WSP09221

• File Number: 7630.425
• Description: Wild and Scenic - Piedra River
• State: CO
• Basin: Western Slope
• Water Division: 7
• Date: 1/1/1991
• Author: Julie Stromberg Dunc
• Title: Instream Flow Requirements for Cottonwoods at Bishop Creek - Inyo County - California
• Water Supply Pro - Doc Type: Report/Study

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003075

.g 1991 by S.E.L. &: Associates

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"earns
Ford, Andrew R.

Instream Flow Requirements for
Cottonwoods at Bishop Creek,
Inyo County, California

Julie C. Stromberg
Duncan T. Patten
Cenler for Environmenlal sludies
Arizona State University
Tempe. Arizona 85287-1201

:en's Guide to

'W, and Richard Roos-

ABSTRACT: Instream flows for maintaining cottonwood (Populus) trees were
determined for Bishop Creek, an eastern Sierra Nevada stream that is partially
diverted for hydroelectric power production. Instream flows were calculated
based on relations between seasonal flow volume and tree ring width, and tree
ring width and canopy vigor. Annual radial growth of 3-4 mm is necessary for
maintenance of healthy tree canopies. The flow volume needed to produce such
a growth rate is about three to four times greater than diversion flows, and
about 40-60% of estimated natural flow volumes. The inadequacy of diversion
flows is evidenced in the low growth rates, low canopy vigor, and high mortality
of the cottonwoods. These adverse effects are apparent in diverted reaches of
Bishop Creek, whether hydrologically gaining or losing, in contrast to a high-
flow release reach where growth is not limited by low moisture availability.

KEY WORDS: Cottonwood, diversion, instream flow, Populus, riparian vege-
tation.

Iwer N euse

51ppi Chronicle

INTRODUCTION

E astern Sierra Nevada streams have
been diverted for decades 10 produce
hydroelectric power. However, increasing
regulatory consideration of non power uses
of instream flows has slowed development
of this power industry and resulted in
modification of flow releases 10 salisfy
downstream ecological or recreational
needs (Prilchard and Rosenman 1989;
Smith 1990). Given Ihe continued presence
of hydroelectric facilities in Sierra Nevada
slreams and demands for high-quality ri-
parian areas, there is a need to better un-
derstand diversion effects and instream
flow requirements of riparian ecosystems
(Stromberg and Patten 1990). Riparian veg-
etation is a key concern because of its in-
trinsic value and role in creating habitat
for aquatic and terrestrial animal species.
Many studies have found full or partial

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)NTRIBUTORS

I Rivers. Volume 2. Number I

diversion to negatively affect riparian veg-
etation in eastern Sierra Nevada streams
and elsewhere (Nilsson 1984). These ef-
fects include increased water stress and de-
creased leaf area (Smith et al. 1989) and
decline in abundance and growlh rale of
riparian Irees (Stine et al. 1984; Stromberg
and Patten 1989, 1990). In olher cases, how-
ever, plant abundance has been found to
be greater below stream diversion points
(Williams and Wolman 1984; Harris et al.
1987; Risser and Harris 1989).
Although prediction of diversion effects
is complicated by many factors. one gen-
eralization is that diversion should have
more impact on riparian vegetation in ef-
fluent reaches than in influent reaches
where flow is augmented by groundwaler
discharge (Guslard 1984; Kondolf et al.
1987; Harris 198B). At Bishop Creek. an

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