Shoreline Changes and Human Influence

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2.2 Shoreline Changes and Human Influence

Coastal erosion is currently one of the major environmental issues of concern at Mbegani Bay as well as many other coastal sites in Tanzania Shaghude et al, 1994, and Shaghude, 2011. Field evidence of wave erosion includes exposure and uprooting of tree roots particularly mangrove trees, collapse of beach cliffs, and the presence of coastal protection structures Figure 3. According to Shaghude 2011 the severity and vulnerability to wave erosion along the coastal section enclosing the Bay is higher on the northwestern part of the Bay, towards the Mbegani Fisheries Training Centre than on the southeastern parts of the Bay towards Kondo village Fig. 4. The difference in severity to erosion and vulnerability to wave erosion between the northwestern side and the southeastern side had been attributed to the fact that the western coastal stretch is relatively more open towards the ocean waves compared to the eastern coast, which seem to be relatively better protected by the raised reef platforms and the sand banks that are located inside the Bay. Furthermore, because of the northwesterly- southeasterly orientation of the Bay, most of the wave erosion seems to take place during the NE monsoon season. Alternatively, the difference in the mangrove forest cover along the coastal stretch between Ras Mbegani and the Kondo Village may also contribute to the observed difference in wave erosion. Protection of the mangroves should therefore be sensitized to the coastal communities as their environmental services along the coastal stretch are clearly evident. The environmental services provided by the vegetation cover on the existing raised reef platforms should also be sensitized to coastal communities and to policy makers. The existing raised reef platforms are currently well covered by vegetation. However, with increasing urbanization of the coastline, the vegetation on the raised reef platforms may be threatened. The removal of vegetative cover on these reef platforms will definitely make the platforms more vulnerable against wave erosion as had happened at Maziwe Island, off the Pangani estuary in Tanga Region, during the late 1970s Shaghude, 2004. Figure 3 Eroding shore at Mbegani as exemplified by the uprooting of trees and collapse of the beach cliff. Source: Shaghude 2011. 7 The red dotted line between 5-10 incidences of eroding coastal sites. encountered, Yellow dotted line Less than 5 incidences of eroding coastal sites encountered, Green dotted line No erosion observed. Source: Shaghude 2011. While most of the observed erosion at Mbegani Bay is attributed to natural causative factors, mainly waves Shaghude, 2011, accelerated erosion in limited locations of the coastal section are attributable to human influence. The concrete jetty installed at the Old boat yard located 300 m west of Mbegani Fisheries Training Centre, provides a good example. At this site the concrete jetty functions as a groyne which interrupts the longshore sediment drift, thereby promoting erosion on one side of the groyne and accretion on the other side CIRIA, 1996. Figure 4 Map showing the status of coastal erosion along the western coastal stretch of Mbegani Bay stretching between Mbegani and Mlingotini 8

3. ECOSYSTEM CHARACTERISTICS