▁the ▁water ▁that ▁formed ▁them , ▁whether ▁through ▁change ▁in ▁sea ▁level ▁or ▁ground water ▁flow . ▁If ▁as ▁a ▁cave ▁grows ▁it ▁breaks ▁through ▁to ▁the ▁surface ▁somewhere ▁else ▁it ▁becomes ▁a ▁natural ▁arch , ▁like ▁those ▁near ▁Kar ame a ▁( O par ara ▁Arch es ). ▁ ▁R ivers ▁and ▁la kes ▁ ▁The ▁proportion ▁of ▁New ▁Zealand ' s ▁area ▁( ex cluding ▁est u aries ) ▁covered ▁by ▁rivers , ▁la kes ▁and ▁p onds , ▁based ▁on ▁figures ▁from ▁the ▁New ▁Zealand ▁Land ▁Cover ▁Database , ▁is ▁( 3 5 7 5 2 6 ▁+ ▁ 8 1 9 3 6 ) ▁/ ▁( 2 6 8 2 1 5 5 9 ▁– ▁ 9 2 4 9 9 – 2 6 0 3 3 ▁– ▁ 1 9 2 1 6 ) ▁= ▁ 1 . 6 %. ▁If ▁est u ar ine ▁open ▁water , ▁mang ro ves , ▁and ▁her b ace ous ▁sal ine ▁veget ation ▁are ▁included , ▁the ▁figure ▁is ▁ 2 . 2 %. ▁ ▁The ▁mountain ous ▁areas ▁of ▁the ▁North ▁Island ▁are ▁cut ▁by ▁many ▁rivers , ▁many ▁of ▁which ▁are ▁swift ▁and ▁un n avig able . ▁The ▁east ▁of ▁the ▁South ▁Island ▁is ▁marked ▁by ▁wide , ▁bra ided ▁rivers ▁such ▁as ▁the ▁W ai ra u , ▁Wa im ak ari ri ▁and ▁Rang it ā t ā ; ▁formed ▁from ▁gla ci ers , ▁they ▁fan ▁out ▁into ▁many ▁str ands ▁on ▁gra vel