Monday, September 6, 2010

River sampling can be very unpredictable

River sampling can be very unpredictable especially in hard rock (e.g. granite) catchments. The River Avoca is very flashy with a discharge rate that can increase from 0.7 m3/s to 70 m3/s within just a few hours during intense rainfall events. Yesterday the height of the River was 1.6 m lower than this afternoon after 18 hours of heavy showers. The picture shows a slightly worse event in January 2010 which resulted in localized flooding. On that occassion the water was 2.2m higher than normal at the same point. Sampling is normally planned many weeks or months in advance but when conditions are like this then it is impossible and dangerous to proceed.  So if at all possible always work in soft rock catchments (e.g. chalk) where discharge rates are largely unaffected by rainfall events. No sampling tomorrow!

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