Hydrography of the Russian River Estuary - Sonoma County Water ...

1. Introduction
The Russian River Biological Opinion written by the National Marine Fisheries Service
(NMFS 2008) requires the Sonoma County Water Agency (SCWA) to manage the
Russian River estuary in such a way as to maintain a closed mouth following natural
closure during the summer management period of 15 May through 15 October. It is
expected that this closed lagoon state was typical in late summer and fall prior to human
perturbations of the system and that this closed lagoon state will provide improved
habitat for the rearing of juvenile steelhead in the estuary (and possibly also coho).
However, long-duration closures of the Russian River estuary have not been observed
recently and it is unclear how stratification and water residence will play out in terms of
the distribution of water properties (specifically salinity, temperature, velocity, and
dissolved oxygen). Water properties are key determinants of juvenile steelhead habitat,
and they are important in their relation to water quality conditions conducive to
ecosystem health and human “beneficial uses”.
Bodega Marine Laboratory (BML) at the University of California Davis was contracted by
the SCWA to conduct a study of the estuary that provides a view of circulation,
stratification, salinity, and residence during the summer and fall of 2009. The aim was to
provide SCWA with a basis for designing a more complete hydrological analysis by
identifying phenomena and processes that are critical to future management of the
estuary and the multiple human and ecosystem uses of this environment. Data were
collected as a basis for (i) assessment of the hydrological condition of the estuary during
the 2009 dry season, (ii) future analyses that will provide understanding of how river
flow and mouth state control estuary hydrology and through that water-column habitat in
the estuary, and (iii) validation and inputs for future numerical modeling of the estuary.
The Russian River estuary is a bar-built, drowned-river-valley estuary. Although this
type of estuary is common – indeed typical – in central and northern California, the
characteristic hydrological patterns and underlying hydrodynamic processes are not well
documented nor understood. In this study, it was necessary to obtain primary field data
and to conduct data analyses in order to obtain a preliminary understanding of this
system and thus to allow discussion of possible future conditions.
This report is a summary of results from the field program in the Russian River estuary
during the summer and fall of 2009, during which river flows were lower than normal.
This report is preceded by a data report (Behrens & Largier 2010), in which all field data
are described and graphically presented.
7