By Junko Bryant, Assistant Director
Somehow it feels predictable that after years of drought, we are now facing flooding, mudslides, and damage to dams and levees from the heavy rains this season. California doesn’t have many “average” winters.
Locally, we have been asked pretty frequently how our project sites are doing with all of this rain. The answer varies a bit from site to site.
Of course, we are thrilled that our new native plantings are receiving lots of moisture and putting down roots. It is also fun to see the creeks flowing and they will probably continue to flow much longer into the year. Our rain barrels have filled to overflowing many times over, and our rain gardens are collecting and sinking water into the ground. But there has also been erosion of creek banks, trails, and dirt roads at many locations, and as a result, our creek water quality monitoring crews have seen turbidity levels (suspended sediment) too high for our instruments to even measure!
The stormy winter also offered a chance to see how some of our projects perform in “real” rain. One of our exciting success stories is Mayfly Creek at Arastradero Preserve, which was daylighted in 2006. It may seem counter to “good” stream management, but at Mayfly we are packing brush into the channel in order to catch sediment and keep the channel shallow so that it floods more often. This year, the creek overflowed its banks numerous times, dumping water and sediment onto its floodplain.
At Arastradero we are also installing berm-and-swale structures on the hillside to capture sheet flow. They are being planted with deep-rooted native bunchgrasses to tie down this water-absorbing function.
By retaining water in the upper watershed, both of these measures increase groundwater recharge and reduce the flows downstream where the creek flows through Palo Alto neighborhoods.
Willows were put to the test at Redwood Grove in Los Altos, where we installed a willow-weave art sculpture with Daniel McCormick and Mary O’Brien in 2012 to revegetate a 40-foot section of Adobe Creek that had been cleared of invasive Arundo donax. We knew going into the project that willows would ideally like more sunlight than what filtered through the edge of the redwood grove, but since there were other willows in the area, it seemed worth trying. The willow stakes took hold, but only did well along the sunnier half of the project site. With the high flows in February this year, the unrooted portion of the project finally washed out. While we are sad to see this damage occur to a beautiful community-built art piece, it has reinforced for us the importance of a healthy root system in the riparian zone.
On San Francisquito Creek, we saw a high flow for the season (so far) on February 7. Just one month prior to that storm event, our staff installed 120 trees and shrubs on the upper bank of the creek upstream of the Pope-Chaucer bridge. When we ran out to see if our plants were still intact, we were relieved to see that our staff did a good job of intuiting the high water mark! Only a few of our trees were inundated, and probably only for a few hours. Willow cuttings installed back in December, however, are along the channel bottom and likely spent weeks submerged in water if they managed to even hang on during the high flows. We will pick up this effort again when the waters recede a bit more, and are feeling optimistic about our chances for long-term success after seeing how well our willow cuttings have done at another site on San Francisquito Creek.
As we enter spring following this prolific rainy season, our Staff Botanist Paul Heiple and Restoration Specialist Alisa Kim report that both the wildflowers and the weeds are “going bonkers.” Indian warrior, starlily, trillium, and wild cucumber are now blooming, and tidy tips, clarkias, and lupine are getting ready to put on their show. Since the invasives are also growing strong, we hope you can join us at a workday soon to remove Italian thistle, mustard, and other weeds to make way for more wildflowers!