Davis, CA, United States
Davis, CA, United States

Time filter

Source Type

Keyes C.R.,University of Montana | Teraoka E.K.,Stillwater science
Forests | Year: 2014

Restoration of second-growth riparian stands has become an important issue for managers of redwood (Sequoia sempervirens [D. Don] Endl.) forest reserves. Identifying differences between old-growth and second-growth forest vegetation is a necessary step in evaluating restoration needs and targets. The objective of this study was to characterize and contrast vegetation structure and composition in old-growth and unmanaged second-growth riparian forests in adjacent, geomorphologically similar watersheds at Redwood National Park. In the old-growth, redwood was the dominant overstory species in terms of stem density, basal area, and importance values. Second-growth was dominated by red alder (Alnus rubra Bong.), Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco), and redwood. Understory species were similar in both forests, with several key differences: Oxalis oregana Nutt. and Trillium ovatum Pursh had greater importance values in the old-growth, and Vaccinium parvifolium Sm., Dryopteris spp. and sedges Carex spp. had greater importance values in the second-growth. Notable differences in structure and composition suggest that restoration practices such as thinning could expedite the acquisition of old-growth characteristics in second-growth riparian forests. © 2014 by the authors.


Booth D.B.,University of California at Santa Barbara | Cui Y.,Stillwater science | Diggory Z.,Stillwater science | Pedersen D.,Stillwater science | And 2 more authors.
Ecohydrology | Year: 2014

Setting instream flows to protect aquatic resources is required by California state law, but this task is not straightforward for an intermittent river that is naturally dry six or more months of every year. The Santa Maria River, 200km northwest of the Los Angeles metropolitan area, lies within the northern range of the federally endangered southern California steelhead (Oncorhynchus mykiss) and is a logical candidate for instream flow protection: the watershed historically supported the anadromous life history of this species, but fish must navigate the lowermost 39km of the commonly dry mainstem river to move between the ocean and freshwater habitats in the upper watershed. Mainstem flows are partly controlled by Twitchell Dam, constructed across one of the Santa Maria River's two main tributaries in 1962. The dam is operated to maximize groundwater recharge through the bed of the mainstem Santa Maria River, thus minimizing discharge to the Pacific Ocean and so reducing already limited steelhead passage opportunities. Conventional criteria for determining suitable instream flows for steelhead passage are ill-suited to intermittent, Mediterranean-type rivers because they ignore the dynamic channel morphology and critical importance of headwater flows in providing cues that once presaged passage-adequate mainstem discharges but no longer do so. Hydrologic analysis of pre-dam flows, coupled with established criteria for successful O. mykiss migration, provides an objective basis for evaluating alternative dam-management scenarios for enhancing steelhead passage, although their implementation would redirect some water that for the past half-century has exclusively supported irrigated agriculture and municipal water supplies. © 2013 John Wiley & Sons, Ltd.


Venditti J.G.,Simon Fraser University | Nelson P.A.,University of California at Berkeley | Nelson P.A.,University of Genoa | Minear J.T.,University of California at Berkeley | And 4 more authors.
Journal of Geophysical Research: Earth Surface | Year: 2012

Sediment supply is widely held to be one of the primary controls on bar topography in alluvial channels, yet quantitative linkages between sediment supply and bar topography are not well developed. We explore the conditions under which alternate bars form and how they respond to the elimination of sediment supply in two linked laboratory experiments. The first set of experiments was conducted in a 28m long, 0.86m wide flume channel using a unimodal sand-gravel mix. The second set of experiments was conducted at field scale in a 55m long, 2.74m wide channel using a unimodal gravel mixture. In both experiments, alternate bars and patchy surface grain-size distributions developed under steady flow and sediment supply conditions. The cessation of the sediment supply induced a reduction in the surface grain-size heterogeneity and the bars were eliminated. In both flumes, mean boundary shear stress had declined, but were capable of moving sediments after the bars disappeared, albeit at relatively small rates compared to when the bars were present. In the smaller flume, the previously stationary bars migrated out of the flume and were not replaced with new bars. A nearly featureless bed formed with limited surface grain-size heterogeneity, a slightly coarsened surface and a slightly reduced slope. In the larger flume, the formation of alternate bars was induced by an imposed upstream flow constriction and as such, the bars did not migrate. Termination of sediment supply led to progressive erosion of bed topography and loss of the bars, coarsening of the bed surface, loss of bed texture patchiness and significant slope reduction. The original alternate bar topography redeveloped when the sediment supply was restored once sufficient deposition had occurred to reconstruct the original channel slope. This shows that the bar loss was reversible by establishing the previous conditions and highlights the importance of sediment supply for bar formation. The role of sediment supply in bar formation and stability is not often recognized in stream restoration. Our results suggest that the loss of sediment supply can significantly affect alternate bar topography and that considerable volumes of sediment may be needed restore channel bars. © 2012. American Geophysical Union. All Rights Reserved.


Downs P.W.,University of Plymouth | Dusterhoff S.R.,Stillwater science | Sears W.A.,Stillwater science | Sears W.A.,San Francisco Public Utilities Commission
Geomorphology | Year: 2013

Understanding the cumulative impact of natural and human influences on the sensitivity of channel morphodynamics, a relative measure between the drivers for change and the magnitude of channel response, requires an approach that accommodates spatial and temporal variability in the suite of primary stressors. Multiple historical data sources were assembled to provide a reach-scale analysis of the lower Santa Clara River (LSCR) in Ventura County, California, USA. Sediment supply is naturally high due to tectonic activity, earthquake-generated landslides, wildfires, and high magnitude flow events during El Niño years. Somewhat typically for the region, the catchment has been subject to four reasonably distinct land use and resource management combinations since European-American settlement. When combined with analysis of channel morphological response (quantifiable since ca. 1930), reach-scale and temporal differences in channel sensitivity become apparent. Downstream reaches have incised on average 2.4. m and become narrower by almost 50% with changes focused in a period of highly sensitive response after about 1950 followed by forced insensitivity caused by structural flood embankments and a significant grade control structure. In contrast, the middle reaches have been responsive but are morphologically resilient, and the upstream reaches show a mildly sensitive aggradational trend. Superimposing the natural and human drivers for change reveals that large scale stressors (related to ranching and irrigation) have been replaced over time by a suite of stressors operating at multiple spatial scales. Lower reaches have been sensitive primarily to 'local' scale impacts (urban growth, flood control, and aggregate mining) whereas, upstream, catchment-scale influences still prevail (including flow regulation and climate-driven sediment supply factors). These factors illustrate the complexity inherent to cumulative impact assessment in fluvial systems, provide evidence for a distinct Anthropocene fluvial response, and underpin the enormity of the challenge faced in trying to sustainably manage and restore rivers. © 2013 Elsevier B.V.


PubMed | Stillwater science and U.S. Department of Agriculture
Type: Journal Article | Journal: Journal of fish biology | Year: 2016

A flume was used to estimate the carrying capacity of streambed substrates for juvenile steelhead or rainbow trout Oncorhynchus mykiss seeking refuge from simulated freshets. The simulated freshets had mean water column velocities of c. 11ms(-1). The number of O. mykiss finding cover within the interstices of the substrate was documented for different substrate sizes and levels of embeddedness. The availability of suitable refuges determined the carrying capacity of the substrate for O. mykiss. For the size of the O. mykiss tested [means.d. fork length (L(F))=12212.6mm], the number of interstices with depths 200mm measured with a 14.0mm diameter flexible plastic tube was the best predictor of the number of O. mykiss able to find cover (r(2) =0.75). Oncorhynchus mykiss seeking refuge from freshets may need deeper interstices than those seeking concealment at autumn or winter base flows. The availability of interstices suitable as refuge from high flows may determine autumn and winter carrying capacity.


Cui Y.,Stillwater science | Wooster J.K.,National Oceanic and Atmospheric Administration | Braudrick C.A.,University of California at Santa Cruz | Orr B.K.,Stillwater science
Journal of Hydraulic Engineering | Year: 2014

The 14-m-tall Marmot Dam was removed during the summer of 2007, and the cofferdam protecting the working area was breached during a storm on October 19, 2007, allowing approximately 750,000 m3 of reservoir deposit to be eroded freely and released downstream to the Sandy River. Prior to the Marmot Dam removal, sediment transport models were developed to predict the transport dynamics of both gravel and sand, providing key pieces of information for stakeholders and regulatory agencies to select the most appropriate dam removal alternative. A monitoring program was implemented following dam removal that was designed to examine model predictions and assess when potential fish passage issues related to dam removal were no longer of concern. Comparisons of model predictions with field observations indicate that the model successfully predicted the erosion of the impoundment deposit, the deposition of sediment in a short reach downstream of the dam, and the lack of deposition in the majority of the Sandy River. The model overpredicted sediment deposition in a reach 7 to 12 km downstream of the dam. Further examinations indicated that the overpredicted sediment deposition may be attributed to underestimating the gravel particle abrasion coefficient during initial modeling. Comparisons also indicated that the model significantly underpredicted the suspended sediment concentration during the first 10 h immediately following cofferdam breaching but correctly predicted the minimal increase in suspended sediment concentration thereafter. © 2014 American Society of Civil Engineers.


Sloat M.R.,Stillwater science | Sloat M.R.,Oregon State University | Osterback A.-M.K.,Stillwater science | Osterback A.-M.K.,University of California at Santa Cruz | Osterback A.-M.K.,Southwest Fisheries Science Center
Canadian Journal of Fisheries and Aquatic Sciences | Year: 2013

To determine individual and population responses of steelhead trout (Oncorhynchus mykiss) to stream temperature, we sampled summer stream temperature and juvenile steelhead occurrence, abundance, and behavior in a small stream near the species' southern limit. Maximum annual stream temperature (22.3-33.1 °C) exerted a strong threshold effect on steelhead occurrence. Steelhead persisted through summer in all pools that did not exceed 30 °C, but the probability of persistence rapidly decreased to zero at warmer sites. Below the threshold for fish persistence, thermal effects on steelhead abundance were inconsistent, with temperature receiving strong support for inclusion in models of fish abundance at the beginning of summer but weak support for inclusion in models of end-of-summer abundance and summer fish loss. Thermal refugia that would allow steelhead to behaviorally thermoregulate were rare. In response to elevated stream temperatures, steelhead reduced foraging and agonistic activity, presumably to minimize energetic costs. In anticipation of the effects of global climate trends on stream temperature, management actions that limit or reduce stream heating will be critical for conservation of steelhead populations in habitats approaching thermal tolerance thresholds.


Stella J.C.,New York University | Battles J.J.,University of California at Berkeley | McBride J.R.,University of California at Berkeley | Orr B.K.,Stillwater science
Restoration Ecology | Year: 2010

Seasonal water limitation exerts a strong ecological filter on stream communities in semiarid regions. For first-year riparian willow and poplar tree seedlings, desiccation from rapidly declining river flows can limit reproduction, especially on rivers in which flow regulation and land conversion have limited the amount of area available for recruitment. We investigated survivorship of first-year riparian seedlings to simulated river stage declines, focusing on the three dominant species in California's heavily regulated San Joaquin Basin: Fremont cottonwood, Goodding's black willow, and sandbar willow. Seedlings grown in mesocosms were subjected to water table decline rates typical in spring on unregulated and regulated rivers. We compared species' differences in survival time and fit the empirical data to accelerated failure time models that predicted time until death as a function of drawdown rate, initial seedling size, and maternal line. We used Akaike information criteria to select the best model for each species. Water table decline rates ≥ 6 cm/day were lethal to all species. At an intermediate rate (3 cm/day) survival varied most among species (12-38%) and was highest for Goodding's black willow. Failure time models indicated no maternal effects on survival but that initial seedling size was important for cottonwood. Using these models, we simulated survivable flow scenarios on the Tuolumne River (CA) and assessed the survivability of actual flow releases in two representative years. This modeling approach shows promise for optimizing flow releases to restore pioneer riparian habitat on regulated rivers in some of the world's most water-limited regions. © 2010 Society for Ecological Restoration International.


Downs P.W.,University of Plymouth | Singer M.S.,Stillwater science | Orr B.K.,Stillwater science | Diggory Z.E.,Stillwater science | Church T.C.,University of California at Berkeley
Environmental Management | Year: 2011

The goal of restoring ecological integrity in rivers is frequently accompanied by an assumption that a comparative reference reach can be identified to represent minimally impaired conditions. However, in many regulated rivers, no credible historical, morphological or process-based reference reach exists. Resilient restoration designs should instead be framed around naturalization, using multiple analytical references derived from empirically-calibrated field- and model-based techniques to develop an integrated ecological reference condition. This requires baseline data which are rarely collected despite increasing evidence for systematic deficiencies in restoration practice. We illustrate the utility of baseline data collection in restoration planning for the highly fragmented and regulated lower Merced River, California, USA. The restoration design was developed using various baseline data surveys, monitoring, and modeling within an adaptive management framework. Baseline data assisted in transforming conceptual models of ecosystem function into specific restoration challenges, defining analytical references of the expected relationships among ecological parameters required for restoration, and specifying performance criteria for post-project monitoring and evaluation. In this way the study is an example of process-based morphological restoration designed to prompt recovery of ecosystem processes and resilience. For the Merced River, we illustrate that project-specific baseline data collection is a necessary precursor in developing performance-based restoration designs and addressing scale-related uncertainties, such as whether periodic gravel augmentation will sustain bed recovery and whether piecemeal efforts will improve ecological integrity. Given the numerous impediments to full, historical, restoration in many river systems, it seems apparent that projects of naturalization are a critical step in reducing the deleterious impacts of fragmented rivers worldwide. © 2011 Springer Science+Business Media, LLC.


Bowen H.L.,Stillwater science | Marchetti M.P.,Saint Mary's College of California
Environmental Biology of Fishes | Year: 2015

In the Central Valley of California, environmental characteristics differ between perennial and ephemeral stream types and therefore present different challenges for rearing salmonids with respect to water discharge, water temperature, food availability, and habitat complexity. Body shape of juvenile fall-run Chinook salmon (Oncorhynchus tshawytscha) reared in a perennial stream environment was compared to juveniles reared in an ephemeral stream environment. Using geometric morphometrics and multivariate analyses, this study presents morphological differences of rearing juvenile Chinook salmon both within and between ephemeral and perennial stream types. We found that shape differences between stream types were primarily associated with expansion of the mid-body region relative to differences in body length. Specifically, juvenile Chinook salmon reared in the ephemeral stream expressed increased body depth dominated by dorsal-ventral elongation of the dorsal, adipose, and anal fins. Eye position and gill opercula-body insertion points also were anteriorly shifted in the juvenile body shape of the ephemeral stream. Our findings support that juvenile Chinook salmon are morphologically flexible and can express habitat-specific developmental differences. © 2015 Springer Science+Business Media Dordrecht

Loading Stillwater science collaborators
Loading Stillwater science collaborators