Digital Signal Processing Reference
In-Depth Information
Ev [L/T] is the lake evaporation,
In other words, the rate of change in storage of the volume of water in or on the given area per unit
time is equal to the rate of inflow from all sources minus the rate of outflows.
Inputs - outputs = Storage
The input or inflows to a lake may include surface inflow, subsurface inflow, and water imported into
the lake. The outputs may include surface and subsurface outputs and water exported (e.g. water
supply) from the lake. Some of these flux terms are estimated from the literature (e.g.
evapotranspiration) while others are empirical (e.g. discharge at the gauging station). Most
components of a water budget are easily measured or estimated. Ground-water flow is the exception,
and is an important and largely overlooked component of water budgets because it is the most difficult
to quantify as it cannot be measured directly.
In the study catchment of Edko one of the important steps needed as a reference to the mathematical
modelling, was to calculate and estimate the water budget of the lake. That was done based on the
available collected data from different sources in addition to the two field work survey missions that
were done in the study area. Inflow to the lake are measured on monthly basis, but for the outflow
from the lake into the sea through the exit channel, no fixed temporal records were present but some
field measurements were taken for the purpose of average estimate. Therefore the calculation was
done on daily average flows due to the data limitation at the outflow location.
The following terms were evaluated to generate the summary water budget for Lake Edko:
Inputs
1.
Surface discharge from two main drains (Edko and Barseek)
Surface-water flow is the largest inflow component of the water budget. Average monthly data exist
for the drainage inflow into the lake, but due to the lack of similar measurements at the exit channel,
field measurements were taken. The average input discharges measured from the main surface drain
Edko during field measurement of 4.01 M m
3
/day, in May 2005 were used for calculation. Another
measurement of 5.36 M m
3
/day was taken in November for validation. Based on hourly discharge
rates at Barseek pump station given by DRI, the average discharge rate of Barseek pump station is 0.7
*10
6
m
3
/day.
Outputs
1.
Outflow from exit channel to the sea (Bougaz Maadia)
To define the interaction between the sea and the lake, the outflow measurements should be measured
on a fixed temporal basis, such as monthly, in line with the inflow measurements into the lake. The
only available data for the outflow were measurements at the exit channel during field work during
May 2005. The average of these measurements was 6.25 M m
3
/day. Another field measurement
exercise was undertaken in November 2007 in order to validate the calculation; an outflow value of
6.67 M m
3
/day was obtained.
2.
Evapotranspiration losses
Evapotranspiration is the combined water loss as vapour via evaporation and transpiration from plants.
Because the contributing individual processes are difficult to measure separately, they are usually
considered together. Evapotranspiration is a complex function of many environmental factors (e.g.,
windspeed, humidity, temperature, day length, radiation intensity) and has been estimated using
various empirical (observation-based) relationships (Thornthwaite 1948, Penman 1948, Thornthwaite
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