might've been where, originally, expansion jnt mtl was placed OR where a form was removed,,, you can use a closed cell backer rod to stuff in it & then seal w/an appropriate sealant, NOT caulk,,, the backer rod'll provide the correct depth:width ratio IF you installed it correctly,,, you don't want 3-sides adhesion for sealants.
this MIGHT prevent your wtr seepage but i doubt it,,, w/that post'd amt of rain, look for an ark instead