Ecological Systems and 

H the Water Resource

GEOLOGICAL SURVEY 

CIRCULAR 414-D
Part D

Ecological Systems and 

the Water Resource

By Luna B. Leopold

CONSERVATION AND WATER MANAGEMENT

GEOLOGICAL SURVEY CIRCULAR 414-D

This volume complete in four parts

Washington I960
United States Department of the Interior

STEWART L. UDALL, Secretary

Geological Survey

William T. Pecora, Director

First printing 1960 

Second printing 1962

Third printing 1965 

Fourth printing 1967

Free on application to fhe U.S. Geobgica/ Survey, Washington, D.C. 20242
.GEOLOGICAL SURVEY CIRCULAR 414 

CONSERVATION AND WATER MANAGEMENT

PART D

Ecological Systems and the Water Resource

By Luna B. Leopold

Presented before the Sixth Biennial Wilderness Conference, sponsored by California Academy of Science, San Francisco, Calif, 

March 20-21, 1959.

In ancient Sparta there were two principal 

classes of society, the citizen and the helot. 

The citizen was trained principally to be a 

warrior. The helot, a serf, was the tiller of the 

land but could be called to military duty. The 

history of Herodotus makes it amply clear that 

making war was the biggest business of the 

times. Because the Spartans were always marching off to war with someone, they found the landbound position of their city, located as its is in a 

small central basin nearly surrounded by moun- 

. tains, somewhat of a disadvantage. When they 

were under attack, of course, this situation was 

a favorable one inasmuch as a seaborne enemy 

had to march inland to come to grips with the 

Lacedaemonians. The relatively small size of 

the independent states meajit that the Spartans 

had no direct access through their own lands 

to the sea.

There is evidence that the Spartans reached 

an agreement with surrounding states concerning a free corridor. There would be maintained 

by all the Grecian states of the Peloponnesus 

an access route stretching essentially from Sparta 

to Corinth, through which a marching army 

could have access to a seaport. As a secondary 

benefit, this no man's land, which in our western 

lingo might be called a stock driveway, allowed

merchants and their caravans to move freely 

between the flourishing trading port of Corinth 

and the inland cities to the south and west.

Apparently one portion of the agreement 

between the states with regard to the use of this 

access zone was that there should be no permanent agricultural or grazing in the driveway. 

As a result, through several centuries B.C. during 

which there was high population density in the 

Aegean area, one strip of land was exempted 

from the pressures of grazing, lumbering, and 

agriculture which characterized most of the rest 

of the landscape. Today this driveway maintains 

a forest cover. In contrast, mountainsides 

nearby with an even larger annual rainfall 

support hardly a tree.

It is not entirely apparent why subsequent 

centuries did not see this area denuded. Even 

with the scanty details known to me it seems 

clear that the peculiar history of this one area 

potentially offers us a greater insight into some 

aspects of forest and land conditions of classical 

times than extant written records. The several 

references to sources of timber and cutting of 

forests contained in the vivid chronicle of 

Herodotus are valuable, but they lack species 

identification for the most part. Though rkh 

in human understanding and psychological insight, his history strongly resembles the travel 

sagas of the Spanish Conquistadors of our Southwest, who had no real eye for "country." Even

21
a careful reading of the works of early travelers 

such as Coronado, Garces, and Espejo, gives no 

picture of the nature of the country, its vegetation, or its rivers.

To describe a biota there is no substitute for 

a sample. It is logical to ask what one might 

want to know which would require the preservation of a sample. Whether such a question 

is asked at all is a reflection on the stage of 

intellectual maturity of a civilization. We take 

for granted that there is social gain in the 

erection and maintenance of a museum of fine 

arts, a museum of natural history, or a historical 

museum. Sooner or later we should be mature 

enough to extend this concept to include a 

"museum" consisting of samples of land types 

as nearly as possible unaffected by man.

There is a growing interest in the preservation 

of pieces of wilderness. The proponents of the 

wilderness movement speak about the need for 

peace and serenity, the rejuvenation of soul as 

well as body by contact with Nature, and the 

preservation of scenery for the edification of 

our grandchildren. Real as these reasons may 

be, wilderness continues to shrink in size and, 

in many areas, in quality. Though man cannot 

live by bread alone, the continual encroachment 

of civilization into the areas previously untouched or not yet severely modified by man 

proceeds apace.

It is interesting that this trend continues at 

the same time that our society is experiencing 

a sharp awakening to the importance of science 

for the maintenance and further development of 

this same society. We seem to recognize the 

intellectual as well as the economic advantages 

of exploring the moon and outer space, but we 

still have corners of our own backyard which 

are worthy of study.

But they are worthy of study only if natural 

biological and physical processes are in operation. Some natural processes simply stop 

operating when the vegetation, the soil, the

microbiology, and the hydrologic environment 

are seriously disturbed. It is to these natural 

processes in an undisturbed or little disturbed 

environment, that I wish to call attention.

It is often stated that water tables are falling, 

that floods are increasing, that the soil resource 

is deteriorating, and that much of our irreplaceable top soil is slipping seaward. As scientists, 

it behooves us to take some interest in these 

questions and, as scientists, to obtain the truest 

and most objective answers possible. But 

whether one approaches these problems as a 

citizen or as a scientist, he immediately faces 

the fact that answers to these questions must be 

stated relative to some standard base or datum. 

What are you going to compare against? Is 

the standard or datum itself a fluctuating one? 

Can we agree on a reference point? If each 

person who tackles such a question uses a different reference for comparison it is quite

obvious that answers will all be different.

Let us take the question of falling water 

tables. We must begin with a mutual understanding of certain hydrologic principles. 

During rainless periods the flow of water in 

any small stream is the water which is contributed from ground-water storage. Streamflow 

in periods between storms represent the overflow of a full ground-water reservoir. When 

you fill the bathroom basin preparatory to the 

morning shave, water flows out the drain holes 

only after the basin has been filled. Such outflow ceases when the water level in the basin 

drops to the lip of the overflow orifice. So 

also in a headwater tributary, the stream will 

stop flowing when the water table drops to the 

elevation of the streambed nearby.

When an irrigator drills a shallow well near 

the stream, pumping may reverse the direction 

of flow, which normally proceeds from the valley 

deposits toward the stream. When pumping 

lowers the water level in the valley fill to an 

elevation below the surface of the nearby stream,

22
water from the stream flows into the valley 

deposits. So the shallow weH actually may be 

yielding water which a very short time ago was 

merrily flowing down the river. In many semidesert areas, the normal flow is from the river 

laterally into the valley fill.

Under certain circumstances one can increase 

the amount of ground water available by pumping the water out of the ground-water reservoir. 

Such pumping induces infiltration of streamflow 

into ground-water storage. Pumping of ground 

water results in local lowering of the water 

table, because some local lowering is necessary 

to provide a water-table gradient toward the 

well. Thus, any use of ground water necessarily implies at least local lowering of the 

water table. Lowering of the water table is a 

natural and expected in fact, necessary result 

of pumping. The question is: how much lowering of the water table is permissible, how much 

more is deleterious, and in what way?

The answer to this is neither simple nor unequivocal. In the first place, the natural daily, 

seasonal, and secular changes in precipitation 

cause responsive changes in natural recharge. 

These changes in rate of replenishment to 

ground-water storage do not show up immediately, because first, water in the ground usually 

moves slowly, and second, because available 

volumes of storage in an aquifer may be very 

large.

Ground-water levels are constantly changing 

as natural conditions change. Because of the 

slow and often attenuated response, changes 

due to natural causes cannot be computed with 

any accuracy. This being so, it is often nearly 

impossible to segregate clearly, changes in water 

level due to natural causes and those due to 

man's activities. By man's activities we must 

obviously include not only pumping, but the 

effects of land use, changes in ecologic associations, and changes in soil properties in recharge areas.

There are very few areas, except in the special 

hydrologic environment of some mountainous 

terrain, where one could follow ground-water 

changes that are due to natural causes alone. 

Nearly all environments are not only altered 

from their original state, but are constantly in 

the state of still further change. For this reason, 

only in areas of severe ground-water depletion, 

primarily in some portions of the Southwestern 

and Southern States, it is absolutely clear that 

ground-water withdrawal is greatly exceeding 

recharge. In those places, continuation of 

withdrawals at present rates will, in time, lead 

to exhaustion of the supply, or to pump lifts 

in excess of the limit of economic feasibility.

It is said by some that a large number of 

small reservoirs in the headwaters of a drainage 

basin and the maintenance of forests or grassy 

cover would increase ground-water recharge and 

would thus help to solve the problem of overdraft. The evidence for this view is mostly 

inferential. The ability of a good plant cover 

to maintain soil tilth and thus infiltration 

capacity is well known. But infiltration into 

the soil mantle is not synonymous with infiltration to an aquifer. At each level, soil 

capacity for moisture, that is field capacity, 

must be satisfied before water can move to 

greater depth. Nearly all vegetation draws its 

moisture from this source. Recognizing that 

in the hydrologic cycle, on the avera-ge, three 

fourths of precipitated water is returned to trie 

atmosphere by transpiration and evaporation, 

we can see that the take of the first claimant, 

evapotranspiration, is large. Thus it should 

not be assumed a priori that there will be a 

net gain of water to surface streams or to aquifer 

storage by building surface-storage reservoirs. 

In the only adequate study so far available, it 

was shown that small reservoirs or stock ponds 

in the Cheyenne basin, Wyoming, caused a net 

decrease of streamflow by about 30 percent.

With regard to a heavy cover of vegetation

23
increasing ground-water recharge, we may remind ourselves of the well known fact that 

selective cutting of forest increases water yield 

under at least some circumstances. The increase 

of water yield comes from decreasing transpiration by cutting some of the trees.

To summarize, the ecological system man, 

lancl, pump, plow, trees, and climate experiences much larger variations in ground-water 

levels than existed in the simpler system of 

land, trees, and climate. How much larger and 

how important these variations are is difficult 

to assess until the situation is flagrantly out of 

balance. By that time, the trend is nearly irreversible and usually continues until the limit 

of economic feasibility is reached.

One connotation of the word civilized is 

awareness of the consequences of one's actions. 

A civilized nation could and should, in my 

opinion, afford the maintenance of control areas 

to study natural variations in physical phenomena, such as ground-water conditions. But the 

lack of a datum increases greatly the difficulty 

of making a thorough diagnosis of trends and 

prospects of ground-water conditions in an area. 

The lack of such a datum greatly increases the 

difficulty of appraising the volumes of water 

available, rates of recharge, of understanding 

the implications of changes of water table, and 

in making prognoses of future status of an 

aquifer. These difficulties partly account for 

the dearth of adequate appraisals of the water 

situation in major aquifers in the country.

To take another and perhaps simpler example. 

Are floods inceasing because of man's activities? 

Again it is necessary to begin with a common 

understanding of some of the hydrologic principles involved. For example, a river floods 

when its water fills the channel and overflows 

its bank. It is a characteristic feature of river 

channels that they are constructed by the river 

large enough to contain only a relatively frequent flow. The bankfull stage in natural

channels occurs on the average about once a 

year, regardless of the size of the river. Flows 

larger than this must spread over the flood 

plain. Thus overbank flow may normally be 

expected on the average as often as once in 2 

years.

Overbank flows or floods cause damage 

because man builds structures, grows crops, or 

otherwise uses the flood plain. With increase 

in population and industrialization, the fertile 

and level flood-plain lands become more intensively used and thus there is a tendency to 

increase the amount of damageable property 

potentially within the reach of floods. This is 

one of the principal reasons for the progressive 

increase in actual flood damage in the United 

States up to the passage of the Flood Control 

Act of 1936. Since the passage of flood-control 

legislation in 1936, about 3VS billion dollars 

have been expended on flood control. As a 

result, a large amount of damage has been prevented, damage which would have occurred in 

the absence of the flood-control works. Yet, 

since 1936, the actual flood damage experienced 

annually has not decreased, presumably owing 

to still further encroachment on river flood 

plains.

But again it is very difficult to determine 

accurately how much natural or strictly climatic 

vicissitude accounts for the flood experience on 

any given river; conversely the hydrologist cannot evaluate the extent to which flood occurrence, in contrast with flood damage, has been 

altered because of the various direct and indirect 

influences of man on the environment.

In water yield that is river flow the separation of the effects of natural from man-induced 

changes ought to be easier, because the seasonal 

and daily fluctuations can be eliminated by expressing water yield as total flow on, say, an 

annual basis. Yet even these data are difficult 

to interpret. Many gaging stations in the upper 

Missouri River basin, for example, show what

24
appears to be a rather consistent trend toward 

lower values of total runoff in the past two or 

three decades. Yet some individual stations in 

the same area do not show the trend. Over 

the United States as a whole there is no distinctive and consistent trend in the records.

Knowing that long-term temperature records, 

glacier recession, and certain oceanographic and 

meteorologic elements.indicate a general warming in the northern hemisphere, we might 

expect an accompanying trend toward aridity 

and consequent decreasing runoff. But because 

there is no adequate control which shows such 

trends uncomplicated by man's activities, clearcut conclusions cannot be reached. There is 

reason to believe that even our long records of 

precipitation and temperature have been affected 

by influences of man on the environment.

When the total period of record of streamflow and other hydrologic elements becomes 

much longer, let us say twice as long as the 

presently available 60-odd years, statistical variance will be better defined. But by that time 

man's effects and his pressures on the environment will be even more extensive and pronounced. It may well be that it will never be 

hydrologically or statistically possible to demonstrate what part of the experienced variations 

in hydrologic conditions is natural and what 

part is man-induced.

Is it important that we know? Well, much 

confusion in several fields of activity has resulted 

from the fact that such questions cannot be 

clearly answered. For example, graziers maintain that livestock has little to do with the 

widespread gullying of western valleys, while 

many others maintain that grazing is the principal cause.

Because no unused area exists which is, in all 

principal respects, similar to the region under 

discussion, the factors must be analyzed by 

roundabout and indirect means. Even now, 

after years of study by many specialists, there

is much we desire to know.

It is clearly shown by geologists that alluvial 

valleys were channeled by gullies several times 

in late Pleistocene and geologically Recent time 

long before man could have had any important 

effect. It is believed that these gullies eroded 

the floors of alluvial valleys in response to 

changes in rainfall-runoff relations associated 

with climatic variations, but the magnitude of 

climatic change required to cause the observed 

results is unknown.

It seems equally clear that the epicycle of 

erosion which began in the 19th century must 

have resulted from a combination of climatic 

and manmade effects. The relative importance 

of each is still quite unclear. Partly for this 

reason it is not possible to forcast with any 

certainty what will be the future of these arroyos. 

My own studies of this question lead me to 

believe the gullies in western valleys will not 

aggrade by deposition in the next several generations, but will gradually tend to stabilize, 

with their banks rounded and eventually covered 

with vegetation. I, for one, would be intensely 

interested in seeing some area typifying the 

alluvial valley-gully problem protected indefinitely from further use by man or by grazing 

animal, so that we could observe what erosion 

or deposition will occur naturally.

For long-term observation of the effect of 

climatic changes on runoff, the United States 

Geological Survey is eager to establish and 

maintain what we would call "benchmark" 

gaging stations, measuring streamflow from 

areas which are as free as possible from future 

man-induced changes. Out of 7,000 gaging 

stations now maintained in the United States 

only a few seem to fit the requirement. Even 

for those, there is no guarantee that the drainage 

basins will remain free of man's influence indefinitely.

The vast national programs of hydrologic 

measurement are motivated .by the same things

25
that alter the landscape: water shortage, flood 

control, and river regulation, to name a few. 

Virtually none of these programs is devoted 

first to finding out what changes in the natural 

regimen these works effect. Much goes into 

an evaluation of a benefit to cost ratio, but 

none into an evaluation of man as an agent of 

ecologic and even of geologic change. The 

most powerful tools of statistical inference cannot do what benchmark stations can do unravel 

man from nature in the records.

Many branches of science would benefit from 

the study of representative areas maintained as 

nearly as possible in their original condition. 

Not only the hydrologist and botanist, but 

many other specialists might find knowledge 

of great practical and intellectual interest in 

such areas. The Belgians have already recognized this need, and the administrative direction 

of the great national parks in Africa is specifically oriented with this in mind. One of the 

fathers of the Belgian park system in Africa, 

M. Van Straten, told me that in one of these 

untouched areas scientists found a spot where 

the bacillus causing tetanus does not occur. 

Tetanus is so ubiquitous that to discover a

place where it does not exist is indeed rare luck. 

Study of its natural enemies there might eventually provide a hint as to how the disease 

might be controlled.

In the field of hydrology, many natural processes can be studied adequately in very small 

areas. Even the preservation of small basins 

typical of some of the important ecologic and 

lithologic types could be of significant value 

for research purposes.

Science is shooting for the moon. I should 

be content with much less. If we have learned 

enough to reach the moon, one would hope 

that we had learned enough to apply some of 

this great scientific energy to a few small areas 

in our own backyard. But we undoubtedly 

will reach the moon and start to alter its hydrologic economy before we have set aside some 

representative land museums for science here.

The Spartans left us a sample through inadvertance. Though that sample leaves much to 

be desired, it is still better than nothing. Presumably we should not have to rely on inadvertence to leave something similar in America, 

and it is never too late to begin.

26

* U.S. GOVERNMENT PRINTING OFFICE : 1967 O 276-031