Groundwater Law – Physical – “the water budget myth”

by Jay Lundgroundwater-streamflow

This week’s short post is on groundwater law – from the viewpoint of physics.  Water policy, management, and human law often misunderstand how groundwater and surface water work physically.

Bredehoeft, et al. (1982) distill a longstanding lament of many groundwater experts, “Perhaps the most common misconception in groundwater hydrology is that a water budget of an area determines the magnitude of possible groundwater development.  Several well-known hydrologists have addressed this misconception and attempted to dispel it.  Somehow, though, it persists and continues to color decisions by the water-management community.”

Long ago, the venerable Theis (1940) summarized:  “Under natural conditions … previous to development by wells, aquifers are in a state of approximate dynamic equilibrium.  Discharge by wells is thus a new discharge superimposed upon a previously stable system, and it must be balanced by an increase in the recharge of the aquifer, or by a decrease in the old natural discharge, or by loss of storage in the aquifer, or by a combination of these.”

As Bredehoeft, et al (1982) conclude:

“1. Magnitude of [groundwater] development depends on hydrologic effects that you want to tolerate, ultimately or at any given time (which could be dictated by economics or other factors).  To calculate hydrologic effects, you need to know the hydraulic properties and boundaries of the aquifer. Natural recharge and discharge at no time enter these calculations. Hence, a water budget is of little use in determining magnitude of [sustainable groundwater] development.

2. The magnitude of sustained groundwater pumpage generally depends on how much of the natural discharge can be captured.

3. Steady state is reached only when pumping is balanced by capture, in most cases the change in recharge is small or zero, and balance must be achieved by a change in discharge. Before any natural discharge can be captured, some water must be removed from storage by pumping. In many circumstances the dynamics of the groundwater system are such that long periods of time are necessary before any kind of an equilibrium condition can develop.  In some circumstances the system response is so slow that mining will continue well beyond any reasonable planning period.

These concepts must be kept in mind to manage groundwater resources adequately. Unfortunately, many of our present legal institutions do not adequately account for them.”

Water budgets are important in managing water, but better water budgets include both surface water and groundwater, which interact naturally and through management.  Most groundwater pumping is ultimately from surface water, taken at some time or place.  Water budgets consisting only of groundwater neglect the laws of physics that govern the sustainability of water management.

In California, local, regional, and state managers and regulators of Sustainable Groundwater Management programs and plans will need to integrate surface water with groundwater.  It’s the physical law, and it is always, eventually enforced.

Further reading

Bredehoeft, J.D., S.S. Papadopulos and H.H. Cooper. 1982. Groundwater: the Water Budget Myth. In Scientific Basis of Water-Resource Management, Studies in Geophysics, Washington, DC: National Academy Press, pp. 51-57.

The Nature Conservancy, RMC Consultants, Inc. (2016), Groundwater and Stream Interaction in California’s Central Valley: Insights for Sustainable Groundwater Management, The Nature Conservancy, Sacramento, CA, 149 pp.

Maven’s Notebook, CA WATER LAW SYMPOSIUM: Questions of common supply: SGMA requirements for interconnected surface water and groundwater, panel discussion summary, June 19, 2019.


About jaylund

Professor of Civil and Environmental Engineering Director, Center for Watershed Sciences University of California - Davis
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3 Responses to Groundwater Law – Physical – “the water budget myth”

  1. Jai Rho says:

    The Sustainable Groundwater Management Act (SGMA) was enacted to mitigate decades of overdraft and subsidence of groundwater basins. However, it continues to allow local agencies (Groundwater Sustainability Agencies, or GSAs) to manage groundwater through “plans” (Groundwater Sustainability Plans, or GSPs) that are based on localized criteria.

    While the SGMA requires GSPs to avoid six “undesirable results,” it implicitly allows groundwater usage to have “significant” effects on groundwater levels, groundwater storage, seawater intrusion, degraded water quality, land subsidence, and depletion of interconnected surface water. Under the SGMA, such effects are not “undesirable” unless they are also “unreasonable” which is undefined and subject to local adjudication.

    This means that GSPs may plan for significant depletion of interconnected surface water, as well as diversion of other surface water for purposes considered to be “beneficial use” by the State Water Board. Significantly, the State Water Board includes “reductions in pumping costs” as beneficial use. (Raising groundwater levels with surface water almost always reduces pumping costs).

    Integrating surface water may be sound groundwater management in principle. In practice, however, GSPs should not be allowed to continue overdrafting of groundwater basins through depletion of surface water, especially during dry years when surface water flow is diminished.

  2. J Rizzi says:

    We can help replenish and Store more (ground) water when rivers and stream are have extra; by installing large shaft near water that is filled only when water level is high enough to fill. At the bottom of the shaft are horizontally drilled paths to the porous ground water layers and the pipe that connects the two is like a drainage pipe (filled with holes). This allows for quick or quicker recharging of ground water basins.

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