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 a contingency measure implemented after sufficient landing craft became available, intended to give the Allies an initial advantage in capturing the port city of Cherbourg and bolstering their logistical capacity. Without these craft, the river would have shielded the vulnerable right flank of the Allied invasion base.