COST Action ES0901: European procedures for flood frequency estimation (FloodFreq) [Keynote]

The aim of COST Action ES0901 European Procedures for Flood Frequency Estimation (FloodFreq) is to undertake a Pan-European comparison and evaluation of different methods for flood frequency estimation under the various climatologic and geographic conditions found in Europe, and different levels of data availability. A scientific framework for assessing the ability of these methods to predict the impact of environmental change (climate change, land-use and river engineering works) on future flood frequency characteristics (flood occurrence and magnitude) will be developed and tested. The availability of such procedures is crucial for the formulation of robust flood risk management strategies as required by the Directive of the European Parliament on the assessment and management of floods. The outputs from FloodFreq will be disseminated to: academics, professionals involved in operational flood risk management from private and public institutions, and relevant policy makers from national and international regulatory bodies. This Action enable cooperation between researchers involved in nationally funded research projects to, thereby enabling testing of methods free from the constraints of administrative boundaries, and allowing a more efficient use of European flood research funding

A joint probability approach to flood frequency estimation using Monte Carlo simulation

In the UK, flood estimation using event based rainfall–runoff modelling currently assigns pre-defined design values to the input variables which control the size of the flow events, apart from the rainfall magnitude which is treated as a random variable. The use of design values, rather than allowing the variables to be described by their full probability distribution, is a practical simplification but may lead to biases in the output flood magnitudes. The present study simulates a large number of flow events using sets of input variables from distributions fitted to observed event data, taking into account seasonality. These simulated datasets are used for running a rainfall-runoff model, and a frequency analysis is applied to the peaks of the output flow hydrographs. The simulated inputs are the rainfall intensity and duration, and the soil moisture deficit (SMD) and initial river flow at the beginning of the rainfall event. An inter-event arrival time is simulated so that a series of events is obtained. The initial conditions of SMD and river flow of each event are made dependent on the (simulated) time elapsed since the previous event, and on the SMD at the end of the previous event

Estimating single-site design flood variance using a generalised logistic distribution

An easy-to-use equation is presented for calculating the variance of a design flood estimated using a generalised logistic distribution with model parameters estimated using single-site analysis, as described in the UK Flood Estimation Handbook. The equation is applicable for return periods in the range 2-1000 years and for annual maximum flood series with L-skewness of -0.45 to 0.45, which is considered representative of most UK flood data and practical uses. </p

Assessment of trends in hydrological extremes using regional magnification factors

Detection and attribution of trends in individual at-site series of hydrological extremes is routinely undertaken using simple linear regression-based models. However, the available records are often too short to allow a consistent assessment of trends across different stations in a region. The theoretical developments presented in this paper propose a new method for estimating a regional regression slope parameter across a region, or pooling group, of catchment considered hydrologically similar, and where annual maximum events at different sites are cross-correlated. Assuming annual maximum events to follow a two-parameter log-normal distribution, a series of Monte Carlo simulations demonstrate the ability of the new framework to accurately identify the regional slope, and provide estimates with a reduced sampling variability as compared to the equivalent at-site estimates, thereby enhancing the statistical power of the trend test. This regionally-based trend estimates would allow for a clear characterization of changes across several stations in a region. Finally, the new method is applied to national dataset of annual maximum series of peak flow from 662 gauging sites located across the United Kingdom. The results show that the regional slope estimates are significantly positive (p &lt; 0.05) consistently in the west and north of the country, while mostly not significant in the east and south. This translate into a corresponding increase in design flood (as measured by regional magnification factors) of up-to 50% for time horizon of 50-years into the future.</p

Infiltration capacity of cracked pavements

Understanding the hydrological behaviour of urban surfaces is imperative in the design of surface water drainage systems and flood mitigation strategies, as well as for the modelling of groundwater recharge and pollution. This study has examined the hydrological behaviour of cracked impervious surfaces through field infiltration testing and image analysis of the cracks themselves. Infiltration tests were undertaken on a section of concrete slab pavers paving. Our results showed that cracks in impervious surfaces allow significant volumes of water to infiltrate through them, with infiltration rates comparable to those found in sands and gravels. Using a regression model, infiltration rates were related directly to crack characteristics obtained from image processing software, thereby enabling the first published quantitative link between percentage cracked area and infiltration capacity. The implications of accounting for this infiltration for surface water management systems are estimated to be in the order of £20 million annually for the construction industry in England

Flooding through the ages: Reconstructing historical floods in the city of Bath

The City of Bath is a historical UNESCO world-heritage site and is an instructive case study in how the history, architecture and development of a city can be closely connected to the city’s relationship with its river, the River Avon. As the City has always been located close to the river, communities in Bath have experienced the effects of flooding since the Roman times. Bath has a particularly rich record of historical evidence left on buildings in the City (the earliest flood mark dates back to 1823) as well as documentary evidence in contemporary newspapers and technical reports. This book hopes to take you on a journey of flooding through the ages. Starting from some important historical flood events and the multiple efforts of the City to combat the scourge of flooding, Dr Ioanna Stamataki and Dr Thomas Kjeldsen describe the different phases of the current Bath Flood Defence Scheme and discuss how historical flood events from 1823 to 1960 in the City of Bath were reconstructed using a 1D hydraulic model. This research area, drawing from the combination of the use of historical documentary evidence and modern technological modelling techniques, allows an assessment of long-term flood risk of the City and paves new avenues towards future research

HYDRIC BATH—recent learnings and a new research methodology for the assessment of long-term flood risk using documentary evidence

The HYDRIC BATH Project was a multidisciplinary project which aimed to investigate and assess the utility of documentary evidence of past flood events (1823-1960) for contemporary flood risk assessments. By bridging the fields of engineering, history and statistics and drawing from the combination of the use of historical documentary evidence and modern technological modelling techniques, it allowed an improved assessment of long-term flood risk of the City of Bath, United Kingdom. Bath is a historical UNESCO world-heritage site and as it has always been located close to the river, communities in Bath have experienced the effects of flooding since early settlements in Roman times. The novelty of this research was the different methodology adopted for information and data gathering compared to current scientific practice. A 1D hydraulic model representing the River Avon through the city of Bath was constructed using data collected from a variety of sources and in various formats, including historical photographs, local knowledge, engineering drawings, technical reports, water level charts, and physical markings of historical water levels in the city. Identification and translation of this material into a unified and useful format was a major and challenging undertaking, at times relying purely on serendipity. This project showed that the inclusion of historical flood data can have a dramatic effect on the outcome of a flood frequency analysis for contemporary flood risk assessments showing a 20-30% increase in the 100-year flood. The use of documentary sources is relevant to many disciplines, thus, central repositories of this information need to be created to facilitate this. This research was an important paving stone towards the integration of social science and digital / IT to aid scientific investigations in the field of engineering.<br/