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Changes in Physical Environment of the Southwestern Coastal Bangladesh: a River Basin Approach

Md. Saifuzzaman
Department of Geography and Environment, Jahangirnagar University, Savar, Dhaka-1342, Bangladesh

Mohd. Shamsul Alam
Department of Geography and Environment, Jahangirnagar University, Savar, Dhaka-1342, Bangladesh

Abstract/ Executive Summary:

This study deals with the nature and state of geomorphic environmental changes of a coastal river basin at southwestern Bangladesh over a period of three decades (1973-2009). The study concentrates on the Kholpetua river basin, which receive fresh water flow from Betna in the upstream and tidal flow in the middle from Morichapa and finally drains to the Bay of Bengal through Kapotakshi River. The whole Kholpetua basin may be divided into three distinct parts: fresh water upstream, brackish water middle part and saline lower part.

Large-scale population increase, both in the upper and middle basin; infrastructure development, in the form of road network and introduction of HYV rice in the floodplain of Betna and shrimp farming on the brackish water have lead to the loss of both quality and extent of wetland resources in the basin area, endangering the geomorphological balance in terms of input and output between upstream and downstream. A large section of Betna has dried-up, and most of the tributaries and distributaries of the Morichapa have been silted up, partly because of extensive polders of the sub-basin. As a result, energy exchange (through tide) between basin plains and channels ways has lost vitality.

Multi-spectral remote sensing data, in conjunction with topographical maps and ancillary data analysis reveals that throughout the basin, a wide range of anthropogenic interference have physically altered the characteristic ecosystem of the basin. The agricultural land is about 79,395 ha. in 1973, which is reduced at about 53,328 ha in 2009. With 1779 to 2001, a strip of about 20 km wide mangrove forest has been disappeared. Such physical alteration has been initiated with the poldering of middle brackish water part of the basin and later with the introduction of extensive shrimp cultivation. Attempt has been made to explore the linkage of upstream landuse activities and drainage alteration to the hydrological and geomorphological behavior of the downstream basin areas, extrapolate ecological sensitivity of the basin.

Keywords: South-western Bangladesh, River basin Environment, Hydro-geomorphology, Coastal embankment (Polder), Land use and Land cover, Remote Sensing and GIS

Location: Upazila Kaloroa and part of Satkhira, the middle basin covers part of Assasuni and Shyamnagar covers the lower part of the basin. It covers the Upazila of Shyamnagar

Start Date:

End Date:

Program Area: Socio-economic and Policy

Commodity: Adoption and mitigation technology, Remote sensing

Objectives:

The aims of this research is to describe and explain the nature of environmental transformation in the Kholpetua river basin during (1973-2009) with the particular reference to its geomorphological, environmental setting, land use and land cover changes and human interventions.

Methodology:

Study area: Kholpetua basin has developed from the combination of two important channels; the Betna and the Morichapa at the upper and middle part respectively. The upper part of the basin covers upazila Kaloroa and part of Satkhira, the middle basin covers part of Assasuni and Shyamnagar covers the lower part of the basin. It covers the Upazila of Shyamnagar in the lower middle and lower estuarine part.

Topographically, ridge and valleys are two common features of the flood and tidal plain. Slope declines from 5m at the upper Betna to 0.6m at the lower Kholpetua. High tide reaches approximately up to 4 meters which means more than 90 percent of the basin area are under regular tidal influence. Agro-ecologically, the basin covers five characteristic zones such as Lower Ganges flood plain, saline calcarious, saline mixed, saline acid sulphate and mangrove areas.

The broad agro-ecological zonation clearly reflects the local tidal soil and agro meteorological condition. Among the zones only lower Ganges floodplain are under intense agricultural practice. The other zones are limited to rice cultivation in the wet season. The major part is under mangrove forest with very dense river network. The upper part of the Kholpetua basin area (Kolaroa) witnessed intense human pressure in the form of agriculture. The middle and lower mid basin area covering lower Satkhira, Debhata, Kaligonj and Shyamnagar area under polder/coastal embankments, since early seventies. Being protected against regular tidal effects through polder/embankment, the land witnessed a transformation from paddy cum grazing agriculture to protected agriculture up till the middle of 80’s, when shrimp farming was introduced. Originally, the whole area was under mangrove forest even in the late 18th centuries (Rennells, 1779). Fierce competition between low yielding rice cum grazing and shrimp within the semi-saline belt came into surface (DDP, 1985). The local traditional agriculture practices are more of local demand driven; the shrimp farming, however, is more of international market demand based.

Traditional agricultural practices are on retreat more rapidly mid basin to upper basin. Therefore, diversified demand agriculture has also declined in the area. The shrimp farming practice support very limited population, reduced in surplus agricultural labor. Moreover, net cultivable agricultural land has declined quite dramatically, putting tremendous pressure on the marginal farmers and landless people. Methods: Optical satellite remote sensing and hydrological data were used primarily in this study. Secondary data such as agro-ecological, hydro-geomorphological, elevation, population census and land use, and infrastructure related information’s were also used. Renells map of 1779 and Thuilier’s Map of 1872 were analyzed to record the extent of changes occurred in the mangrove forest. Digital image processing software was used to process the images and analyzed to identify and classify the basin area into different land use and land cover units. Bangladesh Water Development Board’s data on tidal records and embankment alignments were analyzed in Microsoft excel and access environment and for documenting the nature and form of the changes occurred in basin landscapes.

Source of Information: Khulna University Studies Special Issue (SESB 2010): 1-7: June, 2010

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The present study is only indicative of the types and direction of environmental changes occurred in a coastal river basin arising out of present human activities. Large-scale population increase, expansion of human settlements and intensive agricultural practices in the Kholpetua basin area has created the ground for major environmental transformation. Similar transformation of the river basin are widely taking place elsewhere of the coast. Further research is needed to generate the hydro geomorphological and bio-geomorphological aspects in a basin approach, so that measures and related to the environmental quality of the basin may be maintained in a sustainable manner.

Knowledge Management: Journal