Volume:
Volume 8,
2015
Issue:
Issue 2 ,
2015,
September
2-D Modeling of the Impact of Changing Hydraulic Parameters on the Flow Pattern at Rightangled Open Channel Confluences
On Wednesday, 1st of July, 2015. 11:16:44 AM
By Reda M radey
Topic: GIS and modeling applications in river engineering
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AbstractIn fluvial networks, confluences are inevitable and produce significant flow changes. Its presence is
vital for the ecological connectivity, flood co read more
In fluvial networks, confluences are inevitable and produce significant flow changes. Its presence is
vital for the ecological connectivity, flood control, navigation, water quality, etc. Thus, analysis of flow
behavior at the confluence of two natural rivers or two artificial channels is of special importance. Flow
behavior at the channel confluence area depends on various variables. In this paper, Fluent-2D
numerical model was used to simulate and evaluate the effect of three different and most influential
parameters; namely; discharge ratio, width ratio, and downstream Froude number on the flow pattern
and the flow separation zone dimensions at right-angled open channel confluences. To accomplish this,
the model was validated using the experimental data collected by (Weber et al., 2001) on a 90 degrees
channel confluence. The Validation process yielded a fair comparison between simulated and
experimentally determined velocity and water surface profiles. After validation, the open channel
confluence was modeled with various width and discharge ratios as well as with different Froude
numbers. It was observed that increasing the distributed discharge ratio decreased the length and width
of the separation zone. The results also indicated that convergence of the tributary channel reduced
streamwise flow velocity in the main channel and decreased separation zone dimensions. On the other
hand, the model results revealed that increasing the value of Froude number decreased the dimensions
of separation zone. Despite having 3D characteristics in most cases, the results of this research showed
that a much simpler and computationally effective 2D numerical model is also capable of detecting
most important features of flow in confluences, including separation zone and zone of high-velocity.
The results suggested that Fluent-2D can be promising tool for designing the layout of lateral intakes
and outlets or the study of alluvial river bifurcations. less
Estimation of the Climate Variability Impact on Water Resources in the Nyabugogo Swamp in Rwanda
On Wednesday, 1st of July, 2015. 11:16:44 AM
By Omar Munyaneza
Topic: Enviromental aspects of river engineering
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AbstractClimate varies on all time scales, from one year to the next, as well as from one decade, century or millennium
to the next. The complex nature of cl read more
Climate varies on all time scales, from one year to the next, as well as from one decade, century or millennium
to the next. The complex nature of climate variability is a major obstacle to the reliable identification of global
changes brought by the presence and activities of humanity on this planet. The aim of this study was to
investigate the recent trends and variability of annual minimum, maximum and mean temperatures, evaporation,
rainfall and streamflow trend in the Nyabugogo catchment (ca. 1,647 km2) with the goal of estimating the
impact caused by this trend on water resources in the Nyabugogo swamp (220 ha). A data set of daily
maximum, minimum temperature, rainfall and evaporation recorded at Kigali airport station from 1981-2013
were collected from Rwanda Meteorology Office, and the streamflow data (1981-2012) recorded at Cyamutara
gauging station in Gasabo district were collected from Rwanda Natural Resources Authority (RNRA).
Variations and trends of annual mean temperature time series, evaporation, rainfall and streamflow were
examined. The Mann-Kendall test statistic was used to detect trend of climate variables and Pettitt tests was
used to detect the abrupt change points. The Statistical Package for the Social Science (SPSS) was used to find
out whether there is any correlation between them. Results show that annual mean temperature, evaporation and
discharge revealed an increasing trend while rainfall trend is decreasing. The increasing temperature trends
observed are possibly linked to human activities (e.g. deforestation, local urbanization). Pettitt tests revealed the
abrupt change points in all climate parameters except discharge data whose analysis results are not significant
due to a large number of missing data for a long period (around 50%). A strong correlation between temperature
and evaporation was detected but the correlation between rainfall and discharge was found to be weak. This
research provides possible major causes of such trends and correlations between climate variables and hence
highlights their potential impact on water resources in the Nyabugogo swamp. less
Assessment of the Impact of Land Use Change on Nutrients Flow and Establishment of the Level of Key Pollutants of Nyangores River
On Wednesday, 1st of July, 2015. 11:16:44 AM
By francis karanja kigira
Topic: Enviromental aspects of river engineering
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AbstractThis study was carried out with the aim of assessing the effect of Riparian land use/ land cover change on the
hydrology and water quality of the uppe read more
This study was carried out with the aim of assessing the effect of Riparian land use/ land cover change on the
hydrology and water quality of the upper Mara River catchment specifically Nyangores River. The study
incorporated remote sensing and GIS tools to prepare and analyze the data. It involved sampling of sediments
deposits and water flows at various points of the river to quantify water quality parameters such as N, P, Ca and
Fe etc. These parameters were tested in the laboratory.
Land cover change was analyzed from dry season Land Sat MSS, TM and ETM images of 1976, 1980, 1985,
1990, 1995, 2003, 2006, 2010, and 2014 respectively. Digital image analysis for the riparian zone showed that
between 1976 and 2003, crop land increased by about 100%, other vegetation and forests reduced by 32% and
34% respectively with the river line decreasing by 50%. Comparatively high percentages of N, P, Ca and Fe i.e.
0.07meq/100g soil, 0.66meq/100g soil, 12meq/100g soil and 17mg/kg respectively were detected from soils
collected along the cattle tracks and in the water directly below the animal tracks. Grass strips along the rivers
were found to filter sediment and nutrients and soil from the urban set up and tested high for Fe=46 mg/kg, N=
0.03meq/100g soil K=0.21meq/100g soil caused by channelized flow. Soil composition of 89% sand, 3.4% clay
and 7.5% silt which is sandy soil forms the downstream banks of river Nyangores and this is the main cause of
the river banks erosion and subsequent sedimentation. Channelization should be controlled and a lot more of
grass should be planted along the riparian zone also deep rooted trees should be planted at the downstream of
river Nyangores to control river bank Erosion. less
Long-Term Morphological Changes along the 2nd Nile River Reach through Half Century after "HAD" Construction
On Wednesday, 1st of July, 2015. 11:16:44 AM
By Ahmed Fahmy
Topic: River morphology
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AbstractWith the progress of High Aswan Dam "HAD" construction and filling the upstream reservoir, out of an average
annual sediment load of 125 mi read more
With the progress of High Aswan Dam "HAD" construction and filling the upstream reservoir, out of an average
annual sediment load of 125 million tons, only about 26.3 million tons passed downstream of the Old Aswan
Dam "OAD" in year 1968 which was enormously decreased to about 2.0 million tons in year 2000. This led to
conclude that, the average annual suspended sediment downstream "HAD" is enormously decreased from 1600
ppm before "HAD" construction to about 50 ppm. So far, several studies anticipated general degradation along
the four Nile River reaches and sever local scour downstream the main hydraulic structures. Therefore, the
present study aimed to explore the variation of water surface levels with time and location along the second
river reach since the construction of "HAD" till year 2010. The daily records of flow discharges and the
corresponding water surface levels along the second reach from year 1962 to 2010 were utilized to deduce the
matching stage discharge rating curves.
Following a similar study for the first Nile River reach, assessment of the attainable water surface levels for
various periods and locations along the second river reach - at passing 200 million m3 / day – revealed that El-
Mataana and El – Shanhoria gauge stations were the only sites subjected to water surface level decline and
possible degradation after "HAD" construction. The decrease reached its maximum value of 0.225 m and 0.115
m at El-Mataana and El-Shanhoria gauge stations respectively at years 1979 and 1980 then turned over to
increase and possible sedimentation at year 1992 for El-Shanhoria gauge station which reached 0.18 m and
0.355 m in years 2000 and 2010 respectively. On the other hand, the downstream part of the study reach from
El-Sheikheya to Qena gauge stations did not subject to any decrease in water surface levels since "HAD"
construction till year 2010. The monitored increase in water surface levels in year 2010 revealed a maximum
value of 0.675, 0.355, 0.575 and 0.460 m at Luxor, El-Shanhoria, El-Sheikheya and Qena gauge stations
respectively with respect to the condition before "HAD" construction. Moreover, the attained results for the
condition before and after "HAD" construction revealed narrow distinction for the variation in longitudinal
water surface slope which ranges between maximum and minimum values of 5.51 cm/km and 4.98 cm/km
respectively. Therefore, unlike the concluded results for the first reach, the second one was not subjected to
significant or considerable variations in the longitudinal water surface slope after "HAD" construction.
Considering the increase in water surface level is due to general sedimentation of 0.516 m as an average value in
year 2010, a total deposited material of 49.16 million m3 was worked out along the represented river reach. This
led to conclude that the second River Nile reach is being subjected after "HAD" construction to general regular
sedimentation and not degradation as expected from several studies. less
Assessment of Sediment Monitoring of Khashm el Girba Dam
On Wednesday, 1st of July, 2015. 11:16:44 AM
By Amira A. A. Mekawi
Topic: River morphology
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AbstractKhashm el Girba Dam (KED) on Atbara River was completed in 1964 with an initial storage capacity of 1.3
BCM. The main purpose of the dam is to supply read more
Khashm el Girba Dam (KED) on Atbara River was completed in 1964 with an initial storage capacity of 1.3
BCM. The main purpose of the dam is to supply Halfa agricultural scheme with irrigation water. Over the last
five decades, the storage capacity was decreased due to heavy sediment depositions. The present capacity of the
KED reservoir is below 50% of its original capacity.
Khashm el Girba Dam authority used to determine sediment concentrations (SC) at upstream and downstream of
the dam during flood season by adopting the volumetric method. Long time series of sediment concentration
records in (%) are available. However, it is necessary to check the accuracy of such a method and its reliability
to provide accurate estimates of sediment concentrations. Laboratory analysis has been carried out to determine
sediment concentrations of KED sediment samples over the last two years 2013 and 2014. In addition to
volumetric method, two methods were used namely Gravimetric method and by using HACH 2100AN
Turbidimeter device.
The results have shown that volumetric method, which is subjected to reading errors, can represent an indicative
technique to determine sediment concentration in situ especially during flushing period. However, it is of utmost
importance to stick to the ordinary laboratory analysis instead of the volumetric method to establish reliable
sediment database for KED which could be used for accurate determination of reservoir sedimentation and for
other relevant studies. less
The Use of Statistical Performance Measures in Validation of MERIS Case 2: Water Quality Processors in Nasser Lake, Egypt
On Wednesday, 1st of July, 2015. 11:16:44 AM
By mohamed ahmed reda hamed
Topic: Other
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AbstractNasser Lake is considered the main and strategic storage of fresh water in Egypt, so that, the preservation of the
lake and continues monitoring of i read more
Nasser Lake is considered the main and strategic storage of fresh water in Egypt, so that, the preservation of the
lake and continues monitoring of its water quality is considered very important. Satellite-based remote sensing
(RS) has become a useful tool for coastal and inland waters (management/preservation).RS contributes to
estimating water quality parameters especially optical ones including suspended sediment (SS) and Chlorophylla
(Chl-a) for the surface layer. Statistical measures will be used to validate MERIS Case 2 water quality
processors, such as Case2 Regional (C2R), Eutrophic Lake and boreal Lake for Nasser Lake. Adjacency effect
using Improved Contrast between Ocean and Land (ICOL) processor will be applied to images. A comparison
between field and estimated SS and Chl-a will be conducted in case of using ICOL and without it. The results
show that for SS, Eutrophic lake processor without using ICOL can be successfully used during maximum water
level season. Also, C2R and eutrophic lake processor without ICOL can be used to estimate SS values during
falling period (low flow season). While during rising period all tested processors failed to estimate SS. The
statistical performance measure Chl-a indicates that eutrophic lake processor with using ICOL process is
indicate a good results. It is recommend to have more field missions during multiple season(s) to better validate
and/or create a new water quality processor for the case of Nasser Lake. less
Morphodynamic Study of A River to Attenuate Flood Waves, Case Study of Nyabugogo River in Rwanda
On Wednesday, 1st of July, 2015. 11:16:44 AM
By L. Nzabonantuma
Topic: River morphology
Paper |
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AbstractFloods are the most frequent and damaging of all type of natural disasters and annually affect the lives of
millions people all over the globe. The s read more
Floods are the most frequent and damaging of all type of natural disasters and annually affect the lives of
millions people all over the globe. The strategies (fight) against this natural disaster require knowledge mainly
about river morphology, rainfall, land use, etc. The aim of this study is to assess different hydrological
parameters that contribute to the Nyabugogo river flooding and evaluate whether geometric alteration would
allow for a deduction in flood waves. Different approaches were used, firstly the analysis of hydrometeorological
data collected nearby the Nyabugogo catchment in 2011 and ArcGIS approaches to delineate,
calculate the area, slope of the catchment and the length of the river. Thereafter, statistical and hydrological
analyses of the existing and acquired data were done by the use of Unit hydrograph method and computer
program like MS Excel and ArcMap. The Exner principle was applied to analyze the law of mass conservation
for sediment, also named “sediment balance”. Results showed that the total area of Nyabugogo catchment is
1,647 km2 while the length of the Nyabugogo River is 42.69 km. This length allows the river to drain most of
runoff in the catchment. The calculated discharge of the surface runoff due to a 3 hours storm of 13 April 2007
was 33.04 m3/s. The knowledge of probability and frequency of high discharges and rainfall of Nyabugogo
catchment that cause flooding helped to make strategies of flood management. Flooding occurred in Nyabugogo
river and in its surrounding areas during rainy season are caused mainly by meanders at some Nyabugogo river
reaches. These floods are not flash floods because they like to occur every year and for a long event. It is to say,
response to flood hazards that can be undertaken in two ways; engineering approach, to control flooding such as
elimination of meanders by a straight reaches of the river. In addition, regulatory approach like forestation of
side hills where the agriculture is no longer practiced as well as creation of buffer zone along the Nyabugogo
river channel, should be designed to decrease vulnerability to flooding. less
Nile Water Science & Engineering Journal
