Morphometric Analysis Of Kala Oya River Basin, Sri Lanka .
International Journal of New Technology and Research (IJNTR)ISSN:2454-4116, Volume-2, Issue-12, December 2016 Pages 59-66Morphometric Analysis of Kala Oya River Basin,Sri Lanka Using Geographical Information SystemsN.S. Withanage, N.D.K.Dayawansa, Ranjith Premalal De Silva , R.M.C.W.M. Rathnayake Abstract— Morphological characteristics of river basins areassessed widely by means of morphometric analysis which is amathematical quantification of different aspects of river basins.In the present study, Kala Oya River Basin of Sri Lanka wasmorphometrically analyzed to assess its flood characteristicsbased on the morphological characteristics with the help ofGeographical Information Systems and the methods availablein scientific literature. Further, the soil and topographicalconditions like land use and terrain characteristics of the basinwere also identified. Results of the study revealed that the KalaOya River Basin has a 6th order river network according toStrahler’s classification with a dendritic drainage pattern andcoarse drainage texture. The obtained low values of bifurcationratio, circularity ratio, elongation ratio and form factor valuesrevealed that a lower and extended peak flow for a longerduration would result from the basin. The drainage density,stream frequency and drainage intensity values indicated thatthe basin has highly permeable soil, good vegetation cover andlower relief where a low rate of runoff could be resultedreducing the risk for both soil erosion and flooding. Theanalyzed relief aspects revealed that the basin is less susceptiblefor severe soil erosion. Confirming the results of themorphometric analysis, the basin area was with 85% of ReddishBrown Earth and Low Humic Gley Soils soil types which arepermeable soils and 66% of vegetation cover and a lower reliefas more than 95% of the basin was below 200 m and the highestpoint was also below 1000 m. However, the findings of rainfallanalysis for the basin revealed that there were increasingpatterns in receiving heavy rainfalls greater than 50 mm/dayand maximum rainfall amounts during a day over last 30 years.Similarly, flood occurrences also showed increasing patternswith time. Thus, sustainable management plans should be madein advance to cope with the potential floods that can occur dueto high rainfall events and/or due to the degradation ofprotective vegetation cover, although the studied Kala OyaRiver Basin is morphometrically capable enough to reduce theflood risk.Index Terms— Flood characteristics, GeographicalInformation Systems, Kala Oya River Basin, Morphometricanalysis, Soil and topographical conditionsI. INTRODUCTIONThe origin and circulation of the waters of the earth hasbeen a subject of speculation since ancient times.Measurement and quantitative expression of drainage basinhas begun with the work of James Hutton in 1775 as cited byN.S. Withanage, 1Postgraduate Institute of Agriculture, University ofPeradeniya, Sri LankaN.D.K.Dayawansa, Department of Agricultural Engineering, Universityof Peradeniya, Sri LankaRanjith Premalal De Silva, Department of Agricultural Engineering,University of Peradeniya, Sri LankaR.M.C.W.M. Rathnayake, Uva Wellassa University of Sri Lanka,Garde [1]. However, the modern approach of quantitativeanalysis of drainage basin morphology has commenced byHorton [34], the first pioneer for developing several Laws onstream flows. Horton‟s laws were subsequently modified anddeveloped by several geomorphologist, most notably byStrahler [2] [3] [4] [5], Schumm [6], Morisawa [7],Scheidegger [8], Gregory [9], Gregory and Walling [10].Recently published a number of books by Bloom [11], Kellerand Pinter [12] further propagated the morphometric analysis.Morphological features of river basins are widely assessedby determining morphometric parameters of the river basins[13]. Morphometry is the measurement and mathematicalanalysis of the configuration of the earth's surface of theshape and dimensions of its landforms [14]. This is the mostcommon technique in basin analysis, as morphometry formsan ideal areal unit for interpretation and analysis of fluviallyoriginated landforms where they exhibit an example of opensystems of operation. In fact, morphometry incorporatesquantitative study of the area, altitude, volume, slope profilesof the land and drainage characteristics of the area concerned.Morphological characteristics of river basins are dealt withthe form of the streams and adjoining areas as brought aboutby erosion, transportation and deposition of sediment by therunning water [1]. According to Strahler [5], systematicdescription of the geometry of a drainage basin and its streamchannel requires measurement of linear aspects of thedrainage network, areal aspects of the drainage basin andrelief (gradient) aspects of the channel network andcontributing ground slopes.The morphological characteristics of various basins havebeen initially studied by many scientists [15], [16], [2], and [5]using conventional methods viz, using strings, planimeter, etc.With the emergence of Spatial Information Technology (SIT)viz, Remote Sensing (RS), Geographical Information System(GIS) and Global Positioning System (GPS), estimation ofmorphological characteristics of river basins have becomemore convenient for many researchers [13], [17], [18], [19],[20], [21] and [22] as those methods have effective andefficient tools to overcome most of the problems of land andwater resources planning and management on the account ofusage of conventional methods of data processing. GIStechniques are widely used at present for assessing variousterrain and morphological parameters of the drainage basinsand watersheds, as they provide a flexible environment andpowerful tools for the manipulation and analysis of spatialinformation.59www.ijntr.org
Morphometric Analysis of Kala Oya River Basin, Sri Lanka Using Geographical Information SystemsMorphological characteristics of river basins have long beenbelieved to be important indices of surface processes. Theseparameters have been used in various studies ofgeomorphology and surface-water hydrology, such as floodcharacteristics, sediment yield, and evolution of basinmorphology. For instance, it has been discovered that higherthe drainage density, faster the runoff and the moresignificant the degree of channel abrasion for a given quantityof rainfall [23]. Further, the author has stated that themeasurement of drainage density provides hydrologists andgeomorphologists with a useful numerical measure oflandscape dissection and runoff potential. In homogeneousbedrock, bifurcation ratio influences the landscapemorphometry and plays an important control over the “peak”of the runoff hydrograph [24]. Waugh [25] noted that as theratio is reduced the risk of flooding within the basin increases.Strahler [5] noted that the shape of a drainage basin mayconceivably affect stream discharge characteristics. Jain andSinha [26], Okoko and Olujimi [27] and Ifabiyi [28] reportedthat the morphological characteristics of drainage basins playa key-role in controlling the basins hydrology. Jones [29] hasreported that morphological characteristics affect catchmentstream flow pattern through their influence on concentrationtime. Morphological characteristics of drainage basins thusprovide not only an elegant description of the landscape, butalso serve as a powerful means of comparing the form andhydrological processes of drainage basins that maybe widelyseparated in space and time [30].11 topographic map sheets viz Wilpattu (24), Tantirimale(25), Kalpitiya (29), Kalaoya (30), Anuradhapura (31),Puttalam (34), Galgamuwa (35), Kekirawa (36),Polonnaruwa ( 37), Dambulla (42) and Elahera (43) in1:50,000 scale published by the Survey Department of SriLanka in 2007 were used for the study.The ArcGIS-9.3 software package was used in preparingall digital layers used in the study and all the maps wereprepared in Sri Lanka National Grid based on TM coordinatesystem. River basin boundary of the selected Kala Oya RiverBasin in the Dry Zone of Sri Lanka were digitized based onthe river basins boundary map published by the Departmentof Agrarian Services, Sri Lanka (2012) and then it wasverified with the help of contour map published by the SurveyDepartment of Sri Lanka (2007).The digital layers of the hydrological network and land usepattern of the river basin were obtained by digitizing 11topographic map sheets. Further, the digital layer of soil typesof selected basin was prepared by scanning and digitizing theSoil Map available in the National Atlas of Sri Lanka [31].The Digital Elevation Models and slope maps were generatedusing Shuttle Radar Topography Mission (SRTM) dataobtained from http://earthexplorer.usgs.gov.Linear, areal and relief aspects of morphologicalparameters were assessed using GIS Software analysis toolsand different models developed and published through thescientific literature in Geomorphology (Table 1).II. STUDY AREAThe Kala Oya is a river which originates in the Matale Hillsand falls to the sea North of Vanathavillu off Puttalam,traversing the Wilpattu National Park. Among 103 majorriver basins spread in Sri Lanka, Kala Oya River Basinprocesses the third longest river in Sri Lanka, Kala Oya [31].There are about 600 small irrigation tanks and largereservoirs viz Kala Wewa, Balalu Wewa, langamuwaReservoir,KandalamaWewa,Dewahuwa Wewa, Ibbankatuwa Reservoir, Dambulu OyaReservoir and Katiyawa Tank. The average annual rainfallover the basin is 1192 mm and the discharge volume to thesea is 386 MCM leading to a runoff/rainfall ratio of 12% [31].The basin more or less is within Dry Zone of Sri Lanka whilea small area of the upper catchment of the basin is only withinIntermediate Zone of Sri Lanka. The basin extends withinIM1b, IM3b, IL3, DL1b, DL1c, DL1f and DL3 Agro-ecologicalRegions. The basin is totally within 0 - 500 m elevation leveland only a few mountains are above 500 m level. Asclassified by Cooray [32], the geology of the basin falls underHighland Complex, Wanni Complex and Limestone.Further, areal share of the different soil and land use typesspread in the river basin were calculated as percentages usingthe information produced by the attribute tables of the digitallayers with soil types and land use. Moreover, terrainconditions of the selected basin were identified by preparingelevation and slope maps.Rainfall data at different gauging stations located in the uppercatchment area of the river basin obtained from theMeteorological Department of Sri Lanka and the floodrecords at downstream area of the basin obtained from theweb site of the Disaster Management Centre of Sri Lanka[33] were further used to assess the hydrologicalcharacteristics and flood potentials of the selected river basin.Table 1: Methods used for the morphometric analysisMorphometricMethodReferenceParameterLinear AspectsIII. MATERIALS AND METHODSRiver basin boundary map published by the Department ofAgrarian Services, Sri Lanka in 2012; Soil map of Sri Lankapublished in National Atlas of Sri Lanka by the SurveyDepartment of Sri Lanka in 2007; Map of Topography of SriLanka generated using Shuttle Radar Topography Mission(SRTM) data available in http://earthexplorer.usgs.gov and60Stream order (U)Hierarchical rank[5]NumberofStreams (NU)Stream length inkm (LU)MeanstreamLength (LUM)NU N1 N2 N6[34]LU L1 L2 . L6[34]LUM LU / NU[5]www.ijntr.org
International Journal of New Technology and Research (IJNTR)ISSN:2454-4116, Volume-2, Issue-12, December 2016 Pages 59-66Bifurcation Ratio(RB)StreamlengthRatio (RL)RB NU/NU 1[6]RL LU / LU-1[15]Area in km2 (A)Area calculation[6]Perimeter in km(P)Basin length in km(LB)Drainage density(DD)Stream frequency(FS)Circulatory ratio(RC)Elongation ratio(RE)Perimetercalculation[6]Length calculation[6]DD LU /A[34]FS NU/A[34]RC 12.57*(A/P²)[35]RE 2/LB* (A /π )[6]Form factor (RF)RF A/LB²[34]DT NU/P[15]LO 1 / DD*0.5[15]Basin relief in m(H)H Z-z[3]Relief ratio (RH)RH H / LB[6]Relative(RHP)RHP H*100 / P[37]together with numerous small tanks and several large tanks orreservoirs in the basin (Fig. 1).The decreasing NU with the increasing U in the basinconfirm the Horton‟s [15] and Strahler‟s [3] findings.Gregory and Walling [10] have found that the increasingorder of network is associated with greater stream flowvalues.The stream length (LU) is one of the significant features ofthe basin, as it reveals surface runoff characteristics. Streamsof relatively smaller lengths indicate that the area is with highslopes. Longer lengths are indicative of flatter gradient [15].Usually, the total lengths of stream segments are highest inthe first order streams, and it decreases as the stream orderincreases [15] and Kala Oya river basin also shows similarpattern (Table 2). The mean stream length of each order (LUM)is a characteristic property related to the drainage networkcomponents and its associated basin surfaces and LUM valueare increasing with increasing order [5]. The studied rivernetwork also confirms that finding (Table 2).Areal AspectsDrainage texture(DT)Length overlandflow of (LO)Relief AspectsReliefIV. RESULTS AND DISCUSSIONA. Linear aspects of Kala Oya river basinThe stream links and the nodes (confluences) characterize„Linear aspects‟ of the basin and they are basically associatedwith the stream orders which represent the hierarchicalranking of the stream segments from the origin of those in thebasin to the outlet [38]. Table 2 shows the stream orders (U)obtained according to Strahler‟s [2] classification and thenumber of streams in each order (NU) of the studied Kala Oyariver network.Table 2: Linear Aspects of Kala Oya river basinStreamOrder (U)NULU 84.001.386141.8741.873.00RBRL2.06Total976 1666.35As per the Table 2, Kala Oya stream network is with a totalnumber of 976 stream segments extending up to 6th orderFig. 1: Strahler‟s Stream Orders of Kala Oya River Basin(Source Data for Stream Network: 1:50,000 TopographicMap Sheets published by Survey Department of Sri Lanka,2007)The RB is a dimensionless property and generally rangesfrom 3.0 to 5.0 [3] and the RB values of all 6 orders of thestudied river network are within this range (Table 2). It canalso be observed that RB is not same from one order to thenext order in the studied basin. According to Strahler [5]these irregularities are dependent upon the geological andlithological development of the drainage basin. The lowervalues of RB are characteristics of the watersheds, which havesuffered less structural disturbances [5]. Further, Chorley etal. [24] has noted that the lower the bifurcation ratio, thehigher the risk of flooding, particularly of parts and not theentire basin. Hence, the almost higher RB values together withthe elongated shapes of the studied river basin would result alower and extended peak flows, which will reduce the risk offlooding within the basin.As Horton [15] stated that the stream length ratio (RL)tends to be constant throughout the successive orders of abasin. But, the RL values of the studied basin are varyingamong the orders without showing any consistency (Table 2).According to Singh and Singh [39] changes of stream length61www.ijntr.org
Morphometric Analysis of Kala Oya River Basin, Sri Lanka Using Geographical Information Systemsratio from one order to another order indicate their late youthstage of geomorphic development in the streams of the area.In river basins, RL ranges between 1.5 and 3.5 and is typically2 [40] and the obtained RL values for the studied basin alsoshow similar evidences (Table 2).Finally, a dendritic drainage pattern can be identified in thebasin and it is probably the most common drainage patternidentified in Sri Lankan river basins as well as in the world.This is characterized by irregular branching of tributarystreams in many directions and at almost any angle usuallyless than 900. Dendritic patterns develop on rocks of uniformresistance and indicate a complete lack of structural control.This pattern is more likely to be found on nearly horizontalsedimentary rocks or on areas of massive igneous rocks. Theymay also be seen on complex metamorphosed rocks [1].and good vegetation cover prevailing in the basin asexplained by Strahler [5].The stream frequency (FS) introduced by Horton [34] is anindicative of stream network distribution over the river basin.Kale and Guptha [41] have found that the FS value may rangefrom less than 1 to 6 or even more depending on the lithologyof the basin. In the present study, the FS value of the basin(Table 3) is less than 1.0 indicating a low value. This revealsthat the basin possesses low relief and almost flat topographyas stated by Horton [34] and also as confirmed by theidentified low relief conditions of the studied basin (Fig. 4and Fig. 5).The drainage texture (DT) is one of the important conceptsof geomorphology which means the relative spacing ofdrainage lines. The DT depends on the underlying lithology,infiltration capacity and relief aspect of the terrain. Accordingto Smith [16] the DT depends upon a number of naturalfactors such as climate, rainfall, vegetation, rock and soiltype, infiltration capacity, relief and stage of development.Further he explained that, the soft or weak rocks unprotectedby vegetation produce a fine texture, whereas massive andresistant rocks cause coarse texture. Sparse vegetation of aridclimate causes finer textures than those developed on similarrocks in a humid climate. Smith [16] has classified thedrainage texture into five different textures i.e., very coarse( 2), coarse (2 to 4), moderate (4 to 6), fine (6 to 8) and veryfine ( 8). Based on this classification, Kala Oya has a coarsedrainage texture (Table 3).B. Areal aspects of Kala Oya river basinThe areal aspects are the two dimensional properties of abasin that basically explain the shape parameters. The basinshape has a significant effect on stream dischargecharacteristics and finally on the flood characteristics of thebasin. Table 3 shows the results of the calculated differentareal aspects of the studied river basin.Table 3: Areal aspects of Kala Oya river basinParametersValues2Area in km (A)2850.00Perimeter in km (P)319.00Length of the basin in km (LB)116.60Drainage density (DD)0.58Stream frequency (FS)0.34Drainage texture (DT)3.06Length of overland flow (LO)0.86Circulatory ratio (RC)0.35Elongation ratio (RE)0.52Form factor (RF)0.21The length of overland flow (LO) refers to the length of therunoff of the rain water on the ground surface before it getsconcentrated into definite stream channels [15]. The overlandflow is higher in the semi arid regions than in the humid andhumid temperate regions; in addition, absence of vegetationcover in the semi arid regions is primarily responsible forlower infiltration rates and for the generation of highersurface flow [41]. Thus the resulted low LO value (Table 3)gives evidences for the existence of good vegetation covers inthe basin.Basin area (A) and perimeter (P) are important parametersin quantitative geomorphology. Perimeter is an indicator ofwatershed size and shape [34]. Horton [34] introduced thedrainage density (DD) as an important indicator of the linearscale of landform elements in stream eroded topography. TheDD indicates the closeness of spacing of channels, thusproviding a quantitative measure of the average length ofstream channels for the whole basin [34]. Strahler [5] statedthat DD values may be 1 km/km2 through very permeablerocks, whereas they increase to over 5 km/km2 throughhighly impermeable surfaces. It has been observed from DDmeasurements made over a wide range of geologic andclimatic types that a low DD is more likely to occur in regionsof highly permeable subsoil material under dense vegetativecover and where relief is low. A high DD is the resultant ofweak or i
The Kala Oya is a river which originates in the Matale Hills and falls to the sea North of Vanathavillu off Puttalam, traversing the Wilpattu National Park. Among 103 major river basins spread in Sri Lanka, Kala Oya River Basin processes the third longest river in Sri Lanka, Kala Oya [31].
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