The Utah beach landings were part of contingency planning only scheduled after ample landing craft became available and designed to give the allies a leg up on taking a port city, in this case, Cherbourg, to bolster Allied logistical capacity. Had the landing craft been lacking, the river would have protected the exposed right flank of the allied invasion lodgement.
The Utah beach landings were part of a supplementary plan only undertaken after sufficient landing craft became available, designed to grant the Allies an initial advantage in capturing the port city of Cherbourg and augmenting their logistical infrastructure. Without these craft, the river would have safeguarded the exposed right flank of the Allied invasion foothold.