50,000 dams later: Erosion of the Yangtze River and its delta

How effective were mangroves as a defence against the recent tsunami

Wave influence in the construction, shaping and destruction of river deltas: A review

The eustatic sea-level rise due to global warming is predicted to be about 18 to 59 cm by the 2100 (IPCC 2007), which necessitates identification and protection of vulnerable sections of coasts. Assessment of vulnerability level of Andhra Pradesh (AP) coast as an example is demonstrated in this study using five physical variables, namely coastal geomorphology, coastal slope, shoreline change, mean spring tide range, and significant wave height. A coastal vulnerability index was prepared by integrating the differentially weighted rank values of the five variables, based on which the coastline is segmented into low-, moderate-, high-, and very high risk categories. About 43% of the 1,030-km-long AP coast is under very high-risk, followed by another 35% under high-risk if the sea level rises by ~0.6 m displacing more than 1.29 million people living within 2.0 m elevation in 282 villages in the region.

Sea-level rise and coastal vulnerability: an assessment of Andhra Pradesh coast, India through remote sensing and GIS

Climate change, particularly its associated sea level rise, is major threat to mangrove coastal areas, and it is essential to develop ways to reduce vulnerability through strategic management planning. Vulnerability has three dimensions of exposure to stresses, associated sensitivity, and related adaptive capacity, and ways to measure components of each were trialled at sites in Africa and the South Pacific to develop an analysis procedure based on ranking. The approaches of the ranking system for vulnerability assessment of mangrove systems integrate biotic and abiotic factors along with human management components, using validated methods previously developed for other research questions. These include determining mangrove forest health, adjacent ecosystem resilience, the extent and effects of human impacts, and the environmental conditions of different mangrove settings. Results of the vulnerability assessment ranking using up to 20 measurements found all sites to have some components of vulnerability. Douala Estuary, Cameroon showed the highest vulnerability, owing to low tidal range, impacts from non-climate stressors, and evidence of moderate seaward edge retreat. Tikina Wai, Fiji showed inherent vulnerability owing to location on a subsiding coastline with a low tidal range, but this was offset by strong local community management capacity. Rufiji Delta, Tanzania showed inherent resilience owing to location on an uplifting coastline with a macrotidal range, but showed vulnerability from human impacts and lower local community management capacity. The most critical components to the vulnerability assessment were found to be exposure components of relative sea level trends and sediment supply, and sensitivity components of forest health, recent spatial changes and net accretion rates. The results provide a baseline against which to establish long-term ongoing monitoring, allowing continued assessment of the complex dynamics of climate change impacts, and providing an information base for strategic management decisions.

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Vulnerability assessment of mangroves to climate change and sea-level rise impacts

Analysis of multi-date satellite sensor data and maps indicated loss of 1836 ha of land during 1976–2001 along the Godavari deltaic coast resulting in displac ement of coastal communities and mangrove destruction. Decrease in sediment loads from an annual average of 145.26 million tons in 1971 –79 to 56.76 million tons during 1990–98, apparently due to construction of dams, largely diminished vertical accretion at the delta, while continued coastal subsidence that might have been accentuated by possible neotectonic activity and consequent relative sea level rise led to shoreline retreat. The e xtant conditions indicate that the problem may compound in future causing irreparable damage to this important deltaic ecosystem. COASTAL erosion has been one of the major en vironmental concerns in many parts of the world. The situation is pa rticularly serious in the deltaic regions due to construction of dams in the river basin that impede sediment supply at the river mouths as a result of which the rates of subs idence and sea level rise may exceed rates of vertical a ccretion leading to erosion of coastal lands 1 . In India, delta ecosystems that are considered as cradles of civilization have significant economic importance in terms of agricu lture, water resources, wetlands, w ildlife habitats, fish production and tourism. For instance, the Godavari delta, which is termed as the rice bowl of Andhra Pradesh, is one of the major prograding deltas on the east coast of India bordering the Bay of Bengal and is a densely populated zone of intense economic activity. Fed by a large 312,812 km 2 drainage basin, the delta of this second longest river (1465 km) in the country spreads over an area of about 5100 km 2 . As evident from the presence of relict beach ridges far inland from the prese nt shoreline, the delta a dvanced into the sea by sustained deposition during the past 5 to 6 thousands of years 2,3 . As a result, the seaward bulge of the delta overlaps the continental shelf across by about 30–35 km (Figure 1) when compared to the general trend of the east coast. Several studies on the nature of coastal landforms along the delta front also indicated i ncreased sedimentation rates through the river during the nineteenth century and even over a major part of the twentieth century. Mahadevan and Prasada Rao 4 based on an analysis of multi -date maps spread over a period of 100 years traced the growth of a 21 -km long sand spit at the delta, east of Kakinada that began around AD 1850 and reached more or less the present shape by the 1958 owing to i ncreased sediment supply from the catchment due to deforestation . Sambasiva Rao and Vaidyanadhan 5 reported overall cumulative accretion of land due to d evelopment of several other sand spits at the distributary mouths of the Godavari during the period between 1937 and 1977, based on the study of toposheets (1937), aerial photographs (1968) and field mapping (1977). However, a recent field study 6 revealed predominance of erosion rather than deposition along the estuarine banks and delta front shoreline. Similarly, field observations by us during 1999–2002 also revealed pronounced erosion at certain sections of the deltaic coast due to which even some vi llages were to be evacuated. In this background, it is essential to understand the magnitude of, and the factors responsible for, the degradation of this important coastal ecosy stem in the country. The present study is such an attempt in this direction.

Coastal erosion and habitat loss along the Godavari delta front - a fallout of dam construction(?)

River deltas are the major repositories of terrestrial sediment flux into the world's oceans. Reduction in riverine inputs into the deltas due to upstream damming might lead to a relative dominance of waves, tides and currents that are especially exacerbated by coastal subsidence and sea-level rise ultimately affecting the delta environment. Analysis of multi-date satellite imagery and maps covering the Krishna and Godavari deltas along the east coast of India revealed a net erosion of 76 km2 area along the entire 336-km-long twin delta coast during the past 43 years (1965–2008) with a progressively increasing rate from 1·39 km2 yr−1 between 1965 and 1990, to 2·32 km2 yr−1 during 1990–2000 and more or less sustained at 2·25 km2 yr−1 during 2000–2008. At present the Krishna has almost become a closed basin with decreased water discharges into the delta from 61·88 km3 during 1951–1959 to 11·82 km3 by 2000–2008; and the suspended sediment loads from 9 million tons during 1966–1969 to as low as 0·4 million tons by 2000–2005. In the case of the Godavari delta, although the water discharge data do not show any major change, there was almost a three-fold reduction in its suspended sediment loads from 150·2 million tons during 1970–1979 to 57·2 million tons by 2000–2006. A comparison of data on annual sediment loads recorded along the Krishna and Godavari Rivers showed consistently lower sediment quantities at the locations downstream of dams than at their upstream counterparts. Reports based on bathymetric surveys revealed considerable reduction in the storage capacities of reservoirs behind such dams. Apparently sediment retention at the dams is the main reason for the pronounced coastal erosion along the Krishna and Godavari deltas during the past four decades, which is coeval to the hectic dam construction activity in these river basins. Copyright © 2010 John Wiley and Sons, Ltd.

Impacts of sediment retention by dams on delta shoreline recession: evidences from the Krishna and Godavari deltas, India.

Interpretation of multi-date satellite imagery has revealed changes in land use/land cover pattern in the Godavari deltaic region during the past 26 years. The area under intensive agriculture has increased from 1459 to 3500 km2 and the extent of wetland from 368 to 648 km2 during the period 1973-1999, while the seasonal fallow has decreased by 2321 km2. Analysis of the climatic data of 1970-1998 from different stations covering the entire 5100 km2 area of the delta indicated that the day time temperatures have decreased by 0.2° C to 0.7° C, while the night time temperatures have increased by 0.5° C to 0.6° C during the past three decades. At the same time the rainfall has increased by about 75 to 479 mm. These trends in the climatic parameters arc attributed to the increased vegetation cover and wetland extent in the Godavari deltaic region.

Landuse/Landcover change detection through remote sensing and its climatic implications in the godavari delta region

2 , the Kolleru has turned into a freshwater body, except in its southeastern part where brackish conditions prevail, espe- cially during dry summer months due to incursion of tidal water through Upputeru. The lake continued to exist through thousands of years after its formation, in spite of sedimentation through inland streams and reduction in the flushing capacity of Upputeru due to the overexten - sion of its course by progre ssive advancement of the coastline far away into the sea. Perhaps its topographical location over a deep -seated tectonic depression, which is geophysically known as Gu divada sub-basin or graben between the Bapatla and Tanuku subsurface ridges or highs

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B. Hema Malini

Papers

Sea-level rise and coastal vulnerability: an assessment of Andhra Pradesh coast, India through remote sensing and GIS

Coastal erosion and habitat loss along the Godavari delta front - a fallout of dam construction(?)

Impacts of sediment retention by dams on delta shoreline recession: evidences from the Krishna and Godavari deltas, India.

Landuse/Landcover change detection through remote sensing and its climatic implications in the godavari delta region

Kolleru lake is vanishing - a revelation through digital processing of IRS-1D LISS-III sensor data