Surface Water Diversions vs Baseflow Augmentation

Our Entrainment to Surface Water Thinking

In 1824 the U.S. Army Corps of Engineers was placed in charge of the linear, surface waters focus of navigable waterways. As noted in “Water Yield” vs Baseflow Augmentation, a century passed before investigations of groundwater began to yield insights through the U.S. Geological Survey. So the U.S. focus on surface waters was well entrenched and entrained long before groundwater emerged to conscious consideration.

As also noted on that other page, while the U.S. study of groundwater began as a multidisciplinary practice, by the end of the 20th century its purview strictly pertained to the saturated zone, where it could safely remain a purely physical science – without intrusion of bio/ ecology to mess up its pretty equations.

Until groundwater became regulated in California with the late 2014 passage of the Sustainable Groundwater Management Act (SGMA), the hydrologic models most prevalent in public processes, such as environmental review analyses, were predominantly models of surface water processes, which, for the most part, have also done their best to ignore interference from bio/ ecology. Plants in an Ecohydrology Context and Surface-Groundwater Systems in a Holistic Water Cycle offer an overview of one important area where bio/ ecology does enter into this – the vadose zone.

Thus, especially as it applies to public interests, the major thrust of hydrology has long been on surface waters. Post-SGMA, not surprisingly, as earnest public servants and academics began considering ways to enhance groundwater recharge, the public agency and academic focus has been on diversion of surface waters to recharge groundwater basins.

We’ve seen, for example, in California Department of Water Resources’ (DWR) Water Available for Replenishment (WAFR) report, exultation of 20th century models of diverting surface waters to engineered, biology-free percolation basins. Absolutely nothing new there, as noted in blog post 5 DWR, Great Job on WAFR! Now Add R2G.

OK, we can give DWR some slack there, as they really didn’t have all that much time to generate new approaches. (Though Verna certainly did what she could to help them realize there are other approaches and DWR just ignored that input.) More laughable is their graphic exultation of engineered percolation structures over the much more expansive natural processes of rivers/ streams and their floodplains, as also pointed out in blog post 5.

But DWR hasn’t been alone in that. We’ve seen quite a few academics and nonprofits jump in, generating presentations, reports and fund-raising tools advocating application of surface waters to, again, engineered percolation basins, to orchards for infiltration, to floodplains, with such catchy acronyms as MAR – Managed Aquifer Recharge.

[For some reason, that reminds Verna of another page in this Alternate Paradigms section – Domination vs Collaboration.]

The unifying concept behind all such proposals is Diversion of Surface Waters. But, in many California hydrologic regions WAFR showed there really isn’t all that much surface water available for recharge.

Hence the emphasis on catching/ diverting flood flows. But then, for Delta tributaries at least, how does that comport with State Regional Quality Control Board emphases on allowing unimpeded flows to reach the Delta?

Furthermore, all these approaches are predicated on infiltrating diverted surface flows into lowland basins. Especially during times of high flows, those basins will likely be experiencing natural recharge on their own. Just how much water can we possibly force into ground that is already saturated???

Other Alternate Paradigms

Other Alternate Paradigms also apply. SGMA doomed us from the start to reductionistically imagine groundwater as existing solely in the basins we generally withdraw it from, disconnected from the watersheds/ catchments that actually feed those basins. To Verna that’s apparent devolution from the more holistic early 20th century perspective highlighted in blog post 3 How Watersheds Relate to Groundwater.

This emphasis on Sink vs Source is analogous to the points made in Stream Networks vs Watersheds/ Catchments, which, in turn, gets back to the Figure vs Ground bias.

While It has been said on other pages on this site, the fact that the vast majority of precipitation falls on uplands, not streams, bears repeating here. To route the greatest amount of precipitation directly to groundwater, think uplands/ watershed/ catchment. At the same time, we must restore fully functional riparian zones as part of the watershed/ catchment restoration process.

Baseflow Augmentation: Enhancing Natural Recharge as the Superior Paradigm

By routing precipitation into the ground right where it falls we can catch more of it and achieve baseflow augmentation, provided that groundwater basins remain in compliance with SGMA. That also means more for groundwater users to draw from. Part of this section is replicated from “Water Yield” vs Baseflow Augmentation, so you need not refer back to that page.

Verna recognized baseflow augmentation as the appropriate paradigm, when, after searching academic literature databases fruitlessly for years, she used Google Scholar Beta in early 2005 to find, among other gems, “Baseflow augmentation by streambank storage” (Ponce 1989a), along with Ponce and Lindquist (1990a & b). She asked Professor Ponce to serve on her doctoral committee and he skillfully guided her along her path.

As noted in the Rainfall to Groundwater Glossary,
Baseflow: “the flow of perennial streams . . . , consisting of interflow and groundwater flow intercepted by the stream” (Ponce 1989b); “the fraction of streamflow that originates in ground water” (Ponce 2007). Baseflows are the low flows that sustain aquatic life like steelhead and salmon through the summer months in California and other regions with dry summer seasons. See What’s in it for steelhead & salmon? and What does Rainfall to Groundwater offer for vernal pools?

To get a sense of how interflow fits in, please refer to the Jigour (2018) drawings on Stream Networks vs Watersheds/ Catchments, a complementary page in this Alternate Paradigms section.

Source: USGS

Click image to expand

The basic idea behind Rainfall to Groundwater is to enhance natural recharge of groundwater by restoring the infiltration and percolation functions of anthropogenically degraded watersheds/ catchments in order to restore natural detention functions. By routing more precipitation into the ground right where it falls – Rainfall to Groundwater – baseflows will be naturally augmented.

By restoring degraded watershed/ catchment functions on the land surface and in the vadose zone, as elaborated on Plants in an Ecohydrology Context and Surface-Groundwater Systems in a Holistic Water Cycle, we facilitate the infiltration of rainfall and its interflow and/or percolation to bedrock aquifers, thence to alluvial aquifers, thence to river/ stream baseflows .

Not only will this improve baseflow conditions for anadromous fish, other aquatic species and other groundwater dependent ecosystems, it will enhance the groundwater recharge needed by many California Groundwater Sustainability Agencies to bring their groundwater basins into compliance with SGMA, while facilitating the ongoing withdrawals needed by agriculture and other human uses – all without the need for expensive new engineered structures.

Watershed/ catchment restoration will doubtless be less expensive to implement than engineered structures, but as these proposed natural systems mature they will become essentially self-sustaining, which cannot be said for the engineered structures, that require ongoing human maintenance – great for jobs, if that’s the objective, but hard on taxpayers/ ratepayers.

As noted in blog post 5 DWR, Great Job on WAFR! Now Add R2G, engineered recharge structures require continuous maintenance to remove the buildup of fine sediments that clogs percolation functions.

In contrast, natural systems do that essentially free of charge – ecohydrological services. Restored/ naturalized floodplains flush such fine sediments into discreet pockets where they become substrate for riparian vegetation.

Restored watersheds/ catchments can become largely self-sustaining, although some natural resource and adaptive management will be necessary. All far less costly to implement and maintain than the widely proposed engineered responses to SGMA, beginning with the requisite environmental review.

Groundwater Recharge Options

So, in California we have a couple ways we can go on this, not necessarily mutually exclusive.

We can invest the enormous amounts of public/ private funds needed to implement engineered approaches, including expensive environmental review and mitigation, to diverting surface waters toward limited lowland infiltration/ percolation opportunities.

We can shift the prevailing paradigm to baseflow augmentation/ natural recharge on uplands, as well as lowland opportunities. This will still require some up-front investment in ecological restoration and payment to owners of uplands – principally rangelands to begin with – and riparian zone properties for enhancement of ecohydrological services.

The program can/ should ultimately be expanded to forestland owners to fully maximize watershed/ catchment functions, although a bit of additional research is likely needed to support that.

In both cases, not nearly as much funding will be needed as is true for the engineered approaches. This is partly because environmental review will go more smoothly for bonafide ecological restoration. But also, ecological restoration in itself is far less costly than the concrete and other hard materials needed for engineered approaches.

Citations

Ponce, V. M. 1989a. Baseflow augmentation by streambank storage. Environment, Health, and Safety Report 009.4-89.13, Pacific Gas and Electric Company Department of Research and Development, San Ramon, California, USA.
http://ponce.sdsu.edu/baseflow_augmentation.html

Ponce, V. M. 1989b. Engineering Hydrology: Principles and Practices. Prentice Hall.
Englewood Cliffs, New Jersey. Now, the Second Edition (2014) is online:
https://ponce.sdsu.edu/enghydro/

Ponce, V. M. and D. S. Lindquist. 1990a. Management of baseflow augmentation: a review. Water Resources Bulletin 26:259-268. http://ponce.sdsu.edu/baseflowaug259.html

Ponce, V. M. and D. S. Lindquist. 1990b. Management strategies for baseflow augmentation. Pages 313-322 in Proceedings, ASCE Irrigation and Drainage Divsiion, Watershed Management Symposium, Durango, Colorado.
http://ponce.sdsu.edu/watershedplanbaseflowaug313.html

Ponce, V. M. 2007. Sustainable yield of groundwater. San Diego State University.
http://ponce.sdsu.edu/groundwater_sustainable_yield.html