Clearance and repair to reduce flood risk: local authority guidance

6. Works of Clearance and Repair

6.1 Definition

Clearance and repair works

Works that consist of any or all of the following:
(a) removing obstructions from a body of water,
(b) removing things that are at significant risk of becoming such obstructions,
(c) repairing artificial structures which form part of the bed or banks of a body of water.

The focus of clearance and repair works are therefore clearly dealing with 'clearance' of obstructions and 'repair' of artificial structures. These areas are considered further in this chapter along with consideration of erosion and sediment management, which may be a cause of obstruction.

6.2 Obstructions

Removing obstructions or the risk of obstructions are works of clearance and repair under the Act.

Obstructions could include:

• Rubbish or natural debris blocking or partially blocking a structure such as a culvert so giving rise to flooding with substantial adverse consequence. However, care should be taken not to destabilise the systems with any works undertaken.
• Rubbish or natural debris in the channel significantly reducing its hydraulic capacity so giving rise to flooding with substantial adverse consequences
• Vegetation (noting issues with Invasive Non-native Species) within the channel significantly reducing its existing hydraulic capacity so giving risk to flooding with substantial adverse consequences
• Sediment is accumulating within a channel significantly reducing its existing hydraulic capacity so giving rise to flooding with substantial adverse consequences.

Things at significant risk of becoming obstructions could include:

• Where rubbish, natural debris or riparian vegetation is close to a structure such as a culvert or bridge and is likely to block or partially block the structure which could result in flooding with substantial adverse consequences, or in the extreme damage the structure itself.
• Where rubbish, natural debris or riparian vegetation is likely to restrict the channel significantly reducing the hydraulic capacity which could result in flooding with substantial adverse consequences.

Example – removing an obstruction or potential obstruction by modification

A large culvert passing under the West Coast Mainline was subject to significant blockage due in the main to large woody debris getting trapped. This backing up of flow did not impact upon the railway but did cause significant damage to a public road and led to property flooding. One of the mitigation measures, undertaken by the upstream landowner was to put in a programme of inspection of the watercourse including the banks. Any fallen trees either in the watercourse or adjacent to the watercourse were removed or if this was not possible, were cut into small pieces that upon entering the watercourse would not cause a blockage issue. Local Authorities should consider that option of on-site cutting rather than physical removal of debris.

6.3 Artificial structures

Repairing artificial structures which form part of the bed or banks of a body of water to substantially reduce the flood risk are works of clearance and repair under the Act.

Artificial structures forming part of the bed and banks of a water body could include:

• Weirs, culverts, bridges, floodwalls and floodbanks, whether or not these are set back from the natural banks, and/or constructed as part of a statutory Flood Protection Scheme and any ancillary apparatus such as flood gates.

Where an artificial structure has not been constructed as part of a Flood Protection Scheme, the local authority may choose to carry out works where substantial flood risk will be prevented; any such works should be proportionate to the risk as well as the benefit. Where an artificial structure forms part of a Flood Protection Scheme then guidance on Part 4 duties should be referred to.

Where these works to artificial structures would exceed the definition of clearance and repair they should be carried out under the relevant section of the Act. For instance, extensive investigatory works required to establish the stability of an artificial structure may require a substantial flood study which could take it beyond the scope of clearance and repair and into a separate measure within a Local Flood Risk Management Plan.

The test in all cases is whether the execution of clearance and repair works would substantially reduce the risk of flooding and is a proportionate response to the risk.

The process to be followed in undertaking assessment of bodies of water, which may lead to clearance and repair works or other actions to be recorded on the section 18 schedule is shown in the flowchart in (in Guidance Flow Chart fold-out – see appendix 9.6).

Example – Replacement not repair

A culvert on a steep hillside above residential property was found to be in a poor condition with an inlet screen both inaccessible and of below-standard design. Repair works had in the past been carried out to both the screen and the culvert, with short sections excavated and replaced.

The condition of the culvert and the screen was a cause for concern in terms of substantially increasing flood risk. The small nature of the screen meant that it was forever blinding leading to over-topping.

Rather than continue to undertake repair works to the culvert the decision was taken to replace as a works of "clearance and repair". This also offered the opportunity to replace the screen with one that met current standards and was situated in an accessible location.

There are many artificial structures which form part of the bed or banks of a water body but which do not serve a flood risk management purpose, for example walls marking a property boundary or a retaining wall protecting land from erosion or land slip.

The Act does not affect the primary responsibility of riparian owners for their own property so the repair of, for example, damage to a garden wall through scour is a matter for the relevant owner. However, these may also become matters for the local authority under the Act if there is an immediate or on-going flood risk.

Riparian ownership and responsibilities

Riparian owners are those whose property adjoins a watercourse. Ownership may stop at the bank or extend to the centreline of the watercourse. Assuming there is no other legal undertaking by another, riparian owners will generally have the authority to undertake works of clearance and repair to the watercourse banks, subject to appropriate permissions ( e.g. CAR licence, Planning Permission, etc.).

Local authorities in the past have considered that riparian owners have responsibility for maintenance. Good relationships with landowners, farmers, estates, etc. will be beneficial in terms of encouraging the maintenance of watercourses and riparian areas to reduce flood risk. However the riparian owner has no duty to undertake works of clearance and repair, merely the authority to do so, and this clearly has the potential to lead to the local authority having to gain access to undertake works of clearance and repair if assessment determines such work should be scheduled.

Local authorities have held primary responsibility for the repair of many artificial structures which serve a flood risk management purpose and which have been promoted by them under the Flood Prevention (Scotland) Act 1961 or Roads (Scotland) Act 1984, etc. or have otherwise been acquired in the course of their wider functions for example, leisure and recreation. Authorities should review their internal asset management procedures to ensure compliance with the Act, and that opportunities for better coordinated services are explored.

Repair of artificial structures could generally be considered as any repairs which would be expected in the ordinary course of good maintenance, such as the repair of a flood bank affected by erosion whether by river flows or by the passage of livestock or other traffic or the effects of burrowing animals or maintaining ancillary apparatus such as flood gates, flap valves and trash screens to ensure operational efficacy of the apparatus in flood conditions. Again, the test would be that carrying out the repair would substantially reduce the risk of flooding.

Example – Artificial bed of banks of a body of water

A mill lade was constructed from stone. At points along the watercourse there were boundary walls separating the garden from the lade.

The wall of the mill lade, below adjacent ground level was subject to scour with the potential for not only the lade wall to collapse, but also for the boundary wall above to collapse. Given the relative size of the lade and the boundary wall, it was clear from assessment that the boundary wall was a significant risk of becoming an obstruction, should it be completely undermined.

Repair works were undertaken to the wall of the lade, including the removal of the boundary wall. The reinstatement of the boundary wall was not part of the local authority funded works.

6.3.1 Considerations of agricultural embankments

The integrity of an artificial structure against flooding depends on its weakest part. So, when contemplating a repair of a flood bank for example, an authority should consider the integrity of the overall flood bank and not simply any section of it in need of local repair. Where the condition of a defence is so poor that local repair, say of a breach, might not substantially reduce the risk, an authority should investigate and consider all relevant options, such as new build on an alternative alignment and removal of the embankment allowing land to flood and only include repair works in its clearance and repair schedule after it is satisfied itself that this is the most sustainable option.

With respect to the assessment of agricultural flood embankments and the need to undertake repairs to reduce flood risk, local authorities should be mindful of the following. Agricultural embankments were constructed principally to improve agricultural land and while they may now offer some, often limited protection to small numbers of residential property, their presence is often restricting the river from its natural floodplain. In doing so, the presence of an agricultural embankment may in fact make flood risk at a downstream settlement greater. In considering undertaking, or being requested to undertake repairs to agricultural embankments, local authorities should consider whether actually leaving breaches reduces flood risk in downstream settlements by bring back into use the floodplain, even though there may be a local increase in flooding to agricultural land.

6.4 Other works of clearance and repair

'Removing things that are at significant risk of becoming such obstructions' and 'repairing artificial structures which form part of the bed or banks of a body of water' are works of clearance and repair that can be precautionary. It is therefore considered that there are some key elements of works of clearance and repair that should be considered in assessments, for example erosion and sediment management.

In addition, objectives to reduce flood risk though Natural Flood Management (' NFM') are included in Local Flood Risk Management Plans. Erosion control and sediment management are underlying principles of NFM. As is explicitly required under the Act, section 18 and section 59 activities must contribute to the implementation of current measures described in any relevant local flood risk management plan or otherwise not affect such current measures.

6.4.1 Erosion

Erosion of watercourse banks or embankments is a natural process and over time a watercourse will inevitably chose a different route. Management of the route of a watercourse should be undertaken with care as constraining in one location could have implications for another location, potentially increasing scour. A precautionary principal should be applied unless there is evidence that intervention would substantially reduce flood risk.

In many urban situations watercourses will be constrained or controlled by artificial banks. In situations where there is evidence of scour damage to artificial bed or banks of a body of water consideration should be given to the impacts this will have on flood risk. For example, the natural scour of a garden, even one protected by rock armour, may not increase flood risk. It may result in the loss of a section of the garden, but this does not necessarily equate to increased flood risk.

There may be an issue with erosion if said erosion is impacting on a structure adjacent to a watercourse that offers a level of flood protection, which have the potential to block and cause flooding. For example, scour of the base of a river bank or riverside embankment may lead to failure . If that failure then leads to increased flood risk during high flows or afterwards, repair works may be required to be scheduled in accordance with s18.

6.4.2 Sediment management

The management of sediment through removal of gravel berms above natural bed level or dredging below bed level is often viewed as a flood risk management option. In smaller watercourses, accumulations of sediment may significantly contribute to flood risk, generally, where watercourses have been historically modified. However interventions of this nature should be undertaken with extreme caution as in addition to the potential environmental impacts, it is likely that having undertaken gravel removal / dredging, there will be an expectation to continue to undertake such works regularly.

Dredging and gravel removal can be modelled when undertaking flood risk assessments and this can be useful for engagement with the public. However, to undertake such modelling work for every request for gravel removal or dredging is clearly not practical.

When it is not practical to undertake direct study, it is worth directing public to the very-readable 2014 publication from CIWEM entitled Floods and Dredging – A Reality Check states:

"Dredging of the river channels does NOT prevent flooding during extreme river flows" and

"It is simply not practical to contemplate dredging of the channel (let alone the floodplain) to the extent that would be required to confine such large and rare flood flows from the wider floodplain, since the storage and conveyance capacity of the channel is a small fraction of that of the wider floodplain. In this respect, dredging cannot prevent flooding."

Further information on sediment management, dredging and its effectiveness are available in the SEPA leaflet on Floods, found at https://www.sepa.org.uk/media/147022/floods_dredging_and_river_changes.pdf .

6.5 Scale of works required and a proportional response

The application of a pragmatic approach to the assessment will see that in the main large watercourses are unlikely to benefit substantially from works of clearance and repair. While gravel build-up may reduce waterway capacity, at flood flows its volume will be so insignificant as to offer no measurable benefit in removal.

Likewise, the collapse of a small retaining wall into a large river is unlikely to lead to significant increase in flood risk, so repair works to the bed of banks of a body of water is unlikely to be undertaken in accordance with requirements under section 18. It may however be necessary to undertake this kind of repair to prevent failure of public road.

Clearance and repair works can range from minor works such as raking out woody debris/ leaves from the face of a culvert or screen to the reconstruction of a major culvert or screen. A watercourse inspector is able, following a risk assessment, to carry out such minor works during their inspections. 'Little and often' good watercourse husbandry/ stewardship can in itself, substantially reduce the probability of flooding from watercourses.

If there is a high likelihood that the removed material may be washed back into the watercourse or dumped back into the watercourse, then an item would be raised in the section 18 Schedule for the waste material to be removed from site (this may not be undertaken by the inspector due to not having the appropriate vehicle for such tasks).

For such minor works, it would be disproportionate response to sit down, with a risk matrix or hydraulic model to assess the effect of the proposed works in order to determine whether it would substantially reduce the risk of flooding. Common sense and engineering judgement are all factors that should be employed to make decisions whilst on site. The initial (pre) and post condition of the watercourse should be noted and photographed on their inspection records, but adding this item (which is already completed) to a section 18 schedule is considered to be of little benefit and overly administrative.

Medium scale works may be classified as works which the inspector would not be able to carry out as it requires plant and more resource (usually provided through the Direct Labour Organisation). These works cannot be completed at the time of the inspection, and a Works Item/Order may need to be processed between departments and planned. In order to justify whether or not an item should be placed on the section 18 schedule, the local authority may choose to develop a simple risk matrix to assess the pre and post flood risk. Alternatively, a discussion with Engineering staff and Area Managers may be sufficient to draw out the relevant factors to be considered, and benefits of carrying out the proposed works. Either way, a logical reasoned process should be employed and recorded. If the works are necessary and of benefit, then these works should be added to the section 18 schedule. This records that the local authority has identified clearance and repair works that will substantially reduce flood risk, and will carry them out (in due course, when resources and funds allow). A decision not to add an item to the schedule should be recorded on the Inspection Records for review during the next inspection.

Medium scale works may still be authorised under General Binding Rules, but if there was any doubt SEPA should be consulted.

If the works considered to be necessary were of significant scale, the item would be placed on the section 18 schedule as above, but it may be that more detailed assessment (using modelling) would be required in order to justify the expenditure and gain permissions through CAR.

What constitutes 'substantial' cannot be given a definitive description and to try and do so is likely to 'water down' the value of the section of the Act. The important issue is to document the decision taken for each scenario, evaluating risk and the associated reduction to justify undertaking works, or perhaps more contentiously not to undertake works.

For the majority of 'minor' clearance and repair items, a 'common sense approach' should be employed and this will draw on the experience of the inspector and flood risk staff.

Generally where an inspection and initial assessment identifies clearance and repair items that would require greater expenditure or resource, a more technical approach using hydraulic modelling may be required in order to determine the existing condition and post clearance works condition to quantify the reduction and benefits.

Assessing the impact (what would be affected, what would be the damage caused and to what extent) can help put the problem into some perspective. Whilst the Act requires Local Authorities to assess adverse consequences to 'human health, the environment, cultural heritage and economic activity' it is pragmatic for a local authority to prioritise the relative significance of these. This approach is consistent with the broader plan-led, risk-based and prioritised approach being applied to flood risk management planning.

For example, a fallen tree in a watercourse that would clearly result in out of bank flooding affecting a medical centre should be scheduled section 18 works as to not carry out the work would have significant consequences for human health. If the same scenario would result in flooding to a lower risk receptor , the impact would be viewed as being of lesser significance (and therefore of lower priority). Both scenarios may need to be identified on the schedule 18 schedule, but the time for the next assessment (and likely visual inspection to inform the assessment) may be significantly different.

Having placed the item on the schedule, the local authority is duty bound to carry out the works. However, it would be reasonable for an Authority (with limited resources) to prioritise the works required at the medical centre over that of the low risk receptor, e.g. a field, the local authority may set a longer period for re-inspection to allow them time to liaise with the landowner affected, or those with riparian responsibilities under common law, to get the works carried out.

Other relevant matters

Section 17 refers to mapping of 'relevant bodies of water and sustainable urban drainage systems'. Section 18 takes forward the assessment of these 'relevant bodies of water'. 'Relevant body of water' is defined clearly in section 17(5). Whether a local authority chooses to assess a body of water this does not determine whether it is 'relevant' under the Act.

The risk of flooding refers to a risk from the body of water assessed and not the risk of flooding from an isolated section of a body of water. From this it is implied that should clearance and repair of a section of watercourse result in a significant reduction in flood risk to a section of land at the expense of another section of land associated with this watercourse, then the works may not be appropriate to be included in the section 18 schedule. For example, repair of an embankment may lead to a substantial reduction in flood risk to an area of agricultural land whilst also resulting in an increase in flood risk to a residential area downstream due to loss of flood plain. In this situation taking the body of water as a whole, there may not be an overall substantial reduction in flood risk and the item should not then be added to the section 18 schedule.

Not all 'blockages' or items at risk of blockages should be seen as a negative. A build of woody debris can help slow the flow of water, create natural meanders and habitats for ecology and make use of natural flood plain. These NFM factors should be taken into consideration when weighing up the consequences of flooding from the identified risk.

The Act does not make any reference to available budget for the authority to undertake clearance and repair works and budget is not a consideration in whether or not the item of works is added to the s18 Schedule. Therefore, whether the authority has a lesser or greater budget for watercourse maintenance, and whether there has been proportionately greater or lesser weather impacts affecting the volume of items of clearance and repair, these factors should not influence the inclusion of works on the section 18 schedule.

A lack of budget or a high quantity of section 18 schedule items requiring attention may be justification for an authority not carrying out all items contained within the section 18 schedule, but should not form justification for not having added the item to the Schedule in the first place.

As detailed elsewhere in this guidance, section 59 places a duty to undertake the works described in the schedule, subject to conditions. Although it is of note that there is no indication of timescale to undertake the works. There is however, through section 18(3)(a) a duty to identify when the authority will re-assess items which are on the section 18 schedule. In an ideal scenario, the timeframe provided for re-assessment would provide sufficient time for the authority to undertake the required works such that when re-assessed, the risk of flooding has been substantially reduced and the item can then be marked as complete. However, there are a number of reasons why the works may not have been undertaken within the time period for re-assessment. In such circumstances, the flood risk is re-assessed and a new timeframe is added to the schedule identifying when the item is to be further re-assessed. The following scenarios are possible:

• since the original assessment, the item has cleared, either due to landowners undertaking riparian responsibilities, or due to having been cleared by flow in the watercourse and can now be removed as there is no longer a need to substantially reduce flood risk;
• the item remains as it had been previously and the risk of flooding has not changed, in which case the time for re-assessment would be re-established as it had been originally;
• there is a further increase in risk of flooding and the timeframe for re-assessment is reduced.

6.6 Justification for not adding works to the section 18 schedule

Based on each of the decision points in the flow chart (in Guidance Flow Chart fold-out – see appendix 9.6), the following are examples of reasons why items may be considered as not requiring to be added to the section 18 schedule:

• Item not classified as 'clearance & repair' – guidance already provided earlier in the document.
• Item presents low risk of out of bank flow – An item of 'clearance & repair' may be evident yet the consequence is such that predicted flows would still remain within the watercourse channel.
• Item does not represent adverse consequence on receptors – Out of bank flooding occurs but does not impact on human health, the environment, cultural heritage or economic activity. It is considered acceptable for flooding to occur to areas of scrub land and areas of land where flooding is not considered to represent an adverse consequence (note that the duration of flood water on such land may have a bearing on whether or not adverse consequence is significant – it may be acceptable for a park to be under water during a flood for a day but not for it to be flooded for a week). Note should also be taken that where the previous Act did not apply to agricultural land, this is no longer the case.
• Works would not substantially reduce flood risk – Natural transportation of sediment/gravel within a watercourse may lead to deposition with the consequence that flow capacity is significantly reduced at a particular location. Removal of such deposition may increase flow capacity, however if it is considered that flood flows would immediately replace the deposited material, then there is no 'substantial' reduction in flood risk. In this scenario it may be prudent to address the source of transported material. It may be that a particular area of erosion represents 'things that are at significant risk of becoming such obstructions'
• The costs disproportionately outweigh the benefits.