Taupo District Flood Hazard Study - Whareroa Stream June 2012

Taupo District Flood Hazard Study - Whareroa Stream
consequently can on occasion carry a relatively high sediment load. In the lower catchment
the channel slope decreases, reducing the flow velocity (Figure 2.4). As a result, the energy
of the river decreases reducing its ability to transport sediment. Consequently, a
considerable volume of material has been deposited on the flood plain. Changes to the river
channel can be caused by both natural and anthropogenic processes. Floods, eruptions,
land use change, and tectonic uplift in the upper catchment can all increase the sediment
supply to the river. Higher lake levels and tectonic subsidence can affect where this material
is deposited within the lower Whareroa catchment.
The Whareroa catchment has a relatively flat rainfall gradient. The mean annual rainfall in
the headwaters, the area likely to produce the greatest runoff, reaches 1500mm. Rainfall
then decreases with altitude to be only approximately 1220mm at Lake Taupo. Those areas
which experience the highest annual rainfalls are also likely to experience the greatest
rainfall intensities. Runoff from the upper catchment therefore has a critical affect on the
flood magnitude and risk towards the river mouth (Figure 2.5).
Figure 2.5:
Mean annual rainfall over the Whareroa catchment.
350855.00
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