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USGS sees problems, successes in ground water management

Another very good article from Shar Porier of the Sierra Vista Herald/Review on the San Pedro River and the related groundwater issues with Fort Huachuca. Is it any wonder that the definition of sustainable yield remains up in the air and that the Upper San Pedro Partnership is almost a decade late in achieving it.

The article is reprinted in its entirety below with a link at the end. Photo courtesy of Mark Levy of the Herald/Review.

SIERRA VISTA — One of the main complaints environmental groups have with Fort Huachuca and the Upper San Pedro Partnership (USPP) is the goal of sustainable yield within the Sierra Vista Subwatershed was not attained by the Congressionally–set date of 2011.

But, just what does “sustainable” mean? It is a question the U.S. Geological Survey (USGS) tried to answer and evaluate in a report released a year ago using data collected for over the past 100 years.

Called Hydrological Conditions and Evaluations of Sustainable Groundwater Use in the Sierra Vista Subwatershed found sustainability has two distinct meanings.

One is: “The critical limits view, which considers certain resources such as water as essential to both humans and ecological systems and that such resources constrain the Earth’s population and its manner of living. Spoiled, destroyed, or otherwise wasted resources impact future populations and lifestyles.”

The other is: “The competing objectives view, which looks to balance or optimize resource use among different systems, typically environmental, economic, and social systems. This can be seen as attempting to meet a broad range of human needs and aspirations.

“Although distinct, the two sustainability concepts are compatible — the resource requirements of the environment and economic and social systems today are balanced not just against each other, but also against the same needs in the years to come.”

The Upper San Pedro Partnership (USPP), a think tank of 21 state and federal agencies, local jurisdictions and nongovernment organizations, was formed to tackle the water problem after the U.S. Congress established the San Pedro Riparian National Conservation Area (SPRNCA) in 1988. The organization was tasked by the U.S. Congress with resolving the aquifer decline problem to protect the SPRNCA and reach sustainable yield by Sept. 30, 2011, through Public Law 108-136 (Section 321).

Section 321 stated, “For purposes of section 7 of the Endangered Species Act of 1973, concerning any present and future federal agency action at Fort Huachuca, Arizona, water consumption by state, local and private entities off of the installation that is not a direct or indirect effect of the agency action or an effect of other activities that are interrelated or interdependent with that agency action, shall not be considered in determining whether such agency action is likely to jeopardize the continued existence of any endangered or threatened species or result in the destruction or adverse modification of designated critical habitat.”

One thing not included in the Section 321 rule was the definition of “sustainable yield of the regional aquifer,” researchers found.

For the most part, they found modeling trends defined it as: “Groundwater withdrawal is sustainable, if the effects of that withdrawal are acceptable to all who are or who will somehow and in any way be affected by it.”

They used an example from the California Water Foundation which in 2014 defined sustainable groundwater management as: “The management of a groundwater sub-basin to provide for multiple longterm benefits without resulting in or aggravating conditions that cause significant economic, social, or environmental impacts such as longterm overdraft, land subsidence, ecosystem degradation, depletions from surface water bodies, and water quality degradation, in order to protect the resource for present and future generations.”

The USPP determined the definition as: “the use of groundwater in a manner that can be maintained for an indefinite time without causing unacceptable environmental, economic or social consequences.”

Further, the USGS reported, “There is no single, correct formula to derive some accurate sustainable yield value. Sustainability is a value-laden concept and one that in many respects is in the eye of the beholder.”

However, the needs of the ecosystems, the economy and society must be kept in balance. Groundwater can be used up to a point just short of causing unacceptable adverse impacts, while ensuring the groundwater for the three systems “remains plentiful in the future,” noted the USGS.

The researchers point out that currently within the subwatershed, sustainable use of groundwater is dependant on stabilizing groundwater discharge to the river. “There are no serious constraints on water availability for the economic and societal needs, although this could change in the coming decades. A sustainable pumping rate for a region requires local stakeholders to determine the balance between the benefits of groundwater use versus the impacts on riparian systems and streams and other downstream users.”

Through the designation of the SPRNCA by the U.S. Congress, USGS says society has already determined the riparian system is a valid and important use for groundwater in the Sierra Vista Subwatershed and sustainable pumping rates can “permanently maintain groundwater levels and hydraulic gradients that will, to some degree, maintain the upper San Pedro River riparian system.”

Researchers stated, “In the subwatershed, decreases in groundwater levels of just a few feet could be the difference between health and degradation of the San Pedro River aquatic system, near stream herbaceous plant groups, and the cottonwood-willow riparian forest.”

And, the USGS repeated as other researchers have in the past, “Even if groundwater pumping were to stop today and the groundwater budget balance was positive for decades to come, the effects of pumping over the past century would eventually capture surface flow from the river. According to recent modeling, some capture of surface flow from the San Pedro River is already occurring, although widespread capture was not yet obvious based on many of the indicators and related monitoring found in this report.”

The cone of depression beneath the Sierra Vista/Fort Huachuca area will continue to spread for decades or more without significant mitigation measures. Data indicated it may be too late to prevent declining water levels from reaching the SPRNCA from the Charleston to Tombstone reaches. Ongoing evaluations can help determine the rate of propagation toward the river and where development and implementation measures may be successful to help prevent deteriorating hydrological conditions.

The USGS recommends the continuance of monitoring data to improve the regional groundwater model so more accurate projections can be made regarding the sustainability of various rates and locations of groundwater withdrawal, as well as regarding the mitigating effects of various rates and locations of enhanced recharge in the subwatershed.

In conclusion, they report, “In fact, to stabilize groundwater discharge to the riparian area and base flow in the river in spite of a spreading cone of depression would represent a major groundwater management success.”

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