eChapters

Abstract

The landslides have become the fast spreading disaster all over the Indian sub-continent. As such landslides were mostly occurring in the Mighty Himalayan Mountains, it was all along attributed to active tectonics. But when it started occurring in most of the mountain belts of India, various geological parameters, the anthropogenic phenomenon and rain fall were inferred to be the main causes for the landslides. Hence when this concept emerged, and again the Remote Sensing and the GIS technologies have phenomenally evolved, different types of variables, again on different resolutions and different methodologies have been adopted to prepare landslide vulnerability maps and this has started yielding varying types of outputs. As the landslide vulnerability zonation mapping (LVZ) is the first step in landslide studies it is essential to evolve a suitable methodology for the same. So the present study was carried out in a test site of around 300 sq.km in between Coonoor and Otacamund, Nilgiri mountains, Western Ghats, South India. In the said study, a set of 12 Earth System Parameters/Variables which could contribute to landslide vulnerability were prepared as GIS raster databases from the data interpreted from satellite MSS data and field geological and geophysical data sets. Similar GIS database was generated on 144 landslides. These landslides were superposed over such 12 Earth system parameters data and landslide vulnerability weightages were assigned to each subvariables of these Earth system parameters. In assigning weightages using such landslide incidence data various methods viz; slope, integrated terrain, information value, weight of evidence, index overlay and BIS methods were used and landslide vulnerability zonation maps were prepared adding all the 12 weightages assigned Earth system variables. In this, all the 12 earth system parameters were having same resolutions. Then the outputs were compared which revealed that the information value method is the best suited method for LVZ mapping followed by weight of evidence method.

Abstract

Prediction of the occurrences of Landslides requires a set of complex analyses, involving multitude of factors which are to be studied systematically in order to evaluate the landslide vulnerability. The increasing availability of computer-based tools and data storage capabilities are found to be useful in landslide vulnerability mapping. One such significant tool in landslide studies is Geographic Information System (GIS). In this article some approaches were made to model the land slide hazard for Sirumalai Hills, Dindigul District, Tamil Nadu, India using Geographical Information Systems and the same is presented in this paper.

Abstract

Landslides are the most common hazards in hilly regions. Rapid development and the resultant uncontrolled interactions with ecosystems are the major reasons for the landslides, besides the rainfall. So, the assessment of landslides hazard vulnerability is a prerequisite before making any developments related to settlements, hill resorts, hydropower projects and the related network of Ghat roads. The present study deals with the assessment of landslides in two different sites; Site-1 located in the Ghat section of Yercaud hills between 10/4 and 29/6 km stones in the southwestern slopes of Shevroy hills, Salem, and the Site-2 located in the Ghat road between Lower camp and Kumuli in Theni districts, Tamil Nadu. The Theni ghat road in the National Highway-220 is connecting Tamil Nadu with Kerala and is the lifeline for Sabarimala, Tekkadi and Munnar. Besides, a series of pan stacks conveying water from Periyar reservoir in Kerala to the power house located at Lower camp in Tamil Nadu also lie in this stretch of hills. Landslide vulnerability mapping was carried out in an area of 130sq.km in Site-1 and 6.7 sq.km in Site-2 by assigning numerical values to the causative factors of slope instability such as lithology, structure, slope morphometery, relative relief, land use and land cover, and ground water conditions following the BIS code No. 14496 (1998) for preparing landslide hazard zonation maps. The study in Yercaud hills revealed that out of 12 slope facets, facet 1 to 6, 9 and 12 fall under moderate landslide hazard zone whereas facets 7, 8, 10, and 11 fall under high hazard zone. The area falling in facets 3, 4 and 5 of Kumuli ghat section fall under high landslide hazard zone, the slope facets 1, 2, 9 and 10 fall in the moderate hazardous zone and other facets in low hazardous zone.

Abstract

Similar to other north eastern states of India, the state of Manipur is also prone to recurring landslides. The National Highway 150 and the state Highway in Ukhrul, Nunghar and Paorei sectors often witness landslides due to geological complexities, rainfall and anthropogenic activities. So a study was conducted to prepare the landslide hazard zonation map for the region using the method developed by Bureau of Indian Standards, which indicates that 67.32 km² (nearly 56%) fall under high hazard zone. The RMR and SMR studies carried out in five test sites in such high hazard zone show that four sites fall under highly unstable category (class IV) and one under partially unstable category (class III). The kinematic analysis indicates dominant wedge failure. The improper landuse, lack of adequate drainage and toe removal for road widening are the major causative factors for the recurring landslides.

Abstract

The softer rock types belonging to Tertiary period, intense deformation and the related more frequent tectonic weak planes, high degree of weathering and extensive road cutting are the inherent systems in provoking Landslides in Noney-Nungba segment of NH-53 in the state of Manipur. So Landslide Hazard Zonation mapping was carried out in this segment using BIS method and also geotechnical investigations were carried out in Awang Khull part-II slide and Raungdai slide and on the basis of type of failure and the morphotectonic conditions mitigation strategies were suggested.

Abstract

The state of Nagaland located in the northeastern part of the Indian subcontinent is also prone to landslides similar to the other north eastern states due to the softer lithologies, intense deformation and extensive anthropogenic activities. So in order to understand the landslide vulnerability and to evolve remedial measures, a 12 km stretch of the NH-2 from Kohima town in the south to Zhadima junction in the north was studied. The study comprises the preparation of landslide hazard zonation map using BIS method and detailed studies in six major landslides involving RMR, SMR and Kinematic analysis and also the suitable remedial measures for such landslide phenomenon.

Abstract

Due to fragile lithology belonging to Disang and Barail groups of the Cretaceous-Tertiary period, intensive structural deformation related to collision tectonics, extensive weathering and the anthropogenic activities in the form of slope cutting for the development and widening of roads lead to frequent landslides in the state of Manipur, India. In this connection, the road section between Tengnoupal and Sita has been studied to understand the landslides vulnerability and to evolve mitigation strategies. The study involved the Petrochemical analysis to elucidate the weathering potential of the rocks, kinematic analysis to understand the network of joints and the strain, slope stability analysis to prepare Land Hazard Zonation mapping and estimation of factors of safety in selected locations. On the basis of these studies, long & short term remedial measures were suggested to mitigate the landslide hazards.

Abstract

Geological conditions in the Tertiary mountainous areas of the western and eastern hill ranges of Manipur often cause landslide movements. These repeatedly occur mostly in old landslide regions during rainy seasons on a large scale, causing considerable economic loss and injuries and deaths of humans. In order to improve such landslide hazard assessment of the region for effective mitigation, Electrical resistivity surveys were conducted using Schlumberger array technique on the very unstable and problematic frontal part of the Kotland landslide, NH-37, Manipur along three profiles. Electrical resistivities aided the characterization and quantification of the subsurface rock units, structure and tectonic conditions of the Landslided area which can contribute for the better planning of mitigation strategies. The results lead to the elucidation of depth of the different litho-units and the geometry of failure surface. The probable failure surface was observed between 10 and 22m depth, characterised by low resistivity (< 150 Ωm) and geometry of the sliding surface was rotational. In addition, a fault was also inferred in the resistivity pseudosection model and hence the area may be highly vulnerable to landslides.

Abstract

The present study deals with the slope instability analysis of a vulnerable stretch of 16 km between Pratapgarh road intersection and Mahabaleshwar town, which is a part of the state highway-72, Satara district, Maharashtra, India. The highway remains closed during the monsoon seasons, due to the recurrent instances of cut slope failures. So the present research work was conducted with an aim to study the reasons, extent and mechanism of the cut slope failures along the road sections as well as optimization of tools for the assessment of road cut stability of the area. The 16 km stretch was divided into seven vulnerable sections (M1; near Mahabaleshwar - M7; near Poladpur) based on the geological, geometrical and structural attributes. The slope forming mass primarily consists of laterite, weathered basalt and fresh jointed basalt, which are interbedded with red bole at some sections. Limit equilibrium, finite difference and finite element simulation were performed for seven cut slope sections, using similar geometries and material strength attributes for all the analyzing techniques. The assessment was carried out for both dry and saturated conditions to emulate the monsoons. The factor of safety yielded through the limit equilibrium method was the most conservative of all the tools; while the finite element method gave the least conservative figures in terms of factors of safety, being close to the field observations, the safety factor results of finite difference methods were between the limit equilibrium and finite element methods. The cut slope sections composed of weathered basalts and laterites (M1, M2, M3, M6) were found most vulnerable to failure during rains, while the sections composed of fresh jointed basalts (M4 & M5), though overall stable, are susceptible to planar and wedge failures.

Abstract

The Himalayas of Himachal Pradesh is prone to landslides due to inherent geodynamic conditions, rainfall and anthropogeny. Besides multi-variate studies on the landslides of Himachal Pradesh, instrument based early warning system was attempted by taking Jhakri landslides as the test site. Various instruments viz; piezometer, vertical inclinometer, Rain gauge, etc. were installed and the paper discusses about the methodology adopted in the installation of the instruments and the observations made from the instruments. While Piezometer did not reveal much information, the Tiltmeter showed minor movements.

Abstract

The landslide is a disaster which causes rampant loss to life, property and ecosystems. With increased awareness and technological development, the number of monitoring stations near hazardous regions have increased. To give warning prior to the occurrence of a landslide, the soil/rock mechanics of the underlying bed needs to be studied and understood. This paper examines the current literature and elucidates some features of state-of- the-art landslide monitoring systems.

Keywords: Field based sensors, Wireless sensor network, Landslide monitoring

INTRODUCTION

Advancements in technology have helped us to understand nature better than before, yet the geotechnical parameters causing landslides could not be quantified accurately. The efforts taken in predicting landslides are clearly moving towards this objective and this can be seen by the number of monitoring stations that have been setup in landslide prone areas around the world. The data that is obtained at each location is important in understanding landslides. Each location is unique in terms of soil properties, groundwater, inclination of the slope and weather conditions and consequently, each deployment is unique.

The paper narrates the instrumentation based forewarning systems functioning around the world. The paper discusses these aspects hierarchically viz; Landslide prone areas in India, geotechnical instrumentations and their merits, influence of rainfall on landslides, correlation between rainfall and pore pressure, the relevance of different systems for different scenarios etc.

Abstract

Since the landslides have started spreading over to the most of the mountain provinces of all over the world, having developed expertise in Landslide vulnerability mapping, Factor of safety, Rock mechanic studies etc. the scientists and the technocrats have started focusing towards developing landslide early warning systems using instruments. As the instrumentation in such vast areas is not feasible satellite based monitoring of landslide movements is fast emerging. In this connection the paper discusses InSAR interferometry based landslide movements carried out in Nainital and Mansadevi areas, Uttrakhand Himalayas, India.

Keywords: SAR interferometry, Monitoring movements, Nainital & Mansadevi Landslides.

INTRODUCTION

Landslides pose greater threats to the population of India also, especially those living in mountainous regions, the top being the Himalayas. Many villages and vital transport routes are endangered by landslides and losses of lives and important infrastructure now become a routine phenomenon. Therefore, studies on surface displacements and landslide movements have become very important. However, due to the large aerial extent of the landslide prone provinces, this task may not be effectively carried out by ground based methods. In the recent years, the availability of interferometric Synthetic Aperture Radar (InSAR) data from a variety of satellite and airborne remote sensing sensors has emerged, as a potential tool that can yield accurate data on surface displacements. Although, monitoring of such low velocity deformations, as we observe in landslides, is only possible if considerably long time series images are available. InSAR derived displacement measurements are not only feasible but also moderate in their costs compared to many ground-based methods. This paper discusses Small Baseline Subset (SBAS) algorithm used to monitor landslide movements.

Abstract

Kaliasaur landslide located 18km from Srinagar on the NH-58 in Uttrakhand Himalayas has been repeatedly sliding for the last over 5 – 6 decades totally paralyzing the transport operations in the region and causing beeline of issues not only for the people living in the hilly state but also the tourists and the pilgrims. The study of Geosystems & geodynamics, large scale micro zonation and geotechnical studies using RMR and SMR techniques show that the slide is located in high hazard zone and follow the pattern of wedge and planar failures with vulnerable zone of factor of safety. The toe erosion by the acutely turning Alaknanda river and the mitigation measures in the form of slope disturbance in the upslope part rather protecting slide, has been responsible for the recurring slides. The study further revealed that excessive rainfall is also a triggering parameter and the crown part is widening. On the basis of the studies, mitigation measures have also been brought out.

Keywords: Kaliasaur landslides, Micro LSV zonation, Factors of landslides, Mitigation.

Abstract

The Nilgiri Mountains of South India is one of the Landslide prone hill ranges in India. The landslides, in general, are due to the independent, interdependent and the combined effects of natural earth system processes, triggering phenomenon and anthropogenic activities. So the scientists, technocrats and the academicians from all over the world have started studying the landslides using various techniques and advanced tools in mapping the morphology, preparing the vulnerability maps and carve out mitigation strategies. But the discrimination of active slides is a difficult task and also needs continuous monitoring and further a time consuming process too. So, in this context, an attempt has been made to study the signatures of active sliding in one of old slides namely the “LINGASLIDE” in which frequent minor sliding events are often reported. In the study, Total station based large scale topographic survey was carried out in LINGASLIDE and from the same 50 cm topographic contours were generated. From such large scale contours, Digital elevation Model (DEM) was generated and from the DEM, shaded relief map was generated.Uutilizing both the contours and shaded relief maps, small slides were mapped in the LINGASLIDE from the well exhibited subsidiary crowns, toes and the traverse cracks. Resistivity tomography surveys were also carried out along two longitudinal profiles and one traverse profile to identify the subsurface geology, the slip surface and the zones of moisture accumulations, if any. The subsidiary crowns, toes, the conjugate fracture systems and the resistivity tomography showed that the LINGASLIDE is active and the sliding is going on towards easterly because of the easterly compression,resulted from the higher slopes caused by the settlements raised over Lingaslide and the obstruction provided by the retaining walls at the toes in the east. Such compressive forces are clear from the NW-SE and NE-SW fractures seen in Lingaslide and the sliding is clear from the cracks seen and monitored in the buildings constructed over Lingaslide.

Abstract

The Rawana landslide, located in Sirmuar district of the Shimla Himalayas, Himachal Pradesh is repeatedly active in the recent years. It is a NE-SW oriented slide with the crown in the southwest and the wider toe in the northeast resting in Giri River. During some of the sliding events emanations of heat and gases were also inferred. In order to understand the landslide phenomenon and the causative factors, and there from to evolve mitigation measures, detailed studies of the slides were under taken. The Landslide hazard zonation mapping carried out in Rawana landslide using LHEF rating based BIS method indicates that it is located in high hazard zone. The detailed studies show the complex geological, structural, morphotectonic and hydrological setting. From the studies it is surmised that the toe erosion by Giri river and the rainfall infiltration in the mid slope region are responsible for the slide. Remedial measures have been accordingly evolved.

Abstract

The landslide vulnerability of the state of Mizoram is already high due to lithology, structure, geomorphology and seismotectonics and also the rainfall, like the other states of the northeastern region of India. The extensive mining activities along the highways for the building and road materials appear to cause additional problems of landslides. So two prominent landslides occurring in Keifang and Tlungvel quarries,Mizoram were studied. Besides taking stock of the geosystems, boreholes were drilled in both slides and from the total depth drilled and the modified core recovery, the RQD were worked out for the rocks which indicates that geotechnically the rocks of Keifang quarry are weak when compared to Tlungvel quarry. The geophysical surveys too lead to similar inferences. On the basis of the studies a set of mitigation strategies have been suggested.

Abstract

The landslides that swallowed the whole of Malin village, Maharashtra on the early morning hours of 30 July, 2014 is one of the major disasters, next only to Kedarnath episode in the recent years. Consequently, the Department of Science and Technology, New Delhi, constituted an expert committee comprising the authors of the article which made a visit and took the on the spot assessment of the disaster. Their observations show that the area is covered by the Deccan basalts, which are layered with compact and vesicular basalts; fractured and jointed basalts due to tectonics and the cooling of the basalts; and have also undergone extensive geomorphic evolution. Due to such geologic/geomorphic setting, the flow layered basaltic hillock in which Malin is located is naturally benched, which is further being leveled for the agriculture purposes. The deforestation, leveling of the hills, excessive usage of water for irrigation and the lack of drainages outlet in such benched and leveled slopes have assigned high degree of landslide vulnerability to the area. Over this, when torrential rainfall occurred in the last week of July, the landslide was triggered. On the basis such inferences, some mitigation measures have been evolved after the visit.

1.1 Introduction

Water is the basis of all forms of life. It supports life system not only to the plants but also to all other animals. The embryo from the conception till birth floats in the liquid medium. Cell, the basic unit of life, contains as high as 95- 98% water. Cellular metabolism is controlled by content of water. Majority of this water requirement of the crops is met from different forms of precipitation. However, when the water requirement is not fully met from precipitation, then growth of the crops is affected. This results in reduction of yield of the crops. The reduction in yield depends on the amount of scarcity of water requirement of the crops. Water requirement of crops depend on many factors. It depends on the type of crops, irrigation schedules practiced, soil texture, position of groundwater table below the effective root zone of the crop and management practice followed in crop cultivation. The pulses, oilseeds, vegetables which are also otherwise termed as dry land crops need less water compared to rice which is a water loving crops and perennial crops like sugarcane and banana.

Water requirement of crops is partly met by the upward flux of groundwater. The capillary rise of shallow water table in the form of upward flux helps in meeting the water requirement of crops to some extent. The upward flux depends on the type of the soil, effective root zone depth of the crop, depth of water table below effective root zone depth of the crop and potential gradient of soil moisture suction. The residual soil moisture helps in supporting water requirement of crops also. The heavy soil like clay has more moisture retention capacity than the light soils like sandy soil. The residual soil moisture held in clay soil is released slowly and supports soil moisture to the crops for a longer period than the sandy soil which has less soil moisture retention capacity. After meeting the water requirement of crops from all sources including different forms of precipitation, ground water contribution by capillary rise and residual soil moisture, if there is any shortage of water, then this shortage should be met from other sources which is called as irrigation.

2.1 Introduction

Farm ponds are the most commonly used source of ex-situ water harvesting structures. It has wide adaptability in farmers’ fields and used as handy source for water supply to crop fields. It has been used since time immemorial not only as an assured source of water supply to crops but also to meet demands in other sectors. However, these ponds have wide variations in shape and size as per the method of construction and their suitability for different topographic conditions. Most of the ponds, initially constructed in fields have regular shape. However, as time progresses and because of the poor or no repair and maintenance, these ponds loose their regular shape and become irregular.

3.1 Introduction

Different types of farm ponds with their characteristics features are discussed in this Chapter. It is observed that farm ponds can be constructed at different sites starting from the plain areas with relatively flat slopes to valley terrain having steep slopes. The choice of a particular type of pond largely depends on the kind of water supply available and on the existing topography of the site selected. In general for valleys with bottom width less than 100 m, barrage ponds may work well whereas valleys with bottom width more than 100 m, diversion ponds find suitable.

3.2 Collection of Basic Information

Basic information on different data relating to the soil, climate, plant, topography, groundwater table, catchment characteristics, and livestock populations are to be collected for the area where pond has to be constructed. Estimation of water supply from different sources and water demand form the pond for various purposes are to be done and a pond water balance study needs to be done before designing a pond in a particular place.

4.1 Introduction

A farm pond is basically small scale water harvesting and water recycling structure. It harvests water mainly in the rainy season when there is abundant rainfall producing sufficient runoff and the harvested water may be used for single or multiple cropping. When there is deficient supply of water to the crops it may supplement as supplemental irrigation. The leftover water in the pond can be used for growing another crop in winter when there is no or less rainfall. Ij addition, the stored water in the pond can be used for domestic and other uses and rearing fish. Thus it serves as viable medium for integrated farming system in rainfed farming ecosystem. Before designing a pond in a given location, it is very important to estimate the total quantity of water supply to the pond. The two main sources of water supply to pond are (i) in situ rainfall and (ii) runoff (some times called as discharge) generated from the catchment and conveyed to the pond. Some times there is groundwater contribution to the pond when the pond is unlined and the underlying groundwater table with reference to the ground level is at lower elevation than the depth of water in the pond such that there is a hydraulic gradient in the direction of underlying groundwater level to the water level in the pond.

5.1 Introduction

A farm pond that collects and harvests in-situ rainfall as well as runoff from the catchment area can be used for many purposes: the most important of which is the supply of water to crops as supplemental irrigation. It is no doubt a viable source for integrated farming system. In addition, the water of the pond can be used for domestic and to some extent for the industrial uses. It is also a good source for recreational use. Total water demand of the pond including irrigation to different crops in different seasons, domestic and other non agricultural uses are to be assessed. While estimating the crop water requirement and irrigation requirement, various crops to be grown in the service area of the pond, their water requirements, crop duration, extent of coverage and water management practices followed are to be taken into consideration. Multiplying the irrigation requirement with crop coverage area, volumetric irrigation water requirement of crop can be found out. Summation of irrigation requirement of all crops grown in service area of the pond, gives total irrigation demand of the pond.

Farm ponds are normally used for irrigation to crops as well as to meet the live stock water demand. Normally the large live stocks like horse, cattle require 20 thousand litres of water per head per year whereas the small live stocks like sheep, goat, pigs require 2 thousand litres of water per head per year. Adding the irrigation demand to the livestock demand, total water requirement of the pond is calculated. In addition to this, if the pond water is used for industrial, domestic and other sectoral purposes, then water used in all such sectors are to be added to irrigation and livestock demand to estimate the total water demand of the pond.

6.1 Introduction

Farm ponds used in farmers’ fields are generally square shaped or rectangular shaped pyramidal structures. It has a regular side slope, depth, and top and bottom dimensions. It may be excavated/dugout pond or embankment pond. In excavated pond, the pond is constructed below the ground level. Water is collected in the pond by gravity from the adjacent catchment. In embankment type, the pond is partly above the ground and partly below. This type of pond has higher storage capacity than the dugout type pond. This type of pond has a berm and dyke/embankment around the pond. The embankment has some side slope. The pond has bottom dimensions, dimensions at the ground level as well as some dimensions at the top above the embankment. In this chapter, various dimensions of pond like depth, side slope of the pond, as well as the various dimensions at bottom, ground and top level will be discussed.

7.1 Introduction

The practice of rainwater storage in the pond is quite common but still there is a need to improve its design. Most of the ponds used for rainwater storage are designed on thumb rule: either they are under or over designed. An over designed farm pond can meet the supplemental irrigation needs of the crop but it may not be economical. On the other hand, an under designed pond though economical, may not be able to meet the irrigation needs of the crops at all times. It is reported that in some case up to 20% of the farm area is used for construction of farm pond. These farm ponds are found not to be optimal. Although these ponds are able to meet the crop water demand at most of the stress periods, but considering the economics, they are observed not to be optimal. The big size farm ponds need large areas to be wasted for the digging of the structures. They need huge investment for their construction and lining. Hence, proper scientific studies are needed so that its storage becomes adequate to save the crops from the adverse effects of the drought in monsoon and to assure the possibility of growing a second crop in the winter and at the same time, it is economical also. Simulation studies by daily water balance models of both the crop field and the pond help to understand the availability of water in the pond to meet the supplemental irrigation demand of the crops.

8.1 Introduction

After deciding the optimum size of farm pond and its dimensions, the next step begins the construction of farm pond. Further the site selection and location of the pond in the selected site to be finished before the construction of pond starts. The selection of site and location of farm pond areas have been discussed in Chapter 3. In this chapter, discussion on methodologies for construction of farm pond including spillways, inlet and outlet structures, design of grassed waterways and embankment have been presented. As a guiding principle, the construction of farm pond involves the following steps:

8.2 Site Clearing

The area where the pond is to be constructed has to be inspected first. The site where pond has to be dug out should be cleared to an extent of about 10 m from all sides of top dimensions of the pond. All bushes, shrubs, stumps and other unwanted materials should be dug out and removed. If there are roots of plants, they should be uprooted. The land may be ploughed and harrowed, if necessary, to get a more or less even topography.

9.1 Introduction

The water harvested in the farm pond is a very valuable commodity. Every care should be taken so that not a single drop is wasted. The two major forms of losses in farm pond are (i) evaporation losses and (ii) seepage losses. Evaporative water loss (E_loss) and losses due to seepage are the two vital natural outflow components of unlined farm ponds. Studies conducted byGuerra et al. (1990) and Pal et al. (1994) indicated that the seepage loss from unlined ponds amounts to 45-67 per cent whereas the E_loss constitutes 30 per cent of the total out flow from the system. Water losses by evaporation and seepage were 5.3 and 9 mm day^-1, respectively amounting to 70% of total storage in the ponds (Syamsiah et al.1994).

Estimate of evaporation across the country indicates that it is as high as 2000 mm in the semi-arid tropics. Annual average value of the evaporation loss varies from 1400 to 1800 mm across major parts of the country: the value being highest in west Rajasthan, parts of Saurasthtra and Tamilnadu and lowest in coastal Mysore, Bihar plateau and east M.P. Reliable statistics reveal that about 70 M ha m of water evaporates from the water bodies and land surfaces out of the total annual precipitation of about 400 M ha m received by the country. The total evaporation losses from the water surfaces are about 5 M ha m from the total storage of 15 M ha m in the reservoirs including ponds, lakes spread all over the country (Belgaumi et al.,1997). In this section, the methods to estimate the losses like seepage and evaporation and various techniques to control them are discussed.

10.1 Introduction

Rainwater is the main source of water for agriculture but its current use efficiency for the crop production is low ranging between 30-45%. The rising demand for water for non-agricultural uses is proportionately decreasing its share for agricultural uses. Efficient methods of water harvesting in the farm reservoirs including farm ponds and its management for subsequent uses in agriculture with improved water use technologies are vital for increasing the productivity and reducing poverty in rainfed ecosystems. It is not to be forgotten that the harvested water in the pond is a very valuable commodity. It may be used for industrial use or for irrigation in agriculture. The harvested water is also a good source to meet the water demand of domestic animals and for human beings (Fig. 10.1). The stored water of the pond can be used for fish farming, tree plantation, intensive irrigation to small area and extensive supplemental irrigation to rainfed crops. Stored water in a pond is developed resource and is, therefore, more expensive than the natural resource. Hence, there is a need to utilize it judiciously and efficiently.

11.1 Introduction

Economic analysis is the most important parameter for determining the optimum size of farm pond. It is, no doubt that a big size farm pond can meet the irrigation demand of the crops grown in the command areas in addition to meeting the other demand in the command areas. But a big size farm pond is an oversize structure which necessitates large investment to be incurred which may not be economically viable. On the other hand, a small size structure may not be able to meet the crop water demand and also other demands in the command areas and so is called as under-designed structure. It has been observed that as the size of the farm pond gradually increases from a certain minimum size, the total investment cost increases. At the same time, the benefits from the increasing storage capacity of the farm pond also get increased. In such cases, from a purely business point of view, the most economical capacity is that which provides the highest rate of return on investment. As the size of the farm pond increases, the proportion of the benefit/profit to the cost also increases from certain minimum size, attains maximum value at a particular size and then declines as the size further increases. This particular size of the farm pond at which the net profit is maximum, is called as the optimum size. It is to be noted that at the optimum size, the other economic indicators like the benefit-cost ratio and internal rate of return are also high. The variation of net profit with size of the farm pond is a concave curve. The size of the farm pond corresponding to the peak of the curve which represents the highest net profit is the optimum size of the pond.

The principle of obtaining the optimum size of farm pond is to first assume a certain minimum size say five percent of the farm area and conduct the economic analysis by studying the costs and net profits of the assumed size. Then the size is gradually increased and the economic analysis is conducted for each increased size. Then a curve relating the size of the farm pond and net profit is drawn. Such a curve is generally concave shaped. The size of the structure corresponding to the maximum net profit gives the optimum size. It is to be noted that any size chosen more or less than the optimum size would give less net profit and benefit-cost ratio than that of the optimum size.

12.1 Introduction

Farm ponds are used for multipurpose including as a viable source for supplemental irrigation to rainfed crops, a good place of entertainment, a vital place for wild life habitats, livestock and fish and aquatic plants. Like any other structure, the farm pond needs regular repair and maintenance for effective operation. The purpose of construction of the pond will be fruitful and the life span of the pond will be enhanced if proper care and maintenance are taken. In this chapter some salient discussions on care and maintenance of the pond are mentioned.

12.2 Maintenance Against Silting

The farm ponds constructed in medium to deep black soils are subjected to getting silted up. Hence, periodic desilting to restore the original storage capacity is required. If the pond is used for supplemental irrigation to crops, then desilting may be done once in every 5 to 10 years depending on the amount of silt getting deposited in the pond.

The breaches and rill formed in the spoil bank and shoulder bunds should be immediately repaired. The inlet and outlet structures should be maintained periodically. The silt deposited in the silt trap should be removed periodically. In areas where silt carried by the runoff is more, a vegetative filter near the inlet structure may be used. The pond may be desilted manually if it is small in size otherwise mechanical measures may be used to desilt. It is easy to desilt the pond when it is dry. A Simple and inexpensive method to desilt the pond is to stir the water of the pond and then allow the desilted water move away from the pond through the outlet (Belgaumi, et. al., 1997). Fig. 12.1shows a badly maintained pond with excess silting and weed infestation causing severe reduction of its storage capacity.

In addition to farm ponds, irrigation to crops can be met from other sources. The main sources can be broadly classified as: (i) Canal irrigation, (ii) Well Irrigation and (iii) Lift irrigation. In arid and semi arid areas, where availability of water is scarce, pitcher irrigation is practiced. These sources of irrigation are briefly mentioned as follows.

13.1 Canal Irrigation

To feed the world population of 8 billion in 2025 AD, it is necessary to bring more area under irrigation because irrigated farms typically get higher yield under provision of irrigation. The food production will have to increase by about 50 percent to feed some two billion more people by 2025 AD, and a large part of that increase needs to come from irrigated agriculture. It is reported that the yield of different crops are generally 2-3 times higher than the crops grown under rainfed conditions. Furthermore, it is possible to raise 2-3 crops round the year under irrigated agriculture whereas hardly a single crop is successfully grown in a year under rainfed condition. It is reported that about 40% of the world’s food production comes from only 17% of the irrigated land of the world (Sivanappan, 2000). Everybody is aware of the fact how the irrigation played a crucial role to make the Green Revolution in India successful. A major part of irrigation is achieved by canal irrigation through different irrigation schemes.

A project that makes use of weir or a barrage for providing irrigation to fields is called as direct irrigation scheme. On the other hand, a storage irrigation scheme makes use of storage reservoir by construction of dams. In order to provide irrigation by both the schemes, it is necessary to have a network of canal systems including main canals, branch canals, distributaries, minors and watercourses. It is imperative to design the canal systems properly for a certain realistic value of peak discharge that must pass through them so as to provide sufficient irrigation to the command areas. These canals have to be aligned and excavated either in alluvial soils or non-alluvial soils; depending upon which they are called alluvial canal or non-alluvial canal.

Sustainable development and efficient management of water is an increasingly complex challenge in India. Increasing population, growing urbanization, and rapid industrialization combined with the need for raising agricultural production generates competing claims for water. There is a growing perception of a sense of an impending water crisis in the country. Some manifestations of this crisis are:

(a) Increasing costs of developing new water resource – Many major and medium irrigation projects seem to remain under execution forever as they slip from one plan to the other with escalating cost and time overruns.

(b) Siltation of reservoirs and owing to lack of maintenance, the capacity of the older irrigation systems seems to be going down.

(c) Declining groundwater table due to over-exploitation imposing an increasing financial burden on farmers who need to deepen their wells and replace their pump sets and on State Governments whose subsidy burden for electricity supplies rises.

(d) Water pollution and degradation of water-related ecosystems - Water in most parts of rivers is not fit for bathing, let alone drinking. Untreated or partially treated sewage from towns and cities is being dumped into the rivers. Untreated or inadequately treated industrial effluents pollute water bodies and also contaminate groundwater,

(e) Wasteful use of already developed water supplies, often encouraged by the subsidies and distorted incentives that influence water use,

(f) Besides in many rural habitations there are pockets where arsenic, nitrate, and fluoride concentration in drinking water are posing a serious health hazard

(g) Rise in water-logging and salinity resulting in degradation of soils in irrigated areas,

(h) Increasing water conflicts about water rights between upper and lower riparian states in a river, conflicts about quality of water, people’s right for rainwater harvesting in a watershed against downstream users, industrial use of groundwater and its impact on water tables and conflicts between urban and rural users etc

(i) The gross irrigated area does not seem to be rising in a manner that it should be, given the investment in irrigation. The difference between potential created and area actually irrigated remains large. Unless we bridge the gap, significant increase in agricultural production will be difficult to realize.

Plants and any from of living organisms cannot live without water, since water is the most important constituent about 80 to 90% of most plant cell.

2.1 Role of water in crop and crop production

(A) Physiological importance

•The plant system itself contains about 90% of water

•Amount of water varies in different parts of plant as follows

•Apical portion of root and shoot >90%

•Stem, leaves and fruits - 70 - 90%

•Woods - 50 - 60%

•Matured parts - 15 - 20%

•Freshly harvested grains - 15 - 20%

The soil is a heterogeneous, polyphasic viz., solid, liquid and gaseous, particulate, disperse and porous system (Fig. 3.1). The solid phase constitutes the soil matrix, the liquid phase consists of soil water, which always contains dissolved substances so that it should properly be called as soil solution and the gaseous phase is the soil atmosphere.

4.1 Soil Moisture Tension

Soil moisture tension is a measure of the tenacity with which water is retained in the soil and shows the force per unit area that must be exerted to remove water from soil. The tenacity is measured in terms of the potential energy of water in the soil measured, usually with respect to free water. It is usually expressed in atmospheres, the average air pressure at sea level. Other pressure units like cm of water or cm or mm of mercury are also often used (1 atmosphere = 1036 cm of water or 76.39 cm of mercury). It is also sometimes expressed in bars (1 bar = 106 dynes / cm² = 1023 cm of water column. 1 millibar = 1/1000- bar).

Soil moisture tension is brought about at the smaller dimensions by surface tension (capillarity) and at the higher dimensions by adhesion. Buckingham (1907) introduced the concept of ‘capillary potential’ to define the energy with which water is held by soil. This term, however, does not apply over the entire moisture range. In a wet soil, as long as there is a continuous column of water, it might be called ‘hydrostatic potential’, in the intermediate range the term ‘capillary potential’ is appropriate. In the dry range the term ‘hygroscopic potential’ would be suitable. However, the term ‘soil moisture potential’, ‘soil moisture suction’ and ‘soil moisture tension’ are often used synonymously to cover the entire range of moisture (Khonke, 1968).

5.1 Kinds of Soil Water

The following re the three main classes of soil water:

(i)  Hygroscopic water. Water held tightly to the surface of soil particles by adsorption forces.

(ii) Capillary water. Water held by forces of surface tension and continuous films around soil particles and in the capillary spaces.

(iii) Gravitational water. Water that moves freely in response to gravity and drains out of the soil.

The water contents expressed under certain standard conditions are commonly referred to as soil moisture constants. They are used as reference points for practical irrigation water management. The usage of these constants together with the energy status of soil water gives useful knowledge. These constants are briefly explained below:

6.1 Saturation Capacity

Saturation capacity refers to the condition of soil at which all the macro and micro pores are filled with water and the soil is at maximum water retention capacity”. The matric suction at this condition is essentially zero as the water is in equilibrium with free water. Excess water above saturation capacity of soil is lost from root zone as gravitational water.

The measurement of soil moisture is needed to determine when to irrigate and the amount of water needed when irrigating, to evaluate evapotranspiration, and to monitor soil matric potential. The soil moisture is measured in two ways- direct and indirect methods as follows:

8.1 Moisture extraction pattern

The moisture extraction pattern reveals about how the moisture is extracted and how much quantity is extracted at different depth level in the root zone. The moisture extraction patter shows the relative amount of moisture extracted from different depths within the crop root zone. The moisture extraction pattern of plant growing in a uniform soil without a restrictive layer and with adequate supply of available soil moisture throughout the zone is shown in Figure. 8.1.

Crop water requirement is the water required by the plants for its survival, growth, development and to produce economic parts. This requirement is applied either naturally by precipitation or artificially by irrigation. Hence the crop water requirement includes all losses like:

• Transpiration loss through leaves (T)

• Evaporation loss through soil surface in cropped area (E)

• Amount of weather used by plants (WP) for its metabolic activities which is estimated as less than 1% of the total water absorption. These three components cannot be separated so easily. Hence the ET loss is taken as crop water use or crop water consumptive use.

• Other application losses are conveyance loss, percolation loss, runoff loss, etc., (WL).

• The water required for special purposes (WSP) like puddling operation, ploughing operation, land preparation, leaching, requirement, for the purpose of weeding, for dissolving fertilizer and chemical, etc.

• Hence the water requirement is symbolically represented as:

10.1 Evapotranspiration (ET = Evaporation + Transpiration)

Evaporation is a diffusive process by which water from natural surfaces, such as free water surface, bare soil, from live or dead vegetation foliage (intercepted water, dewfall, guttation etc) is lost in the form of vapour to the atmosphere. It is one of the basic components of hydrologic cycle.

Likewise transpiration is a process by which water is lost in the form of vapour through plant surfaces, particularly leaves. In this process water is essentially absorbed by the plant roots due to water potential gradients and it moves upward through the stem and is ultimately lost into the atmosphere through numerous minute stomata in the plant leaves. It is basically an evaporation process. However, unlike evaporation from a water or soil surface, plant structure and stomatal behaviour operating in conjunction with the physical principles governing evaporation modify transpiration.

Thus, evapotranspiration is a combined loss of water from the soil (evaporation) and plant (transpiration) surfaces to the atmosphere through vaporization of liquid water, and is expressed in depth per unit time (for example mm/ day). Quantification of evapotranspiration is required in the context of many issues:

Allocation of the water receipt including anticipated within the crop period and its detailed account of expenditure for efficient and profitable farm management is called as water budgeting.

Water budgeting may be for an irrigation system planned by irrigation engineers; may be for a canal or for an area (block) or may be for a farm according to the need and plan by responsible persons who plan the irrigation efficiency.

Irrigation Methods

Surface

Sub-surface

Pressurized irrigation

12.1 Surface Irrigation

Surface irrigation method refers to the manner or plan of water application by gravity flow to the cultivated land wetting either the entire field (uncontrolled flooding) or part of the field (furrows, basins, border strips). Most irrigated areas have characteristic land features and differ from those in other areas. Hence, for efficient application of water it is important to select such method of irrigation, which fits one’s own land.

The adoption of a certain method need not be necessarily based on convention or that followed in the adjoining farm. The factors, which determine the suitable method of irrigation are local conditions (soil type - its permeability & water storage capacity; land topography, climate, water availability & water quality), crop type, type of technology, previous experience with irrigation, required labour inputs etc. Good yield of crops can be obtained from irrigated land only if the water is applied judiciously to meet the needs of the plant, but not to cause waste and damage. Irrigation water is applied to cultivated land by the following surface methods of irrigation:

An efficient irrigation system implies effective transfer of water from the source to the filled with minimum possible loss. The objective of the efficiency concept is to identify the nature of water loss and to decide the type of improvements in the system.

Evaluation of performance in terms of efficiency is prerequisite for proper use of irrigation water.

Whatever may be the source of irrigation water viz., river, canal, tank, open well or tube well, some soluble salts are always dissolved in it. The main soluble constituent in water are Ca, Mg, Na and K as cations and chloride, sulphate bicarbonate and carbonate as anions. However ions of other elements such as lithium, silicon, bromine, iodine, copper, cobalt, fluorine, boron, titanium, vanadium, barium, arsenic, antimony, beryllium, chromium, manganese, lead, selenium phosphate and organic matter are also present. Among the soluble constituents, calcium, sodium, sulphate, bicarbonate and boron are important in determining the quality of irrigation water and its suitability for irrigation purposes. However other factors such as soil texture, permeability, drainage, type of crop etc., are equally important in determining the suitability of irrigation water.

The following are the most common problems that result from using poor quality water.

When rocks and minerals under go weathering process large quantities of soluble salts are formed. In humid regions these salts are washed down to the ground water and to the sea. But in arid and semi arid regions they accumulate in the soil. Excessive irrigation and poor water management are the two chief causes of water logging and salt accumulation. An accumulation of salts in soil leads to unfavourable soil water-air relationship and effect the crop production.

The following are the main causes which leads to development of salty soils (salinity or alkalinity)

16.1 Water logging

For optimum growth and yield of field crops, proper balance between soil air and soil moisture is quite essential. Except rice many of the cultivated plants cannot withstand excess water in the soil. The ideal condition is that moisture and air occupy the pore spaces in equal proportions. When the soil contains excess water than that can be accommodated in the pore spaces it is said the field is water logged.

Causes of water logging

1. Excessive use of water when the water is available in abundance or cheaply due to the belief that more water contributes better yield.

2. Improper selection of irrigation methods

3. Percolation and seepage from lands canals and reservoir located at nearby elevated places

4. Improper lay out and lack of outlets

5. Presence of impervious layer with profile impeding percolation

6. Upward rise of water from shallow ground water table or aquifer.

17.1 Rice

Rice culture at present dominates irrigated agriculture. About 64% of the irrigation water resources in Andhra Pradesh are used for cultivation of rice. An adequate water supply is one of the most important factors in rice production. In many parts of India including Andhra Pradesh rice plants suffer from either too much or too little water because of irregular rainfall and land topography.

Percolation losses in rice fields

Percolation losses are a function of the local soil and topographic conditions. Therefore, at any time the amount of rainfall or irrigation water entering the soil becomes greater than its water holding capacity, losses by downward movement of free water (vertical percolation) will occur. Percolation is often defined as the movement of water through saturated soils due to gravity, hydrostatic pressure or both.

Thus where the soil is heavy and the water table is close to the soil surface, percolation losses are low, about 1 – 2 mm/day. On the other hand, where the soil is light and the water table is deep, percolation losses may be high, about 8 – 15 mm/day, or more. About 50 to 60% of applied water to rice is lost by deep percolation. The percolation losses can be reduced by adopting following agronomic practices:

Fill in the Blanks

1.The highest amount of rain is received in India by _______ Monsoon

2.Country with largest irrigated area in the world is _______

3.The major source of irrigation water in Andhra Pradesh is _______

4.The annual water budget of India is about _______ million ha meters

5.Ultimate irrigation potential in India is _______ m. ha.

6.The portion of the total rainfall that is retained in the soil directly for evapotranspiration is _______ M ha m

7.The first irrigation commission was constituted in the year _______

Microbiology is a branch of science dealing with the study of organisms which are too small to be seen clearly by unaided eye. Roughly the organisms with a diameter of 0.1mm or less, which can not be seen by the human eyes unaided, come under the domain of microorganisms.

Thus, the laboratory work dealing with the microorganisms needs special care to avoid infection and infusion for maintaining good health. In fact all microorganisms should be treated as potential pathogens. Thus, for working with microorganisms aseptic techniques must be followed by students as well as by the laboratory assistants and teachers.

Microorganisms, being ubiquitous, are found in soil, air, water, food, sewage, on body surfaces as well as on degrading and decomposing substances. Their survival and continued growth mostly depend on an adequate supply of nutrients and favourable growth environments. The culture media (nutrients) consisting of chemicals support the growth of microorganisms in a given condition. They are devised in such a way that the organism should get all the nutritional requirements. These are usually prepared in laboratory by weighing and dispensing the individual ingredients. Generally, the common media contain both inorganic and organic nutrients; however, for the cultivation of large number of microorganisms, specialized media are required.

Basically the culture media are of three types: (1) Natural, (2) Semi synthetic and (3) Synthetic.