measured throughout the aquifer system – a 1:1 correlation. (BTW, I recalibrated the numbers on the horizontal and vertical axes for reasons I will include in my memoirs.) Aside from that, as for the ability to predict past and future aquifer behavior accurately, the results of the BVHM computer model, according to the USGS Report, "indicate that the model reasonably represents seasonal changes as well as major features in the climate record." More examples of model predictability will be in later issues.

"Reasonably represents," means there are caveats; it's not a perfect correlation in this example or any of the other simulations generated for the USGS Report, but pretty darned close, outlying data points notwithstanding (but explainable). Like folks say, close enough for government work.

In generating the various computer simulations via the BVHM, the USGS Report presents six different 'scenarios.' Five scenarios are tied to aquifer sustainability options over the fifty-year period between 2010-2060, while a sixth scenario is called the 'Status Quo' option for the same time period; for us Borregans that means, "Do nothing!" And this option is sobering, as given. Perhaps purposely so.

The last graphic literally paints a color-coded picture of aquifer draw-down if we make no changes to our current consumption rates, from 126-175 feet lower (gray and white squares, respectively) than from 2010 levels in the northwest agricultural sections. There is generally less draw-down as one moves down the valley, and the simulation even shows a predicted rise in the water table in the southeastern valley! It's an interesting feature of the model, but it's not like we can pack our bags, move fifteen miles, and start building a water park.

These are all simulated numbers from a computer model, yet given the positive predictive nature described earlier, I think it's fair to say the USGS Report findings pretty much put to rest the option for the Status Quo (Whistling-Past-the-Graveyard) scenario. It's patently clear we must do something. The questions are what and when and at what cost?

Therefore, we need to address how various options in the USGS Report and from the Water Coalition, together with decisions made by the Borrego Water District along the way, will impact Borrego Valley in regards to not only our natural desert-living environment, but also our water future and economic future.

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