The reservoir would be formed by accepting water from the Delta-Mendota Canal in wintertime and storing it in Del Puerto Canyon behind four earthen dams, to be released as needed over the summertime. Whatever water flows down Del Puerto Creek will also be retained in the reservoir, but 99% of the stored water will come from the canal. The reservoir’s maximum capacity is to be 82,000 acre-feet or 27 billion gallons of water. The reservoir would extend past Graffiti and Owl Rocks and the creek that the community enjoys so much. Two of the four dams are of significant size and present dangerous problems to the community of Patterson.
The main dam will cut off Del Puerto Creek and faces onto I-5 just north of the Patterson entrance to the freeway. It will be 260 feet high and 1,409 feet long, roughly speaking, the height of a football field stood on end, and fourteen football fields long. This dam will close off what has been historically known as Del Puerto, meaning "The Door". The second large dam facing Patterson will be located along Del Puerto Canyon road and will be 150 feet high and 1,300 feet long.
The dams are earthen because the canyon is not solid rock but is subject to movement, and earthen dams can settle into unstable ground as it moves. The typical basic design of earthen dams includes standard safety features that are hoped will protect the dam against failure; as the old saying goes, “hope springs eternal” – but no guarantees!
For interesting geologic reasons, Del Puerto Canyon is highly prone to landslides – in fact, there are seven known landslides in the area to be inundated. A major one can be easily seen just past the three miles marker PM3 along Del Puerto Canyon road. You can actually pull off the road by that marker to take a look over to the right at the base of the hillside. It extends well back into its canyon and will be mostly covered when the reservoir is full, and that creates a real danger because in this type of geologic situation, water acts as a lubricant and causes landslides. More landslides are inevitable and unpredictable. Of course, if you’re a dam geologist it will be a fascinating experiment to lubricate these hillsides and watch what happens – but Patterson will be the experimental guinea pig, and landslides are only one set of issues this project poses.
Altogether, this is a lethal mix for the City of Patterson because the combination can unleash a major landslide producing a tsunami capable of breaching either of those large dams facing the city. That would destroy property and people – us!