The Effects of Surface Runoff on Hart Prairie from Arizona Snow Bowl Facilities, Coconino National Forest

     HART PRAIRIE IN NORTHERN ARIZONA is a famous scenic area noted for its mountainous viewscape that is enhanced by grasslands and colorful aspen groves; it is heavily visited in summer and fall. Beyond esthetics, the prairie is in the San Francisco Peaks Traditional Cultural Property, which constitutes part of the cosmology of more than 13 Indigenous Nations and Peoples. They revere the place in all its forms and have
sought to reduce harm to the prairie and the peaks (Gitlan, 2022; Jocks, 2022).

A cycle of erosion (i.e., gullying) is incising the prairie’s surface outside Arizona Snow Bowl’s permitted area where gullies were previously unknown. Gullies are caused by stormwater runoff from Arizona Snow Bowl’s stormwater drainage system. Generally, the erosional process is discontinuous and involves deepening, widening, and downstream and upstream extension of one or more gullies. The runoff, originating entirely in the Snow Bowl drainage basin, is opaquely turbid, nutrient-rich, and potentially harmful to the prairie’s ecosystem. Sampled phosphorus and nitrogen concentrations of the runoff are significantly larger than current nutrient standards, including the expected predevelopment levels of this volcanic geological terrain, suggesting a
human-made source. Snowmaking on the basin’s ski slopes requires large amounts of reclaimed water. The water itself contains relatively high nutrient concentrations. The concentrates accumulate seasonally in the snowpack and can infiltrate ski-slope soils during periodic melting. 

Excess nutrients in the sampled stormwater could be derived from erosion of the deforested ski slopes during relatively frequent runoff-producing monsoonal rainfall. Remediation includes holding runoff on-site in retention ponds or rerouting it into its natural channel on the prairie. Additionally, runoff volumes are needed, and geochemical studies of the forest, bedrock, and prairie soils can establish natural nutrient concentrations for comparison with those of ski slopes.

A major concern in the area has been the potential disturbance of natural resources resulting from ski-slope construction and the application of artificial snow made with reclaimed water on the slopes. These disturbances can affect the soil, water, vegetation, and wildlife of the Snow Bowl basin and the Hart Prairie study area. For the most part, even after the passage of nearly two decades since a call for scientific study, little is known about the environmental effects of reclaimed water on ecosystems in the basin and those of Hart Prairie (Niraula and Tecle, 2006).

Ongoing disturbances of the prairie identified in this report are increased surface runoff and the potential chemical pollution of the prairie’s ecosystem. Specifically, runoff in the study area has two undesirable effects—the erosion of the prairie and the potential of the nutrient-rich runoff to alter the prairie’s native vegetation. These environmental problems could be exacerbated by a planned expansion of Snow Bowl operations (https://www.azcentral.com>snowbowl expansion).

Richard Hereford
Research Geologist Emeritus (USGS)*
*This study is not affiliated with nor funded by the U.S. Geological Survey.