Annex 4

1. Introduction

Highway drainage assets are considered an integral component to operating a safe and well-maintained carriageway which is why they are included as part of the carriageway lifecycle plan. Highway drainage systems are installed to capture surface water run-off to alleviate flooding and protect the fabric of the road. Getting water off the carriageway quickly is important in that it not only makes the road surface safer for drivers but also helps reduce deterioration of the road. Water egress and ingress into the road surface, the pumping action of tyres and freezing thawing damages and weakens the road surface leading to the development of potholes and the need for routine maintenance of the surface course.

Other objectives include preventing the formation of ice on the highway, elimination and preventing safety defects occurring on the carriageways, footways and cycleways, and preventing the ponding and flooding to buildings and commercial properties. The main responsibility is to ensure that the highway is available and safe to all users

This document should be read in conjunction with the current Devon Local Flood Risk Management Strategy (FRMS). As a requirement of the Flood and Water Management Act 2010, there is a duty for Devon as the lead Local Flood Authority to develop, maintain, supply and monitor a strategy for local flood risk management. The FRMS identifies the role of various Risk Management Authorities in managing the risk of flooding from different sources. The highway authority has a responsibility for managing the risk of flooding from surface water originating on the highway. A table outlining roles and responsibilities of Risk Management authorities and others such as landowners is available in the FRMS.

The impact of climate change will mean that winters may become warmer and wetter, summers hotter and dryer, there may be more frequent and intense extreme weather events. The effects of flooding, storms and extreme heat will affect our highway infrastructure including drainage assets. Our historical drainage systems may not cope very well resulting in potential flooding on highways and properties adjacent to the highway. The Council need to invest in drainage assets to reduce the impact of potential flooding. Regular inspections and maintenance and cleaning of our drainage assets is vital.

Due to global warming, heavy precipitation events are expected to increase in frequency and intensity under climate change. This will result in more extreme weather events such as flooding. This will cause damages to private & commercial properties, highway asset infrastructures and potential risks to lives, livestock and pollution of rivers and other water courses. There are moral and financial reasons why we should be investing more in our drainage assets.

The impact of climate change is one of the many challenges facing communities across Devon. More can be found in Section 5 of the Lead Section on the Plan. Drainage networks that are designed based on historical climate regimes may be defunct in the future. This could lead to widespread pluvial flooding, aggravated by inappropriate land-use planning, increased paving, and loss of water storage space.

2. Inventory

Fig 4.1: Image showing who is responsible for various assets alongside a typical highway

Digital drainage data is being collected and constantly updated by Devon County Council.

Drainage Asset Type	No. Assets
Ditches – Ditches on land near the highway help to carry water from the road (often from grips or gullies) into water courses. Typically, responsibility for maintaining ditches and easements sits with the local landowner (riparian owner) and not the Council, however the Council as the highway authority may contact local landowners to request ditch clearances	22,487
Grip – In rural areas the carriageway is generally drained by ‘grips’ cut into the verge which feed water into ditches. Grips are damaged from the passing of vehicles and filled in with silt and detritus during the year so an annual programme of re-establishing or re-cutting grips is undertaken to maintain their effectiveness. The amount of grip cutting is dependent on available resources and governed by the Council’s Siding & Watertabling Policy.	19,765
Small Culvert – Culverts allow the movement of water underneath the road from springs, run-off, small streams, and seepage; as well as to assist in connecting ditches to water courses. Asset inventory data for culverts less than 1.5 metres in diameter is currently not held. Culverts larger than 1.5 metres in size are considered structures, unless it is a corrugated steel pipe then it is 0.9 metres and have been captured as part of the structures inventory. Little is known about the location or condition of culverts and piped drainage runs under the road network. This asset is generally managed on a reactive basis although some known flooding hotspots receive regular jetting or gulley cleansing routine maintenance. Where resurfacing schemes are planned, drainage will be looked at and replacement or repair considered as part of the capital works.	Currently not recorded
Catchpit / Interceptor – Often where a highway drainage system outflows into a natural watercourse a catchpit will be installed to remove grits, silts and excess sediment. Catchpits and associated pipes are cleaned on a reactive basis.	2,294
Channels/Swales – open drainage channels to receive and convey water discharging from the highways.	1,384
Inspection Covers/chambers – mainly for inspections and maintenance.	81,988
Gullies – Gullies are the main asset drainage feature used to remove water from the road, so the frequency of inspection, cleansing and repair is critical to the safe operation of the network. Gullies on the main roads (the salting network) and all rural roads are cleansed on an annual basis to clear the build-up of any detritus or silt. Gullies on all other minor urban routes are cleaned on a 3-year cycle. Some gullies in known flooding hot spots are cleaned at enhanced frequencies	212,236
Buddle holes – Holes or pipes that carries water through a hedge or bank as part of road drainage system.	2,637
Easement – small openings on the side of the road to take water off the highway.	38,432
Ponds/attenuation Basins etc. – Stores runoff water during extreme rainfall events during peak flows and releasing it at a controlled rate during and after the peak flow as passed. Soakaways (including infiltration basins, below ground crated systems etc.)	Currently not recorded
SUDS- Sustainable Drainage Systems- manage surface water on, or as is practicably close to, the ground surface, in a way that mimics natural hydrological processes. Managing surface water in this way controls the rate and quantity of surface water runoff, improves its quality, and provides visual amenity and biodiversity benefits. Generally, the use of a variety of above-ground SUDS components, which manage rainfall close to where it falls, provide the greatest environmental benefits, and can cost less than traditional piped systems. Below is a link to Devon County Council’s guidance for SUDS: https://www.devon.gov.uk/floodriskmanagement/document/sustainable-drainage-system-guidance-for-devon/#3-what-are-suds.	Currently not recorded

Fig. 4.2: Number of different highway drainage assets

3. Performance

The establishment of an effective regime of inspection, assessment and monitoring of asset condition is an essential component of an effective asset plan. The inspection types and condition assessment methods featured below are based on the national code of practice ‘Well-managed Highway Infrastructure 2016.

Inspections are particularly important in the case of network safety where information may be crucial in respect to legal actions. A robust inspection regime therefore forms part of the County Council’s defence against claims and legal proceedings.

3.1 Safety inspections

Safety inspections are undertaken to meet the key objective of Network Safety and they form a key aspect of the authority’s strategy for managing liabilities and risks. They are used to identify defects likely to be hazardous or cause serious inconvenience to users of the highway network or the communities served, including defects requiring urgent attention and the appropriate response is determined using a risk-based approach.

The Highway Safety Policy details how safety inspections are undertaken, the frequency of inspection, investigatory criteria and required response period to an actionable defect. Relevant defects such as standing water, broken or missing ironwork and cracks or gaps are identified. Treatments and Response Times are listed in the Highway Safety Policy.

3.2 Serviceability Inspections

As part of cleansing programmes gully, grips, easement and buddle holes are inspected for function and condition.

When the Council carries out planned maintenance activities and major schemes on the highways, it inspects, cleans, and carries out repairs or replacement of drainage assets where necessary.

3.3 Performance Management

There are two key performance indicators which capture gully emptying and Grips, buddle holes and easements cleaning efficiency.

There are regular cyclic maintenance improvement meetings to monitor performance and asset condition.

4. Maintenance Strategy

4.1 Creation of a new asset

New highway drainage assets are added in several ways. These include:

When new highway infrastructures such as carriageways, footways, or cycleways are created,
As part of development works (both under sections 38 and 278 of the Highway Acts 1980) or major housing developments,
Created in response frequent flooding events or in response to local service needs,
As part of a Local Asset and Capital Programmes (LACP) scheme to alleviate recurring defects or problems on the highway,
Under major structural schemes, and
Work undertaken by the Flood risk team.

4.2 Routine maintenance

Routine maintenance such as gully cleansing is carried out in accordance with our Gully Cleaning Policy.

Urban gullies with sumps on the Priority Network shall be emptied and recharged to flush the system a minimum of once per year,
Urban gullies without sumps on the Priority Network be flushed through to check they are functioning correctly a minimum of once per year,
Urban gullies with sumps on other roads shall be emptied and recharged to flush the system a minimum of once every three years,
Urban gullies without sumps on other roads shall be flushed through to check they are functioning correctly a minimum of once every three years,
Rural gullies with sumps shall be emptied and recharged to flush the system a minimum of once per year, and
Rural gullies without sumps shall be flushed through to check they are functioning correctly a minimum of once per year.

Where it has been assessed that a gully requires more frequent cleansing the frequency shall be increased. Examples of this are gullies in areas where flooding would affect buildings or known to flood the highway.

We aim to clean other drainage assets on an annual basis as follows:

Grips, buddle holes, and easements annually, or prior to LACP schemes or major surfacing works.

Ditches along the side of the road are the responsibility of whoever owns the land on which they are situated and should be maintained in order to keep the ditch capable of carrying water away from the road. The council therefore clean on “as needs” basis.

Knowing where drainage assets are and how many of each type is helpful as we can programme maintenance activities on a cyclical basis. This provides assurance that these assets are inspected and in good working order. Cleaning or cleansing activities are usually all that is required but if further defects exist these can be captured as part of the cyclic operation. Highway users can view the following website to discover when a gully was last cleansed and the maintenance frequency for the next cleanse here.

However, a proactive cleansing regime can only go so far and with budget pressures the frequency of cleansing is a challenge to maintain. Drainage assets operate in a dynamic environment and individual assets can suddenly be overwhelmed by weather events. A reactive approach is also needed to ensure flooded roads and surface water issues are managed appropriately. Public knowledge is crucial to keeping the network available in such circumstances. Highway users can use the website above to report a blocked drain or a flooded road:

The website also provides details of the current level of service that Devon Highways will respond to and enables users to report on a map-based system which also shows if others have reported a particular fault.

Additional cleaning and minor repairs to drainage assets may be carried out following complaints, flooding, claims or in known problem locations as identified by local teams.

4.3 Renewal or replacement

Repair or renewal of drainage assets are carried as part of planned schemes:

As part of major structural or drainage scheme,
As part of LACP schemes,
As part of other resurfacing schemes,
From safety inspection reports (routine and reactive),
Complaints, claims and reported frequently flooding locations, and
winter maintenance reports of flooding and ice formation on roads.

4.4 Decommissioning of the asset

Not done, except when highway is redundant as part of an improvement scheme.

4.5 Maintenance Service Standards

Maintenance Service Standards were developed which define the service of provision for each asset type based on three levels: Safety, Safety and Serviceability or Safety, Serviceability and Sustainability. These are defined in terms of what a road user could expect to see. This is useful in understanding the level of service in the context of what is affordable.    

As pressures on budgets continue and become more restrictive, the ability of the Council to provide a service above that of safety is going to be severely impacted.  

The tables below show the maintenance standards for Drainage on each road category.

Drainage (Gullies)	Provision of safety related issues only	Provision of safety and minimal level of serviceability	Provision of safety and intermediate level of serviceability	Provision of safety, serviceability, and sustainability issues
What a road user would see	Gully may be blocked or overgrown. Grating and frame may be damaged and sunken.	Gullies working most of the time. Grating and frame condition may be poor.	Most gullies working particularly in high-risk areas. Grating and frames in satisfactory order.	Gully seldom not working. Grating and frame in good condition and set just below the road surface.
Maintenance standards and activities.	Some reactive cleansing in response to water flooding. No condition assessment.	Very limited routine cleansing in response to water flooding. Restricted scheduled inspection to ascertain condition and repair defects likely to impact on gully performance. Priority given to high-risk areas.	Limited routine cleansing in response to water flooding. Limited reactive inspection in response to flood warnings on designated routes. Limited routine scheduled inspection to ascertain condition & repair defects likely to impact on gully performance. Priority given to high and intermediate risk areas.	Routine cleansing in response to water flooding. Proactive inspection in response to flood warnings. Routine scheduled inspection to ascertain condition & repair defects likely to impact on gully performance. Extended programmes of maintenance undertaken to optimise future condition and to reduce backlog of maintenance requirements.
Impact	Impact – Likely failure of systems resulting in surface water. Increased likelihood of claims.	Impact – Some flooding and surface water Limited priority and investment. Limited mitigation of claims.	Impact – Some flooding and surface water Limited condition assessment enabling structured prioritised investment. Reduced mitigation of claims.	Impact – Occasional flooding and surface water Increased inspection frequency on wider network. Condition assessment enables for investment. Mitigation of claims and increased response to customer requests.

Fig. 4.3: Maintenance Standards for Drainage

Carriageway Hierarchy	Service Level	Carriageway Hierarchy	Service Level
3 Rural		3 Urban
4 Rural		4 Urban
5 Rural		5 Urban
6 Rural		6 Urban
7 Rural		7 Urban
8 Rural		8 Urban
9 Rural		9 Urban
10 Rural		10 Urban
11 Rural		11 Urban

Maintenance Standard 1	Provision of Safety, Serviceability and Sustainability
Maintenance Standard 2	Provision of Safety and intermediate level of Serviceability
Maintenance Standard 3	Provision of Safety and minimal level of Serviceability
Maintenance Standard 4	Provision of Safety only

Fig. 4.4: Maintenance Standards for Drainage for each Road Category

5. Levels of Service and Investment Strategy

5.1 Levels of Service

Current level of service, informed by condition assessments if available, against the stated Levels of Service in the Plan, funding and Risk assessments.

Levels of Service demonstrate the relationship between the Council’s corporate objectives, including the Strategic Plan for 2021 – 2025, and the performance of highway assets in terms of stakeholder requirements. The Levels of Service represent the fundamental service aimed at helping to deliver a road network which is as safe, reliable and as fit for purpose as possible within the current funding and resource constraints. Table 4.6 is an extract from the Strategy and shows the Levels of Service measures for Drainage along with an indication of how they relate to the Council’s Levels of Service Statements.

Service	Measure	Responding to the climate emergency	Be ambitious for children and young people	Support sustainable economic recovery	Tackle poverty and inequality	Improve health and wellbeing	Help communities to be safe, connected and resilient
Drainage	Investigate reports of highway flooding and damaged or blocked highway drains and take appropriate measures to keep water off the highway, alleviate or mitigate flooding as appropriate.	√		√	√		√
	Prepare a cyclical programme of gully cleansing.	√		√	√		√
	Jet drainage systems on a reactive basis as they are reported or found through inspection.	√		√			√
	Carry out an annual programme of grip cleaning and cutting.	√		√			√

Fig. 4.5: Levels of Service for Drainage

5.2 Investment Strategy

It is challenging to determine the level of funding required to maintain the drainage assets. Each year there is a planned cyclic approach to inspect and cleanse road gullies, and other drainage features. This is funded through the revenue budget. Provision is also made to address defects identified with drainage assets by ensuring drainage jetters and minor works gangs are available throughout the year. Regrettably the funding available is insufficient to address all defects, such as road ploughing, blocked drains, broken and stuck gully covers, so such repairs are prioritised on a local basis.

Demands for drainage improvement works such as renewal of drains or improved drainage systems are funded from the capital programme. Repairs of this nature are largely integrated with road surface and footway needs and the overall investment is determined by the level of funding available and the overall quantity and condition of roads in each local area.

6. Programme Development

6.1 Identifying Schemes for an Initial Works Programme

Locations requiring renewal or new drainage assets are identified through highway inspections/observations, where an issue could arise/ occur resulting in highway flooding and possible structural damage. Locations where historical highway flooding or ponding on the road occurs, or where excessive surface water flows in the channels.

Fig.4.6: Identifying Schemes for an Initial Works Programme

6.2 Selecting and Optimising Schemes for the Forward Programme

Highway drainage improvement schemes are selected for Local Asset Capital Programmes (LACP) using the following guidance:

Where highway surface water is contributing to residential or commercial property flooding,
Where flooding or ponding on the highway is presenting a hazard to road users,
Where seepage or water crossing the highway on bends and gradients is liable to cause aquaplaning or formation of ice,
To eliminate damage to the highway surface requiring immediate works,
Cyclic maintenance of drainage assets, and
From highway inspections where defects are identified.

7. Risks

The greatest challenge is funding, understanding the implications of under investments on the overall condition of our drainage assets. Reduced maintenance standards impact the ability of the assets to function correctly which can accelerate deterioration of road and footway surfaces.

Capability of current drainage assets to cope with increased extreme weather events.

Increased run-off caused by changes in land use.

The likely consequences that we can expect are:

Increase in the likelihood of flooding incidents on the highway,
Increased risk of flooding & damage to properties and highway assets,
Increased risk of embankment damage caused by drainage assets not functioning correctly,
Increase in the cost of cleaning gullies, drainage systems and maintaining roads due to increased erosion and damage from water, and
Roads being temporarily closed more frequently due to flooding, and for maintenance work to be undertaken, leading to negative economic and reputational impacts for the people of Devon and the Council.

8. Improvement Actions

Alongside the Highway Infrastructure Asset Management Plan, this Annex is a live document. It will be subject to continuous improvement and ongoing development with input from Council Officers and Stakeholder feedback. Areas for improvement are identified within the Annex which are summarised as Improvement Actions in this section. These Actions are aligned with Strategic Goals and are assessed as part of a wider cross-asset prioritisation process that prioritises their implementation taking account of the framework of funding and resource availability.

The actions that have been identified as being required to ensure the Drainage asset management objectives are achieved are:

Improve and increase asset data collection to better inform decisions for maintenance, and LACP capital investments i.e., frequency of cleansing of Gullies, Grips, Easements and Buddleholes,
Develop a more targeted risk-based maintenance regime, clean problem gullies before storm events, understand cost of delivering effective maintenance policy and programmes,
Review training needs to upskill our staff in designing and delivery of drainage schemes, and managing defective drainage assets, and
Improve collaboration with the Flood Risk Teams and other stakeholders in Devon.

Version Control

Version	Date	Summary of Changes
1.0	12 April 2023

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Annex 4 – Drainage

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