It looks good and all, for a park. I have to be honest but I liked it better in the pic showing just after you applied the sand. It doesnt really look like a battlefield at all, but it still looks good. Whatever makes you happy.
In video games, I
love battlefields that start out as beautiful pristine places! Games like Company of Heroes and World In Conflict especially are great examples of this. However, they have the ability to pour pure
ruin into places like these every time an artillery shell lands/bomb goes off/etc with dynamic terrain/object alteration. 40k doesn't have this ability unless you make modular pieces with it in mind, like craters, burned out trees, destroyed versions of buildings, etc to put down throughout the course of the game. This would be difficult as you'd be nearly doubling your work and tedious to add another task to gameplay.
It would be very interesting to incorporate "destructible terrain" rules into 40k. Whenever blasts/barrages go off, put appropriately sized craters counting as 5+ cover. Buildings/bunkers could have different protective qualities depending on if they are standing or ruined, and woods could be burned to ashes via incendiary weapons. Of course, the existing rules set doesn't balance for this very well, so it would need some adjustment and possibly additions to certain army lists to work.
At any rate, your table would be the perfect one to do something like this to. One of the disadvantages of your board is that it is not modular and will be the same every time you play on it. Destructible terrain rules would change the battlefield every turn, giving troops new cover to hide in, forcing them to flee from what used to be a position of saftey, opening up new routes for vehicular maneuvering or closing them off entirely.
It would be difficult to pull off though. However, I've played on both static boards (built to stay as they are like yours) and on boards with movable terrain. I've found that the biggest difference tends not to be the variety involved, but the surfaces in general. Modular boards tend to be much easier to arrange models on, while static boards may have beautiful set pieces which are very difficult to use because models simply won't stand up on them, or will be forced into odd/detrimental formations. You seem to have done a good job making large playable areas on your board, so I doubt it will be much an issue.
Great job, enjoy!