The SuDS Manual

Part C : Applying the approach

Part D : Technical detail

Part B : Philosophy and approach

Part E : Supporting guidance

Appendices

WHY SUDS?

There are four main categories of benefits that can be achieved through SuDS: water quantity, water quality, amenity and biodiversity. Continuous pavements provide a hard surface that can be used by pedestrians or vehicles, while allowing rainwater to pass through to the ground or underground storage. High quality SuDS designs integrated into the overall design of the development can attract tourism and investment, driving economic growth for the local area.

When SuDS are designed to make efficient use of available space, they can often cost less to implement than underground piping systems. SuDS can be used for new buildings and renovations and can be retrofitted into existing buildings. Most sites present challenges of one kind or another, but the range of SuDS components and solutions available means that effective SuDS schemes can be provided for all developments with timely involvement of the appropriate expertise.

Assemble the right team early in the process, so that urban planning, landscape architecture, architecture, drainage design and environmental aspects can be considered together. A range of resources for those involved in delivering SuDS, including case studies, videos, presentations, fact sheets and links to research, can be found at: www.susdrain.org.

SCOPE OF GUIDANCE

DELIVERING MULTIPLE BENEFITS

Sustainable Drainage Systems (SuDS) can deliver multiple benefits Surface water is a valuable resource and this should be reflected in the way it is managed and used in the built environment. The philosophy of sustainable drainage systems is about maximizing the benefits and minimizing the negative impacts of surface water runoff from developed areas. The SuDS approach involves slowing and reducing the amount of surface water runoff from a developed area to manage downstream flood risk, and reducing the risk of that runoff causing pollution.

Water then becomes a much more visible and tangible part of the built environment, which can be enjoyed by all. To maximize these benefits, surface water management needs to be considered from the start of the development planning process and throughout – affecting site layout and design, and the use and characteristics of urban spaces (see Case Study 1.1). There are many different ways in which SuDS can be applied to deliver effective surface water management that is both value for money and inspirational.

SuDS can be used even in the smallest of spaces - the apparent lack of space should never be a reason not to use SuDS. This chapter discusses how SuDS can bring multiple benefits, the importance of managing surface water runoff in a sustainable manner, and what makes a sustainable drainage system.

MANAGING SURFACE WATER RUNOFF

SuDS aims to restore or maintain ecologically significant elements of pre-development runoff processes for a range of flow conditions from low to high rainfall. When surface water runoff washes a developed watershed, it mobilizes sediments, debris, and a wide range of pollutants associated with human activities (such as oils, grit, metals, fertilizers, pesticides, animal waste, salts, and pathogens). Without intervention, these eventually flow into rivers, groundwater and the sea, posing a risk to the environment and public health.

Since the pollution is widespread and comes from many types of sources and locations, it is known as "diffuse pollution" and although individual sources may not pose a threat, collectively they can potentially lead to significant impacts on groundwater or surface water. Grassland and wetlands with native planting (courtesy . Atelier Dreiseitl and GreenWorks) Floating reed beds (courtesy Grant Associates) Figure 1.3 SuDS with natural processes.

DELIVERING RESILIENCE

Water from the rainwater tanks slowly seeps into the living wall, watering the plants, dampening the currents and reducing runoff through evapotranspiration. Green roof (courtesy Green Roof Consultancy) Pond fed with water (courtesy Tim Crocker) Figure 1.4 SuDS provides city cooling.

MAKING DEVELOPMENTS MORE SUSTAINABLE

COMPLYING WITH LEGISLATION AND REGULATIONS

Measures to prevent or control diffuse sources of pollution are a basic requirement of the Directive (Article 11(h)). This effectively rules out the use of the traditional approach to drainage unless special controls are used to slow the flow and treat the runoff. In particular, national and local flood risk regulations and guidelines exist that encourage better surface water management, with some explicitly promoting the use of SuDS (following the Pitt Review, 2008).

National planning policy across the four administrations of the UK requires planning authorities to give priority to SuDS in planning applications.

THE SUDS DESIGN PHILOSOPHY

There are many types of SuDS components, which means that sustainable drainage can be delivered anywhere. These can be "wet", where the water is designed to remain permanently at the bottom of the swale, or "dry", where water is only present in the channel after rainfall events. Engineered soil (gravel and sand layers) and improved vegetation can be used to improve treatment performance.

Trees can be planted within a number of infiltration SuDS components to improve their performance as root growth and decomposition increase the soil's infiltration capacity. This can be paving stone with spaces between solid blocks or porous paving where the water filters through the block itself. Water can be stored underground and potentially allowed to seep into the ground.

Large, underground voids can be used to temporarily store runoff water before infiltration, controlled release or use. Facilities with a permanent pond can be used to provide both attenuation and treatment of runoff, controlling outflow and water level.

THE PRINCIPLE AND OBJECTIVES OF SUDS DESIGN

SUDS DESIGN CRITERIA

THE ROLE OF THE DESIGNER

ASSESSING AND APPROVING SUDS SCHEMES

Health and safety It is safe for those living near or visiting the system, and for those involved in

WATER QUANTITY DESIGN OBJECTIVE
WATER QUANTITY DESIGN CRITERIA
WATER QUANTITY DESIGN STANDARDS
REFERENCES
WATER QUALITY DESIGN OBJECTIVE
WATER QUALITY DESIGN CRITERIA
WATER QUALITY DESIGN STANDARDS
REFERENCES
AMENITY DESIGN OBJECTIVE
AMENITY DESIGN CRITERIA
REFERENCES
BIODIVERSITY DESIGN OBJECTIVE
BIODIVERSITY DESIGN CRITERIA
SUDS DESIGN CHARACTERISTICS TO SUPPORT BIODIVERSITY
REFERENCES
INTRODUCTION
SUDS AND THE PLANNING SYSTEM
SUDS DESIGN AND STAKEHOLDER ENGAGEMENT
STAGE 1: SETTING STRATEGIC SWM OBJECTIVES
STAGE 2: CONCEPTUAL DESIGN
STAGE 3: OUTLINE DESIGN
STAGE 4: DETAILED DESIGN
REFERENCES
INTRODUCTION
CONTAMINATED SOILS OR GROUNDWATER BELOW THE SITE .1 The challenges
HIGH GROUNDWATER LEVELS BELOW THE SITE .1 The challenges
SLOPING SITES .1 The challenges
VERY FLAT SITES
SITES WITH POTENTIALLY UNSTABLE SUBSURFACE ROCKS OR SOIL WORKINGS
SITES WITH VERY DEEP BACKFILL .1 The issues
SUDS ON FLOODPLAINS
REFERENCES
INTRODUCTION
APPROVAL AND ADOPTION OF SUDS IN OR ADJACENT TO ROADS
INTERFACE WITH BURIED UTILITY SERVICES
CONNECTIONS BETWEEN FEATURES BELOW ROADS
APPLICATION OF SUDS FOR ROAD DRAINAGE
ALLOWING WATER TO INFILTRATE IN CLOSE PROXIMITY TO THE ROAD PAVEMENT
FILTER DRAINS FOR ROAD DRAINAGE
SWALES FOR ROAD DRAINAGE
ROADS FOR EXCEEDANCE FLOW MANAGEMENT
TREATING ROAD RUNOFF
DESIGNING SAFE SUDS ADJACENT TO ROADS
RETROFITTING SUDS FOR ROADS
THE MAINTENANCE OF SUDS ADJACENT TO ROADS
ADDITIONAL GUIDANCE RELEVANT FOR SUDS DRAINING ROADS
REFERENCES
OBJECTIVES FOR SURFACE WATER MANAGEMENT IN THE URBAN ENVIRONMENT
DELIVERING THE SUDS DESIGN CRITERIA WITHIN URBAN AREAS

To maximize these opportunities, the design criteria must be considered at an early stage of the design process and fully integrated into that process. The natural hydrological drainage systems on the site are preserved or improved as part of the landscape and/or surface water management system. A key requirement of the surface water management system is that it drains the site efficiently.

The design of the drainage system should take into account the time it is likely to take for water to drain through the system. At the same time, they must be visually neutral or positively interesting as part of the SuDS Management Train (Chapter 28). Structural diversity can be achieved through the use of a variety of SuDS components as part of the overall SuDS scheme.

The first stage of the SuDS design process is to establish strategic surface water management (SWM) objectives for the development. The site area should be defined in terms of potential for infiltration (eg good/poor/not possible). How the pre-development use of the area will affect the extent to which runoff must be managed by the SuDS for the proposed area.

1 aims to meet each of the criteria set out in the individual criteria sections, to the maximum extent practical for the site:. Where the outline design phase is omitted, the design steps described in section 7.7 should be included as part of the detailed design phase. It should be checked that the final plan meets all design criteria established for the site (section 7.6.2).

3 Pollution can have a negative effect on the materials used in the construction of SuDS. If possible, SuDS design and repair strategy design should be integrated to maximize efficiency and opportunities and minimize costs. The layout of buried utilities should be considered as part of the SuDS design.

In Figure 9.7 the grass around the edge of the detention basin is trimmed regularly to maintain site lines. The vegetation in the center of the detention basin can be allowed to grow higher. The extent and type of SuDS components that can be used for a retrofit site will be influenced by the specific characteristics of the site.

Where SuDS discharges into a sewer (Section 10.2.2), the effect of water levels in the downstream sewer on the operation of the SuDS must be considered.