Department of Water Resources Engineering

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Analysis of Flow Estimation Methods for Small Hydropower Schemes in Bua River
(Scientific Research publishing, 2015-02) Kasamba, Chisomo; Ndomba, Preksedis M.; Kucel, Samuel Baker; Uamusse, Miguel M.
Any hydropower project requires an ample availability of stream flow data. Unfortunately, most of the hydropower projects especially small hydropower projects are conducted on ungauged river and consequently hydrologists have for a longtime used stream flow estimation methods using the mean annual flows to gauge rivers. Unfortunately flow estimation methods which include the ru- noff data method, area ratio method and the correlation flow methods employ a lot of assumptions which affect their uncertainty. This study was conducted on Bua River in Malawi to unveil the un- certainties of these flow estimation methods. The study was done on a well gauged catchment in order to highlight the variations between the observed, true stream flows and the estimated stream flows for uncertainty analysis. After regionalizing the homogenous sites, catchments using L-moments, an uncertainty analysis was done which showed that the area method is better fol- lowed by the correlating flow method and lastly the runoff data method in terms of bias, accuracy and uncertainty.
Analysis of Institutional Arrangement for Greywater Management in Unplanned Settlements of Kinondoni Municipality Tanzania
(IWA Publishing, 2015) Ndunguru, Teresia W.; Mulungu, Deogratias M. M.
Greywater (GW) may contain pathogens and organics thereby calling for its management. Institutional arrangement (IA) is the heart of planning, coordination and management of initiatives. Analysis of IA is key for determination of what could be rectified within organisations based on the existing structure, resources, strategies, data and information, stakeholder participation and involvement, policy and by-laws. Kinondoni municipality has the largest population of the three municipalities in Dar es Salaam city. In this study, the IA for GW management in Kinondoni municipality was analysed using weighted strengths, weaknesses, opportunities and threats (SWOT). The weights for the SWOT criteria were obtained from field interviews with households and key informants, and then integrated using expert judgement. Overall, from the analysis matrix, the SWOT was towards weaknesses (73%) and opportunities (60%).Weaknesseswere largely due to internal factors, otherswere lack of horizontal and vertical coordination, accountability, and stakeholder participation. With respect to GW management, these results revealed that there is inadequacy in the existing institutional structure, which accelerates poor performance in GW management practices in Kinondoni municipality. Accordingly, this study proposed an IA that induces stakeholder involvement and participation, accountability mechanisms and collaboration between departments in GW management
Application of SWAT in Natural Wetland Catchments. A Case of Rugezi Catchment in Rwanda
(College of Engineering and Technology, University of Dar es Salaam, 2010) Ndomba, Preksedis M.; Magoma, D.; Mtalo, Felix W.; Nobert, Joel
Hydrologic models are increasingly used to support decisions at various levels and guide water resources policy formulation, management and regulations. In this study the Soil and Water Assessment Tool (SWAT) was examined for its applicability in wetland catchment of Rugezi in Rwanda covering an area of, approximately to, 197 Km2 . The study adopted SWAT model as recommended by others workers in the region in order to extend its testing. The application of SWAT model entailed setting up the model using readily available data, sensitivity analysis and calibration. In this study wetland model physical parameters such as width, depth, length, slope and area were generated by GIS based SWAT interface. The ground photos available from literature supplemented and validated the GIS data. An independent simulation was also conducted without implementing the wetlands in order to study its impacts on the hydrology. Sensitivity analysis indicated that Channel effective hydraulic conductivity (CH_K2), Surface runoff lag time (Surlag), SCS runoff curve number under moderate moisture condition (CN2), and Manning’s n value for main channel (Ch_n) are the most sensitive parameters. Comparable results between simulated and observed streamflows at the catchment outlet, Rusumo gauging station, were obtained. The Nash and Sutcliffe coefficient values (CE) and Index of Volumetric Fit (IVF) were 49.15% and 95.6% for calibration and 51.4% and 98.6% for validation periods, respectively, indicating a satisfactory simulation. It was evident from this study that the wetland was a major hydrological controlling feature in the basin and should be safeguarded. These results suggest that SWAT model is potentially useful in studying the hydrology of natural wetland catchments with limited data. Besides, the authors would like to recommend extensive testing of the model in other wetland catchments in the region.
Application of SWAT Model for Mountainous Catchment
(FWU Water Resources Publications, 2007) Birhanu, B. Z.; Ndomba, Preksedis M.; Mtalo, Felix W.
A GIS based hydrologic model, SWAT (Soil and Water Assessment Tool) was applied for modeling the WeruWeru catchment at the foot slopes of Mt. Kilimanjaro in Northern Tanzania. The catchment has an approximate drainage area of 101 km2 and a mean annual precipitation between 1500mm and 3000mm. The water balance modeling was performed on annual and monthly bases using spatial and temporal data. A statistical weather generator file WXGEN was prepared for ten years to generate climatic data and fill in gaps in the measured records of climatic data. Various GIS data preprocessor modules involving watershed delineation, input map characterization and processing, stream and outlet definition, the computation of the geomorphic parameters, and characterization of the landuse/land cover and soil were developed in the course of modeling. Surface runoff computation was done using Soil Conservation Service-Curve Number (SCS-CN) method; and Muskingum routing method was used for flow routing. The Rainfall-Runoff modeling was based on a long term global water balance simulation for 15 years (1972-1986) and temporal calibration technique. The Nash and Sutcliff efficiency criterion (R2 ) and the Index of Volumetric Fit (IVF) were adopted for the measure of efficiency of the performance of the model. An R2 of 82% and 59% was obtained during calibration and verification periods respectively. The predicted mean daily stream flow was found to be 1.92m3 /s exactly as observed during the water balance simulation. Besides, modeling result gave a total annual water yield of 597.1mm, from which the annual surface water component was 155.8mm and that of the base flow component was 441.4mm in the long term simulation period with IVF unity. While demonstrating the catchment is rich in ground water sources as a result of high magnitude of precipitation and good water retention capacity, this study shows that SWAT model can be a potential monitoring tool for watersheds in mountainous catchments.
Applications of the Soil Water Assessment Tool (SWAT) in Simiyu River Catchment
(2005-11-14) Mulungu, Deogratias M. M.; Mtalo, Felix W.; Bauwens, Willy
The physically based Soil Water Assessment Tool (SWAT) model is applied on the Simiyu river catchment at Ndagalu outfall, Tanzania. Input data are spatially distributed data set such as topographical, land cover and soil data, climatic and river flow time series data. The model was calibrated for the period 1970-1974 based on the availability of coinciding climatic data and validated in the period 1976-1983. The calibration involved fine-tuning the land coversoil parameters to match the observed discharge at Ndagalu flow gauging station. The weather generator tool of the SWAT was used to fill in the missing climatic data and enabled flow simulation in the periods with missing data. Several model fit techniques and water balance matching techniques were used to assess model performance. Results and analysis was presented to show model performances in calibration and validation periods. During model set-up it was found that the land use (especially vegetation types) classification was a sensitive issue for the river flow estimation. The study identified optimum parameters for better discharge simulations. However, since some model parameters were obtained manually by fine-tuning, in future study the more physical basis of the parameters need to be considered. Also, the analysis of observed and estimated hydrographs showed that the rainfall data used is not representative and more rainfall data is required especially in the headwaters of the catchment so as to have better rainfall representation, which may produce better model fits. Considering the good results of SWAT in this study and comprehensiveness of the model in land surface processes representation, the model is very promising for land and water management studies and expected to give valuable information to land and water resources managers.
Appraisal Study to Select Suitable Rainfall-Runoff Model(s) for the Nile River Basin
(2005) Bashar, Kamal E.; Mutua, Francis; Mulungu, Deogratias M. M.; Deksyos, T.; Shamseldin, A.
This paper presents an appraisal study to select a suitable model(s) that can be used in forecasting flows in the rivers of the Nile basin. Flow forecasting is an important step in river basin management in particular and water resources management in general. River flow models are used as components in actual flow forecasting schemes. They are also used in providing for efficient operation of storage reservoirs. Usually, flow forecasts are obtained in real time by transforming the input into a discharge using models. These forecasts may subsequently be modified or updated in accordance with the errors observed in the previous forecasts up to the time of making the new forecast. The system analysis or black box approach depends on a prior assumption of flexible linear and time invariant relationship the expression of which can be obtained by the application of systems analysis approach to records. The conceptual model provides an alternative approach in which the input-output transformation goes through a series of steps. In this appraisal study, systems and conceptual modelling techniques are applied to lake Victoria catchments (Simiyu, Sondu and Nzoia), Awash and the Blue Nile catchment up to Eddeim of the Ethiopian high lands. The models were applied in non-parametric and parametric forms. Parameter optimisation is carried out by ordinary least squares, Rosenbrock, Simplex and genetic algorithm. The areal rainfall which is the main input to these models was estimated using arithmetic mean. However, attempts to estimate the areal rainfall by the Thiesen polygon method was made but the improvement in the model performance can not justify the amount of work involved in making Thiesen’s estimate. It is shown that the simple assumption of linearity is not adequate in modelling the rainfall runoff transformation. However, in catchments which exhibit marked seasonal behaviour good results can be obtained with Linear Perturbation Model (LPM) which involves the assumption of linearity between the departures from seasonal expectations in input and output series. The application of the GFFS (collection of systems and conceptual models) software proved to be possible with variable efficiencies in the Nile River basin. The LPM in non-parametric or parametric form, the LVGF model the ANN and the SMAR model can be used to forecast (reproduce). In catchments that exhibit marked storage effects e.g Sondu and Nzoia LPM and SMAR performed better than the other models. In Simiyu river it seems that the transformation can not be done under the assumption of linearity and hence the ANN performed better. Within the range of the tested models LPM was found to be the best candidate model that can forecast the flows under a wide range of conditions ranging from marked seasonality to marked storage effects accounting for more than 90% of the initial variance.
Assessment of Impact of Climate Change and Adaptation Strategies on Maize Production in Uganda
(Elsevier, 2015) Kikoyo, Duncan A.; Nobert, Joel
Globally, various climatic studies have estimated a reduction of crop yields due to changes in surface temperature and precipitation especially for the developing countries which is heavily dependent on agriculture and lacks resources to counter the negative effects of climate change. Uganda's economy and the wellbeing of its populace depend on rain-fed agriculture which is susceptible to climate change. This study quantified the impacts of climate change and variability in Uganda and how coping strategies can enhance crop production against climate change and/or variability. The study used statistical methods to establish various climate change and variability indicators across the country, and uses the FAO AquaCrop model to simulate yields under possible future climate scenarios with and without adaptation strategies. Maize, the most widely grown crop was used for the study. Meteorological, soil and crop data were collected for various districts representing the maize growing ecological zones in the country. Based on this study, it was found that temperatures have increased by up to 1 °C across much of Uganda since the 1970s, with rates of warming around 0.3 °C per decade across the country. High altitude, low rainfall regions experience the highest level of warming, with over 0.5 °C/decade recorded in Kasese. Rainfall is variable and does not follow a specific significant increasing or decreasing trend. For both future climate scenarios, Maize yields will reduce in excess of 4.7% for the fast warming-low rainfall climates but increase on average by 3.5% for slow warming-high rainfall regions, by 2050. Improved soil fertility can improve yields by over 50% while mulching and use of surface water management practices improve yields by single digit percentages. The use of fertilizer application needs to go hand in hand with other water management strategies since more yields as a result of the improved soil fertility leads to increased water stress, especially for the dry climates.
Assessment of nutrient retention by Natete wetland Kampala, Uganda
(2010-12) Kanyiginya, V.; Kansiime, Frank; Kimwaga, Richard; Mashauri, Damas A.
Natete wetland which is located in a suburb of Kampala city in Uganda is dominated by Cyperus papyrus and covers an area of approximately 1km2. The wetland receives wastewater and runoff from Natete town which do not have a wastewater treatment facility. The main objective of this study was to assess nutrient retention of Natete wetland and specifically to: determine the wastewater flow patterns in the wetland; estimate the nutrient loads into and out of the wetland; determine the nutrient retention by soil, plants and water column in the wetland; and assess the above and belowground biomass density of the dominant vegetation. Soil, water and plant samples were taken at 50m intervals along two transects cut through the wetland; soil and water samples were taken at 10cm just below the surface. Physico-chemical parameters namely pH, electrical conductivity and temperature were measured in situ. Water samples were analyzed in the laboratory for ammonium-nitrogen, nitrate-nitrogen, total nitrogen, orthophosphate and total phosphorus. Electrical conductivity ranged between 113μS/cm and 530μS/cm and the wastewater flow was concentrated on the eastern side of the wetland. pH varied between 6 and 7, temperature ranged from 19°C to 24°C. NH4-N, NO3-N, and TN concentrations were retained by 21%, 98%, and 35% respectively. Phosphorus concentration was higher at the outlet of the wetland possibly due to release from sediments and leaching. Nutrient loads were higher at the inlet (12,614±394kgN/day and 778±159kgP/day) than the outlet (2368±425kgN/day and 216±56kgP/day) indicating retention by the wetland. Plants stored most nutrients compared to soil and water. The belowground biomass of papyrus vegetation in the wetland was higher (1288.4±8.3gDW/m2) than the aboveground biomass (1019.7±13.8gDW/m2). Plant uptake is one of the important routes of nutrient retention in Natete wetland. It is recommended that harvesting papyrus can be an effective way of nutrient removal especially phosphorus which is not easily lost to the atmosphere like nitrogen. Natete wetland needs to be left in its natural state for better efficiency in nutrient retention. Bio-manipulation of the wetland by spreading the wastewater as it enters the wetland could enhance the interaction between plants and wastewater and subsequent nutrient removal.
Assessment of Sustainable Agricultural Practice Using Distributed Crop Soil Moisture Balance Model (D_CSWB): A Case Study of Pangani Basin in Tanzania
(2003-06) Moges, Semu A.; Norbert, Joel; Mashauri, Damas A.
BOD5 Removal in Facultative Ponds: Experience in Tanzania
(1996) Mayo, Aloyce W.
This paper discusses the removal of BOD5 in facultative ponds under tropical conditions. Data was collected from pilot and field ponds at the University of Dar es Salaam and was compared to other ponds in Dar es Salaam. Results showed deviations of performance, in some cases, from assumptions made during the design. The permissible organic loading rate for ponds in Dar es Salaam was 450 kg BOD5/ha/d. To reduce concentration of algae in the final effluent, a sunken outlet structure was suggested.
Breakthrough Characteristics and Flow-Rate Interaction in Water Defluoridation with a Bauxite-Gypsum-Magnesite Composite Filter
(2012-11) Thole, Bernard; Mtalo, Felix W.; Masamba, W. R. L.
Water defluoridation in a fixed bed column may be optimized through choice of flow rate. This, however, affects breakthrough characteristics. In any fixed bed system an understanding of flow rate and breakthrough interactions is therefore important to guide choice of design velocity. Consequently interactions between flow rate and break through characteristics were determined in a fixed bed column in defluoridation with a composite filter of bauxite, gypsum and magnesite. This was an attempt to optimize defluoridation with the three materials. Lower flow rates obtained longer service times but higher residual concentrations of sulphates and chlorides. Higher flow rates registered lower residual sulphate and chloride concentrations but obtained lower service times. There were no significant differences in residual concentrations of aluminium, iron, calcium and magnesium among the different flow rate regimes. Adsorbent exhaustion rates and critical bed depths increased with increase in flow rates, indicating that lower flow rates offered better technical system performance. Critical bed depths ranged from 5.23 to 10.89 cm for flow rate range of 0.68 to 1.25 ml/s. Operating lines were polynomic with generic form δ = C1 t2 - C2 t + C3, where δ is adsorbent exhaustion rate and t is empty bed residence time. Choice of flow rates, in this system requires a balance between service-time optimisation and water quality.
Carbon Footprints of Production and Use of Liquid Biofuels in Tanzania
(2015) Eshton, Bilha; Katima, Jamidu H. Y
Tanzania being a prospective producer and exporter of liquid biofuels, information on local contribution of this sector to the environmental burden of the country is highly required in order to ensure sustainable liquid biofuels. Therefore, this paper evaluates a life cycle carbon footprint (or greenhouse (GHG) gas emissions) of liquid biofuels (biodiesel produced from jatropha oil and bioethanol produced from sugarcane molasses as alternative to fossil fuels in Tanzania. The functional unit (FU) of the study is defined as 1 Giga Joule (GJ) of output energy when a biofuel is combusted in the engine. The study found a positive GHG emissions related to biofuels. A carbon footprint (in CO2 equivalents) of jatropha biodiesel is 23.9 kg FU−1 while that of molasses bioethanol is 17.4 kg FU−1. Biodiesel combustion found to be a major contributor to carbon footprint by 41% which is attributed to methanol used during transesterification of jatropha oil followed by the use of chemical fertilizers (31%). Sugarcane production phase on the other hand found to be the highest contributor to carbon footprint of molasses bioethanol accounting for more than 80%. This is due to the use of diesel fuel, chemical fertilizers and burning of sugarcane prior to harvesting. Sensitivity analysis indicates that higher market prices of molasses increases carbon footprint of bioethanol same as higher market price of biodiesel. For the same energy output of 1 GJ, molasses bioethanol observed to have lower carbon footprint than jatropha biodiesel by 27.2%. Both biofuels observed to save GHG emissions by >70% when used as fossil fuel replacement. The study recommends further research on socio-economic implication of large scale biofuel production; impact of land use change and land use competition and sustainability of biofuels to be carried out in near future.
Challenges and Prospects of Private Sector Participation in Solid Waste Management in Dar Es Salaam City, Tanzania
(Elsevier, 2016) Kirama, Aminatha; Mayo, Aloyce W.
The objective of this research was to evaluate effectiveness of private sector participation in solid waste collection and transportation in Dar es Salaam City. The study covered 20 private service providers in municipalities of Kinondoni, Temeke and Ilala. Information was collected through questionnaires, interview guides, physical observation and field studies. Data were sought from 5 private companies, 15 Community Based Organizations, Dar es Salaam City Council, Waste Departments of Municipal authorities and local governments of ward and streets. The results show that private sector service providers collected and transported 9% of the 29,764 tons of solid wastes generated per week. They have also provided employment opportunities to over 350 people, who are helping to keep the city clean and increase national income through payment of various taxes. It was also observed that private sector operates in difficult conditions because of low cost recovery, the use of inferior wastes collection and transportation equipment, limited scheduling, short contract duration, inefficient system of refuse fee collection, an absence of planned wastes recycling systems, inaccessible roads and weak implementation of relevant municipal policies and by-laws. It was further noted that the success of the system will depend on accountability of municipal authorities by raising the awareness of the communities in order to improve willingness to pay for refuse fees and discourage illegal dumping of waste by individuals, enforcing municipal by-laws, and planning and promotion of environmentally friendly waste management practices.
Challenges of Adoption of Urine-Diversion Dry Toilets Technology as Sanitation Option by Coastal Communities of Mkuranga District in Tanzania
(2015) Mayo, Aloyce W.; Mubarak, Twaha
Mkuranga District council in collaboration with African Medical and Research Foundation (AMREF) introduced ecological sanitation option using urine-diversion dry toilets (UDDT) to the community between 2007 and 2009, which was later declared unsuccessful. This study analyzed factors that hindered the uptake of UDDT by the community by assessing the project implementation strategy. Techniques used for the study were questionnaire, interviews, observation and focus group discussion while respondents were government official and the community at the household level. The study reveals that the literacy level in Mkuranga district is 79.1%, but only 40.6% had some knowledge of ecological sanitation although only 9% proves that. About 52% of the respondents are using conventional pit latrines, but 27.3% have no toilet facilities. There was no evidence of adoption of UDDT technology at household level and only one of the seven UDDTs constructed by the project is operational. There was no sufficient evidence to suggest that Mkuranga District has sufficiently supported the project through supervision, advocacy and addressing community requirements. As a result, the idea came in top-bottom approach which failed because communities were not adequately involved in the project.
Challenges of Modeling the Flows of the Nile River
(University of Dar Es Salaam, 2005-11-14) Mutua, F. M.; Mtalo, Felix W.; Bauwens, Willy
Perceptions and realities of water and conflict in basins such as the Nile vary widely. The river continues to be brought into debates about “water wars” by writers on the subject. One of the major problems with the “water wars” thesis is that it includes only a cursory understanding of “scarcity” issues, and of the actual facts and figures that underlie much of the analysis. This fact is as a result of the difficulties and subsequently the inability to be able to model the Nile flows satisfactorily due to the complexity of the geography, the hydrology and the climate – which are the major drivers of the hydrologic system of the Nile basin. One of the main features of the Nile basin is its varied geography. The second major feature of the of the basin is the hydrological diversity of the two major tributaries of the Nile River. The Blue Nile has a huge seasonality which yields flows mainly concentrated from July to October. The total flow of Blue Nile (including its tributaries) varies greatly from a high of 15.6 BCM in August to just 0.3 BCM in April. The White Nile’s average monthly maximum (October) and minimum (February) discharges var y only slightly from 1.4 billion cubic meters (BCM) to 1.2 BCM, A third major feature of the river system is caused by virtue of the river’s situation in hot, arid areas whe re evaporation losses are high. The north–south orientation of the River Nile on the African continent ensures extreme variability in climate between the extremes of the basin. The Nile Basin receives annually an average rainfall of about 650 mm, or a total of about 1,900 BCM per year. Long-term mean annual flow at Aswan is about 85 BCM per year, making the annual runoff coefficient of the basin to be very small (about 4.5 percent) compared to other basins of the same size in other parts of the world. This paper explores the challenges and opportunities of modeling the flows of the Nile.
Characterization of wastewater from an Abattoir in Rwanda and the impact on downstream water quality
(2010-01) Muhirwa, Déogratias; Nhapi, Innocent; Wali, Umaru G.; Banadda, Noble; Kashaigili, Japhet; Kimwaga, Richard
This study analyzed processes and products at Nyabugogo Abattoir in Kigali, Rwanda, and investigated how they can be optimized for environmental safety. The average capacity of the abattoir is 566 cattle and 1,512 goats and sheep slaughtered per week. The study assessed the quantity and quality of different raw materials, by-products and wastewater streams and the potential impacts of applying cleaner production principles in abattoir processes. The samples were collected fortnightly, and analyzed using Standard Methods. The analysis emphasized on nutrients, biologically active constituents, and receiving water impacts. The data were processed for trends and variance using SPSS computer package. The wastewater parameters analyzed are temperature, salinity, conductivity, turbidity, dissolved oxygen pH, TSS, TDS, BOD5, COD, fat oils and grease, NO3-N, TKN, total phosphorus, chloride, calcium and total coliforms. The findings showed that the abattoir wastewater streams' total chemical oxygen demand (TCOD) ranged from (7,533±723) for evisceration to (23,778±1,673) mgl-1 from slaughtering step and the discharge into Mpazi River increased its TCOD from (213±29) to (852±94) mgl-1. The TSS varied between 2,452±51 from the slaughter process and 5,252±174 mgl-1 for the effluent from the goat and sheep slaughter section. Results from the bacteriological analysis showed that the average abattoir wastewater discharge count was (560±81)105 cfu/100ml of total coliforms which increased from (2.8±0.58)105 to (8.2±0.86)105 cfu/100 ml. It was concluded that the current effluent quality is not suitable for discharge into watercourses. It was recommended that further treatment of the effluent is required coupled with the application of cleaner production principles.
Comparison of Escherichia Coli KO11 and Saccharomyces Cerevisiae ATCC 96581 in Fermenting Pinus Patula Hydrolysate Pretreated at Different Steam Explosion Severity
(2012) Chacha, Nyangi; Dyrset, Nils; Mtui, Godliving; Katima, Jamidu H. Y.; Mrema, Godwill
Bioconversion of wood residues to biofuels such as ethanol is one of the feasible initiatives towards production of renewable energy. This work compares the effectiveness of Escherichia coli KO11 and Saccharomyces cerevisiae ATCC 96581 in fermenting Pinus patula (pine) hydrolysate pretreated by acid-catalyzed steam explosion. The results show no significant difference in terms of the ethanol yield when E. coli KO11 and S. cerevisiae ATCC 96581 were used. The maximum ethanol concentration obtained in test tubes fermentation were 18.30 and 19.41 g/l for E. coli KO11 and S. cerevisiae ATCC 96581, respectively, from samples pretreated at 225°C/5 min. The ethanol yields obtained using bioreactors for samples pretreated at 225°C, 0.5% SO2, and 5 min, were 21.30 and 19.63 g/l for E. coli and S. cerevisiae, respectively. Overall, ethanol yields were higher in bioreactors than in test tubes for both strains. In comparison, S. cerevisiae consumed the substrate faster than E. coli, thus making S. cerevisiae the most preferred strain in fermentation of hydrolysates from steam pretreated P. patula.
Comparison of Forest Canopy Interception Models Combined with Penman-Monteith Equation.
(2002) Mulungu, Deogratias M. M.; Shiiba, Michiharu; Ichikawa, Yutaka
Three models of interception process: Rutter model with Deardorff's power function, Deardorff model and Modified Kondo model, each in combination with Penman-Monteith equation applied to the same climatic forcing over the year of simulation were compared. The modification of the Kondo's model done in our study includes the water balance component, between storms evaporation and transpiration including the power function, storage changes and the canopy drainage. The comparison was meant for assessing the simple Modified Kondo model developed in Japan and demonstration of the importance of the power function. The Penman-Monteith equation was the kernel for determination of evaporation and transpiration rates. Its use in this study was proposed because it has been widely used in Japan and in experimental sites and therefore can be used as a basis for comparison. Since much interest was on net rainfall, the control volume for the water accounting was between top of the canopy and above the ground surface and hence does not include soil moisture and transpiration. Results showed that forest canopy evaporation ranged from 22 to 29% of gross rainfall. Much model prediction differences were observed in winter, with lower rainfall intensity where wet canopy storages or rainfall did not meet the potential (atmospheric) evaporation demand. The annual net rainfall and transpiration ranged from 71 to 78% of gross rainfall and from 727 to 733 mm respectively. The adopted power function had significant impact on transpiration rate and small impact on evaporation rate for the Modified Kondo model. The Modified Kondo model predicted fairly close to the two models and therefore can be used for providing hourly input into hydrological models. The differences in the predicted hydrological fluxes resulted from the different model for mulations especially throughfall coefficients and drainage functions.
Constructed Wetland at the University of Dar Es Salaam
(Elsevier, 2000) Mashauri, Damas A.; Mulungu, Deogratias M. M.; Abdulhussein, B. S.
Following lack of investment in wastewater treatment, high investment and maintenance cost, conventional treatment systems have not been used in Tanzania. On the other hand, cost effective wastewater treatment methods like the use of septic tanks, soak pits, drainage fields and waste stabilization ponds are widely applied. One of the methods of achieving compliance using conventional treatment systems at low cost, producing treated water pollution free and fostering a community responsibility for wastewater treatment involves the use of natural or constructed wetlands. To date, no wetlands have been used for treating wastewater in Tanzania. Therefore in an attempt to promote the use of constructed wetland for wastewater treatment, a horizontal flow constructed wetland at the University of Dar es Salaam was commissioned for treatment of wastewater effluent from the University waste stabilization ponds (WSP).This paper presents results obtained from a constructed wetland (CW) installed at an outlet of the WSP of the University of Dar es Salaam. The field tests were conducted at low and high filtration rates 0.27 m/h and 2.3 m/h respectively for a period of 4 weeks. Treatment effectiveness was evaluated which indicated high mean removal efficiencies; 80% for SS, 66% for COD, 91% for faecal coliforms (FC) and 90% for total coliforms (TC) achieved at the low filtration rate. Thus, wetlands if properly designed, operated and maintained can provide an efficient and economical means of upgrading the quality of secondary treated wastewater to an acceptable level.
Coping with Water Scarcity in Eastern Africa: the Potential Role of Intra-regional Virtual Water Trade
(IAHS Press, 2007-07) Kimwaga, R. J.; Simbarashe, Govere; Mtalo, Felix W.
Virtual water is the amount of water required for the production of a commodity. Trading commodities implies Virtual Water Trade (VWT). This study was conducted to determine the VWT derived from intra-regional trade of six cereals (maize, paddy rice, millet, sorghum, wheat and barley) for ten countries within Eastern Africa from 1998 to 2003. It involved quantifying the VWT, assessing the role of water scarcity in shaping VWT and determining the quantity and nature of water savings generated. Quantifying the VWT included delineating major crop growing zones and calculating Crop Water Requirement (CWR) using a model, CropWat. Virtual water contents derived from CWR were multiplied with intra-regional cereal trade flows to obtain the VWT. Results show that virtual water contents vary significantly within the region, being higher in the arid countries than the humid countries, partly because of water scarcity in these countries. Virtual water flows for the region averaged 150 Mm3 year-1 of water whilst “water savings” averaged 31 Mm3 year-1. Sudan, Uganda and Tanzania are the only net virtual water exporters, exporting a combined volume of 110 Mm3 year-1, whilst the other seven countries are net importers, the largest importer being Ethiopia. No correlation was found between a nation’s water scarcity status and virtual water imports, suggesting that intra-regional cereal-derived VWT is not a conscious choice but arises for other reasons like comparative advantage. Sorghum and maize trade accounted for the largest virtual water flows, 36% and 38%, respectively, the former due to the high unit virtual water content of the major exporting countries and the latter due to the large tonnage traded. In a regional virtual water policy, Kenya, Sudan, Djibouti, Eritrea and Somalia can be potential virtual water importers, whilst Tanzania, Uganda, Rwanda, Burundi and Ethiopia can be potential virtual water exporters. It was concluded that VWT had a big role in water savings in water scarce countries. This has been considered as a change in water resources systems, and hence maintenance in water security and insurance in integrated management.

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