Offset — How To Plan Drainage

Drainage Grade Design

Drainage grade design must connect the contributing area to a suitable outlet. Selecting a numerical fall before checking the outlet can produce a surface that cannot discharge as intended.

Before moving material

Survey entry points, structures and the receiving level.

Receiving operation and checks

Inspect the constructed route and its transitions. Check invert continuity and controls at crossings.

This guide does not size drains or establish discharge permissions.

Poor Surface Drainage

Poor surface drainage can result from a blocked outlet, a reversed fall, a damaged crossing or local depressions. Grading should follow the identified cause.

Before moving material

Trace water from its entry point to the receiving outlet.

Receiving operation and checks

Inspect the drainage route during a suitable water event. Check that the complete route remains connected through boundaries and crossings.

Surface grading cannot remedy every subsurface drainage problem.

Surveying for Land Grading

Surveying for grading establishes the relationship between the site and the intended surface. Machine guidance can assist work, but the survey determines the reference against which results are checked.

Before moving material

Define the survey area, control and required deliverables.

Receiving operation and checks

Use the survey to prepare the design and later acceptance checks. Retain the datum, units and control-point descriptions.

A topographic survey and a legal boundary survey serve different purposes.

Record the job inputs

Use this checklist to turn the scenario into a specific brief. Retain the design revision and agree who accepts each completed layer.

• Existing condition, extent and the reason for intervention
• Required finished purpose, receiving operation and acceptance criteria
• Material type, layer role, source, receiving area and volume state
• Reference levels, datum, survey method and issued design revision
• Available tractor, implement configuration, travel route and turning space
• Checks before work, stopping points and evidence retained at handover

Checklist ticks apply only while this page is open. Include the completed brief in your project records.

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