**3.2 Hydrodynamics**

The hydrodynamic behaviour of the rivers at river Cávado basin is influenced primarily by rainfall regimes in the region and the exploitation of its hydropower facilities. A conceptual framework (Figure 15), where are identified the main structures influencing the hydrodynamic regimes (numbered from 1 to 28) was adopted in order to characterize the data to define the simulation scenarios. For each scenario the rainfall hydrographs and the pumps and turbines operation must be defined.

To illustrate the application of the developed platform thirteen hydrodynamic scenarios were defined in order to estimate average monthly flows and the average flow considering the data included in the information system for the entire available monitoring period.

Turbines were considered fully operational during simulation periods and the water levels at reservoirs are considered near its average level for the month associated with each simulation. It was also considered that other outflow gates at dams are closed. The exceptions were the Venda Nova and Vilarinho das Furnas (Figure 15).

Finally, on the oceanic boundary of the model, no tidal variations were assumed. It was considered that the water level remains at the mean sea level during the simulation period.

All simulations were defined to have duration of 7 days and a computational time step of 15 minutes.

Figure 14 presents a comparison between the estimated (estimation based on monitoring data) and the simulated values at different rivers locations. The presented simulated results refer exclusively to the last instant of the simulation.

From the observation of Figure 14 it is possible to find a close proximity between the estimated and simulated results, with the exception of locations 5, 6 and 12. In the first two locations the difference of 5.6 m3/s is due to the introduction of the flow contribution of the sub-basin limited by the Caniçada reservoir and the Febras river at this last location. A similar situation occurs in location 12. In general, all the other simulations results present a notable approximation to the monitored values.

Web-Based Decision Support Framework for

results in different simulation scenarios.

Table 1. Water quality modelling scenarios

**3.3 Water quality** 

Water Resources Management at River Basin Scale 59

Simulations of water quality were based on hydrodynamic simulations previously presented and on the consideration of different characteristics for the discharges of waste water treatment plants (WWTP), industries, livestock units, and other contributions associated with different tributaries. The establishment of different values for these pollutant discharges

In order to present the potential of the developed modelling system different scenarios were defined for average annual and monthly rivers flows discharges and considering the WWTP efficiency in compliance with their treatment schemes (scenarios 1 to 13). Additionally, for the wettest month (January) and the driest month (August) the effects of discharges from WWTP considering extreme values of its efficiencies were worked out (scenarios 14 to 17). Finally, it was considered three scenarios (scenarios 18 to 20) associated with the failure of

each one of the three main WWTP: Frossos, Esposende and Vila Frescaínha (Table 1).

**Scenario Hydrodynamics conditions WWTP efficiencies**  1 Annual Average 2 January Average 3 February Average 4 March Average 5 April Average 6 May Average 7 June Average 8 July Average 9 August Average 10 September Average 11 October Average 12 November Average 13 December Average 14 January Maximum 15 August Maximum 16 January Minimum 17 August Minimum

18 Annual Frossos WWTP failure 19 Annual Vila Frescainha WWTP failure 20 Annual Esposende WWTP failure

Fig. 14. Estimated average rivers flows and simulated values for a scenario corresponding to the annual mean values of the available monitoring period

Fig. 15. River Cávado model scheme: WWTP discharges
