The Development of Drainage Systems: A Synoptic View

American Geographical Society

The Development of Drainage Systems: A Synoptic ViewAuthor(s): Waldo S. GlockSource: Geographical Review, Vol. 21, No. 3 (Jul., 1931), pp. 475-482Published by: American Geographical SocietyStable URL: http://www.jstor.org/stable/209434 .

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THE DEVELOPMENT OF DRAINAGE SYSTEMS: A SYNOPTIC VIEW*

Waldo S. Glock

Carnegie Institution of Washington

P HYSICAL geography has a dual nature.1 It includes a static or passive phase involving the detailed form of the land surfaces and a dynamic or active phase involving the agents and proc-

esses modifying those surfaces. The first of these phases is known commonly as geomorphology; the second might well be called surficial geodynamics.

The present work desires to confine its attention to streams. It is the purpose of the paper to trace in a summary manner the sequence of pattern during the development of a drainage system after a fashion as nearly ideal as possible for a region of simple rock structure and of humid climate. The following treatment has no intention or wish to ignore the influence of rock and structure nor has it the desire to minimize the fascination in the study of land forms. It does, however, intend to adopt the dynamic viewpoint for the time being.

The sequential stages recognized in the evolution of a drainage system are "extension" and "integration": the first, a stage of increasing complexity; the second, of simplification. The assumption that extension begins on a "new" land surface will be entertained for the present.

THE STAGE OF EXTENSION

Extension may be held to include the genesis (initiation) of streams and thereby the birth of a drainage system, the headward growth (elongation) of the new streams into virgin territory theirs by right of inheritance, and the constant addition (elaboration) of tributaries of decreasing rank up to the time when the system is fully developed from the standpoint of drainage. The form of the drainage system assumed at initiation, which constitutes the first step in the establish- ment of the system, largely determines the general pattern of the drainage during the early phases of growth. The initial phase of

*A summary of parts of a paper presented before the Geological Society of America, Washington, D. C., December 28, 1929. The writer wishes to acknowledge his obligation to the Department of Geological Sciences at Yale University where the investigation into drainage systems was initiated, to the Research Committee of the Graduate School of Ohio State University for a grant of funds which made possible the continuation of the work, to the University's Department of Geology for many valuable favors, and to all three organizations for constant encouragement and material assistance.

Waldo S. Glock: Dual Nature of Physiography, Science, No. 1853, Vol. 72, 1930, July 4, pp. 3-5.

475



FIG. i-The initiation of a drainage system. The first attempts at the formation of definite drainage courses, hence the very beginning of extension.

FIG. 2-Elongation is very nearly, or quite, complete, and the framework of the system has been established. In contrast, elaboration has just begun.

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FIG. 3-The progress of elaboration, or filling in, is clearly evident. FIG. 4-Elaboration completed and extension at a maximum. The territory has been wholly occupied by streams.



FIG. 5-The nature of the stream pattern and the character of the piracy indicate that maximum extension had existed at some time in the past.

FIG. 6-The reappearance of the skeletonized form, and integration rather well begun.



DEVELOPMENT OF DRAINAGE SYSTEMS

extension as illustrated by Figure I is characterized by a notable lack of streams over a large percentage of surface, by the indefinite termination of many streams without combining into a main stream, and by the failure on the part of the existing streams to have started that active conquest of territory so typical of their future histories. These features are highly typical of the phase initiation but are not necessarily habitual. There is in truth a temptation to say that the drainage system is quite amorphous as yet. However that may be, a time of increasing activity follows the genetic period of hesitation and indeci- sion. The streams begin the conquest of territory, some in a highly aggressive fashion, others in a more or less passive way.

Abbreviated streams and skeletonized systems characterize the stage of extension in a broad way, and these two characteristics must be eliminated before the stage is ended. The growing streams reach out into the territory bequeathed them and take possession of their inheritance by means of headward elongation which begins shortly after the efformation of the system. They sketch in, as it were, the lineaments of the future drainage pattern (Fig. 2). After the area has been thus blocked out the process of elaboration gradually elimi- nates the skeletal form by means of the addition and growth of minor streams (Fig. 3). A plexus of these accessory tributaries spreads outward from the mains until a veritable network of drainage covers the area first possessed by the elongated streams. With the progress of extension the abbreviated form commonly disappears first while the elimination of the skeletonized pattern, although beginning more slowly, endures throughout the entire stage.

The attainment of complete elaboration may be simply called maximum extension. It is the time of completed territorial conquest and minute invasion-the time of the fully developed drainage system (Fig. 4). The land surface, in other words, has been entirely occupied. Theoretically, the exact position and nature of maximum extension may appear to present unexpected difficulties in view of the almost infinite variation to be found among individual streams. The question may arise whether the elimination of the abbreviated streams on the one hand and the skeletonized system on the other may not lead to different extensional maxima, especially if opposing systems enter into active competition with each other, an activity tending to elongate certain streams at the expense of others. Should lengthening accom- plished by piracy after elaboration has been completed fall within the scope of extension? It seems not. Figure 5 shows that a system may grow at the expense of a neighbor after maximum extension has been attained, since the pattern of the captured streams themselves indicates that the territory had been completely occupied when the piracy occurred.

From a practical standpoint, also, the essential termination

479



THE GEOGRAPHICAL REVIEW

of the processes of elongation and elaboration may be more readily recognized and circumscribed if held to the simple concept inherent in the attempted description of extension. The scheme of classification

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.... .-M t er-- s re an lt i PRINCETON, IND:ILL.

FIG. 7-Master streams and master tributaries late in the stage of integration.

to be desired is the one that is as simple and, at the same time, as

adequate as possible. True maximum extension may be considered to refer to the completed invasion of the unoccupied surface within the jurisdiction of a particular drainage system after active elongation into rightfully inherited territory has added all possible area to the

system. Hence, the intensity of intersystem strife may wax to a maximum either with, or after, the full development of the drainage systems, and extension may be at a maximum or may have definitely passed away when systems "come to an understanding about their

drainage areas." Piracy between systems does not serve as a limiting criterion for extension. Treated, therefore, in the preferred fashion, the scheme is simple enough to conform to the standards which, it is

480



DEVELOPMENT OF DRAINAGE SYSTEMS

believed, an ideal scheme should follow. Little doubt can exist that such an ideal scheme acts as an axis of variation about which natural phenomena appear to group themselves.

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FIG. 8-An ideal diagrammatic summary of the development of a drainage system given for purposes of comparison only. The first four parts show extension, thus: i, initiation; 2, elongation; 3, elabora-

tion; and 4, maximum extension. Parts 5 and 6 represent steps during integration.

THE STAGE OF INTEGRATION

The processes responsible for integration may be designated as follows: (I) abstraction, the loss of identity suffered by a secondary stream at the hands of its primary; (2) absorption, the disappearance of a stream save immediately after rainfall; and (3) a sort of adjust- ment or aggression, the attempt made by the main stream to reach the sea by the shortest route consistent with regional slope. The reappearance of the skeletonized form out of the intricate plexus of streams some time after maximum extension definitely marks the existence of integration (Fig. 6). It constitutes the second and final stage in the developmental history of a drainage system.

Abstraction refers to the elimination of a secondary stream by its primary. As the stream swings from side to side it constantly

481



THE GEOGRAPHICAL REVIEW

increases its own drainage area and thus abstracts territory from its tributaries. The lower portions of a tributary system may be dis- membered in this way, all of the shorter branches may be completely destroyed, and the lower part of the chief tributary may lose its identity and independence on the meander belt of the master.

With integration well begun many of the minor tributaries seem to be absorbed and thereafter come into existence only for the purpose of discharging the immediate rainfall. Their disappearance quite likely is involved in the flattening of the local ground-water surface during the progress of integration and the consequent sinking of that surface below stream level.

The third process is less easy, if not impossible, to observe to any great extent at the present day. As integration advances into the final phase, the master stream becomes more and more independent of its environment except for the general slope of its drainage area and its relation to the sea or point of discharge. Aggression is said to take place when the stream attempts to gain the shortest (valley) route to the sea governed solely by the general slope of its drainage area, and then only if that direct route did not exist at initiation or was abandoned for any reason later. A stream having worked out such a course for itself may conveniently be called an integrational consequent and undoubtedly finds abundant illustration in geologic history.

The three processes accomplish the elimination of a host of streams and result in the appearance of the simplified form of integration very similar to the skeletal outline of early extension. Master streams joined by master tributaries (Fig. 7) at last emerge from the plethora of previously existing streams and, if necessary, seek the shortest practicable route to the sea.

In some respects integration appears to reverse the procedure of extension, as for instance the disappearance of minor tributaries, the continuation of which appears constantly to accentuate the

original framework of the system. The stages in reality do resemble each other in that the sequence of changes (with one exception) sweeps headward along the trunk streams and thence to the chief branches, arriving finally at the outermost confines of the system-a migration quite naturally anticipated. Here, however, resemblance ceases.

There is no intention to infer that the scheme of development including extension and integration, because of its simplicity, possesses definiteness and perfection to such a degree that each is a distinct stage by itself. In fact, the two may always exist at the same time from a regional standpoint; or, further, extension may be occurring locally among the headwaters while integration is taking place farther down stream. Minor cases of actual overlap should be expected in

any detailed study of a drainage system.

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The Development of Drainage Systems: A Synoptic View