Drainage Strategy for Planning Applications
Fast & Reliable Reports to Accompany your Planning Submissions
Chartered Drainage Engineers, Experts in Drainage Strategies
Drainage Strategies for Planning Permission
Our Drainage Strategies are prepared to support both new planning applications and the discharge of pre-commencement drainage conditions, demonstrating how surface water will be managed in accordance with Lead Local Flood Authority (LLFA) requirements and national planning policy.
Each Drainage Strategy is proportionate to the scale and complexity of the development, providing the level of detail required for validation and determination — without unnecessary analysis or cost.
Our drainage strategy assesses the most sustainable way to discharge water safely whilst complying with the Local Drainage guidelines and the National Planning Policy Framework (NPPF).
Our experience allows us to manage water under challenging sites such as flood zone areas, contaminated land, steep or flat slopes or areas located within groundwater protection areas. Our drainage assessments take into consideration the results of the flood risk assessment and drainage strategy guidance.
Sensitive sites may require a hydrogeological impact assessment in addition to the drainage strategy.
Discharging Drainage Planning Conditions
Planning permission is frequently granted subject to a pre-commencement drainage condition — a requirement that surface water drainage details are submitted to and approved in writing by the Lead Local Flood Authority (LLFA) or Local Planning Authority before development commences on site.
Pre-commencement conditions are standard on major applications and increasingly common on minor developments in flood-sensitive areas or where the proposed discharge point requires confirmation. Commencing development without discharging the condition constitutes a breach of planning permission.
What a Condition Discharge Submission Must Demonstrate
The submission must directly address the specific wording of the condition. LLFA technical review focuses on the following:
- Surface water runoff rates for the 1 in 1 year, 1 in 30 year, and 1 in 100 year (plus 40% climate change) events
- SuDS hierarchy compliance and justification of the proposed discharge method
- Attenuation volume calculations and storage design
- Exceedance flow routes identifying how flows in excess of the drainage system capacity are conveyed safely
- Outline maintenance and management responsibilities for the drainage system
A submission that does not address these points in full will receive a holding direction from the LLFA and delay the start of construction.
Our Approach to Condition Discharge
We structure every condition discharge submission to match the exact wording of the condition and the LLFA’s local drainage requirements. Submissions are prepared to a level of detail sufficient for LLFA approval — not advanced to full construction design, which is unnecessary at this stage and adds cost without benefit.
Where the condition requires drainage parameters to be agreed ahead of reserved matters, or where a phased submission is appropriate, we scope the report accordingly.
All submissions are supported through the LLFA’s technical review process. Where queries or holding directions are issued, responses and revised calculations are prepared within our agreed scope.
Proportionate Drainage Strategies for Planning Permission
Drainage Strategies must be proportionate to the scale, nature, surface water risk, and application type — requirements differ between outline consent, full application, and condition discharge submissions. At Urban Water, we focus on producing Drainage Strategies that are robust enough to satisfy the LLFA while avoiding unnecessary complexity or over-design.
We have prepared Drainage Strategies for a wide range of developments, including residential schemes, mixed-use developments, commercial sites, and infrastructure projects. Our experience includes minor developments through to complex sites requiring detailed surface water management and phased planning approvals.
Our approach prioritises planning compliance, validation, and determination, ensuring the strategy aligns with national policy and local authority requirements.
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Minor developments
Proportionate Drainage Strategies addressing surface water disposal, SuDS feasibility, and runoff management for planning validation.
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Major developments
Detailed Drainage Strategies including runoff rate calculations, attenuation sizing, exceedance routing, and maintenance principles to satisfy LLFA review.
Outline Drainage Strategy for Outline Planning Applications
An outline planning application does not require a fully detailed drainage design. The LLFA’s objective at outline stage is to confirm that surface water drainage is achievable in principle — that the site constraints do not prevent a compliant drainage scheme from being delivered at the detailed design stage.
An Outline Drainage Strategy sets out the evidence needed to satisfy this requirement without advancing to construction-level detail.
What an Outline Drainage Strategy Covers
An Outline Drainage Strategy addresses the following at a level proportionate to the outline consent stage:
- Site drainage constraints — topography, ground conditions, existing watercourses, flood zone designations, and proximity to groundwater protection zones
- SuDS feasibility — assessment of infiltration potential based on desk study data, identifying which SuDS components are achievable on the site
- Indicative surface water discharge rates — greenfield runoff rate calculations establishing the target discharge rate for the detailed design stage
- Drainage hierarchy compliance — confirmation of the preferred discharge hierarchy and justification where lower-order options are proposed
- Drainage parameters — defined runoff rates, storage requirements, and maintenance principles to be carried forward to reserved matters
This scope gives the LLFA sufficient technical information to confirm no in-principle objection, without committing to a fixed drainage layout or attenuation structure sizing that may change as the detailed scheme develops. Where groundwater constraints require specialist investigation, our groundwater consultants can advise on the appropriate assessment.
Phased Planning Applications
Where a development is consented in phases, the Outline Drainage Strategy establishes drainage parameters for the full site while accommodating phased delivery. Each phase is assessed against the agreed parameters, with runoff rates and attenuation requirements apportioned across the development to prevent cumulative increases in discharge rates as individual phases are built out.
Phased strategies are prepared to confirm LLFA acceptance of the overall drainage approach before detailed design is undertaken for each phase.
Surface Water Drainage Strategy
A Surface Water Drainage Strategy sets out how rainfall falling on a development will be collected, attenuated, and discharged without increasing flood risk to the site or surrounding area. It is the primary technical document reviewed by the LLFA as part of the planning determination process.
The strategy must demonstrate compliance with the surface water management hierarchy set out in national planning policy and local LLFA technical standards, and confirm that post-development runoff rates do not exceed the agreed discharge limit.
Technical Scope of a Surface Water Drainage Strategy
A Surface Water Drainage Strategy prepared for a full planning application includes the following:
- Runoff rate assessment — Greenfield or brownfield runoff rates calculated for the 1 in 1 year, 1 in 30 year, and 1 in 100 year return periods, including a 40% climate change allowance, using FEH or IH124 methodology as applicable
- Allowable discharge rate — Confirmation of the maximum discharge rate permitted by the LLFA, and demonstration that the proposed drainage system meets this limit
- Attenuation design — Storage volume calculations to contain the difference between inflow and the allowable discharge rate during the critical storm event
- SuDS hierarchy assessment — Appraisal of surface water management options from source control through to discharge to a public sewer, with justification of the proposed hierarchy
- Exceedance routing — Defined flow paths for storm events that exceed the design capacity of the drainage system, confirming flows are routed away from buildings and sensitive receptors
- Outline drainage layout — A layout plan showing the proposed drainage network, SuDS components, and discharge point, drawn to a level of detail sufficient for LLFA technical review
Discharge Points and Consenting
The proposed surface water discharge point requires confirmation before the strategy is finalised. Discharge to a watercourse requires consent from the Lead Local Flood Authority or the Environment Agency, depending on the watercourse classification. Discharge to a public sewer requires agreement with the sewerage undertaker, who will assess available capacity.
We confirm the discharge point and obtain the relevant pre-application responses before the strategy is submitted, removing a common source of LLFA objection at the planning determination stage.
Surface Water Drainage Strategy
A Surface Water Drainage Strategy sets out how rainfall falling on a development will be collected, attenuated, and discharged without increasing flood risk to the site or surrounding area. It is the primary technical document reviewed by the LLFA as part of the planning determination process.
The strategy must demonstrate compliance with the surface water management hierarchy set out in national planning policy and local LLFA technical standards, and confirm that post-development runoff rates do not exceed the agreed discharge limit.
Technical Scope of a Surface Water Drainage Strategy
A Surface Water Drainage Strategy prepared for a full planning application includes the following:
- Runoff rate assessment — Greenfield or brownfield runoff rates calculated for the 1 in 1 year, 1 in 30 year, and 1 in 100 year return periods, including a 40% climate change allowance, using FEH or IH124 methodology as applicable
- Allowable discharge rate — Confirmation of the maximum discharge rate permitted by the LLFA, and demonstration that the proposed drainage system meets this limit
- Attenuation design — Storage volume calculations to contain the difference between inflow and the allowable discharge rate during the critical storm event
- SuDS hierarchy assessment — Appraisal of surface water management options from source control through to discharge to a public sewer, with justification of the proposed hierarchy
- Exceedance routing — Defined flow paths for storm events that exceed the design capacity of the drainage system, confirming flows are routed away from buildings and sensitive receptors
- Outline drainage layout — A layout plan showing the proposed drainage network, SuDS components, and discharge point, drawn to a level of detail sufficient for LLFA technical review
Discharge Points and Consenting
The proposed surface water discharge point requires confirmation before the strategy is finalised. Discharge to a watercourse requires consent from the Lead Local Flood Authority or the Environment Agency, depending on the watercourse classification. Discharge to a public sewer requires agreement with the sewerage undertaker, who will assess available capacity.
We confirm the discharge point and obtain the relevant pre-application responses before the strategy is submitted, removing a common source of LLFA objection at the planning determination stage.
Drainage Assessment, Drainage Strategy, and Drainage Proforma — What Each Requires
The three terms are used inconsistently across local authorities, which creates confusion at the pre-application stage. Each refers to a distinct deliverable with a different scope and level of detail.
Drainage assessment
A drainage assessment is a high-level appraisal of surface water management options, typically required at the outline planning or pre-application stage. It establishes whether drainage is achievable in principle — assessing site constraints, indicative discharge rates, SuDS feasibility, and the likely drainage hierarchy — without committing to a detailed design.
A drainage assessment is not a substitute for a full Drainage Strategy. Where a full planning application is submitted, the LLFA will require a Drainage Strategy, not an assessment.
Drainage Strategy
A Drainage Strategy is a technical document prepared to support a full planning application or the discharge of a pre-commencement drainage condition. It includes runoff calculations, attenuation sizing, exceedance flow routing, and a defined drainage layout — providing the LLFA with sufficient detail to confirm the drainage scheme is technically acceptable and compliant with national planning policy and local drainage requirements.
Drainage Proforma
A drainage proforma is a structured checklist issued by specific Lead Local Flood Authorities, requiring applicants to address a defined set of drainage criteria before the LLFA will issue a technical response. Proformas vary by authority — some require submission at validation, others at technical review stage.
Where the relevant LLFA operates a drainage proforma, we complete it as part of the standard scope of work. The proforma is prepared in conjunction with the Drainage Strategy, cross-referenced to the calculations and layout plan, and submitted as a single coordinated package.
Failure to submit a completed proforma where one is required will result in the application being returned invalid or the LLFA declining to engage technically until it is received.
Information Commonly Required to Prepare a Drainage Strategy
- Topographical survey data,
- Proposed layout drawings
- Existing drainage records
- Details of potential discharge points.
Where infiltration drainage is proposed, ground investigation or soakaway testing data may also be required to demonstrate feasibility.
Identifying this information early helps ensure the Drainage Strategy can be prepared efficiently and submitted without delay.
Where infiltration drainage is proposed, soakaway testing to BRE 365 may be required at the planning stage to confirm ground permeability rates
Our Drainage Strategy Report
Our reports comply with the lead local flood authority standards, the national guidelines, the CIRIA Sustainable Drainage Systems Manual and Sewer for Adoption 8. See below for a list of our pricing:
Drainage Strategy Costs
Drainage Strategy costs depend on development size, surface water complexity, and LLFA requirements. We offer fixed-fee Drainage Strategies based on development scale, providing cost certainty from the outset.
Our proportionate approach ensures that only the necessary level of assessment is undertaken to support planning approval.
All drainage advice is provided by chartered engineers and supported through the planning process until drainage matters are resolved.
What Is Included in a Drainage Strategy
- Review of existing drainage arrangements and site constraints
- Assessment of surface water discharge options in line with the SuDS hierarchy
- Greenfield and brownfield runoff rate assessments
- Attenuation volume calculations where required
- Exceedance flow routing and flood mitigation measures
- Outline drainage layout plans
- Maintenance and management principles
- Clear technical justification to support LLFA and planning review
Surface Water Runoff Assessment Methodology
- Greenfield or brownfield runoff rates
- Identifying allowable discharge limits
- Determining whether attenuation or infiltration measures are required.
The assessment considers site characteristics such as topography, ground conditions, impermeable areas, and proposed layout, ensuring runoff from the development does not increase flood risk elsewhere. Where attenuation is required, storage volumes are calculated to manage peak flows and comply with local authority requirements.
Application of the SuDS Hierarchy
Drainage Strategies follow the sustainable drainage hierarchy, prioritising solutions that manage surface water as close to source as practicable. Water Harvesting are the starting point. Infiltration-based SuDS are then considered , followed by discharge to watercourses or surface water sewers where infiltration is not feasible.
Each option is assessed and justified within the Drainage Strategy, ensuring that the proposed drainage solution is technically appropriate and acceptable to the Local Lead Flood Authority as part of the planning process.
Will This Drainage Strategy Be Accepted by the LLFA?
Our Drainage Strategies are prepared in line with national planning policy, local authority guidance, and LLFA requirements. We focus on producing clear, well-structured submissions that directly address common LLFA concerns.
Where comments are raised during the planning process, we provide responses and clarifications until drainage matters are resolved as part of the planning determination.
Common LLFA Comments and How They Are Addressed
Local Lead Flood Authorities often focus on a small number of key issues when reviewing Drainage Strategies. Common comments relate to insufficient justification of discharge methods, lack of exceedance routing information, or unclear maintenance arrangements.
Our Drainage Strategies are structured to address these points directly, with clear technical justification, defined exceedance routes, and outline maintenance responsibilities. This approach reduces the likelihood of repeated queries and supports a smoother planning determination process.
Planning Support Included Until Determination
Our service includes ongoing planning support, including responses to LLFA comments, technical clarifications, and revisions where required.
This support is included within our agreed scope, providing certainty during the planning process and avoiding unexpected costs.
How Do We Work?
Go Ahead
We will get the available soil information from online databases and (if required) scope the soakaway tests.
3 working days
You receive our drainage layouts based on expected infiltration rates and public sewer capacity.
Submit Our Report
You will be able to utilise our report to register or validate your planning application. We will support you through the planning process.
Consultations
We will obtain quotes for soakaways, contact the local water company and agree the drainage design with the lead local flood authority.
Fully Approved by the LLFA
Compliant with the water company standards
Exceedance paths assessed
Maintenance schedule
Water quality assessment
All the network modelled using Windes.
How a Drainage Strategy Is Prepared
The preparation of a Drainage Strategy typically follows a structured process, starting with a review of site constraints and proposed development layout. This is followed by an assessment of surface water management options, runoff calculations, and identification of appropriate drainage measures.
The Drainage Strategy is then compiled into a planning-ready report, submitted alongside the planning application, and supported through any subsequent LLFA or planning officer comments until drainage matters are resolved.
Our Sustainable Drainage Strategy Methodology
Our partnership ethos allows us to incorporate benefits into the design at a very early stage. We have worked with developers, contractors, architects and planning consultants to create sustainable developments in which water plays a fundamental part.
Obtain Project Details
We obtain your development’s drawings and topographical survey levels in mAOD and site location.
Consult Authorities
We consult the local water company, the lead local drainage authority and the local council and obtain their records to give the development more certainty on the approval.
Scope Investigations
We scope the soakaways. When required, we obtain quotes from our recommended contractors.
Design and Model
Our designs reflect the most suitable and sustainable drainage system for the soil type, and the quantity and quality of water.
Typical Drainage Strategy Outputs
A Drainage Strategy report typically includes a written technical assessment supported by drawings and calculations. This may include an outline drainage layout, runoff and storage calculations, exceedance flow routes, and maintenance principles.
These outputs are prepared to a level suitable for planning review, providing clarity for planners and drainage officers while avoiding unnecessary construction-level detail at the application stage.
Our Drainage Strategy reports typically include professionally prepared technical outputs such as outline drainage layouts, runoff calculations, exceedance flow plans, and written justification addressing LLFA requirements.
Our drainage strategies are prepared in accordance with best practice guidance, including the CIRIA SuDS Manual (C753), which sets out national standards for sustainable drainage design and adoption.
Example outputs shown within our project portfolio are representative of the level of detail provided to support planning determination.
Typical Drainage Strategy Timescales
In most cases, a planning-ready Drainage Strategy can be prepared within 3–10 working days, depending on site complexity and information availability.
Expedited timescales are available for time-critical planning submissions. We can complete designs within 48 hrs if required.
Our Benefits
First report ready in 48hrs. This allows you to register your planning application.
We are versatile experts on the creation of drainage design, meeting the local drainage and water company standards.
We have 100% success on obtaining planning using our drainage strategies.
Fixed price for all of our drainage strategies.
We are proactive engineers who understand the need for efficient and sustainable drainage solutions within developments. As drainage strategy consultants, we create long-standing partnerships with architects and developers.
Drainage Strategy Prepared by Chartered Engineers
This Drainage Strategy service is led by Argemiro Rivera BEng(Hons) MSC CEng MICE MCIWEM C.WEM CEnv, chartered with the Institution of Civil Engineers (MICE), The Institution of Water and Environmental Management (MCIWEM C.WEM) and a Chartered Environmentalist – Society for the Environment ( CEnv)., and Chloe Detanger BEng(Hons) MSc CEng MICE, with extensive experience delivering drainage strategies to support planning applications across the UK.
All Drainage Strategies are prepared or technically reviewed by experienced drainage engineers, ensuring professional accountability, technical rigour, and compliance with planning and drainage authority expectations.
Other Services
Flood Risk Assessments
Our reliable flood risk assessments aid the progress of your planning application.
Foul Drainage Design
Our drainage designs are fully adoptable by water companies and are in compliance with building regulations.
SuDS Design
Our detailed sustainable drainage designs are fully adoptable and approved by the council.
Planning-focused drainage strategies • Fixed fees • LLFA support included
Frequently Asked Questions
Do all developments require a Drainage Strategy?
A Drainage Strategy is commonly required where surface water management needs to be demonstrated to support a planning application, particularly for new developments or changes of use.
What does the LLFA typically look for first?
LLFAs usually review discharge methods, runoff rates, exceedance routing, and maintenance arrangements as part of the Drainage Strategy.
How are exceedance flows addressed?
Exceedance flows are identified and routed away from buildings and sensitive areas, with this information clearly presented within the Drainage Strategy.
Can a Drainage Strategy be updated during planning?
Yes. Where comments are received, the Drainage Strategy can be updated or clarified to address LLFA or planning officer feedback.
What is a drainage strategy?
The lead local flood authority requires a drainage strategy for all major developments in England. A drainage strategy aims to determine the most sustainable way to disperse and discharge water without causing flooding to others and the development. A drainage strategy includes assessing the soil conditions, the discharge points and the suitability of multiple sustainable drainage systems such as swales, ponds, block paving and water butts.
Drainage strategies are typically required by Lead Local Flood Authorities (LLFAs) as part of planning submissions, in line with national planning guidance issued by the UK Government.
What are surface water drainage systems?
Surface water drainage systems are a group of structures that act to manage and dispose of rainwater falling onto a development. Rainwater is collected as close as possible to the roofs or surface, permitting water to evaporate, retain or soak into the ground, for example, by using green roofs and permeable surfaces that allow infiltration. The extra runoff water can be discharged using ponds or drained to the nearest watercourse. This additional runoff should be released at the same rate and volume or lower as would naturally have occurred before development.
