Water is at once scarce and abundant, and in the midst of this paradox is the absolute epitome of aridity: the drifting, towering heaps of sand that comprise the Great Sand Dunes. Their very existence depends upon water, and yet they seem the ultimate representation of a desert.

Michael Geary, researcher

Imagine taking a voyage on a stream from the top of the Rocky Mountains to the Desert Southwest - in only a few hours. The Great Sand Dunes system contains sparkling, surging streams that follow an incredible journey through almost all Colorado ecosystems—and all within Great Sand Dunes National Park and Preserve. Originating as snow on 13,000' peaks, Medano and Sand Creeks cascade first into high lakes situated at timberline, then flow through dense spruce and fir forest, beaver meadows dotted with mountain wildflowers, large aspen and cottonwood groves, ponderosa forest, massive dunes, and spacious desert grasslands. The water seems to disappear in the sand—only to reappear as ponds and verdant wetlands on the west side of the dunes.

Along the way, these waters have presented scientists with a number of mysteries: Why do these creeks "pulse" around the dunes in rhythmic waves? How do these creeks keep the dunes in place? Why have most of the ponds in the dunefield disappeared in the past 50 years? If the water table were to drop from a proposed commercial water export, how would the creeks and remaining ponds be affected? Why are the creeks low during the day and high at night, the opposite of what one would expect from mountain snowmelt during the daylight hours? How pure are the waters? How long has the water under the dunes been there?

These questions are not merely scientific curiosity, but relate to our responsibility to protect the dunes for future generations. Over the past twenty years, a variety of corporate owners of the northwestern parts of the dunes have proposed large-scale water export projects from the waters beneath the dunes to various quickly growing cities. Because the creeks and wetlands of the dunes are directly affected by this water table, the National Park Service - along with most San Luis Valley residents who also depend upon that water - oppose these commercial proposals. Staff at Great Sand Dunes continues to seek knowledge about the complicated system of water, wind, and sand that created and maintains these incredible dunes. Answers to some of the mysteries are beginning to come to light because of these research efforts.

Streams with a Pulse At only a few places in the world can one experience "surge flow", a stream flowing in rhythmic waves. Three elements are needed to produce the phenomenon: a steep enough grade to give the stream a higher velocity; a smooth, mobile surface with little resistance; and sufficient water to create surges. In spring and early summer, these elements combine to make waves at Great Sand Dunes. As water flows across sand, sand dams or 'antidunes' form, gathering water. When the water pressure is too great, the dams break, sending down a wave. In wet years, waves can surge up to a foot high!

Nature's Recycling Project Without the cradling effect of Medano Creek on the east and south sides of the dunes and Sand Creek on the north, the Great Sand Dunes would look, and be, dramatically different. Sand grains blow into the dunes from the valley floor, bouncing up and down over the sea of sand, until they drop into Medano or Sand Creek, which flow out of the mountains. The moisture in the creeks captures the wind-blown sand, and the creeks then carry the sand back downstream to the valley floor again. The recycling continues, blown by the winds to pile the sand to gigantic heights. However, to a large extent the creeks' flow directly depends upon the water table. If the water table were to drop during the spring and summer runoff seasons—even just a few feet—the creeks' flow over the sand would diminish as the water sank below the surface to meet the lowered water table. The process of sand recycling would be significantly reduced. The dunes, unbounded by the water, would over time spread out over a larger area, perhaps dissipating some of their massive height.

A Complex Pool The water table supports other features important to the dunes, as well. The sabkha is the area around the dunes where the sand is cemented together by evaporite salts from seasonal ponds. Without regular saturation and evaporation, the sabkha would slowly disintegrate. Ponds and wetlands, and the abundant life they support, are supported by the water table and are also subject to sub-surface changes. Rare shorebirds, mammals, amphibians, and the endangered Slender Spiderflower all depend on these fragile wetlands for their existence.

Disappearing Ponds It is possible that the water table has already dropped significantly from historic and current use. Research is ongoing as to why aerial photos in the 1930's and 1940's showed over 80 ponds in the dunes - and why all but 5 had disappeared by the end of the 20th century. While some research indicates that at least part of the cause may be a natural geological change or related to cyclical precipitation patterns, historical evidence suggests significant alteration of the entire regional water system by human use over the past century may be a contributing reason. By 1938, an estimated 10,000 artesian wells had been drilled into the regional aquifer. Many San Luis Valley streams and rivers have been extensively diverted for irrigation both toward and away from the dunes area. The issue of water use, water rights, and conservation in the arid West has come to the forefront in our own valley.

Doing a Lot of Drinking Visitors and park rangers at Great Sand Dunes observing the flow of nearby creeks in the summer months have often noticed that the creeks beside the dunes rise in the evening, peak just before dawn, then drop again as the sun rises. The opposite flow pattern is expected; the sun melting snow on nearby peaks should boost creek flow in the daytime, while cooler temperatures at night should slow the water as the snow stops melting. A few years ago, research suggested an answer: when the sun strikes cottonwood and aspen trees along a sandy stream bank, photosynthesis begins, and trees quickly draw water from the stream up through the porous sand into thirsty leaves. As darkness falls, the trees cool down, photosynthesis slows, possibly influencing stream flow.

Pure and Clean Water quality is monitored continually throughout the monument and preserve. The water is of such rare purity that it qualifies under rigid standards as an "Outstanding Waters" designation from the US Geological Survey. This provides an ideal habitat for all wildlife, especially species that have declined in other areas due to water pollution.

Ancient or Recent? Recent research shows that water appearing as springs on the west side of the dunes has taken over 50 years - perhaps much longer - to flow through the dunes system from the time it fell as precipitation. How can we know this? Throughout much of the West, trace amounts of tritium, scattered from nuclear testing in the 1950's, appear in all surface waters originating as precipitation after that time. The water flowing from the springs today contains no tritium and therefore fell as precipitation before the 1950's. The spring water is currently being carbon-dated to get an idea of how old the water is; results are expected in the next year.

Water is the lifeblood of Great Sand Dunes. As in our own bodies, water is the glue that holds this complex system together. Without water, the dunes and the incredible diversity of life in and around them would become the "Not-So-Great Sand Dunes": creeks would no longer flow across the sand, the dunes and the sand deposit around them would change, and wetlands and ponds that support life would dry up. In 2000, a citizen-based effort supported by most of Congress led to the successful passage of the Great Sand Dunes National Park and Preserve Act. The Act authorizes the creation of a national park (which will include the former Great Sand Dunes National Park) and a national preserve that includes the whole hydrological system of the dunes, from tundra to wetlands. The dunes' mountain watershed has already been protected as the new Great Sand Dunes National Preserve. Complex negotiations are currently underway, in cooperation with the Nature Conservancy, to finalize the purchase of the privately owned lands where water export was proposed. When completed, we'll have taken a major step toward understanding and protecting the pristine, fragile waters of the dunes.