Sand Creek
There are two streams that flow along segments of the dune field perimeter. Medano Creek flows along the east and southeastern sides of the dune field and Sand Creek flows along the northwestern side.The streams have a give and take relationship with the dunefield. They erode sand from some parts of the dune field and deposit it in others. Each exhibits a net erosion of sand from along the mountain front and deposition on the valley floor during high runoff periods. As flows decrease, the depositional areas dry up, exposing wide, braided channels so that the prevailing winds from the southwest can blow the sand back into the dunefield. This results in the dunefield having a crescent shape and the thickest sand deposits.
Medano and Sand Creeks are particularly effective at transporting sand because surge flow can develop in their braided channel sections. Each surge is a pulse of water occurring in regular intervals that can potentially flush more sand down the stream than steady flow. It is a rare phenomena because it requires a high flow regime and a smooth, mobile channel. The fast flow creates bed forms called antidunes. They increase the amount of water stored in the areas where they develop by 20 percent, since they force the water to flow over a sinuous surface instead of a flat surface. The antidunes are not stable and eventually break, releasing the stored water. Since the channel is sandy and creates little turbulence, the pulse of water produced by the collapse of the antidune continues downstream in a discrete packet and picks up more water from other antidune fields.
