Building Structure in the Flood-Affected Site
In the challenging landscape of Sydney, several sites spanning from the southern to the eastern regions lie within flood-prone areas. Identifying if your property is within a flood-affected zone is essential for robust structural design and construction. This information can typically be found in the Section 10.7 planning certificate or obtained from the local council through a Flood Information Letter.
Flood impact varies across sites; some may experience minor flooding, while others are situated entirely within the flood pathway. Consequently, if you are submitting a development application to the local council for a project located in a flood-affected area, the planning office may require a flood study conducted by a specialist flood engineer. Such studies provide valuable insights into the flood level, specifying how high habitable areas must be elevated, typically exceeding half a meter above the maximum 1:100 AEP flood level.
In certain scenarios, the proposed structural elements, like footings and slabs, can impact the flood pathway or hinder flood storage. Put simply, these structural components may restrict the natural flow of floodwater and impede its absorption into the soil.
Flood specialists work diligently to address these issues, determining the ideal floor finish level and recommending a suspended slab or floor frame to remain above the flood level in the event of a significant storm or flood. The responsibility then falls on the structural engineer to provide a design solution that balances cost-effectiveness with structural integrity, all while safeguarding the unrestricted flow of floodwater.
A Marsfield Project: Navigating Flood-Affected Challenges
The images below illustrate a completed project in Marsfield, a location significantly affected by floodwaters. The project required careful consideration of flood-resistant design and structural integrity. The client’s preference for a full double brick construction with a reinforced concrete slab demonstrated a commitment to resilience against harsh environmental conditions.
However, raising the floor level to mitigate flooding posed a unique challenge. The increased elevation exceeded the practical limits for traditional in-situ concrete construction, complicating formwork removal upon completion.
To address this challenge, we proposed the use of Bondek composite concrete slabs supported by core-filled blockwork as centroid supporting points distributed across the span of the concrete slab. During construction, sacrificial propping was employed to support the structure until the concrete had fully cured after 28 days. The results were not only aesthetically pleasing but also streamlined the construction process, making it significantly more efficient for builders and other trades.
While this approach incurred slightly higher costs due to the Bondek and additional propping materials, it eliminated the need for extensive digging and backfilling, allowing plumbing and other services to run concurrently beneath the slab. Accessibility for repairs and maintenance was greatly enhanced, as most components were readily exposed.
In conclusion, the Marsfield project showcases the successful integration of innovative engineering solutions to address the challenges of flood-affected construction. By combining the resilience of materials with efficient design, the project not only meets the client’s preferences but also anticipates the harsh conditions the structure may face, ensuring long-term durability and flood resilience.
