Guidance on determining asset deterioration and the use of ...

<strong>Guidance</strong> on determining assetdeterioration and the use ofcondition grade deterioration curvesProduct Code: SCHO0509BQAT-E-P

The Environment Agency is the leading public bodyprotecting and improving the environment in England andWales.It’s our job to make sure that air, land and water are lookedafter by everyone in today’s society, so that tomorrow’sgenerations inherit a cleaner, healthier world.Our work includes tackling flooding and pollution incidents,reducing industry’s impacts on the environment, cleaning uprivers, coastal waters and contaminated land, andimproving wildlife habitats.This report is the result of research commissioned andfunded by the Environment Agency’s Science Programme.Published by:Environment Agency, Rio House, Waterside Drive,Aztec West, Almondsbury, Bristol, BS32 4UDTel: 01454 624400 Fax: 01454 624409www.environment-agency.gov.ukISBN: 978-1-84911-056-3© Environment Agency May 2009All rights reserved. This document may be reproducedwith prior permission of the Environment Agency.The views and statements expressed in this report arethose of the author alone. The views or statementsexpressed in this publication do not necessarilyrepresent the views of the Environment Agency and theEnvironment Agency cannot accept any responsibility forsuch views or statements.This report is printed on Cyclus Print, a 100% recycledstock, which is 100% post consumer waste and is totallychlorine free. Water used is treated and in most casesreturned to source in better condition than removed.Further copies of this report are available from:The Environment Agency’s National Customer ContactCentre by emailing:enquiries@environment-agency.gov.ukor by telephoning 08708 506506.Author(s):Jaap Flikweert (Royal Haskoning)Peter Lawton (Consulting Engineer)Marta Roca Collell (HR Wallingford)Jonathan Simm (HR Wallingford)Dissemination Status:Publicly available / Released to all regionsKeywords:deterioration rate, asset management, flood defences,maintenanceResearch Contractor:Consortium led by HR Wallingford LtdHowbery Park, Wallingford, Oxon, OX108BATel: +44(0)1491 835381Consortium members:Royal HaskoningPeter Lawton (Consulting Engineer)Environment Agency’s Project Manager:Tim Hopkins/Stefan LaegerScience Project Number:SC060078/SR1Product Code:SCHO0509BQAT-E-PiiScience Report – <strong>Guidance</strong> on determining asset deterioration

Science at the Environment AgencyScience underpins the work of the Environment Agency. It provides an up-to-dateunderstanding of the world about us and helps us to develop monitoring tools andtechniques to manage our environment as efficiently and effectively as possible.The work of the Environment Agency’s Science Department is a key ingredient in thepartnership between research, policy and operations that enables the EnvironmentAgency to protect and restore our environment.The science programme focuses on five main areas of activity:• Setting the agenda, by identifying where strategic science can inform ourevidence-based policies, advisory and regulatory roles;• Funding science, by supporting programmes, projects and people inresponse to long-term strategic needs, medium-term policy priorities andshorter-term operational requirements;• Managing science, by ensuring that our programmes and projects are fitfor purpose and executed according to international scientific standards;• Carrying out science, by undertaking research – either by contracting itout to research organisations and consultancies or by doing it ourselves;• Delivering information, advice, tools and techniques, by makingappropriate products available to our policy and operations staff.Steve KilleenHead of ScienceScience Report – <strong>Guidance</strong> on determining asset deteriorationiii

Executive summaryThis guide provides asset deterioration curves and explains how to use them toestablish the residual life of different types of flood defence assets. Vertical walls,embankments, culverts, dunes and shingle beaches are covered.The curves are based on the condition grades defined in the Condition AssessmentManual (Environment Agency, 2006). The deterioration curves consider the type ofenvironment (fluvial or coastal), type of material, width of the asset, whethermaintenance is carried out and whether there is rear protection.A table with deterioration rates for different condition grades and different asset typesthat summarises information from deterioration curves is also provided. The time (inyears) to move between different condition grades is obtained from the differencebetween figures corresponding to those conditions grades.A step-by-step guide supported with two examples of composite structures is provided.ivScience Report – <strong>Guidance</strong> on determining asset deterioration

Contents1 Introduction 12 Using the deterioration table 33 Step-by-step guide 53.1 Steps to follow 53.2 Examples of application 74 Deterioration curves – supporting explanations of curves providedfor different asset types 114.1 Vertical walls 114.2 Embankments 164.3 Culverts 214.4 Dunes and shingle beaches 225 Structure-specific assessments 236 Conclusions 25References 26Glossary 27Annex: Links with the NFCDD Defence Class Code 28Table 1.1 Condition grades 1Table 2.1 Deterioration times (years) to different condition grades for different asset types and exposures 4Figure 4.1 Vertical brick, masonry or concrete wall 11Figure 4.2 Vertical sheet wall structure 13Figure 4.3 Embankment with turfed surface protection 16Figure 4.4 Embankment with hard surface protection 17Science Report – <strong>Guidance</strong> on determining asset deteriorationv

1 IntroductionCondition grade deterioration curves offer a standardised approach to assess andquantify the deterioration of flood defence assets.Condition grades are based on the Condition Assessment Manual, CAM, (EnvironmentAgency 2006) definitions of condition grades per asset type (as described in text andillustrations in CAM). Five condition grades are used, with their general descriptionsgiven in Table 1.1 and with key features specific to asset types also given in the CAM.Table 1.1 Condition gradesGradeDescriptionof conditionExtent of defects1 Very good Cosmetic defects that will have no effect on performance.2 Good Minor defects that will not reduce overall performance of asset.3 Fair Defects that could reduce performance of asset.4 Poor Defects that would significantly reduce performance of asset.5 Very poor Severe defects resulting in complete performance failure.Source: Condition Assessment Manual, Environment Agency, 2006Deterioration curves quantify the residual life of some type of assets and for differentcondition grades with and without maintenance, allowing the user to evaluate theirdeterioration over time (years).Deterioration rates in these curves are based on the experiences of a range ofpractitioners, asset managers and consulting engineers, with regard to deterioration offlood defence assets in both coastal and fluvial environments.Deterioration curves presented in this guidance used as a starting point the workdeveloped in the Performance Based Asset Management System (PAMS) project,described in the note entitled <strong>Guidance</strong> on asset deterioration and the use of conditiongrade deterioration curves (Defra/ Environment Agency 2009). Curves were modifiedhere to take account of the experience gathered through 20 interviews conducted withEnvironment Agency area staff in operations delivery and asset systems managementand enforcement and with local authority coastal protection engineers. The revisedcurves were established using feedback from a meeting involving the following experts:Jonathan Simm (HR Wallingford), Jaap Flikweert (Royal Haskoning) Peter Lawton(independent consultant) and Tim Hopkins from the Environment Agency (NationalCapital Programme Management Service). Assumptions were made when categorisingcondition grades and deterioration time estimates.This report presents these deterioration curves and explains how to use them with anaccompanying table to determine the residual life of a flood defence asset. It isessential to use engineering judgement and practical experience alongside thisguidance to apply and adapt the deterioration curves appropriately.Envisaged users are asset managers from the Environment Agency or any other assetmanagement organization, such as local authorities and in particular staff makingdecisions about long-term asset management such as SAMPs (System AssetManagement Plans).Science Report – <strong>Guidance</strong> on determining asset deterioration 1

The deterioration table is presented in Chapter 2. Chapter 3 gives a step-by-step guideto forecasting the expected deterioration time to another condition grade, with twoexamples. Chapter 4 describes the different asset types and defence classes,highlighting the assumptions made in developing the deterioration table. It alsoindicates important considerations when assessing deterioration for different kinds ofstructures. Chapter 5 describes the factors to consider when assessing specificdeterioration rates.2 Science Report – <strong>Guidance</strong> on determining asset deterioration

2 Using the deterioration tableThe types of assets analysed in this guide are:• vertical walls• embankments• culverts• dunes and shingle beaches.These assets are further classified depending on the type of environment (fluvial orcoastal), type of material, width of the asset (narrow or wide), whether maintenance isbeing carried out and whether there is any crest or rear protection.For each classification three categories of deterioration rates are provided in Table 2.1,reflecting estimates of the most likely (best estimate), fastest and slowest deteriorationrates. In choosing the most appropriate rate category, account should be taken of:• the loading and environmental conditions acting upon the asset;• the degree of difference from the assumed ‘standard’ conditions (which theasset was designed for).The ‘best estimate’ in the table assumes ‘standard’ conditions. If the loading on, oraggressiveness of environmental conditions around, an asset is likely to be higher orlower than typical design conditions, a faster or slower rate of deterioration should bechosen depending on the severity of this shift. Engineering knowledge and localexperience should be used in making any shift from average conditions.In most cases, it was not possible to distinguish the effects of crest and rear protectionon deterioration rates compared with assets with only front face protection.Foundation deterioration is not taken into account in these discussions unlessmentioned explicitly.Professional judgement is needed to classify flood defence assets as they are uniquestructures, often made up of more than one basic type. In such cases, to develop anoverall deterioration curve, it may be necessary to consider the deterioration curvesassociated with these component asset types in parallel and to choose the points onthe curves which provide the limiting values for the overall asset being considered. Forassets with revetments, this principle was also followed in the development ofdeterioration rates in this guide.Figures in the deterioration table (Table 2.1) indicate the years to move from ConditionGrade 1 to the condition grade (CG) of interest. For example, for a vertical wall ofgabions in a fluvial environment, the best estimate for Condition Grade 4 is 22. Thisindicates that the years to move from CG1 to CG4 are 22. The time to move from anyCG to a worst CG is the difference between both figures. In the same example, thetime to move from CG3 to CG4 is the difference between 22 (CG4) and 10 (CG3),hence 12 years.Only a generalised or “usual” maintenance regime has been considered for the ‘withmaintenance’ curves; no distinction has been made between proactive and reactivetypes of maintenance, though deterioration rates are likely to be different for differentmaintenance types. The type of maintenance is therefore another factor that needs tobe taken into account when choosing between slow, best estimate and fast rates (aswell as exposure to deterioration agents).Science Report – <strong>Guidance</strong> on determining asset deterioration 3

Table 2.1 Deterioration times (years) to different condition grades for different asset types and exposures4 Science Report – <strong>Guidance</strong> on determining asset deterioration

3 Step-by-step guide3.1 Steps to follow• Step 1: Identify the type of asset: vertical walls, embankments, culverts,dunes and shingle beaches. If the asset is of composite construction,identify all significant asset types present. Complete the selection of thetype of asset by identifying:- The type of material that the asset is made of:for vertical walls: gabion, brick and masonry, concrete or sheet pilesfor embankments, the type of revetment: turf, rigid, riprap, flexible,permeable, impermeable- If the asset is an embankment in a fluvial environment: define if it isnarrow or wide and whether there is crest or rear slope protection;coastal embankments are most vulnerable to front face damage andhence these factors are not critical in this case.• Step 2: Identify the factors influencing the asset life:- The environment which influences the asset: fluvial or coastal. For thispurpose, coastal defences are those which are predominantly affectedby a combination of wave action and saline conditions.- Whether there is normal or no maintenance.• Step 3: Identify the appropriate deterioration curves:Select the relevant deterioration curves or figures in the deterioration tablefor that asset. Where the asset is made up of more than one basic type, itmay be necessary to consider deterioration curves from the componentstructure types in parallel and to choose the points on the curves whichprovide the limiting values for the overall asset being considered.• Step 4: Determine the deterioration curveUsing engineering judgement and local experience, determine thedeterioration curve/profile by selecting or interpolating between bestestimate, fastest and slowest deterioration curves/profiles taking accountof:- The loading and environmental conditions acting upon the assetcompared with the assumed ‘standard’ or design conditions.- In case of maintenance, the level of maintenance or approach(reactive/proactive).• Step 5: Assess the current condition gradeUse the Environment Agency’s Condition Assessment Manual to assessthe current condition grade (see Table 2.1).Science Report – <strong>Guidance</strong> on determining asset deterioration 5

• Step 6: Forecast the expected deterioration timeForecast the expected deterioration time(s) to the next condition grade(s)using the selected or interpolated deterioration curve. It is assumed that ittakes the full period to get to the next condition grade; hence, there are nointermediate states between condition grades. For example, to move fromCG2 to CG5 it takes the difference between both figures. For a vertical wallof gabions in a fluvial environment, the fastest estimate to move from CG2to CG5 is 16 years (20 - 4 = 16).6 Science Report – <strong>Guidance</strong> on determining asset deterioration

3.2 Examples of applicationThis section presents two examples of application of the step-by-step guide.3.2.1 Example 1Extracted from the Thames Estuary 2100 project (Topic 4.7 – DevelopRecommendations for Maintenance versus Replacement)Site DescriptionThis asset is located on Eastern Esplanade on the south side of Canvey Island betweenMarine Road and Gazelle Drive adjacent to the St Anne’s pumping station.The current defence comprises a 2.45 m high reinforced concrete wall with wave returnconstructed as a cap around the top of a 10 m long steel sheet pile. The average crestheight of the wall is 6.85 m AOD. A public access area/walkway is located on thelandward side of the wall, on the crest of a sand fill embankment approximately 1.3 mbelow the top of the wall. At the toe of this embankment is the busy Eastern Esplanaderoad. On the riverward side of the flood wall the embankment slope is protected by abitumen-grouted stone revetment, which is subject to wave action and tidal influence. Itis understood that the construction date of these defences was roughly 1984.The defence at this location has a Condition Grade of 1.There are flood gates and public access steps provided at regular intervals along thelength of the flood wall.From the British Geological Survey borehole information adjacent to the site (longsection ref: N20 and borehole ref: BH01C) the immediate underlying ground strata areshown to be soft alluvial silts.Science Report – <strong>Guidance</strong> on determining asset deterioration 7

Step 1: Identify the type of assetThis is a composite structure with three different types of assets:concrete wallsheet pileimpermeable (bitumen-grouted stone) revetmentStep 2: Identify the factors influencing the asset lifeCoastal environmentNormal maintenance in concrete wall and revetmentNo maintenance in sheet pilesStep 3: Identify the appropriate deterioration curvesThree deterioration rates are extracted from Table 2.1 considering the options:Vertical wall / Coastal / Concrete / Both / NormalVertical wall / Coastal / Sheet piles / Both / NoEmbankment / Coastal / Impermeable / Both / NormalBest estimate (m) Fastest estimate (m) Slowest estimate (m)1 2 3 4 5 1 2 3 4 5 1 2 3 4 5Concrete0 10 30 65 80 0 5 15 30 35 0 20 60 120 150wallSheet piles 0 8 30 43 50 0 4 12 25 30 0 10 44 60 70Impermeable0 13 25 42 50 0 5 15 25 30 0 20 60 120 150revetmentThe deterioration curve for the composite structure is obtained from the limiting values ofthe three curves aboveCompositestructureBest estimate (m) Fastest estimate (m) Slowest estimate (m)1 2 3 4 5 1 2 3 4 5 1 2 3 4 50 8 25 42 50 0 4 12 25 30 0 10 44 60 70Step 4: Determine the deterioration curveThe best estimate is chosen as it is assumed that the asset is under standard conditions.Best estimate (m)1 2 3 4 5Composite structure 0 8 25 42 50Step 5: Asses the current condition gradeCondition Grade 1 is the actual CG of the asset, given the information provided.Step 6: Forecast the expected deterioration timeThe time for the asset to deteriorate from its current condition grade (CG1) to ConditionGrade 3, which is considered the minimum condition grade acceptable for that structure,is 25 years.8 Science Report – <strong>Guidance</strong> on determining asset deterioration

3.2.2 Example 2Site DescriptionThis asset is located at Overstrand in North NorfolkThe current defence comprises a 2.74 m high reinforced concrete wall with a 1.43 mwide reinforced concrete apron and 4.3 m long piles as scour protection. The averagecrest height of the wall is 4.50 m AOD. Behind the 5.00 m wide promenade at the rearof the wall, the contorted glacial drift cliffs rise to a height of 23.6 m AOD The defenceswere rebuilt in 1955.The concrete wall has a condition grade of 2, tending to 3, and the steel piles have acondition grade of 3.The beach is in very poor condition, lowering at a mean rate of 70 mm per year. Thebeach has been assigned a condition grade of 5. The sea breaks against the exposedsteel piles at all high tides.Science Report – <strong>Guidance</strong> on determining asset deterioration 9

Step 1: Identify the type of assetThis is a composite structure with two different types of assets:concrete wallsheet pileStep 2: Identify the factors influencing the asset lifeCoastal environment. Aggressive wave action and abrasion. Potential structuralinstability resulting from the lowering of beach levels.No maintenance of the concrete wallNo maintenance of the sheet pilesStep 3: Identify the appropriate deterioration curvesThree deterioration rates are extracted from Table 2.1 considering the options:Vertical wall / Coastal / Concrete / Both / No maintenanceVertical wall / Coastal / Sheet piles / Both / No maintenanceBest estimate (m) Fastest estimate (m) Slowest estimate (m)1 2 3 4 5 1 2 3 4 5 1 2 3 4 5Concrete0 10 30 65 75 0 5 15 25 30 0 20 60 120 150wallSheet piles 0 8 30 43 50 0 4 12 25 30 0 10 44 60 70The deterioration curve for the composite structure is obtained from the limiting valuesof the two curves aboveCompositestructureBest estimate (m) Fastest estimate (m) Slowest estimate (m)1 2 3 4 5 1 2 3 4 5 1 2 3 4 50 8 30 43 50 0 4 12 25 30 0 10 44 60 70Step 4: Determine the deterioration curveThe fastest curve is selected as it is assumed that the asset is under severely adverseloading conditions.CompositestructureFast estimate (m)1 2 3 4 50 4 12 25 30Step 5: Asses the current condition gradeThe condition grade of the composite structure is 3.Step 6: Forecast the expected deterioration timeThe time for the asset to deteriorate from its current condition grade (CG3) to ConditionGrade 4, which is considered the minimum condition grade acceptable for thatstructure, is 13 years (25-12).10 Science Report – <strong>Guidance</strong> on determining asset deterioration

4 Deterioration curves –supporting explanations ofcurves provided for differentasset types4.1 Vertical wallsFigure 4.1 shows a basic line sketch of this type of asset.Figure 4.1 Vertical brick, masonry or concrete wallIn fluvial environments the crest width is not considered to have an impact on materialdrivendeterioration, but might affect geotechnic-driven deterioration (less vulnerabilityfor wider crests). On the other hand, a wider structure will make the wall moreaccessible and hence more vulnerable to human-induced deterioration. On balance,the same deterioration rates are applicable for both narrow and wide walls.No distinction can be made between: front-only protected, front and crest protected andfront, crest and rear protected assets.For coastal vertical walls the main processes happen at the front face of the wall,hence the crest width has no influence on deterioration processes. The same curve istherefore applicable to narrow and wide walls in this case.The foundations of the walls are assumed to be stable.4.1.1 Fluvial environmentGabionThe factors that determine variability of deterioration rates are:• Quality of materials and construction processes; for example, packingquality for the gabion stone is very important.• Acidity and salinity of the water, which affect the corrosion rate of the wirebaskets, though gabions are rarely used in saline water.• Morphological activity, which can cause distortion of baskets, for exampleabrasion of plastic coatings by sand transport.Science Report – <strong>Guidance</strong> on determining asset deterioration 11

As it is difficult to carry out any effective maintenance, the curve for thewith-maintenance scenario is not distinguished from the no-maintenance scenario.Evolution to CG3 occurs rapidly because of settling of stones and corrosion. Asindicated by the fastest curve, the initial quality of construction can speed updeterioration.Values for fastest and slowest deterioration are about 75 and 125 per cent of the bestestimate.Vertical wall - Fluvial Environment - Gabions1Condition grade234BestFastSlow50 5 10 15 20 25 30 35Time (years)Brick and masonryMortar loss from joints by the action of water, animals or plants is the main factor indeterioration. The action of vessels travelling along or mooring alongside walls can alsobe significant for deterioration from damage or abrasion.Lifetimes of over 100 years for such structures are considered reasonable in somecases due to experience in such locations as Manchester; there, structures dating fromthe industrial revolution are still performing well, though the degree of maintenancecarried out is unclear. Masonry structures are rarely constructed now.Simple basic maintenance (such as repointing of brickwork) can have a big impact ondeterioration rates. With maintenance, the best deterioration rates are close to theslowest estimate.The lack of maintenance mainly affects later stages of deterioration (after CG3).For the slowest estimate, the transition to CG2 is related to cracking and the transitionto CG3 to loss of mortar. Evolution from CG4 to CG5 will be very quick.Quality of construction or design is the main factor influencing the fast deteriorationestimate.Vertical wall - Fluvial Environment - Brick&Masonry/ConcreteCondition grade123450 20 40 60 80 100 120 140 160Time (years)Best -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -Maintenance12 Science Report – <strong>Guidance</strong> on determining asset deterioration

ConcreteThe material often used in fluvial environments is mass concrete. In this case,deterioration rates can be considered the same as brick and masonry.For reinforced concrete, though its deterioration rates are generally covered by thebrick and masonry curves, some small differences (more rapid deterioration) from thebrick and masonry curves might appear at the end of the curves. On balance, the samecurves as for brick and masonry structures are adopted.SheetpilesThe main deterioration process of sheetpiles (Figure 4.2) is corrosion and includes:• corrosion of the pans of piles which creates loss of bending capacity;• corrosion of the thinner webs of piles that then allow loss of materialthrough the wall;• corrosion of any tie anchors which lead to the anchors failing and the wallcollapsing.Figure 4.2 Vertical sheet wall structureWhilst corrosion is a uniform process, because the differences between conditiongrades are not equal, the time steps in the deterioration curves are not equal.Information provided by interviewees suggested that sheetpiles 100-120 years oldcould still be performing in non-aggressive environments (in the Thames region), or 50-years old sheetpiles in good condition with limited maintenance in Nottingham, Ipswichand Feering.Maintenance activities such as painting will prolong structural life, although surfacepreparation and correct paint application are often difficult to achieve. Hence,differences between maintenance and non-maintenance are insignificant.The quality of the paint system defines the form of degradation from CG1 to CG2; inthe best and slowest estimates, it takes about 20 years before the paint starts to breakdown. The subsequent time to CG3 takes longer as corrosion only sets in when thepaint has gone.Fastest estimates are related to geotechnical processes (slip, erosion). In this case,deterioration rates are more likely to be in line with those for brick and masonrymaterial. This is because the causes of failure for both types of structure will be similar,not driven by the materials themselves but by the ground conditions.It is assumed that no cathodic protection is provided.Science Report – <strong>Guidance</strong> on determining asset deterioration 13

Vertical wall - Fluvial Environment - Sheet piles1Condition grade234BestFastSlow50 20 40 60 80 100 120 140 160 180Time (years)4.1.2 Coastal environmentConcreteThe rates for coastal walls are higher than for river walls to allow for the effect of waveaction and sediment abrasion. From information collated from the interviews, thereappears to be an enormous range of abrasion of concrete in coastal environments.The life of coastal concrete structures can be prolonged slightly by repairing spalling,resealing joints, and so on. Re-facing works are classified as refurbishment, not asmaintenance.Abrasiveness and salinity control the range of deterioration rates for slowest, best andfastest estimates.In the case of the slowest and best estimates, maintenance works improve the life forthe period from CG4 to CG5 by five to 10 years.The fastest estimate reflects very quick processes: for example, rapid rates of abrasionof the order of 5 mm per year.Concrete repairs need to be carried out by specialist contractors.Vertical wall - Coastal Environment - ConcreteCondition grade123450 20 40 60 80 100 120 140 160Time (years)Best -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -MaintenanceBrick and masonryThere are few examples of brick walls left in coastal abrasive environments. Those thatremain tend to be of limestone masonry or stronger materials.As it is not realistic to carry out any effective maintenance on this type of structure, thesame set of curves applies to both cases.14 Science Report – <strong>Guidance</strong> on determining asset deterioration

For the slowest deterioration estimates, the same curves as those adopted for concretecoastal walls apply.The fastest rates are slower than those for comparable concrete structures becausematerials are likely to be tougher.Vertical wall - Coastal Environment - Brick&Masonry1Condition grade234BestFastSlow50 20 40 60 80 100 120 140 160Time (years)SheetpilesCompared with fluvial sheetpiled walls, coastal sheetpiles have a significantly shorterlife due to the saline environment and constant abrasion.The general shape of the curves remains the same as for fluvial piles but with newratios compared to CG5.Plating is the most likely form of maintenance work that improves the asset life. It isrelevant for slowest and best estimates and once CG3 is achieved.The slowest estimate is based on buried walls in the beach that are out of the abrasionand splash zone.Vertical wall - Coastal Environment - Sheet pilesCondition grade123450 10 20 30 40 50 60 70 80 90Time (years)Best -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -MaintenanceScience Report – <strong>Guidance</strong> on determining asset deterioration 15

4.2 Embankments4.2.1 Fluvial environmentTurf protectionThe deterioration processes for this structure type (Figure 4.3) are based on turf quality(loss of grass cover), rutting, eventual loss of soil, settlement, vermin infestation andgeotechnical problems.Figure 4.3 Embankment with turfed surface protectionThe condition grade of embankments may improve immediately after construction asturf quality improves following seeding.Maintenance works are assumed to maintain grass cover to an average standard,whereas doing nothing will allow it to become poor rather quickly.Normal maintenance works, such as grass cutting, vermin control and repairs of rutting,have a real impact on deterioration processes and can extend lifespan practically inperpetuity. The only limitation on life is when geotechnical problems appear, such asslumping. Topping up and settlement is considered refurbishment, not maintenance.The slowest estimate is governed by the rate of deterioration of natural vegetation andassumes no vermin, no rutting and no geotechnical problems. The transition from CG2to CG3 can be quite fast, unless very active vegetation management is carried out.Fastest estimates relate to the presence of poor quality soils or inadequate design andconstruction of the embankment. There are examples of deterioration from CG4 toCG5 in just two to five years. Normal maintenance works are unlikely to have a bigimpact on the deterioration curves.Having a wider embankment brings both positive and negative influences, but as thesetend to cancel each other out, the same curve applies for wide and narrowembankments. Without maintenance and in the worst (fastest) conditions, however,deterioration of wider embankments is slower than for narrow embankments. Widerembankments are more likely to have been designed better and be less vulnerable togeotechnical problems which tend to dominate the fast deterioration curve.16 Science Report – <strong>Guidance</strong> on determining asset deterioration

Embankment - Fluvial Environment - Turf - NarrowCondition grade123450 20 40 60 80 100 120 140 160 180Time (years)Best -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -MaintenanceEmbankment - Fluvial Environment - Turf - WideCondition grade123450 20 40 60 80 100 120 140 160 180Time (years)Best -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -MaintenanceRigid protectionRigid face protection (Figure 4.4) will prevent some deterioration processes, but notthose related to low quality of soil materials.Figure 4.4 Embankment with hard surface protectionFor rigid protection, material deterioration is the dominant process. A revetment isdesigned only if required because of loading conditions (for example waves), so failureof the revetment will be equivalent to defence failure.This type of embankment has a more uniform and slower rate of deterioration thanturfed embankments, with the deterioration rate limited by deterioration of cover layer.For the fastest estimate, the worst predictions for the material underneath theprotection dominate deterioration.When the rear face is considered, deterioration is only dominated by the material(concrete).Science Report – <strong>Guidance</strong> on determining asset deterioration 17

Condition grade12345Embankment - Fluvial Environment - Rigid protection-Narrow - No maintenance0 20 40 60 80 100 120Time (years)BestFastSlowBest -RearprotectionFast - RearprotectionSlow -RearprotectionCondition grade12345Embankment - Fluvial Environment - Rigid protection-Narrow - Maintenance0 20 40 60 80 100 120 140 160Time (years)BestFastSlowBest -RearprotectionFast - RearprotectionSlow -RearprotectionCondition grade1234Embankment - Fluvial Environment - Rigid protection-WideBest -NomaintenanceFast -NomaintenanceSlow -NomaintenanceBest -MaintenanceFast -Maintenance5Slow -Maintenance0 20 40 60 80 100 120 140 160Time (years)Rip-rap revetmentMaintenance works, including topping up, keep the asset in good condition and hencerip-rap revetments have similar curves to turf embankments.Maintenance works include topping up the crest levels, helping to keep embankment ingood condition.18 Science Report – <strong>Guidance</strong> on determining asset deterioration

Condition grade12345Embankment - Fluvial Environment - Riprap -Narrow - No maintenance0 10 20 30 40 50 60 70Time (years)BestFastSlowBest -RearprotectionFast - RearprotectionSlow -RearprotectionCondition grade12345Embankment - Fluvial Environment - Riprap -Narrow - Maintenance0 20 40 60 80 100 120 140 160 180Time (years)BestFastSlowBest -RearprotectionFast - RearprotectionSlow -RearprotectionCondition grade1234Embankment - Fluvial Environment - Riprap -WideBest -NomaintenanceFast -NomaintenanceSlow -NomaintenanceBest -MaintenanceFast -Maintenance5Slow -Maintenance0 20 40 60 80 100 120 140 160 180Time (years)Flexible revetmentThe suggested curves are based on the performance of such systems as blockrevetments, armorflex and so on.When rear protection is present, the fastest deterioration curves are dominated bygeotechnical deficiencies.When no maintenance is considered, the best and slowest estimates are derived fromthe ones corresponding to turf embankments.If maintenance is considered, the best and slowest estimates are derived from the onescorresponding to turf embankments until CG3 is achieved and from the onescorresponding to material (concrete) for CG4 and CG5.Science Report – <strong>Guidance</strong> on determining asset deterioration 19

Condition grade12345Embankment - Fluvial Environment - Flexible protection -Narrow - No maintenance0 10 20 30 40 50 60 70Time (years)BestFastSlowBest -RearprotectionFast - RearprotectionSlow -RearprotectionCondition grade12345Embankment - Fluvial Environment - Flexible protection -Narrow - Maintenance0 20 40 60 80 100 120 140 160Time (years)BestFastSlowBest -RearprotectionFast - RearprotectionSlow -RearprotectionCondition grade1234Embankment - Fluvial Environment - Flexible protection -WideBest -NomaintenanceFast -NomaintenanceSlow -NomaintenanceBest -MaintenanceFast -Maintenance5Slow -Maintenance0 20 40 60 80 100 120 140 160Time (years)4.2.2 Coastal environmentPermeable and impermeable revetmentThe main processes driving deterioration of these revetments are toe undermining, theeffect of material in the foreshore and deterioration of the material in impermeablerevetments.For the fastest estimate, toe undermining is the main process driving deterioration.Hence, curves are the same for permeable and impermeable revetments. Structureson eroding clay foreshores will last less time than those on chalk or other hardsubstrates.For the slowest estimate, deterioration is driven by the material.20 Science Report – <strong>Guidance</strong> on determining asset deterioration

Condition grade1234Embankment - Coastal environment -Permeable revetmentBest -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -Maintenance50 20 40 60 80 100 120 140 160Time (years)Condition grade1234Embankment -Coastal envirornment -Impermeable revetmentBest -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -Maintenance50 20 40 60 80 100 120 140 160Time (years)4.3 CulvertsOnly deterioration of the culvert itself is considered. Washouts due to overtopping orerosion of adjacent embankments are not taken into account. Culverts are generallywell designed and do not suffer very aggressive situations.Deterioration curves for the best and slowest estimates are based on those for fluvialbrick and masonry and concrete walls, regardless of maintenance.Fastest estimates are quicker in culverts than in fluvial brick and masonry and concretewalls because of variability of materials and difficulties in inspections.Condition grade1234CulvertsBest -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -Maintenance50 20 40 60 80 100 120 140 160Time (years)Science Report – <strong>Guidance</strong> on determining asset deterioration 21

4.4 Dunes and shingle beachesGiven the wide range of natural characteristics and behaviours of this type of asset, it isdifficult to assess rates of deterioration. For shingle beaches, initial deterioration is slowbut then accelerates; later, following substantial beach loss, further deterioration slowsas the remaining beach material ‘rattles around’ the foreshore. A wide range ofsituations can exist and hence the band of curves has been kept wide.Condition grade1234Dune beachesBest -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -Maintenance50 10 20 30 40 50 60 70 80 90Time (years)Condition grade1234Shingle beachesBest -No maintenanceFast -No maintenanceSlow -No maintenanceBest -MaintenanceFast -MaintenanceSlow -Maintenance50 10 20 30 40 50 60 70 80 90Time (years)22 Science Report – <strong>Guidance</strong> on determining asset deterioration

5 Structure-specificassessmentsWhen identifying deterioration curves for specific structures, various options areavailable from selecting from the deterioration curves given here to making a sitespecificevaluation, which could require intensive investigation and monitoring.If the user does not wish to use standard deterioration curves, or must modify themsignificantly in the light of local experience, the assessment should be performancebasedlisting failure modes, parameters of deterioration and how they affect thelikelihood of a breach. The following factors should be taken into account.When assessing specific deterioration rates, it is necessary to take various factors intoaccount. These include:• the type and design of the structure;• construction materials used;• potential weak points;• forces and influences acting upon the structure.In addition to any calibration to take account of historic deterioration rates for thestructure, factors that asset managers might need to consider for different structuresare listed below.Embankments and sloping seawalls• Likely rate of reduction in beach/berm level.• Likely rate of reduction in crest level.• Likely rate of reduction in foreshore level, gradual loss of slope material.• Degree of presence of vermin likely to generate holes.• Degree of cracking (may only be apparent during dry weather).• Likelihood of soft/saturated areas of the defence or ground nearby duringhigh water levels.• Risk of vandalism or damage.• Level of use by vehicles/pedestrians/animals, creating tyre ruts, vegetationand bank damage, worn surface and access points.• Anticipated loss/increase in extent and quality of vegetation, infestation byinvasive plants.• Likely movement of sections of embankment.Science Report – <strong>Guidance</strong> on determining asset deterioration 23

Slope erosion protection• Likely rate of reduction in level in front of defence.• Likelihood of saturated slope or ground at crest of defence.• Potential for future damage to revetment.• Potential for movement of individual parts of revetment.• Potential for movement of structure/slips within cliff.• Potential for local holes and tears within revetment.• Potential for bulging at the toe.Vertical wall structures• Likely rate of reduction in beach level.• Potential for corrosion of reinforcing steel in concrete.• Likelihood of distortion of steel piles/gaps in clutches.• Potential for loss or loosening of tie rod fixings• Potential for cracking.• Potential for surface damage to structure.• Potential for movement of retained ground/defence.• Likely rate of reduction in foreshore level, damage to slope.• Likely rate of loss of joint material, erosion around joints, voiding behindstructure.• Rate of growth of vegetation.• Potential for seepage through wall (from retained section at low water forretaining walls and from landward face or toe during high water levels forwalls with lower land immediately behind).• Likelihood of cracking of concrete with an irregular pattern, disintegration ofconcrete surface (spalling), corrosion of steel.Beaches• Likely rate of reduction in beach level, loss of sediment/beach material.• Likely rate of reduction in dune crest height, loss of sand volume (increasedaeolian transport).• Likely rate of change in profile of sections of dunes or beaches.• Likely rate of toe retreat.• Potential for reduced vegetation cover (dunes).24 Science Report – <strong>Guidance</strong> on determining asset deterioration

6 ConclusionsThis guide provides deterioration curves and explains how to use them to establish theresidual life of different types of flood defence assets. Vertical walls, embankments,culverts, dunes and shingle beaches are covered.The curves are based on the condition grades defined in the Condition AssessmentManual (Environment Agency, 2006). The deterioration curves consider the type ofenvironment (fluvial or coastal), type of material, width of the asset, whethermaintenance is carried out and whether there is rear protection.A table with deterioration rates for different condition grades and different asset typesthat summarises information from deterioration curves is also provided. The time (inyears) to move between different condition grades is obtained from the differencebetween figures corresponding to those conditions grades.A step-by-step guide supported with two examples of composite structures is provided.Science Report – <strong>Guidance</strong> on determining asset deterioration 25

ReferencesEnvironment Agency (2006). Condition Assessment Manual. Managing flood risk.Document reference 116_03_SD01Defra/Environment Agency (2009). <strong>Guidance</strong> on determining asset deterioration andthe use of condition grade deterioration curves. PAMS Project, MSF9.1. UnpublishedHR Wallingford Ltd, UK26 Science Report – <strong>Guidance</strong> on determining asset deterioration

GlossaryBest estimate:Condition grade:Defence system:Design standard:Deterioration curve:Deterioration:Environmentalconditions:Failure mode:Failure:Fast estimate:Load:Deterioration rate estimate assuming standard conditionsaround the asset, that is, conditions foreseen in the designstage of the asset.Standards adopted by the Environment Agency to assess thecondition (and hence likely performance) of flood defenceassets: 1 being a very good condition and 5 a very poor one.Two or more defences acting to achieve common goals.A performance indicator that is specific to the engineering of aparticular defence to meet a particular objective under a givenloading condition. The design standard will vary with load; forexample there may be different performance requirementsunder different loading conditions.Expresses the deterioration with time of an asset, in terms ofthe anticipated time intervals to change from one conditiongrade to another.Process involving a decline in the state of structural propertiesof the asset.Physicochemical and biological properties of the environmentwhich influence the asset and, in the context of this report,affect its rate of deterioration.Description of one of any number of ways in which a defencemay fail to meet a particular performance indicator.Inability to achieve a defined performance threshold (responsegiven loading).Deterioration rate estimate assuming more aggressive loadingsor environmental conditions that the ones envisaged in thedesign of the asset.Factors such as high river flows, water levels and wave heights,to which the flooding and erosion system is subjected.Maintenance regime: Programme of works undertaken to maintain the performance ofan asset to a certain level.Performance:Residual life:Slow estimate:Standard conditions:The degree to which a process or activity succeeds whenevaluating against some stated aim or objective.The remaining time that a defence is able to achieve a minimumacceptable value of defined performance in terms of itsserviceability function or structural strength.Deterioration rate estimate assuming less aggressive loadingsor environmental conditions that the ones envisaged in thedesign of the asset.Conditions for which the asset was designed.Science Report – <strong>Guidance</strong> on determining asset deterioration 27

Annex: Links with the NFCDDDefence Class CodeIn the next table, the types of assets described in Table 2.1 are linked with theirrespective class number following the NFCDD (RASP) Defence Class Code. A list withthe assets as they are described in NFCDD is also provided.Links between the types of assets and the NFCDD Code NumberType Environment MaterialNarrow / RearWide protectionNFCDD Class NoGabion Both 1, 2, 3, 39, 40Fluvial Brick&Masonry / Concrete Both 4, 5, 6, 41, 42, 43Vertical wallSheet Piles Both 7, 8, 9, 44Brick&Masonry Both 28, 29 ,30, 56, 57CoastalConcrete Both 25, 26, 27, 54, 55Sheet Piles Both 22, 23, 24, 52, 53TurfNarrow 10Wide 4511, 12NarrowRigidyes 13Wide 46, 47Fluvial14, 15NarrowEmbankmentRiprapyes 16Wide 48, 4917, 18NarrowFlexibleyes 19Wide 50, 51CoastalPermeable revetments Both 31, 32, 33, 58, 59Impermeable revetments Both 34, 35, 36, 60, 61Culvert 21Dune 37Shingle 3828 Science Report – <strong>Guidance</strong> on determining asset deterioration

List of types of protection as in NFCDD/RASPScience Report – <strong>Guidance</strong> on determining asset deterioration 29