If it was me, I'd start a bait pile in the drainage or near it. I would do it there hoping they would be encouraged to feed in the daylight in the drainage, rather than out in the open. It might take awhile for them to find it but they will sooner or later. Corn, soured in a bucket with beer works good. Just put corn in a bucket, pour a couple of quarts of the cheapest, nastiest tasting beer or malt liquor you can find, my favorite,Old English. Put a lid on it and set in the sun for about a week. Then hang it off the ground and poke some wholes in the bucket and let that foul smelling stuff start dripping. They can smell it a long way off. Once you get them coming they will keep coming back as long as you feed them or kill them off.