▁for ▁the ▁U . S . ▁ ▁By ▁ 1 9 7 4 , ▁treat y ▁power ▁had ▁increased ▁this ▁production ▁three fold , ▁hur ting ▁BC ' s ▁own ▁al umin um ▁production , ▁effectively ▁export ing ▁thousands ▁of ▁jobs ▁in ▁this ▁industry . ▁ ▁Further ▁negative ▁impact s ▁include ▁the ▁flo oding ▁of ▁approximately ▁ 6 0 0   km 2 ▁of ▁fert ile ▁and ▁product ive ▁valley ▁bottom s ▁to ▁fill ▁the ▁Ar row ▁L akes , ▁Dun can , ▁Kin b asket ▁and ▁Ko oc an usa ▁res er voir s . ▁No ▁assess ment ▁of ▁the ▁value ▁of ▁flo oded ▁forest ▁land ▁was ▁ever ▁made ; ▁land ▁which ▁could ▁have ▁produced ▁valuable ▁tim ber ▁for ▁the ▁BC ▁economy . ▁ ▁Environment al ▁Imp act s ▁ ▁Canada ▁ ▁The ▁Columbia ▁River ▁has ▁the ▁greatest ▁annual ▁d rain age ▁as ▁compared ▁to ▁all ▁other ▁rivers ▁along ▁the ▁Pacific ▁coast . ▁Before ▁the ▁introduction ▁of ▁d ams ▁on ▁the ▁river , ▁the ▁changes ▁in ▁water ▁level ▁rose ▁and ▁fell ▁predict ably ▁with ▁the ▁seasons ▁and ▁a ▁nine - meter ▁disp lacement ▁existed ▁between ▁the ▁spring ▁snow m elt ▁high s ▁and ▁fall ▁l ows . ▁After ▁the ▁d ams ▁were ▁built , ▁the ▁river ▁flows ▁changed ▁and ▁in ▁some ▁areas ▁the ▁previous ▁maximum ▁and ▁minimum ▁water ▁levels ▁were ▁alter ed ▁by ▁several ▁tens ▁of ▁meters . ▁High ▁spring - sum mer ▁flows ▁were ▁reduced , ▁and ▁fall - w inter ▁flows ▁were ▁increased ▁to ▁satisfy ▁United ▁States ▁power ▁dem ands