I'm not crayfish expert, but you are getting no replies so I will take a stab at sharing what little I know. If you are seeing this specimen move across open grass, I would guess there is a good chance it is a Devil Crayfish. They bore holes in the ground that have chimneys above the ground. The holes are bored down to water level where they can keep their gills bathed in water. You will find them in areas not too far from where a water table can be within their digging depth. We find them in bottom land farm fields sometimes as far as a quarter mile from the creek, but if you drop a pebble in the hole often times you will hear it hit water. If it is a Devil Crayfish it would not be a desirable one for a pond as they bore holes and could potentially damage a pond dam. That said, if your pond is near a creek (like mine) you likely will have some even if you don't want them. They migrate during wet times to new areas, but always where they can bore down to water.
Your pictures are likely not good enough for anyone to identify the species reliably. You would need to catch one and take close up pictures of both the top but especially the under side of the crustacean. I'm making the guess (and that is all it is) of Devil Crayfish simply becuase you are seeing it moving around in grass. It likely is looking for a new home or a pool of water to reproduce.
Here is a link that shows a picture of both the Devil Crayfish and also a Northern. A northern would be a variety that you likely would only find in a stream around rocks. The only reason a person might find one on land was if its habitat had dried up and it was forced to migrate to another BOW. They normally stay in the water.
Crayfish in Kansas Crayfish species by state Maryland 
