MICHAEL MANGA: Recent Refereed Publications
M. Manga (1997) A model for discharge in spring-dominated
streams, and implications for the transmissivity and recharge of
quaternary volcanics in the Oregon Cascades,
submitted to Water Resources Research.
A model for discharge in spring-fed
streams is described and applied to streams
in the Oregon Cascades. These streams are assumed to be fed by an
unconfined aquifer comprised predominantly of
quaternary basalts and basaltic andesites.
The model is based on the unsteady Boussinesq
equation and is characterized by a single parameter, a normalized
transmissivity. Flow in a runoff-dominated stream is used
as a proxy for the time-dependent groundwater recharge.
Four spring-dominated streams with 50 years of daily discharge
records are studied, and modeling efficiencies are in the
range of 0.76 to 0.89.
The effective transmissivity is found to be
approximately proportional to the length scale of
the aquifers. Groundwater recharge rates are in the range of 60-130 cm/year
and 40-70% of the mean annual precipitation.
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