Comparability of research methods Sampling frequency and duration of studies Capability of researchers Age of information

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1.5.1 Comparability of research methods

Different research scientists have used different methodologies depending on the parameters being investigated. Most researchers have used comparable methods. However, there are some methods that are not so comparable. For example, in measuring waves, Lwiza1987 and Edet 1991 used graduated wave staffs. In cases like these, the results are rather subjective and hard to compare simply because the wave heights are observed visually, a method that has high degree of uncertainty.

1.5.2 Sampling frequency and duration of studies

Sampling frequency has been varied depending on the type of study. In some studies, like those applying General Circulation Models, Computer and Mathematical are used. In this case there is no sampling frequency involved. The same is true for the review studies. In some studies sampling frequency is not stated completely e.g. Edet, 1991. The sampling frequency available in many studies varied from half hourly measurements e.g. Hravey, 1977 to monthly measurements e.g. Mwaiseje, 1973. Others followed monsoon seasons e.g. Newell, 1957, 1959; Dubi and Nyandwi, 1999. The duration of many studies has not been long enough to warrant long-term evaluations. For example, in the investigation of heavy mineral content of Tanzanian beach sands, Cilek 1976 took approximately one year to conduct that study. But since heavy mineral composition is dependent on hydrodynamic conditions, the study is only good for baseline purposes. The situation could change after say, 20 years. This is the same situation for most other studies.

1.5.3 Capability of researchers

Highly qualified scientists have carried out most of the studies. Even in cases where research has been done by students, supervision has been done by capable scientists and most of works have led to postgraduate degrees e.g. Edet, 1991; Nzali, 1998.

1.5.4 Age of information

Information, which is older than 20 years, is considered old and its reliability is questionable. An exception to this fact is of course on geological studies. An overview of the status of some selected studies is summarised in Table 1.2. 18 Table 1.2: Example of the sampling frequency and duration of some studies, where P indicates published articles and G is grey literature. The age of information is classified as either old or recent. Article Duratio n of studies Sampling frequency Publication Age of informa tion Cilek 1976 1 year - P Old Cooke 1974. 1 year - P Old Dubi 1998 25 years Monthly maximum values P Recent Dubi and Nyandwi 1999 1 year Tides, Currents : monthly. Waves : every two-month. Profiles and Sediment : neap and spring tides P Recent Edet 1991 2 years - MSc. Thesis Recent Harvey 1977 20 years offshore data 4 years Zanzibar Channel 3 months at Kunduch i Half hourly for a period of 25 hours Positions of drogues taken at 45 min. intervals. Temperature, turbidity and water sample taken at 2 hours interval P Old Kaaya and Boenigk 1986 1 year - P Old Mwaipopo 1984 2 years Computer sampling P Old Mwaiseje 1973 1 year Monthly P Old Nieuwolt 1973 4 years 3-hourly intervals P Old Nzali et al. 1998 1 year Every two-months for recruitment rates four times a month for temperature and transparency once every 4 – 5 days for sedimentation rates P Recent Shayo 1979 - Computer sampling P Old Temple and Sundborg 1972 7 years data Gage continuous? sampling P Old

1.6 Main findingsobservations