Pajaro Valley Groundwater Overdraft Concerns

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A Watershed Issue examined by the ENVS 560/L Watershed Systems class at CSUMB.

Summary

PVWMA Boundaries copied from the PVWMA Revised Basin Management Plan [1]

The Pajaro Valley is an agriculturally important area of the California Central Coast. Over the past several decades, groundwater pumping for agriculture and municipal use has led to an overdraft of the aquifer. Groundwater overdraft occurs when the pumping rate exceeds the recharge rate over an extended period of time. The situation in the Pajaro Valley is further complicated because aquifer recharge takes tens or even hundreds of years even after mitigating steps have been taken and no further groundwater pumping occurs.[2] [3]

Location

Highlighted Region shows Carneros Watershed copied and modified from the PVWMA Revised Basin Management Plan[1]

The Pajaro Valley lies in Central California and includes parts of Monterey, Santa Cruz, San Benito, and Santa Clara counties. The Pajaro Valley aquifer extends west into Monterey Bay and north to the Soquel-Aptos basin. It is bound to the South by Elkhorn Slough and to the East by the San Andreas fault. The watershed above this aquifer covers approximately 80,000 acres. [1] The Carneros Watershed is the southern boundary of the Pajaro Valley.

Resources at stake

Groundwater overdraft in a coastal region increases the risk of seawater intrusion which can adversely impact water quality. The diminished water table can also lead to increases in concentrations of dissolved solids leached into the soil by agriculture runoff. Resources that can be affected include:

  • Municipal drinking water supplies
  • Agricultural water supplies
  • Land subsidence [4]
  • Permanent loss of groundwater storage

A 2000 Basin Management plan by PVWMA indicates that agriculture and high septic tank density in the watershed have led to concerns that groundwater might experience high nitrate concentrations.[5] If the groundwater overdraft in the Pajaro Valley is not mitigated, parts of Monterey, Santa Cruz, Santa Clara, and San Benito counties could experience diminished freshwater resources.

Stakeholders

The Pajaro Valley includes agricultural, developmental, municipal, and conservation activities into a water district that extends into three separate counties. Some of the major stakeholders include:

  • The Pajaro Valley Water Management Agency(PVWMA) was established in 1984 in order to manage groundwater issues in the Pajaro Valley in the region.
  • The Pajaro River Watershed Flood Prevention Authority was established in 2000 to develop and implement flood prevention strategies for the Pajaro River. Any plans for groundwater recharge will have to be coordinated through the Flood Prevention Authority. [6]
  • The counties of Monterey, Santa Clara, Santa Cruz, and San Benito all have some portion of Pajaro Valley within their borders.
  • The City of Watsonville is in the center of the Pajaro Valley and will require groundwater resources for future development. [7]
  • Potential developers in this region are subject to submitting Environmental Impact Reports that address groundwater overdraft. See Example

Laws, policies, & regulations

Currently in California, landowners possess the ability to pump groundwater as long as it is put to beneficial use. Assembly Bill 3030 [8] was passed in 2002 and enables designated local agencies to form groundwater management plans. The PVWMA is the designated agency that voluntarily creates groundwater management plans for the the Pajaro Watershed. If agencies are unable to resolve local groundwater management issues, actions by local governments to enact local ordinances are necessary.[2]

Science

Groundwater Cycle copied from the USGS Website [9]

Groundwater is recharged through gravity driven infiltration of surface water. Water seeps between substrate particles downward until hitting the water level or impervious surface. Recharge rates depend on other elements of the hydrological cycle including: precipitation, surface runoff, and evapotranspiration rates. Land use (percent cover of impervious surfaces) and topographic features of the land, such as slope and terrain, also play a role in recharge rates. Current studies are examining groundwater recharge times and examining relationships between groundwater quality and watershed land use. [9] University of California at Santa Cruz has lead most of the projects in the Pajaro Valley that investigate the relationship between surface and groundwater interaction. The most recent research in the valley is through a grower-initiated project to help restore the aquifer using recharge ponds.

Tools

The Pajaro Valley Integrated Ground Surface water Model (PVIGSM) was created to help predict future groundwater levels and quality. PVWMA uses the PVIGSM to monitor groundwater and watershed models for the Pajaro Valley and are currently using those resources to better educate stakeholders and decision makers on possible mitigating action to remedy the issue of groundwater overdraft. Additional modeling of the Carneros watershed could prove useful in the future if the Pajaro Valley groundwater overdraft increases and extends into other watersheds. [5] The US Geologic Survey is currently operating monitoring wells in conjunction with PVWMA in order to assess the geophysical and geochemical impacts of groundwater overdraft on the aquifer. [10] Additionally, the PVWMA is conducting a project at Harkins Slough that captures snow runoff in the winter, injects that water into the aquifer, and recovers that water in the summer for distribution to growers. [11]

References

  1. 1.0 1.1 1.2 [PVWMA] Pajaro Valley Water Management Agency. 2006. Basin management plan documents. [30 January 2011]. Available from: : http://www.pvwma.dst.ca.us/
  2. 2.0 2.1 California Department of Water Resources. 2010. Groundwater Information Center [30 January 2011]. Available from: http://www.water.ca.gov/groundwater/index.cfm
  3. Stephens T. 18 November 2007. UCSC hydrologist provides expert advice on Pajaro Valley's water supply. UCSC News [Internet]. [cited 31 January 2011]. Available from: http://news.ucsc.edu/2007/11/1759.html
  4. USGS Land Subsidence Explanation
  5. 5.0 5.1 Central Coast Hydrologic Region. 20 January 2006. Pajaro valley groundwater basin. California's Groundwater Bulletin 118 [Internet]. [cited 2 February 2011]. Available from: Bulletin
  6. Pajaro River Watershed Flood Prevention Authority
  7. City of Watsonville
  8. Assembly Bill 3030: [http://www.water.ca.gov/groundwater/gwmanagement/ab_3030.cfm
  9. 9.0 9.1 USGS Aquifer Description
  10. USGS. August 2003. Geohydrology of Recharge and Seawater Intrusion in the Pajaro Valley, Santa Cruz and Monterey Counties, California. US Geologic Fact Sheet 044-03 [Internet]. [cited 2 February 2011]. Available from: http://pubs.usgs.gov/fs/fs-044-03/.
  11. Harkin Slough Project

Links

Disclaimer

This page may contain student work completed as part of assigned coursework. It may not be accurate. It does not necessary reflect the opinion or policy of CSUMB, its staff, or students.