SWQM - A simple river water quality model for assessment of urban ...

12 nd International Conference on Urban Drainage, Porto Alegre/Brazil, 10-15 September 2011
For practical application, however, neither approach appears to be satisfying: Whilst, on the
one hand, simple approaches might be quick to apply, they lack from features necessary to be
considered when analyzing multiple discharges (e.g. several discharge locations into the same
receiving water body, …), on the other hand, approaches of high complexity and data demand
may not be feasible in “daily life applications” by consenting authorities. The present
contribution attempts to fit this gap by suggesting a water quality model covering the most
relevant processes and by embedding it not only in two software environments, but also, at
the same time, in a consenting framework.
REQUIREMENTS ON A WATER QUALITY MODEL RIPE FOR
PRACTICAL APPLICATION
For river water quality modeling, Rauch et al. (1998) suggest an application-specific model
set up. This was also the intention of the IWA working group compiling the River Water
Quality Model No. 1 (RWQM) (Reichert et al., 2001), which serves as a baseline for
application-specific submodels. Besides many other packages, also the QUAL2 family of
models is widely applied. However, for practical application within the context of the daily
routine processes of authorities responsible for consenting procedures, a river model should
comply with requirements such as:
• Consideration of all relevant processes and water quality objectives:
Even though the importance of particular process may vary from case study to case
study, a generally applicable model approach should comprise of the relevant
processes, without “overloading” the model by non-essential processes. Within the
central European context, assessment of urban discharges is usually carried out with
regard to Dissolved Oxygen and ammonia (NH3-N), the latter being toxic to fish life.
This is also in line with current guidelines. As ammonia (NH3-N) is a key parameter
for the assessment, it should be considered directly. Therefore it is necessary to
consider pH in the water quality model as well, as pH usually is different in various
types of urban discharges.
• Consideration of different characteristics of sewer and treatment plant discharges:
As sewage discharges and treatment plant effluent have different characteristics, such
as different content of easily biodegradable matter, these have to be considered in an
appropriate way.
• Limited data requirements:
For application on a wider scale (such as within a consent setting context), the model
should not require (much) more data than would be readily available. Whilst data on
river geometry and profiles might still be available from digital cadastres of the
responsible government agencies, data on river water quality might have been sampled
only on a rare basis if at all they are available.
• Limited number of parameters, avoiding ambiguity:
In order to a river water quality model to be applied also by non-specialists, it should
have a limited number of parameters, which can be set easily, in a non-ambigious way.
Often, users tend to use default values.
• Easy to use, also by non-experts:
Though this requirement may sound trivial, non-trivial handing of the model
application might render the model unsuitable for practical application. This refers not
only to the nature of the user interface, but also to the procedure of preparing the input
data, of performing simulation runs and of processing output.
2 SWQM - A simple river water quality model