Effect of Groundwater Pumping

A. Santa Cruz River, Arizona

Two repeat photographs of the Santa Cruz river at Martinez Hill, south of Tucson, Arizona, are shown in Fig. 35 (Day et al., 2003).¹³ The photo to the left (1942) shows well established stands of mesquite and cottonwood along the river banks, indicating that sufficient moisture to support this type of vegetation had existed in the soil at that time. The photo to the right (1989) shows that the riparian vegetation has all but disappeared.

Arizona Game and Fish Department Desert Laboratory Photograph Archive 1942 1989 Fig. 35  Repeat photographs of the Santa Cruz river at Martinez Hill, south of Tucson, Arizona.

Beginning in 1940, and through the 1980s, groundwater pumping to support population growth in the Tucson and Phoenix metropolitan areas resulted in a substantial drop in the water table in the flood plain, with concomitant losses of riparian vegetation. Data from two nearby wells indicates that the water table had declined, due to pumping, up to 120 ft (36 m) during the stated period (Webb et al., 2007). Significantly, Meinzer (1927) has pointed out that the roots of mesquite on the flood plain of the Santa Cruz river could reach a maximum depth of 60 ft (18 m). Therefore, it appears very likely that the protracted pumping was responsible for the eventual demise of the riparian vegetation.

B. Ojos Negros Valley, Baja California, Mexico

A significant example of groundwater depletion and related loss of wetlands and natural vegetation is the Ojos Negros valley, located about 25 mi (40 km) east of Ensenada, Baja California, Mexico. Beginning around 1970 and following through the present time (2014), the water table in the valley has dropped an average of 139 ft (42.5 m).¹⁴ The groundwater is being used to support intensive agricultural development (Ojos Negros Research Group, 2003).

The experience of the Ojos Negros valley is particularly instructive, because the valley derives its name (Spanish for "Black Eyes") from two oval-shaped ponds that existed in the valley prior to the development of groundwater. In Fig. 36, each one is labeled "sienega" (sic), to mean cienaga (pond). These ponds have since dried out and disappeared in the face of protracted aquifer depletion. As late as 1999, a dead alamo cottonwood, relic of the vanished wetland, still remained in the valley (Fig. 37).

Source:  Zárate Archives, Ensenada Fig. 36  Extract of a dated map showing the two oval-shaped swamps that gave their name to the Ojos Negros valley (1864).

Fig. 37  Remains of an alamo cottonwood (Populus fremontii), Ojos Negros valley, Baja California, Mexico (1999).

C. Ash Creek and Sawyer Spring, Utah¹⁵

The experience of Ash Creek and Sawyer Spring, in Utah, constitutes a well documented example of the relation between groundwater pumping and the health of riparian vegetation. Ash Creek and its tributary, Sawyer Spring, are located near New Harmony, in Washington County, Utah, about 15 mi south of Cedar City. The streams drain a shallow alluvial aquifer and the fractured-rock aquifer of the Pine Valley Mountains to the west.

The proprietor of a farm located downstream of Sawyer Spring, owned the rights to all the surface flow of Sawyer Spring and a portion of that of Ash Creek. These rights amounted to 2.18 cfs in Sawyer Creek and 7.5 cfs in Ash Creek. Another owner held the property upstream, in the vicinity of Sawyer Spring and Ash Creek.

In 1993, the upstream owner drilled a 12-inch diameter irrigation well near Ash Creek, to a depth of 600 ft. In the three-year period between 1993 and 1996, the 12-in well was pumped continuously at a rate of 750 gpm, during the irrigation season. In 1997, the discharge at this well was increased to 1,700 gpm. Drawdown from this rate of discharge eliminated surface flow in Sawyer Spring and greatly diminished that of Ash Creek. As a result of pumping, Sawyer Spring, which had been perennial until at least 1993, became intermittent [or much reduced in flow] and dried up every year since the pumping was increased to 1,700 gpm.

In 2003, the downstream owner sued the upstream owner claiming that groundwater pumping at the 12-in well interfered with the natural baseflow of Sawyer Spring and Ash Creek. Riparian vegetation along Sawyer Spring and Ash Creek has been adversely affected by the lowering of the water table. Many trees either died or were substantially impaired in their normal growth and development (Fig. 38).

Courtesy of Gary Player Fig. 38  Dead riparian trees near Ash Creek, Washington County, Utah (2008).

In October 2007, in response to the controversy over water rights, the upstream owner stopped pumping at the 12-in well. By the spring of 2008, baseflow had recovered in Sawyer Spring and Ash Creek in response to the interruption of pumping from the 12-in well (Fig. 39).

Courtesy of Gary Player Fig. 39  Ash Creek on May 2, 2008, showing baseflow recovery.

D. Thompson Creek, San Diego County, California

Thompson Creek is located in the rural area of Poway, in San Diego County, California. The mean annual recharge to groundwater in the basin has been estimated to be 205 ac-ft. In the period 2001-2011, annual groundwater capture, including all uses, has totaled 224 ac-ft on the average, i.e., about 109% of recharge.¹⁶ As a result of this intensive pumping, the depletion of the water table in three wells [which the longest and most reliable record] has been measured at 275 ft (2012) (Ponce, 2012b).

Figure 40 (a) shows an aerial view of the confluence of Thompson Creek (to the right) with the much larger Sycamore Creek (to the left). The geologic map of Fig. 40 (b) shows an alluvial/colluvial aquifer underlying both creeks and superimposed on the regional fractured-rock aquifer. The colluvial aquifer, shown as light yellow in color, is labeled Qycsa, depicting younger (Holocene) colluvial and stream deposits of silty sand with clay and gravel.¹⁷

Google Earth ® U.S. Geological Survey Fig. 40  Confluence of Thompson Creek with Sycamore Creek: (a) aerial view; (b) geologic map.

While the same type of aquifer underlies both Thompson and Sycamore creeks, their riparian health appears to be at variance. Figure 40 shows that while Sycamore Creek (left) appears sufficiently healthy, the same does not hold for Lower Thompson Creek (right). Thompson Creek's riparian vegetation is somewhat healthy to the east, but not near its confluence with Sycamore Creek. The combined effect of urban development, wildland fire, and groundwater depletion may be surmised.

Significantly, the geologic map of Thompson Creek has a clearly labeled Spring near Robert Myers' property (Fig. 41). This is clear proof of the presence of a spring in the vicinity, prior to groundwater development. Myers himself recalls that in the spring of 1980, in the wake of three wet years (1978-1980), his well operated under flowing artesian conditions for three to four months.¹⁸ Therefore, the question is appropriate: "What happened to the spring?"

U.S. Geological Survey Fig. 41  Location of spring in Thompson Creek, close to the Myers property.

The answer must lie in the capture, over the period 2001-2011, of annual groundwater volumes exceeding the natural recharge. In all probability, these large capture amounts led to the drying out of the spring, and may have contributed to the impairment in riparian vegetation along Thompson Creek.

E. Tierra del Sol, Boulevard, California

Tierra del Sol is on the southwest side of Boulevard, in southeastern San Diego County, California. Its west side, drained by Tierra del Sol Creek, occupies an area of 2.75 square miles, draining into Mexico at Aguaje del Nat (Fig. 42) (Ponce, 2006). To the west, Tierra del Sol abuts the Campo Indian reservation, which drains in a northwestern direction into Campo Creek, a tributary of the Tijuana river. The land use in Tierra del Sol is native chaparral, albeit with a substantial presence of phreatophytes along well defined moisture paths, and scattered mesophytes, ranch clearings and rural housing.

Fig. 42  The watershed of Tierra del Sol Creek, next to the U.S.-Mexico border.

The region is underlain by the Peninsular Range Batholith, which straddles the mountains of central Southern California. It lies within the La Posta pluton, a deep-seated igneous intrusion (Walawender et al., 1990). This pluton varies inward from rim to core, from a sphene-hornblende-biotite tonalite rim to a muscovite-biotite granodiorite core. The rocks are extensively fractured due to batholith cooling and tectonic uplift.

Figure 43 shows photogeologic lineaments [highlighted in green] depicting alignments of variations in the density of vegetation (Ponce, 2006). These lineaments are known to be the expression of fractures and other discontinuities in the weathered and unweathered rocks. Many of these fractures (14 of them) are shown to cross the boundary between the Campo Indian reservation to the west and privately owned land immediately east of it. Thus, groundwater in the underlying fractured-rock aquifer appears to be entirely capable of crossing the limit between Tierra del Sol Creek and Campo Creek surface drainages.¹⁹

Fig. 43  Map of photogeologic lineaments in the Tierra del Sol watershed.

Figure 44 shows a large 180-ft long dike outcropping to the surface in the Morning Star Ranch. The existence of this dike became apparent in 2012, in the aftermath of the Shockey fire, which burned 2,566 acres in Boulevard and vicinity (CalFire, 2012). The presence of this geologic surface feature attests to preferred paths of groundwater flow in the area (see also Fig. 26).

Fig. 44  A 180-ft dike in the Morning Star Ranch, Tierra del Sol.

Immediately west of Tierra del Sol, within the Campo Indian reservation, extensive groundwater pumping for industrial uses has taken place from July to November 2013, in the middle of a persistent drought (2012-2014). A total of 84 million gallons of water have been used (until October 2014) in the construction of the SDG&E ECO Substation Project, in nearby Jacumba (Ponce, 2013a). Of this amount, about 12.2 million (37.44 ac-ft) was pumped from wells in the neighboring Campo Indian reservation (SDG&E, 2014). This pumping appears to have stressed the vegetation in the vicinity, particularly the mesophytes, which rely on moisture exfiltration through the fractures.

Figure 45 shows two repeat photographs of a sizable specimen of blue eldelberry (Sambucus mexicana), within the Morning Star Ranch.²⁰ The 2006 view shows a healthy tree, in the absence of industrial-level pumping in the vicinity; compare with the same tree, as shown in 2014 (right view). Note that two of the main branches were recently cut (August 2014) due to breakage related to wind damage and water stress. This and other specimens of blue eldelberry in the ranch and vicinity have been stressed since the onset of pumping, many of them to the point of dying.^{21, 22}

2006 2014 Fig. 45  A specimen of blue eldelberry in the Morning Star Ranch, Tierra del Sol.

Figure 46 shows a dead coast live oak tree (Quercus agrifolia) on the entrance to the Morning Star Ranch. This tree is estimated to be at least 100 years old.²³ The tree died in the past year, presumably due to moisture stress and/or other reasons closely related to moisture stress.

Fig. 46  A dead coast live oak tree:  Morning Star Ranch, Tierra del Sol, San Diego County, California (November 2014).

F. McCain Valley, Boulevard, California

The McCain valley is located in Boulevard, in eastern San Diego County, California. It is drained by Tule Creek, which flows east into Tule Lake, and then further east to join Carrizo Creek, in Carrizo Gorge, within the Anza-Borrego State Park. The valley is host to a singular community of coast live oak (Quercus agrifolia), at an elevation of 3,523 ft, in the vicinity of Mount Tule. The vegetative community is sustained by springs originating in Mount Tule, with peak elevation of 4,637 ft.

Figure 47 shows the community of coast live oak (dark green patches on bottom left), Mount Tule (rising at center top), the ephemeral Tule Creek (center bottom), and Tule Lake (large dark blue spot at center right).

Google Earth ® Fig. 47  Aerial view of Mount Tule and environs, McCain valley, Boulevard.

Figure 48 shows a perspective view of the coast live oak community. Within it, one extraordinarily large tree has been documented, with a circumference [at breast height] of 24.8 ft (7.55 m), and an equivalent diameter of 7.9 ft (2.41 m) (Fig. 49). The age of this tree is estimated to be 300 years.²⁴ The existence of such an unusually large tree in this arid region indicates the presence of substantial moisture in the soil, within reach of the roots, and often exfiltrating to the surface (Fig. 7).

Google Earth ® Fig. 48  A community of coast live oak in the McCain valley.

Fig. 49  A very large specimen of coast live oak.

Elsewhere in McCain valley, large fractures intersecting the ground surface lead to springs, which sustain shrubs and trees growing in the immediate vicinity. Several springs are found in Upper McCain Valley; some are large enough to collect water on the surface for various uses (Fig. 50). Several tribal residences located on the Manzanita Indian reservation reportedly rely on spring-fed water sources for their domestic and livestock needs.²⁵

Fig. 50  Boxed spring located in the Manzanita reservation, along the McCain Valley foothills.

Plans are underway by a solar energy company to utilize the groundwater resources of McCain valley [2014]. The Rugged Solar project is being proposed for development in Tule Creek and the surrounding floodplain, with project boundaries shown in Fig. 51 (Ponce, 2013b). For its water supply, the project intends to tap several existing wells in the vicinity. While the total construction water has been estimated at 73 ac-ft, the mean annual recharge has been conservatively estimated at 50 ac-ft.²⁶ Capture amounts exceeding 100% of recharge are likely to substantially lower groundwater levels and, therefore, negatively affect upland spring-fed vegetation and riparian/wetland ecosystems in the vicinity.

Fig. 51  Location of existing wells within the Rugged Solar project site.

Figure 51 shows that the distance between Well #8 and the nearest edge of the coast live oak community (situated immediately outside of the smaller red enclosure) is barely 760 ft (232 m). In light of the unique vegetation resources at stake in McCain valley, the proposed groundwater pumping must guarantee that it will not encroach upon existing springs and wetlands. No development, no matter how lofty its aim, should have the right to place in jeopardy the health of a singular live oak forest ecosystem such as that of McCain valley.

12.  ANALYSIS

[Conclusions]   [Summary]   [Endnotes]   [Acknowledgments]   [References]   •   [Top]   [Introduction]   [Types of water]   [Water needs]   [Geology]   [Geomorphology]   [Hydrology]   [Ecology]   [Hydroecology]   [Hydrogeology]   [Plants and wells]   [Case studies]

The preceding sections have presented theoretical and experimental evidence of the competition between groundwater use and vegetative ecosytems. Climate, geology, and geomorphology have conditioned the type and extent of vegetation throughout geologic time. On the other hand, intensive groundwater use, made possible by mechanical pumping, has occurred only in the past 100 years or so. In order to reconcile the apparent competition, the following questions are posed:

Who uses groundwater? What are plants useful for? Where is the competition between plants and wells most critical? Could a middle ground be found that uses groundwater without encroaching upon ecosystem health?

♦ Who uses groundwater?

Around the world, users of groundwater face the following realities:

• There is not enough surface water to satisfy all the perceived needs or uses.

• Local groundwater is less expensive than imported surface water.

• The available surface water may have been all appropriated; thus, there is no other recourse but to tap the local groundwater.

It is recognized that all groundwater of economic use is in transit to the surface waters; thus, the existence of groundwater as an additional resource is subject to interpretation. In many instances, groundwater is seen to be cheaper than surface water, but when all environmental costs are considered, the difference in cost may be reduced and possibly even reversed. While surface water is completely renewable, the same statement does not follow for groundwater. Therefore, usage of groundwater must be done with caution, anticipating and mitigating the impacts that this usage may have on local stakeholders, both natural and anthropogenic.

♦ What are plants useful for?

Plants provide a host of natural services, many of which still remain to be quantified in conventional economic terms. First and foremost, all green plants sequester carbon dioxide, thus helping to control the climate. Thus, a permanent reduction in plant biomass has exactly the same effect as burning an additional amount of fossil fuels.

In addition to carbon fixation and oxygen production, plants provide several other natural services, including erosion control, habitat for wildlife, filtering of contaminants, low albedo (which encourages rain), and scenic beauty, all of which have an intrinsic value. Thus, the impairment of ecosystem health by excessive groundwater pumping could have far-reaching consequences, that encompass aspects of climatology, biology, sedimentology, and public recreation.

♦ Where is the competition between plants and wells most critical?

The competition between plants and wells is most critical in arid/semiarid environments, where many plants rely almost exclusively on groundwater. Thus, pumping in a desert environment is most crucial, not only because of the dependence of the vegetation on the groundwater resource, but also because replenishment is likely to be slow, with recharge events few and far between.

A conundrum is noted here: Groundwater pumping may not be as crucial in a humid environment, because in this case surface water may be plentiful, largely eliminating the need for pumping.

♦ Could a middle ground be found that uses groundwater without encroaching upon ecosystem health?

A middle ground may be found in the relatively new concept of sustainable yield. The amount of groundwater capture should not be based on the outdated hydrogeologic principle of safe yield. Instead, the allowable capture must be that which can be maintained [for an indefinite time] without causing unacceptable environmental, economic, or social consequences (Alley et al., 1999). These consequences would have to be carefully evaluated and accounted for in the economic analysis before the planned groundwater development takes place. The latter requirement calls for renewed interdisciplinary synthesis in groundwater resource evaluation, to include ecology, surface-water hydrology, and the economics of natural resources.

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13.  CONCLUSIONS

[Summary]   [Endnotes]   [Acknowledgments]   [References]   •   [Top]   [Introduction]   [Types of water]   [Water needs]   [Geology]   [Geomorphology]   [Hydrology]   [Ecology]   [Hydroecology]   [Hydrogeology]   [Plants and wells]   [Case studies]   [Analysis]

The following conclusions are derived from this study:

• Climate, geology, geomorphology, and hydrology interact to foster or discourage the development of vegetation.

• Many plants in arid/semiarid regions rely almost exclusively on groundwater to satisfy their basic need for water.

• The presence/absence of water has a direct bearing on the height, width, and type and density of vegetation.

• The concept of safe yield of groundwater has been widely discredited because it assumes that groundwater is a volume, when in fact it is a flow.

• In a pristine groundwater system, gross recharge equals gross discharge; therefore, net recharge is zero.

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• Plants and wells are in competition for the groundwater resource; this competition is most critical in the arid/semiarid environment, where many plants are seen to rely almost exclusively on groundwater.

• Developed shallow groundwater systems generally result in a lowering of the water table; the greater the amount of groundwater capture, the greater the amount of lowering.

• All groundwater of economic use is in transit to the surface waters and may have already been committed; thus, the existence of groundwater as an additional resource is not always to be taken for granted.

• Riparian ecosystems (i.e., the gallery forests) are typically longitudinal, tapping the water table in the dissected-and-filled alluvial landscape.

• Upland ecosystems (for instance, the lineaments) are more likely to be randomly distributed in space and to follow fractures, springs, and/or other geologic features.

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• Capture that results in a substantial lowering of the water table has a host of negative impacts, of which the most important is a [more or less] permanent reduction in plant biomass.

• A permanent reduction in plant biomass has exactly the same effect as burning an additional amount of fossil fuels, thereby increasing the carbon footprint.

• Usage of groundwater must be exercised with caution, anticipating the impacts that this usage may have on local stakeholders, both natural and anthropogenic.

• The allowable groundwater capture must be that which can be maintained [for a reasonably long time] without causing unacceptable environmental, ecological, economic, or social consequences.

• There is an urgent need for renewed interdisciplinary synthesis in groundwater resource evaluation, to include ecology, surface-water hydrology, and the economics of natural resources.

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14.  SUMMARY

[Endnotes]   [Acknowledgments]   [References]   •   [Top]   [Introduction]   [Types of water]   [Water needs]   [Geology]   [Geomorphology]   [Hydrology]   [Ecology]   [Hydroecology]   [Hydrogeology]   [Plants and wells]   [Case studies]   [Analysis]   [Conclusions]

The effect of groundwater pumping on the health of arid vegetative ecosystems is examined herein. Vegetative ecosystems are supported by a complex interaction of climate, geology, geomorphology, and hydrology. In arid/semiarid regions, many plants rely almost exclusively on groundwater to satisfy their basic needs for water. Globally, it is observed that the presence/absence of water has a direct bearing on the height, width, and type and density of vegetation. It is seen that plants and wells are in competition for the groundwater resource. The competition is most critical in arid/semiarid regions, where surface water is scarce and groundwater is the only recourse. Developed shallow groundwater systems generally result in the lowering of the water table, wherein the greater the capture, the greater the lowering. Lowering of the water table stresses the plants that customarily rely on the groundwater. In extreme cases, plants may die and springs and wetlands may disappear. Groundwater capture that results in a substantial lowering of the water table has a host of negative impacts, notably among them an increase in the carbon footprint. Pumping of groundwater must be performed with caution, anticipating the impacts that this pumping may have on local stakeholders, both natural and anthropogenic. The allowable capture must be that which can be maintained without causing unacceptable environmental, ecological, economic, or social consequences. There is an urgent need for interdisciplinary synthesis in groundwater resource evaluation, to include ecology, surface-water hydrology, and the economics of natural resources.

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ENDNOTES

[Acknowledgments]   [References]   •   [Top]   [Introduction]   [Types of water]   [Water needs]   [Geology]   [Geomorphology]   [Hydrology]   [Ecology]   [Hydroecology]   [Hydrogeology]   [Plants and wells]   [Case studies]   [Analysis]   [Conclusions]   [Summary]

¹ Albedo is the ratio of reflected radiation from a surface to incident radiation upon it. Vegetation has low albedos, ranging from 0.07 to 0.20, while bare soil has higher albedos, ranging from 0.20 to 0.60.

² The carbon footprint is a measure of the amount of [anthropogenic] carbon dioxide (CO₂) and other greenhouse gases emitted by a defined population. Burning of fossil fuels and land clearance (loss of vegetation) contribute to the carbon footprint.

³ Advection is a transport of a substance by a fluid due to the fluid's bulk motion.

⁴ Diffusion is the movement of a substance from a region of high concentration to a region of low concentration.

⁵ A graben is a depressed block of land bordered by parallel faults.

⁶ The condensation of coastal fog may account for a substantial portion of the water consumption of typical cloud forests. In extreme cases, it could exceed the amount of measured precipitation (Kiss and Bräuning, 2008).

⁷ A lineament is a linear feature of a landscape which expresses the location of an underlying geological structure such as a fault. Fracture zones and igneous intrusions such as dikes can also give rise to lineaments.

⁸ The Quaternary Period is the current and most recent period of the Cenozoic Era. It follows the Neocene Period and spans from 2.588 million years to the present.

⁹ In fluid mechanics, a control volume is a mathematical abstraction employed in the process of creating mathematical models of physical processes. In a fixed frame of reference, it is a volume in space through which the fluid flows. Unlike fluid mechanics, in groundwater flow the choice of control volume is not clearly defined, varying with the extent of capture; see, for instance, Prudic and Herman (1996).

¹⁰ In a seminal paper widely credited with originating the scientific study of groundwater, Theis (1940) wrote: "It is evident that on the average the rate of discharge from the aquifer during recent geologic time has been equal to the rate of input into it... Under natural conditions, therefore, previous to development by wells, aquifers are in a state of approximate dynamic equilibrium. Discharge by wells is thus a new discharge superimposed upon a previously stable system, and it must be balanced by an increase in the recharge of the aquifer, or by a decrease in the old natural discharge, or by a loss of storage in the aquifer, or by a combination of these." (Author's emphasis) (See Fig. 32).

¹¹ By way of comparison, the total volume of groundwater pumping in the United States has been estimated to be about 8 percent of the natural recharge (Alley et al., 1999).

¹² Mesophytes are terrestrial plants which are adapted to neither a particularly dry nor particularly wet environment. In arid and semiarid landscapes, mesophytes populate the areas close to sources of exfiltrating water, like springs and depressions.

¹³ Repeat photography consists of taking two images of the same site, with a time lag between the two images; a "then" and "now" view of a particular area, with aim to show changes.

¹⁴ As of November 2014, the depth to water table for the Ojos Negros aquifer was: maximum = 71.25 m; average = 42.48 m, minimum = 13.76 m (Data provided by Victor Hugo Vázquez García, manager of COTAS Ojos Negros, through the auspices of the Municipality of Ensenada).

¹⁵ The information contained in Section C was provided to the author [in 2008] by professional geologist Gary Player, who advised the downstream owner throughout the legal proceedings. Due to confidentiality reasons, no information about this case is available in the open literature.

¹⁶ Of the total amount captured, 73% is used for industrial purposes (a local golf course), and the remaining 27% is used for domestic consumption (individual home wells) (Ponce, 2012b).

¹⁷ The Holocene is a geologic epoch which began at the end of the Pleistocene (11,700 years ago) and continues to the present time.

¹⁸ Robert Myers, personal interview conducted on March 3, 2012.

¹⁹ Unlike surface-water flow, there no limit to the connectivity of groundwater flow. For instance, Prudic and Herman (1996) used the aquifer of Paradise Valley, in Humboldt County, Nevada, as an example of the evolving nature of groundwater capture. In a simulated experiment, they found that pumping 48% of the recharge for 300 years produced first losses in aquifer storage; then reduction in evapotranspiration; subsequently, decreases in flow discharge, and eventually, sizable downstream flow reversal, i.e., increases in recharge coming from the neighboring downstream basin.

²⁰ The water affinities of the blue elderberry and its preeminent role as an indicator of the presence of groundwater have been known for more than one hundred years. Early references to the blue elderberry's moisture habits are scattered throughout the literature. Ball (1907) has stated that in Southwestern Nevada and Eastern California, the elderberry tree is unknown, except in the vicinity of water. Spalding (1909) has noted that the blue elderberry, while being structurally a flood-plain mesophyte, it is nevertheless very limited in its range, growing where there is an ample supply of moisture.

²¹ In a personal interview on December 13, 2004, Melody Pochot, a resident of the Morning Star Ranch, stated that in the past two years she had witnessed many of the eldelberry trees in the yard of her home become significantly moisture-stressed.

²² On December 13, 2014, a cursory inspection of the eldelberry trees in the Morning Star Ranch and immediate vicinity revealed than out of 61 trees surveyed, twenty-one (21) were either dead or near dead.

²³ According to Donna Tisdale, the dead live oak tree shown in Fig. 51 was already well grown when her husband Ed bought the Morning Star ranch in 1963 (personnal communication on December 13, 2014).

²⁴ Other studies suggest that the giant tree shown in Fig. 41 may be much older than 300 years. For instance, a specimen of coast live oak at Stanford University, with a trunk diameter of 55 in (1.4 m) was estimated to be 300 years old (Encyclopedia of Stanford trees, shrubs, and vines). The average rate of annual growth for the Stanford tree would be 0.0047 m. At this average rate of growth, the McCain Valley tree shown in Fig. 41 would be: 2.4 m / 0.0047 m/yr = 510 years old.

²⁵ Interview with Donna Tisdale, on September 18, 2013.

²⁶ There is no general agreement as to what constitutes the "control volume" on which to base recharge calculations. Thus, recharge estimations are only rough indications. Nevertheless, the practice of using the entire amount of recharge as "safe yield" has been widely discredited (Alley et al., 1999).

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ACKNOWLEDGMENTS

[References]   •   [Top]   [Introduction]   [Types of water]   [Water needs]   [Geology]   [Geomorphology]   [Hydrology]   [Ecology]   [Hydroecology]   [Hydrogeology]   [Plants and wells]   [Case studies]   [Analysis]   [Conclusions]   [Summary]   [Endnotes]

This study was made possible by the support of the people of Tierra del Sol and Boulevard, in San Diego County, California. These folks are concerned that excessive development of the desert will end up encroaching upon their livelihood.

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Ponce, V. M. 1995. Management of floods and droughts in the semiarid Brazilian Northeast: The case for conservation. Journal of Soil and Water Conservation, Vol. 50, No. 5, September-October, 422-431.

Ponce, V. M., A. K. Lohani, and P. T. Huston. 1997. Surface albedo and water resources: Hydroclimatological impact of human activities. ASCE Journal of Hydrologic Engineering, Vol. 2, No. 4, October, 197-203.

Ponce, V. M., R. P. Pandey, and S. Ercan. 2000. Characterization of drought across climatic spectrum. Journal of Hydrologic Engineering, ASCE, Vol. 5, No. 2, April, 222-224.

Ponce, V. M. 2006. Impact of the proposed Campo landfill on the hydrology of the Tierra del Sol watershed: A reference study. Online report, May.

Ponce, V. M. 2007. Sustainable yield of groundwater. Online article.

Ponce, V. M. 2011. The 800-mm isohyet. Online article.

Ponce, V. M. 2012a. The salinity of groundwaters. Online article.

Ponce, V. M. 2012b. Thompson Creek groundwater sustainability study. Online report.

Ponce, V. M. 2013a. Cumulative impacts on water resources of large-scale energy projects in Boulevard and surrounding communities, San Diego County, California. Online report.

Ponce, V. M. 2013b. Impact of Soitec solar projects on Boulevard and surrounding communities. Online report.

Prudic, D. E., and M. E. Herman. 1996. Ground-water flow and simulated effects of development in Paradise Valley, a basin tributary to the Humboldt River, in Humboldt County, Nevada. U.S. Geological Survey Professional Paper 1409-F.

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About the author Dr. Victor M. Ponce has taught hydrology at San Diego State University, California, since 1980. His field of study is civil engineering, specializing in hydraulics, hydrology, and water resources. His extensive record of research and practice may be browsed at  ponce.sdsu.edu

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