Judea Catchment Modelling - Long Narrow Catchment with Tidal Influences in Lower Catchment

Tauranga was hit by two major storm events, in May 2005 and recently in April 2013. Some locations within the City were flooded during those storm events.

After the May 2005 storm event, a number of upgrades have been implemented in the stormwater system. A process to build 2D flood models using DHI software has been commenced in the last two years and is continuing.

The flooding due to the recent April 2013 storm event has raised the requirements to have flood hazard maps to cover the rest of the city in a short time frame. TCC has identified 10 catchments in order of priority for building and validating MIKE Flood 2D stormwater models. This paper is on the modelling of the Judea Catchment.

The Judea catchment is approximately 12,817 hectares and drains to Tauranga harbour via Kopurererua Stream. The catchment is unique in that it is long and narrow: it stretches 28.5 km and ranges between 1 and 4 km wide along the length. The lower catchment is subjected to flooding due to low ground elevation combined with tidal effects. The objectives of the Judea Catchment stormwater modelling are:

• Build a MIKE FLOOD stormwater network model;
• Development of hydrological and hydraulic models of the Judea Catchment;
• Verification of the capability of the model to reproduce realistic flooding using the April 19-23, 2013 storm event;
• Validation of the model using three additional storm events;
• Determine flows and levels for specified design storms for future landuse; x Assess the risk of flooding in Judea Catchment; and
• Determine flood hazard maps for 50-year MPD and 100-year ED landuse designevent scenarios.

This paper discusses the challenges of modelling the Judea catchment and the constraints in developing options to provide flood protection.