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Dynamics of River Water Level in Sylhet Basin

M Islam*
Department of Irrigation and Water Management, Sylhet Agricultural University, Sylhet-3100, Bangladesh

S Ahmed
MS Student, Department of Irrigation and Water Management, Sylhet Agricultural University, Sylhet-3100, Bangladesh

Abstract/ Executive Summary:

Rivers carry water and nutrients to areas all around the earth and provide excellent food and habitat for different microorganisms and also important for livelihood resides in the bank of the river. With an ever-growing population demand for water and increasing climate uncertainty, there is pressing need for improved understanding of the underlying patterns of natural variability of water resources and consideration of their implications for water resource management and conservation. In this regard various climatic parameters such as rainfall, temperature, humidity etc. shown significant trends in river water level. Rainfall, which was regarded as a main influencing factor found to same in the changes occurred during the study period, except the month of April to July. The change of the maximum and minimum temperature over the year was also found almost constant. As the temperature increases, the rate of evaporation also increases which tends to decline the river stage. But, the highest rainfall has put a significant influence to maintain the evaporation loss. In respect of humidity, the higher relative humidity occurred during the months from May to July in every year. In the winter season, evaporation occurred at a higher rate as the relative humidity decreases. As a result, river water level declines but during monsoon the river stages regain its original phase. Climatic parameters played an important role on river water level. Studies on geological settings reveal that the sediment deposition during the Holocene passing through the Sylhet basin occurred at a higher subsiding rate. It may be concluded from the study that an optimum utilization of land and water resources by understanding the morphological process and subsequent prediction for any intervention in Sylhet basin for the development of lives and livelihoods in the area.

Keywords: River, Climatic parameters, Livelihood, Sylhet basin.

Location: Sylhet, District

Start Date:

End Date:

Program Area: Crop-Soil-Water Management

Commodity: Water management

Objectives:

The objectives of this study were to evaluate the dynamics of river water level and to observe the influence of climatological parameters on the river water level.

Methodology:

Description of the study area The Surma Basin is a sub-basin of the country situated in the north-eastern part of Bangladesh. The basin is bounded on the north by the Shillong plateau, east and south-east by the Chattogram-Tripura fold belt of the Indo-Myanmar ranges, and west by The Indian Shield platform. To the south and south-west, it is open to the main part of the Bengal Basin (Johnson and Alam, 1991). The published Bouger anomaly map shows gradual higher values (negative) towards the center of the basin. The Aeromagnetic interpretation map by Hunting (1980) indicates a gradual deepening of basement towards the center of the basin and also reveals subsurface synclinal features and faults within the basin. Its topography is predominantly flat with some north-south trending ridges of twenty to several hundred meters elevation present in the north-eastern border. It is actively subsiding (Johnson and Alam, 1991). Geological setting of the north-east region of Bangladesh The Sylhet trough is a sub-basin of the Bengal Basin and consists of 13-20 km thick alluvial and deltaic sediments underlain by much older genesis and granitic rock. Goodbred and Kuehl (2000) estimated the sediment thickness during the Holocene based on the analysis of borehole data and carbon dating information. The long profile of sediment deposition during the Holocene passing through the Sylhet basin up to the sea indicates that higher deposition occurred at the northern boundary of the basin, which suggests a higher subsiding rate. River system The water resources in the area originated from the "Surma" River which is hydraulically connected to the underlying alluvial aquifer system.The Surma originates in the hills of Shillong and Meghalaya of India. The main source is Barak River, which has a considerable catchment in the ridge and valley terrain of Naga-Manipur hills bordering Myanmar. Barak-Meghna has a length of 950 km of which 340 km lies within Bangladesh. On reaching the border with Bangladesh at Amalshid in Sylhet district, Barak bifurcates to form the steep and highly flashy rivers Surma and kushiyara (http://en.banglapedia.org). Surma flows west and then southwest to Sylhet town. From there it flows northwest and west to Sunamganj town. Then it maintains a course southwest and then south to Markuli to meet Kushiyara. The joint course flows up to Bhairab Bazar as the Kalni. Flowing north of the Sylhet basin, Surma receives tributaries from Khasi and Jaintia Hills of shillong plateau. All these rivers and its tributaries are silt-carrying, flashy and eroding. Selection of gauge station and data analysis The study was conducted using secondary data. The selected gauge stations were SW-167 at Surma River in Sylhet, SW-158 at Khowai River in Habiganj, SW-201 at Monu River in Moulvibazar, SW-269 at Surma River in Sunamganj. The daily and monthly rainfall data, relative humidity, the daily temperature of Sylhet rain gauge station was collected from the Bangladesh Meteorological Department (BMD) for the period of 2000-2015. The river water level data were collected from Bangladesh Water Development Board (BWDB) for the period of 2000-2015. The rainfall data were taken as monthly total, the temperature, and relative humidity manipulated as monthly average. The collected data were processed graphically to make them error free and to fill out the missing data where possible. The processed water level, rainfall, temperature and relative humidity data were analyzed to evaluate the variation with time and to observe the pattern of variations.

Source of Information: J. Sylhet Agril. Univ. 4(2):315-324, 2017 ISSN: 2308-1597

Article Link (Online Journal): www.jsau.com.bd

Funding Source:

1.

Budget:

Total Budget (Tk.) :

Achievement/Findings:

Water level fluctuation is very common in the rivers, as they depend on seasonal precipitation and the inflow from upland sources. The rising rainfall tends to increase the river water level. It receives maximum rainfall in the month of April to July which also augmenting the river stage. As the temperature increases, the rate of evaporation also increases which tends to decline the river stage. But, the highest rainfall has put a significant influence to maintain the evaporation loss. In winter season, the rate of evaporation is high as the relative humidity decreases which results in declining river water level. In monsoon season, the river stage rises as the relative humidity increases.

Knowledge Management: Journal