Monday, October 24, 2016
Tuesday, September 20, 2016
Wednesday, May 18, 2016
Monday, May 9, 2016
|High capacity valves on the face of|
O'Shaughnessy Dam release spring
snowmelt to the upper Tuolumne River.
The releases are designed to achieve a number of experimental ecological objectives, including managing foothill yellow-legged frog reproduction, inundating unique wetlands in the Poopenaut Valley, and mobilizing fine sediment, sand, and gravels to improve trout and foothill yellow-legged frog habitat.
Wetlands in the Poopenaut Valley that haven't seen significant flooding since 2011 will be fully inundated by the peak release of 6,500 cfs, providing valuable information on how wetlands may recover from several years of drought.
The sediment mobilizing releases will serve to move silt and sand that has increased in the upper Tuolumne River since the 2013 Rim Fire. Fine sediment can fill the spaces between gravels and cobbles, allowing stream side vegetation to encroach into the river channel and "fossilize" the loose gravel and cobble patches that trout, foothill yellow-legged frogs, and other aquatic life need to successfully reproduce.
Scientists from the SFPUC, Yosemite National Park, and UC Davis are monitoring the releases and will be studying their ecological effects throughout the spring and summer. Data from this work will be used to update and refine analyses and river management strategies described in the Draft O'Shaughnessy Dam Instream Flow Management Plan.
at May 09, 2016
Saturday, April 23, 2016
Friday, April 8, 2016
Wednesday, March 16, 2016
The 2014-2015 water year was dry: precipitation was approximately 58% of average. April 1st and May 1st snow water equivalent, however, were at record lows (9% and 2% of average April 1st, respectively) continuing a historically unprecedented drought in central California. Hydrology studies in spring 2015 focused on monitoring low flow conditions. These low flows precluded any experimental releases from O'Shaughnessy Dam.
Vegetation-related fieldwork in Poopenaut Valley documented the rapid spread of non-native common mullein within and adjacent to the seasonal pond on the north side of the river. Although the 2013 Rim Fire may have contributed to the spread of common mullein in this area, it is most likely related to the nearly continuously dry conditions in the pond over the past few years.
Spring bird surveys in Poopenaut Valley consisted of area searches, point counts, spot mapping, nest searches, and color banding. A cumulative total of 240 individual birds from 38 species were observed. Spot mapping determined breeding territories of the four target riparian focal species (Warbling Vireo, Yellow Warbler, Song Sparrow, and Black-headed Grosbeak) to elucidate their habitat-use patterns. Data collected during spot mapping and nest searching in 2011–2015 were used to calculate arrival, initiation of breeding, and fledging dates for the target riparian focal species. In 2015, NPS found 68 nests, which is substantially more than in previous year. Nest failure rate in Poopenaut Valley seemed unusually high; of the 68 nests found, 60% failed and 25% had unknown fates.
Bat studies have identified an impressive biodiversity of bat species inhabiting Poopenaut Valley from spring 2011 through late summer 2015. Bat detection frequencies decreased in 2015 to levels comparable to pre-2014 levels. The only species with marked increases were western mastiff bat and big brown bat at the south site. Species richness decreased slightly in 2015 at both sites and was fairly consistent with pre-2014 numbers. Seasonal patterns in species richness were also consistent with previous years at both sites.
The 2015 Yosemite National Park Looking Downstream Project report can be accessed here.