A completed Channel mine barrage and the Channel Dash

How would a completed Channel mine barrage affect Dunkirk and the Channel Dash?

It might complicate Dunkirk but would make the Channel Dash difficult to prepare secretly, because a cleared passage would reveal German intent.

The question is understood as a Second World War scenario because the First World War barrage is described as having been completed. Around Dunkirk, a completed barrier could provide protection while making evacuation routes more complicated. A German Channel Dash would require a cleared path, whose preparation could reveal that a major movement was coming. Running through uncleared mines is treated as potentially prohibitive. One dangerous expedient discussed is a vessel packed with concrete and cork, sent ahead to detonate mines and sacrifice itself. A later clarification describes a barrier anchored on concrete towers spaced across the Channel and supported by mines.