A Note on the Geography and Geology of Begusarai

By Ashutosh Shandilya,

     Geologist, ONGC

 ( E mail-ashandilya2001@yahoo.com)

Background

 
The district Begusarai, an important district in the state of Bihar lies on the northern bank of river Ganga. Earlier it was a part of the greater Munger district. Begusarai district was carved out of it as a separate district on. 2^nd October 1972 (A handnote on Begusarai district census-1991). Now it is a part of the Munger commissionery.  Geographically, lying between latitudes 25⁰15’N  & 25⁰14’N and longitudes 85045’E & 85⁰45’E, it covers an area of 1918km ². In the north, it shares its boundaries with Samastipur district; in the east and NE it is surrounded by Khagaria district. In the southeastern part lies the Munger district. In the south is Lakhisarai and in the southwestern side, along the banks of River Ganga, it is shares its boundaries with Patna district. It is situated in a part of Middle Gangetic plains, locally known as North Bihar plains. Administratively it is divided into five subdivisions- Begusarai, Teghara, Balia  Manjhaul and Bakhri and  eighteen  blocks namely Begusarai, Mattihani, Teghra, Samho, Bachhwara, Barauni, Bhagwanpur, Balia, Sahibpur Kamal, CheriaBariarpur, Khudabandpur, Bakhari. Mansurchak, Birpur, Dandari, Nawkothi, Garhpura, and Chhaurahi The average population density is app. 900 persons per square kms. The economy is mainly agriculture based and the major crops are wheat, maize, chilli, sugarcane etc.

: The views presented in this article belongs to the author and in no case represent the views of the organization to which he belongs or the website which hosts the article.

Two big  industries mark the skyline of the district i.e. Thermal power station and Petro-Chemicals factory and Oil refinery complex at Barauni. Earlier Barauni Fertilizer was also an important industry which is now non functional. Rajendra Bridge across Ganges at Barauni forms an important link way connecting north and south Bihar, Resting spot for migratory birds in a wetland known as Kanwar tal and the Ghats of Ganga at Simaria possessing religious importance, exists as a potential tourist spots.

Climate

            Being a part of Gangetic plain of Indian subcontinent, the district experiences three climatic seasons – summer from late March to mid time rainy season from mid June to October and the winter season from November to February. The month of February & March fall in the transitional season from winter to summer described as spring or “Basant”. Similarly the months of September & October falls in the transitional season from rainy season to winter season described as “Shishir”.

    Temperature Data (1993) Source: Meteorological Dept., Patna

During summer due to high temperature this becomes an area of low pressure. During this period Bay of Bengal, due to its geographical characteristics, serves as homeland for cyclones. Being on area of low presser, the plains of Begusarai and associated areas attract these cyclonic winds. This leads to the dust storms. These dry, hot, dusty storms are locally termed as ‘Loo’. These are prevalent in the month of May-June.

The rainfall is average in this area. The average annual rainfall in this belt of Ganga- Burhi Gandak is 1384mm of which 83% falls between Mid June and & Mid-October. Monsoon normally starts in June and lasts till October. The early monsoon currents, channeled to he NW are the principal source of rainfall of the region. 17 % of pre monsoonal rains, which is spread in the different months of the year (specially in the months of November- December-January) have been explained as due to Norwester affect and rest during monsoons due to Himalayan affect. Heavy rains, supplemented by physiographic/geomorphic features lead to heavy flood.

The chilling winter starts in mid-october and continues till initial periods of March. Most part of the winter is dry except some sporadic rains as mentioned above.

Physiography and Relief

   North Ganga plain is a major physiographic unit of the Indian landmass. It extends from the Himalayan terrain in the north to the river Ganga in the south covering about 56980 km². a roughly quadrilateral shape. Generally recognized as "a water-surplus area", this quadrilateral region is bounded by a northern piedmont belt where water oozes to the surface, followed by a broad belt of swampy lands, depressions and lakes, and finally an aggregation of alluvial fans as all these northern streams bend to form confluence points with the Ganga (Singh & Kumar, 1970).Hence, the surface is characterized by palaeo levees, swamps or flood basins locally called "Chaurs", relict palaeo channels aggraded in varying degrees, meander belts, ox-bow lakes and cut-of loops (Ahmad,1971). Its fluvial geomorphology is dominated from west to east by the Ghagra-Gandak Interfluves, the Gandak-Kosi Interfluves and the western Kosi Fan Belt. Some of these rivers frequently change their channels. Their channels are called by different names in different parts of their courses. According to a study in 1976 on Wetlands in Bihar, by Govt. of Bihar, natural wetlands of more than 100 ha each covered about 46828 ha (Directory of Wetlands, Govt. of Bihar)

The district of Begusarai lies in the middle part of this great plain known as mid Ganga plain.  In general, it is a low-lying flat terrain (MSL45m-32m) having a southerly to southeasterly slope. This factor governs the flow of streams. Geomorphologically it is a part of the Gandak- Kosi inerfluve (please refer subheading Geomorphology given below). The southern part of the district, except those of low-lying flood plains of Ganga, appears to be an elevated landmass when compared to the adjoining districts of Khagaria and Samastipur. Hence, being a safer destination amidst the flood drained region, it supports the human activities in a better way.

    The district Begusarai is divided into three flood plains namely
i. Kereha-Old Bhagmati flood plains,
ii. Burhi Gandhak Flood plain and
iii. Ganga Flood plain

                      The first two flood plains of the district are very low lying areaS and are prone to the flood. The floods owe their origin to the complex interplay of fluvial geomorphic elements in the upstream sections of the Kosi, Bagmati-Kareh-Budhi Gandak and related rivers.  These two flood plains converge in the southeastern part of the district, which is lowland. The streams flowing in the region show a shifting tendency. In the course of their shifting, the rivers leave behind their scars of their previous channels. Thus due to shifting nature of streams and physiographic characteristic, this part is full of wetlands, backswamps and oxbow lakes. However, in the southern part, the flood plains of Ganga are least prone to flodd. Interestingly the Railway track passing through the district marks a prominent divider line for Ganga flood plain and Kereha- old Bhagmati flood plains & Burhi Gandhak flood plain. The Flood plains of Burhi Gandak and Kareha are marked by the presence of paleo levees, oxbow lakes, paleochannels, relict streams and chaurs viz Kaulachaur and Bhagwanpur chaur. These chaurs serve as excellent fertile agricultural lands duing summer and are submerged during rains. Also the areas around these chaurs face the problem of submergence for around three-four months a year.  Kawar lake, a large fresh water lake which is basically a huge wetland is present as an important physiographic feature of this part.

In the Gangaflood plain, which is approaximately 50-55km long and 5-6kms wide,in the southern part of the district, except those low lying areas of “Taals and chaurs”, the typical fluvial characteristics of North Bihar rivers are not visible, which are prominent in the north of Railway track. This is the least flood prone area of the district, which gets drowned only in cases of exceptional floods in Ganga and Burhi Gandak. This relatively upland area appears to be the levee of river Ganga.

Geomorphic Setup

The mid-Ganga plains may be broadly divided into a number of major geomorphic units(Fig-).The northernmost part is the region of the Siwalik ranges and is followed by the piedmont fan surface fringing the foothills, 10-30km wide, built up by coalescing fan surfaces of major Himalayan rivers. This surface includes both the bhabar and tarai land. Built upon these surfaces are fluvial regimes classified into megafans (f) and interfluves, characterised by upland terraces (T2), river valley terraces (T1) and active flood plain surfaces (T0). The entire district of Begusarai falls in this T0 surface. The southern and northern banks of the Gangain and around Begusarai are charactersied by tributaries that flow parallel to the Gangafor long distances over the floodplain itself, before it joins at deferred junctions. This belt is named as the Gangayazoo belt (Sinha and Friend,1994).The Gandak-Kosi interfan has been divided into an upper area of gently converging rivers that flow SE , Perpendicular to the mountain front and a downstream area (the district of Begusarai and neighbouring area)where the more sinuous channels of the Burhi Gandak ,Baghmati,Kamla and Balan systems flow gently to the SE.

        Drainage

The district is drained by a no of rivers viz. Ganga, Burhi Gandak, Bagmati and Balan rivers and in addition, small rivulets, dhars, nalas which are originated locally and preserve rain water, mark the landscape. Among the rivers, Ganga,  Burhi Gandak, Kosi, Kareha and Bagmati are perennial, whereas Channa River, Bainti nadi,  Kachna nadi, Monrya nadi and Malti nadi are seasonal.

All the types of streams i.e. the mountain fed, foothill fed, plain fed and mixed fed, drains the district. Ganga is a mountain fed river while Bagmati is a foothill fed river. Burhi Gandak, Baya, Balan, Baintia, Chanha etc are originated in the plains and present examples of plain fed rivers. The small rivulets serve as tributaries to the streams of higher order. These rivulets are often dry lowlands during summer and flooded during rainy season.

In general, the drainage pattern of the rivers of this region forms a part of the greater Gangetic Plain, which is characterized as dendritic drainage pattern. However, locally they exhibit their typical characteristics. The Ganga River here shows Yazoo pattern of drainage and the area is known a Ganga Yazoo belt. Yazoo pattern of drainage is defined by the streams, which travel in a parallel fashion before confluence. Burhi Gandak, Bagmati, Kareha and Balan, Baintia, shows very high sinuosity and are typically meandering rivers.

River Ganga enters into the southwest part draining the Chamtha block in the district. This river along with its flood plains, “Chaurs” and “Tals” determines the boundary of the district in the southern part.

The Burhi Gandak, the 2^nd most important river, also known as Sirkahana in its upper reaches, enters the district near Parihara about 10 km upstream of its confluence with the Balan River.  It forms the boundary with Samastipur district in Khodawandpur and Cheriabariyarpur blocks. This is a river showing very high sinuosity and has characteristically low slit content than other Himalayan rivers. After traversing a distance of approximately 100 Km. it drains in Ganga near Khagaria .The river cause periodic floods in the western part of the district.

River Balan enters the district in the Bachhwara block. After taking a course of app 30kms km. it drains into Burhi Gandak River 5 km west of Manjhaul. This is also a highly sinuous stream

Bagmati – A very Juvenile stream of North Bihar plains, drains only the northeastern corner of district. It enters into the district near Bakhri and is well known for its unstable nature and spill channels. After traversing the low-lying valley areas, it meets the Kosi near Sankosh outside the territories of the district. It is responsible for floods in the northern part of the district.

Baintia River is a plain fed stream originated in the adjoining district of Samastipur and enters in Bhagwanpur block of the district. Upstreams, in the Samastipur district, it is known as Jamwari Nadi. This drains into Burhi Gandak after joining the Balan River. It is also a stream having water round the year. Baya Nadi drains the district Teghra, Bachhwara and Barauni block. It merges with river Ganga at  Roopnagar near Barauni fertilizer factory. This is a stream which does not show any sinuosity in the Begusarai district and is a perrennial stream. In the mid of the Burhi Gandak flood plain lies a vast fresh water lake known as Kawer Tal, which is basically a wetland formed by shifting of river BurhiGandak.  Kawartal gets its water either due to rains or due to near-by overflowing rivers such as Burhi Gandak, Bagmati

Kawar Tal

Kawar Tal is one of the examples of excellent wetlands, which are found in the flood plains, and is the largest freshwater lake in Northern Bihar. It lies between Burhi Gandak, Old Bhagmati and Kareh rivers. The lake is formed by the meandering action of Gandak River and is now a residual ox-bow lake, one of the thousands in Bihar and Uttar Pradesh flood plains. In years of high rainfall, vast areas of these two states get flooded. This causes coalescing of wetlands and forms one huge expanse of water. During these times the wetlands of the Kawartal region may cover hundreds of sq. kms. The floods leave behind deposits of sand, slit and clay in layers of varying thickness. In years of average rainfall, Kawartal gets connected with Burhi Gandak (a tributary of River Ganga) and with nearby Nagri Jheel and Bikrampur chaurs, unite to form a lake of about 7400 ha. By late summer however, the water is confined to the deeper depressions and only about 300-400 ha of Kawartal remains flooded and cut off from the adjacent floodplains (chairs). As the water level recedes, over 2800 ha of the exposed mudflats are converted into rice (paddy) fields. In 1951, a drainage channel was excavated to expose additional areas for agricultural purposes, but the channel silted up in few years, and the lake reverted to its former condition. In recent years, further siltation of the overflow channel has resulted in sight fluctuation in water levels throughout the lake. There is a permanent island (Jaimangalgarh) of about 130ha in the Southeast corner of the lake. The Kawar and its adjoining lakes are probably oxbow lakes fed by highly meandering river, the Burhi Gandak that once flowed through these areas. As this lake area remains wet and submerged for a longer period, it has developed specially adopted wetland vegetation and organisms. The emergent, submerged and floating plants present some unique type or representative flora and fauna particularly of this lake and its adjoining areas. Hence, it is a spectacular wetland habitat and perhaps one of the largest freshwater inland wetlands in the country.

          DRAINAGE AROUND KAWAR TAL

             (From Kumar, Sanjeev, 2004)

Drainage Characteristics of the Gandak Kosi interfan

The district of Begusarai lies in the southern part of the Gandak Kosi interfan area. The region between the Gandak and the Kosi megafans is a vast plain with a south-easterly slope reflected in the drainage directions. The major interfan rivers are the foot-hill-fed and the plain-fed Burhi Gandak, Bagmati, Kamla and Balan. These rivers determine the architecture of the flood plains. However, numerous interconnected minor channels participate in carving out the features of the plains by reworking and redistributing the sediments deposited by the major tributaries of the river. All the channels constitute low-lying areas and remain waterlogged during the monsoon. Channel avulsion and overbank flooding are the two most important factors controlling the floodplain development of the region (Sinha,1996). Avulsion is the sudden diversion of a part or whole of a river channel to a new course at a lower level on the flood plain. There is also a paucity of cut-offs, consistent with their moderate sinuosities.

The Burhi-Gandak river system has developed along the palaeochannel of the Gandak (Mahadevan 2002). Its channel has, however, become much smaller and highly sinuous and provides an example of river "metamorphosis". The river has however, been changing its course locally through avulsion, leaving extensive floodplain scars such as sinuous abandoned channels, "neck cut-offs" and ox-bow lakes, unmatched in their scale and abundance by any other part of the North Bihar Plains. Such cut-offs have resulted in reduction of channel lengths and sinuosity. Distinct topographic levels similar to what has been described earlier in the Kosi channel characterize the Burhi-Gandak floodplains near Muzaffarpur. The development of the different levels is attributed to local fluctuations in discharge and sediment load resulting in downcutting by the channel and lateral migration.

The Bagmati avulsive system is characterized by abandoned channels to the east of the present mid-reaches of the river. These are "underfit" channels and are activated and recaptured from time to time(Sinha1996) .A westward shift of the river is ,however, still evident. The Baghmati system encompasses what are turned "chute cut-offs", that may be a reflection of the "active migration where loop development and floodplain erodability during brief overbank flows are such as to allow the creation of new short-circulating channels". The Kamla and Balan systems show less evidences of avulsion. The westward shift of the Balan river is linked with the growth of the Kosi megafan. The Kamla river,however,is outside the influence of the growth of the Kosi megafan.

The transformation of channels, their metamorphosis, and the development of underfit channels, according to Sinha (1996), are both not due to climatic changes, as often assumed, but due to channel avulsion and channel-floodplain relationships. The development of "cut-offs" in the river systems is not so sudden an event and has taken place over a period of time, which, therefore, opens up scope to investigate the phenomenon more thoroughly. Some of the cutoffs have also evolved into ox-bow lakes. Other features of interest in understanding the evolution of the floodplains include features developing from lateral accretion, such as point bars and bedding structures and featured resulting from vertical accretion as natural levees, crevasse splays, backswamps, wetlands and lakes.

Controls in Shifting Courses

The rivers of this area exhibit a migrating tendency. The migration of rivers has to be viewed in the context of the fluvial evolution of the Indo-Gangetic plains. Brubank et al.(1996 in Mahadevan, 2002) address this question. A plausible model that helps to view the course changes is that the Himalayan provenance for the foreland rivers changed from a period tectonically dominated by thrust–loading and uplift in the Miocene to an erosionally dominated climatic-unloading, causing isostatic uplift. This concept is supported by the onset of suggested monsoonic climate due to Himalayan uplift around 8 Million years back.

As mentioned in the Geology subtitle, this MidGangaplain is a forelend basin which is subsiding with continous sedimentation in front of rising Himalayas. The cross-sectional geometry of the foreland and the patterns of fluvial deposition, inferred from the limited data now available, also support a dichronous evolution. In the Miocene period, when thrust loading dominated, the Indo-Gangetic foreland had an axial river system across its medial and distal parts flowing over its own accumulated sediments. With the onset of climate, induced erosional unloading of the Himalaya, transverse river systems started, dominating. The medial foreland pushing the medial axial river southwards to almost the featheredge of the foreland basin, even as the proximal part of the foreland was witnessing uplift.

In the context of the fluvial setting outlined above, channel shifting has been attributed to regional tilting, depletion of flow by fanhead tilting, derangement of drainage by earthquakes, the coriolis effect and auto cyclic mechanisms (Wells and Dorr.Jr. 1987 and references there in, from Mahadevan 2001).

Recent publications have emphasized the role of neotectonic changes in shifting river courses. Mohindra et al. (1992) and Mohindra (1995) attribute the shifting of the river Gandak to neotectonic tilting of the megafan eastward. However, the recent shifting of the Gandak River to its present channel from the Burhi Gandak channel westwards, suggests that there are also other factors (?autocyclic) which play an important role. A detailed analysis of the causes of shifting of the Kosi river by Wells and Dorr Jr. (1987 in Mahadevan 2002) leads to the conclusion that the

major shifts are "stochastic and autocyclic " and they do not well correlate with many severs earthquakes and floods, though they may have primed the system for shifts.

Diverse avulsion mechanisms have been inferred from the channel systems in the Gandak- Kosi interfluve. The Burhi Gandak shifts its channel eastwards due to paleotopography and sedimentological readjustment. The Baghmati shifts westward through the same mechanisms. The avulsion of the Balan river channels, however, is attributed to neotectonic response and the westward shift of the Kamla to the expanding growth of the Kosi megafan, on whose fringes the channels of Balan flow. The widely differing explanations of the shifting behaviors of North Bihar Rivers underline the complexity of the problem and the need for further research.

GeologyaandbSoil

 

The geology of the area constitutes the highest alluvial plain in the domain of the Himalayan Rivers to the north of the Ganga. It is a part of the Great Gangetic Basin. The basin was formed during late Paleogene-Neogene times and is related to the upheaval of the Himalayas vis a vis flexural downwarp of the Indian Lithosphere under the supracrustal load of the Himalayas (Wadia, 1961). The entire segment abounds in buried faults and grabens. The basin came into existence as a result of the collision of India and China continental Plates (Dewcy and Bird, 1970 in Parkash) during the Paleocene. Collision resulted in intraplate subduction along the MCT(Main Central Thrust lying in the Himalayas) raising the Higher Himalaya to form source rocks and “popping through” of the more southerly part of the Indian plate to form the basin. This “popping through” might have lead to the development of longitudinal and transverse lineaments thougout the basin. With time more southerly areas were raised and by mid-Paleocene subduction also started along the MBF(Main Boundary Fault lying in the Himalayas). These phenomena are reflected in the presence of a coarsening up megacycle with at least two superimposed minor cycle and in the composition of the sandstone and conglomerates of the basin. Later folding of the northern edge of basin to form the Siwalik Ranges during the Early Pleistocene led to cannibalism of this part of the basin.

The basin had east west elongated shape and started with a shallow marine environment, which changed to estuarine and deltaic one with time. By mid-Miocene, continental sedimentation marked by fluvial environment dominated the scene and this set up has continued to the recent with minor modifications. The basin had predominantly transversal pattern controlled by southerly flowing rivers emerging from the Himalaya and during Neogene period, a master stream along the southern margin of the basin drained into the Bay of Bengal. The fluvial sedimentation took place the form of mega-alluvial cones. Sedimentation in the basin was influenced by tectonism through out its evolution.

The Indogangitic Basin, still an active one, needs to be studied for detailed stratigraphic correlation, sedimentary facies relationship, change in climate through space and time and modern sedimentation.  

A Quaternary fault system has been identified in the region. This is an echelon pattern of surface faults associated with Begusarai fault (Fig). Within this fault zone, various geomorphic features are found which have their origin in both the lateral and vertical movement of fault-bounded slices, as well as in the persistent strike-slip. In regions where tectonic activity is less pronounced, streams generally flow more or less perpendicular to the adjacent highlands

The Quaternernay sediments of the Indogangetic plains have been traditionally subdivided into the older and younger alluvium and locally called Bhanger and Khader. Entire area of Begusarai falls in the domain of “Khader” sediments

The soil of this land unit is primarily unaltered alluvium, which is yet to undergo pedogenesis (process of soil formation). Texturally it varies from sandy loam to loam in the meander scroll and levee(the upland  bounding the flood plains of the river) areas, to silty loam and silt in flood basin areas of the Himalayan rivers and from loam in the levees of Ganga to clayey loam and clay in the basin of Burhi Gandak and Bhagmati river. The soil of the area is sandy loam rich with humus and is also very fertile.

Referances:-

1.       The subsurface Geology of the Indo-Gangetic plains M.B.R Rao,1973,no:-3,vol-14,journal of Geological Society of India,pp-217-242.

2.        Geological Evolution of Gangaplains an overview, Indra Bir singh,Journal of Paleontological Society of India vol-41,1996,pp-99-137

3.        The Indogangetic Basin- B.parkash and Sudhir Kumar,Sedimentary burins of India,Tectonic contest.

4.       Study of spatio-temporal changes in the weltands of North Bihar through Remote Sensing,A.K.Ghosh,N.Bose.K.R.P.Singh and R.K.Sinha July 204,ISCO-204,International soil conservation organisation conterence Brisbane

5.       kanwar lake wetlands, strategies for conservation Sanjeev Kumarhttp//sndp.nic.delhi..in, downloaded in March 2004

6.       Tectonic Zonation using Multi-Criteria Decision-Making (MCDM) Techniques: A case study of Kosi Fan, India Ajay Srivastava , www.gisdevelopment.net/application/geology, downloaded in March 2004

 

     MAP SHOWING   LINEAMENTS AND MAJOR FAULTS  AROUND  BEGUSARAI

(from Srivastava, A, 2004 )

   Regional geomorphic elements of the Mid-Ganga Plains of Bihar. T₁ – River valley terrace surface; T0 – active floodplain surface. MP – Marginal plain upland surface; PF Piedmont fan surface (Geomorphic elements after I.B. Singh, 1996).

(from Geology Of Bihar And Jharkhand,T.M.Mahadevan,2002 )

Geodynamic setting of in the three geomorphic domains of Bihar.Projected profile along 85⁰ E longitude.

(from Geology Of Bihar And Jharkhand ,T.M.Mahadevan,2002)