Volume:
Volume 3,
2010
Issue:
Issue 3 ,
2010,
December
Aquifer Storage and Recovery and Surface Basins for a Greener Kilifi District
On Friday, 1st of October, 2010. 11:16:44 AM
By Caroline Onyancha
Topic: Other
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AbstractKilifi District experiences 5-6 months of continuous dry weather and in some instances years of continuous dry periods. When the rains fall, they are read more
Kilifi District experiences 5-6 months of continuous dry weather and in some instances years of continuous dry periods. When the rains fall, they are short and intense causing ground erosion and siltation of surface water sources. Most of rainwater is discharged to the Indian Ocean through the numerous intermittent streams within the area. Currently, majority of the inhabitants of the district depend on food rations and perform no economic activities because of the harsh climatic conditions. The aims of this study were to investigate the suitability of the subsurface materials for storing the rainwater that is lost through run-off, to determine the methods that can deliver the water to the subsurface and to evaluate the expected performance of the storage structures. The process of conveying and storing water in the subsurface during times of abundance, and recovery of the stored water during times when it is needed is commonly referred to Aquifer Storage and Recovery (ASR). When executed well, ASR can recover and maintain groundwater levels thus making it available for domestic use and for agriculture. Several factors that control successful operation of ASR were analysed in a Geographical Information System (GIS) to pinpoint suitable areas. After pinpointing the sites, extensive fieldwork was carried out to compare the results of GIS analyses and the conditions on the ground. The results show that more than 50% of the pinpointed sites are hydrogeologically suitable for recharge. Storage zones comprise of a broad variety of aquifer lithologies at depths ranging from 10 to 100 m. The most notable characteristics of the subsurface are: the presence of salty formations; irregular aquifer system physical properties; sensitive and collapsing fine materials. There is also insufficient information on physical properties of some aquifers, ASR will need to commence in form of pilot projects. Once ASR projects are successful, crop production through irrigation and regeneration of indigenous trees will turn Kilifi District to a green environment. less
River Nile Natural Inflow Changes
On Friday, 1st of October, 2010. 11:16:44 AM
By Sherine Ismail
Topic: River morphology
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AbstractThe River Nile is considered the backbone of Egypt’s water resources. It supplies Egypt with about 95% of its water demands for different purposes ( read more
The River Nile is considered the backbone of Egypt’s water resources. It supplies Egypt with about 95% of its water demands for different purposes (drinking water, irrigation, industry, navigation and power generation). The River Nile is one of the longest rivers in the world. Its length is estimated over 6600 kilometers. The main water supply sources are the Equatorial Lakes, Bahr El-Gazal Watershed and the Ethiopian Plateau. The Nile basin consists of about three million square kilometers in different countries. The Nile Basin characteristics are very unique since it extends in different countries with different climate and the watershed has varied topography, soil nature and flow conditions. The major Nile water supply sources are coming from Ethiopian Plateau through the Blue Nile and Atbara during the period from August to December. Following this period, most of the water supply comes from the White Nile and its tributaries (the Sobat at first, then the Great Lakes Plateau). The flow data for the Blue Nile, Atbara River and White Nile were analyzed during the study period (1900-2009) and statistical tests were applied to monitor changes occurred during the study period. The major observed changes during the study period for the selected stations were highlighted. Moreover, the Lake Nasser arriving water changes were also traced and the correlations of the incoming flow and the major water inflow sources were studied. less
Local Scour as a Result of Spur Dike Implementations
On Friday, 1st of October, 2010. 11:16:44 AM
By karima attia
Topic: Other
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AbstractA2-D hydrodynamic model was developed to investigate the effect of spur dikes on the local scour where Naga Hammadi Barrage was selected as a case stu read more
A2-D hydrodynamic model was developed to investigate the effect of spur dikes on the local scour where Naga Hammadi Barrage was selected as a case study. The model was verified against experimental results of a physical modeling in order to assure its validity. Confident with the verified model, simulations were executed the implementation process. It was intended by these simulations to study the geometry of scour holes presented in terms of depth and length in addition to specific energy at the region of contraction. Eighteen runs (18) were executed where three (3) effective parameters were tested. These parameters are the contraction ratio, which is defined as the spur length to the channel width (L/B), the spur orientation angle; and the spur spacing. The contraction ratio was varied between 0.1 and 0.2 while the used orientation angle were 60 , 90 and 120 (attracting, straight, and repelling spurs) and the spacing were 2, 4, and 7 times the spur length. The study concluded that, the summation of the scour depths is directly proportional to the number of groins which is a function of groin length, spacing, and the required protected length. The scour depth is directly proportional to groin length under constant orientation angle. However, for fixed groin lengths, both scour hole depth and length are directly proportional to the orientation angle. It was also concluded that the continuity of the scour hole length in front of spur dikes installed group is inversely proportional to the spacing between the groins. The groin number 2 in a group of groins consists of 0.1 contraction ratio with 4L spacing acts as a fire wall against flow from diversion channel where the peak bed morphological changes are located. However, attracting groins presents the lowest values. Thus it was recommended to use attracting groins with such specifications in order to protect the bank and reduce the impact on the bed. This should be coupled with a well designed riprap of the second groin that was experimentally tested. As for the impact of groins implementation on specific energy, the tests showed that under constant groin length and orientation angle, the specific energy is inversely proportional to spacing between groins. Also, it is inversely proportional to the groin length, and consequently to scour depth. Both straight and repelling groups showed the same performance from specific energy point of view. On the other hand, a slight increase in values for the attracting group was observed. less
Modeling the Influence of Land Use/Land Cover Changes on Sediment Yield and Hydrology in Thika River Catchment Kenya, Using Swat Model
On Friday, 1st of October, 2010. 11:16:44 AM
By francis karanja kigira
Topic: GIS and modeling applications in river engineering
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AbstractThe Thika River catchment has undergone tremendous changes in land use and land cover in the recent past. These changes are suspected to have impacted read more
The Thika River catchment has undergone tremendous changes in land use and land cover in the recent past. These changes are suspected to have impacted negatively on the hydrology and soil conservation of the catchment. In order to make recommendation for the management of the Catchment, a study was undertaken to assess the impact of the changes in land use and land cover on water and sediment yield on Thika River Catchment, whereby land cover changes from the satellite images of 1987 and 2000 were analysed. Weather and stream flow data for the years 1979-1984 was used to simulate streamflow and sediment yield using Soil and Water Assessment Tool (SWAT) model. Remote sensing and GIS techniques using Idrisi Kilimanjaro software were used in evaluating land use and cover changes. The results revealed that the forest cover in the Thika River catchment decreased by 36%, the area under horticultural crops increased by 32% while the built up area expanded by a whopping 141%. Deforestation is mostly occurring on the highlands forests whereas opening of land for agriculture is in the upper midland and along the river channels. The calibrated SWAT model accurately predicted the streamflow in the Thika River under different land use and land cover scenarios with an R2 of 82%. The scenario studies indicated that increasing forest cover would substantially reduce sediment yield and modulate stream flow. A 100% forest cover would decrease the current sediment yield by 30%, while a decrease in forest cover of 20% would increase sediment yield by 40%. It is therefore recommended that planting of trees and agroforestry should be undertaken to increase the forest cover of the catchment and consequently reduce sediment yield. less
Application of One-Dimensional Hydraulic Model to Irrigation Systems with Complex Inner Boundary Conditions: Case Study on Fayoum Governorate
On Friday, 1st of October, 2010. 11:16:44 AM
By Reda M radey
Topic: GIS and modeling applications in river engineering
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AbstractRealizing the need for improving water resources management in Fayoum Governorate, Egypt, the SOBEK hydrodynamic model was applied to Bahr El-Gharq, B read more
Realizing the need for improving water resources management in Fayoum Governorate, Egypt, the SOBEK hydrodynamic model was applied to Bahr El-Gharq, Bahr El-Bashawat and Bahr El- Gargaba canals using the data measured during the hydrographic survey. In this paper, SOBEK was employed to simulate the flow in three conveyance canals with complex inner boundary conditions. The developed model incorporated different inner boundary conditions, including regulators and weirs. The study aims at evaluating the influence of illegal irrigation practices along the three canals on the system operation through examining different hydraulic scenarios, taken into consideration the futility of present weirs and the use of pumping machines along the streams.
The model was calibrated for a 5 days period and the calibrated parameter (Manning Coefficient) was found to be 0.023. Observed and simulated water levels were in close agreement. The model was operated using a time step of 10 min for a simulation period of 5 days. Five different scenarios were investigated. The model results revealed that the impact of lowering weirs’ crest levels become insignificant when reduced by more than 50 cm. Therefore, it is recommended to lower the weirs’ crest levels of the three canals by 50 cm. This solution will help in lowering the water levels by about 40 cm less than the design water levels, and hence the irrigation water will be allocated to fields via pumps rather than by gravity. Moreover, this solution will help in avoiding the risk of having the water levels in the three canals close to the bank levels. Also, the three canals could easily accommodate the design discharges with the possibility of increasing these discharges in case of future expansions. less
Application of SWAT in Natural Wetland Catchments. A Case of Rugezi Catchment in Rwanda
On Friday, 1st of October, 2010. 11:16:44 AM
By Preksedis Marco Ndomba
Topic: GIS and modeling applications in river engineering
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AbstractHydrologic models are increasingly used to support decisions at various levels and guide water resources policy formulation, management and regulation read more
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, 196 Km2. The study adopted SWAT model as recommended by other 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. less
Reliability of Rainwater Harvesting Systems in Suburbs. A case study of Changanyikeni in Dar es Salaam, Tanzania
On Friday, 1st of October, 2010. 11:16:44 AM
By Preksedis Marco Ndomba
Topic: Other
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AbstractThe objective of this paper is to report on reliability problems and modelling of Rainwater Harvesting Systems (RHSs) for suburbs households. Although read more
The objective of this paper is to report on reliability problems and modelling of Rainwater Harvesting Systems (RHSs) for suburbs households. Although RHSs are believed to be alternative source of water supply, little has been done by other researchers in analyzing the same in the Nilotic countries. The case study is the area comprising the suburbs of Changanyikeni in Dar es Salaam, Tanzania. In this study, two parameters of reliability analyses i.e. Reliability index and Demand Satisfaction level were determined. Besides, they were modelled based on climatic, field measured physical and household social status data by probabilistic approach using Direct Integration Method for representative house. The climatic data used for the analyses are monthly rainfall data spanning for fifteen (15) years (i.e. 1988 to 2002) collected from the University of Dar es Salaam meteorological station, the nearby station to the case study. Physical and social status data were obtained after carrying out multistage random sampling starting with the sampling of the suburb and then representative households in the selected suburb. The physical data inputs include storage tank sizes and roof areas. Social status data includes household size and water demand pattern. This study showed that about 60% of the RHSs in the study area are not reliable having reliability index less than 70% and has been attributed to poor design, for instances provision of the systems without considering the stochastic nature of rainfall. Thirty percent (30%) of all unreliable RHSs had been designed deterministically. The modelling outputs is presented in a graphical formats so that one given data on household size, per capita water demand and roof area would obtain the reliable size of the water storage tank. The research findings presented in this paper could be applied in areas with similar socio-economic status and climatic condition. less
Sediment Accumulation in Roseires Reservoir
On Friday, 1st of October, 2010. 11:16:44 AM
By K.E. Bashar
Topic: Other
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AbstractSedimentation is a serious problem that faces natural and manmade reservoirs. It is the major problem which endangers and threatens the performance an read more
Sedimentation is a serious problem that faces natural and manmade reservoirs. It is the major problem which endangers and threatens the performance and sustainability of reservoirs. It reduces the effective flood control volume, presents hazards to navigation, changes water stage and groundwater conditions, affects operation of low-level outlet gates and valves and reduces stability, water quality, and recreational benefits.
Reservoirs are often threatened, by loss of capacity due to sedimentation. While causes of reservoir sedimentation are many; watershed, sediment and river characteristics are among the main natural contributing factors. Other important ones are reservoir size, shape and reservoir operation strategy. Manmade activities play also a significant role particularly in land use pattern.
This paper is an attempt to assess the sediment accumulated as well as the rate of sedimentation in the Roseires reservoir. The basis for the study is the previous bathymetric surveys carried out on the reservoir in the years 1976, 1981, 1985, 1992, 2005 and 2007.
Analysis and comparative studies were carried out between the different surveys to quantify the amount of sediment deposited as well as the rate at which sedimentation took place. The design storage capacity of 1967 for the different reservoir levels was taken as base line. The sediment accumulation rates for the different bathymetric surveys are obtained as the difference between base line capacity and the computed capacity at the respective levels during the specific survey.
It was found that sedimentation in Roseires reservoir resulted in the reduction of the reservoir capacity from design storage of 3.0 milliard m3 in 1966 to 1.9 milliard m3 in 2007 i.e. a loss of about 1.1 milliard m3 in 41 years of operation. The sedimentation rate varies both with time and levels in the reservoir. less
Impact of Arid Climatic Conditions on Engineered Wetland Design and Performance: Egypt Case Study
On Friday, 1st of October, 2010. 11:16:44 AM
By Ghada El-Refaie
Topic: Enviromental aspects of river engineering
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AbstractEgypt's water resources are becoming increasingly polluted due to the excessive use of these limited resources. The pollution of the Nile River S read more
Egypt's water resources are becoming increasingly polluted due to the excessive use of these limited resources. The pollution of the Nile River System (main stream Nile, drains, and canals) has increased in the past few decades and caused serious deteriorations of the irrigation and drainage water quality, especially in the Nile Delta. Engineered wetland wastewater treatment technology is gaining wide recognition in Egypt as a prominent and efficient low-cost treatment technology. There are several plans to replicate this new technology in the field of wastewater treatment on the national level. This research aims at investigating and exploring different design and performance aspects of the engineered wetland wastewater treatment. PREWet model is used to simulate the performance of Lake Manzala Engineered Wetland (LMEW) and to carry out a sensitivity analysis (SA) of the critical design factors. The results of this research provide the decision maker with the optimum range of the design factors, which contribute to an efficient wastewater treatment considering the local climatic conditions.
PREWet Model has been calibrated and validated on LMEW for assessing the removal efficiency of four parameters; Total Coliform (TC), Total Nitrogen (TN), Total Suspended Solids (TSS), and Biological Oxygen Demand (BOD). Three design factors have been considered, wetland surface area, average flow discharge and detention time taking into consideration temperature variation between the summer and winter seasons.
Wastewater treatment using the engineered wetland in the Nile Delta is a promising treatment technology, which fits the Egyptian economic and climatic context. This research shows that decreasing the wetland surface area and increasing the average flow rate did not affect its removal efficiency for almost all pollutants. This supports the conclusion that replication of this innovative technology on small scale would achieve a comparable performance to the large scale wetlands such as LMEW. The study also, showed that the effect of temperature variation was pronounced in the increase of the removal efficiency in the summer season, relative to the winter season, for all studied parameters. less
Bed Form Types and Dimensions at El Ekhsas Gauge Station From Field Measurements
On Friday, 1st of October, 2010. 11:16:44 AM
By Mohamed Ali
Topic: Other
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AbstractThe study of bed form formation in river beds is a complex process. The formation process results from the interaction between the sediment and flow c read more
The study of bed form formation in river beds is a complex process. The formation process results from the interaction between the sediment and flow characteristics. The bed forms are responsible for increasing bed roughness. In sediment transport, depending on the condition of the bed form, the fraction of the total shear stress that is responsible for bed load transport changes. Therefore, knowledge of bed form characteristics and geometries are very essential in alluvial system integrated management. In natural rivers, the bed form types and dimensions differ along the river cross section as the depth variation results in different hydraulic characteristics. This research represents the analysis of detailed field measurements at El Ekhsas gauge station in two different dates. Bed form types and dimensions were extracted, analyzed, and compared with the dimensions calculated from the most common bed form predictors. Also, the measured bed form dimensions were compared with the corresponding dimensions resulted from formulas developed for Nile River. It was concluded that some bed form predictors are valid and reliable for Nile River. Also the current research developed new relationships which help in predicting bed form dimensions in the Nile. The study recommends that the other gauge stations should be applied for such research to validate the developed relations. less
Nile Water Science & Engineering Journal
