The Stability of Flood Defenses on Permeable Soils: The London Avenue Canal Failures in New Orleans

The two failures of the London Avenue Canal floodwalls contributed largely to the flooding of central New Orleans due to hurricane Katrina. In this paper, both failures are analyzed and compared to each other since the flood defenses are both located on permeable soils. Photo’s observation and calculations are used for the analysis. Both failures are caused by the permeable sand layer below the floodwall that allowed high pore water pressures to develop below the floodwall. However, the south breach seems to be caused by the piping failure mechanism and the north breach by loss of stability. At the South breach, the impermeable top layer was thicker than at the North breach, increasing the stability. The North beach was less vulnerable for piping and the lack of stability caused a large breach. The London Avenue Canal failures are a clear yet tragic example of the failure of flood defenses on permeable soils. The failures show that multiple failure mechanism may occur and since there are many flood defenses on permeable soils world wide, the lessons from Katrina can be used to prevent future catastrophes

Testing and modelling autoregressive conditional heteroskedasticity of streamflow processes

Conventional streamflow models operate under the assumption of constant variance or season-dependent variances (e.g. ARMA (AutoRegressive Moving Average) models for deseasonalized streamflow series and PARMA (Periodic AutoRegressive Moving Average) models for seasonal streamflow series). However, with McLeod-Li test and Engle's Lagrange Multiplier test, clear evidences are found for the existence of autoregressive conditional heteroskedasticity (i.e. the ARCH (AutoRegressive Conditional Heteroskedasticity) effect), a nonlinear phenomenon of the variance behaviour, in the residual series from linear models fitted to daily and monthly streamflow processes of the upper Yellow River, China. It is shown that the major cause of the ARCH effect is the seasonal variation in variance of the residual series. However, while the seasonal variation in variance can fully explain the ARCH effect for monthly streamflow, it is only a partial explanation for daily flow. It is also shown that while the periodic autoregressive moving average model is adequate in modelling monthly flows, no model is adequate in modelling daily streamflow processes because none of the conventional time series models takes the seasonal variation in variance, as well as the ARCH effect in the residuals, into account. Therefore, an ARMA-GARCH (Generalized AutoRegressive Conditional Heteroskedasticity) error model is proposed to capture the ARCH effect present in daily streamflow series, as well as to preserve seasonal variation in variance in the residuals. The ARMA-GARCH error model combines an ARMA model for modelling the mean behaviour and a GARCH model for modelling the variance behaviour of the residuals from the ARMA model. Since the GARCH model is not followed widely in statistical hydrology, the work can be a useful addition in terms of statistical modelling of daily streamflow processes for the hydrological community

Eye Movement Evaluation in Multiple Sclerosis and Parkinson's Disease Using a Standardized Oculomotor and Neuro-Ophthalmic Disorder Assessment (SONDA)

Evaluating the state of the oculomotor system of a patient is one of the fundamental tests done in neuro-ophthalmology. However, up to date, very few quantitative standardized tests of eye movements' quality exist, limiting this assessment to confrontational tests reliant on subjective interpretation. Furthermore, quantitative tests relying on eye movement properties, such as pursuit gain and saccade dynamics are often insufficient to capture the complexity of the underlying disorders and are often (too) long and tiring. In this study, we present SONDA (Standardized Oculomotor and Neurological Disorder Assessment): this test is based on analyzing eye tracking recorded during a short and intuitive continuous tracking task. We tested patients affected by Multiple Sclerosis (MS) and Parkinson's Disease (PD) and find that: (1) the saccadic dynamics of the main sequence alone are not sufficient to separate patients from healthy controls; (2) the combination of spatio-temporal and statistical properties of saccades and saccadic dynamics enables an identification of oculomotor abnormalities in both MS and PD patients. We conclude that SONDA constitutes a powerful screening tool that allows an in-depth evaluation of (deviant) oculomotor behavior in a few minutes of non-invasive testing

The Birthday Party Test (BPT); A new picture description test to support the assessment of simultanagnosia in patients with acquired brain injury

There is broad consensus on the utility of complex pictures in the assessment of simultanagnosia in patients with acquired brain injury (ABI). To overcome various shortcomings of current instruments, we have developed the Birthday Party Test (BPT); a picture description test that contains a neutral scene, a balanced representation of events, and provides clear instructions and a scoring-aid. We have applied the BPT in a large group of patients with ABI (n = 502) and in an age-matched healthy control group (n = 194). Our results show that performance on the BPT was associated with a range of descriptive, neuropsychological and clinical characteristics and that poor test performance appeared to be more common in patients with etiologies that have an increased risk of bilateral damage. Furthermore, we assume a high correspondence between test performance on the BPT and the assessor’s clinical judgment of likely having simultanagnosia in preliminary analyses. This study shows the potential usefulness of the BPT to support diagnostic decision making in simultanagnosia. The BPT is made freely available to facilitate its broad application in the clinical assessment of patients with visual impairment and to enable a further evaluation of its utility and validity in future studies

Neo-Atlantis: The Netherlands under a 5-m sea level rise

What could happen to the Netherlands if, in 2030, the sea level starts to rise and eventually, after 100 years, a sea level of 5 m above current level would be reached? This question is addressed by studying literature, by interviewing experts in widely differing fields, and by holding an expert workshop on this question. Although most experts believe that geomorphology and current engineering skills would enable the country to largely maintain its territorial integrity, there are reasons to assume that this is not likely to happen. Social processes that precede important political decisions - such as the growth of the belief in the reality of sea level rise and the framing of such decisions in a proper political context (policy window) - evolve slowly. A flood disaster would speed up the decision-making process. The shared opinion of the experts surveyed is that eventually part of the Netherlands would be abandoned. © 2008 The Author(s)