ABSTRACT
Water quality in natural systems and, specially, inland water systems influences on the hea1th of water 
ecosystems and on fue different possible uses. An appropriate management of water resources is one of 
the main factors for the efficient use of fue water, and as consequence, for the sustainable development 
that allows fue equilibrium between human life and the environment.
Historically, both concepts, water quality and the management of water resources, have been considered 
scientifically and legally separately. Few developments have been done
over simulation and optimization of the water resources systems taking into account the quality aspect. 
Only when the quality of the water is a limitation for the use it is considered in the management of the 
resource, and usually as a reduction of the available resource.
In the last years, a growth of environmental aspects on the social conscience and the legislation has 
been developed, as it reflects the European Water Framework Directive (UE, 2000). Consequently the 
planning and management ofthe water resources will be done, in the immediately future, under efficiency 
and environmental protection goals. F or this, both fields must be understand as one and inseparable.
In this thesis a module for modeling the quality of water resources systems has been developed. This tool 
works coordinately with the Decision Support System (DSS)
AQUATOOL, developed previously by the DIHMA of the Polytechnic University of Valencia, for the planning 
and management of the water resources systems.
The program GESCAL allows to model the grand majority of the conventional
constituents such as: temperature, dissolved oxygen, nitrogen cyc1e, different forms of phosphorous, 
phytoplankton, and several arbitrary contaminants defined by the user. The user can deal with much of 
the current water quality problems. The program allows to model water quality in rivers and reservoirs 
but considers, also, the influence of the otrer elements of the system, which water quality is not modeled. 
GESCAL is a module for modeling conjunctively the management and the quality of water resources systems.
The utility of the module has been demonstrated with the application to the Jucar river basin. The simulation 
of different altematives of the developed model has allowed, among others, to evaluate the evolution of the 
water quality in all the system facing different scenarios of the use of the resource in the basin, to 
analyze the effect on the water quality of the future water treatment facilities, and to estimate additional 
flows for improving the quality of the water at critical points of the basin.