Flood Forecasting and Flood Warning in the Firth of Clyde, UK

Coastal flooding has caused significant damage to a number of communities around the Firth of Clyde in south-west Scotland, UK. The Firth of Clyde is an enclosed embayment affected by storm surge generated in the Northern Atlantic and propagated through the Irish Channel. In recent years, the worst flooding occurred on 5th January 1991 with the estimated damage of approximately £7M. On average, some £0.5M damage is caused each year by coastal flooding. With the latest climate change predictions suggesting increased storm activity and the expected increase in mean sea levels, these damages are likely to increase. In line with the expansion of flood warning provision in Scotland, the Scottish Environment Protection Agency (SEPA) has developed a flood warning system to provide local authorities and emergency services with up to 24 h warning of coastal flooding within the Firth of Clyde and River Clyde Estuary up to Glasgow City Centre. The Firth of Clyde flood warning system consists of linked 1-D and 2-D mathematical models of the Firth of Clyde and Clyde Estuary, and other software tools for data processing, viewing and generating warning messages. The general methodology adopted in its implementation was developed following extensive consultation with the relevant authorities, including local councils and police. The warning system was launched in October 1999 and has performed well during four winter flood seasons. The system currently makes forecasts four times a day and is the only operational coastal flood warning system in Scotland.This paper summarises the development of the warning system, gives a review of its operation since its launch in 1999 and discusses future developments in flood warning in Scotland.     

Influence of numerical precision on the calibration of AEM-based groundwater flow models

Groundwater modelers have embraced the use of automated calibration tools based on classical nonlinear regression techniques. While clearly an improvement over trial-and-error calibration, it is not clear to what extent these popular inverse modeling tools yield accurate parameter sets for groundwater flow models. The impact of model configuration and precision upon automated parameter estimation is also unclear. An extensive set of numerical experiments was performed to explore the influence of model configuration on the calibration of a regional groundwater flow model developed using the analytic element method. The results provided insight into the manner in which the specified level of model precision and the location of observation points influence the results of inverse modeling based on nonlinear regression. While the importance of these issues is application-specific, obtaining an accurate model calibration for the case study required both a careful placement of test observations and a greater-than-anticipated level of model precision. The required level of model precision for calibration was more than necessary to produce an acceptable flow solution.     

Molecular simulations of interfacial and thermodynamic mixing properties of grossular–andradite garnets

Experimental observations using transmission electron microscopy (TEM) indicate that Fe³⁺-rich grossular–andradite solid solutions with oscillatory zoning tend to occur as separate lamellae of andradite and intermediate compositions (Hirai and Nakazawa 1986; Pollok et?al. 2001). From one lamella to the next, the Fe³⁺ concentration can change significantly within a few nm. In order to understand the Fe³⁺ and Al content of each phase and the thermodynamics, chemistry, structure, and stability at the interfaces, Monte Carlo simulations were performed. According to our calculations, there is an ordered structure with a 1:1 ratio of Al and Fe³⁺ with alternating Al and Fe octahedra along the main cubic crystallographic axes. Even though this ordered grandite is more energetically favorable than a 1:1 mixture of the end members grossular and andradite [by ≈1.6?kJ (mol exchangeable cations)^?1], this structure is stable only at temperatures below ≈500?K. Enthalpies, free energies, configurational and vibrational entropies of mixing, and the long-range order parameter are influenced by the formation of ordered grandite below 500?K. These data also explain why interfaces are stable only between grossular and grandite or between andradite and grandite but not between the end members. The interface energies between the end members and ordered grandite are comparably low [0.16?meV?Å^?2∥(1?0?0), 0.55?meV?Å^?2∥(1?1?0), 0.63?meV?Å^?2∥(1?1?1)] and, therefore, do not hinder the formation of lamellae. Our calculations on the free energies of mixing indicate that there are miscibility gaps between grossular and grandite and between grandite and andradite only below ≈430?K. Since most of these solid solutions are formed at higher temperatures for which we did not find evidence of a miscibility gap, the formation of compositional oscillations is probably due to kinetic hindering of thermodynamically stable complete solid solutions. ?A new methodological aspect is the incorporation of zero-point energies of vibrations and the vibrational entropies into the calculation of the free energy of mixing. In case of the grossular–andradite solid solution, these vibrational effects change the free energy of mixing by only a few percent.