Introducing of Ce-Qual-W2 Model and Its Application - Water Quality Management: Assessment and Interpretation - page 109

receiving lots of wastewater from different sources. The water quality model is used
to simulate the water quality condition in the K ā r ū in River, estimating the minimum

in stream fish survival and propose man-

agement strategies to improve the water quality (Khodadadi Darban 2010 ).
In this work we focused on the region upstream of the Gotvand dam, to the Dam
and two cities which are located downstream of the dam. The reason mainly being
that the Gotvand dam is the last major dam in the K

flow for ecosystem survival especially

in River, so all the untreated
waste from upstream and the many pollutants in this region make this segment of
the river critical for analysis, and the reduction in

ā r ū

flow after the Gotvand dam makes
analyzing its effects on the water quality downstream of the dam (Fig. 6.13 ).
During flow flow becomes minimal and the Dissolved

Oxygen (DO) declines. In this event, the biological habitat of the river is endan-
gered,

flow periods the in stream

fish deaths happen in low DO concentrations, and thus studying the DO is of
importance for this research (J hnk and Umlauf 2001 ). The Gotvand Dam reservoir

is also used for municipal and agricultural water supplies, making water quality
studies in this part inevitable (Lindenschmidt et al. 2004 ).

ö

6.4.2.1 Model Calibration and Veri cation

Reliable simulation can be undertaken for management planning by calibrating and
verifying the model. A water quality model needs to be calibrated and veri ed with

respect to the prototype conditions of the water body to which it is applied. The model
was calibrated by hydraulic constants and coef cients provided byDez Ab for 1999 and

coeffi- cient values from calibration conducted by the Water Resources Management

Company of Iran in 2001. The model was then recalibrated and veri

ed with respect

to the field data taken in 2004 2005 for the K ā r ū in River (Khodadadi Daran 2010 ).

-

cult for the water quality model than for the
hydrodynamic model, due to the large number of water quality state variables and
biochemical reaction coef

The recalibration is far more dif

cients involved. Since the model predictions will change
depending upon the selection of the values of biochemical coef

cients, consistent

coeffi- -

cient values should be transferable for the model predictions to compare with
independent sets of

cient values should be used for different simulation runs. That is, the coeffi-

field observations (Snowling and Kramer 2001 , Wells 2001 ).
The model was run for the year 2005. The model results for daily average
concentrations at the surface and bottom layers was compared with the observed
values at the corresponding stations. The model results and

field measurements are

provided in the respective figures, they indicate that the model results and field

measurements are generally in good agreement, with errors of less than 6.5 %.
The temporal variability of the model results is generally different from those of

the field data, because the model results represent the daily average values of the

lateral average concentrations while the field data were point measurements, and

also because of the random variability inherent to a natural system, thus errors to
this extent were allowable.