Published in the February 1 – 14, 2017 issue of Morgan Hill Life

By Mike Monroe

Mike Monroe

The first few weeks of the New Year began with a series of storms that drenched the South Valley. Naturally, the first idea for a Take a Hike with Mike column that sprang to the lips of the publisher of this journal was … “percolation! Why not write an article about the San Pedro Percolation Ponds?” suggested Marty Cheek. “There is a walking trail and some benches for people to sit and enjoy some quiet time.” I thought about Marty’s inspiration for a while and decided to run with it — of course, adding my own two cents.

For many years, I have driven by the ponds, noticing cars parked either by the fence on San Pedro Avenue or on Hill Road. But I never stopped to see what this place is all about. The property consists of 28 acres with seven percolation ponds developed by the Santa Clara Valley Water District and the San Felipe Water Project in 1996. A few years later, the city of Morgan Hill — with the support of community volunteers — designed the walking paths and planted some trees for shade. And now it’s a nature park enjoyed by residents of the nearby neighborhoods.

So why are we going to Anderson to talk about groundwater recharge? Because the San Pedro ponds have not been filled with water from the San Luis Reservoir in the past few years due to our prolonged drought. Any water that accumulates in the pond basins is the result of local rainfall which so far has been inadequate to leave any lasting effect.
Being undaunted by the dry ponds, I pulled out all the stops to learn more about our water supplies in southern Santa Clara County. Morgan Hill averages 26.13 inches of rain during the past 30 years — and the past five or six years have not helped. In 1940, Morgan Hill experienced record rainfall in January (24.48 inches) and February (21.74 inches). Imagine Coyote Creek, without Anderson Dam, flooding the Coyote Valley and parts of San Jose on its way to San Francisco Bay. Gilroy’s seasonal average is slightly more than 20 inches annually. According to the water district, both Gilroy and Morgan Hill rely almost exclusively on groundwater for our drinking and agricultural needs. So while Anderson Reservoir serves our locale with storage, flood control and recreation, we receive only the water percolated through releases into Coyote Creek.

The raw water that is imported from the California Water Project or the San Felipe system and that is stored at Anderson is blended with runoff from the Anderson watershed and held in reserve for our neighbors to the north. Typically, about 25 percent of the county’s water supply (the balance is groundwater or imported) is maintained in local reservoirs and transported through a network of pipes to water treatment facilities for consumption in the North County. The water district has engineered an infrastructure of channels and pumping plants to move water around.

Gilroy and Morgan Hill sit on top of the Llagas Sub-basin, an aquifer or an underground flow of water found at various depths in our soil sediments, that generally migrates toward the Pajaro River and San Benito County. Many years ago, early pioneers in Santa Clara County developed artesian wells without much effort using sub-surface pressure to simply force the groundwater up, sometimes resulting in uncontrolled geysers. After years of overdrafting our groundwater, not allowing for adequate replenishment, the valley began experiencing severe land subsidence. A call to action rang out to the citizenry and the word “percolation” now pertained to more than just coffee. We desperately needed, and will always need, to manage our groundwater supplies to sustain our future economic and population growth.

Water supply and demand issues are constantly debated in California. The state is struggling with how much water from the Sierras should be retained for the San Francisco Bay-Delta, how much should be allocated for agriculture, how much will Southern California expect. There are no easy answers. Everybody will be disgruntled and our wildlife populations may be in further jeopardy. The Sierra snowpack is our water bank. But with a warming climate we may experience more mountain precipitation as rainfall so the water won’t be stored throughout the year. Water experts are planning for rising sea levels which may mean the Bay-Delta will see increasing salt water intrusion. And in South Valley, a depletion of our aquifers is a cause for concern in terms of nitrate levels. We will really have to be on our toes to manage all these variables.

On our walk along Coyote Creek from the Anderson Visitor Center on Saturday afternoon, I’m sure that we will discuss our regional water challenges as well as enjoy the moment with the water rushing by and the mallards and herons keeping us company.

Keep on sauntering!

Gilroy resident Mike Monroe is a Morgan Hill business owner and naturalist. He is a docent for Santa Clara County Parks.


What: One hour talk and walk along
Coyote Creek dirt trail (dress in layers, rain cancels)
When: 2 p.m. Feb. 11
Where: Anderson Lake County Park Visitor Center, 19245 Malaguerra Ave.
Contact: Mike at (408) 234-6377