The streams (although not Chesney's rivulet) are represented by the taller, yellowish vegetation. They are probably only a few feet across, and don't need to be represented with artificial water. Probably there should be more trees than are shown; as is, it is a challenge to clearly see the minis when they are on the board, much less move them from one spot to another.
The placement of coniferous and deciduous trees on the battlefield loosely follows from participant statements.
Several accounts mention pine trees in connection with the battle. For example, Private John Thomas of Virginia, who was on the left wing of the main line, recalled that "The battle took place in the woods & the timber was mostly pine." David Stewart claimed that the American front line was "drawn up on a rising ground, thinly covered with pine trees." Major George Hanger and Brigadier-General William Moultrie (both of whom were knowledgeable about the battle, even if they were not present) described the battlefield as a pine barren.
Captain Samuel Hammond mentioned that the area between Elevations 1 and 2 was dominated by deciduous trees:
"The ground on which the troops were placed, was a small ridge, crossing the road at nearly right angles. A similar ridge, nearly parallel with this, lay between three hundred and five hundred yards in, his rear. The valley between was made by a gentle slope; it was, of course, brought within range of the eye; passing from one to the other ridge, the land was thickly covered with red oak and hickory with little if any underbrush. The valleys extending to the right of the general's camp, terminated in a small glade or savanna."
The area that Hammond was referring to included the patch of deciduous trees in the upper left corner of the last picture. The area of the "small glade or savanna" begins at the upper left of the last picture and extends beyond the edge of the picture.
John Moncure's online history of the battle, The Cowpens Staff Ride and Battlefield Tour, includes a transcription of the statements by Neel and Hammond.
David Stewart. (1825). Sketches... of the Highlanders of Scotland.