Abstract
Saltwater intrusion is one of the major problems in the coastal zone of Bangladesh. It is increasingly
alarming due to natural and anthropogenic reasons. About 53% of the coastal areas are affected by
increase in salinity. The Ganges River supplies freshwater to the South-West region of Bangladesh
mainly through one of its tributaries-the Gorai River. The Gorai used to discharge into the Bay of Bengal through the Madhumati-Nabaganga, Baleswar and Passur Rivers. The Farakka barrage on the Ganges River commissioned in April 1975 has been diverting water to keep the Bhagirathi-Hooghly
River navigable. This diversion has reduced the dry season discharge of the Ganges and Gorai Rivers
in Bangladesh and as a result the Gorai River has induced accelerated sedimentation and increased
salinity in the South-West region of the country. The mean peak flow in the Gorai River was 6,200
m³/s in 1962 and the recent recorded flow in the dry season was only 10 m³/s in 2008. This study was aimed to know the saltwater intrusion and other climatic factors as well as anthropogenic impact on fish diversity and livelihoods of the riverine inhabitants in the Gorai River System. In order to
determine the extent of the natural range of variation, this study assessed hydrologic flow thresholds
for the Lower Ganges River Basin. The impact of Farakka Dam on the Lower Ganges River flow was
calculated by comparing threshold parameters for the pre-Farakka period (from 1934 to 1974) and the
post-Farakka period (1975–2014). Empirical analysis demonstrates the relationship between the
newly saltwater intruded slight saline area of the Nabaganga River of Kalia Upazila under Narail
district of Bangladesh. Local people's perception and experts' judgment were used in detecting decreasing trend or disappearing of fish diversity with increasing in river salinity. It has been found
that the diversion has reduced the dry season discharge of the Ganges and Gorai Rivers in Bangladesh.
Statistical analyses indicated that the changes in the dry season discharge of these rivers were significant. It has been observed that the major part of the Gorai River basin is dry, and as a result the
saline water from the Bay of Bengal has been penetrating in the upstream of the Gorai River
catchment. Saltwater intrusion along the Passur-Rupsha-Nabaganga systems has largely been
influenced by the dry season flow of the Gorai River. It has been revealed that in Bordia point of
Narail, the salinity varied approximately within the range from 0.00 to 0.92 ppt. It has been observed
that around 1.00 ppt salinity in the Bordia point of the Nabganga River was recorded around 165 km
down of the Harding Bridge, Kushtia and 72 km up from the Khan Jahan Ali Bridge on the Rupsha River, Khulna. Saltwater intrusion and other climatic factors, decline of freshwater flow and other
human interventions exert threats to the fish diversity and existence in the Nabaganga River of the
discharge in the Gorai River and salinity. Fish diversity and livelihoods study was carried out at the
of
Gorai River system. Forty one species belonging to 35 genera, 18 families was recorded. The most
dominant family in this river system was Cyprinide. Besides the truly freshwater forms, some
estuarine species that found in the river during some part of their life were also recorded. Increased
salinity caused the reduction of fish species in Nabaganga River from 41 to 35 species during the
period of 1970-2014 and 6 fishes has already been disappeared. Total fish catch has been reducing day
by day. Aged people mention that during liberation war of Bangladesh (1971), around 2,100 tons
fish were caught and marketed in the Bordia fish market. This quantity has gradually decreased and
after 30 years fish catch has decreased to 50% by 2000 and in 2014, fish availability has decreased to
75% in the Bordia fish market of Narail. Saltwater intrusion not only reduce fish production, but also
it is responsible for the reduction of fish biodiversity, hampering ecosystem, deteriorating natural
environment and creating negative impacts on the socio-economic conditions of the people of study
areas. Moreover, in maximum cases, the people of these areas are changing their occupations, such as
fishers' to shrimp farming, prawn seed collection, shopkeepers, and laborer. So, saltwater intrusion is
one of the major natural hazards affecting the environment and socio-economic condition of the people
of South-Western areas of the country. In this perspective, immediate steps have to be taken to prevent
saltwater intrusion and to find out suitable ways for adaptation with salinity problems through
collaboration of Government institutions and local NGOs. The reduction of salinity level in SouthWest region of Bangladesh can be accomplished by increasing freshwater flow from the Ganges
through the Gorai-Madhumati channel. Further research should be undertaken to understand the nature
of community adaptation and perception of climate change in Bangladesh if we want to stride forward
to negotiate saltwater intrusion and implement community based adaptation to climate change in the
country.