Quantitative Assessment Methods for the Monitoring and Inspection of Flood Defences: New ‎Techniques and Recent Developments

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Journal Title, Volume, Page: 
CIRIA C717
Year of Publication: 
2013
Authors: 
Ahmad Taha
An-Najah National University, Nablus, Palestine
Current Affiliation: 
Department of Geography, Faculty of Economic and Social Studies, An-Najah National University, Nablus, Palestine
Gavin Long
The University of Nottingham, UK
Martin Smith
The University of Nottingham, UK
Mick Mawdesley
Curtin University, Perth, Australia
Preferred Abstract (Original): 

Monitoring and condition assessment underpin any infrastructure asset management programme. They provide the basic information to assess asset condition and to plan asset management. Qualitative expert judgment, based on visual inspection is, and will remain, a major input to assessment of asset condition and its likely performance under service conditions. However, the performance models that these assessments are made for, infrastructure assets and flood defence assets in particular, require quantitative data for many of their parameters if performance assessment is to be evidence-based and properly justified. Work carried out under the initial phase of the Flood Risk Management Research Consortium (FRMRC) devised a measured step towards performance-based visual inspection (WP4.3) and investigated state-ofthe-art methods for acquiring quantitative data for use in flood risk management (WP5.1). Drawing on the results of these two previous projects, a later project under the second phase of FRMRC combined aspects of each and examined how quantitative assessment methods might be successfully used within the context of a flood risk and asset management programme. This resulting guidance contains promising new methods of quantitative assessment that are relevant to flood defence asset management. It focuses on major types of linear flood defence, highlights performance features that would benefit from quantitative assessment and identifies methods for obtaining this data through remote measurement, continual monitoring and detailed asset inspections. Methods proposed range from inexpensive additions to the visual inspection process, aerial surveys using specialist equipment and the installation of state-of-the-art sensor arrays and cameras on site. The benefits and limitations of the various methods and approaches are discussed for each of the main types of linear flood defence asset. Asset surface geometry and any variations to it occurring over time are important areas where quantitative assessment can be used to improve the assessment of performance for all assets. Remote measurement methods can be used to assess asset geometry over large areas quickly and accurately. Airborne LiDAR and photogrammetry show the greatest potential for monitoring purposes. These are particularly suited to the assessment of crest levels, which is a critical aspect in the monitoring of linear defence assets and cannot be effectively assessed through a solely visual inspection. To detect surface changes indicative of asset deterioration, high resolution data is likely to be required. Kinematic GPS is a well proven and accurate method for assessing asset geometry, and in particular crest levels. It is particularly suited for the assessment of small areas (eg individual assets and groups of assets) where an aerial survey would not be resource effective. The use of Kinematic GPS for crest height and detailed surveying will be important for embankment monitoring in the future. It is understood that trials are already being undertaken by several groups involved in embankment monitoring. Standard measurement tools and photography (preferably geo-referenced) can be easily adopted within a visual inspection process to provide quantitative data on asset condition. This will provide asset managers with a historical record of change to asset condition over time. Fixed point continual monitoring through the installation of sensors, gauges or cameras is already widely used in the monitoring of dams and reservoirs. It has the potential to allow asset managers to track asset condition at much greater frequency than the standard visual inspection regime or via occasional topographical survey. However, large scale deployment of sensors is an expensive and invasive process with several logistical issues (eg power use, telemetry) to resolve before it can be successfully adopted in a flood risk management (FRM) context. Smaller scale trials and monitoring programmes (such as the remote camera trial described in Appendix A4) may be necessary where local conditions warrant their deployment.

Site-based trials, computer simulation and several case studies were used to strengthen the findings of the research and to highlight aspects of particular interest and relevance from the perspective of flood iv Quantitative assessment methods defence monitoring and assessment. These are covered in this guidance where considered to be helpful to the reader. The guidance sets out a range of potential improvements to flood defence asset inspection that could be carried out immediately and those achievable in the short- to medium-term. It discusses both the theoretical potential and the practical implications of remote measurement, continual monitoring and detailed asset inspections. All the potentially useful technologies and methods are summarised in Appendix A6.

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