Dr. VishwU3 S. KaleReader in Geomorphology,

UNIVERSI1Y OF '0"PUNE-411007 'NDI \1

BULLETINOF THE

DECCAN COLLEGEPOSTGRADUATE & RESEARCH INSTITUTE

Vol. 45

1986

PUNE

/5'

TERRAIN EVALUATION AND GEOMORPHIC REGIONALISATIONA Case Study of Central Goa (India)

V. S. KALE and S. N. RAJAGURlJ

General

The validity of morphological analysisdepends on being able to establish a relationbetween the various landform and drainageaspects and being able to depict that spatialvariation in geomorphic parameters causesdifferences in the nature of terrain. One of themost significant characteristics of geomor­phic phenomena is that they are the result of anumber of simultaneously operating varia­bles which have to be evaluated separately,relatively and in combination (Chorley 1967).As an example of this approch, a case study ofCentral Goa is presented. A 1110del of geomor­phic regionalisation has also been attempted,by considering various gross landformparameters. Further, by analysing the interre­lationship between the parameters, the rela­tive importance of the landscape developmenthas also been evaluated.

Terrain Evaluation andParametric Systems

The term terrain evaluation involves theanalysis and assessment of a tract of lands­cape; considered with regards to it's naturalfeatures and configuration. The processincludes analysis, classification, characteriz­ing and interpretation of the natural geomor­phic environment (Mitchell 1973). Theevaluation of terrain is normally based eitheron "landscape" or "parametric" methods. Theparametric method, employed here, includesthe analysis of the distribution of selected,quantified and relevent variables and thecombination of the resulting patterns into

composite generilizations. This approch ismore arduors than the "landscape" methodbut it has the important virtue of objectiveapplication and potential for quantitativeanalysis and reproducibility (Cooke 1977,OIlier 1977).

The drainage basin, as a geomorphic unit,provides the basis for studies in geomorphol­ogy. The basins form a natural unit displayingorga nized relations among their constituentparameters of landform and drainage (Cooke& Doornkamp 1974). Therefore, in the pres­ent study, taking into account the river basinas the basic unit and employing the paramet­ric method of classification, a comprehensive"Parametric basin evaluation" has been car­ried out.

The Study Area: an introduction

The area under investigation is occupied bythree river basins viz. the Sal, Zuari andMandvi. The latter two rivers are short, swiftflowing and have esturine mouths (Kale and

. Rajaguru 1983). Nearly 45% of the relief liesbelow 80 m ASL and about 29% area liesbetween 80 and 200 m ASL. The area forms apart of Dharwar Supergroup of south India,and has a general NNW-SSE trend (Dessai &Peshwa 1978). The review area is marked bythree landform associations:

(i) The high declivity Ghat zone,

(ii) The hilly Sub-Ghat zone, and

(iii) The low lying coastal zone.Although, geomorphic investigation of the

area, has been carried out by many scholars,only Sriram and Prasad (1979) have divided

v. S. KALE AND S. N, RAJAGURU

:loa into morphographic regions. Never­heiss, no attempt has been made so far, tolave a detailed geostatistical evaluation and'egionalization, as attempted in the presentlccount.

Methodology

7) Selection and measurment o/the variables:There is no agreement on which variables

He to be used in the evaluation and classifica­tion. A typical list provided by many authors(as Cooke 1977, Oilier 1977) include variouslandform and drainage network variables.Hence, the selection of the parameters wasgoverned by the relevence of the variable andits suitability for numerical expression. Thedetails of the terrain evaluation variables aregiven in Table I. These variables (ten innumber) were chosen with a particular theo­retical structure in mind, which was that thecharacteristics relating to the landformshould focus around dimensions concerningthe relief and slope, while those relating todrainage should cluster aroud the dimensionconcerning the drainage network. Further­more, these parameters are surface experes­sions of a sub-system of the denudationsystem, and therefore there is a predictablecorrelation between the morphometric anddynami'c properties of the landscape. .h) Division 0/ the study area:

Based on the geographical properties, thecentral Goa was divided into two areal unitsviz. The Mandvi basin and the Zuari basin(including Sal basin). For a detailed andmicro-level analysis the two areal units weredivided into small quadrats of I' x I' each,representin roughly an area of 2.25 sq.km.Thus, Mandvi basin was covered by 916quadrats and the Zuari basin was covered by574 quadrats. The values of all the 10 varia­bles (Table I) were obtained for each of these1490 quadrats.c) Geostatistical analysis:

The geostatistical techniques were primar­ily used to evaluate separately, relatively and

in combination, the relationship between thevariables. This was achived by bivariate andmultivariate correlation analysis. Thesemethods are simple and emphasise the majortrends of relationship (Chorley 1967).

Terrain classification is one of the majorconcerns of the earth scientists. Among thevarious methods used in the classification thePrincipal Component analysis and the FactorClnalysis are the main statistical techniques. Inthe present anaIysis the Factor analysis hasbeen employed because it is more suitable,more flexible and less deterministic than theprincipal component analysis. Further,unlike principle component the factor analy­sis assumes that, only part of the variation in agiven population is contained within the vari­able used to define the population (Yeates1974).

The factor analysis can be viewed as con­sisting of five matrices. In the first stage thedata matrix of observations (k ; here 1490)and variables (n ; here 10) is converted intoan n.n. correlation matrix between variables.The factoring procedure then gives an n.n.original factor matrix of loading and n.m.rotated factor matrix with new loadings forvariables on m rotated factors. Finally, thek.m. factor score matrix is computed thatshows scores of the observations (Yeats 1974,.Taylor 1977).

Results of the analysis

a) Bivariate and Multivariate correlations:The correlation matrices obtained for the

two areal units separately, reveal significantassociation between various landform anddrainage variables. The interelationship chartprepared on the basis of the results shows,that most of the variables are positivelyrelated with each other (Fig. I). Although allthe relations do not suggest instances of a realcause and effect relationship, most of thecoefficients display that the variables arefunctions of common controlling factors. Thevariables like spring density and constant of l

TERRAIN EVALUATION AND GEOMORPHIC REGIONALISATION 59

Channel maintenance exhibit weak linearassociations with all other variables (Fig. I).

The interrationship and correspondencebetween the variables is also revealed by mul­tiple correation. The multipl regressioncoefficient btained for the two area unitsdepict that land/' rm and drainage networkparameters have exerci ed a considerableinfluence or each other (Table II). In most ofth cases, more than 70~ variance isexplained.

The two variables viz. pring density andthe on. tant fhannel maintenance exhibita low,explained variance (less than 19%). Thevariable are perhaps trongly related with

ther factors (like lithology stucture weat.h­ering elc.) and hence reveal an insignificantrelationship wit.h the drainage basinparameters.

The bivariate and multivariate relationsstrongly emphasise the correct chioce of vari­ables for terrain evaluation and geomorphicregionalisation.h) Fat'/or Analysis:

-he final utput f the facl r analysisprocedure is given in table III and IV. fheanalysis h w' that the three factors accountfor 58.73% and 64.80% variance for theMandvi and Zuari basins re pectively. TIlevariance value are tatistically ignifi ant inboth the cases.

Interpretation andGeomorphic Regionalisation

. a) Faclor Labeling:The labeling procedure in vol es the hoice

of a name that expresses the pattern f varia­ble loadings. This i based on referring to thematrices of factor loading and localing thehigh loading on a factor. In the present anal­ysis the factor I can be termed as "Morpho­textural Faotor" (i. . structur , constitutionand character of land r rm), because in boththe basins it loads high on mean slope (9) andrelative relief(Rr.). Thefactor2can be namedas the "Hydro-textural actor" (i.e. organiza-

tion and composition of the drainage net­work), because the drainage density andstream frequency variables load high in thetwo basins. The factor 3 in case Of the Mandvibasin can be labelled as the "HypsographicFactor" because that is the only variable withhigh loading. The factor is not significant forthe Zuari basin (vide Table III and IV). Thus,it can be concluded that the terrain of CentralGoa can be described primarily, in terms ofmorpho-textural and hydro-textural dimen­sions. In other words, the geomorphic lands­cape of the study area is the function of fourvariables at this point of time, viz. (in order ofimportance) mean slope, relative relief,stream frequency and drainage density.h) Geomorphic Regionalisalion:

For the purpose of areal classification thefirst two factors were employed because at thethird factor the contribution drops to lessthan 10% and the eigen values are much less(Table III and IV) in case of both the arealunits. The two factors were respectivelyrepresented by vertical and horizontal axisand the factor scores (916 + 574 =1490) werelocated in this space. Thus, four clusters we.reisolated, mapped and geomorphic regionswere identified.

In view of the variables and the methodused in the analysis, the regions should havebeen termed as the morphometric regions(Cooke and Doornkamp 1974). But after thegeoidentification the genetic desctiption ofthe landform was also incorporated. Thisinformation was based on field studies andareial photo interpretation. Consequently,the regions were renamed as "Morphogeneticregions". The four sub-regions (Fig. 2 and 3)identified in this manner are as follows:i) Dominantly dissected regions:These regions include the high relief waterdi­vides and the Ghat scarps. The valleysideslopes and hillslopes are steep (15,<) and arein the youthful stage. The drainage composi­tion is fine and the network depicts a stage ofelaboration. The frequency of first order

60 v. S. KALE AND S. N. RAJAGURU

streams is high in these regions. The slopes arecovered with dense deciduous forests and atplaces the weathered zone is thick. Most ofthe landforms in these regions belong to theNeogene peroid (Sriram and Prasad 1979,Kale and Rajaguru 1983). The erosionalhazards in these regions are high.ii) Highly dissected regions:These regions encompass seco'ndary divideswith relatively low relief and declivity. Thehills lopes and valleyslopes are moderate andare in the maturing stage. The drainage net­work is in the late-elaboration stage with highfrequency of middle oreier streams. Some ofthese slopes are covered by primary or secon­dary laterites. The erosional risk is mod rate inthe,.;e regions. These regions form a very smallproportion of the basins and in reality areecotones of the first regions.iii) Moderately dissected regions:These regions include lateritic hills, pedi­ments, surfaces and plateautops in the twobasins. Geomorpically, the regions have rela­tively mature slopes and drainage. Theseregions are often covered by thick laterites oflate-Neogene or Quanternary period (Kaleand Rajaguru 1983). The laterites are AI richin the coastal areas and Fe! Mn rich in theinterior. Due to low declivity and coarsedrairiage, the erosional hazards are low inthese units and the forms are stable. Placeslike Rivon, Betul, Sanguem, Bati, Bicholi etc.are located in these regions.iv) Slightly dissected regions:The low-lying valleys and coastal plainsoccuping the Molle palaeoplain fall in thisunit. The slopes are gentle « 3°) and are inthe formative or mature stage. Similarly, thedrainage organization is either in the integra-

tion or the initiation stage. Most of the Qua­ternary features like, beaches, dunes,marshes, river terraces, gravels, laterits etc.are observed in these regions. The channels ofthe main rivers like Mandvi, Zuari, Dudha­sagar, Kushavati and Sal occupy theseregions. A large number of modern settle­ments and many of the prehistoric and meso­lithic sites are located in these regions.Geographically, this is the largest and themost important area of the two basins.

Assessment

The parametric basin analysis has been ableto, identify the primary relationships betweenthe landform and drainage aspects, and hasbeen able to assess the degree of associationbetween them on the spatial scale. The analy­sis indicates that the terrain of Central Goacan be explained simply by the intensity ofdissection, diclivity and the drainage organi­zation. The evaluation of terrain on the basisof 1490 observations and 10 variables revealsthat four distinct regions of varying morpho­logical characteristics can be identified. Thesemorphogenetic regions can be considered use­ful for studies in water resources, soil erosion,agriculture, horticulture, forestry andresource management. Thus, such a geomor­phic approch to terrain evaluation andregionalisation has much to offer to theworkers requiring a multivariate and inte­grated approach to the environmentalstudies.

Acknowledgement

The authors are grateful to Dr. S.D. GoreDepartment of Statistics, University ofPoona for advice on the computer analysis.

References

CHORLEY, R. .I., (1967) The Applic~tion of Sat.Methods .to Geomorphology, Es.\'oy in Geunwrphulogy.ed Dury, C. H., Heinem~nn London, pp. 275-388.

COOKE. R. U., (1977) Applied Geomorphologicalstudies in deserts, Applied Geolllorphulogy ed Hails,J.R., Elsevier Scientific Pub. Co. N. York, pr. 183-218.

COOKE, R. U., and DOORNKAMP, J. C, (1974)Geomulphulogy in Enviro. Management, ClarendonPress, Oxford, pp. 352-379.

DESSAI, A. C and PESHAW'A, V. V., (1978) Drain­age anomalies in the West Coast region of Ma harashlr~

and Goa. Proc. Symp. Morph. & Evol. oj'/he Landjemm,

TERRAIN EVALUATION AND GEOMORPHIC REGIONALISAIION. , 61

Jelhi, pp. 255·59.KALE, V. S. and RAJAGURU, S. N., (1983) Some

ISpects of the Quoternary History of Goa. Bull Deccan.':01. Pune.: V. 43, pp. 87-93. '

MITCHELC, C. W., (1973) Terrain Evalualion. Long­nan Group Ltd., London, pp. 4-37

OLLlER, C. D., '(1977) Terrain Classification­nethods, Application and Principles. Applied Geomor­,hologyed Hails, J. R., Elsevier Scientific Pub. Co. N.

York, pp. 277-313SRIRAM .. K'& PRASAD. K. N.• (1979) Observations

on the Geomorphology of Goa. Jour.' Geol. Soc. Ind. V.20 No. 12, pp. 608-614.

TAYLQR. P. J•• (1977) Quant. me/hods in Geo­graphy. Houghton Mifflin Co. Boston, pp. 232-254.

YEATES, M., (1974) An. Intra. 10 Quant. Analysis. inHuman Geog. Mc Graw-Hill Book Company, N. York,pp. 207-236.

Variables

v. S. KALE A.NO S. N. RAJAGURU

Table IVariables used in the terrain evaluation

Symbols Formula

Altitude ARelative Relief Rr Z-zDissection index cf> Rr x IOOjHMean slope 9 Rr/ -J Area

rrMax. slope 9max

I. Spring density Sp No. of Springsj AreaSource density Sd No. of Sources/ Area

'. Stream frequency Sf No. of Streams/ AreaDrainage density Dd Total length/ Area

I. Constant of Channelmaintenance C I/Dd.

Z = height of the highest point,Z = height of the lowest point,H = Total basin relief.

Table IIMultiple Correlation Analysis ResultS'

,r. Variables Zuari (R) Mandvi (R)

1. Altitude 0.956 0.8632. Relative relief 0.994 0.9~1

3. Dessection index 0.982 0.7624. Mean Slope 0.991 0.9935. Max. Slope 0.878 0.9046. Spring density 0.303 0.2577. Source density 0.937 0.9558. Stream frequency 0.973 0.9799. Drainage density 0.951 0.958

10. Constant of Channelmaintenance 0.441 0.413

TERRAIN EVALUATION AND GEOMORPHIC REGIONALISATION 63

Table IIIMatrix of Factor loading (Mandvi basin)

Variables Communality Factor J Factor 2 Factor 3

A 0.87 0.64 0.19 0.63Rr 0.98 0.97 -0.16 0.03e 0.37 0.59 -0.12 0.054J 0.98 0.98 -0.14 -0.02max 0.24 0.48 -0.02 ---':'0.09

Sp 0.15 0.11 -0.04 • -0.04Sd 0.76 0.64 0.60 -0.005Sf 0.96 0.65 0.71 -0.09Od 0.60 0.56 0.51 -0.15C 0.18 -0.21 -0.23 0.10

Eigen value 118.63 18.46 4.82% of Total

variance 38.47 12.35 7.91

Table IVMatrix of Factor loading (Zuari basin)

Variables Communality Factor I Factor 2 Factor 3

A 0.81 0.90 0;01 0.04Rr 0.99 0.98 -0.07 -0.001e 0.92 0.96 -0.06 0.024J 0.96 0.98 / -0.06 0.006max 0.22 0.45 0.05 -0.08

Sp 0.01 0.09 0.04 0.02Sd 0.80 0.66 0.54 -0.27Sf 0.92 0.68 0.66 --0.07Oct 0.89 0.60 0.63 0.29C 0.34 -0.26 -0.36 --0.37

Eigen value 173.48 11.11 1.35% of Total

variance 49.56 11.75 3.49

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