BOARD00970

• Board Meeting Date: 7/22/1993
• Description: Agenda or Table of Contents, Minutes, Memos. Partial.
• Board Meetings - Doc Type: Meeting

little storage of 'groundwater. Thus, many high flows each summer
are desirable to maintain the high water content of alluvial
soils and high groundwater tables.

DISCUSSION
This study establishes several important facts:
1) riparian vegetation along Little Dry Creek in the study area
is in healthy condition, relatively stable, supports cottonwoods
and willows along with many Eurasian plant species,
2) the water source for riparian vegetation appears to be the
groundwater table, and
3) the groundwater system supporting riparian vegetation is
hydrologically connected to Little Dry Creek and any change in
water levels in Little Dry Creek will cause water level changes
in the adjacent groundwater table.
Because the groundwater-surface water connection is so
complete, the question must be asked, can water be removed from
Little Dry Creek and not damage the riparian ecosystem? The
answer is not simple because no definitive research has occurred
to determine the tolerance of woody riparian plant species for
water level changes.
Cottonwoods on the eastern slope of the Sierra Nevada
require water sufficient for growth, and reductions in stream
flow may significantly decrease their growth rates, vigor (as
reflected in leaf area), and result in higher mortality
(Stromberg and Patten 1991). They reported that the flow volume
required to maintain healthy cottonwood growth was 40-60% of the
estimated natural flow volumes. For the Little Dry Creek study
area it appears that a reduction in baseflows by 40-60% probably
would not cause significant degradation of the riparian
vegetation. It should also be mentioned that because Little Dry
Creek is partially incised in bedrock, the reduced flow should
not be entirely on bedrock or the essential recharge to the
alluvium aquifer will not occur.

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