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Pathways of river water to the surface layers of stratified reservoirs
Author(s) -
Cortés A.,
Fleenor W. E.,
Wells M. G.,
de Vicente I.,
Rueda F. J.
Publication year - 2014
Publication title -
limnology and oceanography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.7
H-Index - 197
eISSN - 1939-5590
pISSN - 0024-3590
DOI - 10.4319/lo.2014.59.1.0233
Subject(s) - inflow , stratification (seeds) , entrainment (biomusicology) , geology , dilution , hydrology (agriculture) , current (fluid) , water mass , mediterranean climate , environmental science , oceanography , geotechnical engineering , seed dormancy , ecology , philosophy , botany , germination , thermodynamics , physics , dormancy , rhythm , biology , aesthetics
This study uses tracer experiments to characterize the fate of a cold plunging river into a Mediterranean reservoir under different stratification conditions. Three tracer experiments in Lake Béznar, Spain, demonstrate that a significant fraction of the inflow may be quickly entrained into the surface mixed layer (SML), rather than flowing to lower depths. We observe that a fraction (and possibly all) of river inflow entrains into the SML when the density current forms intrusions at the top of the metalimnetic layer. Intrusions near the base of the SML form due to lighter interfacial fluid at the top of the density current, with intermediate properties between river—reservior water when there is sufficient dilution of the cold inflow, and abrupt density changes at the base of the SML. Consequently, a layer of fluid splits from the denser part of the current and intrudes just below the SML, while any remaining fluid flows to lower depths. We parameterize this splitting behavior in terms of the transition Richardson number, Ri 12 = Γ × ( ρ 2 − ρ 1 )/( ρ 0 − ρ 1 ), where ρ 0 , ρ 1 , and ρ 2 are densities of the inflow, the SML, and the metalimnetic layer underneath, respectively; and Γ is the total dilution through the plunge zone and subsequent entrainment. Splitting occurs when Ri 12 ≥ 1, consistent with previous laboratory experiments. We use this theory to predict the seasonal fate of river water during the stratification of Lake Béznar and identify the conditions that favor the formation of intrusions near the base of the SML.