PROJECT
Helping Tasman District Council build a clearer picture of flood risk across the Tākaka River catchment.
Tasman District Council needed an updated hydrological and hydraulic model of the Tākaka River and its floodplain to support future flood management.
Flood behaviour in the Tākaka catchment is complex.
Flows originate from a large upper catchment and are influenced by inflows from the Waingaro and Anatoki Rivers. Surface water also interacts significantly with groundwater and the area's underground karst cave system, which can affect flows depending on antecedent conditions.
Flood events can also affect different parts of the wider catchment differently, creating varying flood magnitudes across the river system. For the Council, this meant the model needed to realistically represent how different flood events could occur so flood hazard could be estimated appropriately.
Fox combined catchment analysis and flood modelling to build a more realistic picture of how the Tākaka River system behaves during major flood events.
A large rain-on-mesh hydraulic flood model was developed to represent the Tākaka River and its local catchment, including the Waingaro and Anatoki Rivers. Upper-catchment hydrology was represented using flow-gauge analysis and rainfall-runoff hydrological modelling for ungauged catchments.
The flood model was validated against four historic flood events, and statistical analysis was undertaken to assess the likelihood of large floods occurring across each catchment for a given design flood event.
The model was then used to simulate key design events, including climate-change effects, and to test different flood-management scenarios.
Tasman District Council now has an updated flood model that can be used to assess flood hazard and test different flood-management scenarios across the Tākaka catchment, including future climate-change effects.
A more realistic understanding of flood behaviour gives the Council a stronger technical basis for future flood-management decisions and for assessing how flood risk may change over time.
We can model everything from site-specific flood assessments through to large-scale river catchments.
Flood models are normally calibrated against known flood events and levels so they can be verified against real world data. This gives both you and the council confidence that the model results are accurate.
Flood modelling is not typically cost-effective for individual property assessments. However, if your property is within a small or simple catchment, flood modelling may be able to help provide certainty of flood levels for your future development.
Talk to one of our specialists about your catchment, your modelling requirements and the best way forward.
