Soakaway & SuDS Services in Bristol

What Is Assessed During a Soakaway & SuDS Survey?

A thorough site assessment is essential before designing any infiltration based drainage system. Key elements include:

Soil Permeability & Infiltration Rates: Measured using BRE 365 infiltration testing, which determines whether the ground can support infiltration and provides the infiltration rate needed for design. A minimum infiltration rate of 1 × 10⁻⁶ m/s is typically required for soakaway feasibility.

Ground Conditions & Local Geology: Assessment of soil type, groundwater levels and geological constraints to ensure long term performance and structural safety.

Available Space & Site Layout: Ensuring adequate distance from buildings, boundaries and utilities to comply with Building Regulations and protect foundations.

Existing Drainage Infrastructure: Reviewing current pipework, connections and discharge routes to understand how new systems will integrate.

Surface Water Runoff Calculations: Based on roof areas, paved surfaces and local rainfall data, in line with SuDS design principles and the SuDS hierarchy.

Why a Detailed Assessment Matters

A comprehensive assessment ensures the drainage system is safe, compliant and effective:

Prevents Drainage Failure: Avoids undersized or unsuitable systems that can cause flooding, waterlogging or structural damage.

Ensures Compliance with Regulations: Aligns with Building Regulations Part H and SuDS best practice standards, which prioritise infiltration where feasible.

Supports Planning Approval: Bristol City Council and the Lead Local Flood Authority (LLFA) often require SuDS reports and infiltration evidence for planning applications.

Reduces Long Term Costs: Minimises the risk of remedial works by ensuring the correct design approach from the outset.

Types of Inspection Used for Soakaways & SuDS

Different inspection methods may be used depending on the site and project scale:

Visual Site Inspection: Initial assessment of surface conditions, gradients, access and potential constraints.

BRE 365 Infiltration Testing: Determines how quickly water drains through the soil and whether infiltration is viable.

CCTV Drainage Surveys: Used where existing drainage is present to identify blockages, defects or capacity issues.

Drainage Mapping & Utility Checks: Records existing systems and ensures new installations integrate correctly and safely.

Soakaway Installation for Sustainable Drainage

Soakaways are a preferred method of surface water disposal under the SuDS hierarchy, where ground conditions allow.

Design & Planning: Based on infiltration test results, runoff calculations and site constraints.

Excavation & Construction: Installed at the correct depth and distance from structures. Systems may use: Crate based soakaways (high capacity, lightweight, efficient) or Traditional gravel filled pits. Wrapped in a permeable geotextile membrane to prevent soil ingress.

Testing & Commissioning: Post installation testing confirms performance before reinstatement.

Integrated SuDS Solutions

Where infiltration alone is not suitable, a wider SuDS strategy may be required, in line with the SuDS hierarchy and Bristol LLFA expectations. This may include:

Permeable Paving: Allows water to infiltrate through the surface.

Attenuation Tanks or Crates: Stores water temporarily before infiltration or controlled discharge.

Rain Gardens & Bioretention Areas: Treat and slow runoff at source.

Controlled Discharge Systems: Restrict flow to public sewers where infiltration is not feasible (subject to approval).