INTERNATIONAL JOURNAL OF GEOMATICS AND GEOSCIENCES Volume 5, No 1, 2014

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1 INTERNATIONAL JOURNAL OF GEOMATICS AND GEOSCIENCES Volume 5, No, 204 Copyright by the authors - Licensee IPA- Under Creative Commons license 3.0 Research article ISSN Morphometry and its implications to stream sediment sampling: A study on Wajrakarur Kimberlite Field, Penna river basin, Anantapur district, Andhra Pradesh, India Cyient Limited, Plot No., Software Units Layout, Infocity, Madhapur, Hyderabad, India Ramesh.Pothuri@cyient.com ABSTRACT Morphometric analysis, including certain linear, areal and relief parameters, has been performed on watersheds covering pipes in the Wajrakarur kimberlite field (WKF) of Anantapur District, Andhra Pradesh, using hydrological data in corroboration with lithological and structural information. In total, 64 morphometric parameters were calculated for the study area. Litho-structural set up revealed that drainage system is influenced by lineaments. Higher values of morphometric parameters like sinuosity index, bifurcation ratio, gradient ratio, ruggedness number, dissection index, Rho coefficient are indicative of trap site quality, in the study area. As a tool for conceptual understanding, morphometric analysis can be considered as a process step before planning indicator mineral sampling for a terrain, thereby deciphering the category of possible trap sites that can occur in the area of interest, before commencing the actual sampling programme. Taking the WKF as a case, a relation between certain morphometric properties and plausible quality of indicator mineral trap site has been envisaged in this paper. This conceptual relation is perhaps made for the first time. Keywords: Morphometry, WKF, Stream sediment sampling, Penna River Basin, Anantapur Dt., Andhra Pradesh.. Introduction Morphometry refers to the measurement and mathematical analysis of the configuration of earth s surface, shape and dimensions (Clarke, 966). Therefore drainage basin morphometry plays a significant role in not only determining the groundwater potential of a given area but also to understand the geomorphological and tectonic history. Morphometry includes quantitative study of various hydrogeomorphic parameters like linear, areal and relief aspects. Morphometric features such as basin shape and basin relief influence the hydrological parameters. Drainage pattern provides information on the topography and underlying geological structure (Zaidi, 20). The quantitative analysis of the morphometric properties, which depend on various aspects like geology, tectonics, vegetation and climate etc, of a drainage basin has been useful in many application studies like estimation of runoff, flood discharge, groundwater recharge, sediment yield, soil & water conservation, geological and environmental analysis (Tiwari and Mishra, 20). An attempt has been made here to understand certain morphometric parameters which can be applied to envisage the geomorphological and litho-structural aspects of selected watersheds, in WKF engulfing about 4 kimberlite pipes, in Penna river basin using remote sensing and hydrological data. Perhaps for the first time, an attempt is made in this paper, to discuss its relation with trap site characteristics, a concept that can be considered before proceeding to kimberlite indicator mineral sampling on regional scale. Submitted on June 204 published on August

2 2. Study area The study area is located at ~35 km NW of Anantapur town between 5 o N 77 o E and to 4 o N 77 o E. The area falls on the northern bank of Penna River. (Figure ). Figure : Location Map of the study area & Landsat image with lineaments. 3. Materials and methods Morphometric analysis of a drainage system requires a delineation of all existing streams and reaches. Landsat image in conjunction with freely sourced Google Earth, Survey of India (SoI) :50K toposheets (57 E/8 and F/5) and Geological Survey of India :250K geological maps were used in the ESRI ArcGIS 0. and MapInfo 0.5 software in UTM coordinate system (WGS84 / Zone 45N) to interpret various morpho-litho-tectonic parameters like drainage patterns, elevation information, litho contacts and lineaments. The orientation of lineament, fault, dykes and drainage patterns was performed using an in-house- tool built in ArcMap viz. DefineAngle and rose diagrams were constructed using an open online app (GeoRose About 64 morphometric parameters were calculated dividing into three main categories viz., linear, areal and relief parameters. 4. Data analysis and results Various aspects like lithostructural and morphometric parameters delineated from this study are discussed hereunder. The study area is divided into 4 watersheds (WS I to IV). 4. Lithostructural aspects The study area comprises Archean granitoids and gneisses as basement intruded with kimberlite pipes of Proterozoic age, Quaternary alluvium and pedogenic soils. The general lithological hierarchy is shown in Figure 2. The lineaments are drawn by visual interpretation using Landsat as well as Google Earth image typically based on image elements like tone, texture and linear to curvilinear patterns (Figure ). Photo-linears generally represent the surface traces of features of bed rocks, projected more or less vertically upwards to erosion surface by various mechanisms (Srinivasan, 988). It is observed that prominent structural trends orient in NW-SE, NNE-SSW, ESE-WNW directions. (Figure 2D). By studying the lineament patterns in relation to drainage network, it 75

3 can be envisaged that drainage in this area is strongly controlled by lineament orientation. Drainage developed in the vicinity of fault zones, have a strong affinity towards taking disruption of flow, following a straight stream course. Also the area being homogenous granitoid terrain has a dendritic drainage pattern. Figure 2: A. Lithostructural aspects of the study area. B & C. Drainage controlled by lineament (WS II & I). C. Rose diagram of photo-linears. The fault and dike patterns show prevalent orientations trending in NW-SE & NE-SW. There is a correspondence between joint direction and orientation of stream channels in the central sector with a prevalent NNE orientation, whereas E W or WNW ESE are secondary orientations. This correlation (Figure 3 B & C) demonstrates that the trajectory of the streams is largely controlled by the brittle structures affecting the Archean rocks of this area. These trends also have some influence on the drainage orientation in some parts of the study area especially in WS I, II and IV. The possible evidence of structural control on drainage include sharp bends in streams, sudden right angled turn of streams, streams flowing parallel to the major rivers for a considerable distances, convergence and divergence of streams and in general anomalous behavior of streams. 4.2 Morphometric analysis The area, altitude, slope, profile and texture drainage comprise principal parameters of morphometric investigation. Dury (952), Christian (957) applied various methods for landform analysis in different ways and their results presented in the form of graphs, maps or statistical indices. Various morphometric parameters (64 in number), out of which 22 are linear, 2 are areal and 2 are relief parameters were calculated to decipher the geomorphometry of the study area. 76

4 4.2. Linear parameters Stream order (Sn) of drainage basin is the successive assimilation of the stream segments within a drainage basin. Individual counting of the streams in the river basin reveals the total number of the streams. The ordering of the basin, the first step of quantitative analysis of the watershed, has been carried out by the method suggested by Strahler (957). The lower order stream orientations are the youngest components of the drainage network and the preferred orientation corresponds to the orientations related to the most recently active tectonic phase (Centamore et al, 996). The incipient stream that runs off an elevated slope gradually to plains is given order. Where two st order streams meet, a 2 nd order stream is generated. Thus the highest stream order is 6 in the study area. After assigning stream orders, the segments of each order are counted to get the number of segments of the given order (u) (Figure 3). All the linear parameters are listed in Table A & B. Figure 3: Stream orders in the study area with kimberlite pipe outlines. Table -A: Stream characteristics and linear parameters of the study areas WS I II, III & IV. Stream Order Formula Parameter Ref. st 2 nd 3 rd 4 th 5 th 6 th No.of stream order count Stream_Lengt h (Lu), Average stream length, Mean stream length (Lsm) Stream length Ratio (RL) Bifurcation Ratio (Rb) Rho Coefficient (ρ) Cumulative Stream Length, GIS Lsm=Lu/Nu RL= Lu/Lu- Rb=Nu/Nu _ _ 3 ρ= Lur / Rb _ _ Lu,Lu+Lu 2,Lu+Lu2+ Lu

5 Parameters Stream Order (Sn) Total no.of streams (Nu) Total length of all stream orders (S), Perimeter (P), Main Channel Length (Cl), Orginal Length (OL), Expected Length (EL), Weighted mean stream length (LUWM) Maximum length of basin (Lb), Mean bifurcation Ratio (Rbm) Weighted Mean Bifurcation Ratio (Rbwm) Table -B: Linear morphometric parameters in the study area Formula GIS, hierachial rank GIS Average of bifurcation ratio of all orders WS I WS II WS III WS IV Average Ref. to 6 to 6 to 4 to 4 _ Mean Length of Lg =

6 Over land flow (Lg) Sinuosity index (S.I.) Stream Frequency (Sf) /Dd*2 S.I. = OL/EL Fs = Nu/A Stream length (Lu) for the basin of the given order is inversely proportional to the stream order. Stream lengths of the basin indicate surface runoff characteristics. Streams of relatively smaller lengths are characteristics of area with greater slopes whereas longer streams prevail in plains of gentle to moderate slopes. It has been observed that the maximum stream frequency (Sf) is in the case of first order streams and it decreases as the stream order increases. Horton's law of stream lengths supports the theory that geometrical similarity is preserved generally in watershed of increasing order (Strahler, 964). In the current study it is observed that larger the area of watershed, higher is the total stream length and watershed II has the highest S value. The bifurcation ratio (Rb) the ratio of the number of the stream segments of given order Nu to the number of streams in the next higher order (Nu+), (Horton, 945). The Rb is a dimensionless property and generally ranges from 3.0 to 5.0. The significance of Rb is that as the ratio is reduced, the risk of flooding within the basin increases. Thus the flood-prone parts of the basin can be identified. Horton (945) considered the Rb as index of relief and dissertation. Strahler (957) demonstrated that Rb values have a small variance w.r.t region and environment unless there is a strong geologic control. It is observed from the Rb is not same from one order to its next order these irregularities are dependent upon the geological and lithological development of the drainage basin (Strahler 964). The lower values of Rb in watersheds indicate less structural disturbances (Strahler 964) and the drainage pattern has not been distorted due to the structural disturbances (Nag 998). In the present study, the higher values of Rb in watersheds I & II indicates strong structural control on the drainage pattern, while the lower values in watersheds III & IV indicates little or no structural control. The Rho coefficient (ρ) is an important parameter relating drainage density to physiographic development of a watershed which facilitate evaluation of storage capacity of drainage network and hence a determinant of ultimate degree of drainage development in a given watershed (Horton 945) with the influence of climatic, geologic, biologic, geomorphologic, and anthropogenic factors. The ρ values of the watersheds of study area are 0.26, suggesting lower hydrologic storage during floods and attenuation of effects of erosion during elevated discharge. Mean Stream length (Lsm) is a dimensional property revealing the characteristic size of components of a drainage network and its contributing watershed surfaces (Strahler, 964) obtained by dividing total length of stream of an order by total number of segments in that order. It is calculated as 0.66 on an average for the study area. Sinuosity Index (S.I.) deals with the pattern of channel of a drainage basin which is defined as the ratio of channel length to down valley distance. S.I. value varies from to 4 or more. Rivers having a sinuosity of.5 or less are called sinuous, and above.5 are called meandering (Wolman and Miller, 964). It is a significant quantitative index for interpreting the role of streams in the evolution of landforms. Generally, channels in steep, confined valleys have low sinuosity, and channels in broad, gentle-sloped valleys have high sinuosity (Mike et al, 2004). For the measurement of sinuosity index Mueller (968) defined two main types i.e., topographic and hydraulic sinuosity index concerned with the flow of natural stream courses and with the 79

7 development of flood plains respectively. In the watersheds studied here, S.I. is.24 indicating the sinuous type. Horton (945) used length of overland flow (Lg) to refer to the length of run-off on the ground surface before it is localized into definite channels. Since Lg, is about half the distance between the streams, Horton had taken it to be roughly equal to half the reciprocal of the drainage density. In this study, the Lg of the study area basin is 0.26 km, which shows low surface runoff, indicating the intensity of precipitation in the area Areal parameters The basin area (A) of the watershed is another important parameter just like the stream length. Schumm (956) established an interesting relation between the total watershed areas and the total stream lengths. The total basin area computed is 66 Sq. km. All the areal morphometric parameters are tabulated in Table 2. Basin perimeter (P) is the outer boundary of the watershed enclosing its area and is measured along the divides between watersheds and is as an indicator of watershed size and shape. The basin perimeter computed is km. Hack (957) found that for a large number of basins, the stream length and basin area are related by a simple power function, which is calculated as 6.79 for the study area. Form Factor Ratio (Rf) is the dimensionless ratio of the basin area to the square of basin length (Horton, 932) and Rf shows the shape/outline of a drainage basin and provides information about stream discharge behaviors. Smaller the values of Rf, more elongated will be the basin. The Rf value would always be less than for a perfectly circular watershed. The Rf values in the study area have an average of 3.92 indicating that the watersheds are more or less circular in shape with higher peak flow for shorter duration. Shape factor (Sf) of the basin is ratio between square of mean length of basin and basin area (Horton, 932). Sf for the watersheds under present study is According to Schumm (965), elongation ratio ( ) is defined as the ratio of diameter of a circle of the same area as the basin to the maximum basin length. is the ratio between the diameter of the circle of the same area as the drainage basin and the maximum length of the basin. A circular basin is more efficient in run-off discharge than an elongated basin (Singh, 967). The value generally varies from 0.6 to.0 associated with a wide variety of climate and geology. Values close to.0 are typical of regions of very low relief, whereas that of 0.6 to 0.8 are associated with high relief and steep ground slope (Strahler, 964). ' ' values in the present sub-watersheds varies from 0.63 to.2 which fit to Strahler s ranges indicating high infiltration rate. Chorley (957) expressed the lemniscate s (k) value to determine the slope of the basin. The k value for the watershed is 0.29, which shows that the watershed occupies the maximum area in its regions of inception with large number of streams of higher order. Strahler, 964 and Miller, 953 used the circularity ratio (Rc) represent watershed out line, a dimensionless value measured quantitatively. Rc is defined as the ratio of watershed area to the area of a circle having the same perimeter as the watershed and it is pretentious by the lithological character. Miller (953) has described the basin of the Rc values range 0.4 to 0.5, which indicate strongly elongated and highly permeable homogenous geologic country. The 'Rc' values for the watersheds has 0.6 indicating that all the watersheds are of less circular in shape, low to moderate relief and a few structurally controlled drainage systems. The mean basin width (Wb) is ratio of basin area devided by mean basin length which is measured to be 7.85 km on an average. As per Melton (957), the ratio of main channel length to the length of the watershed perimeter is fitness ratio (Rf), which is a measure of topographic fitness. The Rf for watersheds studied is According to Gravelius (94) compactness 80

8 coefficient (Cc) of a watershed is the ratio of perimeter of watershed to circumference of circular area, which equals the area of the watershed. Table 2: Areal morphometric parameters of the study area. Parameter Total basin area (A) Square kilometers Form Factor(Rf) Elongation Ratio ( ) Lemniscate's Ratio (Lr) Mean Basin Width (Wb) Relative Perimeter (Pr) Lemniscate s (k) Shape Factor (Sf) Circularity Ratio (Rc) Circularity Ration (Rcn) Compactness Coefficient (Cc) Fitness Ratio (Rf) Elipticity index(e) Length Area Relation (Lar) Wandering Ratio (Rw) Channel Width (Cw) meters Formula WS I WS II WS III WS IV Avge. Ref. GIS Rf=A/Lb =2* ( (A/Π/Lb)) Lr=L 2 /4A Wb=A / Lb Pr=A / P k=lb 2 / A Sf= Lb 2 / A Rc=4Π * (A /P 2 ) Rcn=A/P Cc=0.284 * P /A Rf= C/ P E=ΠL 2 /4A Lar=.4 *A 0.5 Rw= Cl / Lb Cw= 0.8( A) The Cc is independent of size of watershed and dependent only on the slope. Cc in study area is computed to be.5. According to Smart & Surkan (967), wandering ratio (Rw) is defined as the ratio of the mainstream length to the valley length. Valley length is the 8

9 straight-line distance between outlet of the basin and the farthest point on the ridge. In the present study, the Rw of the watersheds is Drainage texture analysis Drainage characteristics are primarily related to local and regional lithology and major structures in the area. Drainage texture analysis includes calculating certain parameters described in the following sections and parameters calculated are listed in Table Drainage Pattern (Dp) In any watershed, the drainage pattern (Dp) is influenced by slope, lithology, structure and stage of cycle of erosion. Longer the duration of a drainage basin, more easily the dendritic pattern is formed. Dendritic to sub-dendritic pattern is most common in fairly homogeneous country and is controlled by the underlying geologic structures and it holds well in the study area (Howard, 967). An incipient trellis pattern is also observed, which is developed due to lineament control in the watershed II. Drainage texture (Dt) is total number of stream segments of all orders per perimeter of that area (Horton, 945) and is one of the important geomorphological concept and reflects the relative spacing of drainage courses and dependent on the underlying lithology, infiltration capacity and relief aspect of the terrain. As per Smith s (950) classification, the study area has an average Dt of 9.62 indicating very fine drainage texture. Table 3: Drainage textural analysis of the study area. Parameter Formula WS I WS WS WS IV Avge. Ref. II III Drainage Dt = Nu / P Texture (Dt) Drainage Dd=Lu/A density (Dd) Drainage Di=Fs / Dd Intensity (Di) Drainage Dp=L+L2-Ln Pattern (Dp) Constant of Cm=/Dd channel maintenance (Cm) Infiltration Number (If) If=Fs * Dd Drainage density (Dd) is the stream length per unit area in region of watershed (Horton, 945, Strahler, 952 and 958; Melton 958a) is another element of drainage analysis. Dd is a better quantitative expression to decipher the degree of dissection and genesis of landform, although climate, lithology and structures and regional relief history also influence the morphogenesis. The Dd has been computed to be.95 km/km2 (Table 3) indicating moderate drainage densities and that the basin is endowed with moderate permeable sub-soil. Faniran (968) defines the drainage intensity (Di), as the ratio of the stream frequency to the Dd. This low value of drainage intensity implies that Dd and Sf have little impact on the extent to which the surface has been lowered by agents of denudation. This study shows a 82

10 low Di of.85 for the watershed. The low values of Dd, Sf, Di indicate that surface runoff is not quickly removed from the watershed, making it highly susceptible to flooding and gully erosion. Schumm (956) used the constant of channel maintenance (Cm) or the inverse of Dd as a property of landforms. The Cm indicates the relative size of landform units in a drainage basin and has a specific genetic connotation (Strahler, 957). The Cm indicates the number of km 2 of basin surface required to develop and sustain a km long channel. In the study area average Cm of all the four watersheds is 0.52 km 2 /km. The infiltration number (If) of a watershed is defined as the product of Dd and Sf and provides an idea about the infiltration characteristics of the watershed. The higher the If value, the lower will be the infiltration and the higher run-off. The If for the study area is calculated to be 5.48 indicating higher values. 4.4 Relief parameters Difference in the elevation between the highest point of a watershed and the lowest point on the valley floor is known as the total relief of the river basin (Ht). The relief ratio may be defined as the ratio between the total relief of a basin and the longest dimension of the basin parallel to the main drainage line (Schumm, 956). Schumm established a relation between relief ratio and hydrologic behavior and found that sediment loss per unit area is closely correlated with relief ratios. In the study area, the value of relief ratio is 0.0. It has been observed that areas with low to moderate relief and slope are characterized by moderate value of relief ratios which are mainly due to the resistant granitoid basement rocks and low degree of slope. General relief image of the study area is shown in Figure 4 which shows mostly plains and parameters calculated are listed in Table 4. Figure 4: General relief of the study area. Relative relief (Rh) is the difference between the highest and the lowest point in a spatial unit and plays an important role to understand the morphological characteristics of terrain, degree of dissection and denudational characteristics of the watershed, which together control the stream gradient, thereby influencing the flood pattern (Hadley and Schumm, 96). Rh has no significance in the watersheds studied as ~90% of the study area has extremely low to 83

11 moderately low relative relief (Figure 3). Strahler s (968) ruggedness number (Rn) is the product of the basin relief and the Dd and combines slope steepness with its length. Table 4: Relief morphometric parameters of the study area Parameter Starting Height of Stream (Z) meters Height of Basin Mouth (z) meters Basin Perimeter Height Max.(H) kilometers Basin Perimeter Height Min. (h) kilometers Total Basin Relief (Ht) meters Absolute Relief (Ra) meters Relative Relief Ratio (Rhp) Relief Ratio (Rh) Dissection Index (Dis) Gradient Ratio (Rg) Melton Ruggedness Number (MRn) Relative relief (Rr) meters Ruggedness number (Rn) Formula Google Earth WS I WS II WS III WS IV Avge. Ref Ht = Z-z z-mean Sea Level Rhp = H * 00 /P Rh = (Hh)/ Lb Dis = H / Ra Rg= (Z - z) / Lb MRn = Ht / A 0.5 Rr = H- h/lb Rn= Dd*H

12 Calculated accordingly, the watersheds studied in this study have an average Rn of The low Rn value of watershed implies that area is less prone to soil erosion and have intrinsic structural complexity in association with relief and Dd. The Melton Ruggedness Number (MRn) is a slope index that provides specialized representation of relief ruggedness within the watershed (Melton 958b). The study area has an MRn of Dissection index (Dis) is a parameter implying the degree of dissection or vertical erosion and expounds the stages of terrain or landscape development in any given physiographic region (Singh and Dubey, 994). On average, the values of Dis vary between 0 (complete absence of vertical erosion and prevalence of flat surface) and (vertical cliffs/escarpment on land or at seashore). Higher the value of Dis, larger is the undulation and instability of the terrain and more is the degree of erosion leading to large amounts of sediment debris. It expresses the relationship between the vertical distance of the relief from the erosional base and relative relief, which explains surface geodynamics. Dis value of the study area is 0.62, which indicates the watershed is a moderately dissected. Table 5: Slope characteristics of the study area Parameter Formula WS I Contour interval (Cin) meters Total contour length (Ctl) kilometers Area between two successive contours (Ac) Square kilometers Length of two successive contours (L+L2) kilometers Average Slope Width of Contour (Swc) Channel Slope (Cs) % Clinographic Analysis (Cga) Average slope (S) % Mean slope of overall basin (θs) WS II GIS 50 WS III WS IV Avg GIS GIS GIS Swc=Ac /{(L+L2) / 2} Cs=(Ht/ Cl )*00 Tanθ=Cin/Sw c S= (Z*(Ctl/H))/( 0* A)) θs =(Ctl- Cin)/A Ref Gradient ratio (Rg) is an indicator of channel slope, which enables assessment of the runoff (Sreedevi, 2004). The watersheds in the study area have an Rg of 0.0, which reflects the 38, 39 85

13 subtle mountainous nature of the terrain. Some slope parameters are shown in Table 5. Similar to the relation between area and altitude, there is a relation between the ground slope and altitude. This is brought out by construction of clinographic curves from hypsometric data. Out of the many methods available for clinographic analysis, Strahler s (952) method was adopted. 4.5 Implications to stream sediment sampling In mineral exploration for commodities like kimberlite/diamonds, gold etc., reconnaissance starts with regional stream sediment sampling which needs to be pre-planned and later executed carefully to obtain successful results. It is most efficient to pre-select sample locations by plotting intended sites on a suitable scale toposheets. Morphometric assessment of watersheds in a study area provides useful information about drainage characteristics thereby giving information geomorphic-tectonic set up of the area (Reddy et al, 2004). A limited assessment of drainage and tributaries will produce information to solve problems in planning a stream sediment sampling programme enabling to interpret the impacts associated with upstream and downstream processes. A general summary of trap site conditions are interpreted based on certain morphometric parameters for the study area (Table.6). Watersh ed WS I WS II WS III Table 6: Morphometric parameters and terrain- trap site conditions. Sf Cw meters Morphometric parameters Terrain Trap Stream site S Rb ρ S.I. Dis Rg Rn Soil sedime conditi n nt on WS IV Generally speaking, flat country with or without mature rivers creates special problems and makes good quality sampling much more difficult hence loam sampling is recommended. If the gradient of a channel or the velocity of running water is small, a straight pattern is likely to be formed. On the other hand, if the gradient of a channel or the velocity of running water is large, a meandering pattern is readily developed. The gradient of a channel is in proportion to the sediment load and is inversely proportional to the water. The steeper the gradient of the channel, the larger is the diameter of sediment load. Consequently, the channel profile is concave-upward in general, i.e. the gradient of the channel becomes steeper toward the upper reach (Iware, 2004) which gives information of average channel width. Sinuosity index of the study area reveals that the streams belong to sinuous type indicating ability to form curvilinear streams thereby giving rise to accumulation of heavies at the stream-kinks. Also in moderate gradient streams as in the case of study area, with a low to moderate sinuosity of Brown, Resid ual Brown, Resid ual Black, Drifte d Brown, Resid ual Sand, Gravel Sand, Gravel, Clay, Silt Sand, Gravel Modera te Modera te Poor Good 86

14 .24, plane bed morphology may develop. Higher values of parameters like dissection index, ruggedness number, gradient ratio indicate the moderate to higher degree of erosion forming and generate considerable amounts of sediments, making favorable conditions for accumulation of heavy minerals. In the current study it is revealed that the dissection ratios indicate that the streams can form moderate to good trap sites which can be locales for kimberlite indicator mineral sampling. The dyke and vein systems cutting across the streams obstruct the sediment movement and these sites can act as favorable locales for heavy mineral accumulations. However trap site quality is governed in conjunction by other aspects like lithology, structures, climate etc. but not morphometry alone, an integrated understanding may help to arrive at positive results. Field observations indicated some inferences about general stream bed material that can be observed. In general gravel (0.5 to 2.5 inches) with moderate to high erodibility on banks when present as dominant component or as part of the bank materials, sand with high bank erodibility when present as part of the bank materials. Also silt/clay with soft-loose, non-cohesive silt has very high bank erodibility; while cohesive clays are relatively resistant to erosion. A more detailed investigation in relation to morphometric parameters and trap site quality in corroboration with field studies will give a comprehensive understanding of the geomorphologic set up. 5. Conclusions The morphometric analysis of watersheds of in parts of Wajrakarur Kimberlite Field was carried out through calculation of 64 linear, areal and relief morphometric parameters using GIS techniques in ESRI ArcGIS & MapInfo software. The studied watersheds show dendritic patterns with moderate drainage texture. The variation in stream length ratio might be due to change in slope and topography. The bifurcation ratio in the watershed indicates normal watershed category and the presence of moderate drainage density suggesting that it has moderate permeable sub-soil, and coarse drainage texture. The value of stream frequency indicate that the watershed show positive correlation with increasing stream population with respect to increasing drainage density. The value of form factor and circulator ration suggests that WKF watershed is less elongated to oval. The dissection index, gradient ratio, ruggedness number, sinuosity index values indicate moderate dissection, erodibility and show that the area can form moderate to good trap sites, which can be favorable for indicator mineral sampling. This attempt is probably first of its kind in using morphometry for streamsediment sample planning. Morphometric analysis of any basin may be considered as a preliminary step before planning and execution of heavy mineral/ indicator mineral or stream sediment sampling in mineral exploration for commodities like kimberlites or others. Acknowledgements The author is grateful to Mr. V.Krishnamohan Mr. D.Umasankar and Mr. A.Venu for facilitating manpower and software and encouraging in carrying out this work. Mr. T. Jayaram, Mrs. G. Jayalaxmi are thanked for GIS analysis and map preparations. Mrs.U.Jyothy is thanked for drafting the manuscript. Help received from Mr. NVN Suresh, Mr. G. Ramakrishna and Mr. G. Chandrasekhar is duly acknowledged. 6. References. Centamore, E., Ciccacci, S., Montedel, M., Fredit, P., and Lupia Palmieri, E., (996), Morphological and morphometric approach to the study of the structural arrangements of northeastern Abruzzo (Central Italy). Geomorphology, 6, pp

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