Stormwater New Zealand Conference 2025 Rotorua
Urban stormwater practitioners are frequently engaged to “Fix the flooding” in a discrete area. Being able to actually do this requires that a designer needs to know:
- What “the flooding” (i.e. the problem) actually is;
- That a solution can be optimised for best value;
- That success in achieving this goal can be measured.
The word “fix” implies that something is “broken” or is in need of improvement. “Flooding” exists only in the wake of a flood event, and cannot generally be observed on a day-to- day basis making it difficult to study the flooding problem. Historic flood observations can indicate “problems” to be fixed, but we frequently require flood predictions that go beyond observations to fully scope the problem; and it is these predictions that imply the full flooding problem that requires “fixing”.
To some people, “fixing the flooding” can mean removal of any nuisance surface water (i.e. runoff that is not contained within a purpose-built network) in an event of a given or chosen level of severity. It could also mean ensuring that floodwater does not enter any buildings in a given magnitude of event, or it could mean removal of any safety hazards for a different set of events. The flood problem, and possible ways to measure success in addressing it, means different things to different people. There can be a differentiation between nuisance flooding and damaging flooding, and justifying a spend in providing relief from flooding can be somewhat qualitative. In some cases, flood reduction is seen as a success in provision of the sought relief but there remains a question on the degree of reduction (i.e. could more be done?).
Given a sufficiently large flood event, almost all areas are potentially prone to flooding of some sort and to some degree.
Three specific examples are discussed in this paper, where the brief is largely the same (i.e. fix the flooding), but the execution has been different. All three have been completed and deemed successful, and the content of this paper is aimed at showcasing a range of approaches. This includes identification of “the flood problem”, determination of approaches to rectifying the problem (the “fixes”) and different ways to measure the degree of success achieved.
