615
Theme 12: Erosion/Accretion
Erosion/accretion of mangrove stands along shore/river banks can be mapped using
mult- date satellite images. Erosion of mangroves (tide dominated mangroves) over
a period is treated as unhealthy and accretion of mangroves along the shore is
healthy. Accretion of sand inside mangrove stand is unhealthy. The values for this
theme are calculated as per the details given as under:
Erosion
10
Accretion inside mangrove stands
20
Accretion along shore
80
No erosion
100
All the above 12 themes are integrated in GIS environment (Fig. 19.15) to compute Mangrove Health Index (MHI) and to finally create the Mangrove Health
Maps.
19.7.1 Case Study: Mangrove Health Assessment
in Pichhavaram Reserve Forest, India
Pichhavaram mangrove forest, situated at the east coast of India, is one of the two
major mangrove wetlands having richest mangrove diversity in Tamil Nadu state,
southern India. True mangrove species such as Rhizophora apiculata, Rhizophora
mucronata, Avicennia marina, Avicennia officinalis, Exocecaria agallocha and
associate mangrove species like Sueadamaritima, Salicornia and Sueadamonoica
are largely found in Pichavaram wetlands. The wetlands act as the nursing ground
for a variety of fishes and marine organisms such as mollusks, crabs, prawn, bivalves
etc. The wetland lies in the centre of the Coleroon-Vellar estuary in the east coast
and hence fed by sufficient amount of fresh water in monsoon season. In summer,
tidal influence is more than the freshwater flow. Many natural creeks and canals that
have tidal diurnal flow inundating the mangrove vegetation also feed the wetland.
There are about 12 hamlets surrounding the wetlands where people depend on mangroves for their livelihood such as fishing, firewood, grazing and fencing. In 1990s
the restoration of degraded mangroves of Pichhavaram carried out by MS
Swaminathan Research Foundation (MSSRF), Chennai and State Forest Department
led to the increase in mangrove area from 280 ha in 1987 to 820 ha in 2006. The
devastating tsunami which hit on Tamil Nadu coast on December 26, 2004 made the
local community to realize the importance of mangroves in protecting them from
the natural hazards. After that, the dependence on green mangroves for grazing and
firewood collection has reduced owing to the participation of community in restoration of mangroves.
Multi- temporal data from IRS satellite have been used in assessing the health of
mangroves. The oldest satellite image available for this study area is of 1990. Post
19 Mangrove Inventory, Monitoring, and Health Assessment
Theme 12: Erosion/Accretion
Erosion/accretion of mangrove stands along shore/river banks can be mapped using
mult- date satellite images. Erosion of mangroves (tide dominated mangroves) over
a period is treated as unhealthy and accretion of mangroves along the shore is
healthy. Accretion of sand inside mangrove stand is unhealthy. The values for this
theme are calculated as per the details given as under:
Erosion
10
Accretion inside mangrove stands
20
Accretion along shore
80
No erosion
100
All the above 12 themes are integrated in GIS environment (Fig. 19.15) to compute Mangrove Health Index (MHI) and to finally create the Mangrove Health
Maps.
19.7.1 Case Study: Mangrove Health Assessment
in Pichhavaram Reserve Forest, India
Pichhavaram mangrove forest, situated at the east coast of India, is one of the two
major mangrove wetlands having richest mangrove diversity in Tamil Nadu state,
southern India. True mangrove species such as Rhizophora apiculata, Rhizophora
mucronata, Avicennia marina, Avicennia officinalis, Exocecaria agallocha and
associate mangrove species like Sueadamaritima, Salicornia and Sueadamonoica
are largely found in Pichavaram wetlands. The wetlands act as the nursing ground
for a variety of fishes and marine organisms such as mollusks, crabs, prawn, bivalves
etc. The wetland lies in the centre of the Coleroon-Vellar estuary in the east coast
and hence fed by sufficient amount of fresh water in monsoon season. In summer,
tidal influence is more than the freshwater flow. Many natural creeks and canals that
have tidal diurnal flow inundating the mangrove vegetation also feed the wetland.
There are about 12 hamlets surrounding the wetlands where people depend on mangroves for their livelihood such as fishing, firewood, grazing and fencing. In 1990s
the restoration of degraded mangroves of Pichhavaram carried out by MS
Swaminathan Research Foundation (MSSRF), Chennai and State Forest Department
led to the increase in mangrove area from 280 ha in 1987 to 820 ha in 2006. The
devastating tsunami which hit on Tamil Nadu coast on December 26, 2004 made the
local community to realize the importance of mangroves in protecting them from
the natural hazards. After that, the dependence on green mangroves for grazing and
firewood collection has reduced owing to the participation of community in restoration of mangroves.
Multi- temporal data from IRS satellite have been used in assessing the health of
mangroves. The oldest satellite image available for this study area is of 1990. Post
19 Mangrove Inventory, Monitoring, and Health Assessment