Comparative Assessment of Gauged and Observed Calibration Data

Stormwater modelling assessments, and the resulting conceptual flood alleviation designs, are typically hampered by the lack of available calibration and verification data. This is, in part, due to assessment criteria (often 5 -100yrs ARI) being significantly greater than the period of monitored flow data, but even when flow records are of sufficient length, the catchment hydrology (at least in urban areas) has undergone such radical change that the data is no longer valid. At best we are often left to rely on anecdotal information such as historical records of complaints and observed flooding.

This paper utilizes the long term and detailed monitoring network set up as part of the Hikurangi Flood Control Scheme to assess the limitations of substituting anecdotal and qualitative data for detailed monitoring.

The Scheme, which is approximately 2 km in length, has continuous inflow and outflow records spanning 50 years (at 15 min intervals). In addition to this there is over 10 years of continuous and simultaneous monitoring at 8 locations within the scheme. The scheme stake holders are directly and in some cases severely affected by its ability to control flood waters. As a consequence there is an even greater amount of highly usable observational information.