USING LIDAR-DERIVED DIGITAL ELEVATION MODELS TO DETERMINE NATURAL STREAM CHANNELS AT GREAT SAND DUNES NATIONAL PARK & PRESERVE, COLORADO

In 2000, Congress expanded the National Park Service (NPS) boundary at Great Sand Dunes to allow the NPS to manage and protect an extensive aeolian and hydrological system. The former boundary of Great Sand Dunes National Monument encompassed only the dune field; however, the expanded boundary incorporates other aeolian deposits such as a sand sheet and an inland sabkha. Developed on these aeolian deposits is a fluvial system that originates in the Sangre de Cristo Mountains above the dunes, flows around the dune field and terminates on the sand sheet or the playas of the inland sabkha. There are also streams that emerge from the sand sheet and terminate in playas.

The National Park Service is negotiating the purchase of lands within the expanded park boundary that are part of the historic Medano Ranch, currently owned by The Nature Conservancy. These lands are in the southwest portion of the Park where elevations are lowest and the distal stretches of several streams are found.  As a ranch, the land use is agricultural and stream flow is diverted through a network of ditches to irrigate meadows.  Once Park management begins, agricultural activity will cease and an effort to restore natural systems will take place. It is rare in the western US to have and entire stream system be under natural flow conditions.

There are a number of studies underway to determine the effects of the potential land use change. This presentation will focus on the effort to determine where the natural channels of Sand, Big Spring, and Little Spring Creeks would develop if not diverted by ditches. The area is broad, very flat, covered by meadows and 140 years of ranching has obscured signs of historic channels. Lidar data and aerial imagery are available and will be used to indicate where streams would flow through meadows as broad, shallow, grassy channels, and then fill ponds along a lunette front. There is also a need to know where each stream would breach the lunettes, and which playas they would flow into.  The goal is to restore natural processes, and also address how changing water use might impact neighboring water rights holders.