On many projects, engineering services are bundled together for contractual convenience or cost efficiency. However, combining disciplines that have little technical overlap often delivers minimal benefit beyond contract administration.

Hydraulic and civil stormwater design are different; these two disciplines are physically and functionally connected, and when they are delivered by separate consultants, coordination gaps frequently emerge. This commonly leads to design inefficiencies, approval delays, constructability issues, and disputes over scope of responsibility between consultants.

True Integration Starts at the Drainage System

Civil stormwater design typically addresses:

• OSD tank design
• Site grading and finished surface levels
• Overland flow path strategy
• Ground floor pits, pipes, and stormwater discharge points

Hydraulic design, on the other hand, manages:

• Roof drainage and downpipe systems
• Rainwater harvesting and reuse systems
• Pipe transfer from roofs and balconies to the OSD tank
• The ever-contested basement drainage (which often sparks debate over whether it falls within the hydraulic or stormwater engineer’s scope)

When these systems are designed in isolation, critical connections are often poorly resolved. Downpipes may not align with pits (or may be located too far from the OSD), rainwater tanks may not integrate effectively with OSD systems, and discharge paths can conflict with site levels or council requirements.

Better Coordination of Rainwater and OSD Systems

When a single consultancy delivers both hydraulic and civil stormwater design, drainage can be treated as one continuous system rather than disconnected packages.

This approach ensures that:

• Downpipes are accurately coordinated with pits and pipe networks
• Rainwater tanks are properly connected, with compliant overflow paths
• OSD tanks operate as intended and meet council DCP requirements
• Hydraulic and civil calculations align, reducing redesign, RFIs, and approval risk

Reduced Risk and Clearer Responsibility

Separating hydraulic and civil stormwater design often leads to blurred responsibility when issues arise. A combined scope:

• Eliminates scope gaps and overlap
• Improves accountability
• Reduces approval delays and construction variations

Most importantly, it results in simpler, more buildable, and more reliable drainage solutions.

Combining the Right Disciplines Matters

While combining unrelated disciplines may offer administrative convenience, combining hydraulic and civil stormwater design delivers genuine technical value. These systems are operationally dependent, physically connected, and should be designed as a single, coordinated solution.

Horizon’s integrated approach brings hydraulic and civil stormwater together, making complex coordination simple and efficient—both in design and construction.