Delivering sustainable flood risk management: guidance (2019)

2. Understanding and working with catchments and coasts

Introduction

Actions that affect one part of a river, coast or estuary can have consequences elsewhere. This means that flood management actions are most effective when they are planned and coordinated within catchments and along coasts in a way that is uninhibited by administrative boundaries.

Adopting a catchment approach to flood risk management requires an appreciation of catchment and coastal processes, and an understanding of how best to manage the sources and pathways of flood water. This includes looking at how the timing, magnitude and duration of a flood can be managed, e.g. by creating, restoring and enhancing natural features and characteristics of the landscape, including wetlands, woodlands, vegetation, functional flood plains, saltmarshes, beaches and dunes.

This section provides guidance on:

• setting appropriate units of management;
• the application of a source-pathway-impact approach to flood risk management;
• the role of land use and natural flood management in managing flood risk including actions in urban areas;
• promoting and balancing the needs of those living and working in rural areas.

Catchment management units

SEPA and the responsible authorities must coordinate their actions to tackle flood risk across catchments. In most cases this will require coordination of actions at the scale of the river basin or sub-basin- i.e. a catchment that drains to the sea (Figure 3). At the coast, flood risk management should be planned and coordinated within coastal cells.

This move away from an approach based on administrative boundaries has been successfully promoted by SEPA and the responsible authorities. Primarily this has been through the Local Plan District Partnerships and led to the publication of the Flood Risk Management Strategies in December 2015 and Local Flood Risk Management Plans in June 2016. The catchment and coastal cell approach should be further developed and strengthened through the implementation of flood risk management actions and the land use planning process.

In some cases it may be appropriate to sub-divide river basins into smaller catchments (also referred to as sub-basins) to allow for more detailed assessment and analysis of management options. When assessing options to tackle urban surface water flooding, urban drainage catchments can be defined to promote detailed analysis of the urban landscape as long as it is considered as part of the wider catchment.

Where river basins are separated into smaller catchments, the interactions, physical and ecological, with the larger river basin in which they are located must be understood.

Figure 3 Basins, sub-basins and urban catchments

SEPA should work closely with the other responsible authorities to identify the appropriate spatial scales and catchments around which flood risk management efforts should be targeted.

Understanding catchments

Our natural landscape can play an important role in managing flood risk. Over time, human activities have altered the character of our landscape and affected the timing, magnitude and duration of floods. For example, urban creep, loss of natural floodplains, compaction of soils, changes in land cover and increased field drainage can all increase run-off and peak flood flows.

Creation, restoration and enhancement of natural features of the landscape (e.g. floodplains, wetlands and forests) can help to restore more favourable run-off patterns and reduce flood risk whilst at the same time providing widespread multiple benefits beyond flood risk management.

These more natural techniques typically aim to protect, emulate or restore the natural processes which regulate flooding and erosion, often by keeping water in areas where it will cause less damage. Examples include:

• improving water storage and capturing run-off by restoring, protecting or enhancing soil condition and woodland areas;
• reconnecting floodplains, restoring wetlands or creating ponds and reservoirs to help store flood waters;
• planting vegetation and managing hill slopes to help slow run-off;
• restoring watercourses to a more natural channel form by removing culverts and other structures that constrain channels and can contribute to flooding during high flows.

In urban areas, green roofs, permeable paving, flood and surface water attenuation ponds, opening up and realigning watercourses, and establishing green spaces and blue corridors are equivalent examples.

To provide insights into the causes of flooding and the types of management options available, SEPA, in close collaboration with the responsible authorities and other organisations with an interest in catchment management, should work to develop an improved understanding of the hydrological, ecological and geo-morphological condition and functioning of Scotland’s catchments. This should include assessments of the effects of human interventions on flooding processes.

The condition of our soils, our water resources and the health of our ecosystems are all influenced by processes that occur within and across catchments. Understanding and managing these interactions will create opportunities to invest in actions that can simultaneously reduce the risk of flooding, while also improving the quality of our natural and urban environment. SEPA should ensure that information generated on catchment characteristics and natural features can assist with the selection and design of environmentally sensitive defences or other actions. Further, this information can be used to support other work areas, including river basin management planning, biodiversity, benefits for amenity and people, and landscapes as well as providing greater resilience to future change.

SEPA is also responsible for assessing how the restoration or enhancement of natural features and characteristics of catchments could contribute to managing flood risk. SEPA has published maps^[2] showing the areas where implementing natural flood management techniques could be most effective. These maps will help to inform flood risk management decisions and should be used in conjunction with other relevant information and more detailed site specific assessments.

SEPA should develop guidance for responsible authorities to help them identify any additional costs or benefits that can be delivered from these actions, thus ensuring that the full value of these options can be considered.

Understanding coasts and estuaries

Attempts to interfere with the changing nature of the coast and to fix its position have been made in the past with varying degrees of success. Built structures can lead to enhanced erosion further along the coast or just offshore. This is due to an interruption to the natural supply of sediment or alterations to currents and waves. Coastal flood and erosion risk must be managed in a way that takes account of natural coastal processes and how the wider coast will respond to the impact of such works.

The risk of coastal floods will increase as the sea rises higher up the foreshore or onto existing defences. In areas of shallow water, rising sea level will also be accompanied by increases in the height and energy of waves that reach the shore. Climate change impacts on coastal flooding could in future be greater than for river or surface water flooding.

Accelerated coastal erosion that accompanies these conditions can remove protective beaches and increase the risk of flooding by allowing larger waves to approach the shore. Coastlines such as sand and shingle beaches can however be resilient to climate change if there is enough space to allow the natural cycle of erosion and deposition to take place.

Enhancing existing natural features or natural processes can help to reduce flood and erosion risk in a way that has less adverse impacts to adjacent areas and has wider environmental and societal benefits. Examples include transferring additional sediment to a beach, re-profiling a beach to maximise its potential to absorb wave energy and creating saltmarsh in estuaries.

It is vital that the best understanding is developed on coastal flood and erosion risk, how that risk may change over time and how it should be best managed in a sustainable manner.

State of knowledge and using reliable science

The state of knowledge on natural flood management techniques has progressed and continues to improve. SEPA should draw on its broad scientific expertise to advise its partners and the wider stakeholder community on the benefits and role of these techniques. This should include supporting research and promoting demonstration projects to validate the research work.

The uncertainties associated with using more natural approaches have been greater than those for more traditional engineering. These uncertainties are diminishing as the evidence base expands. It is important to take a pragmatic and proportionate approach to deal with uncertainty. Uncertainty should not be a barrier to adopting these techniques where it is appropriate to do so. For example, where uncertainty is around the scale of flood risk benefits that can be achieved, and no adverse impacts have been identified, it would be appropriate to proceed with implementation on a ‘no regrets’ basis.

Natural flood management techniques which seek to restore the landscapes ability to reduce runoff to store flood water and to absorb wave energy at the coast have multiple benefits for the water environment, associated habitats and for people. Interventions should however be designed and implemented in a manner so that flood risk is not inadvertently increased.

SEPA and the responsible authorities must ensure that these uncertainties are examined and communicated to those who may benefit or be affected by the use of these techniques.

Flood risk management and adaptation

Due to the likely impacts of climate change, in some locations, it may become increasing difficult both technically and financially to maintain current levels of flood risk and erosion protection.

It is important that long term plans are made to determine how best to respond to changes in flood risk. Strategies can allow for continued protection from flooding in the short to medium term, but in parallel may need to develop longer term proposals to move critical infrastructure and development away from areas at increasing risk of flooding and erosion. Taking early decisions, informed by the best science, can allow for greater flexibility in terms of future management and adaptation to coastal change. To this end the National Coastal Change Assessment^[3] maps historic rates of erosion and accretion along our coastline and projects these rates forward to a future coastline for 2050 and 2100.

Adaptive actions such as relocation will not be easy to implement and it is important that any affected communities, businesses, land and asset managers are fully engaged in developing a common understanding of the pressures facing rivers and the coast and in developing adaptive strategies for the future. Based on experience elsewhere in the UK and across the world, the coast is the area where the greatest need for adaptation will be in the future.

Promoting and balancing the needs of rural areas

Rural land use is important to a successful Scottish economy. There are many and varied demands already placed on land managers, and rural land use contributes to delivering many wider economic, environmental and social benefits, with a large number of people directly employed in these sectors. A large proportion of Scotland’s land is under agricultural production and the sector is responsible for much of Scotland's domestic food supplies and exports.

Some of the greatest opportunities to restore our landscape’s natural capacity to cope with floods are in rural areas. In preparing flood risk management strategies and local flood risk management plans, SEPA and local authorities should consider carefully the views and needs of land owners and rural businesses so that the correct balance is struck between all competing demands on rural areas.

It is important that land management changes are focused at a scale/ distance that is relevant to the area at risk of flooding.

The Scottish Government provides funding to enable local authorities to deliver general duties under the Act, including, where appropriate, natural flood management. Traditionally, some funds are available to support voluntary action, including the Scotland Rural Development Programme (SRDP) and the Water Environment Fund. The SRDP supports actions that reduce the effects of pollution, deliver biodiversity benefit, flood risk management and other societal and environmental benefits. Funding opportunities may change as the UK’s relationship with the European Union evolves.

SEPA and the responsible authorities should consider carefully how the range of existing funding routes and instruments can be used to support flood management and wider restoration initiatives and, in particular, how local authority powers under the Act can be used to deliver flood risk reductions through land management. For example, in allocating funding for environmental improvements SEPA should give consideration to promoting projects that deliver coincident flooding and environmental benefits.

Where land management and restoration forms part of a flood protection scheme, local authorities have a new wide range of powers to compensate land managers. Options include one off payments, service agreements and compulsory land purchase. In all cases voluntary action or voluntary agreements should be pursued. However, the voluntary agreements still need to be set down in a legal framework which gives both parties security.

The Scottish Government will continue to work with stakeholders and local authorities to ensure that local authorities have access to a toolkit of options for delivering improved flood risk management and a reduction in flood risk. Particular attention will be paid to any limitations of current instruments and to instruments that encourage land owners to participate through voluntary actions^[4].