Many of the sewage networks that carry wastewater in cities operate on a unitary system. In
this system, domestic wastewater and stormwater are combined in a single sewerage network.
This type of design means that when there is a large volume of rainfall, the systems cannot
manage it and overloading occurs, causing excess water and pollutants to be discharged
directly into watercourses in the form of unitary system discharges (DSU).
DSUs represent a growing environmental concern in many cities around the world by severely
affecting the water quality and also the ecosystem functions of watercourses. For this reason,
this study aims to estimate the volume of water generated by DSU previous flow
measurements made in the sewage network collectors of Girona. These measurements have
been made by two flow meters placed just before the spillways where the DSU are produced.
With the data from the flow meters and rain gauges available from CATSA, it has been possible to plot the variations in wastewater flow as a function of rainfall. This made it possible
to identify a clear relationship between rainfall intensity and overflow volume in different rain
episodes.
In addition, the rainfall threshold at which the DSU of Hospital Josep Trueta overflows is
produced has been determined in this study. This is estimated at 2 mm of rainfall based on
data collected. This information is crucial to assess the current state of the sewer network and
to plan future interventions to improve this rain threshold.
To minimize the adverse effects of overflows, several measures are proposed. These include the implementation of separate sewer systems, the use of computer modelling to monitor the
network and the creation of retention basins to jointly manage stormwater and wastewater.
These solutions would allow a more efficient management of water resources, reducing
environmental impact and improving water quality.
In conclusion, this research not only identifies and quantifies DSU, but has also proposed
strategies to mitigate their effects, thus contributing to the protection of the environment in
Girona specifically the Ter river
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