Overland Flow Path and Depression Mapping for the Auckland Region - full article
Automating the Overland Flow Path and Depression Area Mapping
In urban areas, overland flow paths are the path that water takes overland, often when the capacity of a piped network is exceeded or when inlets are blocked. Depressions are areas that have a potential to ‘fill up’ with water if the piped system is blocked or its capacity is exceeded. Both of these datasets are a critical element of integrated stormwater management, hydraulic modelling and flood hazard mapping.
The combination of climate change leading to increased and more intense rainfall, aging infrastructure, and intensification of development mean mapping, understanding and protecting these catchment features is more important than ever.
Historically urban development has relied on a piped network for stormwater management. Little consideration was given to what might happen if the piped network was exceeded or inlets became blocked. Understanding the location of overland flow paths and depression areas is essential for creating resilient and future ready communities.
WSP has worked with multiple clients to map overland flow paths and topographical depression areas across Aotearoa New Zealand.
WSP has developed innovative ARCGIS Models to automate the overland flow path and depression area mapping, enabling clients to quickly understand flood risk at a large spatial scale. This analysis does not require complex hydraulic modelling and outputs are provided in compatible GIS format at a fraction of the resource and cost required to produce floodplains for a catchment. WSP are also able to attribute a range of useful information to each overland flow path or depression area, such as peak flows and runoff volumes and the rainfall required in the catchment to fill up each depression area.
The overland flow path and depression area datasets can inform and answer Client questions like:
- What existing buildings or new housing developments are at risk of flooding?
- Where are streams likely to be?
- What areas would flood if a culvert blocked?
- What is the catchment area upstream?
- Where should catchpits be located?
- Are there any inadvertent ‘large dams’?
- Where would water or wastewater flow if a pipe burst?
WSP have mapped over 100,000 km of overland flow paths and 40,000 depression areas across New Zealand. The total length of the overland flow paths in the Auckland Region alone would stretch around the earth one and half times.