Decision support framework to incorporate river bank stability in pipeline crossing risk assessment

Scottish Water has identified the need to develop their approach to dealing with uncertainty when assessing the risk of river erosion at pipeline crossings. In particular, there is a need to develop and pilot methods that can use data from initial asset inspections to quantify risks and uncertainties in making decisions on where to invest additional resources in more detailed inspections, for assets deemed to be at greater risk from river bank erosion or scour around bridge abutments. This challenge arises from the reality that, over the past 10-15 years, pipeline crossing inspections have been undertaken in an ad-hoc manner. The aim of this proposal is, therefore, to develop a decision support framework to incorporate river bank stability in pipeline crossing risk assessment. This will be used immediately during 2016 in Scottish Water's first, national-scale pipeline bridge asset inspection programme. The specific objectives are to: (i) evaluate uncertainty in the existing low-cost app-based inspection database that is used to screening risk; (ii) assess the uncertainty that arises from the initial desk-based phase of river bank stability assessment; (iii) develop a pipeline crossing scour assessment framework for analysing river bank stability at the screening phase and determining appropriate analysis for the initial assessment phase; and (iv) recursively test the risk assessment framework. To address these objectives there will be three methodological phases, results from which will be progressively reported. First, a sample of the pipeline crossings will be re-surveyed using a replicate inspection app. Results will enable evaluation of uncertainties in data capture and their consequences for river stability decision making at the screening stage of risk management. Second, uncertainty in assessing bank erosion will be assessed considering data from the asset inspection app, Google Earth imagery, high-resolution aerial images commissioned by Scottish Water, and legacy LiDAR acquired by the Scottish Government. Evidence of river instability will be mapped from imagery. Change will be quantified using appropriate techniques to represent errors in digitising and topographic change analysis. Finally, results will be used to produce a framework to: (i) characterise risk during screening; and (ii) determine the most appropriate forms of desk based analysis for initial risk assessment. The framework will include a multi-criteria process for calculating risk after the initial assessment phase to determine whether a more detailed assessment phase is necessary and, if so, necessary actions. This framework will be tested at a further set of 20 sites. Project outputs will be operationalised and used to improve decision making. App-based data capture will be improved with enhanced data fields and training material for asset inspectors. Results from evaluating uncertainty in data and analysis will be input to a multi-criteria scoring framework that will improve decision making at the screening and initial assessment stages and will thus enable scarce resources to be prioritised for desk-based river bank stability analyses. The framework will be used in the current drinking water pipeline crossing inspection programme and will also be of value for a future waste water pipeline crossing inspection programme. The project will last 12 months which will enable evaluation of uncertainty in a sufficiently large sample of data, analysis approaches and sites. The total cost (80% FEC) of the project is £89,707. This includes staff costs for Williams and Hoey, 9 months research assistant time, computer hardware, and travel.

This project aims to develop a decision support framework to incorporate river bank stability in pipeline crossing risk assessment. The project will focus upon evaluating the uncertainty associated with using different data sources, and different analytical approaches, to measure river stability. It will also develop a multi-criteria scoring system that can be used to calculate risk at each pipeline crossing, based on uncertainties in associated data and analysis. Quantifying how different uncertainties propagate through decision making to determine whether an asset is classified as being at sufficient risk to warrant further investment in scour risk management will contribute to an improved asset inspection workflow at Scottish Water. Kirby et al. (2015) estimate that stages in scour risk assessment take the following amounts of time per asset: initial screening (3-5 hours); initial assessment (10-15 hours); and detailed assessment (25-40 hours). Scottish Water estimate that initial screening costs £500 per asset. Making appropriate decisions about whether to pursue further assessment following this screening is thus critical to focus scarce resources, provide value for customers, and support statutory and regulatory compliance. The framework that will be developed by this project will also provide guidance on future frequency of screening and assessment, explicitly accounting for uncertainty in data analysis. This framework will guide the review and development of pipeline management plans, informing Scottish Water's future business and investment planning from 2021.

The main expected benefits and outcomes for Scottish Water are as follows:
(1) Improved forms to capture river stability information using the asset inspection app;
(2) Improved technical capability of asset inspectors through river stability training;
(3) Enhanced ability to use a range of Geographic Information System (GIS) data layers to make decisions about river stability, with tools that explicitly measure how uncertainty contributes to what conclusions should be made;
(4) A support framework to make decisions after screening. This will focus upon aiding decision making about which desk-based approaches to adopt, which high-resolution survey technologies to commission if further information is needed, and when to scope different erosion or scour prevention measures;
(5) A support framework to determine the frequency and method (site visits or remote sensing) of future river stability screening activities. This will be based on the comparison between uncertainty in river stability measured from the low-cost app versus a range of desk-based assessment methods, to guide future inspections to assess changes in river stability; and
(6) Quantification of the uncertainty associated with data capture on river stability from the low-cost asset inspection app will enable Scottish Water to demonstrate that its asset management programme meets statutory and regulatory compliance.

Overall, the project will impact decision making in the asset management of pipe bridges by influencing the ongoing site-visit based asset inspection programme (from month 3 of the project) and the framework for desk based assessment. The project will also impact longer term planning beyond the current asset inspection programme.

Reference: Kirby et al., 2015, Manual on scour at bridges and other structures.