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The Verde Independent | Cottonwood, Arizona

home : latest news September 15, 2014

5/26/2009 1:46:00 PM
Big Chino: The big water bank
The headwaters of the Verde River emerge at a point where the Big and Little Chino Valleys meet, amidst a complex pathway formed through subterranean basalt flows, alluvial sediments and Paleozoic rock.
The headwaters of the Verde River emerge at a point where the Big and Little Chino Valleys meet, amidst a complex pathway formed through subterranean basalt flows, alluvial sediments and Paleozoic rock.
The upper end of the Verde River watershed has but two rich aquifers. The Big Chino and the Little Chino basin fill aquifers shaded in yellow. The blue areas are the carbonate aquifer, which acts as a pass-through zone for water from the highlands. The pink areas are metamorphic and igneous rock, which does a lousy job of capturing water.
The upper end of the Verde River watershed has but two rich aquifers. The Big Chino and the Little Chino basin fill aquifers shaded in yellow. The blue areas are the carbonate aquifer, which acts as a pass-through zone for water from the highlands. The pink areas are metamorphic and igneous rock, which does a lousy job of capturing water.

Steve Ayers
Staff Reporter

The Big Chino Basin, on the upper watershed of the Verde River, has been front-page news for over ten years. It will remain there for the foreseeable future as interest groups and stakeholders continue their fight over its rich aquifer. This four-part series explains its geology, its history, its current status and provides insights into its future.

In an arid land, water is money.

And so it follows that where there is water, there is wealth.

Deep aquifers are nothing less than underground vaults stacked with liquid currency -- measured not in dollars, but by the acre-foot.

As such, an undisturbed aquifer is nothing less than a buried treasure.

The treasure box

The Big Chino Basin is a 1,850 square miles of drainage on the upper reaches of the Verde River watershed.

Near the southeast border of the basin, beneath the grassland surface of the Big Chino Valley, is a deep, rich and, by standards, undisturbed aquifer -- 28 miles long, two to six miles wide and 2,500 to 3,000 feet deep.

Depending on the estimate, the aquifer contains between 6 and 12 million acre-feet of potable water, enough to conservatively sustain a city of 1 million for 40 years, or any fraction thereof, without additional replenishment.

In a land of little water and few restrictions on its exploitation, The Big Chino aquifer looks remarkably like an unguarded vault.

The wealth beneath has not escaped the attention of landowners above, or the adjacent municipalities.

Guarding the vault

But the aquifer contains another form of wealth, one that is less tangible, immeasurable in either dollars or acre-feet.

As long as the Big Chino's aquifer remains full, it will continue to spill its excess water out a series of springs located along its southeast edge, sustaining the first 24 miles of the Verde River.

However, if enough withdrawals are made, the flow will stop.

It is a concept that has not escaped the attention of those who wish to see one of the desert southwest's last flowing rivers continue flowing.

And that is precisely why so many people, living in both the Prescott area and the Verde Valley, now find themselves chained to the unguarded vault.

Creation of a Basin

The Big Chino basin began life sometime during the late Miocene age.

Around 6 million years ago, a piece of the North American plate, which we recognize as Baja, Calif., welded itself to the northward traveling Pacific plate.

As it was torn away from its parent, it rent open what is now the Gulf of California and, in the process, stretched the crust east of it to such an extent, it created a deeply faulted and fractured landscape of parallel mountain ranges and intervening basins.

Between the newly created basin and range of what is now southern Arizona, and the uplifted Colorado Plateau in the north part of the state, a transition zone formed -- a jumble of fractured blocks with characteristics of both provinces.

As the huge blocks of crust rose and fell, canyons, basins and highlands took form. One of those basins, formed below the plateau's northwest reach, became the Big Chino.

The deep aquifer

Near the southeast edge of the basin, a graben -- a keystone-shaped block of crust -- dropped, tilting dramatically downward along its faulted northeast facing edge, creating the Big Chino Valley within the surrounding basin.

As the graben subsided, the ancient Mogollon Rim shed its crumbling face onto the basin floor, filling the valley's empty pocket as the rim retreated to the northeast.

At the same time, the mountains lining the basin's southwest edge also shed their fine grain sands into the voids.

As the valley filled with these loose alluvial deposits it also filled with water -- vast amounts of water trapped on three sides and the bottom by billion-year-old, impervious Precambrian rock.

On the remaining side, its southeastern boundary, a complex pathway formed through subterranean basalt flows, alluvial sediments and Paleozoic rock, creating a permeable border through which the basin drained.

At some undetermined point in time, likely in the last 2 million years, the Verde River began following a path of least resistance from the basin's edge, through the jumble of fractured blocks, on to the Gulf of California.

Today the river continues to carry off what moisture falls from the sky, what drains off the surrounding hills, what drains through Coconino Plateau and what spills out the basin's southeastern edge.

Basin facts

The Verde River Basin is one of 53 groundwater basins in Arizona, many of which are divided into subbasins.

The assumption among hydrologists is that subbasins have a hydrologic connection with adjoining subbasins within the same groundwater basin, while the larger basins are distinct geologic enclosures with little or more connectivity to other groundwater basins.

The Verde River Basin is comprised of four sub-basins, Big Chino, Little Chino, Verde Valley and, further downstream on its way to its confluence with the Salt River, the Verde Canyon sub-basin.

The Little Chino sub-basin includes the incorporated communities of Prescott and Chino Valley. It has a population in excess of 50,000.

Together with the adjoining Upper Agua Fria basin, in which is located the Town of Prescott Valley, it forms the Prescott Active Management Area basin, which has a population in excess of 130,000.

It is designated an active management area because its groundwater supplies are currently over-allocated, requiring active measures to bring it back in balance.

The Verde Valley sub-basin includes the incorporated communities of Sedona, Cottonwood, Jerome, Clarkdale and Camp Verde, and has an estimated population of 75,000.

There are no incorporated communities within the Big Chino sub-basin, which has a population of approximately 7,500.

The Big Chino sub-basin is comprised of Big Chino Valley, Williamson Valley, Big Black Mesa and the western part of the Colorado Plateau.

Its four primary surface drainages are Big Chino Wash, Partridge Creek, Walnut Creek and Williamson Valley Wash.

The Big Chino basin contains an estimated 155 million acre-feet of saturated sediment, most of which is concentrated in the 570 square miles beneath Williamson Valley and Big Chino Valley.

The basin's basic problem

In an average year, if such a thing exists, the Big Chino basin receives 1.6 million acre-feet of precipitation from rain and an additional 200,000 acre-feet from snow.

The U.S. Geological Survey estimates only 1.3 percent of the precipitation that falls on the basin makes it to the aquifer. The rest is lost through runoff, evaporation and evapotranspiration (loss through vegetation).

The entire basin takes in an average of just 23,000 acre-feet of recharge a year.

Those who wish to tap this vault contend it does a remarkably ineffective job of capturing moisture because it is always full.

By contrast, the Verde Valley sub-basin is a sponge, capturing 146,000 acre-feet a year or about 4.4 percent of the precipitation that falls upon its watershed.

The Big Chino has remained full because, up until the latter part of the 20th century, it remained unexploited and relatively undeveloped.

In 1991, following a statewide fight by rural counties (read: groundwater basins) to keep large municipalities from appropriating their groundwater, the Legislature limited the ability of one basin to tap the water in another basin

Exceptions, however, were made. One of those exceptions allocated up 14,000 acre-feet of Big Chino basin groundwater to the City of Prescott and other communities in the Verde River watershed.

Within eight years, the exception would spark a controversy. But over the last 10 it has become a minor share of a much larger problem.

Related Stories:
• Big Chino: The Big Rush

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Reader Comments

Posted: Thursday, October 22, 2009
Article comment by: Water theft

The land owners above the aquifer must be remunerated for the theft of their water. Land Patent holders have exclusive ownership of al minerals,water etc. from the center of the earth thru the heavens..

Posted: Wednesday, May 27, 2009
Article comment by: PAUL F. MILLER

for me, this single line in Steve Ayers' article sums it up ..."In an arid land, water is money"... The potential water in the Big Chino basin makes it the perfect eye of the storm respecting "water-wars" into the coming years. We have yet to reach that point where we honestly set aside proprietary and territorial, partisan, interest and take a view through the lens of humanity. Merely suggesting an humanitarian perspective is sufficient to polarize some folk's position on water, which they see as sacrosanct rights. Understandably we find it difficult to see "right" from a holistic perspective when we feel the rights being attacked directly affect us. Until "we" are able to see water from the perspective ... ... "everyone has the right to clean & accessible water, adequate for the health & well being of the individual & family, and no one shall be deprived of such access or quality of water due to individual economic circumstances" ... Water will be a paramount ingredient in our warring action. Paul F. Miller striving to promote sustainable awareness BLOG SITE NAME ... AUTHENTICALLY WIRED BLOG SITE ADDRESS ... http://waterman99.wordpress.com/2009

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