The lakes are the largest water body which is surrounded by land. The flowing river gets space in lower landform, and it becomes lakes. The lakes are formed by the earth movement, erosion, deposition, vulcanicity. Lakes are essential to recharge underground water, positively influence the water quality of downstream watercourse. The study is based on remote sensing and GIS techniques for assessing of the drainage basin/watershed which are used as a powerful tool for the manipulation and analysis of spatial information.

Lakes are the natural manifestation of nature, which is governed by geomorphology, geology, relief, rainfall, Land use and land cover, climate, slope, and the drainage system. Among the above-mentioned determinants relief plays a significant role in the formation of lakes. Generally, the higher the relief, greater the rainfall and greater the scope for the water accumulation. In contrast to this, the lower the relief greater the flow accumulation and greater will be the scope for the formation of lakes. 

Different inferences are possible to be drawn on the concentration of the lakes in a region. The extraction of lakes of 1993 is based on spectral water index, especially Normalized Difference Water Index (MNDWI) calculated from the green and shortwave -Infrared (SWIR) bands. From this point of view, the geomorphologic analysis of lakes has been done on the basis of the lake location and its Assemblage in relationship and influence with the local physical parameters which govern in its formation (origin) as well in its drying or vanish or extinction. Thus, this analysis was considered important. Lakes are the natural manifestation of nature which are governed by relief, rainfall, slope, geomorphology, geology, land use and land cover drainage system. Hence, all the parameters map is generated with the intersection of 1993 year lakes and results are analysed in detail.

Figure 1

Mid Cauvery river Basin is the largest sub Basin with the area of 57,280.98 sq.Km and comprising 86 watersheds. The mid Cauvery river Basin lies in Tamil Nadu and Karnataka. In Karnataka it covers Mysore, Chamarajanagar, Ramanagara Disrtricts. In the Mid segment of mid Cauveri river Basin, Kabini River and its tributaries flow. The main source of water in Mysore and Chamarajanagar District is Kabini River. In Chamarajanagar Districts water scarcity is increasing. To understand the causes of problems and its scenario, the mid segment of Mid Cauvery river Basin is selected as the study area of the research topic and it gains much more importance because it is the large river basin comprising Mysore and Chamarajanagar districts.

Kabini River is the main tributary of the Cauvery River. The location of the river basin is between 11⁰ 37' 10" to 12⁰ 50' 30" North latitude and 75⁰ 22' 25" to 76⁰ 58' 02" east longitude. It originates in the Pakramthalam hills of Wayanad district of Kerala state. The confluence of the Panamaram river and the Mananthavady river takes place at an elevation of 2140 mt. The length of the river is 230 km, and the drainage area is 7808sq. Km. Kabini river enters Karnataka and its channel path starts from Heggadadevanakote and flows through Hunsur, Nanjangud, Gundlupet, and Mysore. Nanjangud, Heggadadevankote taluks are drained 100% by kabini. The major portion of Mysore city drains towards Kabini river basin which accounts to 70% and only 30% by Cauvery River. The Kabini river takes its path towards southwest of Nanjangud that is up to Gundlupet and the main river cauvery flows north of Kabini and both flows eastwards and both join at Tirumakudalu Narasipura in Karnataka.

Figure 2

For the detail study of the Kabini River Watershed it is sub divided into five sub watersheds.

• Gundal Watershed

• Nugu Watershed

• Upper Kabini Watershed

• Mid Kabini Watershed

• Lower Kabini Watershed

Figure 3

The physiographic parameters considered in lake formation and vanish are the following. These parameters provide the clue to understand the reason behind its extinction. The following are the few chosen parameters. Assemblage of lakes based on relief, Assemblage of lakes based on rainfall, Assemblage of lakes based on Slope, Assemblage of lakes based on Geomorphology, Assemblage of lakes based on Drainage density.

Slope is a significant determinant in the formation of lakes. Generally, the gentle slope paves way for the formation of lakes. Secondly the lakes can also be formed in the steep slopes, provided if the land attains an abrupt gentle condition. Most of the lakes which are formed in the mountains come under this category. Slope determines the flow accumulation point. Obviously, the flow accumulation point will result in the formation of a lake.

In a river basin the survival of lakes is determined by the surrounding slope condition. Greater the gentleness of the slope greater the survivability of the lakes. Having said this, it is Not only by the slope but also the underlying bedrock and its aquiferous condition that also determines the life of the lake. Lakes formed due to Erosion have greater life than the lakes formed by deposition. The site of erosion always keeps the phase of erosion and keep the flow accumulation point intact, whereas in the case of deposition it is most uncertain. Therefore, most of the lakes are formed due to erosion. In the study area the upper regions with higher altitude are formed by erosion and in the case of the lower altitude with less rainfall and gentle slope are the result of the spring action added with flow accumulation. 

In the present study on the basis of the slope, the river basin has been categorized into five types, such as Nearly Level (0 - 1’), Most Gentle (1 - 2’), Gentle (2 - 3’), Moderate (3 - 5’) and Strong Slope (5 - 10’). 

Figure 8

Lakes formed under different slope conditions are an eye opener to the landform analyst. Because the true cause for the formation of lakes can be understood. Generally, lakes are highly prevalent in the plain lands rather than in the sloped land. In the study area the assemblage of lake is positive in correlation to the slope. Nearly gentle slope land possesses 540 number of lakes in the study area. This clearly indicates that the lakes are formed either due to the flow accumulation or due to spring action. 

The land possessing 1⁰ - 2⁰ slope, that is, mostly gentle category region holds 277 lakes in the study area.  The lakes formed at this condition of slope are formed due to the flow accumulation point. Nearly 94 percent of the lakes in the study area fall under the first two slope conditions. In the category of Gentle Slope 18 lakes have been formed. In the fourth category that is Moderate Slope condition there are 28 lakes; this is a clear sign of piedmont lake formation. The southern, south western and southeastern parts of Kabini river basin is covered by mountains.  The lakes that are formed in the strong degree of slope that is between 5⁰ - 10⁰ slope is a clear indication of tectonically influenced lakes or due to spring action. In the study there are 8 lakes formed in the Strong Slope category. 

Figure 9

Generally, lakes are highly prevalent in the plain lands rather than in the sloped land. 

Geomorphology plays a significant role in the formation of lakes. The type of landform decides the location and the origin of the lakes. Lake origin is a geomorphic process except in the glaciated regions and the volcanic crater lakes. The geomorphic agents active in the past determine the formation of the lakes. Similarly, for the vanishing of lakes the present geomorphic process and the prevailing climate influences. Undulating topography acts as a prime element in the origin of the lakes. The Geomorphology of the Mid Cauvery River basin is filled with undulating topography. Due to which the formation of lakes is more in number in this form of land. The minor geomorphological setups like the escarpments play a major role in the formation of the lakes. Understanding the role of geomorphology on the basis of its assemblage presents an interesting output.

Geomorphologic classification of the study area

Figure 10

In Gundal SW 142 lakes are formed in flood plain deposited land and it accounts for 58% of the Gundal SW total lakes. It includes 90 water bodies such as different streams, rivers and reservoirs. It accounts for 36.7 % of the total lakes of SW. in the active quarry region due to human intervention 6 lakes are formed. The Gundal reservoir sites had 7 lakes in 1993. The total number of lakes in Gundal are 245. It is possessing the second highest lakes based on Geomorphology in 1993.

In the Nugu SW, the highest no of lakes are formed in the Pedi plain region i.e., 26 lakes and it accounts for 49% of the lakes in the Nugu SW. In the pediment Pedi plain complex 19 no of lakes are formed and it accounts for 40% of lakes of this SW. In stream confluence and stream paths 3 lakes are assembled each. In moderately dissected denudational lower plateau 2 lakes are formed.

The Upper Kabini SW possess complex Geomorphology. It is highly elevated region with plateaus and valleys. In the Upper Kabini SW, 86 no of lakes are formed in Pedi plain and it accounts for 45% of the Upper Kabini SW. In the pediment Pedi plain, complex region 40 lakes are assembled and it accounts for 21% of the SW. In river valley 34 lakes are formed and it possess 18%. The stream confluence region possesses 2 lakes. In highly dissected denudational hills and valleys, highly dissected structural hills and valleys, moderately dissected denudational hills and valleys, low dissected denudational hills and valleys, active flood plain only one lake is formed respectively. The total no of lakes in Upper Kabini SW is 188 and based on Geomorphology, it possesses third highest no of lakes.

In the Mid Kabini SW the Pedi plain region comprises 69 no of lakes and it accounts for 71.1%. The highest no of lakes is formed in this region. In the pediment Pedi plain region 22 no of lakes are formed and accounts for 22.6%. In the unclassified waterbodies 6 lakes are formed.

In the Lower Kabini SW, the flood plain deposited land comprising the highest number of lakes within the Watershed and also total Kabini study area. There are 200 lakes and accounts for 70% of lakes. The other water bodies such as streams, river have supported the formation of 88 lakes. The total no of lakes in this SW is 53.

Drainage density is one of the key components in the formation of lakes. Higher the number of stream orders greater the scope for the formation of lakes. Drainage density is the length of streams in a channel per unit of drainage basin. It is also a sum of lengths of all the streams divided by the catchment area. In this connection the level of stream density in the watershed and the number of lakes should hold direct correlation. But if this relationship is missing and it is vice versa this indicates some strange development in the formation of the lakes. 

Drainage density= (Total Length of Channels/ Catchment Area)

Figure 11

Figure 12

In the Gundal SW, moderate drainage density possesses the high lakes i.e., 215 and it accounts for 87.75% of the Gundal SW. In low drainage density and high drainage density there are 15 lakes  in each. 

In the Nugu SW, 43 lakes are situated in moderate drainage density zones. It only accounts for 84% of the lakes of Nugu SW.

In the Upper Kabini SW 151 lakes are formed in moderate drainage density zones. It accounts for 80% of the lakes of Upper Kabini SW. In the high drainage density and very high drainage density just 7 lakes and 2 are formed in the SW.

In the Mid Kabini SW 82 lakes are formed in the moderate drainage density zone. It accounts for 84.53% and 15 lakes are situated at low drainage density and accounts for 15.4%. 

Lower Kabini SW possess the highest lakes i.e., 288. In the total 288 lakes the moderate drainage density zone has 263 lakes formed, and it accounts for 91.3 %. Only 25 lakes are situated at low drainage density zones and it accounts to 8.6%.

Land Use/ Land Cover (LULC) generally refers to the categorization or classification of human activities and natural elements on the landscape within a specific time frame based on established scientific and statistical methods of appropriate source materials. It has various type of LULC elements is there like Agriculture land, Forest land, built up rural, Built up Urban, Water bodies and many more.

Figure 13

In the Gundal Sub Watershed highest number of lakes are formed in the Agriculture cropland. 222 lakes are formed in this feature.

Geology is the determined element in the formation of lakes and ground water percolation. In the study of formation of lakes, the type of geology prevailing as the bed rock controls the percolation of water. Greater the porosity of the underlined bed rock, greater the scope for the storage of underground water. The surface bed rock itself happens to be non-porous in nature will not allow the water to percolate and where ever there are eroded depression are formed, those points becomes the seasonal lakes.

Suppose the catchment of area of the Sub watershed happens to be aquiferous in nature, this condition will positively impact on the flow hydrology from the higher altitude to lower altitude given scope for the formation of lakes at the lower altitude.

From this point of view, the distribution of Geological formations and the analysis of lake formation are important aspect of research in understanding the formation lakes.

Figure 14

The Gundal Sub Watershed possess lakes only in Peninsular Gneissic complex i.e. 245 lakes are formed in this Geological structure and it accounts for 28% of total lakes of the sub watershed.

Among the above-mentioned determinants, relief plays a significant role in the formation of lakes. Generally higher the relief, greater the rainfall and greater the scope for water accumulation at the lower level of the basin.  In this context, lower the relief, greater the flow accumulation and greater will be the scope for the formation of lakes. Greater the elevation, the number of lakes has decreased in its formation at the higher elevation. The study clearly envisages that, the elevation is the significant element in determining lake formation. As per research as a result of piedmont landform situation, the entire upper kabini sub watershed has become good place for flow accumulation from the higher rainfall region towards the lower rainfall zones, all through the watershed emerging into formation of lakes.

There is inverse relationship in the assemblage of lakes with respect to rainfall. Lakes are highly prevalent in the plain lands rather in the slope land. In the study the assemblage of lakes positively corelated with slope, 540 number of lakes are formed in 0-1 degree (nearly gentle slope). Based on geomorphology, highest number of lakes are formed in flood plain and Pedi plains of lower Kabini sub watershed. With respect to drainage density, highest number of lakes (80%) of lakes are formed in the moderate drainage density zone (0.8518054-1.645411). Geology plays major role in the formation of lakes and 778 lakes are formed in the peninsular Gneissic complex which is considered as the major geological structure of the basin. From this point of view, assemblage of lakes according to the relief, rainfall, geology, geomorphology, gradient and drainage network were considered as the prime factors determining the number of lakes at different locations.