The drainage pattern in the entire part of Rajasthan is generally dendritic. The river system of the State can be conveniently divided into two major groupsi The rivers, which drain their run off to the Bay of Bengal, and ii The rivers flowing to the Arabian Sea.
Two other important rivers which flows to the Arabian sea are the West Banas and Sabarmati. The West Banas originates from the western slope of the Aravalli Mountains and drains some parts of Sirohi District, finally draining its run off in the Rann of Kachchh. Aravalli HillsThe Aravalli hill ranges constitute the most dominant hilly area of Rajasthan. The ranges run diagonally across the state from north-east Delhi to south-west upto the plains of Gujarat, covering a distance of about kms.
Within Rajasthan, the ranges run from Khetri in the north-east to Khed Brahma in the south-west for a length of about kms. In the north-east, the hill ranges become more prominent near Khetri and Alwar. Quartzite, being very resistant, form most of the hills in the northern and central parts. Granite forms the high hills in the south near Abu. Apart from the hills, the other major landforms within this region are the rocky uplands, shallow to moderately deep colluvial plains and narrow alluvial plains at few locations.
The Aravalli Mountains: The Aravalli Mountains, which crosses the state of Rajasthan diagonally for a distance of about km. It is a typical ensialic mountain range of olden Proterozoic rocks having an age span between and million years from today. The Archaean rocks, which form the foundation of the mountain, have a history of one billion years; the oldest rocks are believed to have originated earlier to million years ago.
Although Heron described the Aravalli Mountains as 'being perhaps the oldest mountain range in the world', it is doubtful if the present relief can be ascribed entirely to the Precambrian orogenesis. References to the Aravalli Mountains are traceable in ancient literatures as a mountain that stands askew to the east-west trending Himalaya and the Vindhyan ranges known as the Satpura Mountains in geological literatures.
The mountain not only prevented the sand movement to the east, but also formed a formidable barrier for the ancient people to cross over particularly in the southern part. In spite of being an ancient geomorphic 'welt', the mountain has very prominent relief features, which normally characterises the much younger mountain chains, like the Appalachians in the eastern North America, or the Urals that joins Europe with Asia.
Heron's description of the main component of the geomorphic mountain as a syncline or synclinorium "Main Delhi Syncline" is naively simplistic. Detailed studies subsequent to the publication of the Heron's classical memoir helped in erecting an evoluntary history comprising three successive Proterozoic cycles of basin evolution, magmatism, metamorphism and tectonic inversion, on an Archaean basement.
Known as the Mewar Hills, this high-hilly tract is bounded by the Eastern Mewar and Chappan plains in the east, Cambay Graben in the south, and the extension of the Kui-Chandravati Fault in the west. The northern part of the triangle between the Fort of Kumbalgarh '' and Gogunda 24'46'' is a region of high elevation, locally called the Bhorat Pathar plateau.
Lying at a level of nearly m, the plateau has a steep and precipitous western fall. There are a number of peaks, which rise over m above the average m level. The highest peak of the Bhorat Pathar is the Jarga Parvat rising to m. The Fort of Kumbalgarh is perched majestically at m high overlooking the plains of western Rajasthan Bagar. The Bhorat Pathar is made of several subparallel bold ridges of quartzite separated by valleys underlain by phyllite and clacareous schists.
From south of Gogunda, sets of subparallel ridges branch in the southwesterly, southerly, and southea sterly directions. The southwesterly branch of the southern Mewar Hills runs straight upto the Gujarat border where the ridges undergo abrupt truncation. Because of this, the highly mountainous Aravalli landscape is taken ov er by the low-lying alluvial plain of Cambay Graben.
The abrupt termination of Aravalli ridges is a major PAGE 21 12 geomorphic feature that also constitutes the southern boundary of outcrops of the Rajasthan. Another prominent feature in the geomorphology of this part of the Aravalli ranges is the presence of number of circular and semi-circular relief features, possibly related to intrusions that shoved astride the tectonic pattern of the host rocks.
The middle branch of the Aravalli ridges, which runs more or less in the north-south direction, makes its appearance from east of Gogunda. These are very prominent ridges of quartzites in a milieu of phyllites, all belonging to the Aravalli Supergroup.
All the ridges of the Aravalli Mountains described earlier, geologically belong to the Delhi Supergroup. The angular relationship between the two trails of the Aravalli Mountains that run southwesterly and southerly respectively, mark an important tectonic feature presumably representing the trace of unconformity between two geological formations. The angular relationship appears very prominently in the satellite imageries.
The ridges trend southward upto Kherwara '' and Rishabdev '' , where from starts a gradual southeasterly swing of the bold quartzite ridges. On a plan view, the ridges assume queer patterns particularly in the region between south of Dungarpur and Lunavada '' in northern Gujarat. The ridges become more subdued until these get covered under Deccan basalts in the east. The highest elevation in this part of the Mewar Hills is in the region west and northwest of the city of Udaipur, where there are a number of peaks rising abov e m.
The highest point is m near Jharol ''. The most easterly trail of ridges, which runs in southeasterly direction, starts from the upland north of Udaipur. The city itself is surrounded by chains of hills. The valley where the city of lakes is situated is called Girwa.
The continuity of southeasterly ridges, which are traceable beyond Salumber, is breached at the Jaisamand Lake. Some hills in the neighbourhood of Jaisamand Lake rise upto m, whereas the highest level of lake water stands at m.
PAGE 22 13 The Aravalli ranges are the most prominent hill features extending from Sirohi, Udaipur and Dungarpur districts in the south-west to Jaipur and Alwar districts in the north-east. These ranges form a Labyrinth of low hills in Udaipur, Dungarpur and Bans wara districts, and stretch Northeastwards in the form of undulating low hills through parts of Ajmer, Tonk, Sawai Madhopur, Jaipur and Alwar Districts, Isolated outcrops of Aravallies occur in Jhunjhunun, Sikar and Nagaur districts.
Archaean Metamorphics, represented by Bhilwara Super Group more than 2, million years old to sub-recent alluvium and wind blown sand. The western and north-western parts of the state are covered by vast blanket of young unconsolidated deposits including the blown sand of the Thar Desert Marusthal of Western Rajasthan. The remaining area exposes wide variety of hard rocks which include various types of metamorphic schists, quartzites, marbles and gneisses of Pre-Cambrian age with associated acid and intrusive rocks.
The south-eastern extremity of the state is occupied by a pile of basaltic flows of Deccan Traps of Cretaceous age. Several mineral deposits of economic importance occur in association with the above rock units Map 1. The geological sequence of the state is highly varied and complex, revealing the co-existence of the most ancient rocks of Pre-Cambrian age and the most recent alluvium as well as wind-blown sand. The Aravallis, one of the most ancient mountains in the world, have the oldest granitic and gneissic rocks at their base.
Delhi Super Group, the Vindhyan Super group and younger rocks are highly metamorphosed at certain places and show rich occurrences of minerals of great commercial importance. PAGE 23 16 The characteristic feature of the geology of Rajasthan is the presence of several groups of rocks belonging to Archaean and Pre-Cambrian ages.
They form the Aravalli mountain system which runs across the state from the north of Delhi in the north-east to the Gulf of Cambay in the south-west. The central part of the Aravalli ranges is occupied by a great synclinorium composed of Aravalli and Delhi rocks.
Because of the thin deposits of sand in this region, the rock PAGE 24 17 exposures are good but in the west and the south-west, they are often engulfed in sandy alluvium and desert sands. The Aravallis, an enormously thick series of argillaceous rocks, came into existence at the close of the Archean era when the sediments which were deposited in the seas of that age, underwent an upheaval by orogenic activities. These vast mountains were peneplaned in pre-cretaceous time but were again rejuvenated in later ages.
The Aravallis Super Group is a vast formation composed of basal quartzites, shale's, conglomerates, composite gneisses and slates. The Delhi Super group overlies the Aravallis.
Delhi Super group is divided into lower Railo group, middle Alwar group and upper Ajabgarh group. Railo group is rich in crystalline li mestones, grits, schistose rocks and quartzites.
The famous marble of Makrana Nagaur district belongs to this group. Alwar group and Ajabgarh group consist mostly of calc-silicates, quartzites, grits and schistose rocks. The other important lithological formations consist of a thick series of sedimentary rocks comprising sandstone, limestone and shales. These have been classified as upper and lower Vindhyans in the east and Marwar in the west. The deposition of these rocks in western Rajasthan was preceded by igneous activity which included a thick pile of lava, mostly of an acidic nature.
The plutonic equivalent of these lava are seen in the form of granite bosses and sills in Jalor, Siwana, Mokalsar and Jodhpur areas. Rocks of the above mentioned igneous activity has been designated as Erinpura granite and Malani igneous suit.
There was an encroachment of an arm of the sea from the SouthWesternly direction into western Rajasthan during the Jurassic period. Jurassic formations are distinctly notic eable in a vast area around Jaisalmer and some of the fossils of this age are found in these rocks. The outcrops of these rocks are, partly, covered by wind-blown desert sands. Of special interest are the Bap Jodhpur district and Pokran Jaisalmer district beds of upper Carboniferous age which have now been exploited for ground water.
Violent volcanic activity in the form of fissure eruptions marked the close of Mesozoic era in the lower Cretaceous age. The main characteristic of this was a stupendous outburst of covered volcanic energy, resulting into eruption of thick streams of lava over vast areas. These rocks, known as Deccan traps, are found in southern and south-eastern Rajasthan.
The Deccan trap, extending over a vast area in southern Jhalawar and in the eastern parts of Chittorgarh and Banswara districts, are notable formations of Upper Cretaceous to Lower Eocene age when a large area of peninsular India was also covered with fissure eruptions of black lava. During Eocene times, marine transgression seems to have inundated a large part of western Rajasthan with the deposition of thick beds of fossiliferous limestone.
To the nort h of Jaisalmer, the Jurassics are overlapped by nummulitic limestone. Pleistocene alluvium, blown sand, kankar calcium nodules , carbonate beds and evaporate deposits of recent and sub-recent age are found over a large area of western and eastern Rajasthan. The Great Boundary Fault through which the River Chambal has carved its course, passes through south-eastern parts of the state.
This fault is visible in Begun Chittorgarh district and northern parts of Kota. It reappears again in Sawai Madhopur and Dhaulpur districts. Besides this, several mega lineaments also traverse in the state. PAGE 26 17 1. About 66 per cent of the global population, comprising of farmers derives its livin g directly from the soil.
There are no natural resources more important than soil resource. Whatever its production capacities, whether high in some places of irrigated pockets or low in major areas of dry land and desert, due to inherent limitations, the soil resource of Rajasthan, as a medium of growing crops, has furnished directly or indirectly, a significant share in the income of the state. Rajasthan, being geographically the second largest state in India, has proportionately a greater soil resource.
Therefore, the soil resource in the state needs to be used extensively and efficiently so that the state finds an appropriate place in the national food, fiber and fodder production and the state economy is sustained without any depletion through erosion, degradation or overuse. The information and knowledge of soils of the state which could be gained through the study of their physical and chemical properties and their geographically distribution pattern is an essential prerequisite for their proper utilization, management and conservation.
It also helps in proper selection of crops and better land use. When seen in detail at the village level, the soils of Rajasthan are complex, and highly variable reflecting a variety of differing parent materials, physiographic land features, range of distribution of rainfall and its effects, etc. However, broadly, the soils can be put in five major groups, based on the basic fabric of soils i.
They are, 1 sandy soils or light soils, 2 sandy loam or light medium soils 3 loan or medium soils, 4 clay loam to clay or heavy soils and 5 skeletal soils or shallow rocky and hilly soils Map 1.
The soils are generally evaluated for their production capacity through study of their ability to supply plant growth requirements in terms of water, nutrient and rooting media. The capacity to retain, as also to conduct soil PAGE 27 19 moisture in profile, depends upon the soil texture, soil porosity and soil structure.
For example, heavy soils due to their fine texture and porosity, provide effective capillary tubes for moisture movement. In loose sandy soils, PAGE 28 19 due to big particles and pores, with fewer fine capillary pores, there is lesser soil moisture movement. Further, heavy soils are more difficult to work with implements than in light soils. On the other hand, the sandy or light soils that are loose and single grained are more prone to wind erosion and are often subject to sand drift, but due to their coarse and open texture, coarse pores and resultant high infiltration capacity, they are not susceptible to water erosion, even during heavy cloud bursts.
Medium textured soils have moderate condition between the above extremes. As such, these different soils create different types of habitats for plant growth and therefore, the crop choice and cropping patterns on such kind of soils greatly vary. Soils are thus, variable in their soil-water-plant relationship, conservation needs and production potentials. To assess the potential of agricultural development and to plan proper conservative land use, soil survey is the basic requisite.
The knowledge of soils gathered through soil such surveys is not only useful in finding out agriculturally potential areas but also those areas which have remained unnoticed under on or the other soil degradation process for a long period and are now considered as problematic areas.
Further, the agronomical and soil moisture conservation technologies, developed for crop production, are often more suitable, particularly for one or the other kinds of soils. Therefore, the distribution of such differing soils depicted through soil survey maps, is useful for easy and proper transfer of such technologies to suitable areas. Soil resource is also a malleable environment moulded by the agriculturist in many ways e.
Its sustainability can also be maintained by its conservation against damages PAGE 29 20 through erosion, preventing salinization, alkalinization, compaction, depletion in nutrient level, etc. These are all known soil degradational processes which lessen the current or potential capability of soils to produce crops or biomass.
Many technologies are available to check this and conserve soils for sustained productivity. To the west of the Aravalli range, the climate is characterised by low rainfall with erratic distribution, extremes of diurnal and annual temperatures, low humidity and high wind velocity.
The climate is semi-arid to sub-humid in the east of the Aravalli range, characterised by more or less the same extremes in temperatures but relatively lower wind velocity and high humidity with better rainfall. The entire state is characterised by hyperthermic conditions.
The annual rainfall in the state varies significantly. The general trend of Isohytes is from north-west to south-east. There is a very rapid and marked decrease in rainfall west of the Aravalli range, making western Rajasthan the most arid part. The average annual rainfall in this part ranges from less than 10cm in north-west part of Jaisalmer lowest in the state , to to 30cm in Ganganagar, Bikaner and Barmer regions, 30 to 40cm in Nagaur, Jodhpur, Churu and Jalore regions and more than 40cm in Sikar, Jhunjhunun and Pali regions and along the western fringes of the Aravallis range.
On the eastern side of the Aravalli range, the rainfall ranges from 55cm in Ajmer to cm in Jhalawar. In plains, Banswara Mount Abu Sirohi district in the southwest, however, receives the highest rainfall in the state The yearly total rainfall is highly variable at different places all over the state and it is most erratic in the western half with frequent spells of drought, punctuated occasionally by heavy downpour in some years, associated with the passing low pressure systems over the region.
PAGE 30 21 The south-west monsoon which has its beginning in the last week of June in the eastern parts, may last till mid-September. Pre-monsoon showers begin towards the middle of June and post monsoon rains occasionally occur in October. In the winter season also, there is sometimes, a little rainfall associated with the passing westerns distribution over the region. At most places, the highest normal monthly rainfall is during July and August. The availability of ground water depends upon the nature of rocks and their water bearing characters.
The Deccan traps show low to medium permeability depending on the primary and secondary porosities and their variation from place to place. In the hard rock terrains, the valley fills consisting of river and stream laid deposits, often contain highly producti ve aquifers, with limited groundwater resources.
The alluvium and the blown sand which occupy the major part of PAGE 31 22 the state and the semi-consolidated formation comprising the Tertiaries and the Mesozoic rocks. Ground water development is significantly high in the eastern part of PAGE 32 23 Rajasthan as compared to the western part.
The annual ground water recharge is relatively less in western Rajasthan, due to low and erratic rainfall, absence of surface water resources, and high evapotranspiration.
However, in some of the thick aquifers, the storage is many times and annual recharge and hence, sustained pumpage can be achieved even during a dry spell, without causing adverse effects.
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