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Vernal Pool Hydrology

Principal Investigators:
Niall McCarten, Thomas Harter

Co-Principal Investigators:
Mark Cable-Rains, Graham Fogg

Graduate Researchers:
William Williamson

Solano County Water Agency

The Hydrology Program in the Department of Land, Air, and Water Resources has been conducting vernal pool hydrology research since 2003 (under the leadership of Dr. Graham Fogg and Dr. Thomas Harter).  The research is in collaboration with former UC Davis post doctoral research Dr. Mark Cable Rains, now with the Department of Geology at the University of South Florida.

Occurrence of Vernal Pools

Vernal pools are seasonal wetlands occurring in Mediterranean and subtropical regions of the world, including the Western US (California, Oregon, and Washington), the former glaciated Midwest and extending into Canada in areas known as Prairie Potholes, and the forested northeastern US.  Vernal pools also occur in the Mediterranean region, France, Portugal, Spain, Turkey, and Morocco.  In Sub Saharan Africa they occur in Kenya and Botswana and probably elsewhere but they have yet to be studied.  They are known to occur in South America in Chile. They also are well known from Western Australia and New Zealand.  In California, they occur in X regions (Figure 1). Their occurrence is due to a range of geologic and soil conditions including 2-4 million year old alluvial deposits on the eastern Central Valley that formed a hardpan (duripan) water restricting soil layer.  Younger alluvial deposits in the Central Valley and other parts of California have developed a claypan (fragipan) with a somewhat porous water restricting layer.  Other vernal pool types include surface depression with little or no groundwater processes.

Vernal Pool Research

The Hydrology Program’s vernal pool research has often been in collaboration with other scientists at UC Davis. Vernal pool research has had a long history at UC Davis that has included plant ecologists such as Dr. Michael Barbour (retired) and Subodh Jain (retired) and wildlife biologists such as Dr. Brad Shaffer studying California tiger salamanders.  Over the past decade, soil scientists from the UC Davis Biogeochemistry Program, including Drs. Randy Dahlgren and Anthony O’Geen, have continued research into vernal pool soil forming processes.  In addition, our vernal pool research has now extended its’ collaborative work to include Dr. Jamie Kneitel, aquatic invertebrates, and Dr. Michelle Stevens, restoration ecologist, from the California State University, Sacramento; and Dr. Ellen Bauder, plant ecologist, and Dr. Andrew Bohonak, aquatic invertebrate evolution, at San Diego State University; and Dr. Sharon Collinge, community ecologist, with the University of Colorado.

The Hydrology Programs’ current vernal pool research includes:

  • Field measurements of saturated and unsaturated groundwater flows and surface water depth of seasonally high elevation water tables in surface depressions associated with hardpan and claypan vernal pools (Figures 2 & 3),
  • Field measurements of seasonally variable volumetric soil moisture content of high clay content soils of depressional vernal pool watershed and basins as well as depth and duration of surface ponding,
  • Topographic measurements and 3-dimensional modeling (Figure 4) of vernal pool catchments to measure the contribution of surrounding watershed groundwater to vernal pool basins,
  • Ground penetrating radar is being used to identify the depth to hardpan and claypan layers as well as changes in soil texture,
  • HYDRUS 2-D & 3-D modeling of seasonally, variably saturated soils associated with vernal pool watersheds and basins,
  • Hydroperiod fidelity of vernal pool plants and their role in soil hydrology and biogeochemistry through transpiration and carbon uptake, oxygen release, and it affects on soil redox potential, and
  • Climate change affects to the hydrological functioning of vernal pools based on regional climate models identifying changes in precipitation and temperature.

The vernal pool research has received generous funding from the California Department of Transportation (CALTRANS) and the Solano County Water Agency’s Endangered Species Conservation Program.



Rains, M.C., R. A. Dahlgren, G. E. Fogg, T. Harter, and R. J. Williamson, 2008. Geological control of physical and chemical hydrology in California vernal pools. Wetlands 28(2):347-362. (pdf file for personal use only)

Cable-Rains, M., G. E. Fogg, T. Harter, R. A. Dahlgren, and R. J. Williamson, 2006. The role of perched aquifers in hydrological connectivity and biogeochemical processes in vernal pool landscapes, Central Valley, California. Hydrol. Process. 20, 1157–1175. (pdf file for personal use only).