En­gi­neers use replica to pin­point re­pairs for Cal­i­for­nia dam

The Washington Times Daily - - AMERICAN SCENE - BY BRADY MCCOMBS

LO­GAN, UTAH | In­side a cav­ernous north­ern Utah ware­house, hy­draulic en­gi­neers send wa­ter rush­ing down a replica of a dam built out of wood, con­crete and steel — try­ing to pin­point what re­pairs will work best at the tallest dam in the U.S for a spill­way torn apart in Fe­bru­ary dur­ing heavy rains that trig­gered the evac­u­a­tion of 200,000 peo­ple liv­ing down­stream.

The sound of rush­ing wa­ter is deaf­en­ing as Utah State Univer­sity hy­draulics en­gi­neer­ing pro­fes­sor Michael John­son kneels in front of the Oroville Dam replica the size of a small house to ex­am­ine one of two chan­nels that run the width of the spill­way to al­low air into the wa­ter to pre­vent bub­ble for­ma­tions that can dam­age the con­crete spill­way of the real dam.

The new chan­nels, called aer­a­tors, are one of the key fea­tures in the pro­posed $300 mil­lion spill­way re­con­struc­tion set to be com­pleted by Novem­ber — when win­ter rains and snow will once again in­crease the flow of wa­ter into the lake above the dam.

While a sep­a­rate team of dam ex­perts tries to solve the mys­tery of why the spill­way crum­bled in Fe­bru­ary, the hy­drol­o­gists who built the replica are us­ing it to guide Cal­i­for­nia au­thor­i­ties on how they should build a new spill­way so that it can with­stand rush­ing wa­ters.

Be­sides con­firm­ing that the chan­nels to aer­ate wa­ter go­ing down the spill­way would ease pres­sure on the spill­way, the Utah test­ing has de­ter­mined that an ad­just­ment to a curve about half­way down the spill­way would only slightly im­prove its ef­fec­tive­ness.

The idea was to make the curve more grad­ual near a steep part of the spill­way where it caved in and left a gap­ing hole the size of a foot­ball field in the con­crete chute.

Though com­puter mod­el­ing is be­ing used ex­ten­sively to plan the spill­way re­pairs, Cal­i­for­nia of­fi­cials and the hy­drol­o­gists say high-tech test­ing is no re­place­ment for dam replica re­search. Mr. John­son’s team has a $277,000 con­tract for the work and will is­sue its fi­nal re­port in the early fall.

Wa­ter flow pat­terns, pool­ing and waves can be dif­fer­ent than com­puter mod­els pre­dict, said Ted Craddock of Cal­i­for­nia’s De­part­ment of Wa­ter Re­sources.

“This is an im­por­tant val­i­da­tion process,” Mr. Craddock said. “Wa­ter be­haves very sim­i­lar at a smaller scale as a larger scale.”

Phys­i­cal mod­els to test pro­posed dams and dam re­pairs are nec­es­sary be­cause “the flow of wa­ter is very com­plex and mo­men­tum is trans­ferred at the molec­u­lar level,” Mr. John­son said.

“We haven’t got enough com­puter power to model that many mol­e­cules at once,” he said.

Each sim­u­la­tion of the 100-foot-long replica that took 40 days to build be­gins when a crew mem­ber slowly opens a large steer­ing wheel like valve that sends wa­ter scream­ing down a chute mod­eled af­ter the spill­way and crash­ing into blocks that dis­perse it and send it in waves to a replica of the river.

Mr. John­son al­most has to shout for his team to hear him above the noise of the wa­ter mim­ick­ing a flood.

The hy­drol­o­gists cal­cu­late the ve­loc­ity of the wa­ter, track how much air is be­ing ab­sorbed in the wa­ter and doc­u­ment what they see in weekly re­ports to Cal­i­for­nia au­thor­i­ties.

AS­SO­CI­ATED PRESS

Hy­draulic en­gi­neer­ing pro­fes­sor Michael John­son is us­ing a replica of the Oroville Dam at a lab in Lo­gan, Utah, to fig­ure out what re­pairs are needed.

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