Digital Terrain Model — How To Plan Drainage

Digital Terrain Models

A digital terrain model represents a surface from measured or designed data. It can guide cut-and-fill calculations, but poor boundaries and missing breaklines can create a misleading model.

Before moving material

Confirm data source, coordinate system and model extent.

Receiving operation and checks

Issue a controlled design model for the intended workflow. Compare selected model elevations with known field observations.

A model image is not proof of survey accuracy or a certified design.

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.

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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