Plant two each of the three types of reality anchors. Place these anywhere around the barricades on the beach; closer to the barriades may avoid accidental tab-targetting of them.
Run back and speak to Veris. If someone else has triggered the horde you may have to wait to talk to him.
Kill 50 Horde. They will attack the anchors and appear near the water by the barricades.
At the end of this quest you should receive a notification that "Your understanding of of the Harrowing Horde has grown, increasing your ability to damage them."
