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Pacific Southwest Research Station


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Sierra Nevada Research Center


Aseasonal pulsed flow effects on the foothill yellow-legged frog (Rana boylii): Integration of empirical, experimental and hydrodynamic modeling approaches

Study Plan
Research Project Summary


photo of foothill yellow-legged frogThis study is a collaborative effort between the USDA Forest Service, Pacific Southwest Research Station, Sierra Nevada Research Center, the University of California, Davis, and an independent scientist. The primary goal of the study is to better understand the effects of pulsed flow releases resulting from hydroelectric power generation on the foothill yellow-legged frog (Rana boylii).

The foothill yellow-legged frog is one of a few California amphibians whose complete life cycle is associated with stream environments. The life stages of the foothill yellow-legged frog occur along a mobility continuum from immobile (eggs) to highly mobile (adults) such that adaptations which improve survival rate vary in relation to ontogeny. To avoid disturbance, the timing of this complex life history and set of habitat preferences is synchronized with the seasonality of runoff during the predictable cycle of wet winters and dry summers occurring across the range of the foothill yellow-legged frog. Over the last half century, the foothill yellow-legged frog has declined dramatically, especially in southern California and the southern Sierra Nevada mountains. Dams and reservoirs have been cited as likely factors in this decline because they drastically alter the disturbance regime and sediment budget of rivers in which native species have evolved, resulting in permanent alteration to instream habitats. The ensuing impact on foothill yellow-legged frog survival has been a focus of study over the last decade, but many knowledge gaps remain. Of primary concern to us in this proposal are the short-term direct and indirect effects of extreme aseasonal fluctuation in water discharge during the foothill yellow-legged frog's larval rearing season.

photo of the Feather River DamDue to its declining status, foothill yellow-legged frogs have increasingly become a focal species in water management planning, especially in FERC re-licensing programs for hydroelectric dams. However, due to the dispersed nature and different agency involvement in the licensing efforts, a comprehensive assessment of pulsed flow effects on foothill yellow-legged frogs has yet to be conducted. With such an assessment, our understanding of the influence of pulsed flows relative to foothill yellow-legged frogs survival will be improved and obvious knowledge gaps could be identified. Once these gaps are clearly identified, it will be possible to develop hydrodynamic modeling tools to determine how changes in habitat availability and habitat heterogeneity resulting from differing flow regimes affect the reproductive success and survival of foothill yellow-legged frogs. Finally, to link this habitat-based modeling approach to actual rates of survival and reproductive success, controlled experiments on foothill yellow-legged frog physical tolerances are needed. In particular, data are lacking on the tolerances and responses of the larval life stage of the foothill yellow-legged frog to pulsed flows.


To better understand the effects of pulsed flows on foothill yellow-legged frogs, we are addressing the following objectives in a two phased approach:
Phase I
blue arrrow1. Document relationships between characteristics of pulsed flows (e.g. timing, ramping rates, ratio to base flow) and survival, reproductive success, and habitat suitability for all life stages of the foothill yellow-legged frog through a review and analysis of existing data and reports.
blue arrrow2. Identify specific knowledge gaps regarding aspects of fluctuating or pulsed flows (e.g. timing, duration, ramping rates, volume) and their impacts on foothill yellow-legged frog survival rates, reproductive success, and habitat suitability.
Phase II
blue arrrow1. Address specific knowledge gaps identified in Phase I with a series of laboratory and field experiments designed to quantify larval swimming abilities and behavioral responses to changes in shear stress created by manipulations of depth, velocity, and substrate.
blue arrrow2. Develop a model-based methodology to evaluate changes in habitat-scale hydrodynamics from a series of low and high pulse flow scenarios and subsequent changes in habitat availability and heterogeneity.
blue arrrow3. Use results from lab and field manipulations to assess how modeled changes in habitat availability and heterogeneity may influence foothill yellow-legged frog survival and reproductive success. By integrating these two components we will be able to translate model predictions regarding habitat parameters into actual effects on various life stages of the foothill yellow-legged frog.


We are conducting a two-phased project conducted over two years to address the above described research and water management needs. Phase I involves a review of published and unpublished literature, collation and analysis of data from recent studies, and identification of knowledge gaps. Phase II then directly applies the information gathered in Phase I to refine the focus of experiments regarding relative vulnerabilities of various life stages and to develop hydrodynamic models of foothill yellow-legged frog habitat. In Phase I, data are being analyzed with respect to quality and in terms of direct and indirect effects on foothill yellow-legged frogs. Variables representing foothill yellow-legged frog status, life stage, abundance, reproductive success and habitat components (depth, velocity, substrate) are being summarized and analyzed relative to pulsed flow events and characteristics (timing, duration, ramping rates, flow magnitude and volume).

photo of foothill yellow-legged frog tadpolePhase II consists of complementary experimental and hydrologic modeling components. The experimental component of Phase II includes both field transplant and laboratory flume experiments. In field experiments, foothill yellow-legged frog larvae are moved from shallow margins into deeper, higher velocity areas and their response observed. Laboratory flume experiments provide opportunities to vary water velocities and availability of cover and record the response of different aged larvae. Phase II modeling is being done using River 2D, a two-dimensional depth averaged finite element model, that is used by California Fish and Game and others in fish habitat evaluation studies. The output from the modeling scenarios are being analyzed in a variety of ways to determine how velocities (magnitude and direction), depths and habitat types change as flow fluctuates. Changes in velocity magnitude and direction at each modeled discharge will provide information on whether mobility thresholds of vulnerable life stages are exceeded. Changes in habitat availability and heterogeneity will provide information on base flow discharges that provide the highest proportion of suitable habitat for all life stages.



The integrated results of this work should provide a better understanding of the current impacts of pulsed flows on foothill yellow-legged frogs along with a model-based methodology that could be used to mitigate impacts on various aquatic species in future pulsed flow planning.


Study sites for field experiments and hydrodynamic modeling have not yet been selected,but will be in low-mid elevation streams on the west slope of the Sierra Nevada, with a known R foothill yellow-legged frog populations, and downstream of a hydroelectric facility. Laboratory experiments will be conducted in an artificial stream/laboratory flume at the USFS PSW Redwood Sciences Laboratory in Arcata, California.



1.)Lind, A. 2) Yarnell, S. 2) Mount, J. 3) Kupferberg, S.

1)USDA Forest Service
Pacific Southwest Research Station
Sierra Nevada Research Center
ph: 510-530-1700

2) University of Calfiornia, Davis
Davis, CA

3) Questa Engineering

The study was funded by the Public Interest Energy Research Program of the California Energy Commission and the Division of Water Rights of the State Water Resources Control Board via the Pulsed Flow Program, Center for Aquatic Biology and Aquaculture, University of California, Davis (



The study proposal (23pp) is available by request from A. Lind (
* Previous research related to this project includes Lind et al. 1996.

Available PowerPoint presentations from the Pulsed Flow
Conference can be viewed online by clicking on the author's names at

Pulsed Flow Effects on the Foothill Yellow-Legged Frog (Rana boylii): Ingetration of Emplirical, Experimental and Hydrodynamic Modeling Approaches. Pier Final Project Report


Last Modified: Mar 28, 2013 02:54:30 PM