Planform Observation of De-Connectivity of Old Brahmaputra Offtake in Lean Period Using Satellite Images

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1 Journal of Modern Science and Technology Vol. 6. No. 1. March 2018 Issue. Pp.1-9 Planform Observation of De-Connectivity of Old Brahmaputra Offtake in Lean Period Using Satellite Images Md. Safin Ahmed 1 and Umme Kulsum Navera 2 Old Brahmaputra River takes off from the left-bank of Brahmaputra River and flows towards the south-eastern region of Bangladesh over Jamalpur and Mymensingh districts and falls into the Meghna River near Bhairab Bazar. Old Brahmaputra is a distributary of Brahmaputra that carries a small but significant amount of the Brahmaputra-Jamuna flow to the Upper Meghna River. Old Brahmaputra River offtake is one of the four major offtakes in Bangladesh and it is the most dynamic one. The flow of Old Brahmaputra River has been decreased significantly due to siltation at the offtake. Therefore, a study has been carried out to observe the planform changes of Old Brahmaputra River offtake over the period of 1973 to 2017 by different Landsat image composite. From the study, it has been observed that the Old Brahmaputra offtake has been silted up and de-connected with the parent river after 1990 during every selected lean period. Field of Research: River Hydraulics, Open Channel Flow, River Bank Protection, Geographic Information System and Remote Sensing, Nearshore Hydrodynamics. 1. Introduction Bangladesh is located at the lower part of the basins of three mighty rivers, the Ganges, the Brahmaputra, and the Meghna. Among them the Brahmaputra River is originated from the northern slopes of Himalayas. The main right bank tributaries of Brahmaputra River are the Teesta, the Dharla, the Dudhkumar and the left bank distributaries are Old Brahmaputra and the Dhaleshwari. Brahmaputra-Jamuna and Old Brahmaputra, with their main tributaries, and a good number of small tributaries and distributaries constitute the largest floodplain of Bangladesh. Old Brahmaputra and Dhaleshwari are the loop channels carrying a small part of the Brahmaputra- Jamuna flow to the Upper Meghna River (Banglapedia). The Old Brahmaputra takes off from the left bank of the Brahmaputra or the Jamuna to the north of Bahadurabad. Flowing more or less southeast it passes by Jamalpur and Mymensingh towns and falls into the Meghna at Bhairab Bazaar (Wazed, 2011). Most of the distributaries of major river system of Bangladesh have been silted up.presently, the mouth of Old Brahmaputra River is being dried up due to heavy siltation in the vicinity of the offtake (Noor, 2013). It receives a little but significant amount of flow from Brahmaputra River.The average migration rate of the Old Brahmaputra mouth is m/yr during (Ali, 2010).During the lean 1 Graduate Student, Department of Water Resources Engineering, BUET, Dhaka 1000, Bangladesh, safinporag23@gmail.com 2 Professor, Department of Water Resources Engineering, BUET, Dhaka 1000, Bangladesh, uknavera@gmail.com 1

2 period there is very little amount of water in the Old Brahmaputra River which is not adequate for maintaining perennial flow. The water level has also decreased significantly in the Old Brahmaputra River. Mortuza, et al., 2011, found the declination of water level has gone at faster rate during than in wet period. At present, heavy deposition has been taken place at the mouth, induced by intense sediment movement and char development. To observe this siltation problem Landsat satellite images have been collected and water level data has been collected to compare the physical condition of flow. From the study it has been found that the flow of water decreases significantly during the lean period because of the de-connectivity at the offtake. The paper is organized as follows: Section 1 deals with Introduction and Section 2 focuses on Literature Review and Section 3 contains Methodology. Results are provided in Section 4 and Conclusion is in Section Literature Review Different morphological analysis related to planform analysis, bank line shifting, erosion-deposition and bed level changes for the major rivers like Ganges, Jamuna, Padma and Meghna have been carried out in many studies which are reviewed for this study. Few studies have been found about the Old Brahmaputra offtake. The present study has been performed to observe the overall changes in plan form due to siltation problem around the Old Brahmaputra offtake by using remote sensing approach for the period of 1973 to In addition, previous studies and researches relevant to current study is discussed in the following articles. The offtakes are important links between the main rivers and the distributaries. The distribution of discharge and sediment transport at river offtake is a key factor for the long term morphological development of the main rivers (FAP 24, 1996a). Ali, 2010, studied about the siltation at the intake reach of the Old Brahmaputra River. In the study, satellite images, cross-sectional, water level, and discharge data of Old Brahmaputra River within the period from 1973 to 2005 were analyzed. It was found from the study that the overall trend line of Northing is increasing and Easting is decreasing, which indicates that the mouth of the Old Brahmaputra River is shifting towards north-west ward. It is also visualized that the river has become comparatively narrower. Noor, 2013, found that the mouth of Old Brahmaputra River is being dried up due to heavy siltation in the vicinity of the offtake and from numerical analysis found that the flow condition of Old Brahmaputra offtake can be improved by the combination of guide bund and dredging at the vicinity of the offtake. Ali, 2010, found that the percentage of flow from Jamuna to Old Brahmaputra was 6.67% in 1973 and it decreased to 0.7% in year 2007.FAP 24, 1996b, studied the Gorai offtake in detail on the Special Report No 10. Gorai is the only source of fresh water inflow to the Southwest region so offtake management is of prime importance. 2

3 Baki and Gan, 2012,studied riverbank migration and island dynamics of the braided Jamuna River of the Ganges-Brahmaputra basin using multi-temporal Landsat images. Hossain et al., 2013, assessed morphological changes of the Ganges River using Satellite images. Other research works have also been carried out by identifying the morphological changes of a distributary of the Ganges in response to the declining flow using remote sensing. Analysis of Water Level difference was not clearly mentioned in any of the previous study which is one of the important factors for water flow. 3. Methodology The study area is shown in Figure 1. The study area is located in North-central Bangladesh between longitude E E and latitude N N.The main part of the study area is under the district of Jamalpur. Coming across the Indian Border, Jinjiram River joins the Old Brahmaputra River just at the downstream of the offtake and constitutes the dry period flow. Figure 1: Location Map of Old Brahmaputra River off take The dynamic nature of Old Brahmaputra River offtake has been observed in this study. For this Landsat Look Images with Geographic Reference and Level-1 GeoTIFF Data Product have been collected from Earth Explorer ( different months of different years to observe the overall change in the plan form of Old Brahmaputra River offtake within the period of 1973 to Table 1: Data Collected for Old Brahmaputra River off Take Behavior Analysis Satellite Landsat Sensor Band Spatial Resolution of Composite Band Composite(m) Year MSS 2, 3, TM 3, 4, OLI 4, 5,

4 For the present study the following types of data have been used: Satellite images Water level data Analysis of Satellite image and water level difference are used to evaluate the deconnectivity of Old Brahmaputra offtake. Satellite image analysis is reliable and also widely used to find the changes in land and water surfaces. Multi-temporal Landsat image composite has been used for the plan form analysis. Different image composition with different band combinations has different appearance. Images have been presented as Landsat Look Natural Color Image and the study region has been showed in the map for observation. Historical Water level patterns have been analyzed by plotting water level data against different years. Historical water level data of different stations (Table2) have been collected and characteristic curves have been plotted for different time periods. Table 2: Water Level Data for Brahmaputra and Old Brahmaputra River River Station Station ID Year Kamarjani 46 Brahmaputra Kholabarichar and Bahadurabad Old Brahmaputra Jamalpur 225 Previously, Discharge data and Satellite data have been used for the analysis of Old Brahmaputra River offtake. In this study Water level data has also been incorporated with the satellite image analysis. 4. Results and Discussions The plan form change analysis has been performed within the period of 1973 to For this study dry and monsoon period images have been collected. A river shows different physical characteristics in dry and monsoon period. The image of the months of December, January and February have been chosen for dry period, on the other hand, June, July and October months have been selected as monsoon period. Analyzing the Landsat Satellite images of the old Brahmaputra River offtake area within the study period, it is found that significant changed has been occurred at the Old Brahmaputra offtake. 4

5 Figure 2: Land sat Image Composite of the Old Brahmaputra River Off take for (a) Lean Period and (b) Monsoon Period (a) (b) It can be observed from the composite satellite imagery that the Old Brahmaputra offtake is very dynamic in nature. It changes its course in every 3-4 years and the appearance of the offtake in the satellite images during dry and monsoon period are quite different. During the dry period (Figure 2 (a)) the river width shrinks considerably and the image of monsoon (Figure 2 (b)) shows a healthy river offtake carrying large amount of discharge. Figure 3: Land sat Image Composite of the Old Brahmaputra River Off take for (a) Lean Period and (b) Monsoon Period (a) (b) 5

6 Figure 4: Land sat Image Composite of the Old Brahmaputra River Off take for (a) Lean Period and (b) Monsoon Period (a) (b) In the Figure 3, the Old Brahmaputra offtake seems to be narrower and the connection has been lost from the Brahmaputra in dry season 1990 (Figure 3 (a)). During the monsoon period in the year of 1991 (Figure 3 (b)) the offtake is also narrower than the past. The decreasing trend continues in the following years. The effect of offtake congestion is reflected through the whole River. From Figure 4, it can be observed that the river offtake has been de-connected due to siltation which means the offtake is no longer an active offtake. The offtake has lost its connection with the Brahmaputra River especially during the dry period (Figure4(a)). The monsoon period image (Figure4(b)) is also no longer as like as it was previously. This indicates that the Old Brahmaputra River is no longer carrying the amount of discharge it carried previously. The connectivity of the Old Brahmaputra offtake during lean period: Table 3: Connectivity Period of Old-Brahmaputra Off take Connected Offtake Disconnected Offtake Table 3 shows the period of connectivity of Old Brahmaputra River offtake with the parent river. Until 1987 there was a good connectivity at the offtake but it lost its connectivity from the year 1990 to Due to the de-connectivity at the offtake the discharge through the River has decreased significantly. Figure 5 shows the long term change in the Old Brahmaputra offtake. It is clearly visible that the offtake has been silted up and narrower channel is observed in the year 2017 with compared to the year

7 Figure 5: Detailed Image of the Old Brahmaputra Offtake Figure 6: Time Series Plot of Water Level ( ) Water Level (m PWD) Time Series Plot of Water Level Kamarjani Kholabarirchar Bahadurabad Jamalpur Year Figure 6 shows the time series plot of water level data at different station of Brahmaputra and Old Brahmaputra River. The water level at station Kamarjani is higher than the Kolabarichar and Jamalpur stations so the offtake can carry considerable amount of water flow in to the Old Brahmaputra River. Figure 7: Time Series Plot of Water Level ( ) 25 Time Series Plot of Water Level Water Level (m PWD) Kamarjani Kholabarirchar Bahadurabad Jamalpur Year 7

8 It can be seen from figure 7 that the water level at Jamalpur station has been reduced than the previous data shown in figure 6 for the year 1973 to According to the time series plot of water level data, it is obvious that the water should pass through Old Brahmaputra offtake and flow as gravitational flow as the water level is higher at the Kamarjani station than the Jamalpur station. But the discharge is not as expected because of siltation at the offtake. The offtake has lost its connectivity with the parent River Brahmaputra. Figure 8: Water Level at Jamalpur Station from 1973 to 2016 Water Level (mpwd) Water Level at Jamalpur Station Year The lowest dry period water level at Jamalpur station found to be mpwd in 18 th April 1973 whereas it has reduced by 1.55mPWD on 29 th March 2015 and became 10.40mPWD which can be clearly seen in Figure Conclusions The Rivers of Bangladesh carries a considerable amount of sediment of which a substantial amount is deposited along the bed and the rests are flushed to the sea (Ali, 2010). The Old Brahmaputra River is facing the problem of sedimentation at the offtake. From this study the Old Brahmaputra offtake has found to be dynamic in nature. But its activeness has decreased due to siltation. The physical characteristics have changed also over the study period. The major change in the offtake is found after 1990 and gradually it has shrunk to such an extent that it cannot carry remarkable amount of discharge anymore. So a comprehensive study on morphodynamic changes of Old Brahmaputra Offtake need to be carried out and alternate solutions like dredging, guide bund, construction of different hydraulic structures to revive the flow in lean period need to be taken into action. After analysis of Satellite images and water level data, the morphological analysis, sediment movement pattern analysis can be conducted for future planning to manage the offtake properly. 8

9 Reference Ali, F., 2010, A Study on siltation at the intake reach of the Old Brahmaputra River, M.Engg Project, Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh. Baki, A. B. M. Gan, T. Y., 2012, Riverbank migration and island dynamics of the braided Jamuna River of the Gangese Brahmaputra basin using multitemporal Landsat images, doi: /j.quaint Banglapedia, Brahmaputra River, < FAP24, 1996a, River Survey Project, Morphological Process of Jamuna River, Special Report 24, GoB/FPCO, Prepared for Water Resources Planning Organization, Dhaka, FAP24, 1996b, River Survey Project, Morphology of Gorai Offtake, Special Report 10, GoB/FPCO, Donor: Commision of the European Communities (CEC). Delft Hydraulics, Danish Hydraulic Institute, Osiris, Hydroland, Approtech. Hossain, M. A., Gan, T. Y., Baki, A. B. M., 2013, Assessing morphological changes of the Ganges River using Satellite images, doi: /j.quaint Mortuza M. R., Rashid, U. S., Rajib, M. A., Rahman, M. M., 2011, Temporal Variation Characteristics of Flow and Water Level in the Old Brahmaputra River, Published in ISWREP, Noor, F., 2013, Morphological Study of Old Brahmaputra Offtake Using Two- Dimensional Mathematical Model, M. Sc. Thesis, Bangladesh University of Engineering and Technology (BUET), Dhaka, Bangladesh. Wazed A., 1991, Bangladesher Nadimala (Rivers of Bangladesh, in Bangla),Labani, Dhaka. 9