Terraced Rain Garden for Urban Flood Control and Biodiversity

Client

Royal Borough of Kensington and Chelsea

Location

Sectors

Products & Services

Project overview

The pedestrian area at the Lancaster West Estate end of Clarendon Road suffered frequent flooding due to poor drainage and rapid surface water runoff along a sloped grass border adjacent to residents’ properties. Our team delivered and planted a terraced rain garden to intercept, slow, and absorb runoff from surrounding paved areas. This SuDS solution reduced flooding, soil erosion, and damage to paved footways while enhancing biodiversity and creating a resilient, attractive green space for the community.

Goal

To resolve persistent flooding caused by insufficient drainage and rapid runoff on a sloped pedestrian area by designing a terraced rain garden that improves water absorption, prevents soil erosion, and increases biodiversity in an urban residential setting.

Scope

Manage runoff from approximately 450 sqm of paved surfaces draining into a sloped grass border.
Expand and reshape the border by 8 sqm, creating a 96 sqm terraced rain garden.
Reduce slope gradient with a wooden sleeper terrace to slow water flow and boost infiltration.
Replace compacted soil with a shingle drainage layer and SuDS planting medium for better permeability.
Introduce diverse, drought- and wet-tolerant plants suited for partial shade under mature trees.
Protect existing trees and infrastructure while preventing vehicle access to avoid further soil compaction.

Solutions

A range of strategic design measures were implemented to address flooding, improve drainage, and enhance biodiversity within the rain garden. These included terracing the slope, improving soil permeability, expanding the catchment area, and introducing SuDS-appropriate planting.

Terracing

Installed a low wooden sleeper terrace to reduce slope steepness, slowing runoff and improving water absorption.

Soil and Drainage

Removed compacted soil and added a permeable shingle base with sandy loam and SuDS planting medium to enhance drainage and retention.

Rain Garden Expansion

Increased catchment edge by 11m to intercept more runoff and ease pressure on drainage systems.

SuDS Planting

Planted resilient herbaceous perennials, shrubs, and grasses adapted to wet and dry cycles, boosting biodiversity and pollinator habitat.

Biodiversity Features

Added log piles for insect habitats and designed a seasonal living wall with moss and sedum on the adjacent brick wall.

Protective Edging

Used granite kerbs, corten steel, and timber sleepers to prevent vehicle damage and blend with local architecture.

Impact

Flood Mitigation and Soil Stabilisation

The terraced rain garden effectively captures and slows surface runoff, preventing puddling and erosion that previously damaged footways and caused soil displacement. This leads to a more stable, safer pedestrian environment.

Enhanced Urban Biodiversity

The diverse planting scheme creates a dynamic habitat for pollinators and insects, encouraging a new ecosystem to develop in an area previously dominated by grass and bare soil. Log piles and seasonal living walls further enrich this microhabitat.

Community Engagement and Wellbeing

By transforming a problematic flood-prone area into an attractive green space, the project offers residents a place to reconnect with nature and observe seasonal changes, improving local quality of life and fostering environmental awareness.

Long-Term Resilience

The rain garden’s design addresses current drainage deficiencies while adapting to future weather extremes through increased soil permeability, retention, and vegetative water uptake – supporting sustainable urban water management on the Lancaster West Estate.