Abstract:
In some regions, measurements made at springs can be used
to study regional hydrogeologic processes, and determine
hydraulic and transport properties of aquifers.
Here, input-output models,
spectral analysis, and time series analysis are used
to identify
three different timescales characterizing
discharge at springs.
First, the ``hydraulic time scale'' depends on
the transmissivity of the aquifer
and relates long term changes in discharge to long term
changes in recharge. The hydraulic time
scale will describe, for example, the
secular decrease in discharge
during a period of drought. A second hydraulic time scale,
referred to as the ``time lag'',
measures the time lag between groundwater recharge (in
the studied examples recharge is snowmelt
during the springtime) and the time of peak discharge at the spring.
Finally, the ``age'' or mean residence time of groundwater
represents the transport time of tracers and the volume
of water in the aquifers.
Springs in the Oregon and California Cascades are studied
as examples.