Completed in 1892, the Searsville Dam sits astride San Francisquito Creek, which connects watershed in the mountains above Silicon Valley to the San Francisco Bay. Sedimentation has “reduced the reservoir to 10 percent of its original capacity“. At this rate, the reservoir will completely fill in 15 years, and then, sediment would wash over the dam, through the creek, and into the bay. This old dam and silted-up reservoir pose both a threat and an opportunity for the Bay Area: sediment washing down the creek returns an age-old flood threat to downstream communities like Palo Alto and Menlo Park; one reservoir of sediment is a potential source of mud needed to help save the South Bay from sea-level rise.
Sediment washing over a completely filled dam could clog the creek and lead to flooding. Floods aren’t new to the alluvial Santa Clara Valley. Resting on up to 1,500 feet of sediment, the valley floor is broad and flat because of past floods deposited sediment across the valley. The Bay Area was thinly settled when the dam was built in 1892. Since then, Silicon Valley homes and offices have been built next to the creek, limiting flood control options.
In addition to flood risk from the creek, the Bay Area has a long shoreline that is at risk from rising seas. “Back in June 2016, Bay Area voters approved Measure AA to raise $500 million to pay for wetlands restoration, flood control and wildlife projects around San Francisco Bay.” But to protect the Bay Area, the structures will need more mud than is available, per the Scientific American post.
Searsville Dam holds “approximately 2.7 million cubic yards of sediment that has built up behind the dam since its construction in 1892“. This sediment is a potential source of mud for the Bay.
Finally, Searsville Dam filling with sediment illustrates that a dam has a limited lifetime. The Bay Area is planning to build another dam. As we do this, we should consider the life-cycle costs of new dams as well as existing dams.
Continue reading Stanford’s Searsville Dam
This weekend I divided and transplanted a clump of this purple Douglas Iris, a California native plant. The purple iris has beautiful flowers. Our favorite iris, it’s more delicate than the white irises I propagated several years ago. They’ve done great so we’re trying the purple ones this year.
I followed the same technique I used for the white irises.
Continue reading Propagating purple Douglas Iris
After visiting Kauai last summer, we went to Honolulu where we joined a family hike in the Koolau Range that forms the backbone of Oahu. Shown above, we are hiking up the Wiliwilinui Ridge to the top of the Koolaus in the distance.
Continue reading Wiliwilinui Trail
The day after seeing the Na Pali Coast by helicopter, we saw the Coast from land, hiking part of the Kalalau Trail. On the windward side of Kauai, the Na Pali Coast is hard volcanic rock battered by wind, rain, and erosion. Shown above from my helicopter ride, the Kalalau Trail starts on the left at Ke’e Beach, climbs up the cliff, and goes back down to the ocean at Hanakapi’ai Beach on the right.
Continue reading Hiking the Kalalau Trail
After walking through Antelope Canyon on our southwest parks road trip, we drove to Zion National Park, where we crossed the Virgin River to hike to Emerald Pools. In early June, the Virgin River is quiet, so it’s hard to imagine that this river carved the Zion Canyon through the red rock. The peak in the photo is 1,400 feet above the river.
Continue reading Zion’s Emerald Pools
After seeing the Windows at Arches National Park, we hiked the Devil’s Garden Trail to Landscape Arch and Double O Arch. Shown above, Landscape Arch is the fifth-longest arch in the world, with a span of 290 feet (88 m).
Continue reading Devil’s Garden
On the second morning of our southwest parks road trip, we saw Courthouse Towers and the Windows, an area of Arches National Park with several large arches. That Friday, roads were closed for construction until 7 am, an hour past sunrise, so we missed the dawn light.
Continue reading Courthouse Towers and Windows