Volume:
Volume 3,
2010
Issue:
Issue 1 ,
2010,
March
Assessing the Tail Behaviour of Empirical Distributions Using the Extreme Value Theory
On Friday, 1st of January, 2010. 10:16:44 AM
By Alaa El-Sadek
Topic: Other
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Downloaded: 1
AbstractIn this research, an extreme value analysis methodology was used to recognize the anomalies in tail
behaviour of the flood frequency distribution in read more
In this research, an extreme value analysis methodology was used to recognize the anomalies in tail
behaviour of the flood frequency distribution in an easy and visual way by means of the so-called
Quantile-Quantile plots (Q-Q plots). The type of distribution and the optimal threshold level can be
derived with this method in a most efficient way. The methodology was applied to data from Tanzania
(catchment of Victoria Lake in Tanzania; which includes Mara, Mwanza and Kagera Regions, daily
discharge values from January, 1954 to December, 1986) for testing and first application. Based on the
expertise built up for the Tanzanian data, the extreme value analysis was applied using Kenyan
discharge data. The methodology is especially interesting because of the visual nature and it can be
used afterwards in combination with the traditional Method Of Moments (MOM) and Maximum
Likelihood Method (ML) methods. In that way, the advantages of both methods could be combined and
an efficient extreme value analysis is made. The research results indicated that, to get a precise result
applicable to the hydraulic engineering practice, it is strongly recommended to use daily data (as for
Victoria Lake catchment in Tanzania; which includes Mara, Mwanza and Kagera Regions). This is
because of the peak flow that will determine the flooding. The monthly values (as only available for the
Kenyan stations) are only indirect measures.
The results indicated that, monthly averages should not necessarily follow the extreme value theory as
this theory is only valid for maxima of a large number of variables; monthly averages can be
considered as 'volumes' and these can also follow distributions other than the Generalized Pareto
Distribution (GPD). By analyzing the behavior of the data points in different types of Q-Q plots, the
asymptotic behavior of the tail of the distribution can be determined and discrimination can be made
between Pareto-, exponential and bounded-type distributions. The discrimination is mainly based on an
estimation of the extreme value index as the slope of the linear path in a so-called UH-plot. This slope
is estimated by a weighted linear regression. Finally, it can be concluded that, the optimal threshold
level can be derived easily as the threshold level that minimizes the mean-squared-error of the
regression. less
Development of Rainfall Curves for Crops Planting Dates: A Case Study of Pangani River Basin in Tanzania
On Friday, 1st of January, 2010. 10:16:44 AM
By Preksedis Marco Ndomba
Topic: Other
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Citations: 4 |
AbstractAgriculture is the backbone of Tanzanian economy. The population is sustained by crops, which are
largely produced under rain-fed agriculture. The ty read more
Agriculture is the backbone of Tanzanian economy. The population is sustained by crops, which are
largely produced under rain-fed agriculture. The types of crops to be produced are determined by the
amount of rainfall received in a given location and time. In recent years farmers in Pangani River Basin
(PRB) located in the north eastern part of Tanzania have experienced variable rainfall and significant
droughts. Most of the peasants are not getting enough products from their farms because of the rainfall
variability, which give rise to the change of planting dates. Therefore there’s need to predict the crops
planting dates by developing rainfall curves. The probabilistic and statistical indices used in developing
curves include probability of occurrence, percentiles, and onset and cessation of rainfall. The data used
in this study was daily rainfall amount obtained from Water Resources Engineering Department of the
University of Dar es Salaam (UDSM), Ministry of Water and Irrigation, Ministry of Agriculture and
Food Security and Tanzania Meteorological Agency (TMA). The probability of occurrence of rainfall
for each day in this study was calculated by considering the amount of rainfall which would contribute
to additional soil moisture. Traditional planting dates for validation were collected through field visits
and interviews. The analysis was conducted for areas around 4 representative rainfall gauging stations
in PRB. The study has established the planting dates that will coincide with the onset of rainfall.
Comparison between traditional planting dates and observed planting dates showed that farmers delay
to plant during long rains by two to three weeks. Consequently, such practice has resulted into reduced
rainy days for crops and hence affects the plant growth. The analysis further shows that farmers should
plant between 10th and 17th March for area around Moshi Airport rainfall station (09337004), between
14th and 25th March for Kibosho Mission rainfall station (09337005), between 26th February and
3rdMarch for Mweka station (09337098), and between 8th and 15th March for Kilimanjaro International
Airport, K.I.A, station (09337115). Also for the case of short rains the farmers seems to plant earlier
than the established planting dates. As a result grains wait for a long time before getting the moisture
required for them to germinate. The analysis recommends the following crops planting dates for this
season: for station 09337004 from 7th – 14th November, for station 09337005 from 21st- 31th October,
for station 09337098 from 20th -27th October and for the last station 09337115 from 1st – 8th November.
It is recommended for further studies to consider issues such as climate change, effective rainfall and
rainy days, and soil types and its properties in order to improve the results. less
Role of Hydropower in Offsetting Electricity Consumer Behavior Contribution to GHG Emissions
On Friday, 1st of January, 2010. 10:16:44 AM
By Mohd Elmuntasir Ahmed
Topic: Enviromental aspects of river engineering
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AbstractThe main objective of this study is to illustrate the electricity consumer behavior which accelerates the
greenhouse gas emissions growth by increasi read more
The main objective of this study is to illustrate the electricity consumer behavior which accelerates the
greenhouse gas emissions growth by increasing energy consumption, and to estimate the role of
hydropower in offsetting the GHG emissions as a result of electricity consumer behavior in Sudan. The
study used a questionnaire survey of 500 consumers from 445349 NEC electricity subscribers ( as of
2007). The questionnaire was administered by telephone and face to face interviews among the random
sample of 500 householders with different social categories; the questionnaire was then subjected to
data analysis. The greenhouse gases emission from thermal power generation plants was evaluated
based on different types of fuels and CO2 was selected to represent GHGs. The residential sector was
selected as an indicator since the electrical consumption of this sector represent more than 47% of the
total electricity consumption, further more the consumer behavior of this sector represents, to some
extent, other sectors. It has been extracted from the results that the growth rate of GHG which emitted
from thermal power plant would increase in 2014 by a factor of 4.5 relative to that of 2000. More than
25% of the energy consumption and CO2 emissions contributed by the residential sector are the result
of energy “lost” due to the users' behavior and the use of old technology. The acceptance of the society
to have a role in the reduction of electrical consumption is very low due to their poor awareness of the
consequence of their behavior and the benefit they are going to gain, if they respond positively. Clean
hydropower played a role in reducing these ‘behavioral GHG emissions’ and it was found that
consumer behavior contributed 53 (Gg. CO2) in 2007 while it could have contributed 66 (Gg. CO2) if
there was no hydropower generation in the Sudan. In 2010 and 2014 it is expected that consumer
behavior contribute 105 and 97 (Gg. CO2) if demand is met by hydropower development plus regional
cooperation in power trade, versus 175 and 207 (Gg. CO2) if demand was met via thermal generation
expansion. less
Behavior of Stretched Water Supply Networks
On Friday, 1st of January, 2010. 10:16:44 AM
By STEPHEN NYENDE-BYAKIKA
Topic: River morphology
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Downloaded: 6
AbstractA growing demand for massive water supply systems, as a result of increasing urban populations,
industrialization, and rising water consuming lifesty read more
A growing demand for massive water supply systems, as a result of increasing urban populations,
industrialization, and rising water consuming lifestyles, has put extra stress on the existing water supply
networks. When the systems inevitably expand, other problems set in namely the likelihood of
development of transient flow conditions that range from excessive and deficient pressures, fluctuating
pressures, open-channel flow conditions, and decreasing flows culminating into very low pressures
with very low flow or sometimes no flow at all. Such problems would best be solved through
infrastructural upgrades; however this is an expensive option not easily affordable in many developing
countries that are often faced with this problem, a case of Kampala Water Supply. Many pressurised
water supply systems thus exhibit open channel flow behaviour due to excessive low transient pressure
conditions; while some sections operate as gravity flow (GFS) systems under low reservoir conditions
and pressurise under high reservoir level conditions as force mains with low pressures. This type of
situation is difficult to analyze using conventional approaches and may require special treatment
different from that of fully pressurized systems, with more sophisticated/complex algorithms and
robust scenario management to model. A further complicating factor is that most water supply
modelling softwares assume a demand driven analysis, which is not always the case since in several
real cases, water supply to consumers is less than the consumer asks for. There is therefore a need to
analyse the situation of unstable flows and pressures in order to give very useful insight into the system
state and condition. To this end, numerical simulation has been identified as a modern tool in the
management of piped water supply as it would identify situations of low-pressure-open-channel flow
condition even when in a pressurised network. less
Setup of a Hydrological Instrumentation Network in a Meso-Scale Catchment - the Case of the Migina Catchment, Southern Rwanda
On Friday, 1st of January, 2010. 10:16:44 AM
By Omar Munyaneza
Topic: GIS and Remote Sensing applications in river engineering
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Citations: 8 |
Reads: 263 |
AbstractThe proper implementation of Integrated Water Resources Management (IWRM) plans requires the
collection and analysis of hydrological and meteorologic read more
The proper implementation of Integrated Water Resources Management (IWRM) plans requires the
collection and analysis of hydrological and meteorological time series. This paper introduces the
current situation of existing hydro-meteorological stations in Rwanda and describes a detailed
hydrological and meteorological instrumentation network that was setup in the Migina catchment (214
km2). This compromises 13 rain gauges and three tipping buckets gauges, two evaporation pans, one
weather station, five river gauging stations and eleven shallow piezometers for groundwater
monitoring. Based on the data collected, rating curves for the 5 river gauging stations have been
established. During the period from May to December 2009, the maximum rainfall of 52.5 mm d-1 was
observed in November at Mpare rainfall station (1691 m a.s.l.). The highest peak flow was observed on
19 November 2009 at the outlet of the Migina catchment at Migina River (4.8 m3 s-1), and the lowest
flow was observed on 8 August 2009 at Munyazi-Rwabuye River (0.0002 m3 s-1), which is located at
upstream of the Migina catchment. In future, this catchment will be developed further to the water
resources and environmental management research site of the National University of Rwanda. less
The Use of Remote Sensing and Fractures Analysis for Investigating the Proposed Site for the Sabaloka Hydropower Dam Project, River Nile State, Sudan
On Friday, 1st of January, 2010. 10:16:44 AM
By Abdalla El Sheikh
Topic: GIS and Remote Sensing applications in river engineering
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Citations: 2 |
Reads: 570 |
Downloaded: 1
AbstractThis study was carried out to investigate the selected site for the proposed hydropower dam that located
at the six cataract in the River Nile State, read more
This study was carried out to investigate the selected site for the proposed hydropower dam that located
at the six cataract in the River Nile State, Sudan. The study based on the use of the enhanced landsat
imageries and the structural analysis of the fractures in the investigated site. The River Nile bisects the
Sabaloka volcanic plateau at the proposed dam site. The exposed rocks are Agglomerate, Rhyolite and
Ignimbrite. The proposed dam axis is located in the relatively less fractured Agglomeratic rocks. The
main fractures trends are NW and NE directions and cut, respectively the western and eastern flanks of
the dam axis. The higher values in the fractures frequency and length density contour maps are
considered to be as the most risky areas in the proposed reservoir, through which the water seepage is
highly expected. The existence of the tensional fractures related to the Um Maraheik fault may affect
the efficiency of the dam wall. Engineering mitigation measures are to be considered to increase the
efficiency and stability of the proposed dam. less
Flood Propagation of the Blue Nile in the Sudan Using Muskingum Routing
On Friday, 1st of January, 2010. 10:16:44 AM
By Amira A. A. Mekawi
Topic: Flood Management
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Citations: 1 |
Reads: 31 |
Downloaded: 2
AbstractThis work has dealt with the flood routing of the Blue Nile using the Muskingum method. It is wellrecognized
by hydrologists and water resources engi read more
This work has dealt with the flood routing of the Blue Nile using the Muskingum method. It is wellrecognized
by hydrologists and water resources engineers that river flood routing models have a wide
spectrum of sophistication. The Muskingum method which represents a linear reservoir concept is an
example of the simplest form. The linear form of the Muskingum model has been widely applied to
river flood routing because of its simplicity among the many models used for flood routing in natural
channels and rivers. This study demonstrates the application of the Muskingum method for routing
floods using daily flood data (from year 1965 to 2000) available for three reaches of the Blue Nile from
Eddeim on the Ethiopian/Sudanese border to Khartoum the Sudanese capital. The study illustrates how
to estimate the routing parameters using one day as a routing time interval without considering any of
the limited channel cross sections data. The routing parameters are derived from past observed flow
hydrographs available at the inlet and outlet of the studied reaches. Model simulations were compared
and evaluated by applying a popular statistical measure to determine the degree of goodness of fit
between observed and simulated hydrographs namely: the coefficient of determination. The obtained
results reveal the appropriateness of the method for practical flood routing in the river channel. In terms
of overall performance, the Muskingum method proved to be a simple and reliable method avoiding
complicated mathematical and numerical computations for the case considered. The major advantage
of the routing approach followed in this work is that no information on channel roughness and
geometry are required to estimate the corresponding parameters. less
Study of the Efficiency of Downstream Blanket in Heading-Up Structures
On Friday, 1st of January, 2010. 10:16:44 AM
By N. Aboul Atta
Topic: River morphology
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Downloaded: 6
AbstractIn this research, an electrolytic tank is used to study the effect of using a perforated blanket
downstream the aprons of heading-up structures on th read more
In this research, an electrolytic tank is used to study the effect of using a perforated blanket
downstream the aprons of heading-up structures on the safety against piping through making different
scenarios for length of blanket, intensity of perforations and presence of cutoffs. The study lead to
conclude that when a blanket is added downstream the apron of the heading up structure, it acts as if
the apron is extended, the uplift head increases at the critical section because the blanket blocks
partially the pores of the soil downstream the apron and changes the distribution of the uplift diagram
under the apron, so it is needed to increase the perforation ratio of the blanket in order to dissipate the
increase in the uplift head at the end of apron due to the addition of the blanket. The conclusions also
include determining the optimum length and perforation ratio for the downstream blanket with and
without cutoffs. less
Modelling Versus Analytical Calculation of the Loading Chamber
On Friday, 1st of January, 2010. 10:16:44 AM
By
Topic: GIS and Remote Sensing applications in river engineering
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AbstractThe contributions of small hydropower have grown worldwide substantially in recent years and the
potential for future growth is even stronger. In dev read more
The contributions of small hydropower have grown worldwide substantially in recent years and the
potential for future growth is even stronger. In developing countries, small hydro offers perhaps the
greatest benefits being the fastest way for rural electrification, improving living standards, stimulating
industrial development and enhancing agricultural production. Consequently, the concern of the
designers for a sustainable hydraulic design of the small hydropower plants triggered several
professionals to refine the design process. One of the important components of a small hydropower
layout is the loading chamber. A correct design requires the understanding of the flow behaviour in the
basin but also the settlement of fine particles that may wear parts of the turbine and decrease its
efficiency and lifetime. The selection of the loading chamber dimensions and the divergent angle of
transition zone are important to provide more uniform flow profile and to minimize the separation of
flow along the walls of the transition zone. The divergence angle at the entrance of the flow into the
basin should be established based on the minimization of the head losses condition to limit the effect
due to the sudden expansion of the section at the entrance to the loading chamber. The increased
turbulence and the oscillation of the water level due to sudden reduction or increase of the turbine load
are raising additional design problems. The paper presents the results obtained by using a mathematical
model to study the flow pattern in a loading chamber estimating the process of flow instability in a
confined area. To analyze the flow and the influence of the transient regime due to variation of the
turbine load on the position of the penstocks in the front wall of the loading chamber and consequently
to derive the recommendations for a correct design of the loading chamber, a particular system has
been accepted. A significant output of the modelling can be considered the results showing the
influence of the valves closing time on the hydraulic transient in the basin. For a selected discharge and
gradual closing time of the valves larger than 7minutes, no significant rise in water surface elevation
was observed. Appropriate design recommendations derived from the comparison of the results
obtained by using mathematical models with the results obtained from a simplified analytical approach
and indication from engineering experience, are also presented and discussed. less
