Summary of Del Puerto Canyon Reservoir Final Environmental Impact Report, Part I

At the western edge of the Great Central Valley, within Stanislaus County, lies a canyon of cultural, biological and geological significance.  A rift in the earth slicing through the Coast Ranges, the canyon exposes millions of years of geologic history, and shows evidence of being occupied by humans long before European settlers arrived on the scene.  A spring at the heart of the canyon feeds into an intermittent stream, bordered by oasis-like pockets of riparian wetlands, cottonwoods, sycamores and ephemeral pools.  In the spring, grasslands within the canyon are verdant with a luxurious covering of new growth and dotted with annual wildflowers, while steep canyon walls are adorned with hardy chaparral and oak scrub habitat.  In the autumn, western sycamores and Fremont cottonwoods lining the creek put on a color show no less spectacular for its subtleness.  

This is, of course, Del Puerto Canyon.

And this canyon is in imminent danger of being dammed and flooded, its rich habitat and cultural heritage lost forever.



I don't expect that my humble words have any power to sway the almighty decision-makers behind this proposed project, but my hope is that someone will read my message and learn to think twice about the heavy impact we as humans have on the natural world around us.

Footprint of the proposed reservoir in Del Puerto Canyon. 
Source: https://delpuertocanyonreservoir.com/
The proposed dam would flood the lower part of the canyon, covering about 800 acres and holding up to 82,000 acre feet of water (source), amounting to a relatively small reservoir in our area.  (To put it in perspective, San Luis and Don Pedro Reservoirs both have surface areas of just over 12,000 acres and both hold around two million acre feet of water.  Is increasing storage capacity of existing reservoirs an option?  Especially as sedimentation reduces water storage capacity?  I am not informed enough in this area, but one has to wonder.)



Water issues in the West are often touted as being complex, and indeed they are, at least as they relate to politics and policy.  Really, the issues are quite simple: in the arid West, there is not enough water to indefinitely support the levels of water consumption demanded by agricultural (and residential) users.  Why we, as Valley residents, get virtually unlimited water (which is largely misused) at such a low cost boggles my mind.  Why farmers and land owners are allowed to plow up thousands of acres of grassland - i.e. unirrigated rangeland - in the foothills (as all valley floor land is already taken) to plant water-demanding monocultures of wine grapes and almonds is a question that makes me crazy.  

Maybe we don't need more water storage after all.  Maybe we just need to rethink our current rate of water use and commit to living in a way that befits our arid climate!  Even if more water storage is built, what guarantee is there that water will be available to fill it?  Are we to starve our rivers and streams, holding so much water in reservoirs that there is none left to reach the Delta, like the case with the Colorado River in Mexico?  But I digress.

If additional water storage must be constructed, Del Puerto is not the only canyon in the Coast Ranges that has the potential to support a reservoir such as this.  Opponents of the Del Puerto Canyon site have suggested several other canyons as alternatives, most favorably a site about ten miles north.  If a dam must be built, an alternative site to Del Puerto Canyon would be preferred!


Arguments against damming and flooding Del Puerto Canyon include:

  • Flood risk to the city of Patterson in the event of dam failure or landslides within the reservoir
    • According to the report, the construction of a dam at the mouth of Del Puerto Canyon would have a high likelihood of causing "potential substantial adverse effect, including the risk of loss, injury, or death involving: strong seismic ground shaking; seismic-related ground failure, including liquefaction; [and] landslides."  It would also be located on "a geologic unit or soil that is unstable, or that would become unstable as a result of the Project, and potentially result in on- or off-site landslide, lateral spreading, subsidence, liquefaction, or collapse;" and "expansive soil... creating substantial direct or indirect risks to life or property."
  • Loss of access to an area used heavily for education and recreation
    • I have spent countless happy hours exploring the natural wonders of the canyon, on my own as well as with guided field trips to study the botany, geology and wildlife of the canyon.  As the only publicly accessible canyon in our county, Del Puerto Canyon is one of Stanislaus County's premier birding sites, as well as a living laboratory showcasing the geology of the Coast Ranges.  Losing access to this site as an educational resource would be a great loss to our community, an area already suffering from a lack of knowledge of and connectedness to the natural world, as well as so-called "brain drain."  
  • Loss of geological resources 
    • The proposed dam would "directly or indirectly destroy a unique paleontological resource or site or unique geologic feature."  In the 1930's, California's first dinosaur fossil, a type of hadrosaur or duck-billed dinosaur called a Saurolophus, was found in the canyon, within the area that would be flooded.  Additionally, the canyon walls provide a nearly perfect geologic record of the Coast Ranges, with pieces of the earth's mantle exposed in several places.
  • Loss of cultural resources
    • Del Puerto Canyon was home to Yokuts people for thousands of years before Europeans arrived, as evidenced by grinding rocks and other cultural artefacts.  According to the report, "site P-50-344 is a prehistoric occupation site consisting of four bedrock mortars and cupule features, an artifact surface scatter of lithic debitage (stone chips and flakes from making stone tools), groundstone (a stone tool for grinding) fragments, and one obsidian biface tool fragment located along the slope and base of a hill overlooking Del Puerto Creek to the south. Subsurface testing at the site identified a deposit of lithic debitage, a bone awl fragment, burned faunal material, freshwater mussel shell fragments and marine shell beads. The features and artifact deposit at the site are indicative of habitation along Del Puerto Creek, containing information important in prehistory, specifically to the prehistoric inhabitants of the local area."  There is a high likelihood that the proposed dam would "cause a substantial adverse change in the significance of a historical resource...; cause a substantial adverse change in the significance of a unique archaeological resource...; [and] disturb... human remains, including those interred outside of dedicated cemeteries."
  • Loss of habitat and biological resources
    • Just take a look at the chart below, as it appears in the report.
Del Puerto Canyon Reservoir Final EIR Vol. II  Appendices, page 25 of PDF.  https://delpuertocanyonreservoir.com/assets/pdf/reports/Del-Puerto-Canyon-Reservoir-Final-EIR-Vol-II-Appendices.pdf


Read the final environmental impact report by following the links below.

Vol. I (421 pages) https://delpuertocanyonreservoir.com/assets/pdf/reports/Del-Puerto-Canyon-Reservoir-Final-EIR-Vol-I.pdf

Vol. II (786 pages) https://delpuertocanyonreservoir.com/assets/pdf/reports/Del-Puerto-Canyon-Reservoir-Final-EIR-Vol-II-Appendices.pdf


Stay tuned for Part II of this series, where we will take a look at the specific species that are at risk of being displaced by the dam project.

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