DEMM Engineering & Manufacturing - - CONTENTS - JANE WARWICK

I caught a piece of in­for­ma­tion while chan­nel surf­ing the other day that said one in ten of the more than 100,000 dams that block rivers across the USA are con­sid­ered a risk to hu­man life. And more than 13 per­cent of those are con­sid­ered struc­turally de­fi­cient. Dams in the US have a life ex­pectancy of 50 years, and more than a quar­ter of these have passed their life ex­pectancy af­ter decades of ne­glect. A breach in most would be cat­a­strophic. Those are hor­ri­ble-sound­ing odds. Dams stir up emo­tions from con­ser­va­tion­ists and those who will live in their shadow. Some­times the naysay­ers might be proved right – the Te­ton Dam in Idaho was built in a seis­mi­cally ac­tive area and did in fact col­lapse. Tens of thou­sands died in China af­ter a cas­cade of dam col­lapses. There haven’t been any sig­nif­i­cant dam col­lapses in New Zealand – although a break in a nat­u­ral dam caused the Tangi­wai Dis­as­ter – but there have been some in­ci­dents. Not too long ago Pic­ton was thought to be un­der threat from a wa­ter sup­ply dam in Es­sons Val­ley; the Matahina Dam was ac­cused of caus­ing flood­ing; the Opuha dam breached be­fore it was com­pleted; and in 2016 a wary eye was be­ing kept on a nat­u­ral dam on the Ha­puku River. The writer and con­ser­va­tion­ist, Dou­glas Adams, growled, “We must have beaver genes or some­thing... There’s just this kind of sen­sa­tional de­sire to build dams, and maybe that should be looked at and ex­cised from hu­man na­ture. Maybe the Hu­man Genome Project can lo­cate the beaver/dam-build­ing gene and cut that out.”

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