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SUMMARY:Salinity intrusion in Northern San Francisco Bay: Observations and
  models - Stephen Monismith (Stanford University)
DTSTART:20161024T120000Z
DTEND:20161024T130000Z
UID:TALK68115@talks.cam.ac.uk
CONTACT:Doris Allen
DESCRIPTION:The problem of predicting how the salinity field in estuaries 
 responds to freshwater inflows is one that draws attention from both physi
 cal oceanographers and hydraulic engineers since it has both scientific an
 d practical dimensions. In Northern San Francisco Bay\, examination of 20+
  years of data spanning the estuary shows that the overall structure of th
 e salt field can be described using a single parameter\, X2\, the distance
  in km measured from the Golden Gate Bridge  to where the salinity on the 
 bottom is 2. Analysis of long-term monitoring of biological data (e.g. fis
 h abundance) shows that much of ecological functioning of the estuary depe
 nds on X2 and so regulations have been developed specifying X2 position de
 pending on time of year and hydrologic conditions. Because these regulatio
 ns can require substantial amounts of water\, it is necessary to efficient
 ly predict the behavior of X2 with some accuracy so as to help manage the 
 competing demands for California’s limited water supply.\n \nIn this tal
 k\, using several data sets including one that goes back to ca. 1960\, I w
 ill discuss the observed behavior of X2 and how it responds to flow\, Q. I
 n general\, the tendency of freshwater flows to carry salt out of the estu
 ary is balanced by the tendency of dispersion to move salt upstream. A sur
 prising aspect of the X2-Q relation in Northern San Francisco Bay is that 
 it is much weaker than would be inferred from classical estuarine circulat
 ion theory\, behavior that we attribute to the effects of stratification o
 n the turbulent flows that support upstream salt flux. I will present a ri
 gorously derived albeit simplified integral model of salinity dynamics tha
 t can be used to understand this behavior and that can be used to create a
  dynamically based (rather than purely empirical) model of unsteady salini
 ty intrusion. Finally\, examination of the relevant data also suggests tha
 t inability to accurately measure freshwater flows during relatively dry p
 eriods may be a bigger limitation on accurate predictions of low-flow beha
 vior than is choice of model str
LOCATION:MR5\, Centre for Mathematical Sciences
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