Lakes and Wetlands

Copyright © 2015 by S. Vasudevan, T. Ramkumar, R. K. Singhal, A. Rajanikanth, G. Ramesh.

ISBN:      Softcover      978-1-4828-4545-7

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CONTENTS

Preface

L akes and wetlands play a vital role as freshwater resources for drinking

water, agricultural water, and industrial water. They include saline waters and serve for fishery resources and for recreational activities. They act as a shield against natural disasters, like floods (protecting downstream areas), droughts, and tsunami, and serve as sinks for sediments and contaminants. In developing countries, lakes and wetlands are often centres of livelihoods for small-scale local fishers as well as a base for much larger fishing operations. Despite knowing their environmental, social, and economic significance, these water bodies are being continuously ignored. In recent years, however, there is growing concern especially in developing countries about the degradation of lake and their basin environments caused by inappropriate management. Facts and figures of the recent knowledge and issues pertaining to the sustainable development of lakes and wetlands in India are of paramount importance for appropriate management and prospect planning. Considering this alarming situation of negligence of these water bodies, this book intends to evaluate the fundamental concepts to processes involved with respect to the water bodies in India.

The determination of this book is to explore the treasures of lakes and wetlands. The topics are intended to discuss and augment the understanding of this fragile ecosystem. Essentially, all the familiar facts from basic to high-level research appear here. The important topics like morphometric characteristics, water quality, hydrogeochemical characteristics, impact of urbanization, hydrodynamics, tank rehabilitation, ecology, textural and trace element geochemistry, environmental-impact assessment, heavy metals in Indian mangroves, pollution threads to coastal wetlands, ostracod distribution, environmental implications of foraminifer distribution, and physico-chemical changes in the coastal environments form key subjects.

S. Vasudevan

T. Ramkumar

R. K. Singhal

A. Rajanikanth

G. Ramesh

Prabhat Semwal, Suhas Khobragade, C. P. Kumar, Sudhir Kumar, and R. D. Singh

National Institute of Hydrology, Roorkee 247 667 (Uttarakhand)

Email: [email protected]

ABSTRACT

M orphometric analysis of catchments helps in comparing the forms and processes of the catchments and sub-catchments and thereby helps in prioritization of the catchment for various purposes, such as soil and water conservation and soil erosion assessment. The present investigations have been carried out for the catchment of Sukhna Lake, Chandigarh, with the objective of determining the various morphometric characteristics, such as linear, areal, and shape factors. The morphometric analysis has been carried out using remote sensing and geographical information system (GIS) techniques. The special catchment map of Sukhna Lake prepared by the Survey of India, which has a scale of 1:25,000, has been used.

The catchment area has been further divided into six sub-catchments, and different morphometric parameters have been computed for the catchment as a whole, as well as for the various sub-catchments. Land-use andand-cover map, drainage map, etc. have also been prepared. The major land use in the catchment area is forest, which is about 76.44% of the total catchment area.

A total of 731 streams have been identified in the catchment; 565 of which are first order streams. The drainage pattern in the catchment is mainly dendritic to sub-dendritic pattern. The average drainage density is estimated to be 5.5 per square kilometres. The stream length ratios of different sub-catchments show an increasing trend from lower order to higher order, which indicates their mature geomorphic stage, except for the lower foothill and foothill villages. The mean bifurcation ratio value of the catchment has been estimated to be 4.89, which indicates that, in general, the geological structures are not distorting the drainage pattern. The relief ratios indicate that the various sub-watersheds lie between low to gentle slope and exhibit small ridges. Form factor and circulatory ratios indicate that the sub-catchments are mostly elongated in shape. The various morphometric parameters obtained for the catchment of Sukhna Lake shall be helpful for detailed analysis of rainfall run-off process as well as for erosion assessment and watershed prioritization for erosion control.

INTRODUCTION

Hydrological investigations on a lake involve analysis of the complex interaction between various physical processes and morphometric parameters of the lake and its catchment, including their interactions with atmospheric processes of inputs of energy and matter like radiation and precipitation. Many of the processes—for example, erosion and run-off from the catchment—are determined by the physical character of the catchment, such as its geomorphology and land use, besides depending upon the atmospheric processes like rainfall and evaporation. As such, for any scientific investigations, data on physical characteristics of the study area under investigation (such as morphometric data and hydro-meteorological data) are required. Morphometric data, in particular, are crucial for such investigations and form as the starting points for many investigations. Morphometric analysis deals with the measurement, quantification, and analysis of the configuration, shape, and dimensions of a landform (Clarke 1966).

Morphometric analysis of drainage basins not only provides an elegant description of the landscape but also serves as a powerful means of comparing the form and processes of drainage basins that may be widely separated in space and time (Easterbrook 1993). Quantitative morphometric parameters throw light on lithology and structural control of basin, relative run-off and recharge, erosion, and stage of development of the basin. Quantitative and qualitative analyses of the interrelationships of the morphometric parameters with other hydro-meteorological data have proven their importance in watershed prioritization for various purposes, such soil and water conservation and soil erosion assessment.

Use of morphometric studies for hydrological analysis was initiated by Horton (1940) and Strahler (1950). Due to their flexibility and accuracy in processing and analysing spatial information and ability to integrate information from the various sources, geographical information system (GIS) techniques are fast becoming very popular and a powerful tool for morphometric characterization and analysis of the catchments and drainage basins in recent times.

SIGNIFICANCE AND OBJECTIVES OF THE STUDY

The Sukhna Lake is a very significant lake of Chandigarh because of being an important tourist attraction and centre of recreation. As such, the lake also has some contribution to the economy of the region. However, the lake is in limelight in recent years for various problems being faced by it. High rate of erosion in the catchment and subsequent siltation of the lake, land-use changes in the catchment which caused decline in water availability, etc. are some of the major problems in the lake. Being located in the foothills of Shivaliks, the catchment of the lake is subjected to severe erosion, leading to heavy sedimentation of the lake.

For proper understanding of the problem of water availability, it is pertinent to carry out analysis of the rainfall run-off process in the catchment. Similarly, for controlling erosion in the catchment, it is necessary to identify the high-potential erosion zones in the catchment so that measures for conservation of soils in the catchment can be suggested and taken up. Such analysis needs data on morphometric characteristics of the study area. Although few scattered studies on siltation and ecology of Sukhna Lake have been reported in the past, detailed hydrological investigations have not been reported for the lake and its catchment.

Some historical morphometric data generated by past investigations are available for the study area; however, the reported data show discrepancy and significant variation. Some of the data are very old, inconsistent, or not adequate. Moreover, the lake and its catchment are undergoing variations from time to time on account processes, such as sedimentation in the lake, erosion, and land-use changes in the catchment. As such, many of the data available may not be accurate or relevant in today’s context. Therefore, the present investigations have been undertaken by the National Institute of Hydrology, Roorkee, to determine the various morphometric parameters for the lake catchment so that the same can be used for further detailed hydrological investigations of the system.

STUDY AREA

Sukhna Lake is located at Chandigarh at 30° 44' 8.5 to 30° 49' 3.6 N and 76° 48' 16.8 to 76° 53' 42.8 E at an elevation of 349.15 m AMSL. The lake is kidney-shaped. It is a man-made lake constructed in 1958 across the Sukhna Choe. The lake has a surface area of about 157.6 ha and a maximum storage capacity of 525.23 ha m. It is a shallow lake with a mean depth of 3.3 m. The lake is 2.32 km long and 1.06 km wide. The lake is significant from the point of view of recreation, tourism, and fisheries. India’s longest rowing channel (2,170 m long, 62.5 m wide, and 3 m deep) was constructed in the lake in 1988–1989 for holding the Third Asian Rowing Championship. The lake also serves as a sanctuary for a large number of birds. The lake was notified as wetland of national importance by Chandigarh administration in 1988. The lake has also been notified for conservation by the National Wetland Committee, Ministry of Environment and Forest, government of India.

The catchment area of the lake falls in the union territory of Chandigarh, Haryana, and Punjab (Grewal 2009). It is located in the foothills of the Shivalik hill ranges, which form part of the fragile Himalayan ecosystem called Kandi (Bhabhar) region. Geologically, the subsurface formation comprises of beds of boulders, pebbles, gravel, sand, silt, clay, and some kankar (www.chandigarh.nic.in). The catchment area is rugged terrain, and the soils are predominantly alluvial and sandy, embedded with layers of clay, and are highly susceptible to soil erosion (Singh 2002). As such, the water flowing into the lake is highly turbid. However, a number of soil conservation measures have been taken up in the catchment (Grewal 2009). The climate of the study area is humid subtropical in nature.

DATA AND METHODOLOGY

In the present study, morphometric analysis of the Sukhna Lake and its catchment has been carried out using remote sensing and geographical information system (GIS) techniques. The data have been processed using Erdas Imagine and ArcGIS (version 9.3). The special catchment map (toposheet) of Sukhna Lake prepared by the Survey of India, which has a scale of 1:25,000, has been used. This special toposheet map prepared by Survey of India was geo-referenced using ground control points (GCPs) with the root mean square error (RMSE) of 0.2, and the image was resampled by cubic convolution method. The digital elevation map (DEM) of the catchment area was prepared using topographic contours (10 m interval) and elevation points of the study area, digitized using Survey of India toposheet of 1:25,000 scale. The drainage map was prepared using digital elevation model, IRS P6 LISS-III data, and Survey of India toposheet.

The study area has been divided into six sub-catchments. The morphometric parameters have been determined for the catchment as a whole as well as for each individual sub-catchment. Land-use/land-cover map, drainage map, drainage order map, drainage density map, slope map, aspect map, etc. have also been prepared. The land-use/land-cover map of the catchment has been prepared using IRS P6 LISS-III satellite data. The land use has been classified using semi-unsupervised classification technique. The various results/maps obtained are presented and discussed in the section on results of morphometric analysis.

MORPHOMETRIC PARAMETERS

A number of parameters and indices exist for morphometric characterization of a landform. The parameters can be broadly divided into linear parameters, areal parameters, and shape parameters. The parameters may vary depending upon the landform as well as objective of the analysis. In case of the lake catchments, the important parameters may be basin and sub-basin shape and size, stream order, stream length, stream frequency, drainage density, drainage intensity, drainage pattern, etc. The catchment and sub-catchment shapes are determined by various shape factor indices, such as circularity ratio, elongation ratio, form factor, and basin perimeter. Other important parameters related to the catchments and sub-catchments are soil types, land use, slope, etc.

RESULTS OF MORPHOMETRIC ANALYSIS

Delineation of the Catchment and Sub-Catchments

In the present study, the lake catchment has been divided into six sub-catchments (sub-basins). The various sub-catchments are Kansal, Nepli, Naththawala, Ghareri, lower foothills, and foothill villages. These are shown in Figure 1.1. The details of the sub-catchments are given in Table 1.1.

Figure 1.1. Sub-catchments of Sukhna Lake catchment area.

Table 1.1 Sub-catchments in the Sukhna Lake catchment

It can be seen from Table 1.1 that Kansal sub-catchment, with an area of about one-fourth of the total catchment area, is the largest of all the sub-catchments while the Nepli sub-catchment has the highest parameter of 18.91 km.

Major Land Uses

The land-use/land-cover map of the catchment is shown in Figure 1.2. The catchment area has been broadly classified into five major classes, viz. forest, agricultural land, barren/open land, check dams, and ponds, and settlement. The total area covered by each land use and its percentage with respect to the total catchment area is shown in Table 1.2. As can be seen from Table 1.2, the major land use in the catchment area is forest (32.32 km² area), which is about 76.44% of the total catchment area, followed by barren/open land and agricultural land with 4.46 km² (10.58%) and 3.6 km² (8.54%) area respectively.

Figure 1.2. Land-use/land-cover map of the study area.

Table 1.2 Major land uses in the catchment

Note: The total area shown here varies marginally when compared to the one shown in Table 1.2 above on account of error of digitization of the IRS LISS III data.

Drainage Characteristics

Figure 1.3 shows the drainage map of the study area. The various drainage characteristics of the lake are discussed below.

Drainage Order and Drainage Pattern

Drainage order has been given to each drain following Strahler (1964) stream ordering technique, wherein the smallest fingertip tributaries are designated as first-order drain. When two first-order drains join each other, a second-order stream is formed and so on. In the study area, up to fifth-order drainage basin has been observed. The total number of 731 streams has been identified, of which 565 are first-order streams, 133 are second-order streams, 27 are third-order streams, 5 are fourth-order streams, and 1 is a fifth-order stream. All of them ultimately drains into the lake. Table 1.3 presents the ordering of the drainage in the catchment. As the stream order increases, the number of stream segments decreases. If the number of streams is high, it generally indicates that the area is less permeable and has low infiltration rate. The drainage pattern in the study area is dendritic to sub-dendritic, and parallel to subparallel pattern has also developed in some places. The dendritic pattern indicates the homogeneity in texture and lack of natural (geological) structural control while parallel pattern indicates that the study area has a gentle and uniform slope with less resistant bedrock.

Figure 1.3. Drainage map of Sukhna Lake catchment.

Table 1.3 Ordering of drainages in catchment and sub-catchment area

Drainage Density

The drainage density is the ratio of the total length of streams within a watershed to the total area of the watershed and indicates the closeness of spacing of channels (Horton 1932). Higher value of drainage density indicates a relatively high density of streams, weak or impermeable subsurface material, sparse vegetation, and mountainous relief. Lower value of drainage density indicates relatively low density of streams, highly resistant or permeable subsoil material, dense vegetation, and low relief. The types of rock also affect the drainage density. Massive, hard, and compact rocks with high specific gravity have high drainage density while the loose rock types have low drainage density. Also, rocks with clay minerals/particles may have high drainage density due to very low permeability. In the present study, the drainage density map of the catchment has been prepared using the ArcGIS line density function (Figure 1.4). The average drainage density of Sukhna Lake catchment is estimated to be 5.5m. The maximum drainage density is exhibited by Ghareri sub-catchment with 7.57 km/km² while foothill villages have a low value of 1.78 km/km² (Table 1.4).

Drainage Frequency and Drainage Texture

Drainage frequency, also called stream frequency, is the number of streams per unit area (Horton 1932). It is calculated by dividing the total number of streams in the catchment by the catchment area. The lesser the number of streams, the lower is the frequency. Conversely, the higher the number of streams, the higher is the drainage frequency. The drainage frequency is classified as the following: very poor (5–10), poor (11–15), moderate (16–20), high (21–30), and very high (31–45). The average drainage frequency of Sukhna Lake catchment is 16.64. The drainage frequencies of the sub-catchments vary from 6.13 for the foothill villages to 26.32 for the Ghareri sub-catchment (Table 1.4).

Figure 1.4. Drainage density map of Sukhna Lake catchment area.

Table 1.4 Drainage characteristics of Sukhna Lake catchment

Drainage texture of a catchment is defined as the total number of stream segments of all orders per perimeter of that area (Horton 1945). The drainage texture depends upon a number of natural factors, such as climate, rainfall, vegetation, rock and soil type, infiltration capacity, relief, and stage of development (Smith 1950). Smith further classified drainage density into five different textural classes, i.e. very coarse (<2), coarse (2–4), moderate (4–6), fine (6–8), and very fine (>8). As per the classification of Smith, drainage texture in the study area varies from coarse to very fine texture at individual sub-catchment levels (Table 1.4).

Stream Lengths and Mean Stream