▁once ▁the ▁necessary ▁land ▁had ▁been ▁purchased , ▁but ▁it ▁soon ▁became ▁apparent ▁that ▁the ▁original ▁surve ys ▁were ▁in ade qu ate . ▁The ▁canal ▁engineer ▁John ▁R enn ie ▁was ▁asked ▁to ▁advise ▁the ▁propriet ors , ▁and ▁proposed ▁three ▁options , ▁for ▁boats ▁of ▁, ▁for ▁boats ▁of ▁, ▁and ▁for ▁b arg es ▁which ▁were ▁ ▁wide . ▁The ▁first ▁was ▁ruled ▁out ▁on ▁cost , ▁the ▁third ▁because ▁of ▁the ▁need ▁to ▁trans ship ▁all ▁goods ▁at ▁High bridge , ▁and ▁the ▁second ▁was ▁adopted ▁because ▁it ▁allowed ▁the ▁co aster s ▁that ▁worked ▁the ▁Br istol ▁Channel ▁to ▁use ▁the ▁canal . ▁This ▁option ▁required ▁lo cks ▁of ▁ ▁by ▁, ▁and ▁was ▁cost ed ▁at ▁£ 2 8 , 7 2 0 . ▁The ▁route ▁would ▁be ▁as ▁author ised , ▁but ▁a ▁single ▁lock ▁was ▁required ▁on ▁the ▁upper ▁section ▁to ▁simplify ▁the ▁water ▁supply . ▁Work ▁res umed ▁in ▁July ▁ 1 8 2 8 . ▁ ▁At ▁the ▁G last on bury ▁end , ▁the ▁canal ▁was ▁required ▁to ▁cross ▁the ▁South ▁D rain ▁and ▁the ▁River ▁Br ue . ▁R enn ie ▁suggested ▁invert ed ▁sy ph ons , ▁rather ▁than ▁lock ing ▁down ▁into ▁the ▁river ▁and ▁up ▁again , ▁and ▁a ▁cast ▁iron ▁aqu ed uct ▁for ▁the ▁River ▁Br ue ▁crossing ▁was ▁obtained ▁for ▁nearly ▁£ 3 , 0 0 0 ▁from ▁a ▁G last on bury ▁black sm ith ▁called ▁John ▁Wright . ▁At ▁the ▁High bridge ▁end