Drought shortage by HUC12 in the Eel River basin for June 2014. Red shaded basins have more shortage. Diversion points are shown as squares (riparian rights) and triangles (appropriative rights), scaled in size by use quantity. Web-based maps can show analysis results. (Lord 2015)

By Jay Lund, Ben Lord, Andrew Tweet, Wesley Walker, Chad Whittington, Reed Thayer, Jeff Laird, Quinn Hart, Nicholas Santos, William Fleenor, Julia Pavicic, Lauren Adams, and Bradley Arnold

Drought often means not having enough water to satisfy all water-right holders.

Assessing which water-right holders should curtail their use and by how much is not simple.  California’s complex water rights system includes two water law doctrines: seniority-based appropriative water rights (“first in time, first in right”) and older and generally higher-priority English common-law-based riparian rights (where shortages are shared proportionally across all riparian right-holders).  Assessing curtailments is further complicated by the complex hydrology of large river basins with many sub-basins and local inflows, as well as hundreds or thousands of water right holders scattered throughout these basins with different water use quantities, priorities, and return flows.

Faced with such a daunting task of many complexities and uncertainties, water right administrators have some reluctance to suggest or enforce water right curtailments, even during droughts.  This reluctance works against the property rights of senior right-holders, reduces environmental flows, and hinders user water supply investments, agreements, and markets.

Fortunately, the legal logic of water right doctrines can be represented mathematically.  In the latter years of the 2012-2016 drought, the State Water Resources Control Board funded research at UC Davis to suggest newer methods for analyzing drought water right curtailments in California.  Although these methods were not used during the drought, they point to a more formal way to analyze drought water right curtailments, and quantify likely uncertainties from such analyses which require additional technical work or policy determinations.

The methods, now published (Lord et al. 2018), combine established databases of water right-holders and water availability forecasts with mathematical representations of water law logic and distributed water balances.  All data is stored in spreadsheets for easy review, and public-domain software is used to allocate available water to water users scattered across large basins.

Initial software implementations of these methods have been made for the Eel, Russian, Sacramento, and San Joaquin watersheds.  These are summarized in the table below and detailed in the five masters’ theses under further reading.

These analyses have also included early explorations of how robust curtailment model results are to uncertainties in overall and local water availability estimates due to uncertain flow forecasts, inaccuracy in hydrologic models and return flows, reservoir releases, and water use estimates.

Some overall findings are:

1. So far, the spreadsheet models seem to work well, seem understandable for stakeholders and local experts, and can be tailored to local conditions. (Every watershed has local oddities.)
2. Substantial uncertainties exist in the underlying data for water availability and use calculations: forecasts of basin and local inflows, return flows, and right-holder water use and diversion locations. Although much data is available, estimation and measurement errors are unavoidable for such large complex systems.  There will always be need for policy judgement and interpretation.  Legal and policy controversies, and resultant uncertainties, are also likely regarding particular water right and contract issues.
3. Local environmental flow requirements are systematically lacking across all basins examined, and were largely unavailable for inclusion in these analyses.
4. Simple rules can often be made before the onset of drought to forewarn or assure water right holders about the likely extent of use curtailments that will be needed.
5. Simplifications can and must often be made. All errors are not important and important errors are not uniformly distributed across basins.  Most water users are very small and errors tend to affect upper watersheds more where estimate errors are greater relative to stream flows.
6. The methods developed can be useful inputs to water user and agency curtailment decisions, with interpretation and discussion, and are likely to improve significantly with use. Most models improve with sustained application, but usually need an initiation period of interpretation, refinement, and scrutiny.
7. A common spreadsheet analysis framework should make it easier for local experts, interests, and state water right regulators to develop a common technical understanding of water right curtailments, and more testable and precise descriptions of their disagreements and implications. Results can be displayed easily on maps, tables, and charts.

California needs a better and common water accounting system (Escriva-Bou et al. 2016).  Hopefully available data and more public analysis will reduce the technical controversies of water right administration, particularly during drought.  The mathematical representation of legal doctrines should shorten, better structure, and focus many water right and management controversies.

The authors are or were with the UC Davis Center for Watershed Sciences.  The web site http://watershed.ice.ucdavis.edu/dwrat/?region=0 shows modeled results for the Eel River in the summer of 2014 at the individual water right level.

Further reading

Escriva-Bou, A., H. McCann, E. Blanco, B. Gray, E. Hanak, J. Lund, B. Magnuson-Skeels, and A. Tweet. Accounting for California’s Water – Technical Appendix, 177 pp., PPIC Water Policy Center, San Francisco, CA, July 2016.

Escriva-Bou, A., H. McCann, E. Hanak, J. Lund, and B. Gray. Accounting for California’s Water, 28 pp., PPIC Water Policy Center, San Francisco, CA, July 2016.

Lord, B. (2015), “Water rights curtailments for drought in California: Method and Eel River Application,” Master’s thesis, Department of Civil and Environmental Engineering, University of California – Davis.

Lord, B., B. Magnuson-Skeels, A. Tweet, C. Whittington, L. Adams, R. Thayer, and J. Lund, “Drought Water Right Curtailment Analysis for California’s Eel River,” Journal of Water Resources Planning and Management, ASCE, Vol. 144, No. 2: 04017082, February, 2018.  Pre-publication version available here.

Pavicic, J. (2017), “Uncertainty in Water Right Analyses: Overpromising versus Over-curtailing,” Master’s report, Department of Civil and Environmental Engineering, University of California – Davis.

SWRCB and others on the calculation of water availability in 2014-2015. https://www.waterboards.ca.gov/waterrights/water_issues/programs/hearings/byron_bethany/exhibits.shtml

Tweet, A. (2016), “Water Right Curtailment Analysis for California’s Sacramento River: Effects of Return Flows,” Master’s thesis, Department of Civil and Environmental Engineering, University of California – Davis.

Walker, W. (2017), “Drought Water Right Allocation Tool Applied to the San Joaquin River Basin,” Master’s thesis, Department of Civil and Environmental Engineering, University of California – Davis.

Whittington, C. (2016), “Russian River Drought Water Right Allocation Tool (DWRAT),” Master’s thesis, Department of Civil and Environmental Engineering, University of California – Davis.