Sluice gates brave the shifting tides
Sluice gates are movable barriers that regulate water levels and flow rates in waterways . In a world of changing climate and increased flooding risks , these gates need to be taller and stronger than ever before . Thanks to their strength and corrosion resistance , molybdenum-containing duplex stainless steels are the ideal construction material .
By Karlee Williston , IMOA
Traditionally made of wood or metal , sluice gates make life possible in the world ’ s most populous places : along rivers or coastal regions , which are often vulnerable to flooding . The basic technology behind sluice gates is ancient – Sri Lankan society used them over 4000 years ago – but their refinement continues today . Some modern sluice gates use duplex stainless steel , which offers substantial benefits over other construction materials . The projects detailed below showcase how these gates conserve material , capital , and emissions throughout their service lives .
Mont St-Michel , Avranches Mont St-Michel is a tidal island with an abbey that appears to float on the ocean . The granite rock lies about 1km off the north-western coast of France , near Avranches . Since the 8 th century , religious pilgrims crossed the muddy sands , revealed only at low tides , to reach the abbey . But the everchanging display of water and light around the monastery was under threat . A steady flow of silt from the Couesnon , Sée , and Selune rivers and sand , brought into the bay by high tides , accumulated between the rock and the coast , continuously joining Mont St-Michel with the land . The reasons for this build-up of silt and sand go back to the 19th century , when the rivers were diverted to create pasture land , preventing them from properly carrying the deposits into the sea . To make things worse , a dike built in 1869 to provide visitors with a permanent connection to the island , further impeded free drainage . Now the sands at the foot of Mont St-Michel are 3m higher than they were 200 years ago . To reduce this deposit build-up , the French government had a dam built on the Couesnon river . Eight sets of sluice gates , clad with 2205 duplex stainless steel , retain the river water at high tide and release it at low tide , allowing it to flush sediment out to sea . Additionally , the old dike that blocked water flow was replaced by a
Image courtesy of Skanska .
light bridge on stilts . The bridge allows the free flow of water around the island , improving the efficiency of deposit removal from the bay . Some 36 tonnes of duplex stainless steel plate , supplied by Industeel , clad the gates ’ coated carbon steel frame . 2205 duplex stainless steel , containing 3 % molybdenum , was chosen for its superior corrosion and abrasion resistance . The molybdenum content helps fend off both corrosion from seawater and abrasion from sediments . With lots of abrasive particles and high flow rates , ‘ erosion corrosion ’ is a significant risk for corrosionprone , softer materials like aluminium or carbon steel . Wet-dry interfaces , inevitable in a water management system , can also exacerbate corrosion . A carefully welded duplex stainless steel surface , with its high hardness and corrosion resistance , will resist these perils far better than other metals or lesser alloyed grades . The Couesnon dam , which faces the abbey and the open bay , has become its own tourist attraction . Project architects designed a public space atop the dam , which offers unobstructed views of Mont St-Michel and attracts millions of people to visit this UNESCO World Heritage Site every year .
Twice a day , at high tide , Mont St-Michel is surrounded by water . Image courtesy of FLYHD
Slussen , Stockholm Slussen is a lock right in the middle of the historic city centre of Stockholm , Sweden . It was first built in the 17 th century . This lock protects the two million people of Mälardalen , the area around lake Mälaren
36 Stainless Steel World April 2023 www . stainless-steel-world . net