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ABSTRACT
Rivers are the major geological agents that transport both natural and anthropogenic materials from land to sea. The study investigates the impact of slope and sediment transport on the river morphology and its surrounding landscape. By employing DEM data we have derived slope and sediment transport maps to analyze the risk zones and how these influence near-banks stability of the river. This report highlights the implications for flood risks, land degradation, and sustainable river basin management. This report also suggests the reason for the past issues surrounding the river.
[Fig 1: Vamanapuram River]
INRODUCTION
Study Area- Vamanapuram River Basin
Vamanapuram River Basin lies between the latitudes 8.35 '24 " to 8.49' 13" N and longitudes 76.44 '24 " to 77.12' 45" E of Kerala State, South India. It is one of the major west-flowing rivers in Kerala, originates in the Western Ghats and flows in a north-westerly direction to drain into the Arabian Sea. Vamanapuram River Basin is a 7th order basin with a drainage area of 687 km2 and a length of 88 Km. The two tributaries of this river are the Upper Chittar & Manjapra Yaar streams which originate near Ponmudi hill station. The river originates from Chemmunji mottai hills in the high ranges of Western Ghats, which lies at 1860 m above mean sea level (MSL) and flows north- westerly into the Anjengo Lake. The river flows through all terrains such as highland, midland and lowland of the basin, and it encompasses numerous tributaries in the upper course and midland. The Meenmutty Falls is situated in the upper course of this river. The river is a major source of water for the Municipalities of Attingal and Varkala. There is boating available in the lower course of the river near Chirayinkeezhu. There is considerable tourism activity in the upper course of the river especially at Meenmutty Falls and Thavakkal waterfalls. Moreover, the basin is characterized by undulating topography and intermittent valleys.
Geological Aspect of The Aera
Geologically, Vamanapuram River Basin is occupied chiefly by Precambrian crystalline hard rocks, i.e. khondalite and migmatite complexes, which have undergone weathering to form laterite at varying depths. Khondalites are essentially graphite-bearing garnetiferous biotite gneisses, and charnockites are present as some patches in the khondalitic exposure. The hard crystalline rocks encompass a significant portion of the basin. The coastal rocks of sedimentary origin belonging to ‘Warkalli formation’ include sandstone and clay with lignite intercalation Moreover, the basin is characterised by undulating topography and intermittent valleys. Geologically, Vamanapuram River Basin is occupied chiefly by Precambrian crystalline hard rocks, i.e. khondalite and migmatite complexes, which have undergone weathering to form laterite at varying depths. Khondalites are essentially graphite-bearing garnetiferous biotite gneisses, and charnockites are present as some patches in the khondalitic exposure. Apart from this, a blotch of laterite and basic rocks are present. The hard crystalline rocks encompass a significant portion of the basin. The coastal rocks of sedimentary origin belonging to ‘Warkalli formation’ include sandstone and clay with lignite intercalation and a small portion of sand and silt.
[Fig 2: Study Area]
DATA SOURCES
Digital Elevation Model
DEM provides a detailed representation of the terrain, essential for deriving slope and elevation-related aspects for analysis.
Slope Map
The slope map which can be derived from the DEM indicates the steepness of the terrain, which is vital for assessing many risks related to the area.
Sediment Transport Index
STI is a quantitative measure used to assess the potential movement of sediment in a given area. STI maps visually represent areas at risk of significant sediment transport, aiding in effective planning of environmental management.
METHODOLOGY
[Fig 3: Methodology chart]
ANALYSIS RESULTS
Slope
The slope map showed major alterations throughout the Vamanapuram River basin. Steep slopes were discovered in the upper portions of the river, whereas gentler slopes were found downstream. Steep slopes cause faster runoff, which increases erosion potential and silt transfer downstream. Areas with very steep slopes have caused significant damages to the near banks of Vamanapuram river in the near past
Sediment Transport Index (STI) Map
The STI map indicates overall a low sediment transport rate. But there are few regions with moderate and high sediment transport that makes those areas most vulnerable and contributes to riverbank instability. On analysis we can find that near the regions of the river there is high sediment transport occurrence that can lead to destruction of the nearbanks of the river in those areas.
Risk Analysis of The Region:
The map suggests that the Vamanapuram river basin is mainly under moderate risk zone and there are areas where high risk is measured. We can also find high risk zones which have high STI values in combination with steep slopes indicating zones where erosion is most intense. These areas are vulnerable to bank failures, leading to a loss of land along the river and areas with lower slopes and lower STI values, particularly in the floodplains, are prone to sediment deposition. This leads to the raising of the riverbed, increasing flood risks during monsoon seasons. This map also gives us an insight on the different issues that has been seen around vamanapuram river such as:
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Very deep river banks that lead to huge numbers of casualties.
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Exposure of boulder rocks.
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Accumulation of flood plains
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Braiding of the river.
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Uncontrolled river widening of the river
CONCLUSION
The slope and sediment transport index analysis of the Vamanapuram River highlights critical areas of erosion and sediment deposition. Steeper slopes in the upper river basin contribute to higher sediment transport, while the downstream regions face sediment deposition issues, leading to altered river channels and increased flood risks. The area is in a moderate risk zone and there are few regions with a high risk zone. The near-banks of Vamanapuram river has been a concern all these years due to the shallow depth. The near-banks of this river are nearly 2 man tall in the majority of the places. The study gives an insight about the unexpected depth. Due to regions with steep slopes and moderate to high sediment transport these areas are very prone to Effective river basin management strategies should include erosion control measures, reforestation, and sustainable land use practices to mitigate these impacts.
REFERENCE
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[2] K.C. Chiadikobi, A.O. Omoboriowo, O.I. Chiaghanam, A.O. Opatola and O. Oyebanji., Advances in Applied Science Research, 2011, 2 (6): 287-298.
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RS, Ajin, et al. "Flood hazard assessment of Vamanapuram River basin, Kerala, India: an approach using remote sensing & GIS techniques." Advances in Applied Science Research 4.3 (2013): 263-274.
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Sabarinath, et.al. “Sand mining and its adversities in the near banks of Vamanapuram river, Thiruvananthapuram, Kerala, 2023