Faster, cleaner drainage approvals through a tighter HGL iteration loop.

Context

Drainage design in Australia requires submission of a hydraulic grade line (HGL) analysis as part of the approval package. The HGL is the pressure line running through a pipe network — when it rises above pit cover level, the system is in surcharge, and the design fails. Approving authorities check this before signing off.

The problem is not the hydraulics. Most drainage engineers understand the HGL and can identify what needs to change when it fails. The problem is the workflow: in a conventional setup, every iteration between adjusting the design and checking the result involves manual steps that add no engineering value.

A typical HGL iteration in a conventional workflow looks like this:

1

Adjust pipe size or grade in CAD

2

Manually export or re-enter the updated network into the drainage analysis package

3

Re-run the hydraulic analysis

4

Check the HGL result

5

If it fails: Return to step one

6

Once it passes: Manually redraw the long sections in CAD to reflect the final design

The engineering work is steps one and four — adjusting the design and reading the result. Everything else is data transfer and redraw. On a project with multiple catchments and several failing pits, teams go around that loop more than once.

This friction compounds across project types. Greenfield subdivision, commercial development, road design, infrastructure projects — the HGL iteration problem exists in all of them. The tools change. The approving authority changes. The number of unnecessary steps does not.

How We Resolved It

Civil Site Design connects directly to Drains — the leading hydraulic analysis engine used for drainage design in Australia — through a two-way integration built into the CAD environment. The manual data transfer steps drop out of the loop entirely.

The same iteration in Civil Site Design:

1

Adjust pipe size or grade in Civil Site Design

2

Push the update to Drains directly from your CAD environment

3

Re-run the analysis and read the HGL result

4

If it passes: Long sections update to reflect the change — same step

Pipe network geometry, invert levels, pit locations, and catchment data transfer directly from Civil Site Design to Drains. Results — including HGL level elevations at each pit — return to Civil Site Design and plot directly onto long section drawings. Nothing leaves the CAD environment.

The two steps that disappear — data re-entry and long section redraw — are the ones that tend to pile up at the end of every project. Removing them means each iteration costs less, so engineers run more of them before submission.

A typical HGL iteration in a conventional workflow looks like this:

HGL above pit cover (surcharge to surface)

Upsize the affected pipe or improve grade, push the update to Drains, re-run. On constrained sites, redistributing catchment inflows across additional inlet pits is often more practical than upsizing through an existing services corridor.

HGL below pipe invert

Check the tailwater condition at the outfall. A conservative tailwater assumption can produce an artificially high HGL upstream; an unconservative one can mask a surcharge condition. Particularly relevant where the outfall discharges to a waterway with variable water levels.

HGL within limits but close to cover

A result that passes on paper but leaves minimal freeboard across multiple pits carries review risk on larger sites where downstream catchment contributions may be disputed. Building in adequate freeboard during design is a single iteration. Responding to a review condition after submission is not.

The integration works the same way regardless of project type or approving authority. The design parameters, storm events, and submission standards change — the workflow and the number of steps do not.

Project Type Coverage

Greenfield subdivision

Multiple catchments, pit-to-pit networks, council submission requirements

Road design & reconstruction

Longitudinal drainage, kerb and channel, culverts, state road authority submissions

Commercial & industrial

Tight sites, existing service constraints, private certifier or council review

Civil infrastructure

Trunk drainage, detention basins, outlet structures, hydraulic reports for government agencies

The tools and the number of steps are consistent across all project types. Design parameters, storm events, and submission standards change — the Civil Site Design + Drains workflow does not.

The Outcome

For civil engineering consultancies, contractors, and council design teams working across drainage-intensive programmes, the outcome is consistent: fewer steps between each design decision and a compliant HGL result, and less friction at the submission stage.

Project Type Coverage

Steps removed per iteration

2–3 non-engineering steps eliminated from every iteration cycle — data re-entry and long section redraw no longer required

HGL compliance confidence

More iterations run before submission means failures caught earlier, reducing exposure to redesign requests from approving authorities

Consistent across project types

Greenfield subdivision, commercial and industrial, road design, civil infrastructure — same workflow, same reduced step count

Long section documentation

Long sections generate live from design data and are formatted to Australian drafting standards — no end-of-project redraw bottleneck

Freeboard management

Adequate freeboard built in during design rather than in response to a post-submission review condition

The HGL is not the hard part of drainage design. The hard part is the number of manual steps between adjusting a design and seeing a clean result. Civil Site Design reduces the loop to its essential steps: adjust the design, push to Drains, read the result.

Whether you are a civil engineering consultant working across a development portfolio, a contractor delivering infrastructure projects, or a council design team managing a programme of drainage upgrades — fewer steps between each iteration means you get to a compliant design with less friction, and your submission package reflects the final design from the moment the analysis passes.

Faster, cleaner drainage approvals through a tighter HGL iteration loop

Who it’s for

The problem

How we resolved it

Who it’s for

Context

A typical HGL iteration in a conventional workflow looks like this:

1

2

3

4

5

6

How We Resolved It

The same iteration in Civil Site Design:

1

2

3

4

A typical HGL iteration in a conventional workflow looks like this:

HGL above pit cover (surcharge to surface)

HGL below pipe invert

HGL within limits but close to cover

Project Type Coverage

Greenfield subdivision

Road design & reconstruction

Commercial & industrial

Civil infrastructure

The Outcome

Project Type Coverage

Steps removed per iteration

HGL compliance confidence

Consistent across project types

Long section documentation

Freeboard management

Customer Experience

contact Info

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