466
A.-E. Briciu et al.
The diurnal cycle in rivers is a well-known feature that is studied for a long time,
but it is often revealed only by high temporal resolution measurements done with
instruments able to record fine changes in the studied water parameter (e.g. millimetric variation in water level). Measurements of water parameters done multiple
times per day (at least hourly) are a must because low temporal resolution measurements (such as those done once or twice per day) do only record moments of the
day that represents only a small length on the curve line of the diurnal cycle. Such
low-resolution measurements generate daily values on the longer time series that
may be far from being representative for the recorded day. Even the average value of
the diurnal evolution of a streamwater parameter measured with high temporal resolution does not offer more than a (reasonably) distorted interpretation of the selected
time interval.
Because of the permanent mixing of the diurnal cycle with the (periodic or aperiodic) multi-diurnal evolutions, every day has a unique streamwater evolution in the
24 h cycle. Groups of days or separate days may record similar diurnal shapes in the
evolution of a studied streamwater parameter, just like in the case of the evolution
of an atmospheric parameter. However, unlike the air, the streamwater recorded in
a section tells the story of the entire catchment upstream, which is a much stronger
control factor for a river than for the air above.
Not only consecutive days on a river have different diurnal shapes, but also different rivers have different diurnal evolutions in the same day, as a mark of their
different catchments. As every particular diurnal evolution is unique and heavily
influenced by other evolutions, a question arises: which is the real/denoised shape
of the diurnal cycle of a river at given point in space? Because of the Heisenberg’s
uncertainty principle, a pure diel signal may never be guessed (in our case: if all supradaily/macro-oscillations are removed from time series, which mean value remains
to be changed by the daily cycle (and will it still exist)?).
The purpose of this chapter is to extract abstract/mean diurnal cycles of various
streamwater parameters in different catchments, river sections and time intervals in
western and northern Romania. The selected territory does not have studies that try to
obtain relevant shapes of water parameters of the selected rivers. Our study is useful
for those that undertake case studies about stream waters (by using our methodology) and for researchers interested in Romanian waters (by using our examples and
results).
The meteorological data in this study can be used to understand the water behavior.
Summary studies such as those of Poole and Berman [23] or Nimick et al. [21]
indicated that the diurnal cycle of temperature in stream water is linked to the air
temperature and relative humidity which are, amongst others, control factors.
A.-E. Briciu et al.
The diurnal cycle in rivers is a well-known feature that is studied for a long time,
but it is often revealed only by high temporal resolution measurements done with
instruments able to record fine changes in the studied water parameter (e.g. millimetric variation in water level). Measurements of water parameters done multiple
times per day (at least hourly) are a must because low temporal resolution measurements (such as those done once or twice per day) do only record moments of the
day that represents only a small length on the curve line of the diurnal cycle. Such
low-resolution measurements generate daily values on the longer time series that
may be far from being representative for the recorded day. Even the average value of
the diurnal evolution of a streamwater parameter measured with high temporal resolution does not offer more than a (reasonably) distorted interpretation of the selected
time interval.
Because of the permanent mixing of the diurnal cycle with the (periodic or aperiodic) multi-diurnal evolutions, every day has a unique streamwater evolution in the
24 h cycle. Groups of days or separate days may record similar diurnal shapes in the
evolution of a studied streamwater parameter, just like in the case of the evolution
of an atmospheric parameter. However, unlike the air, the streamwater recorded in
a section tells the story of the entire catchment upstream, which is a much stronger
control factor for a river than for the air above.
Not only consecutive days on a river have different diurnal shapes, but also different rivers have different diurnal evolutions in the same day, as a mark of their
different catchments. As every particular diurnal evolution is unique and heavily
influenced by other evolutions, a question arises: which is the real/denoised shape
of the diurnal cycle of a river at given point in space? Because of the Heisenberg’s
uncertainty principle, a pure diel signal may never be guessed (in our case: if all supradaily/macro-oscillations are removed from time series, which mean value remains
to be changed by the daily cycle (and will it still exist)?).
The purpose of this chapter is to extract abstract/mean diurnal cycles of various
streamwater parameters in different catchments, river sections and time intervals in
western and northern Romania. The selected territory does not have studies that try to
obtain relevant shapes of water parameters of the selected rivers. Our study is useful
for those that undertake case studies about stream waters (by using our methodology) and for researchers interested in Romanian waters (by using our examples and
results).
The meteorological data in this study can be used to understand the water behavior.
Summary studies such as those of Poole and Berman [23] or Nimick et al. [21]
indicated that the diurnal cycle of temperature in stream water is linked to the air
temperature and relative humidity which are, amongst others, control factors.