By K. Nepsa
As we experience one of the best monsoon seasons in recorded history, many people have witnessed the raging waters running through the Pantano Wash. The Pantano Wash runs through our community of Vail and its seasonal waters act like an intermittent heartbeat for our local ecosystems. The section of the Pantano Wash we see in Vail is actually part of a greater watershed, called the Pantano Wash-Rillito River Watershed. The watershed can be defined as the area drained by the Pantano Wash to the confluence with the Santa Cruz River north of Tucson, near Oro Valley. It covers approximately 935 square miles (598,235 acres), representing about 1.0% of the state of Arizona. The watershed has a maximum width of about 25 miles east to west, and a maximum length of about 50 miles north to south.
What is a watershed? A watershed is the area of land where all of the water that drains off of it goes into the same place—a river, stream, lake or sea. A watershed can be small or can encompass thousands of square miles and may contain streams, rivers, lakes, reservoirs, and underlying groundwater that are hundreds of miles inland. Water from hundreds, and often thousands, of creeks and streams flow from higher ground to rivers that eventually wind up in a larger waterbody. As the water flows, it often picks up pollutants, which may have sinister effects on the ecology of the watershed and, ultimately, on the reservoir, bay, or ocean where it ends up. Not all water flows directly to the sea, however. When rain falls on dry ground, it can soak into, or infiltrate, the ground. This groundwater remains in the soil, where it will eventually seep into the nearest stream. Some water infiltrates much deeper, into underground reservoirs called aquifers. In other areas, where the soil contains a lot of hard clay or parched soils, very little water may infiltrate. Instead, it quickly runs off to lower ground. The excess water volume can quickly overwhelm streams and rivers, causing them to overflow and possibly result in floods.
Fun fact: The largest watershed in the United States is the Mississippi River Watershed, which drains 1.15 million square miles from all or parts of 31 U.S. states and two Canadian provinces stretching from the Rockies to the Appalachians!
There are 5 different land ownership/management entities in the Pantano Wash – Rillito River Watershed. Privately held land is the largest category, representing about 32% of the watershed, followed by the US Forest Service with about 29%, and State Trust with about 22%. The National Parks, the Bureau of Land Management, and the Military hold smaller amounts of land in the watershed. The watershed includes forest, urban, range and water land uses, with range land comprising approximately 80% of the watershed. It also includes 172 known ore mines and 153 mines whose ore is unknown. Fun Fact: There are at least 20 gold mines in this particular watershed.
There are resource concerns that have been identified in the watershed that have direct impacts on the ecosystems within the watershed. According to xxxxxxxx, “The main concern in the Watershed is rapidly expanding urbanization and accelerated recreational use of public lands resulting in impacts to vegetation and soil surfaces which may affect hydrologic function. The desert and semi-desert ecosystems have developed in a climatic regime of wide fluctuations of precipitation, ranging from drought to flood. Human uses superimposed on that climatic regime can tend to exacerbate their effects on soils, vegetation and wildlife. Another serious concern is current and future mining, which can result in permanent alterations to the land including removal of vegetation and wildlife habitat, disruption of normal hydrologic flow paths, and potential for water quality degradation (ground water and downstream) (Pima County, 2000). Sand and gravel mining in Pantano Wash – Rillito River can destabilize the channels, remove riparian habitat and alter hydrologic patterns. The Pantano Wash – Rillito River Watershed includes the Pima County Cienega Creek Natural Preserve, designated to protect the rare perennial riparian ecosystem of Cienega Creek and its tributaries. Ground water pumping has lowered the ground water table, thereby reducing or eliminating springs and perennial surface waters flows and impacting the associated wetland and riparian vegetation communities and wildlife species. Riparian areas are highly important to both humans and wildlife. Maintenance of base flow of stream segments and springs is necessary for the health of these critical areas.”
While solutions to these concerns aren’t immediately apparent, it’s important to keep “conservation” in mind for Vail’s natural areas. It’s also important to remember that flooded washes can take lives. So, please be careful while enjoying the views.
References:
Ocean Facts, What is a Watershed?, National Ocean Service, National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce
Pantano Wash-Rillito River Watershed, Arizona, Rapid Watershed Assessment, Natural Resources Conservation Services (NRCS), June 2007, pages 1-1 to 3-21.
