Common SuDS Submission Mistakes That Delay Planning Approval (And How to Avoid Them)

When it comes to Sustainable Drainage Systems (SuDS) submissions, even experienced developers and architects can find themselves facing unexpected delays in planning approval. After reviewing hundreds of SuDS proposals across England and Scotland, we've identified the most common mistakes that consistently cause setbacks – and more importantly, how to avoid them.

The Cost of Getting It Wrong

Planning delays don't just affect timelines; they impact your bottom line. Each week of delay can cost developers thousands in holding costs, contractor standby fees, and missed market opportunities. For architects, delayed approvals can strain client relationships and affect future project pipelines.

The good news? Most SuDS submission mistakes are entirely preventable with proper preparation and understanding of what planning authorities actually need to see.

Mistake No1: Inadequate Site Investigation Data

The Problem: Submitting SuDS proposals without comprehensive ground investigation reports or soakaway testing data.

Many submissions fail because they're based on assumptions rather than actual site conditions. Planning authorities need evidence that your proposed drainage solution will work in the specific ground conditions present on site.

The Solution: 

• Commission proper soakaway testing before designing your SuDS strategy

• Include detailed ground investigation reports with your submission

• Ensure topographical surveys are accurate and provided in the correct format

• Don't assume previous reports from nearby sites will suffice

Real-World Impact: We've seen projects delayed by 8-12 weeks simply because initial soakaway tests revealed unsuitable ground conditions that required a complete redesign.

Mistake No2: Insufficient Hydraulic Calculations

The Problem: Providing SuDS proposals without detailed hydraulic modelling or calculations that demonstrate system capacity.

Planning authorities need proof that your drainage system can handle the required storm events. Generic calculations or rule-of-thumb sizing simply won't pass scrutiny.

The Solution:

• Use professional drainage design software for accurate modelling

• Include calculations for multiple storm return periods

• Demonstrate how the system performs during extreme weather events

• Show clear overflow routes and emergency drainage paths

Professional Tip: Always model for climate change factors – many authorities now require evidence that systems can cope with increased rainfall intensity.

Mistake No3: Incomplete Maintenance Schedules

The Problem: Failing to provide comprehensive, realistic maintenance schedules for proposed SuDS features.

One of the biggest concerns for planning authorities is long-term system performance. Without clear maintenance plans, they can't be confident that SuDS features will continue functioning effectively over time.

The Solution:

• Develop detailed maintenance schedules for each SuDS component

• Include monthly, quarterly, and annual maintenance tasks

• Specify who will be responsible for ongoing maintenance

• Provide realistic cost estimates for maintenance activities

• Include inspection protocols and performance monitoring procedures

Mistake No4: Poor Integration with Site Layout

The Problem: Treating SuDS as an afterthought rather than integrating drainage design with the overall site layout from the beginning.

When drainage design isn't considered early in the planning process, it often results in awkward compromises that don't satisfy planning requirements or site functionality.

The Solution:

• Involve drainage specialists during initial site planning

• Ensure SuDS features complement landscape design and site usage

• Consider maintenance access routes during design phase

• Integrate SuDS with other site infrastructure (utilities, roads, landscaping)

Mistake No5: Inadequate Documentation and Drawing Standards

The Problem: Submitting poorly presented drawings or incomplete documentation that doesn't clearly communicate the proposed drainage strategy.

Planning officers need to quickly understand your proposal. Unclear drawings or missing information will result in requests for additional information, causing delays.

The Solution:

• Provide clear, professional drainage layout drawings

• Include detailed sections and construction details

• Ensure all drawings are to appropriate scales and standards

• Include comprehensive design statements explaining the drainage strategy

• Cross-reference all supporting documents clearly

Mistake No6: Ignoring Local Authority Specific Requirements

The Problem: Using generic SuDS approaches without considering the specific requirements and preferences of the local planning authority.

Different councils have varying requirements for SuDS submissions. What works in one area may not be acceptable in another.

The Solution:

• Research local authority SuDS policies and guidance documents

• Review recently approved SuDS applications in the area

• Engage with planning officers early in the process

• Consider local environmental constraints and opportunities

Mistake No7: Unrealistic Discharge Rates

The Problem: Proposing discharge rates that don't align with local authority requirements or site constraints.

Many submissions fail because proposed discharge rates are either too optimistic or don't account for existing infrastructure capacity.

The Solution:

• Confirm acceptable discharge rates with the local authority early

• Consider existing sewer capacity and connection points

• Include contingency measures for periods when discharge is restricted

• Provide evidence supporting proposed discharge calculations

The Professional Advantage

While it's possible to prepare SuDS submissions in-house, the complexity of modern drainage requirements means that professional expertise often pays for itself through faster approvals and reduced risk of costly mistakes.

Professional drainage designers bring:

• Up-to-date knowledge of changing regulations

• Established relationships with local authorities

• Proven track record of successful submissions

• Access to professional design software and validation tools

Moving Forward: Your Next Steps

If you're planning a development that requires SuDS approval:

1. Start Early: Begin drainage planning during initial site analysis, not after architectural plans are finalised

2. Invest in Proper Surveys: Comprehensive site investigation data is essential for successful submissions

3. Consider Professional Support: Expert drainage design can prevent costly delays and ensure compliance

4. Plan for Maintenance: Develop realistic, long-term maintenance strategies from the outset

Getting It Right First Time

At The Drainage Designers, we've achieved a 75% first-time approval rate for SuDS submissions by focusing on thorough preparation, professional presentation, and deep understanding of local authority requirements. Our approach combines technical expertise with practical experience to deliver drainage solutions that satisfy both planning requirements and project objectives.

Remember, successful SuDS submissions aren't just about meeting minimum requirements – they're about demonstrating that your drainage strategy is robust, sustainable, and appropriate for the specific site and local context.