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by Igor ZEKTSER, Dr. Sc. (Geol. & Mineral.), Institute of Water Management, Russian Academy of Sciences
The words in the headline belong to Academician Alexander Karpinsky, an illustrious Russian scientist. Though uttered so many decades ago, in 1931, these words are more relevant than ever. Underground waters, geologists say, are the Number One mineral...
RELIABLE POOL DEEP UNDER
Water seemed to be a never-exhaustible source to many generations of people. Not in our days, though. Water consumption has soared with the growth in population numbers, and a vast area - about 60 percent of the globe's land surface - feels water shortages the hard way. In many regions the water- shortage factor interferes with economic advancement - be it because of climatic conditions (drought, scanty precipitation, absence of large water sources) or because of intensive and often maladroit consumption. To compound the situation, water pollution keeps up on an ever disastrous scale.
Working within the framework of the International Hydrological Program adopted by UNESCO in 1965, experts of more than 100 countries are joining efforts toward efficient water management in line with scientific recommendations. To begin with, they should take inventory of the available resources, for one, of the underground pools of fresh water as a reliable source of potable (drinking) water. Such bodies of water hold certain advantages over surface waters in terms of purity and quality; besides, they are better protected against pollution and contamination, and least affected by seasonal and perennial fluctuations.
What is most remarkable about underground waters is that their resources are renewed in the process of circulation. Here's a paradox: even when consumed, such waters are never lost but often even add up to the available stock. Saturating the ground surface, they help reduce the evaporation of ground (subsoil) waters. Besides, underground waters are more mobile and persist in close interconnection with the environment, that is with enclosing rock formations, and with rivers, seas, landscapes and vegetation.
RESERVES AND RESOURCES
In point of fact, these are different notions. The term "resources" was put into scientific use by the Russian hydrogeologist Academician Fyodor Savarensky (1881-1946): unlike other useful minerals, he reasoned, underground waters have no constant reserves but are renewed all along in the process of circulation. That is to say, when estimating the total volume of such waters, we should likewise take into account the inflow of moisture, and not just proceed from the amount contained in a particular body of water or in a water-bearing bed (aquifer). That is why Academician Savarensky maintained: one should speak of underground water resources rather than reserves, that is we should also count in the balance of replenishment (recharge) and intake (draw off). As to the term "reserves", it should apply to the available volume of water in a pool or reservoir, regardless of replenishment. Which means that though the capacity (competence) of an aquifer and reserves of water in it may not be large, an associated water reservoir could be quite capacious owing to steady recharge.
Another important consideration is the filtration characteristics of rock. Knowing the amount of water in a bed and its inflow under natural conditions is not enough. That is, when dealing with underground waters we cannot use the same yardstick we do for fossil fuels, oil and gas - suffice if we know their available reserves.
On one hand, we have natural (static, secular, geological or capacitive) accumulations of water which, expressed in volume units, characterize its overall content in a horizon. But on the other hand, we have also head (pressure) horizons with "elastic reserves", or the amount of water released upon stripping (in this case the pressure goes down as result of water intake or natural outflow).
Now what concerns underground water resources: hydrogeologists make a distinction between natural and commercial waters. Natural water resources (often described as dynamic) are a function or the underground water replenishment through atmospheric precipitation and river run-off, intake of an aquifer (water-bearing horizon) and leakages from other horizons. This is a sum total expressed by the water discharge from a flow or by a depth of a water- bearing bed added to an aquifer. In the final analysis, we deal with the recharge (replenishment) indicator.
Commercial resources: this means the flow rate in draw off discharge from an aquifer, given the desired quality of water and adequate technical facilities. By tradition water management experts say "commercial resources" when handling water supply on a regional scale, and they say "commercial reserves" when dealing with the water supply of a specific object.
Today our major headache is how to prevent depletion of an aquifer, its
exhaustion. For this permissible limits of draw off, or water intake, must be imposed. But depletion, as one will often think, is not just any drop of pressure during draw off. This is wrong, for water intake always involves a dropping pressure. It's a different thing, though, if the rate of intake exceeds certain permissible limits. Therefore it is all-important to know the permissible levels of the flow rate, for otherwise irreversible changes could be caused in the resources and quality of water, and they could be depleted indeed. It is commonly believed that an aquifer is depleted only if the water intake is above a definite value of commercial reserves (according to a standard set by water management authorities) or if the water pressure drops below permissible levels.
WHAT DO MAPS TELL?
It was back in the late 1950s that we in this country began studies to assess natural and estimated commercial resources of underground waters, both in particular regions and nationwide. This work was done within a short time, with all the necessary maps and a monograph. It was a pioneering endeavor in many ways. First, our hydrogeologists assessed total natural resources of water. Second, they identified certain essential regularities governing the formation of these resources under different physical, geographical, geological and hydrogeological conditions. And third, our researchers determined changes of different characteristics in time and space - characteristics responsible for subsurface drainage. Besides, special methods for effective analysis and processing of the available data were devised so as to do without extra surveys, which are a very costly undertaking.
Our hydrogeological maps show a variety of data: mean perennial moduli of subsurface drainage (intake of a water flow per 1 sq. kilometer); factors for a correlation between replenishment and atmospheric precipitation; and factors for ground-water recharge within a total river run-off. In addition, these maps indicate natural conditions and regularities responsible for the formation of natural resources (specifically, the composition and stratigraphy of water- bearing rocks, karst, or cockpit areas, ranges of fresh-water lenses, surface water absorption areas, and so forth).
Our experience of water resources mapping gained back in the Soviet times has received recognition in other countries as well. Drawing upon this experience, experts of some European countries have carried out similar studies within the framework of the UNESCO-sponsored Hydrological Program. The results of their work have been incorporated in a map of subsurface drainage of Central and Eastern Europe drawn at the scale 1:1,500,000 and in a respective monograph, all that published in 1982 and 1983.
Recently large-scale international studies were completed in assessing the natural resources of underground waters of the globe's dry land and their mapping for particular regions. Taking part in this project were scientists from many countries; and the results of their work are condensed in the 1999- published map of hydrogeological conditions and subsurface drainage of the world's dry land, on a scale 1:10,000,000 (editors-in-chief, Roald Jamalov and Igor Zektser); in 2001 this map merited an award of the Russian Academy of Sciences-a prize instituted in memory of Academician Fyodor Savarensky.
Over the past few years a good deal of work has been done here in Russia in estimating the commercial resources of underground waters contained in all the artesian basins and in the country's hydrogeological masses in particular regions. Maps of different scale have been drawn for moduli of commercial resources (average consumption of water per 1 km 2 of a corresponding horizon). Estimates have been made for certain potentially water-rich regions in terms of consumption by concrete users and location of appropriate water intake installations. Since most of this country's regions have pools of underground water, it makes sense to proceed with exploration and prospecting work. By the way, surveys made recently by a research team under Leonid Yazvin and Boris Borevsky of
Shorthand showing a connection between subsurface drainage and climatic zones. Map symbols:
1 - excessive humidity;
2 - normal humidity;
3 - insufficient humidity;
4 - aridness; 5 - <1; 6 - 1-3;
7 - 3-5; 8 - 5-10;
9 - 10-20; 10 - 20-50.
the Hydrological R&D Company have allowed to upgrade the prospecting techniques and obtain a well-substantiated classification of commercial reserves of subsurface waters and their pools in aquifers where water intake will be a paying proposition. By now several thousand pools of fresh and brackish (subsaline) underground waters have been surveyed. Data of their commercial reserves have been approved by federal or territorial boards in charge of mineral prospecting.
Since 1979 it has been common practice every year to evaluate information on commercial reserves of underground waters, this work being done within the State Water Cadastre as part of the state monitoring of this country's mineral resources. Such data are published in annual information bulletins. The figures cited below have been borrowed from one such publication for the year 2000 by the State Geomonitoring Center.
The estimated resources of fresh and subsaline (containing 3 g of salt per liter) underground waters countrywide amount to 867.8 million cubic meters per day Around 72 percent of this pool is concentrated in the West-Siberian, East- Siberian, Far Eastern and Northern Economic Regions. Yet the share of proved commercial reserves, according to official statistics by January 1, 2001, made up only 86 million cubic meters per day. The country's average consumption rate is about 3 percent, with a maximum of 26 percent in the Kaliningrad Region, which is Russia's westernmost territory.
In 1999 the underground water intake totaled 33.9 million cubic meters per day, with the actual consumption averaging 28.1 mln m 3 /day, the rest was just drained off.
In keeping with our rather rigorous water-management legislation whereby fresh underground waters of high grade should be primarily used for household consumption, about 76 percent of the water is expended for this purpose by and large; 22 percent is utilized for industrial purposes and a mere 2 percent - for the irrigation of cultivated lands and pastures. As I see it, this is an essentially correct approach: it is better to use subsurface, not underground, waters for irrigation and watering. Even though this involves much higher expenses, the ultimate economic benefit is obvious - keep the fresh-water underground reserves of high quality for generations to come.
OVER THREE THOUSAND SOURCES OF POLLUTION
The anthropogenic factor - that is what relates to man and his activity-has now come to play a dramatic role where the environment is concerned. This is true of underground waters, fresh waters in particular.
The very notion of ecologically pure water must be revised accordingly. That is why, apart from steps to prevent depletion of water reserves, the focus is also on the quality of water within commercial horizons. As to pollutants, these are enhanced concentrations of nitrogen compounds, those of iron, manganese, strontium, selenium, arsenic, fluorine, beryllium and organic substances. Without special treatment, the thus contaminated water is no good for drinking.
According to data supplied by geological organizations of the Russian Federation's Ministry for Natural Resources, there were over three thousand focal points of underground water pollution countrywide by January I, 1999; 75 percent of the number was located in European Russia. These are wastes and effluents contributed by industrial enterprises, oil fields, depots of combustibles and lubricants (that's 36 percent of the above focal points of pollution); also, pollutants drained from irrigated fields, cattle and poultry farms (about 15 percent of the number). The other sources of pollution came from the utilities and every kind of dumping grounds.
Among the most widespread contaminants are these: sulfates, chlorides, nitrogen compounds (the nitrates ammonia, ammonite), petroleum products, phenols, iron-containing compounds, heavy metals (copper, zinc, lead, cadmium). However, by the data of the State Water Cadastre for 2000, the badly polluted aquifers (water-bearing beds) seldom exceed an area of 100 km 2 each - only 24 such aquifers were identified (out of the total number of polluted beds estimated at 2,776). As a rule, polluted aquifers are not larger than several hundred
square meters each - or at worst, taking in a few square kilometers. Yet even this indicator - not too bad, fortunately - cannot attest to the favorable condition of underground waters.
CORRECT REGULATION OF WATER INTAKE COMES FIRST
As part of the environment underground waters have a complex pattern of relationship with its other components. Their depth of occurrence affects the nature of plant life as well as the productivity of farm crops, while their annual and perennial fluctuations are often the cause of flooding in town and in countryside, and are conducive to landslides. An intensive intake of water may result in land subsidence (sinking) and thus activate karst-suffusion (undermining) processes; it affects the depth of rivers and causes a dewatering of land areas.
On the other hand, underground waters are acted upon by the other components of the environment. Say, freshets add to the river run-off and natural water resources. Yet water reservoirs that regulate the surface run-off decrease the time and intensity of freshets and, consequently, change the regime of aquifer alimentation and, in the long run,
deplete underground water reserves. Intensive irrigation with a network of water- supply canals and ditches contributes to enhanced humidity in surrounding territories.
Now let us look into how the intensive draw off (pumping out) of underground waters acts upon the river run-off, vegetation and land surface. But first, let me tell you the worst truth - what could be in store for us in consequence of the wasteful use of underground waters. Apart from the depletion of the reserves of moisture, its lower depth of occurrence, and conical depressions, or sinks, there are bound to be dramatic changes in the interdependence of subsurface and surface waters. This is all-important once we come to deal with water intake of the "infiltration type" along river banks drawing heavily on commercial reserves. Clearly, such kind of intake impacts the river run-off which changes with the further pumping out of water, depending on such natural and anthropogenic factors as the hydraulic connection of an aquifer with a river in different seasons, variability of the river run-off within a year and for many years, the nature and volume of recharge and discharge of a horizon, and other conditions.
All these factors should be taken into account when assessing the efficiency of river bank intakes and possible changes of the river run-off which varies in a very wide range in its course and scope. Such changes do not appear all of a sudden, they are latent and occur with some "time lag". The run-off may even intensify when the utilized underground waters are drained into rivers from deeper horizons.
Using up-to-date theoretical models and appropriate procedures, we can predict fairly accurately possible changes of the river run-off and, consequently, develop an effective system of water intake management on river banks so as to preclude untoward consequences for particular branches of the national economy (fishing, navigation, recreation) as a result of a disastrous, or just unacceptable, cut in the consumption of river water.
As we have already said, a decrease in the level of underground (subsurface) waters affects vegetation depending on the mode of its nutrition, automorphic or hydromorphic. We deal with the automorphic mode of subsistence when plant roots, without reaching the level of subsoil water or the capillary rim (a stratum where moisture is retained in rock pores) get water directly from atmospheric precipitation. The depth of rootage is called critical if it reaches the level of subsoil water. In that case plants get moisture from subsoil waters. This is the hydromorphic mode of nutrition.
Most of the plants do not sink roots all to deep. For instance, if we take the Oka sanctuary south of Moscow*, the roots of a pine-tree do not go deeper than 3 meters; for an oak it is 5.1 meters, for a lime - 2.5 m, birch - 3.4 m, aspen - 4.4 m. This means that the roots of these trees are in the zone of intensive infiltration of atmospheric precipitation.
The thickness of the capillary rim above subsoil waters depends on the composition of subsurface rock. In sands of various granulometric (grain-size) composition it ranges from 0.1 to 0.5 m; in light loams and peat bogs, it is between 2 and 2.5 m; and in heavy loams - as much as 3 to 4 meters.
Hence an essential practical conclusion: when subsoil waters occur below critical depths, a drop in their level in consequence of water intake in no way affects vegetation. That is to say, if this level is deeper than 5 meters in sands and deeper than 7 meters in loams, intensive consumption of underground waters will not tell on a plant community. Yet this conclusion holds only for humid and temperate humidity zones. But the critical depths are different for
* See: M. Kolotova, "Laboratory of Nature Restoration", Science in Russia, No. 5, 2001. - Ed.
Underground water use in 1999 (by data from Russia's State Water Cadastre, 2000).
1 - household (drinking water) supply;
2 - industrial and process water supply;
3-land irrigation and water-supply development of pastures.
arid-climate plants, say, eucalypts, and so is the effect of water intake. The intensive use of water-bearing beds along river valleys in arid zones often kills hydrophytes, or moisture-loving plants; and phreatophytes (plants drawing on phreatic, or subsoil waters) are suppressed. Thus a large-scale pumping of underground waters (ca. 800 I/s) in the valley of the river Karakenghir in Central Kazakhstan (this stream goes dry every now and then) has inflicted much damage on the local flora. According to Matvei Hordikainen, of the All-Russia Research Institute of Hydraulic and Engineering Geology (RF Ministry for Natural Resources), most of the vegetation in the district has withered away, including the meadow grass next to the intake sites, and the river run-off has fallen dramatically.
We know of cases of water pumping when low-land bogs are dewatered and disappear altogether as a result; their moisture-loving vegetation fades away or else changes its species. Now and then there may be a good side to this process - namely, the draining of overmoistened lands has a positive effect on crop productivity and on the species - specific composition of grasses on water- meadows.
The intensive pumping of underground water over extensive areas of dozens and even hundreds of square kilometers may give rise to conical depressions, or sinks, which change the condition of rock as well as the How rate of underground streams; this, in turn, activates suffusion and karst processes. Such sinks lead to subsidences and even pits elsewhere. Subsidences are the commonest in territories where underground waters are enclosed in permeable rocks of sand and gravel, with interstratifications of clayey low-permeability deposits. Water intake in such places brings down the pressure and, as a consequence, there is a compactification of deposits and next, conical depressions. Here are the most eloquent instances. In California, USA, land subsidence has attained a value of 9 meters (in a maritime valley near Los Angeles the annual rate of subsidence is 0.5 to 0.7 cm); the figure for Mexico City is 10.7 meters. Such kind of land sags are as deep as ten meters in more than 150 districts of Mexico, Japan and USA in consequence of the heavy intake of underground waters and mining.
The aftermath of all that is manifest in the frequent flooding and bogging of large tracts of land. Immense damage is done to highways, railroads, electric transmission lines, oil-and-gas pipelines, industrial enterprises and engineering structures. Grades of river beds are changed too.
The only way out is to cut the consumption of water from commercial aquifers and to monitor the level of underground waters and the condition of land surface. In other words, the aim is to preclude or at least minimize the negative effect of underground water use on ecolandscapes and vegetation by regulating major water intakes (mostly by reducing the draw off). The available water reserves should be replenished, and the surface run-off regulated by means of special water management procedures.
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