Do you design to SANRAL TRH drainage guidance?

Yes — culvert hydraulics, sizing, and drainage design for road corridors are scoped against the applicable SANRAL TRH drainage series and any project-specific design manual, alongside municipal or provincial requirements where relevant.

Can you assess an existing crossing that is showing signs of scour or capacity problems?

Yes. We assess existing culverts, bridges, and embankment crossings for hydraulic capacity and scour risk, and design protection measures (rock armour, gabions, energy dissipation) sized to the governing flood event.

How do you handle debris and blockage risk at culverts?

Where blockage risk is material to a crossing's performance, we test it through sensitivity cases rather than a single blanket assumption, so the design accounts for realistic debris conditions without over-conservatism.

Can you size crossings across a batch of sites on one road or rail programme?

Yes — batch culvert and crossing sizing across multiple sites on a single programme is common work, with consistent methodology and design events applied across the batch so results are comparable and defensible as a set.

Do you coordinate directly with the roads or rail designer?

Yes. Crossing hydraulics and drainage design depend on road or rail levels, alignment, and structure type, so we typically coordinate directly with the civil or structural designer rather than working from a fixed brief in isolation.

Do you handle flood risk for the corridor itself, not just individual crossings?

Yes — flood risk assessment and floodline mapping along a proposed or existing corridor inform road/rail level decisions and crossing locations at a route-planning level, ahead of detailed crossing-by-crossing design.

A concrete box culvert crossing beneath a road, carrying a watercourse under the corridor.

Sector

Drainage & Flood Studies for Roads & Rail

Drainage, culvert design, scour protection, and flood studies for roads and rail corridors in South Africa.

Culvert hydraulics and sizing aligned to SANRAL TRH guidance
Scour and erosion protection for crossings and embankments
Flood risk on road and rail corridors
Stormwater drainage for new and upgraded routes

What we offer

Consulting

Flood Risk Intelligence

Flood Hazard Mapping Beta — growing coverage

Custom Software

Flood risk intelligence coverage for this sector

We are building toward national coverage. Each offering below shows where it stands today.

Production

Available today with established methodology.

Beta — growing coverage

Available for selected regions; expanding nationally.

Flood Hazard Mapping

Roadmap

In development — not yet available as a live offering.

Why roads and rail projects work with us

Crossing hydraulics sit at the intersection of hydrology, structural performance, and geotechnical risk — undersize a culvert and you get overtopping and washouts; oversize it and you carry unnecessary cost across a batch of sites. We size crossings to the governing design event with documented sensitivity, and coordinate directly with the roads or rail designer so hydraulics and structure decisions move together rather than being reconciled late.

Scour and erosion protection follows the same logic: sized to the flood event, not to a rule of thumb, with the assumptions stated so a reviewer can verify them.

How we work with roads and rail projects

Typical engagements include:

Route-level flood risk. Flood risk assessment and floodline mapping along a corridor, informing road/rail level and crossing-location decisions before detailed design starts.
Crossing-by-crossing or batch design. Culvert and bridge waterway hydraulics, sized individually or across a batch of sites on a single programme, aligned to SANRAL TRH guidance.
Scour, erosion, and existing-asset assessment. Protection design for new crossings, or capacity and scour assessment of existing crossings showing signs of distress.

We are used to coordinating with the roads or rail designer’s programme and levels, and can scope work as a single crossing or a full-corridor batch.

What crossing sizing actually involves

Culvert and bridge waterway sizing starts with the catchment upstream of the crossing: delineation, time of concentration, and a design flood estimate using the SCS-SA or rational method appropriate to the catchment size, cross-checked against regional design rainfall. From there, hydraulic capacity is checked under inlet and outlet control, headwater rise is compared against the road or rail formation level and any upstream property at risk, and outlet velocity is checked against the erodibility of the receiving channel to decide whether scour protection is needed at all.

Where an existing crossing is under review rather than a new one, the same checks run in reverse: as-built or surveyed dimensions go in, and the output is the flood event at which the crossing starts to constrain flow, overtop, or drive scour — the number a maintenance or upgrade decision actually needs.

FAQs

Do you design to SANRAL TRH drainage guidance?: Yes — culvert hydraulics, sizing, and drainage design for road corridors are scoped against the applicable SANRAL TRH drainage series and any project-specific design manual, alongside municipal or provincial requirements where relevant.
Can you assess an existing crossing that is showing signs of scour or capacity problems?: Yes. We assess existing culverts, bridges, and embankment crossings for hydraulic capacity and scour risk, and design protection measures (rock armour, gabions, energy dissipation) sized to the governing flood event.
How do you handle debris and blockage risk at culverts?: Where blockage risk is material to a crossing's performance, we test it through sensitivity cases rather than a single blanket assumption, so the design accounts for realistic debris conditions without over-conservatism.
Can you size crossings across a batch of sites on one road or rail programme?: Yes — batch culvert and crossing sizing across multiple sites on a single programme is common work, with consistent methodology and design events applied across the batch so results are comparable and defensible as a set.
Do you coordinate directly with the roads or rail designer?: Yes. Crossing hydraulics and drainage design depend on road or rail levels, alignment, and structure type, so we typically coordinate directly with the civil or structural designer rather than working from a fixed brief in isolation.
Do you handle flood risk for the corridor itself, not just individual crossings?: Yes — flood risk assessment and floodline mapping along a proposed or existing corridor inform road/rail level decisions and crossing locations at a route-planning level, ahead of detailed crossing-by-crossing design.