Papers

A modeling system to simulate tidally driven morphodynamics is developed and assessed. The system couples an existing shallow water model with a new morphological updating model. Four innovative features to improve the accuracy and efficiency of the system are implemented and tested. First, two alternatives are proposed to update the velocity field without running the hydrodynamic model. Both alternatives, based on an assumption on the behavior of friction, are more accurate than the traditional "continuity correction". Second, hydrodynamic results are provided in the frequency domain. The harmonic synthesis of the velocity time series simplifies interpolation and extrapolation of the hydrodynamic model results and the use of different time steps for the various components of the modeling system. Third, the time-integration of the sediment fluxes is performed with a Runge-Kutta method so the time step adapts in space and time to the flow characteristics. Finally, a criterion to determine the need for a new hydrodynamic simulation is derived, based on the importance of the errors introduced by the outdated flow field relative to those introduced by the sand-transport formulae.

Degradation of water quality in supply and distribution systems is one of the foremost problems that water companies are faced with. It is every day practice in many countries to maintain a residual quantity of a disinfectant such as chlorine throughout the system, in order to ensure the safety of distributed water. However, the chlorine added at the water treatment plant disappears as it travels to the consumer tap, due to reactions in the bulk of the flow and at the pipewalls. This paper analyses the influence on free chlorine bulk decay of several water quality parameters, such as temperature, initial chlorine dosage, organic matter and iron content. The performance of five alternative kinetic models for describing the disinfectant behaviour is also assessed, considering both static and steady-state flow conditions. For the conditions tested, a parallel pseudo-first order model provided the best results. Although, in practice, parallel first order kinetic models fit experimental data better than the classic first order model, most water quality modelling software still relies on the latter as a base choice. The paper discusses practical conditions that may influence model selection for network simulation purposes, and the relevance of the associated errors.

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This report concerns the Sé Nova, Coimbra, which was used as a case-study of the EU project COMPASS. It focuses the assessment of damage, diagnosis and advice for repair of salt decay anomalies. It concludes that repair of the damaged plasters could be done with a lime-mortar, as similar as possible to the existing one, namely in its high capillary absorption. A paint that does not constitute a barrier to the incoming salt solutions should also be used.

At the Heroísmo station site (of Porto underground) there is a granitic rock mass formation named “Granito do Porto”, where the rock mass presents significant heterogeneity, with highly weathered and fractured rock zones and with frequent and large intercalations of residual (saprolitic) soil from granite. At the request of Transmetro-ACE, LNEC carried out crosshole seismic tomographies on several crosshole sections with about 30m depth in order to zone and to characterize these heterogeneities. The tomographies obtained showed heterogeneous P-wave velocity distributions with frequent velocity inversions in depth according to highly weathered and fractured rock zones detected at the boreholes and even with the core recovery rates, especially for the case of residual soil. The lowest velocity zones occur typically on the surface region, above the water level, where the decomposition, weathering and fracture density are more accentuated and where the rock mass is more uncompressed.

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