Terms

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Acre-Foot(af) – 326,000 gallons.  Picture a football field under one foot of water – more precisely defined as one foot of water covering one acre.  This term is often used in conjunction with a period of time such as acre-foot per year (af/yr).

Aquifer – An underground layer of sand, gravel and porous rock that holds water that contains sufficient saturated materials to be capable of yielding water in usable quantities to a well.

Biological Opinion (BO) – A legally binding contract, pursuant to Section 7 of the Endangered Species Act, between the U.S. Army and the U.S. Fish and Wildlife Service. Review the 2007 Biological Opinion in PDF form.

Checkdam – a small dam constructed in a wash to slow stormwater runoff and increase recharge.

Cone of depression – the area around a well where the water table is lowered due to pumping.  Groundwater flows toward the well into the cone of depression.

Constructed wetlands – constructed wetlands for wastewater treatment consist of shallow depressions or cells built into the ground with level bottoms so that the flow of water can be controlled within the cells and from cell to cell. Roots and stems of the wetland plants form a dense mat where biological and physical processes occur to treat the wastewater.  The constructed wetlands at the City's Environmental Operations Park offer the added benefit of providing a unique habitat for birds and wildlife.

Detention basin – A structure that captures stormwater and releases it slowly to allow more water to soak into the ground, or to control downstream runoff.  Sometimes confused with a “retention basin” that stores the water rather than slowly releasing it. For a map of detention basins in Sierra Vista, see our Detention Basins animated map.

Effluent – liquid waste discharge such as residential and commercial sewage that has been treated to a quality suitable for a beneficial use.   Currently in Sierra Vista the effluent treated at the Environmental Operations Park is being recharged into the aquifer.  In the future, effluent treated through proposed package treatment plants may be used for irrigation. 

Evaporation – when a liquid is converted to vapor

Evapotranspiration - combination of evaporation and transpiration of water into the atmosphere from living plants and soil.  Often used locally to refer to the process through which the vegetation along the San Pedro River “uses” water. 

Environmental Operations Park (EOP) – Located East of Sierra Vista near MM325 on SR 90, the EOP is the location of the City's compost facility, its wastewater treatment facility, 30 acres of recharge basins, 50 acres of constructed wetlands and a 1,800 square-foot wildlife viewing facility.  Nearly 2,000 acre-feet of effluent is recharged to the aquifer annually at the Environmental Operations Park. 

Floodplain – land next to a river that becomes covered by water when the river overflows the banks

Gallons per capita daily (GPCD) – For Sierra Vista's purposes, this number is calculated by dividing the amount of all water pumped within the City limits for any use (residential, commercial and irrigation) by the City's population number, resulting in an average daily use per person within the City limits of Sierra Vista.  

Grey water – Any water that has been used in a home or business, except from toilets, is called grey water.  Dish, shower, sink, and laundry water use comprises a significant portion of  “waste” water, which can be reused, especially for irrigation.

Groundwater – water that infiltrates into the earth and is stored in usable amounts in the soil and rock below the earth's surface.

Overdraft – The amount by which the quantity of water pumped from the ground exceeds the quantity of water that is recharged.  Local use usually refers to annual amounts of recharge minus both environmental and human water uses.

Package plant –a self-contained wastewater treatment system that treats water onsite for a specific purpose.  A package plant is often contained within a building and is designed to treat sewage from a specific area such as a residential neighborhood or a business park.  In the case of the package plants proposed for Sierra Vista, the treated effluent would be used for irrigation.

Percolation – the movement of water through the subsurface soil layers, usually continuing downward to the aquifer.   

Perennial stream – a stream that contains water at all times, except in extreme drought.  Sections of the San Pedro River have perennial stream flows. 

Pumpage – water brought to the surface by means of pumps or pumping.

Recharge –the process by which water soaks into the ground through faults, fractures or through direct absorption or injection, to reach the aquifer.

Retention basin – A structure that captures stormwater and stores it until it soaks into the ground or evaporates.  Sometimes confused with a “detention basin” that slowly releases water rather than holding it. 

Riparian – An area where vegetation depends on open water or water close to the ground's surface. In the Sierra Vista area, the term most frequently refers to the vegetation along the banks of the San Pedro River.

Section 321 Report –The Defense Authorization Act of 2004, Section 321, directs the Secretary of the Interior, in consultation with the Secretary of Agriculture and the Secretary of Defense, and in cooperation with the Upper San Pedro Partnership (USPP), to prepare an annual report to Congress.  The report is referred to as the “Section 321 Report.”  The Section 321 report is drafted by the USPP, and outlines the steps being taken to reduce the overdraft and restore sustainable yield of groundwater in the Sierra Vista Sub-watershed by 2011. To date, two annual reports have been prepared; both of which are available on the USPP website for review.

SPRNCA – San Pedro Riparian National Conservation Area.  The U.S. Congress designated the SPRNCA, which includes approximately 40 miles of the upper San Pedro River, as a National Conservation Area in 1988.  Managed by the Bureau of Land Management, the SPRNCA contains over 58,000 acres of public land running from the U.S./Mexico border to St. David, AZ.

Stormwater runoff –water (originating as precipitation) that flows across surfaces rather than soaking in.  It is the goal in the Sierra Vista area to capture as much stormwater runoff as possible through retention and detention basins, check dams in washes, and other methods.  A portion of stormwater recharge may eventually reach the San Pedro River.  Keeping pollutants out of stormwater runoff is an important component of environmental protection.

Sustainable yield – the management of groundwater in a way that it can be maintained for an indefinite period of time without causing unacceptable environmental, economic or social consequences (excerpted from the USPP Strategic Plan, dated 9/13/06)

Transpiration – direct transfer of water from the leaves of living plants to the atmosphere.

Underflow – movement of water through subsurface material.

Upper San Pedro Partnership (Partnership)  – A consortium of agencies and organizations formed in 1998 to facilitate and implement sound water resource management and conservation strategies in the Sierra Vista Sub-watershed.

Watershed – land area from which water drains toward a common watercourse in a natural basin.  The area from the Mexican border north to Hwy 83, bordered on the east by the Mule Mountains and on the west by the Huachuca Mountains, is the Sierra Vista Sub-watershed.