Wednesday 8 May 2019

April 25 rain-on-snow


A period of fine weather melt with building diurnal snowmelt peaks turned to rain on April 25 to give the sharp rain-on-snow peak in the hydrograph above. Daily precipitation was a moderate 27 mm (Miomote Amedas), but peak intensity reached 5.5 mm/h. Fine weather melt pattern returns and is especially clear during 3-6 May with near-symmetrical sine waves.

The images below are taken from a time-lapse camera, showing the gauging site conditions (upstream view) during the rain-on-snow event from 24 April through to the peak stage of 0.894 m at 13:40 on 25 April. The colour of the water indicates the suspended sediment load, which increases rapidly as rainfall intensity increases after 0840 on 25 April.





The image below shows today's river condition (8 May). Fine weather melt continues and stage is 0.505 m. The gauging cross-section shows evidence of fine gravel accumulation which has caused a deviation from the established stage-rating curve.