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against wave battering and their removal aggravated the problem. Lastly, erosion was also linked to poor planning. There was a trend of erecting beach hotels and residential houses directly on or very close to the
beaches. The hotels at Uroa, Chwaka and the bungalows at Uroa were cited as examples.
Construction of buildings on dunes and eroding cliffs also decrease sediment supply to the littoral zone. A survey conducted by Dubi and Nyandwi 1999 shows that some structures such as residential houses and hotels are built
directly on the beach and some of them on potentially unstable landforms, such as sand dunes.
Coastal protection methods are varied and take many forms. A method of protection can comprise one or more options that fall under three categories, viz. protect, retreat and accommodate. Table 6 shows some of the options
falling under the three categories.
However, in an attempt to control erosion in Tanzania, coastal structures such as groynes and walls, whose design leaves a lot to be desired, have been erected. Such structures change the sediment dynamics regime and realign the
shoreline. Some of the typical protection measures employed in Tanzania include stone and masonry seawalls in Tanga and Bagamoyo, groynes, concrete and masonry seawalls in Dar es Salaam, Zanzibar, Lindi and Mtwara.
1.7.3 Sea-level rise
Sea-level variation can be increased through construction of boat channels and deepening and widening of navigation channels. This activity increases the tidal range, thereby permitting larger waves to enter the harbour
area and adjacent beaches. Larger waves may cause a change in beach profile. The entrance to the harbour of Dar es Salaam is said to have been dredged to increase its water depth. No published information is available on the
impact of this activity.
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Table 1.5:Examples of coastal protective, retreat and accommodative technologies
Applicatio n
Technology Hard structural options
Soft structural options
Indigenous options
Protect
•
Dikes, levees, floodwalls for low countries
•
Seawalls, revetments, bulkheads
•
Detached breakwaters
•
Flood gates and tidal barriers for tidal inlets
•
Saltwater-intrusion barriers
•
Beach nourishment
•
Beach drainage concept
•
Dune restoration and creation
•
Wetland restoration and
creation
•
Afforestation
•
Coconut- leaf walls
•
Coconut- fibre
•
Stone units
•
Wooden Mangrove
•
Stakes walls
•
Stone walls
Managed Retreat
•
Increasing or establishing set-back zones
•
Relocating threatened buildings
•
Phased-out or no development in susceptible areas
•
Wetland creation, managed realignment
•
Creating upland buffers
Accommod ate
•
Emergency planning
•
Hazard insurance
•
Modification of land use
•
Modification of building styles and codes
•
Strict regulations of hazard zones
•
Desalination
1.7.4 Natural protection
Coral reefs act as barriers against wave forcing, once they are destroyed, they may not be able to keep pace with the rising sea level and hence more intense wave energy will cause major erosion to occur. Similarly, shoals and
sandbars dissipate wave energy that would otherwise reach the shoreline. Dredging of the nearshore shoals and bars can change the pattern of energy dissipation on a beach which can in turn have a negative impact on shoreline
stability. Natural protection is also weakened when dunes are levelled, this includes destruction of beach vegetation and paving of large backshore areas.
Coastal and marine resources degradation is a result of many human activities such as agriculture, forestry, urbanisation, fishing and tourism Linden and Lundin, 1996. These activities result in coastal erosion, physical
destruction of mangroves, beaches, sea-grass beds and reefs, biodiversity loss, land degradation and depletion of fish stocks. Agricultural activities and fishing appears to be particularly important contributors to coastal
degradation in Tanzania. Rural poverty is increasingly pushing people toward unsustainable farming on fragile land. In the Rufiji delta and to a lesser extent in Pangani, Bagamoyo, Kisarawe, Kilwa and Lindi, clearing of
mangroves for rice cultivation is often done on a seven-year cycle, from clearing to time of abandoning.
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Fishermen often use destructive techniques such as explosives and small mesh nets, which destroy sensitive habitats and catch juvenile fish. In Tanga, up to 95 of all coral reefs have been destroyed by destructive fishing
practices. Tourism development without proper planning destroys habitats during construction, and unmanaged tourism damages reefs and has a negative impact on local people.
The institutional capacity and legal framework for integrated coastal zone management is clearly inadequate in Tanzania. Sectoral policies fail to take into account inter-relationships among resources. For example, siltation of
rivers like the Rufiji and Pangani are caused by agriculture and energy policies, but affect mangroves and coral reefs further offshore. People cut mangroves for fuel-wood, boiling brine for salt production and agriculture,
particularly in Tanga, Bagamoyo and Rufiji. The loss in mangrove leads to disturbances in the ecosystem, degradation of fisheries, increased sedimentation on reefs and damage caused by flooding.
1.8 Rates of coastal erosion
