Flood inquiry clears quarry

THE quarry near Grantham had only minimal effect on the height or velocity of last year's flood, the Flood Commission's Final Report has found.

THE quarry near Grantham had only minimal effect on the height or velocity of last year's flood, the Flood Commission's Final Report has found.

The report found the quarry reduced the possible height in Grantham, but increased it in other areas.

The Commission examined the claims by a number of Grantham residents at the hearings, that the quarry increased the damage the flood had caused.

Commission hydrologist Dr Phillip Jordan ran three models of the effects of the quarry on the flood: one as happened, one as if the quarry were never built, and a third, in which the quarry's wall had not been breached the day before the flood.

The models found the quarry caused only minimal changes to the flood.

"The Commission concludes, on the basis of Dr Jordan's evidence, that none of the earthworks associated with the quarry caused or contributed to the flooding of Grantham on 10 January 2011," it read.

The report said the models demonstrated the flood would have been horrific for Grantham and the rest of the Valley regardless of the quarry.

"By comparing the results generated for the three scenarios by the model, Dr Jordan's second report to the Commission concluded that the quarry mitigated the impact of flooding through the town area of Grantham," it said.

"The effect of the quarry was to reduce peak flood levels in Grantham by between 0.04 m and 0.1 m. Peak flood velocities in Grantham were not affected; the maximum simulated velocities differed by less than 0.01 m per second across the Grantham town area between the pre-quarry scenario and the 10 January event as simulated.

"The quarry attenuated the flows, causing a five-minute delay in the water rise.

"At some other locations the existence of the quarry did elevate flood levels slightly, for example, by 0.3 m just upstream of where the breach occurred in the quarry wall and by 0.04 m near Dorrs Rd."

Regarding the effects of the breach in the quarry embankment, the modelling showed the pattern of changes in flood levels through the town of Grantham to be very similar whether the embankment was breached or not."

Originally published as Flood inquiry clears quarry