Surface-Groundwater Systems in a Holistic Water Cycle
Hydrologists’ equations for surface flows are hyperbolic, while those for groundwater are elliptical. Paraphrased from Professor V. M. Ponce
And never the twain shall meet? What about when biology enters the equation, as it does in almost every natural interface between surface and groundwater?
By NightElfik (Own work) [CC0], via Wikimedia Commons (Public Domain)
mycorrhizal fungi hyphal networks . . .
as they spread through the soil . . .
interacting with countless other soil life forms . . .
and their exudates . . .
we have yet to identify as critical to our own needs, but certainly sustaining their own habitat needs by ensuring persistence of the soil ecosystem.
Over time, these roots and soil organisms biogenically create soil structure, including systems of macropores that detain water in its otherwise inexorable call to gravity – the “sponge”. Such physical forces/ attractions may be best approximated with fractal, or “pre-fractal” approaches.
Water flow around an obstacle transits to turbulent wake by aarchiba, released to Public Domain
Cloud streets and vortices off the Aleutian Islands by NASA Goddard Space Flight Center from Greenbelt, MD, USA
Pythagorus Baum (Tree)
The problem is, as a group they forgot that the models represent “approximations” and began accepting them as gospel – the whole truth. Regulatory and environmental review processes have similarly viewed standard hydrological models as the final “authority”.
After all, the regulators rarely have the engineering chops to challenge these broadly accepted (reductionist) hydrologic engineering models. So they defer authority to the engineers, counting on the engineering consultants’ liability insurance to cover any potential mishaps that may arise as a result.
How easily the physical scientists dismissed the pervasive influence of life – including our own – on the phenomena they sought to measure and predict.
The 19th through early 20th Century bifurcation of hydrologic science into surface vs. groundwater perspectives in the U.S., at least, was fraught with political maneuvering and intrigue, exemplifying how the complexity of human dynamics, arising from human emotions, colors the seemingly most rational of the sciences.
By 1824, Congress had instructed the U.S. Army Corps of Engineers to improve navigable surface waters, so the national focus on surface waters was entrained a century prior to the U.S. Geological Survey’s (USGS) illuminations of groundwater.
Perhaps “founder effects” from that original surface water bias helps explain why water resource professionals, in the context of California’s Sustainable Groundwater Management Act, emphasize recharging alluvial aquifers by diverting surface waters.
Even the California Department of Water Resources (DWR), in its 2017 Draft Water Available for Replenishment report, conveys the impression that the only means of groundwater recharge is via engineered recharge structures – into alluvial aquifers in valley bottoms. Well, OK, it’s true we withdraw more water from alluvial than from bedrock aquifers, but that doesn’t mean surface waters are the only nor best means of recharge.
How does this emphasis on alluvial aquifers demonstrate a surface water bias?
Because alluvial aquifers are formed through deposition and sorting of sediments by surface waters – over centuries/ millennia. The surface water bias can relate to that.
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To understand how porous seemingly solid bedrock can be, one must comprehend the complex dynamic geologic upheaval involved in creating and sculpting mountains over geologic timescales, which are, themselves, nearly beyond our grasp.
Even in our own time frame, the daily frequency of documented California earthquakes (most low on the Richter scale), reported by some news outlets, should remind us that even bedrock is seldom static.
Bedrock fractures and interstices caused by seismic and other disturbances become part of the groundwater system – fed by rainfall infiltration and percolation on watershed/ catchment uplands, as well as riparian zones, thence flowing to alluvial aquifers, baseflows, ultimately to the ocean and hydrologic cycling back into the atmosphere.
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Aside from seismic and other physical fracturing, most rocks absorb moisture into interstices among grains. If one is outside when it rains, or at the shoreline, one may readily observe how sandstones, limestones, even granite and its igneous variations, absorb moisture from their environments.
So the fact that the prevailing hydrologic paradigm, in California, at least, fails to connect the dots among bedrock and alluvial aquifers –
- imagining that recharge can only occur via surface waters, as true of the Draft Water Available for Replenishment report,
- ignoring hydrological connectivity between bedrock and alluvial aquifers, and thus watersheds and groundwater
A July 7, 2017 incident at San Francisco International Airport serves to illustrate the problem. The July 31, 2017 Mercury News article headlined, “SFO CLOSE CALL: Mental ‘blind spot’ may have affected pilots – Confirmation bias could be to blame for jet nearly landing on busy taxiway” (Gafni 2017) concludes with the following excerpted text:
Capt. Shem Malmquist, a 777 pilot and air safety and accident investigator, has written about aviation confirmation bias. . . .
Once the brain has decided on a solution, it takes an awful lot of evidence to shake it. Our perception is actually influenced greatly by what we believe, where some cognitive scientists take it so far as to state that reality is a shared hallucination,” Malmquist said. “Confirmation bias is one of those factors that is very challenging to see or predict prospectively, but extremely obvious in hindsight.”
Click images to enlarge
Click images to enlarge
Instead, the vast majority of diagrams currently available online tend to suggest that watersheds indeed only shed water, implying that precipitation hitting the ground surface is automatically, immediately transferred to surface runoff, thence to surface waters, from whence all our groundwater resources supposedly hail.
They are missing the HUGE, subterranean [out of sight, out of mind] component of the holistic hydrologic cycle – the one we may most readily influence by restoring the infiltration and percolation functions of historically degraded vadose zones. See Stream Networks vs Watersheds/ Catchments
Thus far we’ve emphasized the catchment aspects of surface-groundwater interactions because those are the functions most overlooked among the water resources crowd. Downstream of catchment functions lie baseflow interactions, which, thanks to the Sustainable Groundwater Management Act, are enjoying greater attention. Baseflow augmentation is the founding paradigm of Rainfall to Groundwater, as discussed on Surface Water Diversions vs Baseflow Augmentation.
The below diagram offers a synopsis of surface-groundwater interactions. Please see blog post #10 How Does Groundwater Get There? Some Basics. for further considerations using this diagram.
Gafni, Matthias. 2017. SFO Close call: Mental ‘blind spot’ may have affected pilots – Confirmation bias could be to blame for jet nearly landing on busy taxiway. Mercury News July 21, 2017.
Garcia, Linda. 1991. The fractal explorer. Dynamic Press, Santa Cruz, California, USA.
Wright, C. E., editor. 1980. Surface and Groundwater Interaction. International Commission on Groundwater, Unesco, Paris.