Pacific Science (1976), Vol. 30, No.1, p. 91-100 Printed in Great Britain

) The Hydrogeology and Water Supply Problems in North-Central !

JOHN W. LLOYD2

ABSTRACT: The north-central zone ofChile is described with respect to ground­ water supply problems. In this region, groundwater is almost exclusively obtained from the thin alluvium in the main transverse valleys, which descend from the in those sections where the valleys cross the northerly trending "central valley." Because of the steep groundwater gradients prevailing, the groundwater resources are closely related to seasonal recharge. As the area is arid to semiarid and has been showing indications of increasing aridity over the past few years, water supply problems are proving to be a serious development constraint. Throughout the area, many examples ofinsufficient water supply may be encoun­ tered, and the problems ofwater use management and the utilization for industrial purposes of supplies such as seawater, brines, and sewage are now being con­ sidered.

THE NORTH-CENTRAL ZONE of Chile discussed importance, and the only significant resources in this paper is located between latitudes 26° occur in the younger sediments, particularly the and 32° S. It is bounded on the east by the Recent alluvial deposits which are confined to mountain chain of the Andes reaching up to the present-day drainage systems. 6900 m above sea level and on the west by the The chiefpopulation concentrations with the Pacific Ocean. A range ofmountains ofaltitudes exception of major ports occur in the central up to 1950 m rises from the coastline and is valley at its junction with major transverse separated from the Andes throughout much of valleys descending from the Andes to the the area by a northerly trending "central Pacific. valley" system which ranges in altitude from Two main industries, copper and agriculture, 350 to 1200 m. The width of the area does not are important. The area produces a large per­ exceed 280 km and in places is as little as 90 km. centage of the copper which forms the basis of The area location is shown on Figure 1. the Chilean economy, and the exploration and The climate is arid in the north and semiarid assessment ofunexploited deposits indicate that in the south. From April to September, sporadic the reserves are considerable and that the area precipitation occurs and temperatures vary will continue to have a high priority in the from about - 8° to +20° C. From October to industrial and mining development of the March, the area is usually dry with a tempera­ country. In view of the future role of this ture range ofabout 5°_32° C. industry, much attention is now being focused Geologically, the area spans the Precambrian on the availability of long-term water supplies to the Cenozoic eras and is a complex history of that are essential in the ore-processing stages. sedimentation, intrusion, and moderately In the central and western parts of the catch­ severe structural movement. With respect to ments of the dos Copiap6, Huasco, Elqui, groundwater, the pre-Miocene rocks, which Limari, and Choapa are large cultivable areas are of widespread occurrence, are of negligible that in times of adequate water supply support a thriving agricultural industry based on grapes,

I Manuscript received 3 January 1974. cereals, and vegetable crops. Because ofthe dry 2 The University of Birmingham, Department of climate, the agriculture is almost exclusively Geological Sciences, P.O. Box 363, Birmingham B15 dependent upon irrigation. 2TT, England.

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north across the area. The orographic effects of CLIMATE AND HYDROLOGY the coastal mountains and the Andes produce The climate is closely associated with that of local increases in precipitation while the coastal the Atacama Desert, which, as far as is known, mountains give rise to shadow effects in has an intensity of aridity unequalled in the the central valley. In Figure 2, the annual world (Trewartha 1961: 22-31). This extreme precipitation distribution for 1931-1960 and aridity is the result of a unique combination of 1968 is shown. Schneider (1969) has analyzed several climatic and geomorphic controls. Of the climatic data to indicate the Thornthwaite primary importance is the fact that the region aridity features of the area for the period 1931­ is under the influence of strong air subsidence 1960, which are also reproduced in Figure 2. associated with the eastern limb of the South These indices will vary with the period ana­ Pacific anticyclone. The anticyclone is a strong lyzed but give a good general picture of the permanent feature in the region; it fluctuates arid-semiarid environment. very slightly and is abruptly terminated by the A feature ofthe climate is the extremely vari­ wall of the Andes. A persistently low tempera­ able precipitation frequency and intensity. The ture inversion therefore occurs in the air mass main precipitation falls in the Andes as both overlying the narrow strip of land and the snow and rain and forms the chief contribution adjacent sea west of the Andes. The inversion, to the runoffofthe transverse rivers which flow 'which frequently reaches down to sea level, is to the Pacific. There are two conditions govern­ intensified by the cold Humboldt Current flow­ ing runoff: (1) the amount of snow and the ing northward from the Antarctic parallel to period and intensity ofmelt, and (2) the amount, the Chilean coast. The current reduces air intensity, and frequency of rain storms. temperatures over the sea and stabilizes the As the transverse river systems are the chief surface air. source of water supply in the area, availability The coincidence between the north-south is closely related to runoff conditions. Runoff trend ofthe coast and the eastern margin ofthe in turn controls the indirect recharge to the anticyclone is considered to be a supplementary valley alluvium and is the only significant aridifying factor (Lydolph 1967). The circula­ recharge element. Bed gradients are extremely tion along the eastern side of the cell produces steep, as would be expected from the topog­ southerly winds and a flow ofair parallel to the raphy; they range down to about 1 in 110 in coast. The difference in drag exerted by the land the upper sections of the valleys but flatten and sea surfaces upon this flow produces a stress considerably in the central valley sections. As a differential in the air mass that results in a wind result, unless significant snow and slow-melting divergence to the east and subsidence in the conditions occur, there is a rapid surface runoff surface air, particularly along the coast. which is also reflected in the alluvial ground­ Further littoral subsidence of the air mass is water discharges. The valley alluvium is thin, associated with the onshore sea breeze that in consequence of which little groundwater occurs during the day and that produces a storage is available so that groundwater sup­ strong temperature inversion at the boundary plies must depend almost exclusively upon where maritime air is in contact with the throughput. In essence, therefore, the avail­ warmer land air. As the maritime air spreads ability of water depends directly upon the fartherinland duringthe day, subsidence occurs. amount of weakening ofthe South Pacific anti­ During the period September to March, the cyclone. Because of the semiarid to arid nature area experiences the arid conditions outlined of the area, any variation in the degree of above. However, during April to August, weakening of the anticyclone is immediately occasional cold fronts penetrate into the area reflected in water resources. from the Antarctic and produce precipitation. Since the early 1960s, the South Pacific anti­ This northerly movement offrontal passages is cyclone has proved unusually stable during the considered to reflect a seasonal weakening of winter season, resulting in a marked fall in the South Pacific anticyclone. The precipitation precipitation and, consequently, in water that occurs decreases in amount from south to resources in the area. The general climatic 72·W 69;W: I / I/ /' CHANARAL I I I I i

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FIGURE 2, Climatic features, north-central Chile, Hydrogeology and Water Supply Problems in North-Central Chile-LLOYD 95 change is related to worldwide events (Lloyd alluvium and the weathered granitic zone 1973a) as described by Lamb (1966). Conditions produce water. in the area have changed from a moderately Because of the limited thickness of gravels at consistent annual precipitation between 1900 Illapel, the most efficient well design has proved and 1960 to a lower modal annual fall but with to be one of2-3 m of screen located at the base more extreme variability, a situation which it is of the aquifer with blank casing above. Screen postulated could last until the end of the cen­ slots are selected to allow the removal of 60 tury. As such, the conditions resemble the percent of material from around the well to pre-1900 type of climate that existed in the produce minimal well losses. Screen develop­ area. ment is carried out by careful surging inside the This change in climate and water availability screen and this process has proved considerably has come at a time when industrial expansion is more effective than surging above the screen. being attempted in north-central Chile and, as a Pump settings are also within the screen. Yields result, when management of the total water have been obtained of up to 27 liters/sec for resources of the region has become of para­ 0.7 m of drawdown with the water table near mount importance. the surface during winter and spring; the rapid throughput, however, results in a drastic drop in water level (1.5 m) in the autumn with a HYDROGEOLOGY AND WATER SUPPLY corresponding drop in well yields by some 60 The area hydrogeology may be divided percent. Throughputs vary considerably from geographically into three parts. The southern about 6000 m3/day in spring to about a mini­ paru:onsists ofrios Choapa, Limari, and Elqui, mum recorded 2200 m3/day in autumn when the c~ntral part ofthe rios Huasco and Copiap6 water supplies are marginally below projected and the north of the Rio Salado. requirements. As all available surface water is There' are few Miocene-Pliocene terrace used for irrigation in the Andes foothills, there deposits in the southern valleys and the Recent is a marked need for the implementation of alluvium is very thin, normally less than 25 m. careful water management plans. This, lack of extensive fluviatile deposits is An interesting feature of the groundwater in attribruted to the very limited development of the Illapel area is its chemistry. The ground­ the central valley, in which such deposits are water in the alluvium is S04 in character, with well developed farther north. positive tritium values of 16-20 TV. During Surface runoff is the most important water summer, however, wells that penetrate to the sourcein this sector supporting agriculture and granitic weathered zone beneath the clay and population. Groundwater resources are poor draw from both aquifers produce non tritiated due to the very thin aquifer thicknesses. In the HC03 water. This water is believed to originate Rio Choapa system, the only groundwater from the weathered zone but initially must have development is in the vicinity of Illapel. Here passed into the zone from the overlying allu­ some 1450 m3/day are abstracted from the vium, presumably at some distance from the Recent alluvium tor town and ore processing wells. As the water throughout the catchment requirements. As with the other valleys in the is S04 in character, ionic exchange must occur south, the Recent alluvium in the Rio Choapa within the weathered granitic zone. consists of a clay unit overlain by coarser In the catchment of the Rio Limari, the material. At Illapel the clay is up to 6 m thick central valley features are poorly developed. and is overlain by 5 m ofgravels. Seismic profil­ A limited but prosperous agriculture based ing at several sites in the southern sector has upon surface-water-irrigated terraces does indicated the presence of material interpreted occur at Ovalle and, throughout the broad as gravel below the clay, which has later been valleys of the major tributaries, surface water revealed to be weathered granitic material that irrigation is quite extensive but heavily depen­ produces ghost seismic reflection surfaces dent upon three major dams which have fre­ within the basement. From the groundwater­ quently failed to supply sufficient water over the resources point of view, the coarse upper past decade. Because of the thin alluvium in the 96 PACIFIC SCIENCE, Volume 30, January 1976 valleys and the construction of the dams with water is available in the catchment and a major cutoff walls to bedrock, groundwater develop­ new ore processing supply required for Anda­ ments in the Limari catchment have been collo is to be obtained from the sea through a minimal. The main interest in the vicinity of 23-km pipeline (Lloyd 1974a). Combarbala has been to provide water for Close to the sea in the vicinity of La Serena, copper ore processing. shallow-dug wells tap thin lenses offreshwater. In the Rio Combarbala, minimum autumn There is recent evidence of overdevelopment throughput has been measured at 170 mS/day from the increase of chlorides in some of the on the basis ofdischarge from a drain construc­ wells, which is attributed to the poor recharge ted to bedrock to abstract the total ground­ conditions over the past few years. water flow. The drain, which is situated near To the south of La Serena, groundwater is the town, commands a catchment of245 km2 in abstracted from late Tertiary fluviatile gravels a relatively high rainfall zone; the runoff, how­ in the Bellavista valley. Rainfall to the catch­ ever, is used largely for irrigation upstream and ment is low, with annual averages not exceed­ the thin nature ofthe alluvium (up to 4 m thick) ing 100 mm. The recharge to the valley is precludes any significant groundwater re­ limited, as indicated by the absence of signifi­ sources. In the neighboring major valley, the cant groundwater gradients and by the low Rio Cogoti Bows from the Andes with high tritium content of the groundwater which is winter and spring discharges. Due to a com­ less than 0.5 TV. Although several wells tap the bination of fast runoff and irrigation use, alluvium, they have been brought into com­ groundwater discharges are also insignificant. mission only recently so that no noticeable Attempts to obtain supplies near to Cogoti water level decline has yet occurred. The valley, have revealed similar stratigraphy to that in the however, has been subjected to late-faulting Rio Choapa catchment. Clays overlie the bed­ river capture and base level changes that may rock and are overlain by coarser material-in have resulted in the impounding of a: limited this case, fine to coarse sands with boulders and volume ofgroundwaterin the Tertiary deposits. up to 6.5 m thick. Both dug wells with slotted To the north of the Rio Elqui catchment the pipe and screened percussion wells have been central valley becomes a dominant topograph­ constructed for supply but neither has proved ical feature, with its boundaries being defined capable of yielding more than 1.5 liter/sec by a system of faults related to the late move­ during the dry periods. A minimum through­ ments associated with the creation ofthe Andes. put of 520 mS/day, with permeabilities of the Throughout this central. valley section, con­ order of 370 m2/day, has been calculated. For siderable thicknesses of late Tertiary gravels supply purposes, the available water is insuffi­ have accumulated. The maximum thickness cient during drought periods. recorded is 400 m, 8 km to the west ofVallenar The chemistry of the groundwater reflects (Lloyd 1973b). The gravels have been eroded to the geology of the catchment of the Rio Cogoti form an impressive series of terraces in the in that it is HCOs, derived from the predomi­ Huasco and Copiap6 valleys. Base level rises nantly granitic terrain, and differs in this respect since the formation ofthe terraces have resulted from all other major water sources in the area in deposition of Recent alluvium which is most which have sulphate chemistry. pronounced in the central valley sections of the In the Rio Elqui, catchment groundwater is transverse valleys. Where the valleys emerge abstracted from a few wells near La Serena from the Andes foothills, a marked reduction in where the wells induce their discharge effec­ bed gradient occurs and the valleys widen. The tively through the alluvium from the base flow. widening is attributed to lesser flow velocities In dry seasons, discharges reduce drastically as that have produced braided channels and to the base flow becomes negligible. Yields range up fact that the late Tertiary gravels are more easily to 20 liters/sec with alluvial thicknesses of up· eroded than are the older harder rocks of the to 25 m; permeability values are ofthe order of hinterland. 700 m2/day. The water is sulphate in quality In the Huasco valley in the vicinity of Val­ and used extensively for irrigation. No surplus lenar where main groundwater development is Hydrogeology and Water Supply Problems in North-Central Chile-LLOYD 97 operative, the Recent alluvium comprises the with sewage, as quality is not a severe con­ main aquifer, ranging up to 50 m in thickness. straint. Except for periods of extremely high floods, a Seasonal recharge to the Recent alluvium 6-km section of the valley at Vallenar receives aquifer in the Rio Huasco is through surface no surface flow, although the water table is only runoffinto the gravels in the Andes. The water very shallow. The lack of flow is attributed to is CaS04 in character with high tritium values, irrigation offtake upstream. Surface flow re­ but, in the vicinity ofVallenar, Ca-NaS04 water appears downstream of the town. is present in a zone along the northern side of Numerous wells have been constructed in the the valley; this indicates a limited lateral non­ valley for potable and industrial uses. Yields tritiated recharge to the main aquifer from the range up to 25 liters/sec, with specific capacities adjacent late-Tertiary gravels. ofthe order of12liters/sec/m. The permeability During studies in the rios Huasco and of the gravels is variable, 1100 to 4200 m2/day, Copiap6, specific yield values were established and, as a result, standard well design is difficult for a number ofareas, with traditional pumping to implement. The most effective designs in­ test analysis techniques being used, particularly corporate screens at the well base where coarse that of Boulton (1963). In general, even with material generally is present, with the slotted delayed yield effects accounted for, the values pipe sections being used against any higher high (0.9-3.7 percent) have appeared to be low for permeability zones. the lithologies present. A possible explanation Hydrogen sulphide has been recognized at for this may be postulated from water level very low levels (up to about 1 ppm) in parts of data obtained in July 1971. A continuous water the valley, and it has resulted in corrosion and level recorder that was in operation during a incrustation of the slotted pipe that have grade 6 (Richter scale) earthquake at Vallenar affected yield-drawdown relationships drastic­ recorded a water level rise of0.07 m at the time ally in a matter of 2 years. Step-drawdown data of the quake with no return to the prequake indicate that the effects are localized at the wells level. Similar changes have since been noted in and do not penetrate the formation; in conse­ minor quakes. It is considered, therefore, that quence, in these areas, slotted pipe is being the loose valley alluvium is being compacted by avoided to reduce active cathodic surfaces, and earthquake shaking and, as a result, porosity stainless steel screens alone are being recom­ and specific yield are being reduced, causing a mended for the production zones. further constraint on groundwater availa­ Immediately downstream of Vallenar, total bility. flow in the Huasco valley was measured during To the west of Vallenar, the central valley is the 1972 drought period and calculated to be controlled by northerly trending faults. Some 5.4 104 m3/day of which 3.4 104 m3/day com­ of the faulting is late-Tertiary in age and has prised irrigation and surface flow. The 2.0 104 affected the Tertiary gravels of the central m3/day of groundwater flow in the vicinity of valley. In some of the lesser transverse valleys, the town is adequate for the present water which rise in the foothills of the Andes, an supply demands of about 1.24 104 m3/day, easterly downthrow of the western central although future development needs have not valley boundary faults has not been countered been established. Downstream of the town, the by subsequent effective downcutting, as has Huasco valley water is oflimited value because been the case in the main transverse valleys ofa rapid increase in water salinity from 680 to such as the Huasco; therefore, groundwater 3450 ppm. This increase is a function of sum­ flowing from the Andes in the Tertiary and mer evaporation of the shallow groundwater younger gravels in such valleys has been im­ depositing salts in the gravels, which are re­ pounded at the faulted margins and has not dissolved by spring flows with the consequent been released westward by subsequent erosion rise in dissolved salts content in the water. With (with the exception of minor overspill). a view to groundwater management, wells for In the vicinity ofDomeyko and Castilla, such copper ore processing have been constructed resources have provided limited groundwater to tap the saline water in places contaminated supplies but water level declines and salinity 98 PACIFIC SCIENCE, Volume 30, January 1976 increases are now occurring as the effect of doned farms and dying stands of trees are groundwater mining becomes apparent. Triti­ present. An example of the reliance of the um evidence indicates that the waters are dead copper industry on the main transverse valley and, unfortunately, radiocarbon dating has system can be seen at Zapallar, 30 km to the proved valueless because of the very low bi­ east of the Rio Copiapo. The ore deposit is carbonate content of the waters. The situation significant, consisting of 15 million tons of is particularly serious in Domeyko where the 0.5-1.5 percent copper. The processing plant supply of one of the main wells had dropped requires a supply of4150 m3/day, but, under the from 1400 to 170 m3/day since 1942. present climatic regime, only 160-250 m3/day In the Rio Copiapo, groundwater abstraction can be obtained at sites near the deposit; as a occurs at a varying amount from a point some result the ore will have to be trucked to a plant 42 km upstream of Copiapo to the river mouth. located in the main Copiapo valley. In such Requirements are for irrigation, population (1.6 areas, any copper deposit must be of sufficient 104 m3/day), and copper processing (1590 m31 grade to counter the additional cost of long day). Italconsult (1963) calculated the total haulage to main water sources. In many in­ groundwater throughput for the valley to be stances, the economics prove impossible; for 7.8 104 m3/day. This value is certainly lower in example, in the vicinity of Inca da Oro on the drought periods and in 1972 it was estimated to watershed between the rios Copiapo and be about 4.0 104 m3/day. Salado, a supply ofonly 2000 m3/day cannot be Tertiary gravels are not so well developed in obtained for a plant, even if a 42-km pipeline the Rio Copiapo valley as in the Rio Huasco is taken into consideration. In another example, and are of negligible groundwater importance. to the northeast of Vallenar, the mining of a The Recent alluvium is much thicker here than porphyry copper deposit of 60 million tons of it is to the south, however, with thicknesses of 1 percent copper ore with 0.04-0.05 percent up to 120 m recorded in wells near Paipote. molybdenum has proved to be totally unfeasible Chemical characteristics of the groundwater do due to the lack ofa local water supply and ofits not appear to be detrimental to well construc­ uneconomic distance from the Rio Huasco. tion, so that slotted pipes can be used. Highly In the region to the north of the Copiapo efficient wells can be constructed up to 70 m valley, freshwater resources are virtually non­ deep in which naturally developed slotted pipe existent except in the high Andean streams. In sections are distributed against selected coarse the Rio Salado valley, the most northerly of the alluvial zones. Specific capacities ofthe order of major transverse valleys, the potable water 30 liters/sec/m can be obtained. Throughout the supply for the port of Chanaral is obtained by valley, individual well yields have decreased pipeline from the Copiapo valley. The most over the past few years, particularly in shallow important water requirements, however, are wells where water level decline has been most industrial. The area is a major world copper­ significant. As water requirements have risen in producing area with the two large porphyry the valley, overall availability has declined and, deposits of Potrerillos and EI Salvador located although the situation is not critical, the main in the upper Rio Salado catchment. Apart from problem revolves around the management of these developments, there is a large investment water resources and the balance between a in small- and medium-scale mining that sup­ socially important agricultural industry, a ports 60 percent of the employment in the area highly profitable copper industry, and potable and this activity in such a climatic zone poses requirements. significant water supply problems (5000 m3/day The changing climate ofthe region is causing requirement). more emphasis to be placed on the water The area is mountainous and highly dissected. resources of the main transverse valleys than The watershed between the Rio Salado and the before. Whereas previously tributary and minor Salar de Pedernales rises to between 3500 and transverse valleys were able to support minor 5280 m elevation above sea level. The latter agriculture and small copper ore processing catchment extends nearly to the Argentinian plants, toda.y in many such valleys only aban- border and rises to just below 6000 m in the Hydrogeology and Water Supply Problems in North-Central Chile-LLOYD 99 main Andes range. As with the other major Ocean, results in very steep bed gradients in the transverse valley, during the uplift ofthe Andes major transverse valleys that flow from the th~ proto-Rio Salado originated in the Andes Andes to the sea. These gradients are mirrored and cut across the central valley and the Coastal by the groundwater gradients in the alluvium, Range to the sea. Sometime during the later so that groundwater availability is closely history ofthe uplift, the upper catchment ofthe related to the seasonal recharge, which is a system was tilted to the northwest (Mortimer feature of the climate, and little storage water 1969), thus separating the system into the high is available. level Salar de Pedernales internal drainage The area under discussion borders the catchment in the east and the present Rio Atacama Desert and is semiarid to arid. Be­ Salq.do catchment drains to the Pacific in the cause of the climate and hydrogeological west. environment, groundwater resources have The hydrogeology of the two present-day historically proved to be a problem; over the catchments is unusual. Base flow from the past decade, unfortunately, there are indications Andes occurs mainly in the Rio ala and flows of a lower modal annual rainfall with droughts into the Salar de Pedernales salt flats. The possibly related to climatic change effects in the important water supply for Potrerillos and EI region. This factor has worsened an already Salvador, which amounts to 5.13104 m3/day, is difficult water supply situation. obtained from a small impounded reservoir on Surface water supplies are largely canalized the Rio ala. Some 110 liters/sec, however, pass in the Andes foothills and are used for irrigation to the salt flats (Constantini 1960). The inflow purposes. As a result, in the central valley area water (2500 ppm total dissolved solids) is where the main population occurs and where enricred in salts in the basin and overspills as industry is most prevalent, water supply is groundwater flow through volcanic ejecta of largely dependent upon groundwater. In the watershed into the upper Rio Salado catch­ addition, the decrease of bed gradient in the ment where the head springs contain 70,760 transverse valleys within the central valley ppm total dissolved solids. The Rio Salado is allows surface water to infiltrate, thus accentu­ perenrlial for several kilometers before it infil­ ating the predominance of groundwater. trates into the Recent alluvium of the valley It is within the central valley area that the floor and reappears as springs (73,040 ppm main groundwater management problems are total c,l.issolved solids) at EI Salado. now being posed. Because of the decrease in Because ofthe absence ofother water resour­ rainfall, the minor tributary valleys no longer ces and because copper ore processing is not provide dependable groundwater supplies, so seriously constrained by water quality, the EI that water requirements for any developments Salado springs are being exploited for process­ in these valleys are consequently being trans­ ing purposes (Lloyd 1974b). To obtain both ferred to the main transverse valleys. The surface and groundwater flow to dewater the population is increasing in the main transverse seepage area where evaporation occurs and to valleys and, as that population becomes more limit the effects of flash floods on surface struc­ sophisticated, it requires more domestic water; tures, a subsurface abstruction system using this factor, together with the emphasis on drains has been designed. The drains are back­ industrial development largely centered on the filled with filtered materials and have perforated copper industry with its significant water needs, wooden-cased wells for pump installation. means that the overall water requirement is multiplying at an alarming rate. Government agencies are looking at the need CONCLUSIONS to ensure reliable potable supplies, but the main The hydrogeological environment ofthe area problem is the need to balance water use be­ described is very distinct, consisting almost tween agriculture and industry so that water exclusively of groundwater resources in thin resource use is optimized to the greatest advan­ valley alluvium. The nature of the terrain, with tage. Agriculture already has been hit severely the towering Andes range close to the Pacific by recent droughts and will probably suffer far 100 PACIFIC SCIENCE, Volume 30, January 1976

more. Increased efficiency in water use is being LITERATURE CITED effectively promoted by the increase in produc­ BOULTON, N. S. 1963. Analysis of data from tion of higher value cash crops and by the nonequilibrium pumping tests for delayed renovation of irrigation distribution systems. yield from storage. Proc. Inst. Civ. Eng. It would appear, however, that agriculture will (London) 26 (6693). more and more suffer from a lack of sufficient CONSTANTINI, R. 1960. Process water and water as farming uses considerably more water hydroelectric plant, El Salvador. Min. Eng. than do industry and population. (N.Y.). April: 375-378A. The copper industry is the major industrial ITALCONSULT. 1963. Aprovechamiento de re­ user of water (Lloyd 1974c). Its requirement as cursos hiddulicos en el valle de Copiapo. compared to agriculture is small, but the cash Consultants Rep., Dep. Recursos Hidduli­ value of copper far exceeds that of agricultural cos, Corp. de Formento de la Produccion, products so that the reliability of the long-term Chile. 253 pp. supplies for copper processing is an importa~t LAMB, H. H. 1966. Climate in the 1960s. Geogr. economic factor and must be assured. It 1S J. 132(2): 183-212. us~ w~ter important that the industry should its LLOYD, J. W. 1973a. Climatic variations in efficiently. Closer attention to the recIrculatlon north-central Chile from 1866 to 1971. of processing water where recovery efficiencies J. Hydrol. 19: 53-70. are often low would be advantageous. More --. 1973b. Hydrogeology of Quaternary consideration should be given to the utilization sediments in the vicinity of Vallenar, Ata­ of seawater and water such as brines or sewage cama Province, Chile. Paper presented at that are not o-enerally suitable for other uses. b . Second Latin American Geological Con­ Costs may prove to be higher than those 1n- gress, Caracas. curred by use of freshwater but, in the long ---. 1974a. Water supply for the Andacollo term, more use of seawater, particularly, may copper ore processing plant, Chile. Trans. prove unavoidable because of its reliability. Inst. Min. Metall., London 83: 1-6A. Eventually, if conditions continue to deteri­ --. 1974b. The hydrogeology and utiliza­ orate, it will be necessary to determine water­ tion of brines in EI Salado, Chile. Ground­ use priorities, a socioeconomic problem outside water 12(2): 72-77. of the scope of this paper. In any case, with the ---. 1974c. Importance of water resources implementation of comprehensive ground­ in the development of the Chilean copper water investigations and coordinated water industry. Trans. Inst. Min. Metall., London management policies, a sound basis can be 83: 63-66A. constructed on which to found development LYDOLPH, P. 1967. On causes ofaridity along a decisions. Sufficient work has already been selected group of coasts. UNESCO Con­ carried out to indicate the critical nature of the ferencia Regional de Zonas Aridas, Lima. water supply situation, but, because of the 6 pp. unusually difficult hydrogeological environ­ MORTIMER, C. A. 1969. The geomorphological ment, much more study is required. evolution of the southern Atacama Desert, Chile. Ph.D. Thesis. University of London. ACKNOWLEDGMENTS SCHNEIDER, H. 1969. EI clima del Norte Chico. Pages 43-125 in Publ. Departamento de The writer would like to thank the staffofthe Geografia, Universidad de Chile, . Water Resources Office ofthe Chilean Empresa TREWARTHA, G. T. 1961. The earth's problem Nacional de Mineria for their assistance in data climates. University of Wisconsin Press, collections and analyses. This paper has been Madison. published with the permission of the Director, Institute of Geological Sciences, London.