Development of a modelling framework for integrated catchment flood risk management

Flooding is one of the most significant issues facing the UK and Europe. New approaches are being sought to mitigate its impacts, and distributed, catchment-based techniques are becoming increasingly popular. These employ a range of measures, often working with the catchment’s natural processes, in order to improve flood resilience. There remains a lack of conclusive evidence, however, for the impacts of these approaches on the storm runoff, leading to considerable uncertainty in their effectiveness in terms of mitigating flood risk. A new modelling framework for design, assessment, and uncertainty estimation of such distributed, nature-based schemes is developed. An implementation of a semidistributed runoff model demonstrates robustness to spatio-temporal discretisation. Alongside a new hydraulic routing scheme, the model is used to evaluate the impacts on flood risk of in-channel measures applied within an 29 km2 agricultural catchment. Maximum additional channel storage of 70,000 m3 and a corresponding reduction of 11% in peak flows is seen. This, however, would not have been insufficient to prevent flooding in the event considered. Further modifications allow simulation of the impacts of wider measures employing natural processes. This is applied within an uncertainty estimation framework across the headwaters of three mixed-use catchments, ranging in size from 57 km2 to 200km2 , across a series of extreme storm events. A novel surface routing algorithm allows simulation of large arrays distributed features that intercept and store fast runoff. The effect of the measures can be seen across even the most extreme events, with a reduction of up to 15% in the largest peak, albeit that this large impact was associated with a low confidence level. The methodology can reflect the uncertainty in application of natural flood risk management with a poor or incomplete evidence base. The modelling results demonstrate the importance of antecedent conditions and of the timings and magnitudes of a series of storm events. The results shows the benefits of maximizing features’ storage utilisation by allowing a degree of “leakiness” to enable drain-down between storms. An unanticipated result was that some configurations of measures could synchronise previously asynchronous subcatchment flood waves and have a detrimental effect on the flood risk. The framework shows its utility in both modelling and evaluation of catchment-based flood risk management and in wider applications where computational efficiency and uncertainty estimation are important

Potential for natural flood management and land management practices to mitigate flooding in upland catchments

PhD ThesisThere is an increasing uptake of Natural Flood Management (NFM) and land use management (LUM) schemes to tackle excessive, rapid runoff in rural catchments. At the local scale, there is a growing knowledge base regarding the impacts of NFM and LUM. However, evidence and understanding of how these local impacts manifest at a larger catchment scale is less well understood. There are many types of model that have been used for investigating NFM and LUM impacts at larger scales (>10 km2), ranging from the comparatively simple lumped conceptual approaches to more complex, physically-based, distributed models. How best to represent NFM and LUM impacts in models is ambiguous. This thesis presents research into impact modelling of flood mitigation measures from the hillslope to the catchment scale, using the lumped FEH rainfall-runoff model and a novel physicallybased, distributed model, Juke. A Flood Impact Modelling (FIM) methodology is proposed for rapid impact assessment using the FEH approach; FEH hydrographs are generated for sub-catchments and routed to the outlet. The impact of changes in timing and runoff generation in specific sub-catchments on the downstream hydrograph can be investigated to inform catchment planning. The Juke methodology is designed to make best use of field observations and existing GIS datasets for parameterising the runoff and routing components. Juke uses some of the knowledge embedded in the FEH approach regarding the timing and runoff generation and applies it spatially. Juke is capable of emulating the FEH, but also allows consideration of spatial changes in LUM. Two catchments in the north of England have been instrumented to characterise the rainfall-runoff behaviour and understand what causes the largest flood events, where NFM and LUM have taken place. This knowledge informs the LUM and NFM scenarios explored as well as for model parametrisation. Results from the lumped FEH modelling suggest that the mitigation of flood flow by managing the volume and timing of fast runoff will have the greatest impact on floods caused by short duration, high intensity rainfall events. The Juke modelling also suggests that the impact of NFM and LUM is likely to be minimal (<10 % flood peak reduction for 12 % coverage of riparian woodland) and depends on the duration and intensity of rainfall events and the internal synchronisation of the component sub-catchments. The flood peaks for some events ii may increase due to the effects of timing and synchronisation of flows from the landscape elements. The outcomes of this thesis recommends flood managers make field observations to better understand the causes of flooding within a catchment. Schemes using NFM and LUM are likely to be most beneficial for comparatively small catchments (<10 km2) that suffer from frequent flooding from short duration, high intensity rainfall.combination of Defra, through the Demonstration Test Catchments (DTC) and the Environment Agency (EA: Great Ayton Flood mitigation

Proceedings of the International Workshop on Hydraulic Design of Low-Head Structures - IWLHS 2013

Scientific standards applicable to publication of BAWProceedings: http://izw.baw.de/publikationen/vzb_dokumente_oeffentlich/0/2020_07_BAW_Scientific_standards_conference_proceedings.pd

Review of Published Climate Change Adaptation and Mitigation Measures Related with Water

Stronger manifestation of climate change impact on global water cycle, water resources, and aquatic ecosystems has given a strong impetus to the development of adaptation measures in water management. The present report gives an insight to potential and planned water related measures tackling climate change causes and consequences, which have been included in the Member States River Basin Management Plans, published in various reports and scientific literature mostly within the last decade. The database of about 450 measures analysed in this report and given in a separate Annex as an Excel spreadsheet, constitutes the most important part of this deliverable. In the context of this report, measures are defined as practical steps or actions taken to (i) reduce the sources or enhance the sinks of greenhouse gases, (ii) to decrease the vulnerability of water resources and aquatic ecosystems to climate change, or (iii) enhance the knowledge base on climate-water relationships and increase the societal capacity to take right decisions on this matter. By strategic approach, the measures belong either to planned adaptation, which specifically focuses on climate change and variability, and autonomous adaptation, which goals are not specifically climate related, but have an added value in improving resilience to climate change. Separate chapters are dedicated to each of the five specific adaptation strategies addressed in the REFRESH Project. The present report is of relevance to the 7th EU Framework Programme, Theme 6 (Environment including Climate Change) project REFRESH (Adaptive strategies to Mitigate the Impacts of Climate Change on European Freshwater Ecosystems, Contract No.: 244121), to JRC Thematic Area 3 (Sustainable management of natural resources) foci on CC, to the European Clearing House mechanism on CC, and to the EC Blueprint on Water.JRC.DDG.H.5-Rural, water and ecosystem resource

Performance-based management of flood defence systems

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

A multi-site methodology for understanding dependencies in flood risk exposure in the UK

PhD ThesisRecent large scale flood events in the UK and the continued threat of a major North Sea surge have motivated a re-appraisal of how flood risk is modelled. A new generation of flood risk models are starting to consider the spatial and temporal dependencies in flood events. This is important for a wide range of risk based decision making, with one of its most significant applications being the understanding of insurance exposure. The aim of this thesis is to increase understanding of flood risk exposure in the UK and identify areas where existing modelling capabilities and data limitations contribute to large uncertainties in the estimation of risk. Illustrating a successful collaboration between academia and the insurance industry, a case study of one company’s exposure from static caravans is used to develop a methodology for flood risk assessment at multiple sites nested within a national framework. This novel nested approach allows for greater detail to be included at sites of interest resulting in increased understanding of the risk driving processes while retaining the large scale dependence structure. This is demonstrated at high risk locations on the Lincolnshire and North Wales coastline and inland on the Rivers Severn and Thames. The proposed methodology takes a flexible component based approach and has potential adaptations to different receptors and end users. A systems based model is used which explicitly considers all key components of risk. Extreme fluvial and coastal events are modelled statistically using the conditional dependence model of Heffernan and Tawn (2004). Coastal flood defences are essential for the protection of static caravan sites however their inclusion in existing risk models contributes significant uncertainties. The quality of data available on flood defence heights is reviewed and a methodology to incorporate spatial variations is proposed. The failure of flood defences is modelled using fragility curves and inundation modelling is used to route water on the floodplain. Finally the damage to the static caravans is modelled using depth-damage curves with reference to the impact of limited observed data on flood damage for caravans. One of the biggest challenges of considering dependencies across multiple scales within a systems model is matching the data requirements across each component. To address this problem this thesis investigates the relationship between skew surge and wave height to estimate the total inshore water level, and develops a UK specific method to transform daily mean flow to peak flow. The modular structure of the proposed methodology means different component models can be used to suit the available data; here the integration of both 1D and 2D floodplain inundation models is demonstrated.EPSR

Exploring the Social Impacts of Flood Risk and Flooding in Scotland

No abstract available