usha chirala et al. / international journal of engineering

CORRELATION OF GEOMORPHOMETRIC PARAMETERS

FOR THE HYDROLOGICAL CHARACTERIZATION OF

MEGHADRIGEDDA WATERSHED, VISAKHAPATNAM, INDIA – A GIS

APPROACH

USHA CHIRALA†

Department of Geo-Engineering, College of Engineering, Andhra University,Visakapatnam-530003, India

Email: [email protected]

NOOKA RATNAM KINTHADA

Assistant Professor Department of Geoinformatics, School of Earth and Atmospheric Sciences

AdiKavi Nannaya University, Jayakrishnapuram, Rajahmundry-533105

East Godavari (District), India Email: [email protected]

MURALI KRISHNA GURRAM

COWI India Pvt. Ltd., Plot No. 121, Phase-I, Udyog Vihar

Gurgaon-122016, Haryana, India Email: [email protected]

ABSTRACT

Meghadrigedda, a non-perennial drainage system is one of the major water resource systems of Visakhapatnam city located in the north coastal part of Andhra Pradesh, India. The study was intended to present a two-dimensional approach to describe the properties of Meghadrigadda drainage morphometry at sub-basin level using GIS as a tool for the analysis. Both linear as well as aerial morphometry parameters were analysed and computed to reveal the morphometric aspects governing the Meghadrigedda basin area and understand the fluviatile activity of it’s drainage system. The morphometry parameters are computed using Horton, Strahler and Deju’s computations and the analysis has resulted in the prioritization and division of the entire watershed into nine sub-watersheds having a catchment area of about 368 km2, which includes the reservoir. Correlated analysis of the geomorphometric parameters established the interdependency and the degree of influence of each parameter on the remaining. The results helped the hydrological characterization of the watershed. Since, the catchment area has been witnessing a large scale anthropogenic activity due to urbanization, the outcome of the study will serve as a basis for the planning and development of a sustainable basin area. Keywords: Drainage Morphometry, GIS, Meghadrigedda, Watershed, Drainage Network

Usha Chirala et al. / International Journal of Engineering Science and Technology (IJEST)

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1. Introduction

Around 70% of India’s population is directly or indirectly dependent on agriculture based economy and availability of water resource is a prerequisite for it. According to a report published by the Central Water Commission (CWC) in 2001, the state of Andhra Pradesh is having a total number of 1157 watersheds, out of which 106 are over exploited and 79 are in deteriorating condition. It is understandable that, optimal utilization of the water resources is a key to the sustenance of the future economy. In this context, the importance of water has been recognized and greater emphasis is being laid on its economic use and better management. Drainage basin geometry is the result of various factors that reshape the topography of the region over a period of time. These factors influence the run-off, sediment, water discharge and also the nature of the pattern of stream channels in a drainage basin. Such factors include climate, topography, bedrock, soil type, and vegetation cover.. According to P. A. Allen and John R. Allen, 1990, these primary factors can be classified into autocyclic and allocyclic controls. Allocyclic controls include ‘climate’, which controls run-off or discharge and weathering of the parent rocks, and ‘tectonics’ which controls basin slopes and relief of hinterlands in the drainage basin. Proper understanding of rework of these elements gives insights into the characteristics of sediment discharge and water resource availability which in turn have far reaching impacts on the dependants. While it is essential to assess, record and measure these elements qualitatively and quantitatively, it may not be easy to do that directly all the times. In such scenario, analysis of drainage morphometry provides a bottom-up approach to unravel the influence and magnitude of the factors responsible for the outcomes. On the other hand, study of the drainage morphometry also plays a significant role in understanding the landform processes, physical properties of the soil and erosion characteristics. 1.1. Literature Review

Few studies have been conducted on Meghadrigedda, among them are studies conducted by Nageswara Rao and Narendra (2009 & 2006) to map and evaluate the impact of urban sprawl. They have also carried out a preliminary analysis of Meghadrigedda river watershed. In yet another study, Nageswara Rao, et. al. (2008) have also attempted to assess the ground water quality of Meghadrigedda watershed. Various studies have been carried out on drainage morphometry analysis and it’s significance in watershed modeling. Nooka Ratnam et. al. (2005) and Sujata Biswas et. al. (1999) have studied the drainage morphometry and it’s importance in prioritizing the watersheds and estimated the sediment yield. Other recent works include Chopra et. al. (2005)on morphometric analysis of Bhagra Phungotri and Hara Maja sub watersheds of Gurdaspur district, Punjab. Srinivasa et. al. (2004) morphometric analysis on sub watersheds of Pawagada area, Tumkur district, Karnataka.

2. Materials and Methods

2.1. Study Area

The study area lies in between the geographic coordinates of 830 00’ to 830 17’ of eastern longitudes and 170 42’ and 170 57’ northern latitudes and is bound by three administrative mandals (sub-districts) of Visakhapatnam district of Andhra Pradesh, namely, Sabbavaram, Pendurthi ,K.Kotapadu,and Kottavalsa mandal of Vizianagaram district. Visakhapatnam is the major city located in the study area and is also dependent on Mehadrigedda for it’s industrial, agriculture and domestic water use. (Fig 1).


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Fig. 1 Location Map of the Study Area

2.2. Details of the Reservoir

Mehadrigedda is an east flowing non-perennial river taking its rise in the eastern ghats at Nandikonda hill. It flows towards Rajapurajapeta village in S. Kota mandal of Visakhapatnam district then it turns south upto Karuvapuvanipalem village and thereafter it runs in the south-eastern direction and joins the Bay of Bengal near Ramapuvanipalem, Visakhapatnam. The reservoir was commissioned in the year 1979 with a storage capacity of 28.31m. Later, during the year 1989, the water withdrawal capacity of the reservoir was increased to 10.00 million gallons per day (source: Zilla PrajaParishad). Unlike the reservoirs constructed in the hilly terrain, Mehadrigedda is a typical shallow reservoir covering a large area. Even a meter thickness of sediment deposit in the bed causes the reduction of huge quantity of water storage. (Table 1), provides the details of the reservoir. Table1. Details of the Reservoir

Maximum water level of the reservoir + 20.33m Low water level of the reservoir +14.66m Daily drawal 10.00, million gallons per day Domestic usage 1.65 Mgd Industrial usages 8.35 Mgd Source: Zilla Praja Parishad, Visakhapatnam. The study area is criss-crossed by a major and minor network of the roads, among the prominent, the national highway 5 (NH 5), which connects Chennai and Kolkata, the other two important cities located in the east coast of India. The other major roads passing through the study area connect the Cities, Visakhapatnam - Anakapalli and Sabbavaram - Pendurti. The south eastern railway line connecting Visakhapatnam - Kottavalasa is passing through the northern part of the study area.


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2.3. Physiography

The areal extent of the entire study area is about 340.34 km2 which also includes the reservoir. Meghadrigedda, Naravagedda and Borramgedda are the three major ephemeral rivers which form the basin area. The area is covered by hill ranges of Eastern Ghats with steep slopes and deep gullies and is bounded by hill ranges elevated between 70 to 594 m above the msl. The most prominent hill ranges are the Narava and Yerrakonda. The study area is manifested mostly with deciduous dry and deciduous scrub vegetation types. The Narava RF and Yerrakonda RF are the two designated reserved forests that covered by the study area. The study area enjoys sub tropical climate conditions and the temperature ranges min. 140-200 C during the month of December and max. 330-420 C during May. The area receives rainfall mostly during June-December from both the southwest and northeast monsoon, and the annual average rainfall is 1110 mm. (Source: Zilla Praja Parishad, Visakhapatnam). The river rises to it’s peak during October-November months and inundates the surrounding low lying areas of Visakhapatnam city, due to the formation of cyclonic storms in the Bay of Bengal. Though, the area is manifested with innumerable number of minor tanks which do not however significantly reduce the flood peaks and their duration. Geologically, the area is composed of sedimentary metamorphosed rocks of the Archean system. These rocks have been intruded by granites, charconites and dolerites. The hill ranges are chiefly garnetiferous sillimanite gneisses (Khondalites). The area is characterized with brown and reddish sandy to loamy, lateritic and alluvium type of soils with less clay and humus content. They are medium to fine grained, essentially, non-clayey and are easily erodable on steep slopes during the heavy rainfall.

2.4. Methodology

Survey of India (SOI) topographic maps no.’s 65 O/1, 65 O/2 and 65 O/5 on 1:50,000 covers the entire study area. The SOI toposheets have been georeferenced and the drainage network has been demarcated as a vector layer in *.shp format. Stream ordering was done according to the rules given by Strahler’s (1964). Subsequently, morphometric parameters have been computed using various standard mathematical equations suggested by different renowned scholars. Processing and analysis of drainage network data was carried out using ArcGIS software.

2.5. Morphometry Analysis

Morphometry can be defined as the mathematical analysis and measurement of the surface, shape and dimension of the landforms. Morphometric analysis is a significant tool for prioritization of micro watersheds even without considering the soil map (Biswas et al., 1999). The correlation between geomorphic and hydrologic variables has been established since 1932 by several scholars under varied lithological and climatic conditions. Horton (1945) studied extensive investigation on drainage basins of stream systems and showed a mathematical relationship between morphometry, hydrology and landscape. Further, Strahler (1952, 1957, 1958) has carried out extensive investigation on the basis of Horton’s morphometric analysis of river drainage basins. Strahler and Smith (1950) have developed quantitative methods using new parameters of geological and climatic variations. Much impetus was given to Horton’s (1945) method of quantitative analysis of morphometric characteristics of drainage basins. Stream ordering is the first step to begin the morphometric analysis. Various scholars like Horton (1945), Strahler (1952), Scheidegger (1966) and Shreve (1966), have proposed different methods for stream ordering. The linear, aerial and relief aspects were studied using the methods of Horton (1932, 1945) Strahler (1952, 1964) Chorley (1957). The list of the mathematical formulae adopted for the analysis of Mehadrigedda drainage morphometry is given in (Table 3).


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Table3. Mathematical formula adopted for computation of morphometric parameters.

S # Morphometric Parameters Formula 1 Order of basin or stream segment µ 2 Number of streams of order ‘µ’ Nµ 3 Total no. of streams within the

basin of order ‘µ’ ENµ

4 Mean length of stream segments of order ‘µ’ Lµ/Nµ 5 Total stream length within a basin of order ‘µ’ Elµ 6 Mean length Total length of Streams / No. of streams 7 Stream length Lµ/ Lµ + 1 8 Form factor Basin Area / Length of the basin 2 9 Drainage density Dd = Lµ/Aµ 10 Stream frequency Fµ = Nµ/Aµ 11 Texture T = Fµ x Dd 12 Texture ratio Tµ = Nµ/P 13 Bifurcation ratio Nµ / Nµ + 1

3. Analysis and Discussion

Morphometric analysis has been performed in the GIS environment to identify the characteristics of various linear, aerial and dissecting parameters of the watershed. 3.1. Linear Aspects

The linear aspects include the stream order, stream length, stream length ratio and bifurcation ratio which have been calculated and mentioned in a table format (Table 8). Table 8. Morphometric characteristics of sub-watersheds

Order No. of streams

Length of streams (km)

Mean length (km)

Stream length ratio

Bifurcation ratio

a) Sub-watershed 1; Area = 27.4 km2, Perimeter = 24.5.km

N1 43 26.5 0.61 0.27 3.58 N2 12 7.3 0.60 0.25 4.00 N3 3 5.0 1.66 0.33 3.00 N4 1 6.0 6.0 -- -- -- -- -- Avg. = 2.21 Avg. = 0.28 Avg. = 3.52

b) Sub-watershed 2; Area = 43.8 km2, Perimeter = 45.5 km N1 76 57 0.75 0.25 4.0 N2 19 25 1.31 0.15 6.33 N3 3 5 1.66 0.33 3.0 N4 1 1 1.00 1.00 1.0 N5 1 12.5 12.5 1.00 1.0 N6 1 3.5 3.5 -- -- Avg. = 3.45 Avg. = 0.54 Avg. = 3.06

c) Sub-watershed - 3; Area = 19.55 km2, Perimeter =19.0 km N1 42 25 0.59 0.30 3.23 N2 13 13.5 1.03 0.15 6.50 N3 2 5.0 2.50 0.50 2.00 N4 1 2.0 2.00 -- -- Avg. = 1.53 Avg. = 0.31 Avg. = 3.91

d) Sub-watershed 4; Area= 31.55 km2, Perimeter = 25.0 km N1 56 42.5 0.75 0.30 3.29 N2 17 16.5 0.97 0.17 5.66 N3 3 2.5 0.83 0.33 3.00 N4 1 7.5 7.5 -- -- Avg. = 2.51 Avg. = 0.26 Avg. = 3.98


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e) Sub-watershed 5; Area=11.0 km2, Perimeter = 14 km N1 18 12 0.66 0.27 3.6 N2 5 7 1.40 0.40 2.5 N3 2 3 1.50 0.50 2.0 N4 1 1 1.0 -- -- Avg. =1.14 Avg. =0.39 Avg. =2.7

f) Sub-watershed 6; Area = 56.52 km2; Perimeter = 32 km N1 116 37.5 0.32 0.29 3.41 N2 34 23.5 0.69 0.26 3.77 N3 9 12.5 1.38 0.22 4.50 N4 2 7.5 3.75 0.50 2.0 N5 1 4.5 4.50 -- -- Avg. = 2.12 Avg. = 0.31 Avg. = 3.42

g) Sub-watershed 7; Area = 86.10 km2; Perimeter = 35 km N1 204 175 0.85 0.26 3.70 N2 55 51.5 0.93 0.18 5.50 N3 10 8.5 0.85 0.40 5.0 N4 4 15.0 3.75 0.25 4.0 N5 1 6.0 6.0 -- -- Avg. = 2.47 Avg. = 0.27 Avg. = 4.55

h) Sub-watershed 8; Area = 45.72 km2; Perimeter = 29.5 km N1 119 75 0.63 0.25 3.96 N2 30 21.5 0.71 0.13 7.50 N3 4 6.0 1.5 0.50 2.0 N4 2 4.0 2.0 0.50 2.0 N5 1 6.0 6.0 - - Avg. = 2.16 Avg. = 2.16 Avg. = 3.86

i) Sub-watershed 9; Area =18.7 km2, Perimeter = 27.5 km N1 18 12.5 0.69 0.27 3.6 N2 5 3.0 0.6 0.25 5.0 N3 1 5.0 5.0 1.00 1.0 N4 1 3.0 3.0 -- -- Avg. = 2.32 Avg. = 0.50 Avg. = 3.2 3.1.1. Stream Order and Runoff (or) Discharge

Stream ordering is the first step in drainage basin analysis. Several scientists have attempted to formulate a methodology for stream ordering, but the work of Horton (1932, 1945) marked the beginning of the wide spread use of channel ordering systems in geomorphology. However, Strahler’s (1952) method of stream ordering has been considered for this work as it is the universal application of stream order. It has been identified that, the number of the streams in the 2nd order is less than the 1st order and more than that of the 3rd order and so on and so forth. The entire watershed has been divided into nine sub basins and the results have been computed for all parameters for each basin. It is found that, 6th is the maximum order obtained in the basin which can be seen in the second basin. It is also noticed that, more number of 1st and 2nd order streams are mostly confined to hilly terrains composed of hard rock substrata located towards northern, eastern and western parts of the basin. Stream orders and prioritization of sub-watersheds can be seen in (Fig. 2).


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Fig. 2 Drainage and Sub-watershed Map


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Fig. 3 Drainage Density Map


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Fig. 4 Map showing the distribution of hydromorphic units in the Meghadrigedda watershed.

3.1.2. Stream Length (Lµ)

Stream Length (Lµ) is a significant hydrological property of the basin which reveals the surface runoff characteristics. Lµ has been computed for all the sub-basins of the watershed based on the mathematical equation proposed by Horton (1945). Stream number, their corresponding lengths and means in the basin are given in (Table 4 and Table 5), respectively.


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Table 4. Stream numbers and their lengths.

Sub-basin N1 L1 N2 L2 N3 L3 N4 L4 N5 L5 N6 L6 1 42 26.5 11 7 3 5 1 6 -- -- -- -- 2 76 58 17 2 3 5 1 1 1 12.5 1 3.5 3 42 25 13 13.5 2 5 1 2 -- -- -- -- 4 56 42.5 17 16.5 3 2.5 1 7.5 -- -- -- -- 5 18 12 5 7 2 3 1 1 -- -- -- -- 6 116 37.5 34 21.5 9 11 2 7.5 1 4.5 -- -- 7 204 17.5 55 51.5 8 8 4 15 1 6.0 -- -- 8 119 75 30 21.5 4 6 2 4 1 6.0 -- -- 9 19 13 4 4 1 7.5 1 -- -- -- -- -- Table 5. Mean lengths (km) of various orders

Sub-basin 1st order 2nd order 3rd order 4th order 5th order 6th order 1 0.61 0.60 1.66 6 -- -- 2 0.75 1.31 1.66 1 12.5 3.5 3 0.59 1.03 2.50 2 -- -- 4 0.75 0.97 0.83 7.5 -- -- 5 0.66 1.40 1.50 1 -- -- 6 0.32 0.69 1.38 3.75 4.5 -- 7 0.85 0.93 0.85 3.75 6 -- 8 0.63 0.71 1.5 2 6 --

9 0.69 0.60 5 3 -- -- Table 6. Stream Frequencies

Sub-basin No.

Area (km2)

N1 N2 N3 N4 N5 N6 F1 F2 F3 F4 F5 F6 ENµ

1 27.4 43 12 3 1 -- -- 1.56 0.43 0.1 0.03 -- -- 2.12 2 43.8 76 19 3 1 1 1 1.73 0.43 0.06 0.02 -- -- 2.24 3 19.55 43 13 3 1 -- -- 2.19 0.66 0.1 0.05 -- -- 3 4 31.55 56 17 3 1 -- -- 1.77 0.53 0.09 0.03 -- -- 2.42 5 11 18 5 2 1 -- -- 1.63 0.45 0.18 0.09 -- -- 2.35 6 56.52 116 34 9 2 1 -- 2.05 0.6 0.15 0.03 0.01 -- 2.84 7 86.1 204 55 10 4 1 -- 2.36 0.63 0.11 0.04 0.01 -- 3.15 8 45.72 119 30 4 2 1 -- 2.6 0.65 0.08 0.04 0.02 -- 3.39 9 18.7 18 50 60 1 -- -- 0.96 0.26 0.05 0.05 -- -- 1.32 3.1.3. Stream Bifurcation Ratio (Rb)

According to Schumn (1956), the term bifurcation ratio may be defined as the ratio of a number of a given order Nµ to the number of streams to the next highest order ‘Nµ + 1’. The bifurcation ratio is the antilogarithm of the regression of logarithm of number of streams to stream order (Morisawa 1962). Rb values in the study range from 2.7 to 4.5. The differences in Rb values can be attributed to geological and lithological development of the drainage basin (Strahler 1964). Higher Rb values indicate for a strong structural control in the drainage pattern, whereas the lower values indicate that the sub-basins are less affected by the structural disturbances (Strahler, 1964). Rb values have been computed for all the sub-basins in the watershed and the results are given in (Table 8). 3.2. Areal Aspects

It is defined as the total area projected on a horizontal plane, contributing overland flow to the channel segment of the given order including tributaries of lower order. The factors associated with the basin area are length of the stream, lithology, degree of slope, stream frequency, drainage density and rainfall of the area. The drainage basin shape is instrumental in governing the rate at which water is supplied to the main streams and proceeds to the outlet.


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3.2.1. Area (Aµ)

The area of a basin of order ‘µ’ is defined as the total area projected upon a horizontal plane, contributing overland flow to the channel segment of the given order and including all tributaries of lower order. The total area of the Mehadrigedda drainage basin is computed as 347.29 km2. Areas of each sub-basin of the watershed and their perimeters are shown in (Table 4). 3.2.2. Perimeter (P)

Perimeter is the length of the boundary of the basin which is drawn from the toposheets and is measured in the GIS environment. It is measured that, Mehadrigedda has a basin perimeter of 192 km. 3.2.3. Drainage pattern and its significance

Varying degrees of the slope and rock resistance of the surface of a region will determine the patterns and form of the streams of specific character. Study of drainage patterns may also reflect the original slope, structure, the successive geomorphic episodes that led to the transformation of the surface, including the geomorphic events, such as, uplift depression, titling, warping, folding, faulting and jointing as well as deposition by the sea glaciers, volcanic winds and rivers etc. (Zernitz, 1932). According to Zernitz (1932), various types of drainage patterns found in nature can be broadly categorized into dendritic, rectangular, parallel, trellis, annular and radial. The analysis has shown that, Mehadrigedda drainage network is predominantly of dentritic pattern. Dentritic pattern is found in regions where rocks offer uniform resistance in a horizontal direction. This pattern is found mostly in the hilly regions of the watershed. 3.2.4. Drainage density (Dd)

‘Dd’ represents the length of stream channels per unit area in the watershed. ‘Dd’ is controlled by the lithology underneath the basin area. ‘Dd’ aids in measuring the fineness of the basin topography. In quantitative geomorphology, ‘Dd’ is used as one of the essential parameter for the study of drainage basin. The other parameters include (a) nature of drainage (b) shape of the basin and (c) relief, slope and aspect. High ‘Dd’ is related to steep slopes and higher average relief. Therefore, normally, mountainous regions will have a high ‘Dd’ values. High drainage density values indicate for high precipitation and runoff volume. Thus, it can be inferred that, the areas with more ‘Dd’ values are more prone to flooding. Drainage is nearly zero in permeable basins with high infiltration rates. Low drainage density indicates relatively long flow of surface water. ‘Dd’ is generally calculated for each grid of the basin area and according to Deju (1971), type of ‘Dd’ of the region can be categorized as poor, medium and excellent as given in (Table 2). Table 2. Deju’s Drainage Density Classification

Density Range in km Poor 0.5

Medium 0.5-1.5 Excellent 1.5 From the drainage density map (Fig. 2), it is inferred that the Mehadrigedda basin is having an excellent drainage density and the chances of soil erosion is more in these areas. Drainage density of the area is calculated by using the formula ∑ L µ /Aµ and the values are given in (Table 7). 3.2.5. Stream Frequency (F)

The total number of stream segments of all orders per unit area is known as stream frequency (Horton, 1932). The study resulted in the stream frequency values varying from 1.36 - 3.18. F = Nµ / Aµ = Number of streams / Area of the Basin.

3.3. Dissection Properties

Various basin dissection parameters were analysed for the prioritization of sub watersheds. The details are given in the Table 7.


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3.3.1. Form Factor (Ff)

The form factor is a quantitative expression of drainage basin outline form (Horton 1945) which is a dimensionless ratio of basin area ‘Aµ’ to the square of basin length ‘Lb’, thus Ff = Aµ / Lb

2 (i.e., Area of the basin / Length of the basin2). If the ‘Ff‘ value of the basin is larger - the basin will have a circular form; and if the value of ‘Ff‘ is smaller - then the basin will have an elongated form. The analysis has inferred that the ‘Ff‘ values of the Mehadrigedda watershed range from 0.12-0.44. (Table 7).

Table 7. Basin geometry and dissection properties of various sub-watersheds

Sub- Basin

Aµ Lµ P Re Ff Dd Tµ T F Ac

1 27.4 10 24.5 0.87 0.27 1.63 2.40 3.48 2.15 2.18 2 43.8 19 45.5 0.73 0.12 2.37 2.21 5.45 2.30 0.26 3 19.55 7.5 19.0 0.83 0.34 2.32 3.05 6.86 2.96 0.68 4 31.55 10 25 1.00 0.31 2.18 3.06 5.31 2.44 0.63 5 11.0 5.0 14 0.70 0.44 2.09 1.85 4.93 2.36 0.70 6 62.07 11.0 32 1.79 0.51 1.37 5.06 3.56 2.60 0.76 7 86.10 16 35 1.71 0.33 2.97 7.82 9.44 3.18 0.88 8 45.90 10.62 29.5 1.37 0.40 2.45 5.28 7.71 3.51 0.71 9 18.25 10 23.0 0.58 0.18 1.28 1.08 1.74 1.36 0.43 Area ( Aµ), Stream Length (Lµ ), Perimeter (P), Elongation Ratio (Re), Form Factor (Ff), Drinage Density (Dd), Texture Ration (Tµ), Texture (T), Frequency (F), Circulatory Ratio (Ac)

3.3.2. Basin Elongation Ratio (Re)

The shape of any basin is expressed by an elongation ratio which is the ratio of diameter of a circle having same perimeter to the maximum length of the basin (Schumm, 1956). The discharge characteristics of any watershed are controlled by the elongation ratio. Normally, for a variety of geological and climatic types, this ratio ranges between 0.6-1.0. As the relief increases, will so the discharge and surface runoff, while it decreases the basin elongation ratio. The study area has shown the elongation ratio values between 0.58-1.71(Table 7). 3.3.3. Circulatory Ratio (Ac)

It is a shape measured related to stream flow. Circulatory ratio is the ratio of the basin area ‘Aµ’ to the area of the circle. ‘Ac’ is having the same perimeter as that of the basin (Miller 1953). Ac = Aµ * 4 /P2

The property of ‘Ac’ is that, it controls the discharge of the watershed. It is noticed that, ‘Ac’ readings of Mehadrigedda watershed range from 0.26-2.18, (Table 7).

3.3.4. Texture (T)

Texture is defined as the average size of the units composing in a given topography (Johnson 1933). Thus texture of topography is synonymous with stream frequency. The texture of the rock commonly depends upon vegetation type and climate (Dormkamp and King 1970).The drainage texture can be expressed by equation Smith (1950). Mathematically the Texture is expressed as T = Fµ * Dd Where Fµ = Drainage topography; Dd = Drainage density The texture values obtained for each sub-basin is given in ( Table 7). 3.3.5. Texture Ratio (Tµ)

Tµ is the number of crenulations on a contour having the maximum number within the drainage basin to the length of the perimeter of the basin. The study reveals that this new approach is very fast in dealing with the morphometric conditions of a region. Texture Ration ‘Tµ’ is given as Tµ =Nµ / p Where ‘Nµ’ is the number of streams of order ‘µ’; ‘P’ = perimeter of the basin. Texture ratios obtained for each sub-basin is given in (Table 7).


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3.3.6. Correlation Analysis of Drainage Morphometric Characteristics

To study and understand the degree of dependency and influence of each of the morphometric parameter of the watershed, a 2-dimensional matrix (Table. 9) have been generated to see the correlation and proportional influence of the aspects which determines the behavior of the basin as a whole. The 2-dimensional matrix and the results provided in the table suggests that, most of the drainage morphometric parameters of the Meghadrigedda watershed are in fact showing a positive correlation with each other which means that these parameters are interdependent on one on another, except in few cases where various factors plays a major role in making them independent. Table 9. Correlation analysis of geomorphometric parameters

Aµ Lµ P Re Ff Dd Tµ T F Ac Aµ 1 0.78 0.84 0.88 -0.07 0.37 0.76 0.40 0.36 0.07 Lµ 1 0.99 0.44 -0.30 0.06 0.26 -0.05 -0.17 -0.33 P 1 0.54 -0.28 0.09 0.35 0.01 -0.08 -0.30 Re 1 0.15 0.38 0.94 0.55 0.66 0.28 Ff 1 0.36 0.25 0.33 0.43 0.36 Dd 1 0.55 0.92 0.69 0.45 Tµ 1 0.76 0.84 0.50 T 1 0.90 0.62 F 1 0.71 Ac 1

For instance, the area (Aµ) parameter of the basin have shown very positive correlation with remaining parameters, except with ‘form factor’ which means that most of these parameters are some way or other influenced by the area of the basin and they share a direct proportional relationship. In case of stream length ratio (Lµ), it has shown a very strong correlation with basin perimeter (P) which indicates that both are interdependent. It means that, stream length ration is directly proportional to the perimeter and in other words the more the stream length ratio the more will be the basin perimeter. It is also observed that, the basin perimeter is also having some positive correlation with the parameters like elongation Ratio (Re), drainage density (Dd), and texture ratio (Tµ), while it has shown a negative correlation with the remaining parameters indicating that, it is independent of these factors. Basin perimeter (P), which is also one of the most influencing factors, however shown positive correlation with some of the morphometric factors like Elongation Ratio (Re), Drainage Density (Dd), Texture Ratio (Tµ), and Texture (T) and it has shown negative correlation with other remaining factors. Elongation ratio (Re), which determines the shape of the basin and controls the discharge throughput in the basin has shown a complete positive correlation with all the other drainage morphometric parameters which indicates that it has certain degree of influence over all the remaining parameters. Form Factor (Ff), which determines whether a basin is circular or elongated in shape has also shown a positive correlation with the remaining parameters. All other parameters like, drainage density (Dd), Texture Ratio (Tµ), Texture (T), Frequency (F) and Circulatory Ratio (Ac) have demonstrated a strong degree of positive correlation with their


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peer parameters, indicating that they are all interdependent and some way or other have been influenced by one on another. In a nutshell, the study of the correlation on 2-dimensional matrix has clearly shown the pull and push nature of the drainage morphometric parameters on one on another. Though, it is possible to study and evaluate each individual parameter separately and the drainage morphometric parameters seem to be independent of each other, but in reality they are closely netted and have a strong control over the other. This inadvertently indicates that, any change occurred to one of the factors is detrimental to another thus one needs to be very careful in assessing the influence of these parameters in characterizing the behavior of the basin. 4. Evaluation of Hydromorphological Conditions

Geomorphometric analysis of the Meghadrigedda watershed also helped in the accurate delineation and mapping of hydromorphological conditions of the study area. Based on the results obtained from various morphometric parameters and through various field investigations, it has been identified that the study area is characterized with various hydromorphological units, such as, structural hills, inselbergs, residual hills, pediment zone, pediment, buried pediment shallow, buried sediment moderate and flood plain were identified and mapped. The distribution of hydromorphic units in the watershed area has been mapped (Fi. 4). The map clearly brings out the various geomorphological units in detail. The Meghadrigedda reservoir as well as the numerous tanks, shown in blue, occupy a prominent place as be expected. The other striking features in the map are structural hills shown in all around the watershed. Subsequently, the areal distribution and percent area coverage of each hydromorphic units have been computed and presented in the Table 8. As it can be seen from the hydromorphic unit wise classification map, majority of the Meghadrigedda watershed area is covered by buried pediment moderate class covering an area of 124.52 km2 with a total cover of 33.9%, followed by the floodplain which accounts for about 25.9% of watershed area housing 29 villages occupying an area of 95.29 km2. The remaining area is covered by various hydromorphic units, such as, buried sediment shallow with 11.74%, structural hills with 11.3%, inselbergs/residual hills with 10.3% and pediment with 6.89% area respectively. 5. Conclusion

The morphometry analysis and subsequent correlation analysis of the Mehadrigedda watershed has revealed that, it represents the dendritic to sub-dendritic drainage pattern with a moderate texture. The variation in stream length ratios and stream bifurcation ratios of the sub-watersheds indicate that they have normal basin category while the low drainage density suggests the presence of highly permeable sub-soil and coarse drainage texture. The values of stream frequency indicate that, all the sub-basins show positive correlation with increasing stream population. The values of form factor and circulatory ratio suggest that the basin is elongated while the sub-basins are in circular form. Correlated analysis of the geomorphometric aspects highlighted the significance of such analysis in establishing the degree of influence and interdependency of each parameter on another. Study on Mapping of hydromorphic units and their spatial distribution helped in understanding erosion susceptibility and water potentiality zones of the watershed. The study demonstrates the effective use of GIS for geomorphometry analysis, prioritization of the sub-watersheds of Mehadrigedda watershed. Results of the morphometric analysis also revealed that the sub-watersheds have varying degrees of erosion intensity. Hence, suitable soil erosion control measures are required for these sub-watersheds to prevent any further erosion activity.

6. Acknowledgements

We sincerely thank Prof. V. Venkateswara Rao of Department of Geo-Engineering, Andhra University and the staff of INRIMT, Hyderabad for their support during the work.

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