The Dibrugarh district extends from 27^o 5' 38'' N to 27^o 42' 30'' N latitude and 94^o 33' 46'' E to 95^o 29'8'' E longitude. It is bounded by Dhemaji district on the North, Tinsukia district on the East, Tirap district of Arunachal district on the South-East and Sibsagar district on the North and South-West. The area stretches from the North Bank of the mighty Brahmaputra, which flows a length of 95km through the northern margin of the district, to the Patkai foothills on the South. The Burhi Dihing, a major tributary of the Brahamputra with its network of tributaries and wetlands flows through the district from east to west.

PHYSIOGRAPHY :

       The Dibrugarh district is located in the north eastern corner of the Upper Brahamputra valley south with an altitude ranging between 99 and 474 meters. A major part of it is and extensive plain formed by the Brahamputra and its major south bank tributary-the Buri Dihing.

       The Physiography of the district is constituted by a variety of elements such as flood plain, beels and swamps, occasional highlands and foothills of the Barail Range. The Brahamputra river is fairly wide here (average width 10km). The general gradient of the district of the area is from south-east to north-west. The altitude of the south-easternmost corner covering the Hapjan Parvat and Hilika Parvat of the Barail foot hills is 200m. The height decreases gradually from this corner to the mouth of the Buri Dihing river where the altitude is 99 m. However the northern belt of the area has a gentle slope from east to west. The altitude of the eastern part is 115 m, while it is 99 m in the western part. The average east-west slope is 152 cm per km. Because of the relatively high slope and large volume of water, the Brahamputra flows with a high velocity causing significant bank erosion in the area. The earthquake of 1950 (magnitude 8.7 in the Richter scale, Poddar, 1952) accelerated the intensity of bank erosion. The impact is alarming in the north of Dibrugarh city and Rahmaria mouza.
       The area may be divided into three distinct physiographic zones stretching parallel to the Brahamputra river. These are : (i) The active floodplain and 'charland', (ii) the middle plain; and (iii) the southern foothills.

       The first zone is an extensive and active floodplain of the Brahamputra. The 'charlands'(sandbars) have also been included in this zone. The charlands are suitable for grazing during the winter season. The second zone is extensive because of the presence of fairly large tributaries like the Dibru (which has now merged with the Brahamputra) and the Buri Dihing through their headward erosion added alluvial land substantially to the great plain of the Brahamputra. This plain contains the rich belts of tea and rice cultivation. All the mouzas excluding only Joypur are partly or wholely in this zone. The highly meandered course of the Burhi Dhing here has left cut off as many as 39 wetlands in the form of ox-bow lakes and swamps. The foothill zone on the other hand consists of isolated hillocks interspersed with plain embayments extending into the Naga hills. The high grounds of this zone composed mostly lateritic soils are covered by tea gardens or dense forests. Located in this zone, the Joypur Reserved Forest occupies an area of 10,666,08 hectares.

RIVERS AND WETLANDS :
       On the northern margin of the district lies the river Brahamputra which basically drains the whole area. The Brahamputra here is very wide and braided. Near the Dibrugarh City the river is 10km wide with a large number of sandbars. Till the great earthquake of 1950 the north easternmost corner was drained by the Dibru River. The Dibru was a main tributary of the Brahamputra the confluence of it being at about 18km east of Dibrugarh City. By raising the bed of the Brahamputra , the earthquake caused severe erosion on its south bank and as a result the Dibru river got merged with its master stream in Rahmaria mouza. Earlier, the interfluves of the Brahamputra and the Dibru was on an average 6-8 km wide within the district. Some of the inhabited villages like Sainaki, Erasuti, Chabaru Kalioro, Sairsuti, Nepali Block, Mohmora, Charisuti, Nepali South Block in between the Brahamputra and the Dibru, and Rangajan, Laruparia Pathar, Guiphala Habi, Laruporia Saugaon, Guiphala, Nagaon, part of Rahmaria Gaon, Gaharipathar, Piporatoli, Nefafu grant on the south bank of the Dibru alongwith their fertile agricultural land and forest cover were wiped away by the Brahamputra. Now, Maijan stream, a tributary of the former Dibru has become a tributary to the Brahamputra.
       Buri Dihing river flows from almost east to west through the area. It has many tributaries such as Digboi, Tingrai, Tipling, Telpani, Deherang and Sessa in the north bank and Tipam and Disam in the south bank. In addition to the tributaries of the Burhi Dihing, there are three other tributaries of the Disang river( in Sibsagar district) namely Gela Disam, Tiolo and Demow flowing mainly from the Tingkhong mouza. Official reports , in fact suggest that Burhi Dhing is the erstwhile Namphuk river. It flows for 90 km through the Patkai Hills before it comes down to the foot hill zone. Thereafter flowing in a south-west direction for 20km it meets the Khaikhe and Meganton to form what is called Burhi Dihing. The Burhi Dihing meanders through the plains facing Patkai Hills for a length of 50km and then enters into Joypur-Digboi low hill range. It then comes out near Joypur to flow through the plains for a length of 120km and ultimately joins the Brahamputra at about 32 km south-west of Dibrugarh city.

WETLANDS :Like any other parts of Assam, the area is endowed with extensive water resources. The district possesses a large number of wetlands of varying sizes. The larger ones are popularly know as beel, while the marshes and swamps are generally known as jalah, doloni, pitoni, doba, etc. In some areas, the beels are referred to as gadang. However, all these features may be include under the comprehensive term ' wetland'. The wetlands may broadly be divided into two categories : the lake-like ones , i.e beel with clear wide-spread water area and the others i.e. swamps and marshes covered by weeds, grasses, etc.

       Both the beels and the swamps are geomorphologically, ecologically and economically very important features. These comprise a major component of the area's ecology. The beels are traditionally used as natural fisheries. Even today, the beels produce more fish per unit area than any many other man-made fisheries. A large number of beels are connected with the rivers by one or more feeder channels. These feeder channels are lifeline of such water bodies.

Table : Mouzawise distribution of beels in Dibrugarh district Mouza Number of Beels Name Larua 12 Bhangamukh, Morisuti, Rongabeel I, Kutuha Borbeel, Kawaimari beel, Garudhoria, Alichiga, Chahjan, Larua, Rongabeel II, Chapara beel, Nowjan Lengri 6 Merbeel, Chenimari, Hakoibeel, Desang beel, Garuhara, Choichiga bee Tengakhat 5 Bhereki beel, Ghulong, Nalani beel, Balibeel, Dhoni beel Kheremia 5 Bhereki beel, Ghulong, Nalani beel, Balibeel, Dhoni beel Sassani 5 Merbeel, Godhabeel, Singibeel, Disam, Gola Disang Joypur 3 Lakhutipota beel, Longhari beel, Kaliapain beel Mancotta 2 Borbeel, Bahuguwa Moran 1 Jaliyani beel Bogdung 1 Sarujan CLIMATE : Being located on the north of the 27o North latitude and with its unique physiographic elements, the area experiences subtropical monsoon climate with mild winter, warm and humid summer which may be designated as CWB (Borthakur,1986). Rainfall decreases from south to north and east to west in the area. The average annual rainfall of the Dibrugarh city in the north is 276 cm with a total number of 193 rainy days, while at Naharkatia in the south, it is 163 cm with 147 rainy days. The temperature generally decreases from south to north. The average annual temperature in Dibrugarh and Naharkatia is 23.9 C and 24.3 C respectively. Located on the bank of the Brahmaputra, the Dibrugarh city experiences mild climate with low temperature and high rainfall as compared to Chabua in the east and Moran in the west. The average annual temperature in Chabua and Moran is 28 C and 32 C respectively. Rainfall records show a decreasing trend towards east and west of Dibrugarh city. The annual amount of rainfall in Chabua and Moran is 250 cm and 171 cm and 171 cm respectively. On the basis of the climatic characteristics such as distribution of temperature, rainfall, rainy days, humidity, presence of fogs and thunderstorms, the climate of the area may be classified into four seasons :         (a) winter, (b) pre-monsoon, (c) monsoon and (d) retreating monsoon   WINTER : The winter covers the months of December, January and February. In this season, fair weather prevails occasionally associated with fogs and haze. December and January are the driest months and January is the coldest. The minimum temperature ranges between 8 C and 10 C and the maximum between 27 C and 29 C. The average rainfall in the season is 20 cm. PRE-MONSOON : The months of March, April and May constitute the pre-monsoon season. From March the land surface gets steadily heated and the temperature starts rising. Strong convection develops due to the local depressions formed especially in the afternoon. The nor'westers locally called Bordoichilla appears during the period. Rainfall ranges between 59 and 160 cm and maximum temperature ranges between 28 C and 32 C. This season is, in fact, a transitional phase between the dry cool winter and the warm moist monsoon. MONSOON : With the onset of monsoon in early June, heavy rainfall occurs.Widespread low clouds and high humidity together maintain almost uniform temperature over the area. The maximum temperature ranges between 33 C and 37 C. The average annual rainfall during the period is 300 cm. The occurrence of thunderstorms is the most conspicuous characteristics of the monsoon weather. This is the season of dominant agricultural operation in the area. RETREATING MONSOON : The monsoon withdraws from the area in the last week of September or first week of October. The cool north-easterly winds originating over the lofty mountains of the Arunachal himalayas brings the temperature down. The orographic low is replaced by high pressure and a flat pressure gradient occurs. Rainfall decreases abruptly and the sky becomes progressively clear. Sunny days prevail till the end of November.The CWB climate thus has a profound influence on the economy and lifeof the people of the area. It is most suitable for the cultivation of a variety of grain and horticultural crops. SOIL : The soils of the area are basically the products of the fluvial processes of the Brahmaputra and its tributaries. The plains are composed of alluvium which may be classified as new and old. The new alluvium varies mostly from clayey to sandy loam in texture and is slightly acidic in reaction. it is deficient in phosphoric acid, nitrogen and humus, but rich in lime and potash. It is found in the vast plain of the district along the river valleys, especially in their lower courses.The old alluvium on the other hand occurs in the upper and middle parts of the valleys. It occurs mainly in Joypur,Tipling, Kheremia and Tengakhat mouzas in the form of terrace deposits. These deposits contain alternating beds of pebbles, gravel or boulder with loose sand and clays. In certain parts, both the old and new alluvium are so combined that it is difficult to distinguish them.        The old alluvium has relatively high percentage of acid and soluble Mg accompanied by Ca in general, its HCL soluble material contents are lower and the percentage of MgO is higher. The pH value ranges between 4.2 and 5.5 with very low quantity of exchangeable calcium which varies from 0.1 to 5.0 mg per 100 gms of soil        The new alluvium is less acidic as compared to the old alluvium. Its pH value varies from 5.5 to 9.0. These soils are rich in PO4'K and Ca (6 to 21mg per 100 gms of soil), but its N2 content is somewhat low, being 0.1percent .Tea is abundantly grown in the old alluvium as it has high percentage of acid. The tea estates are located over relatively high lands covering mainly the mouzas of Chabua, Bogdung, Rahmaria, Tengakhat, Tipling, Kheremia,Gharbandi, Lahoal, Moderkhat, Mancotta, Jamira, Joypur and Tipling with discernible slopes containing both old and new alluvium. Heavy clays, with high percentage of N2 are suitable for rice cultivation. The silty river banks lying in Lengri, Khowang, Mancotta and Larua are favourable for pulses and vegetables.        The river banks bear texturally three types of soil: sandy loam, loam and clayey loam. These favour the cultivation of winter rice, mustard, pea, vegetables, etc. Of the total river bank area, 82.0 percent is arable, 7.0 percent is non arable land and 11.0 percent is not available for cultivation. As per the reports of the National Watershed Development Project for Rainfed Areas (NWDPRA) , 1991-92, soils of the flood plain may be classified into four classes : Land having moderate limitations and good land which is subject to wind and water erosion and can be cultivated with some corrective measures, Second, Land having moderate limitations and good land with excessive sand structure, gravel and stony conditions that can be cultivated with some corrective measures), Third, land having severe limitations like excessive wetness or too much overflow where regular cultivation is possible if hazards are removed and well treated by corrective measures and fourth land not suitable for cultivation due to excessive overflow or water-logging condition which can not be drained out and can be used only for fishing (Fig.2.4). The percentage strength of area under the these classes are 82.0, 8.0, 4.0 and 6.0 respectively.