sh ore ▁current ▁meets ▁an ▁out flow ▁from ▁a ▁river ▁or ▁flo oding ▁stream . ▁ ▁The ▁removal ▁of ▁sed iment ▁from ▁the ▁beach ▁b erm ▁and ▁d une ▁thus ▁decre ases ▁the ▁beach ▁profile . ▁ ▁In ▁tropical ▁areas , ▁the ▁storm ▁season ▁tends ▁to ▁be ▁during ▁the ▁summer ▁months , ▁with ▁cal mer ▁weather ▁commonly ▁associated ▁with ▁the ▁winter ▁season . ▁ ▁If ▁storm s ▁co inci de ▁with ▁unus ually ▁high ▁t ides , ▁or ▁with ▁a ▁fre ak ▁wave ▁event ▁such ▁as ▁a ▁tid al ▁sur ge ▁or ▁t sun ami ▁which ▁causes ▁significant ▁coast al ▁flo oding , ▁substantial ▁quantities ▁of ▁material ▁may ▁be ▁er oded ▁from ▁the ▁coast al ▁plain ▁or ▁d unes ▁behind ▁the ▁b erm ▁by ▁re ced ing ▁water . ▁ ▁This ▁flow ▁may ▁alter ▁the ▁shape ▁of ▁the ▁coast line , ▁en large ▁the ▁mouth s ▁of ▁rivers ▁and ▁create ▁new ▁del t as ▁at ▁the ▁mouth s ▁of ▁streams ▁that ▁had ▁not ▁been ▁powerful ▁enough ▁to ▁overcome ▁long sh ore ▁movement ▁of ▁sed iment . ▁ ▁The ▁line ▁between ▁beach ▁and ▁d une ▁is ▁difficult ▁to ▁define ▁in ▁the ▁field . ▁Over ▁any ▁significant ▁period ▁of ▁time , ▁sed iment ▁is ▁always ▁being ▁ex changed ▁between ▁them . ▁The ▁dr ift ▁line ▁( the ▁high ▁point ▁of ▁material ▁depos ited ▁by ▁waves ) ▁is ▁one ▁potential ▁dem arc ation . ▁This ▁would ▁be ▁the ▁point ▁at ▁which ▁significant ▁wind ▁movement ▁of ▁sand ▁could ▁occur , ▁since ▁the ▁normal ▁waves ▁do ▁not ▁wet