THE AMERICAN ASSOCIATION OF PETROLEUM GEOLOGISTS BULLETINV. 51. NO. 11 (NOVEMBER. 1967), P. 2248-2259. 4 FIGS., 1 TA8LE

DRAINAGE ANALYSIS IN GEOLOGIC INTERPRETATION: A SUMMATIONl

ARTHUR DAVID HOWARD2

Stanford, Califomia 94305

ABSTRACTDrainage analysis is useful in structural interpretation, particularly in areas of low relief.

Analysis incIudes consideration of drainage patterns, drainage texture, individual stream patterns,and drainage anomalies.

Drainage patterns generally are subdivided into basic and modified basic. To these rnight beadded pattern varieties. A basic pattern is one whose gross characteristics readily distinguish it fromother basic patterns. Modified basic patterns differ from the type patterns in some fairly obviousregional aspect as, for example, a tendency toward parallelism of the larger tributaries in a dendriticpattern. Thus many modified patterns are transitional in character between basic patterns, and thenamingof such patterns may be a matter of judgment. 'Pattern varieties are characterized by internaldetails, commonly obscure. In a broad sense, the basic patterns, the modified basic pattems, and thepattern varieties are analogous to the genera, species, and varieties of the zoological cIassification.

A complex pattern consists of two contemporaneous patterns adjacent to each other ; a compoundpattern consists of two unlike superimposed patterns. The palimpsest pattern consists of two super-imposed patterns, but one is a paleopattern.

Drainage texture depends on a variety of factors. In any one smalI area where alI other factorsare constant, drainage texture may provide information on underlying materiais and indirectly onstructure.

Individual stream patterns may display characteristics similar to those of the gross drainagepattem and may be referred to by the same name. Thus individual patterns may be referred to bysuch terms as rectangular, angulate, or contorted. Other stream patterns include irregular, rectilinear,meandering, braided, misfit, and beaded.

Drainage anomalies are local deviations from drainage and stream patterns which elsewhereaccord with the known regional geology and/or topography. The expectable pattern is regarded as thenorm; the anomalies indicate departures from the regional geologic or topographic controls. Analysisof drainage anomalies has revealed structural data in some flatland regions where other methods ofinvestigation have been unsatisfactory.

INTRODUCTION

Drainage analysis is an important tool in pho-togeologie interpretation, particularly in areas oflow relief. It may provide clues to inaetive strue-tural features exposed at the surfaee, to structur-aI features eurrent1y rising, and, possibly, to bur-ied structural features. The density of drainagemay provide information on permeability andtexture of materiaIs, and may infer the identityof materials. The eharacteristies and signifieaneeof drainage patterns, drainage texture, individualstream patterns, and drainage anomalies are con-sidered here.

Teehniques involving grid sampling and lhe useof digital computers eventual1y may result in 'lheapplieation of numerieal values to drainage pat-terns (Merríam and Sneath 1966). It is toaearly, however, to speeulate on the advantagesand disadvantages of this proeedure.

1 Manuscript reeeived, June 25, 1966; accepted, Feb-ruary 3, 1967.

2 Geology Department, Stanford University. Thewriter is indebted to Chester R. LongwelI and StanleyN. Davis for review of the manuscript, but only he isresponsible for its contento

DRAINAGE PATTERNS

A drainage pattern is the design formed by theaggregate of drainageways in an area regardlessof whether they are occupied by permanentstreams. A stream pattern is the design formedby a single drainageway.

Both basic and modified basie drainage pat-terns have been described (Zernitz, 1932). In ad-dition to these there are drainage varieties. Abasic pattern is one whose gross characteristiesreadily distinguísh it from other basic patterns. Amodified basic pattern differs from the type basicpattern in some regional aspect as, for example,the dose spacing of small parallel tributaries inthe pinnate-dendritic pattern or the preferred or-ientation of longer tributaries in the directional-trellis pattern (Fig. 2, B and G). Drainage vari-eties differ from the basie and modified basie pat-terns in internal details. Varieties are legion andthe application of individual names is impractieal.In a broad sense, the basic patterns, lhe modifiedbasic patterns, and the pattern varieties may belikened to the genera, species, and varieties of thezoological classifieation.

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DRAINAGE ANALYSIS IN GEOLOGIC INTERPRETATION 2247 '

BASIC PATTERNS

Most of the basic patterns are controlled byregional structure. Zernitz (1932) classified asmajor (basic?) the following patterns: dendritic,parallel, trellis, rectangular, radial, and annular.Because these are discussed in most elementarygeology texts, only a pictorial review (Fig. 1,A-F) and a brief summation of characteristicsand geologic significance (Table I) are included.Two other patterns, multibasinal and contorted,are grouped with the basic patterns in this report(Fig. 1, G and H; Table I). The original or ear-liest known references to most of the basic andmodified basic patterns are recorded in the foot-notes to Table I.

MODIFIED BASIC PATTERNS

Modified basic patterns, although usually rec-ognizedas belonging to one of the basic types,differ in certain regional characteristics. For ex-ample, the degree of paraIlelism of the mainstreams in a region of dendritic drainage 1S gener-ally a function of the regional slope. On differentdeclivities, therefore, there may be alI transitionsfram dendritic to parallel drainage. Transitionaltypes also may result from changes with time.The change toward parallelism might result fromprogressive steepening of a slope. Trellis charac-teristics may appear in a dendritic pattern asstreams are superposed from an overlying coveronto dipping rocks. Transitions among alI thebasic types seem possible. Some of the modifiedpatterns are considered below.

Dendritic Pattern ModificationsSubdendritic.-This pattern differs frorn the

type dendritic only in the lack of perfection.Deviations are presumably due to secondary re-gional contraIs, either structural or topographic.Thus, in part of the Amazon basin recentlystudied by the writer (Howard 1965), lhe den-dritic pattern, inherited from an unconformablemantIe, is being transformed to a trellis patternby adjustment of tributaries to the strike ofunderlying íormations, Along the lower YelIow-stoneRiver in eastern Montana, lhe dendriticdrainage is slowly developing trellischaracter-istics under the influence of a prevailing systernof poorly expressed joints (Fig. 2, A).

Pinnate.- This pattern is characterized bymany closely spaced, more-or-less parallel tribu-

taries entering the larger streams at an acuteangle. The drainage, therefore, has a featherlikeor frondlike appearance (Fig. 2, B). The patternis best developed in fine-textured, easily erodedmateriais such as loess. The fine texture of themateriaIs accounts for the dose spacing of thesmall tributaries, and the steep vaIley sides arethe cause of their parallelism. On some slopes,particularly solifluction slopes in the Arctic, theclosely spaced parallel tributaries are long com-pared with those in Figure 2. They are barely in-cised into the gentle slopes and extend to thecrests of the rounded divides. The pattern resem-bles feathery plumes.

Anastomotic.- This pattern, characterized by anetwork of interlocking channels, sloughs, bayous,and oxbow lakes, is found on floodplains and dei-tas and in tidal marshes (Fig. 2, C). Varieties ofthe pattern have been termed "reticular" by Par-vis (1950, p. 43-44) and "reticulate" by White-house (1944, p. 9).

Distributary.-This is the branching patternfound on alluvial fans and deltas (Fig. 2, D). Itresembles the dendritic pattern except that thetributaries diverge from, rather than converge to-ward, the main stream.

Parallel Pattern ModificationsSubparallel.-The subparallel pattern (Zernitz,

1932, p. 518) shows less parallelism than thebasic pattern. If due to slope alone, the patternresembles that formed by the branches of a pop-lar tree. Where due to mild structural control by -deformed strata of relatively uniform resístanceto erosion, there is sufficient parallelism amongsegments of the main streams and tributaries tosuggest the bedrock contraI, but streams com-rnonly diverge from the geologic grain. The elon-gate streams are not ordinarily as continuousalong the strike as those of the trellis pattern.These differences from the trellis pattern alsoapply to the subparalIel pattern of drumlin areas(Fig. 2, E).

Colinear.-This pattern (Zernitz, 1932, p. 519)is characterized by remarkably straight parallelstreams or channels which alternately disappearand reappear (Fig. 2, F). The pattern is foundin areas of linear loess and sand ridges.

Trellis Pattern ModificationsSubtrellis.- The subtrellis pattern differs from

the type trellis only in the degree of continuity

-2248 ARTHUR DAVID HOWARD

-FIG. l.-Basic drairíage patterns. Each pattern occurs irf ã wide range of scales. Examples shown may beregarded as types. Dendritic pattern resembles spreading branches of oak or chestnut tree with tributariesentering at wide angles. In trellis pattern, small tributaries to long parallel subsequent streams are aboutsame length on both sides of subsequent streams. "

DRAINAGE ANALYSIS IN GEOLOGIC INTERPRETATION 2249

TABU: r. SIGNIFICANCE UF BASIC AND MOUIl'lED BASIC })Ri\INAGE l'ATTERNS

Basic Sig1l1jicance Addcd SiKltijicl/llce or l.ocale

Dendritir! lIoriwntal sediments or beveled, uni-lormly rcsistant, crystulline rocks.Gentlc regional slope at prcscnt or attime 01 drainuge inccption. Typc pat-tcrn resernbles spreuding oak or chest-nut trcc.

Modijicd Busic

Subdcndritic Minor sccondary control, I(cncrallystructural.

Pinnatev Fine-textured, casily crodablc ma-tcrials.

Auastomotic'v Floodplains, deltas, and tida Imurshes.

Distributary(Dichotornic)'! Alluvial íaus anel eleitas.

_________________ L . __ . • _

Intcrrnediatc slopes or control hysubparallel landíorms.

Parnllelt Generally indicares moderare to stecl'slopcs but also Iound in arcas of para -lei, elongate landlurrns. Ali transitiunspossiblc between this pattcrn andtype dendritic and trellis.

Trcllis" Dipping or íolded sedimentary, vol-canic, or low-grade mctasedimcntaryrocks; arcas 01 parallel Iructures: ex-posed lake or sea floors ribbed bybeach ridges. Ali transitions to paral-lei pattcrn. Type pattern is regarderlhere as one in which srnall tributariesare essentially same size on oppositesides of long parallel subsequcntstrearns.

Rcctangular- Joints and/or Iaults at right angles.Lacks orderly rcpetitivc quality oftrellis pattern; strearns and divideslack regional continuity.

Su bparallelu

Colinear» Bctwccn linca - loess and sandriducs.

Subtrellis Parallel clongate landíorrns.

Gcntle hornoclines. Gentle slopeswith bcach ridges.

Plunging folds.

Di rectional Trcllis

Recurved Trellis

Fault Trellis» Branching, converging. diverging,roughly parallel Iaults.

Joint Trellis Straight parallel faults and/orjoints.

Angulate» Joints anel/o r faults at other thanright angles. A cornpound rec-tangular-angulate pattcrn is COI11-

mono

Radial; Centripetalw Craters, calderas, anel other ele-pressions. A cornplex of centripetalpatterns in area of multiple depres-sions might be calleel multi-centripctal.

Volcanoes, domes, anel erosion residu-ais. A cornplcx of radial pattcrns in avolcanic field might be called multi-radial,

Annularv Structural domes and basins, dia-tremes, and possibly stocks.

Longer tributaries to annular sub-sequent streams generally inelicatedirection of dip anel perrnit distinc-tion between elome anel basin.

Multibasinal"

Limestone.

Hummocky surticial eleposits; differ-entially scoureel or deflated bedrock;áreas of recent volcanism, limestonesolu tion, anel permaírost. This ele-scriptive term is suggested for alimultiple-depression patterns whoseexact origins are unknown.

Glacially Disturbed Glacial erosion and/or deposition.

Karst

Therrnokarst!" Permafrost.

Elongate Bayl8 Coas tal plains anel eleitas.

Contorteds Contorteel, coarsely layereel meta-morphic rocks. Dikes, veins, anel mig-rnatized bands provi ele the resistantlayers in some areas. Pattern differsfrom recurveel trellis (Fig. 2, H) in'lack of regional orelerliness, discon ti-nuity of ridges and valleys, anel gener-ally smaller scale.

The longer tributaries to curvedsubsequent streams generally indi-cate dip of metamorphic layers andperrnit elistinction between plunginganticlines anel synclines.

1 Describeel by Dutton (1882, p. 6, 62, 63) anel applied as a drainage term at least as early as 1898 (Russell, p, 204). Classified as a Pltsic-pattern by Zernitz (1932, p. 499).

2 Zernitz (1932, p. 510).3 Willis (1895, p. 186).4 First used in moelern sense by Zernitz (1932, p. 503), but the pattern was recognized much earlier (Daubrée, 1879, p. 357-375; Kernp,

1894, p. 438-440; Hobbs, 1904, pl, 47)_5 Raelial elrainage is described anel illustrateel in Jaggar (1901, p. 174, pl. XVIII) and is referred to by Dake anel Brown (1925, p. 134).6 j aggar (1901, p. 277) refers to annular elraniage, but Zernitz (1932, p. 507) may have been the first to apply the na me to the drainage

pattern.7 The elescriptive term "multibasinal" is useel here as a substitute for genetic terrns such as "kettlehole"and "sinkhole" which have

been applied to patterns characterizeel by numerous elepressions. The term "poly basin" (Parvis, 1950, p. 57) woulel have been appropriatehad it not been restricteel to the area of the Ogallala Formation in the Great Plains and specifically related to the presence of an impervioussubstratum.

8 Von Engeln (1942, p. 113, 336).9 Zernitz (1932, p, 512).10 Described as a pattern by Zernitz (1932, p_ 514). The descriptive adjective "anastornosing," however, had been useel long prior to 1932.

J ohnson (1932, p. 497) restricted the term "braided" to the interlacings oí.an individual stream.11 Parvis (1950, p. 41) attributeel the term "dichotomic" to Finch and Trewartha (1942). Tbe writer was unable to locate the term in the

1942 reference or in the first edition of their Elemenis o] Geograph», but may have overlooked it. Distributaries are mentioned on pages307,342, and 355 of the 1st ed., 1936, and on pages 290, 326, and 340 of the 2d ed., 1942.

12 Zernitz (1932, p. 518).13 Zernitz (1932, p. 519).14 Dake and Brown (1925, p. 191).15 Zernitz (1932, p. 517).16 Davis (1889, p. 249).17 Muller (1943), p. 50.18 Parvis (1950), p. 43.

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2250 ARTHUR DAVID HOWARD

8. Pinnate

F. Colineor

FIG. 2.-Moclified basic pattems. Each pattern occurs in a wide range of scales.

-

and parallelism of the dominant drainage. Thedistinction between subtrellis and subparallel iscommonly a matter of judgment.

.Directional treUis.- This term is suggested fora modification of the trellis pattern in which thetributaries to the long subsequent streams are

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DRAINAGE ANALYSIS IN GEOWGIC INTERPRETATION

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consistently longer on one side of the valley thanon the other (Fig. 2, G). The pattern most com-monly is found in areas of gently dipping homo-clinal beds, but also occurs on gentle slopes withparallel beach ridges.

Recurved trellis.- This is a modification of thetrellis pattern in which the pattern as a wholeforms sweeping curves around the noses of plung-ing folds (Fig. 2, H). It is more orderly and sys-tematic, and generally larger in scale, than thecontorted pattern in metamorphic terrain. Com-parison of the lengths of small tributaries on op-posite sicles of the curved subsequent streams,particularly at the noses of the folds, commonlyperrnits distinetion between plunging anticlinesand synclines; the direetion of flow of the longertributaries generally indicates the direetion ofdip.

Fault trellis.- This pattern has been attributedby Dake and Brown (1925, p. 191) to "alternat-ing grabens anel horsts or a suecession of paraIlelrifts." It is described as less closely spaced thanthe trellis pattern on tilted or folded strata, witha tendency toward e1endritic drainage between thefaults. Right-angle turns are also less common. lnthe San Mateo quadrangle, just south of SanFrancisco, California, the fault-controIleelstreams, although grossly parallel, loeally e1iverge,converge, and branch, and the broader inter-stream segments show dendritic, radial, or otherdrainage patterns (Fig. 3, A).

Joint trellis.-A second fracture treIlis pattern,charaeterizeel by short, remarkably straight paral-lei streams, may be referreel to as joint treIlis,although the fractures may include faults. A gooelexample is found in the Zion Park region of Utah(Fig. 3, B).Both of the fracture treIlis patterns differ from

the reetangular pattern in having one dominantset of paraJlel streams.

Rectangular Pattern ModificationsAngulate.- This pattern (Zernitz, 1932, p. 517)

is charaeterized by numerous aeute-anglebends and barbed tributaries. It is generaIlyfound in areas where an additional set (or sets)of fraetures is superimposed on a reetangular set.There may be two superimposed rectangular sys-tems of different orientation. Figure 3C is ageneralized portrayal of the drainage of part ofthe Yellowstone plateau. The drainage alignments

22~1

c1early indieate one rectangular system with ele-ments oriented approximately north-south andeast-wcst, and another system oriented northeast-southwest and northwest-southeast.A rernarkable example of joint control is pres-

ent in French Guiana, where several sets of moreor less equally spaced joints impart a geometricpattern to both the drainage and topography. Thepattern has been referred to as "honeyeomb" byZonneveld et alo (1952, p. 1'53). Another geomet-rie pattern, on a much smaller scale, is found inpermafrost arcas where ice wedges thaw aroundthe margins of soil polygons. This pattern is bestdeseribed as polygonaI.

Radial Pattern ModificationsCentripetal.-This pattern (Davis, 1889, p.

249) is a modification of the radial pattern inwhich the streams flow inward toward a closed ornearly cJosed central depression (Fig. 3, D). Thepattern commonly is assoeiated with caters, cal-deras, and a wide variety of depressions. In someareas, sueh as the "pan belt" of the Union ofSouth Africa (King, 1951, p. 91), there is a com-plex of centripetal patterns. The regional patternmight be referred to as multicentripetal.

Multibasinal Pattern ModificatíonsThe multibasinal pattern occurs principally in

are as of glacial erosion and deposition, eolian ero-sion and deposition, solution, and permafrost. Italso is found, however, in regions of recent vol-canic activity and in landslide areas. There aremany modificatíons of the pattern, even withinindividual regions. Thus in glaeiated areas, themajority of the depressions may be smaIl orlarge, closely spaced or widely scattered, and thedrainage may display varied amounts of integra-tion. ln sandy areas, the depressions may displaygreat diversity in shape and size in accordancewith the charaeteristics of the dunes within whichthey occur, and may also display a certainamount of integrated drainage. The pattern maythen closely resemble the drainage pattern in mo-rainal areas.ln volcanic areas, the depressions may include

craters and calderas, lava-dammed valleys,interflow basins, or collapsed lava caves or tun-nels. In many lava fields, depressions largeenough to be shown on topographic maps are lessprofuse than in morainal or sand areas.

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.~2252 ARTHUR DAVID HOWARD

Compound

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Polimpsest > /.. -: //;/1!I I {f

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-FIG. 3.-Modified basic patterns (A-D); complex, compound, and palimpsest patterns (E-H).

Each pattern occurs in a wide range of scales.

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DRAINAGE ANALYSIS IN GEOLOGIC INTERPRETATION~,

2253

In landslide arcas, dcpressions are Iound citherhchind rotated slump blocks, within chaoticallyjumbled landslide debris, or whcre drainage hasbccn blocked, This multibasinal pat tern is usuallyo f small regional extent.

The multibasinal pattcrn is rarcly diagnostic initself of either process or material; patternsformed by elifferent processes rnay be rcrnarkablyalikc. A pitted outwash arca in Minncsota illus-trated by Cooper (1'035, Fig. 4, p. 10) is rernark-ably similar to the solution-pan landsrapc of partsof Florida. Multibasinal patterns in arcas ofmorainc, sanei duncs, limcstonc, recent lava flows,landslidcs, anel permafrost may resernhle eachother at least superficia\ly. Conclusions reachcdas to process or type of materiaIs based on pat-tem alone coulel be in error. Nevertheless, severa]gcnctic terms have bcen suggestccl for varietics ofthe multibasinal pattern: glllcilllly disturbed, de-nmged, kettle hole, swallow hole, korst, andothcrs. If there is doubt as to gencsis, thc patternis best referred to sirnply as multibasinal. If. onthe other hand, the pattern includes featurcs thatIcave no doubt as to process or material, theremay be justification for using onc of the estab-lished genetic terms. Thus, a multibasinal patternwith (I) depressions ranging fram tiny steep-sided pits, many of which are circular, to large.deep, irregular valley-like basins, (2) some de-pressions aligned rectinearly, and (3) scattereddisappearing and/or reappearing streams, mayperhaps be referred to as a swallow-hole or karstpattern. Or, a multibasinal pattern associatedwith evidence of thawing permafrost, such as po-lygonal ground and beaded drainage, might be re-íerred to as thermokarst (MulIer, 1943, p. 50).Parvis (1950, p. 43) suggested the name "elon-gate bay" for a rnultibasinal pattern in which thedepressions are large, elliptical, anel parallel. Thepattern is íound in some coastal-plain anel deltaareas and has been variously attributed to meteo-rite impact, solution, segmentation of lagoons athigher stands of the sea, and to thaw of formerlyfrozen ground. The value of the purely descrip-tive term "elongate bay" for this pattern is obvi-ouso

ing arcas. Parvis (1950, p. 43) suggested theterrn "anomalous" for complex pat terns found inarcas of differing topography anel materiaIs. Theterrns "cornplcx" and "anornalous" have thusbcen applied to situations that are in part similaranel in part dissimilar. Inasmuch as' the tcrrn"cornplcx" has priority, it should be retained butperhaps with its scopc enlargecl 10 inclucle ali pat-terns representing an aggregate of adjoining dis-similar patterns due to structure, materiaIs, anel/or differences in topography. In Figure 3, E, thecontrasted patterns are duc to differences instructural Icatures. An example of drainagedifferences causecl by diffcrences in topographyon identical materials is the multibasinal clrainageof moraine ucrsus the subparallel clrainage ofdrumlin topography.

The terrn "cornpound" was applied by D. W.Johnson (personal commun., 1931) to drainageconsisting of two or more conternporancous pat-tcrns in the sarne arca, as, for example, the com-bination of radial anel annular patterns character-istic of many domes (Fig. 3. F). Dendritic anelmultibasinal patterns commonly are combined inareas whcre streams have cut youthful valleysinto a rclativcly insoluble formation below a solu-tion-pitted limestonc formation. The depressionsare restricted to the limestone-capped divides be-tween the streams. A somewhat similar combina-tion of patterns results from partial integrationof drainage in morainal areas.

The writer encountered an interesting drainagepattern which he has calleel palimpsest (Howarcl,1962, p. 2255). In the palimpsest pattern, anolder, abandoned drainage or stream patternforms the backgrounel for the present pattern.The example (Fig. 3, G) is in the western coastalplain of Taiwan. At the site of the anornaly, thepresent drainage pattern is radial. Faintly visiblethrough the rice paddies is a meandering channe!whose presence is indicated primarily by thesomewhat smaller size of the paddies within itsconfines. The meandering channel crosses thepresent Iow topographic bulge toward its crest.Clearly, the topographic high was not presentwhen the meandering stream crossed the area.

. Themeandering stream apparently wasdeflectedCOMPLEX, COMPOUND, AND.PAÚ1\1:PSEST PÁTTERJ'J"S' by th~growing arch onwhich the present radialZernitz (1932, p. 521). proposed the term ~r.~'!}!)<l:giç_a~~ )g!º.~xistence. The situation sug-

"complex" for an aggregat'eof:~i~"s~iúll: patterhs,' gests either active deformation within the coastalreflecting different structural controlsIn adjoin- plaln,nofanúrÚikeiy;possibilityc!ànsiclering' the

2254 ARTHUR DAVID HOWARD

instability of lhe island of Taiwan as a whole, ordifferential settling over a buried topographichigh, or both. Any drainage pattern that includestraces of an older, unlike pattern may be re-ferred to as palimpsest. Remnants of originalstream courses are common in many arcas of gla-cial anel eolian activity, multiple piracy, and re-cent warping and íaulting. Figure 3H ilIustratesin generalized fashion the relation of the Mis-souri River (or the Ohio River) to abandonedpreglacial valleys.

PATTERN VARIETIES

Pattern varieties differ from basic anel modi-fied basic patterns in internal details. They com-monly provide use fui geologic information.

Regional differences, such as contrasts in densi-ty of drainage, do not distinguish varieties. It isexpectable that a dendritic pattern in shale willbe finer than that in sandstone, and that a trellispattern in slate wilI be finer than that in in-terbedded sedimentary strata. Any drainage pat-tem may be fine, medium, or coarse textured.

Intrapattern differences in texture, however, dodistinguish varieties. Thus, a dendritic pattern inan area in which thick, horizontal beds of sand-stone and shale are exposed in the slopes maydisplay a coarse texture in the sandstone and afiner texture in the shale. The pattern is "textur-ally zoned."

ln another variety of the dendritic pattern,many streams consistently are closer to one sideof their valleys than the other. ln the Leaven-worth quadrangle (Kansas-Missouri), streamsthat flow generally east or west hug the steepersouth (north-facing) slopes. The dendritic patternsuggests essentially horizontal sedimentary rocksor beveled, uniformly resistant crystalline rocks,but the valley asymmetry suggests an additionalinftuence such as a gentle southward dip, activetilting. or differences in degree of erosion of thevalley slopes due to direction of exposure. Thatthe asymmetry is not due to stream deflectionresulting from terrestrial rotation is evident fromthe fact that 'lhe steep slope is on the left side ofsome streams and on the right side of others."

Another variety of the dendritic pattern, char-acteristic of granitic areas, displays numerous sick-lelike curves. These apparent1y are the result of

3 The term right and Ieft apply when facing down-current.

deílection of strearns around bodics of relativelyunfractured or otherwise resistant rock.

Comparable varicties are found in cach of lheother basic and modified basic patterns. A de-tailed treatment of these is beyond thc scope ofthis report. The important point is that carefulstudy of local departures frum the regional pat-terns rnay revcal unsuspcctecl information of con-siderable value. The analysis of drainage varietiesand of the reJated drainage anornalies discusseclbelow presents a unique chaIlcngc to thc gcolo-gist.

DRAINAGE TEXTURE

Drainage texturc refers to the rclativc spacingof drainage lines regardless of occupancy byperennial streams. The terms "fine," "medium,"and "coarse" generally are used in a relativesense to indicate the spacing. A fine texture isone in which there is a high degree oframification of drainage lines resulting in a densenetwork involving myriad small streams. Finetexture is typical of clay, shale, silt, and otherrelatively impervious materiaIs. A coarse texture,in contrast, exhibits very little ramification, andlonger, more widely separated valleys prevail.Coarse texture is typical of permeable materialssuch as sand, gravei, and rocks that weather intocoarse fragments. Medium texture is interrne-diate between the two extremes.

The use of these textural terms withoutclarification is inadvisable, not only because theymean different things to different people, but be-cause texture varies with scale. Attempts havebeen made to express textures quantitatively onthe basis of the number (stream frequency) andtotal length (drainage density) of drainage linesper unit area (Horton, 1945; Smith, 1950). How-ever, quantitative determinations of texture in-volve laborious, tirne-consuming procedures, andthe resulting degrees of refinement are greaterthan necessary for many geologic problems. Asatisfactory procedure for reports is to preparediagrams showing the drainage textures, at thescale of the maps ar photos, that are regarded asfine, medi um, and coarse, and perhaps as ultrafmeand ultracoarse.

Drainage texture is influenced by (1) clima ti-cal1y controlled factors such as amount anel dis-tríbution of precipitation, vegetation, anel per-mafrost; (2) rock characteristícs, including tex-

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22 5'0 ARTHUR DAVID HOWARD

unlike materiais. klisJit meandering streams, inwhich the dimensiuns of the meanders do notagree with those of meander scars or of flood-plain scrolls, suggest geologic or cIimatic change.The sickle pattern displays some arcuate curvesand is most common in areas of plutonic rocksand migmatites. The barbed pattern indicates ei-ther piracy or the presence of joints, faults, orlayers of weak rock trending obliquely across thepath of the stream. The term "beaded" has beenapplicd to streams in the subarctic along whichsrnall tha w sinks are present at irregular inter-vais. Successions of beaver elams give asuperficially similar pattern, as elo, on a largerscale, strings of glacial lakes.

The writer has nameel a new pattern, spatulate,which could be inc\udeel uncler beaded, but whichhe believes is elistinctive enough to warrant a sep-arate elesignation. In essence, it consists of alter-na te broad valley segments anel narrow defiles.The pattern is clisplayed by some of the valleys,such as the Aragva, that drain south from theCaucasus in southern Russia. The Aragva anel itssister streams pass intermittently through resis-tant anel weak Cretaceous seelimentary rocks(Renngarten, 1937, p. 104). The streams are re-stricteel to defiles where the more resistant car-bonate rocks of the Upper Cretaceous arebrought elown to river levei in the troughs ofsynclines, but they meaneler in broael open reachesin the weaker, sandy-argillaceous Lower Creta-ceous seeliments of the anticlinal cores. Thedefiles anel open reaches range in length from 0.5to 2 mi or more. The pattern is quite regular inthese open folels, with the broael, elongate seg-ments occurring at uniform intervals along thevalley.

Other spatulate patterns may have no structur-al significance. The spatulate pattern displayed bythe Missouri River in eastern Montana and west-em North Dakota is glacial in origin (Howard,1958). The Missouri trench is locally 1 mi or lessin width; in intervening areas its wielth may ex-ceed 4 mio The narrow segments represent ice-marginal paths cut across former divides,whereas the broad elongate segments representparts of preglacial valleys. The pattern is irregu-lar in that the broad segments inherit theirtrends from an ancestral drainage whose trendswere opposed to the trend of the ice front. Thusthe broad segments are considerably varied in

orientation anel are irregularly distributed alongthe present valley,

DRAINAGr: ANOMALIES

Anomalies in drainage patterns and in the pat-terns of individual strcarns have bccn t he subjcctof discussion in recent years, They are of partic-ular importance in lhe flatlaads. The analysis ofdrainage may provide clues to structural ícaturcsundetectable by other methods.

A drainage anomaly can hc dcfincd as a localc1eviation from the regional drainagc ancl/orstrearn pattern which elsewherc accords with theknown regional structure anel/o r topography.The expectable pattern is regarded as the norm(DeBlieux, 1949, p. 1253-1254), and thc devia-tions are anomalies. An alternation of broad val-ley segrnents anel narrow defiles along transversostreams in areas in which the structure is knownto consist of foleled weak anel resistant rock isherein regareled as normal, as are sicklelikecurves in granite areas, However, in many othergeologic environments these phenomena areanomalous. Anomalies suggest structural or topo-graphic eleviations from the regional plano Manycomposite patterns, for example, involve a smallenclave of one pattern within another, ratherthan two adjacent patterns of equal magnitude.An illustration is the local occurrence of radialand annular drainage within a regional c1enclriticpattern (Fig. 4, A). Many pattern modificationsanel varieties also involve anomalies as, for exarn-pIe, local parallelism of streams in a dendriticpattern (Fig. 4, B). Many anomalies are localizeclalong individual streams. Some of these are listedbelow.

Rectilinearity.-Long, rectilinear segments ofstreams, particularly if aligned across divideswith rectilinear segments af other streams, con-stitute an anomaly if the regional pattern is otherthan rectangular, angulate, or íault-trellis. A frac-ture, or an easily erodable vein or dike is indi-cated. In Figure 4C the arrow indicates a recti-linear stream.

Abrupt and localized appecrance of meanders.-DeBlieux (1949, p. 1259) has clescribed an inter-esting stream anomaly at the Lafitte oiI field inJefferson Parish, about15 mi south of NewOrleans (Fig. 4, D). The channel of an aban-doned Mississippi River distributary is relativelystraight and simple for several miles upstream

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DRAINAGE ANALYSIS IN GEOLOGIC INTERPRETATION 2257 -e

D. Local meondering E. Compressed meonders

Plottedstructuralanomaly ""

2milesL--....J

H. Anomolous flore involley 11

} (/,( )\ /

l/I11// Schematic

K. F Iying levees

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~ ~ '4!!..l!.

1!!. ~ ~ ~.:::=:::. ~~~ ~:h1l!J

-JJ,'::y~ ., ~

ili, 4llL lU

Schematic.w

J. Voriotion in levee width

2 miles

F. Local broidingI 2miles I

I. Anomolous pond,morsh, orolluviol fill

~.>/,.. l. KioQa):j:-

.~ ~.{/ B A 5Z It\~~li /}...,

L.Victaria I:.j~

200 milesL-.-....J

L. Anomolous curves ond

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'1n; 6~.~.~FIG. 4.-Examples of drainage anornalies. A, B, C, G-Amazon basin ; E-Kent County, Texas, after

DeBlieux and Shepherd, 1951; D, F, J-Louisiana, after DeBlieux, 1949; Ks--Louisiana, generalized afterDeBlieux, 1949; I-East Africa, after Holmes, 1965; H, L-generalized exarnples,

and downstream from the Lafitte salt dome. At No explanation of the anomaly is offered. Mc-the dome, however, two meanderlike curves are Kenzie Creek, a tributary from the south, dis-present. This interruption of the normal pattern plays an anomalous curve apparently influencedmay be related to a subtle upstream reduction in by the dome.stream gradient caused by the appearance of the Abrupt and localized braiding.-DeBlieuxdome along its path. (1949, p. 1\259) reported the abrupt and local ap-

Compressed meanders.-DeBlieux and Shep- pearance of braiding at Scully salt dome in aban-herd (1951, p. 98) described a stream pattern doned distributaries of Bayou Lafourche about 30in which several meanders of an otherwise nor- mi southwest of N ew Orleans (Fig. 4, F). Braidingmal and continuous series are squeezed, com- generally indicates inability of a stream to trans-pressed, and incised (Fig. 4,E).The~anoIYlaíy,p~rtltsbedload {Leopold and Wolman, 1957, p.along the Double Mountain ForkoftheBtazos 50').· Inability.rnay result.frorn local' acquisitionRiver in Kent County, Texas;:is atthesit~~óf ~·'~:-ó(;~o~rser l~ad' iha~ the stream is competent tosubsequently demonstrated ' sG~ctutal~n6~·aiy.handle; loss' of volume due to locally íncreased

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ARTHUR DAVID HOWARD225;)

underfíow, loss of velocity caused by ftattening ofthe gradient (perhaps by a rising structure), orsome other geologic or hydrologic factor. De-Blíeux attributed the braiding to fiattening of thegradient. The presence of similar anomalies inneighboring streams may permit regional delinea-tion of the area or zone of anomalous behavioranel allow a more iníormed consideration ofcause. Correlation of meandering and braidedreaches ín adjacent streams conceivably mightpermit the delineation of formational boundaries.The same may be indicated by more subtIe varia-tíons ín stream patterns (Tator, 1954, p. 414),such as zonal variations in draínage densíty with-in the draínage pattern.

Anomalous pinching or flaring of valleys orchannels.-Local wideníng or narrowíng of val-leys or channels, not a repeti tive feature of theregional draínage pattern, may indicate localstructure. A shallow upwarp, for example, mightbring slightly weaker or more resístant materíalsto stream leveI, thereby ínfiuencing the rate ofvalley wídening; or upwarpíng might result in in-cision of the stream, the valley being broader up-stream and downstream (Fig. 4, G and H).

Anomalous ponds, marshes, or alluuial fills.-The presence of an isolated pond,marsh, or allu-vial fill along the path of a mature stream wherelandslides or other surficial causes can be exclud-ed, may indicate dammíng by subsidence or byuplift directly downstream. Some streams havebeen able to maintain their courses across risingobstructions; other streams have been diverted.ExcelIent examples of anomalous ponding areprovided by Lakes Victoria and Kioga in EastAfrica (Fig. 4, I). The lake basins originallydrained westward by way of the streams labeledA and B in the figure. Relative subsidence of thecentral area contemporaneous with creation ofthe western and eastern rift vaJIeys resulted indrowning of the lake basins and reversal of thedírection of fiow of the outlet streams, many ofwhose tributaríes are barbed and locally drowned.Blocking of lhe western outlets diverted the wa-ters of newly created Lake Victoria northward toLake Kioga and thence northwestward around thenorthern end of the western ríft valley.Althoughthese drainage modifications are .011a grand scale.;similar phenornena may occur atall scales.

Anomalous breadth of levees» ..-Russell (1939, '..p. 1212) noted that lea ves of abandoned channels

I,I

I1

along the Mississippi River are narrower in someplaces than others. He suggested that subsidenceof the levees at these placcs permittecI encroach-ment by the neighboring swamp or marsh result-ing in the reeluced levee wic\th.It is recognizecI generally that subsidence in the

Mississippi delta is differential, being retareledover the sites of burieel slructural features. Thus,levees are generalIy broaeler where they crosssuch structural features than they are up- ordownstream. This is true of the levees of theabandoned Bayou Lafourche (Fig. 4, J) where itcrosses the Valentine dome about 30 mi south-west of New Orleans in Laíourche Parish (De-Blieux, 1949, p. 1253). DeBlieux recognized thatlevee broadening may be caused by factors otherthan subsidence, such as crevassing, bífurcation,and coalescence, but believed that these causesare readily recognízable.

Flying levees.-In many parts of the Missis-sippi delta, former channels have subsíded belowmarsh leveI and only small fragments arepreserved, perhaps because they are on buriedstructural features (Fig. 4, K). Because theseIevee remnants are cornpletely isolated, theexpression "flyíng levee" is herein proposeel. De-Blieux (1949, p. 1253) citeel the levee remnantsat Four Isle dome, about 70 mí southwest ofNew Orleans in Terrebonne Parísh, as an exam-ple. Here, the flying levees are more than 3 midownstream from the present terminus of BayouGranel Caillou.

Anomalous curves and turns.-An anomalouscurve or turn is one that is abnormal within thedrainage pattern in which it occurs. The varietiesare legion, being most common in the flatlands(Fig .. 4, L). For example, a domal upwarp acrossthe path of a stream may gentIy "shoulder" thestream aside, forcing it to follow a curved, com-monly semicircular path around the structuralfeature. Barbeei junctions similar to those result-íng írom piracy may be formed where tributaríesto one stream are blocked by an upwarp and aredefiected sharply into neighboring drainage. If adomal upwarp takes place between parallelstreams, both streams may be defíected, resuItingin a~..peculiar .."blowlegged' pattern..Astream"crossíl1ganactivestrike-slipiaultináy be ..offset>, ,.laterally anddisplay sharp righ"t~àngle turns .where '..jt: entersand Ieàves th!(rÜt.Fâulls"núiyl~adto· . ::anomalous Íengthening andâattening ofa curve ..

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DRAINAGE ANALYSIS IN GEOLOGIC INTERPRETATION,2259

SUMMARY

Drainage analysis may provide information onstructural features and type of materiais. Theanalysis should consider not only basic patterns,but also modified basic pattems, pattern varieties,drainage texture, stream patterns, and anomalies.

The drainage patterns, individually and in com-bination, provide a certain amount of informationwhich, in the tlatlands at least, may not be ob-tainable by ordinary field methods. The palimp-sest pattern is of special interest inasmuch as itmay indicate current tectonic activity.

Drainage texture within any one small area inwhich climate, topography, and erosional historyare reasonably constant commonly may be indica-tive of the permeability of materiais or of thesize of particles provided by weathering.

Individual stream patterns may provi de infor-mation on structural features, rock type, hydrau-lic conditions, or geomorphic changes.

Drainage anomalies may provide informationon local structural features, active deíormation,differential subsidence, or changes in the hydrolo-gic regimen.

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--- and G. F. Shepherd, 1951, Photogeologic studyin Kent County, Texas: Oil and Gas j our., v. 50,no. 10, p. 86, 88, 98-100.

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