Browsing by Author "Dubi, Alfonse M."

Now showing 1 - 12 of 12
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    Design and preliminary results of an integrated mariculture pond system (IMPS) at Makoba, Zanzibar,Tanzania
    (National Centre for Mariculture, 2001) Mmochi, Aviti J.; Mozes, N; Kite-Powell, H.L.; Dubi, Alfonse M.; Gordin, H; Jiddawi, Narriman; Kissil, G; Msuya, Flower E.; Mwangamilo, J
    Mariculture development in Zanzibar Island, Tanzania, is limited by the lack of appropriate technology for local conditions and cost-effective solutions for preventing nutrient enrichment of the marine environment. An integrated mariculture pond system (IMPS) concept originally developed in Israel is considered as a possible model for mariculture development in Zanzibar. An experimental IMPS has been established near the estuary of Kiwani Creek at Makoba on the west coast of the island. Water supply is provided by a reservoir fed by tidal fluctuations in the creek. The experimental system consists of six ponds of 170m3 each, for the culture of fish, shellfish and seaweed. The ponds were stocked during June and July 1998 with 4000 fingerlings of rabbitfish (Siganus sp.) and with different species of shellfish and seaweed. Water quality parameters in the ponds, such as temperature, oxygen and salinity, were kept within acceptable limits by a periodic water supply. Fish were fed daily with a diet developed for this project. Preliminary results indicate reasonable growth of the fish but also mortality of fish, shellfish and seaweed.
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    Effects of Fish Culture on Water Quality of an Integrated Mariculture Pond System
    (Western Indian Ocean J., 2002) Mmochi, Aviti J.; Dubi, Alfonse M.; Mamboya, F. A.; Mwandya, A. W.
    Six mariculture ponds were flooded with seawater since 1996. During this time the ponds were stocked with finfish (milkfish and rabbitfish), which were fed on locally produced fish feed. Some water quality parameters such as temperature, salinity and oxygen saturation were measured twice a day for three years (1998 – 2000), while nutrient concentrations were measured weekly for one year. Both nutrient concentration and oxygen saturation levels have shown a trend indicating eutrophication. Oxygen concentration changed from an average of 7.16 mg/l in October 1998 to 2.2 mg/l in March 2000 with a negative linear regression of 0.69 during the morning hours. From August 1998 to April 1999 dissolved inorganic ammonia concentration increased by 9 mg-at N/l, from 8.91 to 18.02 with a positive linear regression of 0.79. During this period soluble reactive phosphorus increased by 3.55 mg-at P/l from 4.36 to 7.91 with a positive linear regression of 0.75. In this paper the rate of eutrophication and the limit at which the ponds have to be dried/limed before restocking are discussed
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    Episodic Atmospheric Changes and Their Impact on the Hydrography of Coastal Waters in Tanzania
    (2001) Nyandwi, Ntahondi; Dubi, Alfonse M.
    A shift in the time of occurrence and duration of the rainy and dry seasons has been observed over Tanzania and the East African region in recent years. During 1998, El Niño rains produced substantial fresh water and sediment supply to the coastal zone. During that period, large sand bodies were deposited off river mouths and at stream entrances. Hydrographic measurements showed a persistent decrease in salinity and temperature of inshore waters indicating that coastal waters have been trapped along the shore. Such environmental changes could have negative effects on the biodiversity of the coastal zone. Based on beach profile measurements, the shoreline was predominantly eroding prior to the rains but accreted during the El-Niño rains. The tidal flats received a larger volume of sand. While the beach and tidal flats were receiving this supply of sand, river banks eroded as channels deepened and widened. In many instances, newly cut flood channels have remained semi-permanent serving as tidal inlets leading to tidal inundation of the low lying areas behind the beaches. These observations point to the significance of episodic events in maintaining or shaping the coastal zone.
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    Impact of hydrographic parameters and seasonal variation in sediment fluxes on coral status at Chumbe and Bawe reefs, Zanzibar, Tanzania
    (Elsevier, 2010) Muzuka, Alfred; Dubi, Alfonse M.; Muhando, Christopher A.; Shaghude, Yohanna W.
    Coral reefs which are an important resource to coastal communities and nation at large are adversely affected by rate of sediment flux to the reefs. However, there is little information on seasonal trend in sediment flux and its impact at the reefs off Zanzibar. Two years’ monthly data on sedimentation at Chumbe and Bawe reefs were used to assess seasonal variability in sediment flux and its implication on the coral status. Sediment flux to the Bawe reefs for the duration of the study ranged from 0.2 to 41.5 mg cm 2 d 1, while it ranged from 0.8 to 65.8 mg cm 2 d 1 at the Chumbe reefs. Sediment fluxes at Bawe reefs were highest between November and March, while they were highest between April and September at Chumbe reefs. Generally, sediment fluxes at Bawe reefs were low compared to those at Chumbe. The total sediment input to the reefs ranged from 4615 to 123,403 kg d 1 for Bawe reefs and 2750 to 79,636 kg d 1 for Chumbe reefs. High sediment fluxes at Bawe reefs between November and March; and the Chumbe reefs between April and September can be attributed to water currents and wind pattern in the east African region which are under the influence of the monsoons. The observed trend suggests that the period for coral transplant as a management option for the two sites should be different. Coral transplant can be undertaken in such a way that stress of the corals due to sedimentation can be felt after they have overcome stress from transplant process and temperature. The results from this study contribute to the much needed information for coral transplant, restoration, and management
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    Impact of hydrographic parameters and seasonal variation in sediment fluxes on coral status at Chumbe and Bawe reefs, Zanzibar, Tanzania
    (Elsevier, 2010) Muzuka, Alfred; Dubi, Alfonse M.; Muhando, Christopher A.; Shaghude, Yohanna W.
    Coral reefs which are an important resource to coastal communities and nation at large are adversely affected by rate of sediment flux to the reefs. However, there is little information on seasonal trend in sediment flux and its impact at the reefs off Zanzibar. Two years’ monthly data on sedimentation at Chumbe and Bawe reefs were used to assess seasonal variability in sediment flux and its implication on the coral status. Sediment flux to the Bawe reefs for the duration of the study ranged from 0.2 to 41.5 mg cm 2 d 1, while it ranged from 0.8 to 65.8 mg cm 2 d 1 at the Chumbe reefs. Sediment fluxes at Bawe reefs were highest between November and March, while they were highest between April and September at Chumbe reefs. Generally, sediment fluxes at Bawe reefs were low compared to those at Chumbe. The total sediment input to the reefs ranged from 4615 to 123,403 kg d 1 for Bawe reefs and 2750 to 79,636 kg d 1 for Chumbe reefs. High sediment fluxes at Bawe reefs between November and March; and the Chumbe reefs between April and September can be attributed to water currents and wind pattern in the east African region which are under the influence of the monsoons. The observed trend suggests that the period for coral transplant as a management option for the two sites should be different. Coral transplant can be undertaken in such a way that stress of the corals due to sedimentation can be felt after they have overcome stress from transplant process and temperature. The results from this study contribute to the much needed information for coral transplant, restoration, and management
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    Impact of hydrographic parameters and seasonal variation in sediment fluxes on coral status at Chumbe and Bawe reefs, Zanzibar, Tanzania
    (Elsevier, 2010) Muzuka, Alfred N. N.; Dubi, Alfonse M.; Muhando, Christopher A.; Shaghude, Yohanna W.
    Coral reefs which are an important resource to coastal communities and nation at large are adversely affected by rate of sediment flux to the reefs. However, there is little information on seasonal trend in sediment flux and its impact at the reefs off Zanzibar. Two years’ monthly data on sedimentation at Chumbe and Bawe reefs were used to assess seasonal variability in sediment flux and its implication on the coral status. Sediment flux to the Bawe reefs for the duration of the study ranged from 0.2 to 41.5 mg cm 2 d 1, while it ranged from 0.8 to 65.8 mg cm 2 d 1 at the Chumbe reefs. Sediment fluxes at Bawe reefs were highest between November and March, while they were highest between April and September at Chumbe reefs. Generally, sediment fluxes at Bawe reefs were low compared to those at Chumbe. The total sediment input to the reefs ranged from 4615 to 123,403 kg d 1 for Bawe reefs and 2750 to 79,636 kg d 1 for Chumbe reefs. High sediment fluxes at Bawe reefs between November and March; and the Chumbe reefs between April and September can be attributed to water currents and wind pattern in the east African region which are under the influence of the monsoons. The observed trend suggests that the period for coral transplant as a management option for the two sites should be different. Coral transplant can be undertaken in such a way that stress of the corals due to sedimentation can be felt after they have overcome stress from transplant process and temperature. The results from this study contribute to the much needed information for coral transplant, restoration, and management.
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    Morphodynamics of the Manyema Tidal Delta at Kunduchi, Tanzania
    (WIOMSA, 2013) Nyandwi, Ntahondi; Shaghude, Yohanna W.; Mburu, J. W.; Dubi, Alfonse M.; Sanga, I.; Arthurton, Russell
    The prevailing northward longshore drift of beach sand on the northern part of Msasani Bay, north of Dar es Salaam, is interrupted at Kunduchi by the tidal flushing of Manyema Creek, a mangrove ecosystem partially developed for salt production. Shoreline changes around the creek mouth in recent decades have eroded coastal land and destroyed buildings, prompting stakeholders to construct protective groynes and revetments. Sand is transported across the delta by the interaction of two forcing processes – currents that flush the creek in response to tidal variation and, more generally, those generated by monsoonal wind-driven waves. A study of the sand morphology of the creek and delta platform together with time-series satellite imagery permitted demarcation of the respective sand transport pathways and morphodynamic changes in the delta over the last decade. The sand transport regime has promoted erosion of the shore to the south of the creek mouth, and has resulted in intermittent delivery of sand to beaches north of the channel. Attempts to stabilise the shore around the creek mouth are described and their effectiveness evaluated.
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    Review of Pre-feasibility Study: Main Report and Financial Model on the Mtwara Common User Quay Facility Project for Oil and Gas Supply Base Project
    (University of Dar Es Salaam Consultancy Bureau, 2015) Philemon, Diana; Dubi, Alfonse M.; Bwire, Hannibal; Minja, Elinami
    This report contains views on the Pre-feasibility Study Report by AECOM on the proposed Mtwara Common User Quay Facility Project for Oil and Gas Supply Base. The review was undertaken by a multi-disciplinary team of experts ranging from port engineering, transportation planning and engineering to economics and marketing. The concept design is in principle applicable, but for the case of Mtwara, it should be supported by appropriate geotechnical information, met-ocean data and other factors mentioned in the relevant sections of this report. The financial model proposed in the pre-feasibility study is at a very early stage and only provides basic outlook of the economic and financial viability of the project. As noted in the supplementary notes “… [Themodel] has been developed for the purpose of sensitivity testing and to provide and [sic] baseline for adjustments and future assumptions”. The report is clear about the depth of the contents of the model by giving a caveat that “... [The] model should not be relied upon for budget or business case purposes”. It is our view that the caveat be taken seriously and cannot therefore be relied upon. As for Traffic forecast: A thorough review of the Market Assessment Report reveals no forecast model is presented as purported in the main report, instead traffic forecasts are presented. As for the Concession Strategy, the build-own-operate-and-transfer (BOOT) is recommended. Monitoring mechanisms need to be in place to ensure the quality of the assets agreed by the parties is upheld from construction to the end of the concession period. At the same time, proponents of the project should adhere to the National Public Private Partnership (PPP) Policy (2009), the Public Private Partnership (PPP) Act (2010), as well as the PPP Operational Guidelines for Tanzania Mainland (2010) and PPP Regulations (2011). Overall, information contained in the report is very course and hence it is recommended that a proper pre-feasibility study be conducted.
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    Sediment Characteristics and Hydrodynamic Setting of Reef Platform Sediments of Kunduchi, North Of Dar es Salaam Harbour
    (2006) Shaghude, Yohanna W.; Nyandwi, Ntahondi; Muzuka, A. N. N.; Dubi, Alfonse M.; Mwaipopo, O. U.
    Sediment grain size distribution, carbonate content and current velocities for the Kunduchi area are used to determine its hydrodynamic setting and sediment characteristics. The sediment mean grain size generally decreases northward. The sediments consist of medium to coarse sand south of the Tegeta River and fine sand further north. The sediment sorting values, which lack a northsouth trend, vary from moderately well sorted to poorly sorted. The skewness of the sediment vary from near-symmetrical to very negatively skewed while the peakedness (kurtosis) varies from platykurtic to leptokurtic. The carbonate content increases with distance offshore, whereas the siliciclastic component decreases with distance offshore. The siliciclastic/carbonate transition of the investigated area is characterized by a narrow transition with no inter-fingering of the two facies. The lack of inter-fingering of the two facies suggests that there is a limited offshore transport of land-derived sediments. This is further supported by the drogue experiment results, which shows that the predominant surface current flows northward irrespective of the tidal phase
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    Sediment Suspension on a Tidal Flat near an Eroding Beach
    (2000) Dubi, Alfonse M.; Nyandwi, Ntahondi
    Kunduchi Beach is located approximately 10 kilometres north of Dar es Salaam City on the coast of Mainland Tanzania. The whole area north of the Dar Es Salaam City is endowed with beautiful, but eroding sandy beaches. The severe coastal erosion that is taking place threatens the buildings and the land as a whole. The aim of this study is to collect information on erosive forces and the littoral processes in the area so that options for the control of the erosion are based on good quality scientific data.Currents and sediment concentrations were measured using a multi-sensor self-recording current meter. Waves were measured using pressure gauges. Some physical features were measured visually.The general orientation of the shoreline is 330 degrees and the tidal flat is characterised by ripples. At about 150 m from the shoreline, ripples are 7-9 cm high and their wavelength is about 40 cm. Closer to the beach, ripple orientation is 350 degrees; ripple height is 5 cm and ripple wave length is 5 cm. Results show that during flood tide the current direction is southerly (an average of 210 degrees) and at high tide the average direction is 150 degrees. The direction of the ebb tidal current is northerly (an average of 360 degrees). On the average, the current speed was 0.1 m/s. Significant waves heights increased with increasing water level, from 0.1 metres in water depth of 0.5 metres to about 0.4 metres when the water depth reached 2.4 metres. The wave period did not show significant variation with increasing water depth. The average wave period was 8 seconds.Suspended sediment concentration varies in phase tide level. Sediment concentration is related with water level by an exponential function C / C max = 0.107 exp( 0.6597 D) , where D is water depth.There is a remarkable variation of sediment concentration between the two main seasons. Sediment concentrations are much higher during the southerly winds than during the northerly winds.Longshore sediment transport rates are found to be in the order of 3x10-8 m3/s/m.
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    Shoreline Change in Tanzania and Kenya: Manual for Assessment and Design of Mitigation Strategie
    (WIOMSA, 2015-01) Shaghude, Yohanna W.; Mburu, J. W.; Arthurton, Russell; Dubi, Alfonse M.; Gachuiri, S.; Kangwe, J.; Magori, C.; Msuya, Flower E.; Nyandwi, Ntahondi; Ochiewo, J.; Ong'anda, H.; Sallema, R.; Sanga, I.; Shalli, Mwanahija. S.; Uku, J.
    The aim of the manual is to raise awareness of the complex causes of, and the issues and risks associated with, shoreline change at local and national scales in Tanzania and Kenya, but also within the context of the WIO region. A greater awareness and application of shoreline planning and management can benefit coastal stakeholders, livelihoods, as well as local and national economies. The manual promotes the management of risks associated with shoreline change within the context of ICAM, with an emphasis on protecting the natural capital of the region’s coastal areas.