1. Overview

From 2001 to 2005, the Arizona Department of Water Resources ("ADWR") evaluated the Upper San Pedro River Basin ("the Basin") to see if it should become an Active Management Area ("AMA") -- an area in which the ADWR controls mandatory water conservation.

The entire report is online through

This digest provides the parts of the report most relevant to current politics in Cochise County. I have added some comments to point up interesting differences between current politics and the facts presented by ADWR, and also between ADWR's information and information provided from other sources. I've tried to keep each section short enough to be comprehensible and interesting.

Under Arizona law, a watershed basin should become an AMA if either 1) active management practices are necessary to preserve the supply of groundwater for future needs, or 2) land subsidence or fissuring is endangering property or potential groundwater storage capacity, or 3) the use of groundwater is causing or threatening a degradation in water quality. In other words: if the water is disappearing or turning bad, or the land surface is collapsing.

The ADWR's report, issued in March 2005, finds that the Basin should NOT become an AMA.

However, the report adds that the ADWR "will continue to work with the Upper San Pedro Partnership as a Partnership member on local water management and planning efforts." In other words: there is no water crisis in the Basin, but the ADWR is going to support the Upper San Pedro Partnership, whose constant message is that there IS a water crisis. This seems a little odd.

2. Basic information and terms

The San Pedro River ("the River") drains about 700 square miles in Mexico, and 1800 square miles in the United States. The Babocomari River is the River's only significant tributary.

Inside the US, the River flows north from Palominas to "The Narrows" north of Benson, where the Basin ends. The Basin includes the Sierra Vista and the Allen Flat sub-basins, but the Allen Flat sub-basin is negligible, so this report discusses only the Sierra Vista sub-basin.

For practical purposes, the Sierra Vista sub-basin is divided into the "Sierra Vista sub-area," from the Mexican border to Fairbank, and the "Benson sub-area," north from Fairbank.

The Sierra Vista sub-basin has two primary aquifers: a deep, regional aquifer, and a shallow, floodplain aquifer.

"Groundwater" is water that is either taken from a well, or located in an underground aquifer; in other words, groundwater is not flowing water such as a river.

Sierra Vista sub-area water comes almost exclusively from groundwater, for lack of another source. However, the Benson sub-area uses a large amount of River water for irrigation.

"Recharge" is water returning from the surface to an aquifer.

"Net use groundwater" is groundwater which does not return to the aquifer through recharge -- water that is really, really used up and gone.

A "cone of depression" is a drop in the water level of an aquifer, centered on the wells that are taking the water.

Some ADWR figures are EXTREMELY approximate, especially in calculating a "water budget" of inflow and outflow for the entire Basin. There is a good deal of guesswork, and some reasoning that seems unnecessarily obscure. However, in apology for the ADWR, some data are not available, and some data cannot even be theoretically calculated.

3. The Basin's 2000-year supply of groundwater

The Basin has about 20-26 million acre-feet of water.

In 2002, about 27,720 acre-feet were used, mostly for municipal and military uses near Sierra Vista/Fort Huachuca, and farming near Benson/St. David. About 9500 acre-feet was net use groundwater -- really used up and lost. That is less than 1/20 of 1% of the Basin's groundwater. In other words, the Basin has a 2000-year supply of groundwater.

For 2030, the ADWR predicts about 26,900 acre-feet of net use groundwater. That is about 1/7 of 1% of the Basin's groundwater. In other words, in 2030, the Basin will have a 700-year supply of groundwater.

As county residents know, there is a current push, led by Judy Gignac and her circle of politicians such as Pat Call, to convince Basin residents that there is a water crisis. The push is not based on reality. A federal law requires water conservation, but the law cannot create an actual crisis. Whatever the law says, the Basin has a 2000-year supply of groundwater.

4. Cones of depression

Between 1940 and 1961, a cone of depression developed near Fort Huachuca/Sierra Vista, dropping the groundwater up to 50'. By 1978, the cone was falling up to 4'/year. In other areas, wells were steady or dropping 9"/year or less. However, the cone is now definitely deepening slower than it used to.

Two other minor cones of depression are forming, one associated with pumping in the Benson area, the other associated with the Bisbee wellfield.

5. Overall, the Basin's water level is dropping only slowly, and in some areas is even rising.

Basically, the Basin has two aquifers: a shallow floodplain aquifer under the River, and a deep artesian aquifer. The two aquifers have different patterns of rising and falling.

The floodplain aquifer has shown no long-term drops in water level; in fact, water levels near Pomerene have risen. The deep artesian aquifer has had a modest drop.

Climate change, especially summer drought, may be contributing to groundwater level declines in some areas. At Tombstone, annual summer rain fell by about 1" from 1897 to 1997.

Here are some details about water-level changes in different areas of the Basin:
-- Mexican border/Hereford: changes from +7' to -4.9', with most between +3' and -3'.
-- Naco/Bisbee: the highest concentration of major declines, from -9.8' to -32.1'; but, toward the River to the west, changes from +1' to -4.1'.
-- Tombstone: drops, from less than -1' to -23.1'.
-- Sierra Vista/Huachuca City/Nicksville: Changes from -1.2' to -14.8' in a public well; in the cone of depression, most wells dropped, but less than 1'/year. Between Sierra Vista and Huachuca City, declines slower since 1990-2001, but from -5' to -7'. North of Huachuca City, from -1' to -5'; one public well was -13.4'. South of Sierra Vista, from -35.4' to +16.6'.
-- St. David: changes from +12.9' to -11.1'.
-- Pomerene/Benson: in the shallow aquifer, +6" to -10.2', mostly -1' to -5'. In deep wells, +4" to -18.9', with most declines from 4' to 9'. Near Benson, -5' to -11.8'.
-- "The Narrows"/North of Pomerene: south of "The Narrows," changes from +1" to -5.3', with an average of -1.5'. However, wells along the River rose an average of +4.7', up to +11.1'.

6. Different kinds of water use

Water use is classified as municipal, agricultural, livestock, industrial, or riparian.

In 2002, municipal demand was the largest use, at 18,800 acre-feet; 13,700 were net use.
-- Sierra Vista sub-area municipal use was about 15,100 acre-feet, about 80% of the 18,800 total. Of the 15,100 acre-feet, 14,500 came from groundwater. 3500 acre-feet were recharged.
-- Benson sub-area municipal use was about 3700 acre-feet, with 3300 acre-feet, about 85%, from groundwater. About 600 acre-feet were recharged.

Agricultural use was not measured, but calculated: acres irrigated, times crops' theoretical use of water for growth and transpiration. Agricultural use dropped about 40% from 1985 to 2002, and is expected to keep dropping. However, ADWR predictions through 2030 use the same acreage as for 2002.
-- Sierra Vista sub-area agricultural use was about 2500 acre-feet in 2002. Acres being irrigated dropped from 2000 acres in 1985, to 1400 in 1990, to 800 in 2002.
-- Benson sub-area agricultural use was about 7300 acre-feet in 2002, about 61% of the total Benson sub-area demand. Agriculture is predicted to remain the largest user in 2030. Acres being irrigated dropped from 3200 acres in 1985, to 2600 in 1990, to 2200 in 2002.

Livestock use was calculated at 300 acre-feet per year, based on 12 gallons per head per day (which implies about 22,500 head of cattle in the Basin.)

Industrial use means an industrial-type use that is served by its own well. Sierra Vista sub-area industrial use includes five sand & gravel facilities, and two golf courses. Benson sub-area industrial use includes a golf course, a dairy, and the Apache Nitrogen ammonium nitrate plant. In 2002, total use was 2100 acre-feet, all from groundwater; 2000 were net use.

Riparian use means vegetation along the River and the Babocomari; ADWR estimates this at 17,350 acre-feet/year. This figure will increase as conservation efforts increase.

In 2002, 79% of the water demand was municipal in the Sierra Vista sub-area, but only 30% in the Benson sub-area. In both sub-areas, municipal use provides the fastest-growing demand.

7. Water management, i.e. conservation

Since 1988, there has been an increase in conservation. Notably, Fort Huachuca reduced its use by almost 45% from 1993 to 2002 (though some people ask if troops have been moved to off-post housing to reduce on-post water use). Conservation has been implemented in the Sierra Vista area, but water use has increased with population. Basin-wide, municipal demand increased by over 5000 acre-feet from 1985 to 2002, and per capita use has not changed appreciably.

The ADWR will NOT assume a reduction in per capita use, because the estimated savings from conservation programs are affected by many variables, including the ability to measure program effectiveness, the impact of weather, the difficulty of modifying behavior, and the need for ongoing efforts to ensure that initial savings are maintained.

8. Effluent, i.e. treated sewage

In 2002, effluent production was about 5300 acre-feet.

Effluent from the Sierra Vista and Benson wastewater treatment plants is used for golf course irrigation and groundwater recharge; about 800 acre-feet went for golf courses. Fort Huachuca has built stormwater recharge projects.

Some plans are underway to use more effluent. For 2030, effluent production is predicted at 7700 acre-feet, with about 7300 acre-feet recharged or used directly. With these efforts, the Basin's net use of groundwater MAY NOT INCREASE by 2010.

Clearly, effluent may become significant in water conservation.

9. Golf courses

Four golf courses were noted as using a large volume of water:

Course --------------- Water Provider ----- Demand (acre-feet/yr)
Chaffee Parade Field - Fort Huachuca  ----- 53
Mountain View ------- Fort Huachuca ------ 371
San Pedro ------------ City of Benson ------ 500 (est.)
Veterans Park ---------City of Sierra Vista -- 179

All those courses except Veterans Park use effluent. Their total use was 1103 acre-feet/year -- about 10% of the total water deficit for the Basin. It is not unreasonable to guess that the ten biggest courses in the Basin cause 20% of the net water deficit. Should golf courses be restricted?

10. Water usage from water systems

In the Basin, 30 water systems serve municipal users. Eight of those systems provide 250 acre-feet or more per year, and account for 96% of total demand, but only 57% of municipal demand. The eight systems are:

Location - - - System - - - - - - - - Actual/Estimated Water Demand (acre-feet)
inside Sierra Vista city limits
- - - - - - - - - Bella Vista Water Company - - - - -  3640
- - - - - - - - - Pueblo del Sol Water Co. - - - - - - -1355
- - - - - - - - - Arizona W.C. – Sierra Vista - - - - - 1299
inside Sierra Vista sub-area
- - - - - - - - - Fort Huachuca - - - - - - - - - - - - - 1947
- - - - - - - - - Arizona W.C. – Bisbee - - - - - - - - 1222
- - - - - - - - - East Slope Water Company - - - - - - 306
- - - - - - - - - Huachuca City - - - - - - - - - - - - - - 250
outside Sierra Vista sub-area
- - - - - - - - - Benson, City of - - - - - - - - - - - - - - 813
total 10,832

ADWR estimates that a person on these systems uses between 124 and 196 gallons/day.

HOWEVER, if you actually run the ADWR's water usage numbers for a 2002 Basin population of 82,300, the 10,832 acre-feet amounts to only 117 gallons/person/day, less than the "124 to 196" range that ADWR says the numbers show.

117 gallons/person/day is, in fact, not much above what is shown by the data from Cochise County water companies that serve only households.  A few months ago, I found that average usage to be about 90 gallons/day/person, very close to the 87.5 gallons/day/person figure found independently in 2003 by the International Arid Lands Consortium.

If 117 gallons/person/day is an accurate average for the Basin, but 90 gallons/person/day is an accurate average for the entire county, then households in the Basin are using 27 gallons/person/day over the average, and to make the average work out, households outside the Basin must be using something less than the average.  The population of the Basin is roughly 2/3 of the entire county; if 2/3 of the people in the county are using 117 gallons/person/day, and the average use for the whole county is 90 galllons/person/day, then to make the numbers work out, the 1/3 of the people outside the Basin must be using 36 gallons/person/day.  This is somewhat below the national average for rural well users, of about 50 gallons/person/day (see section 11 immediately below).  However, the 36 gallons/person/day figure may be slightly lowered because many people outside the Basin have their water hauled in by truck.  In any case, the numbers in this analysis are probably not far from reality.

Since households outside the Basin -- in, say, the Sulphur Springs Valley -- use noticeably less water than households in the Basin, then, ALL OTHER THINGS BEING EQUAL, non-Basin households should not be held to the same water conservation standards that are imposed in the Basin.   However, it is a matter for a separate report about the Sulphur Springs Valley that ALL OTHER THINGS ARE NOT EQUAL.

11. Water usage from wells

Especially in unincorporated areas, many households use wells, that are either private or shared with neighbors. In 2002, about 3200 active domestic wells served about 14,400 people, concentrated southeast of Sierra Vista north of Hereford Road, south of Sierra Vista, and around St. David/Benson. Most domestic wells can only pump less than 35 gallons per minute, so are "exempt," meaning exempt from regulation.

The ADWR had to estimate the water taken from exempt wells, based on usage patterns in the Tucson AMA and the San Pedro HSR. A higher percentage of small lots is irrigated in the Benson sub-area, so ADWR estimated 312.5 gallons/person/day in the Sierra Vista sub-area, and 491 gallons/person/day in the Benson sub-area.

HOWEVER, ADWR's estimates are seriously at variance with other figures. The International Arid Lands Consortium said in 2003 that "a typical household that gets its water from a private well or cistern uses about 200 gallons for a family of four," or 50 gallons/person/day.  The ADWR guess of 312.5 to 491 gallons/person/day is about 6 to 10 times the national average, so is statistically highly unlikely.

To help figure out this discrepancy, here is the entire paragraph in which the ADWR guess is made:  "Other information on municipal water demand came from direct communication with water providers and from estimates of water demand for domestic wells.  The demand associated with exempt wells is not metered or reported to any entity.  This demand was estimated based on large lot parcel use in the Tucson AMA for which a long history of metered water use is available, with an additional demand associated with irrigated lands of less than two acres in size based on information in the San Pedro HSR.  Because proportionately more small, irrigated lands exist in the Benson sub-area, the acreage per person demand estimate differs between sub-areas.  The estimated demand in the Sierra Vista sub-area is therefore .35 acre-feet/person and .55 acre-feet/person in the Benson sub-area.  The pumpage for Fort Huachuca comes from the Fort Huachuca Biological Opinion Annual Report for 2002.  Information on municipal water demand assumptions is found in Appendix J."

In short, all the numbers about exempt wells are based on estimates, and the ADWR report gives no basis for its figures of .35 acre-feet around Sierra Vista and .55 acre-feet around Benson.  .35 acre-feet translates to 312.5 gallons/person/day, and .55 acre-feet translates to 491 gallons/person/day.  The .35 and .55 acre-foot numbers come from the 1991 "Final San Pedro River Watershed Hydrographic Survey Report."  The derivation of the .35 and .55 numbers was recently tracked down, and is set out below.

The calculation is in a document not readily available.  (Its relevant part is now online at
http://littlebigdog.net/ADWR2005calcwelluse.html .)

The calculation is valid only for the Sierra Vista and Benson sub-areas of the Upper San Pedro Watershed, with pastures and gardens of up to 2 acres, watered by domestic wells.  Other parts of the county, such as the Sulphur Springs Valley have very different conditions; and and the calculation does not apply to them.

The calculation begins with water use inside homes.  For a certain area near Tucson, the average residential water use during 1992-2002 was about 107 gallons/person/day.  The calculation takes this as the basic indoor use, plus a few fruit trees and livestock, by rural areas using domestic wells in Cochise County.

Of course, many households also use water more intensively outside the home.  This use was calculated, not measured, for parcels containing pastures or gardens of up to 2 acres, irrigated from domestic wells, in the Sierra Vista and Benson sub-areas.  Such pastures and gardens comprised 572 acres around Sierra Vista, and 307 acres around Benson.  Their total water use (according to a complicated and imprecise calculation) was 1490 acre-feet/year around Sierra Vista, and 906 acre-feet/year around Benson.  Dividing by the number of people using domestic wells in 1990, the average was 205 gallons/person/day (.35 acre-feet/person/year) around Sierra Vista, and 393 gallons/person/day (.55 acre-feet/person/year) around Benson.  To repeat, these figures for around Sierra Vista or Benson cannot be applied to dissimilar areas of the county, such as the Sulphur Springs Valley.

To obtain total water use, the pasture or garden figures were added to the 107 gallons/person/day for inside use.

Around Sierra Vista, the total was 312 gallons/person/day (.35 acre-feet/person/year)..  Around Benson, the total is 500 gallons/person/day (.55 acre-feet/person/year).

However, for properties not using a private well to water pastures or gardens intensively, the use is less, and a property with no outdoor use except a few fruit trees and livestock would use an average of 107 gallons/person/day.

12. The Basin's population

In 2000, the population of the Basin (plus part of Bisbee outside the Basin but using wells inside the Basin) was 79,944 people, distributed as follows:
-- 28,113 people in unincorporated areas
-- 51,831 people in incorporated areas
-- -- Sierra Vista complex, 39,526, consisting of:
-- -- -- -- Sierra Vista 29,362
-- -- -- -- Fort Huachuca 8,413
-- -- -- -- Huachuca City 1,751
-- -- Bisbee 6,090
-- -- Benson 4,711
-- -- Tombstone 1,504

The Sierra Vista sub-area had about 56,600 people in 1990 and 70,100 in 2002, and will have about 76,500 in 2010. The Benson sub-area had about 8700 people in 1990 and 12,200 in 2002, and will have about 15,300 in 2010.

By 2030, the Sierra Vista sub-area may add about 22,000 people, and the Benson sub-area about 6000.