Typically, this work is all ...

Typically, this work is all accomplished through an engineering consulting firm in some form of initial study where alternatives are identified and preliminary cost estimates generated.  Costs for an initial study are often relatively modest. The POA could "go it alone" initially but, ultimately and prior to construction work of any kind, they would need to involve a PE.  Recommend looking for a local firm that specializes in site work or storm water management.  The local government entity responsible for SWM would probably be able to proved a list of firms that they have worked with or have a pre-approved list (they might even let you know the companies that are the best to work with).  The POA should set up a subcommittee to oversee the process and report to the POA board.  The subcommittee would interview prospective engineering consultants, evaluate fee schedules and recommend a selection to the board.  The selected engineering firm should be able to lead the subcommittee and the board through further steps in the process of ultimately addressing the issue.  During initial interviews, I would personally ask any consulting firm how they address climate change issues in their designs and recommendations, especially in a coastal community.