Asset Management Plan Culverts
Culverts This Supporting Section should be read in conjunction with Council’s Asset Management Plan, the Asset Management Policy (which sets out Council's philosophy of asset management) and Council’s Asset Management Strategy (which provides Council with a clear direction and goal for managing the community's $1.185 billion (as at June 2010) worth of assets).
1
Current Asset Base
Size of the Network Council manages 3,924 culverts located throughout the Wagga Wagga Local Government Area (LGA). This equates to 24,901m of infrastructure. The following map details culvert locations across the Wagga Wagga LGA.
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Culverts The condition of Council’s assets has been audited as part of the asset inspection regime, rated against the asset condition reference sheet and captured in Council’s electronic mapping system. The condition of all Council’s assets is rated from excellent to very poor. The colours on the following map indicate the condition of the asset, as detailed in the below table. 1 2 3 4 5
Excellent Good Average Poor Very Poor
Dark Green Green Yellow Orange Red
Challenges of the Network The culvert network covers a large geographic area (the Wagga Wagga LGA) and is made up of a significant number of individual assets. There is considerable distance between each individual asset. As culverts are under the road it is often difficult to locate them if the guide posts, which mark their location are damaged or missing. Culverts are often damaged in flood or storm events as they are often located in water ways. Debris can be caught in a culvert, limiting water flow and adding pressure to their structure.
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Culverts Map – Condition The following map indicates the condition of the culvert infrastructure from excellent to very poor across the Wagga Wagga Local Government Area (LGA) and the table highlights the proportion of the network in each condition. Excellent Good Average Poor Very Poor
1.5% 50.1% 32.4% 11.0% 5.0%
306m 9,947m 6,422m 2,185m 984m
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Condition Assessment
Condition Ratings Reference Sheet The condition of culverts is audited against a rating scale which ranges from excellent to very poor. This scale is used as the basis of all assessments of culverts by Council’s Surveillance Team. The rating scale forms the Condition Rating Reference Sheet below.
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Culverts Risk and Condition Ratings Indicators Council also uses Risk and Condition Rating Indicators to determine a prioritised works schedule for the maintenance, renewal and replacement of large asset categories. These indicators are used in addition to the Condition Ratings Reference Sheet to enable further analysis of the worst sections of the asset class. The indicators are used to develop an overall Works Schedule Priority Rating for each individual asset or section of an asset. The first stage considers the risk the condition of the asset poses to the community based on location, road classification and traffic volumes. The following table details the Risk Rating Indicators for the culvert asset base. Culvert Risk Rating Indicators - Based on Location and Road Type Weighting
Road Type/Traffic Volume
1.3
Arterial Road or Highway
1.2
Sub Arterial/Regional Road
1.1
Collector/Distributor Road
1.0
Residential Road
The second stage of the process considers the Condition Rating Indicators. The following indicators are considered for each culvert:
blockage cracking/breakages and misalignment/separation of culvert units
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Culverts The more deteriorated a culvert is, the higher the rating for blockage and cracking. Each culvert is rated against the following indicators. Culvert Condition Rating Indicators- Based on Inspection Performance Measurement Guidelines Score
Blockage
Cracking/breakage
Misalignment/Separation of Culvert Units
1
Culvert clear
No cracking
Nil
2
10% blockage
Minor cracking
Minor misalignment
3
11- 20% blockage
Some cracking
Major misalignment
4
21 – 40% blockage
Major cracking, partly functional
Minor separation <5mm
5
Greater than 41% blockage
Broken â&#x20AC;&#x201C; non-functional
Major separation >5mm
The results of the Risk and Condition Rating Indicators analysis are combined to give an individual asset or section of the asset a Works Schedule Priority Rating. For example a culvert could be rated as follows:
Blockage (B) Cracking /broken (C) Road Type (RT) Works Schedule Priority Rating Formula Works Schedule Priority Rating
Culvert XYZ 4 5 1.1 (Collector) (B + C)RT (4 + 5)1.1 = 9.9
The Work Schedule Priority Ratings for culverts are then ranked from highest to lowest to produce a prioritised schedule of works for maintenance, replacement and renewal of the network.
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Culverts Intervention Levels To guide Council’s response to customer requests a set of reactive triggers has been developed for each asset category. These triggers are called intervention levels and include expected response times. The following table details the intervention levels and response times for maintenance of the culvert networks. Culvert Intervention Levels Blockage
Inspection within one week. Corrective action taken within one month.
Guardrails missing
Corrective action taken within 1 month
Major failure
Immediate inspection and immediate corrective action
Condition Inspection Regime The condition and risk of the culvert network will be assessed simultaneously as part of the Condition Inspection Regime. This inspection will audit the condition of each culvert against the Condition Rating Reference Sheet and also assess the risk based on location and usage. The entire culvert network will be audited every three years. The inspections will be in the form of a GPS audit routine for all culverts in the Wagga Wagga LGA. The inspections for the culverts should audit the following:
guardrails protection barriers road surface and expansion joints (where relevant) and vegetation of the inlets and outlets
Ad hoc inspections will be conducted in response to customer requests, on a needs basis and where the asset degrades due to un-foreseen or unusual circumstances, like a storm event. These inspections are done onsite by trained Surveillance Officers and the results are captured in Council’s electronic mapping system (ArcGIS).
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Life Cycle Management
Life cycle management details how Council plans to manage and operate the asset category at the agreed level of service while minimising life cycle costs throughout the useful life of the asset. For most local government assets there are four key phases to the life cycle, namely: acquisition, operation and maintenance, renewal, and disposal.
Costs occur in each phase of the asset life cycle. It is important to attribute these life cycle costs to each phase to allow for effective decision making about how the asset will be managed. The life cycle costs of assets include:
initial capital investment operation and maintenance refurbishment and renewal administration, overheads and taxes depreciation capital use rate charges or rate of return and disposal of the asset at the end of its useful life
The initial capital or investment cost of a new asset is a significant cost and often dominates the decision as to whether to acquire the asset or expand the infrastructure network. However, it is important to include all the costs associated with each phase of the asset life cycle, including ongoing operation and maintenance, future renewal and disposal.
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Culverts Target Maintenance Events The following table details the target maintenance events associated with culverts annually. Culvert Target Maintenance Events Event Target Maintenance Events per Year Cleaning Every two years Vegetation Removal Twice per year per culvert
Renewal A detailed work plan for the renewal of culverts is developed annually to support this Asset Management Plan. This renewal program is prioritised based on condition and risk.
Disposal Currently, Council includes the cost to dispose of an asset in the unit rate of that asset type. As Council moves towards strategic asset management this cost will be captured separately. The Asset Management Plan will be updated to reflect this change as it occurs across the asset types.
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Level of Service
The Asset Management Plan for 2011 has been developed based on data collation, research outcomes and the results of Councilâ&#x20AC;&#x2122;s internal stakeholder engagement process. The next stage of the process is to ask the community to identify which asset condition is satisfactory to them. This will begin with an extensive community consultation process. The consultation will be in the form of a community survey which will be conducted online, at community gatherings, through focus groups and stakeholder meetings. The survey will use new technology, be based on images and a simple selection process. The outcomes of the consultation will form the foundation for true community engagement to occur in relation to the management of infrastructure across the Wagga Wagga LGA, in particular the development of agreed levels of service, supported by Council and the community. As Council gathers data from the community about the level of service for each asset category the outcomes will be integrated into the Asset Management Plan. Until the outcomes of the community engagement are known Council will provide costings to achieve an average condition for each asset category and use this as the satisfactory level of service.
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Financial Considerations
The following graph details the proportion of the culvert network in each condition.
Councilâ&#x20AC;&#x2122;s current liability in relation to the infrastructure network is the sum of all asset units which have a condition rating of poor and very poor. The current liability of the culvert network is $2,272,593 (in 2010 dollars). The following table provides the details of the culvert network current liability. Asset Condition 4 - Poor 5 â&#x20AC;&#x201C; Very Poor Total Current Liability
Amount 3,398m 1,181m 4,579m
Estimated Cost in 2010 Dollars $1,528,586 $744,007 $2,272,593
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Culverts Projected Annual Maintenance Costs For Council to achieve the target maintenance events as detailed in Section 3 of this Asset Management Plan, the projected annual maintenance budget for the culvert network is estimated to be $2,002,313 (in 2010 dollars). This estimate was developed by Councilâ&#x20AC;&#x2122;s Asset Management Planning and Program Integration Teams in 2010. It is a first principle estimate and is expected to vary as Council improves its asset management process and strategies. The following table provides further details of the maintenance costs associated with maintaining the culvert network each year: Culvert Network Projected Annual Maintenance Costs Event Projected Annual Maintenance Costs Cleaning $697,200 Minor repairs $605,150 Vegetation control $699,963
Required Increase to Annual Maintenance Budget per Additional Unit As the asset base increases it is important to ensure that the annual maintenance budget also increases. As the culvert network expands the annual maintenance budget should increase by $175 per additional culvert cell. (NB. A culvert cell is the individual water outlet within the culvert. A culvert can have single or multiple cells.)
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Assumptions
There are some generic assumptions made in the management of assets in Wagga Wagga City Council, these are found in the Asset Management Plan. In addition, the following assumption has been made in relation to culverts: ď&#x201A;ˇ
This Asset Management Plan Section includes those culverts which are 6 metres in length which are under the road. A bridge sized culvert is considered to a culvert with a greater length than 6 metres.
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