Research Repository :: Browsing by Author "Mtalo, Felix W."

Browsing by Author "Mtalo, Felix W."

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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.
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.
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.
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.
Developing innovations for adsorptive removal of arsenic from drinking water sources in North Mara gold mining area, Tanzania
(Taylor & Francis, 2016-06) Irunde, Regina; Lesafi, F . J .; Mtalo, Felix W.; Bhattacharya, Prosun; Dutta, Joydeep; Bundschuh, Jochen
Arsenic (As) contamination in drinking water have been reported to occur in areas where mining are practiced such as North Mara, lake Victoria basin in Mwanza, Geita and Rukwa. The removal of As requires methods such as ion-exchange, reverse osmosis, electrodialysis, contact precipitation, activated alumina, bone charcoal and activated clay. The use of ion-exchange, reverse osmosis and electrodialysis are expensive to be implemented in Tanzania. In order to safeguard the drinking water supplies, it is important to explore the low-cost and efficient locally available adsorbents such as activated alumina, bone char and clay for the removal of As for drinking water consumption.
Eco-hydrology of the Pangani River Downstream of Nyumba ya Mungu Reservoir, Tanzania
(Elsevier, 2008-01) Mwamila, Tulinave B.; Kimwaga, Richard; Mtalo, Felix W.
Eco-hydrological studies are highly emphasized worldwide at the moment especially where hydraulic structures such as dams are concerned, mainly focusing on benefiting both humans and existing ecosystem for the present and future generations. The study at Pangani basin was aimed at assessing the sufficiency and the amount of flow reaching the downstream area of the Pangani River for maintenance of ecosystem. Fish species were considered as the indicators for ecosystem health. Flow duration curves (FDC) and hydrographs were developed by using the collected historical daily flow data and used for assessing the flow variation before and after Nyumba ya Mungu (NYM) dam construction. The results showed that there is no seasonality and that for most part of the year the flow is within 20–40m3/s. From the comparison it was found that there is 42.7% decrease in Q5, 2.1% decrease in Q95, 38.9% increase in Q75, 23.4% increase in Q50 and decrease of percentage exceedence of 50m3/s by 61.5%. Physical habitat simulation model (PHABSIM) was used for hydraulic simulation incorporating geometric and flow data collected in the field. From the simulations minimum flow for habitat protection is about 15m3/s and for flood formation flows should be greater than 50m3/s. Thus the required reservoir outflow for sustainable water resources management at the NYM should follow the above specifications.
Effect of Particle Size on Loading Capacity and Water Quality in Water Defluoridation with 200°C Calcined Bauxite, Gypsum, Magnesite and their Composite Filter
(College of Engineering and Technology, University of Dar es Salaam, 2012-01-12) Thole, Bernard; Mtalo, Felix W.; Masamba, W. R. L.
Defluoridation was carried out with bauxite, gypsum, magnesite and their composite calcined at 200°C to determine relationship between particle size, capacity and water quality, in an attempt to formulate a composite filter in the ratio of loading capacities. Particles of 0.5 to 1.0, 1.0 to 1.4, 1.4 to 2.0 and 2.0 to 3.0 mm diameter were employed in batch defluoridation. Color, hardness, pH,   3 2 F ,Cl , Al ,Fe were determined hourly until fluoride equilibrium was obtained. Results showed that capacities were inversely correlated to particle size obtaining polynomial, linear and logarithmic relations of capacity (mg/g) to particle size (mm); Cs   Pz Pz 2 ( ) (composite, gypsum), Cs  Pz  (bauxite) and Cs   ln Pz  (magnesite). Bauxite, gypsum and composite decreased but magnesite increased pH. Particle size and pH changes were positively correlated, highly for bauxite (r2 = 0.915), fairly for composite and magnesite (r2 = 0.855 and 0.853, respectively) and lowly correlated for gypsum (r2 = 0.562). Smaller particles obtained higher apparent colour, hardness, alkalinity and sulphate. There was no relationship between particle size and  3 2 Cl , Al ,Fe . Sorption capacities of these materials increase with decrease in particle size, however decrease in particle size enhances colour, hardness and sulphate levels. In optimizing the materials for defluoridation particle size can be decreased while monitoring colour, hardness, alkalinity and sulphate levels. Particles of diameter 2 mm were optimum in the present experiments.
Estimating Gully Erosion Contribution to Large Catchment Sediment Yield Arte in Tanzania
(Elsevier, 2009-12) Ndomba, Preksedis M.; Mtalo, Felix W.; Killingtveit, A.
The objective of this paper is to report on the issues and proposed approaches in estimating the contribution of gully erosion to sediment yield at large catchment. The case study is the upstream of Pangani River Basin (PRB) located in the North Eastern part of Tanzania. Little has been done by other researchers to study and/or extrapolate gully erosion results from plot or field scale to large catchment. In this study multi-temporal aerial photos at selected sampling sites were used to estimate gully size and morphology changes over time. The laboratory aerial photo interpretation results were groundtruthed. A data mining tool, Cubist, was used to develop predictive gully density stepwise regression models using aerial photos and environment variables. The delivery ratio was applied to estimate the sediment yield rate. The spatial variations of gully density were mapped under Arc View GIS Environment. Gully erosion sediment yield contribution was estimated as a ratio between gully erosion sediment yield and total sediment yield at the catchment outlet. The general observation is that gullies are localized features and not continuous spatially and mostly located on some mountains’ foot slopes. The estimated sediment yield rate from gullies erosion is 6800 t/year, which is about 1.6% of the long-term total catchment sediment yield rate. The result is comparable to other study findings in the same catchment. In order to improve the result larger scale aerial photos and high resolution spatial data on soil-textural class and saturated hydraulic conductivity – are recommended.
Estimation of Soil Erosion in the Pangani Basin Upstream of Nyumba ya Mungu Reservoir
(2002) Mtalo, Felix W.; Ndomba, Preksedis M.
Evaporation Modelling in Data Scarce Tropical Region of the Eastern Arc Mountain Catchments of Tanzania
(College of Engineering and Technology, University of Dar es Salaam, 2011) Zemadim, Birhanu; Mtalo, Felix W.; Mkhandi, Simon; Kachroo, Raj; McCartney, Matthew
This paper focuses on developing methods for both potential and actual evapotranspiration (ET) models for the data scarce conditions of the Eastern Arc Mountains catchment of Tanzania. For reliable estimation of the components of the hydrological cycle and plant water uptake, potential ET estimates are required, and for catchment water balance actual ET estimates are needed. These potential and actual ET estimates, however, depend on reliable and good quality data records. The study catchments in this work are characterised by general lack of reliable meteorological (MET) data, though good records of rainfall, flow and pan evaporation data do exist in a few places. In the study reported here the Penman-Monteith (P-M) estimates were found to be closer to the pan evaporation model in areas where reliable records of pan data exist. By comparison, estimates derived solely from temperature (i.e. the Standard Thornthwaite method), were a lot lower. Assuming the P-M estimates to be reliable, new temperature based regional equations were developed using data obtained from six climate stations. The study also presents simpler methods for estimating actual ET from catchments.
Feasibility of Rain-fed Agriculture in the Pangani River Basin Tanzania
(2005) Mtalo, Felix W.; Moges, S. A.; Kimaro, T. A.
Distributed soil moisture model was used to estimate daily soil moisture balance for different crops in the Pangani River basin in Tanzania. The model calculates the soil moisture balance using rainfall and reference crop evapotranspiration at grid resolution of 1 km. The reference crop evapotranspiration was estimated using growth stage dependent crop coefficients making the model able to make crop-type sensitive spatially distributed soil moisture balance estimates. The simulated soil moisture balance at each grid was compared to readily available soil moisture (RAM) for a specific crop and a failure of crop was established if the simulated soil moisture was less than RAM for a critical period over which that specific crop starts wilting. Probability of crop failure for each crop were estimated grid wise and mapped to show areas where rain-fed agriculture for specific crop is feasible in the basin. The results shows that beans have probability of failure less than 20% for most parts of the basin. This crop may be considered as drought resistant and suitable for rain-fed agriculture in the basin. The probability of failure of the Maize crop was found to be less than 20% in Maasai steppe, part of the Usambara and areas around mount Kilimanjaro. Rain-fed agriculture is considered feasible only in these areas while areas around North and south pare mountains would not be feasible for rain-fed maize cultivation. The probability of failure for the rice crop was found to be higher than 80% for most parts of the basin and this crop is considered infeasible for rain-fed agriculture in the basin.
Geogenic Contaminants in the Groundwater in the Rift Valley of Tanzania- The Case of Arsenic and Fluoride
(University of Dar Es Salaam, 2015-11) Bhattacharya, Prosun; Mtalo, Felix W.; Mato, Rubhera A. M.; Annaduzzaman, M.
The access to safe and clean drinking water in Tanzania is challenged by geogenic contamination sources and intensification of mining activities. Nevertheless, the population growth, economic and industrial development activities also deplete the quality of drinking water sources in Tanzania, thus posing a great threat to source water quality including groundwater. The availability of safe groundwater for domestic, industrial and agricultural development is of the prime concern in developing countries like Tanzania. Majority of the inhabitants in the large cities and small rural communities in Tanzania depend on rivers, springs, hand-dug and shallow groundwater wells as their main drinking water sources. Hydrogeologically, about 75% of Tanzanian aquifer systems are in crystalline complex rocks with variable composition and age. However, predominantly Precambrian, which form the basement aquifers (e.g. the Pangani and Makutopora basins) and unfortunately this subsurface layer are highly contaminated with arsenic and fluoride. The contamination level of arsenic and fluoride in the soil, sediment, surface water and groundwater are related to the variation of hydrological conditions or geochemical factors (e.g. evaporite dissolution, cation exchange and carbonate weathering, redox potential etc.). Thus there is a huge gap within the primary information about the overall water quality and scarcity information and understanding of the fate and mobility of geogenic contaminants in the groundwater aquifers and surface water supply sources. This information is crucial in exploring aquifers as safe drinking water sources to delineate the associated human health risks of arsenic and fluoride pollution in groundwater sources. On the other hand, the limited studies have been used the locally available materials for developing arsenic and fluoride removal treatment technology for drinking water. These lab scale studies showed the significant potentiality of locally available adsorbent media for innovation and upscaling as water purification technology and develop policy strategies to provide safe drinking water.
Geogenic Fluoride and Arsenic Contamination in the Groundwater Environments in Tanzania
(2016) Bhattacharya, Prosun; Lesaf, Fina; Filemon, Regina; Ligate, Fanuel; Ijumulana, Julian; Mtalo, Felix W.
Adequate, safe and accessible drinking water is an important aspect to human health worldwide. Understanding this importance, the Tanzanian Government has initiated a number of programmes to ensure access to high quality water by the citizens. However, elevated concentration of geochemical pollutants in many drinking water sources pose a serious challenge to water suppliers and users in the country. Fluoride is a widespread drinking water contaminant of geogenic origin occuring in both surface- and groundwater around volcanic mountains and many parts within the East African Rift Valley in regions including Arusha (10 mg/L), Shinyanga (2.9 mg/L) and Singida (1.8 mg/L). An estimated 90% of the population living along the Rift Valley region are affected by dental or skeletal fluorosis and bone crippling because of long term exposure to very high levels of fluoride in drinking water sources. In the mining areas within Lake Victoria basin, groundwater wit elevated concentrations of arsenic has been discovered over an extended area. Most of these geochemical and naturally occurring drinking water pollutants are patchy with uncertainities in their spatial and temporal distribution patterns. The adverse health effects of skin disorder and cancer due to an elevated As concentration are reported from the North Mara gold and Geita mining areas in the Lake Victoria basin. About 30% of the water sources used for drinking in Tanzania exceed the WHO guideline values of fluoride (1.5 mg/L) and arsenic (10 µg/L). There is a scarcity of baseline information on the water quality data especially on geogenic contaminants in the groundwater and surface water as potable sources. This information is crucial in exploring sources of safe drinking water aquifers, associated human health risks of fluoride and arsenic pollution. using Laboratory based studies during the past two decades have shown promising results on the removal of fluoride and arsenic using locally available adsorbent materials such as pumice, bauxite, ferralsols and bone char. Developing innovative technologies, pilot-scale implementation and scaling-up water purification based on the locally available adsorbents is thus necessary to safeguard the public health for communities exposed to high levels of fluoride and arsenic in drinking water.
A Guided SWAT Model Application on Sediment Yield Modeling in Pangani River Basin: Lessons Learnt
(Universidade Federal da Paraíba, 2008-12-10) Ndomba, Preksedis M.; Mtalo, Felix W.; Killingtveit, A.
The overall objective of this paper is to report on the lessons learnt from applying Soil and Water Assessment Tool (SWAT) in a well guided sediment yield modelling study. The study area is the upstream of Pangani River Basin (PRB), the Nyumba Ya Mungu (NYM) reservoir catchment, located in the North Eastern part of Tanzania. It should be noted that, previous modeling exercises in the region applied SWAT with preassumption that inter-rill or sheet erosion was the dominant erosion type. In contrast, in this study SWAT model application was guided by results of analysis of high temporal resolution of sediment flow data and hydro-meteorological data. The runoff component of the SWAT model was calibrated from six-years (i.e. 1977–1982) of historical daily streamflow data. The sediment component of the model was calibrated using one-year (1977–1988) daily sediment loads estimated from one hydrological year sampling programme (between March and November, 2005) rating curve. A long-term period over 37 years (i.e. 1969–2005) simulation results of the SWAT model was validated to downstream NYM reservoir sediment accumulation information. The SWAT model captured 56 percent of the variance (CE) and underestimated the observed daily sediment loads by 0.9 percent according to Total Mass Control (TMC) performance indices during a normal wet hydrological year, i.e., between November 1, 1977 and October 31, 1978, as the calibration period. SWAT model predicted satisfactorily the long-term sediment catchment yield with a relative error of 2.6 percent. Also, the model has identified erosion sources spatially and has replicated some erosion processes as determined in other studies and field observations in the PRB. This result suggests that for catchments where sheet erosion is dominant SWAT model may substitute the sediment-rating curve. However, the SWAT model could not capture the dynamics of sediment load delivery in some seasons to the catchment outlet.
Hydrological Response of Watershed Systems to Land Use/Cover Change: a Case of Wami River Basin
(University of Dar es Salaam, 2012) Nobert, Joel; Jeremiah, Jiben; Mtalo, Felix W.; Mkhandi, S. H.
Wami river basin experiences a lot of human disturbances due to agricultural expansion, and increasing urban demand for charcoal, fuel wood and timber; resulting in forest and land degradation. Comparatively little is known about factors that affect runoff behaviour and their relation to landuse in data poor catchments like Wami. This study was conducted to assess the hydrological response of land use/cover change on Wami River flows. In data poor catchments, a promising way to include landuse change is by integrating Remote Sensing and semi-distributed rainfall-runoff models. Therefore in this study SWAT model was selected because it applies semi-distributed model domain. Spatial data (landuse, soil and DEM-90m) and Climatic data used were obtained from Water Resources Engineering Department, government offices and from the global data set. SWAT model was used to simulate streamflow for landuse/landcover for the year 1987 and 2000 to determine the impact of land use/cover change on Wami streamflow after calibrating and validating with the observed flows. Land use maps of 1987 and 2000 were derived from satellite images using ERDAS Imagine 9.1 software and verified by using 1995 land use which was obtained from Institute of Resource Assessment (IRA). Findings show that there is decrease of Forest area by 1.4%, a 3.2% increase in Agricultural area, 2.2% increase in Urban and 0.48% decreases in Waterbody area between 1987 and 2000. The results from SWAT model simulation showed that the average river flows has decreased from 166.3 mm in 1987 to 165.3 mm in 2000. The surface runoff has increased from 59.4mm (35.7%) in 1987 to 65.9mm (39.9%) in 2000 and the base flow decreased from 106.8mm (64.3%) to 99.4mm (60.1%) in 1987 and 2000 respectively. This entails that the increase of surface runoff and decrease of base flows are associated with the land use change.
Impacts of Land-use/cover Changes on the Hydrology of the Transboundary Mara River, Kenya/Tanzania
(Blackwell Publishing Ltd., 2008-05-04) Mati, Bancy M.; Mutie, Simon; Gadain, Hussein; Home, Patrick; Mtalo, Felix W.
The Mara River is the lifeline of the transboundary Mara basin across Kenya and Tanzania. The basin is considered one of the more serene subcatchments of the Lake Victoria Basin and ultimately the Nile Basin, and traverses the famous Maasai Mara and Serengeti National Parks. The basin also contains forests, large-scale farms, smallholder farms, pastoral grazing lands, as well as hunter gatherers and fishers. There is growing concern, however, regarding land degradation in the basin, particularly deforestation in the headwaters, that is affecting the natural resource base and the river flows. Accurate scientific data are required to advise policy, and to plan appropriate mitigation measures. This study utilizes remote sensing and geographical information system (GIS) tools, and hydrological and ground-truth studies to determine the magnitude of the land-use/cover changes in the Mara River Basin, and the effects of these changes on the river flows over the last 30 years. The study results indicate that land-use/cover changes have occurred. In 1973, for example, rangelands (savannah, grasslands and shrublands) covered 10 989 km2 (79%) of the total basin area. The rangelands had been reduced to 7245 km2 (52%) by 2000, however, while the forest areas were reduced by 32% over the same period. These changes have been attributed to the encroachment of agriculture, which has more than doubled (203%) its land area over the same period. The hydrology of the Mara River also has changed, with sharp increases in flood peak flows by 7%, and an earlier occurrence of these peaks by 4 days between 1973 and 2000. There is evidence of increased soil erosion in the upper catchments, with silt build-up in the downstream floodplains. This has caused the Mara wetland to expand by 387%, adversely affecting riparian agriculture. There is need for urgent action to stem the land degradation of the Mara River Basin, including planning and implementing appropriate mitigation measures.
Long Term Hydrologic Modeling for Simiyu Watershed, Tanzania Using Hydrologic Simulation Program-Fortran (HSPF)
(2005-11-14) Salah, Ahmad M.; Mulungu, Deogratias M. M.; Mtalo, Felix W.
Simiyu watershed is one of the relatively mid-size river basins draining into Lake Victoria. The objective of this paper is to investigate the hydrologic response and to build a hydrologic model for the watershed. Hydrologic Simulation Program-Fortran (HSPF) and Watershed Modeling System (WMS) are used to build a long term model for the basin. WMS is used to analyze digital elevation and land use data as a pre-processor whereas HSPF is used to simulate daily stream flows. The initial model run indicated a need for calibration. Some model parameters are, thus manipulated to obtain a better fitting model. The calibrated model is, then, validated on a different data set. Statistical comparisons for calibrated and validated model showed no evidence of a great difference between the simulated and observed data. Hence, the model can be used for future runoff predictions in the basin. On the other hand, continuous enhancement efforts are required to improve the model predictive power.
Modeling Variation of Rainfall with Altitude in Usambara Mountains
(2006) Mtalo, Felix W.; Safari, T.

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