Abstract:
Erosion has become an important issue for Kaptai watershed, the largest man made
freshwater body in Bangladesh which generales a significant share of Bangladesh's
power supply by usiog hydro-power. It contributes significantly to the production of
freshwater fish, flood oonlrol, tourism and agriculture. Over lhe past few decades forest
depletion has become a main problem here because of human intervention, replacing the
forest cover with shllUng cultivation which eventually increasing soil erosion and thus
contributing large amounlS ofscdirncll1lltion to the reservoir posing 3 serious threat to the
power plant as well as navigability. Studies have been done \0 assess the sedimentation in
Kaptai Lake have found that the expected tife time ofthc lake has considemhly reduced.
This study is an effort to look into this met and II)' to understand the spatial variation of
erosion that leads to siltation.
The study has two major goals - first to nwnitor the change ofvcgctation and other major
land coven; OYl:rlast two decades (1980-2000) and ~econd to develop a simple spatial
model to identify potential erosiOll prone areas in Kaptai watershed.
Land cover maps have been produced from satellite image~ of Landsat program. NOVI
and bi-spectra! plot techniques were u~ed to identify land covers. Appropriate NOVI has
been set chosen based on ground tnllt! data, high resolution satellite image (IRS LlSS 111)
and sccondlll'Y land cover maps. Two land cover map~ have been prepared for two
nominal years (1980 and 2000). Finally map~ have been compared with each other. It has
been found lIlat non-furest land has increased by 10.6% \\'hile low density forest area has
decreased by 18.4% but high density fOrest has increased by around 7.9%. However
overall forest coverage (Iow+high density) has decreased by 10.6% which is highly
significant for20 years time period (1980-2000).
A simple potential erosion model has been developed to assess the distribution of
potential erosion prone areas in the watershed. This model cmphasize~ potential erosion
because it does not estimate the actual erosion; rather it indicates areas that are potentially
i,
erodabte based on ~npe, soil, land cover and rainfall in the watershed. Modelling result
shows that 45% of the area has low erosion risk while 17% has high erosion risk. The rest
36% falls into llVerage erosion category. This is an indication of how much area is to bc
conserved for erosion management in Kaptai Watershed.
This study is a small preliminary effort to look into the erosion problem spatially. But this
might be useful as a starting point for further in depth spatial study of this problem to
figure out possible remedies.
