The coastal zone is also under two broad classification namely, wetland and dunes. The coastal wetland zone is very productive and provides an essential ecosystem for marine and terrestrial life-mainly bird life which have an important primary production role in providing nutrients for prawns and juvenile fish in the lagoon systems. In recent times, wetlands are however being encroached upon. Protection of the coastal wetland zone is very important to the long-term sustainability of the fishing industry which is common among the indigenes.
The dune lands which are formed through a combination of wave and wind action are very unstable and extend several hundred metres in certain portions of the coastline. Coconuts and palms are examples of species that grow well in the area and provide protection of the coast as well as an economic crop. The coconuts were planted in the 1920s but it is estimated that over 80% of those plantations have disappeared as a result of felling, disease and coastal erosion. The loss of these trees is one of the principal reasons for the severity of erosion in some areas.
It is also worth mentioning that apart from the above natural vegetation, a number of introduced trees and shrubs also thrive in the area such as neem trees, mangoes, cassias, avocados, palms and bouganvilia.
Due to urbanisation of the landscape of the municipality, different categories of animals have been pushed further inland or northwards. There are however many species of snakes (some venomous) and lizards found throughout the area and large numbers of domestic animals such as donkeys, sheep, goat, chicken etc. A wide range of indigenous, migratory and exotic bird species are also found in the lagoon regions but the dangers posed by pollution threatens the sustainability of such species. However bird life is generally diverse in the area and in spacious residential areas it is found to be prolific.
Apart from mangroves and salt marsh grasses, which are found in the intertidal zone, sea grasses or attached algae are also very common in rocky areas and wave cut platforms which facilitate the sustainability of the coastal ecosystem for the survival of shrimps, prawns and many species of fin fishes. The ocean floor regime is however too unstable to support large areas of sea grass.
The open lagoon systems is home to a wide range of crustacean, mollusks, gastropods, predatory and bottom feeding fish. These areas are important breeding grounds due to adequate protection against large predator species and a continual supply of nutrients and organisms for food. Such areas have however been modified by development and increasing levels of pollution. In this regard, some species in the lagoons are no longer suitable for human consumption. Protection of the water quality and vegetation in the lagoons is therefore important for the long-term sustainability of aquatic fauna along the coastline.
The common species of fish that dominate the local fishing industry are grouper, mackerel, cassava fish, African lookdown, sole shark and tiger fish. Stocks of off shore species have not been depleted mainly because fishing techniques result in a significant loss of smaller fish from nets. Evidence suggests that on-shore species are nearing exhaustion caused by excessive catches of juvenile and small fish. The loss of this resource will have a substantial impact on the indigenous population of the area whose livelihood is dependent on fishing. Apart from harbouring a variety of important commercial fish species like tilapia and catfish, the lagoons also provide very breeding grounds for animals, which are adapted to the characteristic coastal Savannah vegetation.
The drainage catchment area of the municipality is found within the Songo-Mokwe area which covers about 50km2, draining the area of Teshie to the ridgeline with the Sakumo II catchment. Two main streams drain the area flowing into the Mokwe and Songo Lagoons. Much of this catchment is undergoing residential development leading to extensive flooding during the rainy season.
General factors leading to flooding in the LEKMA Area
Natural features such as the underlying geology, soil conditions and localised topographic features create some drainage problems. The majority of the problems are created by the growing urbanisation of the area and the impact that this has on increase surface water runoff and flooding in low lying areas.
As the municipality expands and surface water runoff increases there will be a corresponding increase in siltation and more severe floods downstream, especially in areas surrounding the lagoons. If this situation is to be avoided engineering and conservation measures will need to be applied to reduce the rate of runoff. There is also the need to introduce measures to protect the upper catchment areas and streams where development may take place.
Physical Development within water ways
In recent time there has been unauthorised development along water ways due to ineffective development control mechanisms thereby causing severe floods in such areas. This calls for proactive measures at enforcement to ensure sanity in the system.
Siltation of Drains
Most channels are also heavily silted and choked with refuse thereby hampering the smooth flow of storm water. A well-organised public health and environmental enhancement programme for seasonally clearing drains is required to ensure they remain free flowing to help address the problems of flooding.
In most parts of the Municipality, drains also lack concrete lining. This is due to the huge investments that such an intervention would attract. There should therefore be a high level of prioritisation of such projects to ensure that flooding is reduced. The Challenge of the Assembly is to bring on board institutions such as the Hydro Division and other related organisations to help address this problem.
Poor design of Drains
Many localised flooding problems in the area can be attributed to poor design of storm and local drains. Under sizing of culverts and drainage channels, poor consideration of maintenance requirements and under-estimation of siltation loads are common faults. Converse and concrete lined drainage channels on both sides of residential streets are often more expensive to construct than the road itself. Simpler design standards could however be adopted to enable much larger areas to be serviced by storm water drainage. There is therefore the need to review many of the current design standards to ensure all drainage systems have adequate capacity and also that standards adopted are not excessively expensive.
Areas with perennial flooding problems
Drainage channels in the western part of the Songo-Mokwe Catchment are not adequate resulting in serious flooding in the Teshie/Nungua Estates and the cutting of the main coastal road to Tema. The storm-water channels constructed alongside and under this road are completely inadequate.
Southern Teshie is als subject to severe flooding in the rainy season while large parts of Teshie are without proper drainage with only the lower channel sections leading to the sea outfall.
In central Nungua, the market cannot operate regularly because of waterlogged ground and poor drainage. The valley before the police barrier at Nungua also has inadequately sized culverts. Poor maintenance of the earth drains along the area of the Maritime Academy also causes flooding of the coastal road.
Compared to the air quality of cities in some developed countries, the LEKMA area generally has relatively good air quality. Minor incidents of localised pollution in the Teshie Compost Plant area as well as automobile fumes arise periodically and are a matter of concern to city authorities and residents alike. During the months of December to February, the effect of the Harmattan (fine wind blown dust from the Sahara region) causes loss of visibility and some health problems but these are seldom prolonged.
Key Issues relating to the Physical Characteristics
The need for sea defence mechanism to protect shore line
Siltation of lagoons
WSW to NNE wind direction with speeds ranging between 8 to 16 km/hr should be considered in by the construction sector
Loss of natural vegetation such as coastal wetlands and fauna due to uncontrolled urbanisation
The need to introduce measures to protect the upper catchment areas and streams where development may take place.
Physical development of waterways, poor design of drains and siltation of drains are the major causes of flooding in the Municipality.
Date Created : 11/20/2017 8:04:09 AM