. ▁ ▁Castro gi ▁Brook ▁The ▁water course ▁comm ences ▁as ▁the ▁Castro gi ▁or ▁Cas - T ro gg y ▁Brook ▁from ▁multiple ▁spr ings ▁in ▁the ▁vic inity ▁of ▁Cas ▁Tro gg y ▁on ▁the ▁north west ▁side ▁of ▁W ent wood . ▁It ▁flows ▁first ▁n ortheast ▁and ▁then ▁sout heast ▁through ▁a ▁series ▁of ▁ent rench ed ▁me and ers ▁to ▁the ▁east ▁of ▁W ent wood . ▁The ▁bro ok ▁then ▁enters ▁the ▁broad ▁vale ▁in ▁which ▁Ca er w ent ▁s its ▁and , ▁passing ▁under ▁the ▁A 4 8 ▁road ▁at ▁Cas - T ro gg y ▁Bridge , ▁it ▁assumes ▁the ▁name ▁Ned ern ▁Brook . ▁ ▁History ▁In ▁Roman ▁times , ▁it ▁is ▁likely ▁that ▁trad ing ▁vessels ▁sa iled ▁up ▁the ▁Ned ern ▁Brook ▁to ▁Ca er w ent . ▁ ▁The ▁water way ▁later ▁s ilt ed ▁up . ▁ ▁This ▁may ▁have ▁been ▁the ▁result ▁of ▁natural ▁processes , ▁possibly ▁accompanied ▁by ▁active ▁land ▁re clam ation ▁in ▁the ▁media eval ▁period , ▁and ▁certainly ▁ex ac erb ated ▁by ▁work ▁rel ating ▁to ▁the ▁exc av ation ▁of ▁the ▁Se vern ▁rail ▁tunnel ▁in ▁the ▁ 1 8 7 0 s . ▁ ▁In ▁ 1 8 7 9 , ▁work ▁on ▁the ▁tunnel ▁was ▁tempor arily ▁stopped ▁when ▁it ▁was ▁in und ated ▁by ▁fresh ▁water ▁from ▁what ▁was ▁known ▁as ▁the ▁" Gre at ▁Spring ". ▁ ▁Im pro ved ▁p ump ing ▁was ▁introduced , ▁the ▁spring