|
|
 Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي (Re: Asskouri)
|
52
Applying this formula, a residence time of 54 days (own calculation, see the Sedimentation subchapter), provided temperature difference between surface and hypolimnion in Merowe Reservoir of about 10 °C. This is in good agreement with the temperature difference of 6 and 10 °C measured in the AHD between surface and 30 m depth (Latif, 1984).
Consequently, during the summer period starting in April or May, the water column in the Merowe Reservoir will become stratified. The stratification can extend over the entire reservoir length. During the flood period from August to October, the thermal stratification may be destroyed, especially on the upper stretch of the reservoir. The extent of the vertical convective mixing and the level of the remaining thermal stratification will depend upon the water level in the reservoir and the flood regime. With a total length of 200 km, it may be possible that a large part of the reservoir volume will be subject to totally mixing during the flood period although some stratification on the lower stretch will probably remain. Similar to the AHD, the overturn due to cooling during the winter periods will result in convective mixing between deep waters and the surface, allowing oxygenated waters to penetrate into the deeper waters of the reservoir.
4.6 Sediment balance
Located about 700 km upstream of Lake Nubia, where no additional water input contribute to the total flow of the Nile River, it can be assumed that the sediment load entering the Merowe Reservoir will be the same or slightly higher than at AHD: 1.7 g l-1 or 143 x 106 t yr-1 at a flow rate of 84 km3 yr-1.
Heavily loaded with sediments, the deposition of the particles in the reservoir depends upon several factors. The retention time and the depth are the most important ones. Retention time within the Merowe Reservoir was postulated by the EIAR (2002) to be as high as 0.2 yr, equivalent of 73 days. A reservoir volume of 12.4 km3 and an annual flow of 84 km3 yr-1 allowed as calculating a lower residence time of 0.15 yr (54 days). It seems
53
that EIAR (2002) use in their calculations the same average flow of 65 km3 yr-1 of Failer (2004). For a maximum length of 200 km and a residence time of 0.15 yr, the average water velocity in the reservoir will correspond to 4.3 cm s-1.
Water velocities of between 2.7 km h-1 (75 cm s-1) to 3.3 km h-1 (92 cm s-1) could be calculated for the present natural river flow condition using the EIAR (2002) travel time from Khartoum to the dam site of 10-20 days (Page 3-5) and a distance 800 km (Page 4-7). Therefore, a slowdown of the water velocity in the range of one order of magnitude is expected to occur after the river impoundment. Sediment deposition dominates typically at low velocities below 10 cm s-1 (Hakanson and Jansson, 1983).
A residence time of 4.5 days and a main stream velocity of 33 cm s-1 resulted in the case of Iron Gate I Reservoir (Danube River) in a TSS retention of 56 % of the incoming load (Teodoru and Wehrli, 2005). For a residence time of 2.7 yr which correspond to a water velocity of 0.016 cm s-1, the TSS retention in Lake Brienz (Switzerland) was found to be as high as 97 % of incoming load (Finger et al., submitted). Water velocity between 0.06 to 0.89 cm s-1 during November and 0.01 to 0.55 cm s-1 in December were measured in AHD (Eldardir, 1994). With a residence time of 1.9 yr and a reservoir length of 500 km, an average flow velocity of 0.62 cm s-1 for the AHD corresponds to sediment retention of between 96 and 98 %. As the average velocity in the Merowe Reservoir seems to be higher compared to the AHD, one might expect that the sediment retention to be lower. A simplified linear correlation between the above mentioned cases of Iron Gate I, AHD and Brienz implies that the sediment retention capacity of the Merowe Reservoir will be up to 92 % of the incoming load (Figure 11). Therefore, with a retention capacity of more that 90 % of the incoming load, a suspended solids accumulation of about 130x106 t yr-1 is expected in the Merowe Reservoir. For a surface area of 800 km2, this corresponds to an average sediment flux of 164 kg m-2 yr-1. Using the bulk same density of 1.56 g cm-3 calculated by Shalash (1982) for AHD Reservoir, the volume of the sediment expected to accumulate annually in the Merowe Reservoir is 84x106 m3 yr-1, equivalent to an average sedimentation rate of 10.5 cm yr-1.
54
Studies on the AHD Reservoir have shown that the major part of the sediment is deposited close to the reservoir inflow (southern part) where a New Delta of about 200 km in length, 12 km in width and 40 m thickness was formed in less than 30 years (Eldardir, 1994).
Therefore, as the main volume of the sediment will be deposited in the upper stretch of reservoir, the “special sluices” of the Merowe Dam will not play any important role in decreasing reservoir sedimentation. It is expected that this situation will extend at least over the half lifetime period of the reservoir when half of the dead storage capacity and part of its active capacity has been already lost.
However, our calculation implies that with a deposition rate of 84x106 m3 yr-1, the Merowe Reservoir will lose its total volume of 12.4 km3 in about 150 yr at an annual rate of 0.7 % yr-1, whereas the dead storage capacity of 4.1 km3 will be lost in less than 50 yr at an annual rate of 2 % yr-1. Therefore, over a 50 years period, the total storage capacity could be diminished with 34 %.
Figure 11. Estimated sediment retention (% of the incoming load) function of water velocity
55
Although it seems rather difficult at this stage to predict the extent of downstream erosion, it is clear that with less than 10 % of the total incoming sediment load passing through the Merowe Dam, downstream sedimentation will be proportionally diminished. Therefore, the erosion rates of the river bed and the banks are expected to increase dramatically. Scouring of the river channel downstream may result in lowering the river level with possible influences on the adjacent aquifers water table. Since no natural flooding will occur below the dam, traditional flood recession agriculture along the river course will not be possible any longer. These potentially severe consequences are not adequately discussed in the EIAR (2002). As a positive effect of high sediment accumulation in the Merowe Reservoir, the lifetime of the downstream AHD Reservoir will be prolonged. However, retaining almost the entire sediment load of the Nile River, both reservoirs will substantially accelerate the general erosion of the Nile Delta and the coastal Mediterranean Sea.
4.7 Biogeochemical cycles
4.7.1 Primary production
The thermal stratification with higher suspended particle sedimentation and higher temperature in the epilimnion is expected to increase reservoir production. Extremely high rates of a few 1’000 g C m-2 yr-1 were measured in some specific side bays of the AHD. As such extremely high rates can not be representative for the entire AHD Reservoir, we considered an weighted average of 370 g C m-2 yr-1 to represent a more realistic estimate based on the observed phosphorus content and calculated input.
Using the average primary production calculated for the AHD of 370 g C m-2 yr-1 and applying to the Merowe area of between 350 and 800 km2 at the minimum and maximum capacity, respectively, the organic carbon in-situ produced within the reservoir may varies between 130’000 and 300’000 t C yr-1. Note that this value represents a lower
56
estimate as the primary production reported for the AHD was one order of magnitude higher.
4.7.2 Greenhouse gas emissions
Generally, starting with the impounding phase which result in flooding of the landscapes, terrestrial plants die and not longer assimilate carbon dioxide (CO2) by photosynthesis and therefore the sink for atmospheric CO2 is highly reduced. In the same time, increased reservoir productivity is responsible for in-situ production of large amount of organic carbon. Therefore, additionally to the current existent biomass described by the EIAR (2002), a large fraction of organic carbon will be annually produced in-situ. Moreover, a larger fraction of particulate organic carbon may be transported from upstream areas and accumulated in the sediment of the reservoir, and therefore, contributing to the total greenhouse gas emission.
The organic carbon stored in plants, algae and soil is converted by bacterial decomposition within the water column or sediment to: (i) CO2 under oxic conditions or (ii) methane and CO2 in the absence of oxygen, and then released to the atmosphere. The methane can be exported by ebullition or by diffusion. Ebullition results in direct flux of methane bubbles from the sediment to the atmosphere with limited impact of CH4 oxidation in the water column. The ebullition flux is related to the net CH4 production rate in the sediment and the hydrostatic pressure changes, usually due to water level fluctuations. As the diffusive transport is much slower than ebullition, a large proportion of the diffusive CH4 flux exported from anoxic sediment will be reoxidized by methane-oxidizing bacteria into CO2 which has a lower global warming potential.
In the case of stratified water column as in the chase of Merowe, CH4 will be stored in the anoxic layer. The storage will be emitted rapidly by diffusion during the winter deep mixing periods. The diffusive flux component will depend on the difference in methane concentration between the water and the atmosphere, and on the physical rate of exchange between the water and the air (turbulence, wind speed). The flux of CO2 and
57
CH4 released from the reservoirs surface are quite variable as they depend on a number of factors including the lake area, amount of organic carbon flooded, age of the reservoir, water temperature, primary production, water column stratification, the frequency and the extent of reservoir drawdown, lake sediment conditions, etc.
To calculate the potential greenhouse gas emission from the Merowe Reservoir, we follow the same scenario as for the AHD. Out of the total in-situ carbon production of 130’000 and 300’000 t C yr-1, we assume that (i) 20 % (26’000 – 60’000 t C yr-1) is accumulated at the lake sediment; (ii) 20 % (26’000 – 60’000 t C yr-1) undergoes bacterial decomposed within the water column and release mainly as CO2. Further, it can be assumed that half of the total carbon accumulation will be buried in the sediment of the reservoir whereas the other half (13’000 – 30’000 t C yr-1) will be converted into greenhouse gas. As the percentage CO2 to CH4 produced during decomposition of organic matter depends upon many unknown parameters (the oxidation rates, the time and the extent of oxygen-free condition in the water column and below the sediment water interface or the diffusive fluxes from the sediment), we limit our evaluation to the total organic carbon available for CO2 and CH4 production. Therefore, according to this scenario, annually between 13’000 – 30’000 t C yr-1 will be potentially available for greenhouse gas production in the sediment of the reservoir, whereas decomposition of the organic matter in the water column can contribute with between 26’000 and 60’000 t C yr-1. The available carbon is actually expected to be much higher considering that a large fraction may comes with the river inflow and will be accumulated in the sediment of the reservoir or decomposed within the water column.
Eldardir (1994) measured for AHD a sedimentary organic matter content of between 8 to 40 mg g-1, with lower values characterizing the upper stretch of the reservoir where the New Nile delta is presently forming. Considering 8 mg OM g-1 measured in the upper stretch of the AHD to represent the organic matter content of the suspended load, the retention of 130x106 t TSS yr-1 in the Merowe Reservoir will result in annual accumulation of more than 1’000’000 t OM yr-1. As the OM consists of 40 % C, the accumulation of equivalent 400’000 t C yr-1 is therefore expected. Further, assuming that
58
50 % of the total amount will be buried in the sediment whereas the rest of 50 % will be a subject of microbial degradation, the incoming load is anticipated to contribute annually with up to 200’000 t C yr-1 to the total degradable carbon.
Therefore, using this balance approach we were able to predict that annually, between 240’000 and 290’000 t C yr-1 will be available for greenhouse gas production. Note that, this annual value is one order of magnitude higher than the total reservoir degradable biomass of 34’000 t reported by EIAR (2002).
4.7.3 Phosphorus balance
As phosphorus was ascribed to limit the primary production in the AHD, a simplistic mass balance approach was used to predict the changes in dissolved phosphorus concentration within the reservoir (Figure 12). The reservoir can be described with a box-model approach where the input is compensated by the net sedimentary retention and the output.
Considering an inflow concentration of around 77 μg P l-1 as estimated for the AHD, the input flux (Finput) into Merowe Reservoir would represent 6.5x109 g P yr-1. For a maximum reservoir area of 800 km2, an average primary production rate of 370 g C m-2 yr-1 will be responsible for a phosphorus uptake up to 7.3x109 g P yr-1. We can consider that 20 % of this as 1.5x109 g P yr-1 settles to the reservoir floor where half is buried in the sediment and the other half released back into the water column. Therefore, the net sedimentary P retention represents 0.75x109 g P yr-1. Using the net P retention of 6 % of the total phosphorus uptake as calculated for the AHD, the sedimentary retention in the case of Merowe would represent about 0.4x109 g P yr-1, a value comparable with the previous estimate.
Approximated by the equation below, with an inflow load of 6.5x109 g P yr-1 and a net P retention of between 0.4 and 0.7 x109 g P yr-1, the output flux would range between 5.7 and 6x109 g P yr-1.
59
Pinput – Pnet_retention– Poutput = 0
Figure 12. Dissolved phosphorus mass balance for the Merowe Reservoir
Compared to the input of 6.5x109 g P yr-1, the output will be between 4 and 8 % smaller. The average output concentration for an annual discharge of 84 km3 yr-1 corresponds to about 70 mg P l-1.
Therefore, the internal processes within the reservoir are expected to play a relative minor role in the overall nutrient budget. The nutrient concentration in the Merowe Reservoir will be highly dependent on the input and to a lesser extent on primary production or sedimentation.
4.7.4 Increased salt content
Even not addressed in the EIAR (2002), increased salt content within the reservoir is expected due to evaporation and irrigation. Following a simple assumption of linear dependency between the evaporation rate and the increased water salinity, an annual loss of almost 15 % (1.7 km3 yr-1) of the reservoir volume by evaporation is expected to increase the reservoir salt content by 15 %.
Moreover, during irrigation, the water become enriched in nutrient and dissolved solids. Up to 9 % (7.4 km3 yr-1) of the river inflow is expected to be annually used for
60
agriculture purpose. As part of this volume will eventually return to the reservoir or to the river downstream, an increased nutrient and salt content is therefore expected.
4.8 Aquatic ecology
In general, reservoirs are complex and dynamic ecosystems, characterized by reduced diversity (less species than natural ecosystems) but on a higher productivity level. Presently, the fish population of the Nile River at the Merowe section is mainly dominated by the riverine (lotic) species, well adapted to seasonal changes of flowing water and to a lesser extent by lake (lentic) species. Any alterations of their natural habitats resulting form hydrological changes of the river system is therefore expected to influence the biological productivity, affecting the entire food web on the long term. Consequently, the transformation of a relatively large area of the river stretch into a reservoir is anticipated to result in a gradual disappearance of specific riverine species, whereas the lacustrine or easily adaptable ones may benefit from the Merowe Reservoir construction.
Riverine fish species that usually inhabit shallow water and benthic ecosystems will seek similar depths and habitats in the new reservoir. Species that cannot find suitable habitat will not adapt to the new conditions and will disappear from the reservoir area. Accordingly, a number of river species are expected to disappear gradually as a result of inappropriate conditions for their life cycle.
The migratory species might be impacted by the dam which will hinder their movements (landlocked). The migration should be altered as early as the initial stages of construction. It is expected that a landlocked population will establish in the reservoir and migrate towards the upstream reaches or tributaries for spawning. More critical problems will appear for the migratory fish populations below the dam as they will be trapped in about 700 km of river stretch between AHD and Merowe. No ladder construction was recommended by the EIAR (2002) based on the “evidence” of no migratory fish and
61
technical details (“the ladder would be far too high and too long for fish to be able to pass”).
Changes in water level will affect structural and functional aspects of the aquatic ecosystems in the reservoir. Important changes in water level can have both positive and negative consequences for fish populations. If the water level will be raised during the spawning season, fish spawning and recruitment may increase. Negative impacts may result primarily from the drawdown zone: fishes could be stranded during spawning, and habitats or spawning areas will be destroyed. Also, weed beds and food sources will be altered and deep waters will be depleted in oxygen.
Downstream changes in flow regime, temperature, water chemistry and turbidity will have an adverse effect on the majority of fish species. As bottom release, the temperature of the outflow water will be lower in summer than it would be for natural conditions. Therefore, coldwater pollution together with low dissolved oxygen concentration in the discharged water during the summer can have major impacts on the downstream fish population. However, if the oxygen content in the water downstream would tend towards natural values during re-oxygenation, the water temperature is expected to need a longer distance before reaching the equilibrium values. If the impacts generated by the reduction of oxygen will be limited to relatively short distance, the temperature changes can induce higher impacts, especially in the summer period.
The daily water release in normal operation will fluctuate depending on the power demand. However, a daily water level fluctuation in the downstream river up to 5 m is expected. Even this may not affect the lotic species that are generally better adapted to large variations both in temperature and in river flow, impact on the lentic fishes may be significant as they use to live in systems where the amplitude changes at much lower frequency.
Daily operation of the powerplant together with high sediment retention in the reservoir will result in increased downstream erosion. Fish species that spawn on sand bars will see
62
their spawning area reduced or dried up, especially on weekends when the flow provided at the powerhouse will be minimal. This can also lead to the elimination of backwaters that provide aquatic habitat for native species and the reduction of riparian or wetland vegetation. Therefore, conditioned by the daily and weekly flow variability, reduced downstream spawning areas will have negative impacts on both lotic and lentic fish population. Nutrient retention in the reservoir may also lead to a decrease of downstream aquatic productivity resulting with subsequent lower fishing yield.
Flood events act as biological triggers for reproduction in some fish species of cyprinids and characins. As the reservoir will alter the natural distribution and timing of downstream flow regimes, this will alter the spawning of those fish species.
During operation of the powerplant, some fish will transit through the turbines being wounded or killed. Depending on the number of fishes that will eventually move through the turbines, this phenomenon is generally expected to have little influence on the overall fish population of the reservoir.
It seems that new reservoirs construction always creates hope among local people in terms of commercial fishing, so productivity becomes an important issue.
In general, stratified water column with high nutrient availability and reduced turbidity favor an increase of the productivity of the reservoir, especially right after impounding. The production of plankton in the early stages of the reservoir impounding is the basis for the reservoir productivity. Even the changes from riverine to lake environment will result in decrease of river specific fish species in favor to lake species, high food availability may support an overall increase in total fish biomass. The initial period of increased biomass is generally expected to be followed by stabilization in fish productivity, as the environmental conditions of the lake are expected to reach a steady-state. This can be related to the carrying capacity of the reservoir. An increase in population of predator species or an increase in fishery activities are generally used to predict a decline in fish yields in the next years. Therefore, the new environmental conditions resulting form the
63
Merowe Dam construction can be favorable for commercial fishing in designated areas of the reservoir.
The similarity of the Merowe Reservoir with the AHD allow as to predict that after few years, the composition of fish species in the future reservoir will be probably be comparable to the actual composition of the AHD Reservoir. Therefore, the important species in the Merowe Reservoir for commercial fishing are expected to be represented by: (1) cichlidae dominated by Tilapia nilotica and Tilapia galilaea; (2) cyprinids with Labeo nilotica, L. horie and Barbus bunni; (3) catfish Bagrus spp. and the large species Clarius lazera; (4) characins with Alestes baremose, Alestes dentex and Hydrocynus spp., (5) centropomids with Lates niloticus; (6) synodontids and (7) schilbeids.
Traditional fishing methods practiced and observed on the Nile will be ineffective during the reservoir impounding and operation. Commercial fishing however may be initiated in the reservoir only after the fish populations have increased to a certain level. The period before the commercial fishing can be initiated may be a few years after impounding.
4.9 Health-related impacts
Although it is not necessary expected to trigger dramatically health problems, the arid conditions of the reservoir site and the characteristics of the reservoir area with large seasonal water level fluctuations seems to justify a cautious approach.
Serious consequences which accompany changes in the aquatic environment related to dam construction is the explosive spread of water-borne human disease. In several parts of Africa, the creation of vast areas of standing waters by dam construction favored the increase of the population of the vector snail host of schistosomiasis.
Stagnant waters will create perfect breeding condition for mosquitoes, vectors of malaria and yellow fever and the water flea host of the guinea-worm. As malaria was endemic in
64
Sudan in 1942 resulting in about 100’000 deaths (George 1972), precautionary measures for local transmitting malaria may be justified.
Thus, the reservoir could increase the existing risks especially at high water levels favoring water column stratification with deep-water oxygen depletion and CH4 and H2S accumulation in the hypolimnion and the release during the turnovers periods of late fall and winter. In the upstream area of the reservoir, the accumulation of large amounts of sediment may result over decades, as in the case of AHD, in development of submerged islands. Seasonally, during the low water level they may become wetlands or pounds, offering ideal conditions for insects and mainly mosquitoes to reproduce. This may also favor an increase in anopheles transmitting malaria.
The presence of stagnant water around the construction site due to excavation, ditches or other activities may induce good breeding conditions for anopheles in the immediate area and generate malaria among the construction personal or local population if not managed properly.
65
5. Summary of the environmental impacts
5.1 Hydrology and water balance
The Merowe Dam is the biggest hydropower project in Sudan and second major component of the water development scheme on the lower Nile River after Aswan High Dam. Scheduled to be completed in summer 2008, the goal of the project is to provide economic development through electricity generation and irrigated agriculture. With an installed capacity of 1’250 MW, the Merowe Dam will produce twice the current amount of electricity in Sudan. Little is known about the irrigation scheme
At the time of completion, Merowe Dam will create a reservoir “lake” with a surface area of 800 km2, a maximum depth of 57 m, storing a volume of 12.4 km3. The location of the reservoir in a geological inter-plate region with a complex tectonic situation, the existence of active historical faults, and the additional stress on the water volume or the increase in pore water pressure along faults can induce seismic activity at the Merowe within the first few years after the reservoir has reached its maximum level. However, it is believed that the magnitude of the possible reservoir-induced earthquake at Merowe will not exceed the Maximum Credible Earthquake design of 6 on the Richter scale. Even unlikely to become a seismic hazard, an assessment of the potential consequences of dam failure due to seismic activity or other kind of accidents on downstream population appears nevertheless advisable.
By storing the annual runoff of the Nile, the construction of the Merowe Dam will significantly affect the present natural hydrology of the about 900 km of the river stretch between AHD Reservoir and Merowe Dam, eliminating the annual flooding which flushed and cleanse the river once a year. However, the downstream hydrology of the Nile River below the Egyptian border to the Mediterranean coast was already affected by the earlier AHD construction of 1971.
66
Storing the high summer flood flow and releasing over the rest of the year, the operation of the Merowe Dam will create large seasonal and annual water level fluctuations in the reservoir between 6 to 10 m (EIAR 2002, page 3-6). Water level fluctuations may expose extensive areas of the reservoir slops to soil-forming conditions degrading previous formed lacustrian organic matter. Consequently, the operation schedule will have direct influences on the texture and composition of the reservoir sediment with direct influence on the submerged plant community and abundance on the disturbed littoral zone. Overall, this may have a substantial environmental impact on the aquatic life.
Large downstream daily water level fluctuations of between 4 to 5 m, will expose large spawning areas along the river stretch to impropriate habitat conditions with direct consequences on the downstream fishes and fishery. Wide-ranging daily fluctuations of the water level may have also socio-economic implications representing an issue for ferry the landing sites and pumps along the river. Additionally, a general lower downstream water level together with seasonal or daily fluctuations will produce high river banks erosion, induce scouring of the river bed lowering the river level and possibly lowering the water table of the adjacent aquifers.
The evaporation from the reservoir will result in a total water loss of 1.75 km3 yr-1. Slightly less than 1.9 km3 yr-1 calculated by the EIAR (2002), the annual losses by evaporation will represent 2 % of the annual Nile River inflow of 84 km3 yr-1.
The water use for irrigation scheme proposed by the EIAR (2002) represents a total of 7.4 km3 yr-1. Therefore, the water abstraction for agricultural use would reach a value of 9 % of the annual river inflow.
The annual precipitation in the area characterized by an average of 50 mm yr-1 would represent an additional input of 0.04 km3 yr-1. Representing only 2 % of the total evaporation, the contribution of precipitation to the total water balance can be considered negligible. The lateral seepage from the reservoir may contribute annual with 0.07 km3 yr-1, a value twice as high as the annual precipitation but rather negligible.
67
According to our calculations, the total water losses from the Merove Reservoir including evaporation, irrigation and seepage corresponds to 9.2 km3. This represents 11 % of the annual Nile River inflow.
The daily dam operating rules will correspond to an annual total turbinated volume of or 31.5 km3 yr-1. According to the Nile Water Agreement of 1959, Sudan has the right to use 18.5 km3 yr-1 from an average flow of 84 km3 yr-1, and must annually ensure a minimum release of 55.5 km3 yr-1 downstream to Egypt. Therefore, during the dam operation, additionally to the turbinated flow of 31.5 km3 yr-1, a supplementary minimum flow of 24 km3 yr-1 must be provided.
During the impounding period when no electric power is generated and therefore, no water is released through turbines, ensuring a minimum release downstream of 55.5 km3 yr-1, and neglecting the evaporation and irrigation needs, the reservoir can gain annually 28.5 km3. With an annual inflow of 84 km3 yr-1, the average time required to fill up the reservoir volume can be calculate as 159 days (5 months). This period can be shorter or longer, depending on the starting time. The extent of the impounding period can be predicted running a simulation model for different starting dates. In the absence of sufficient hydrological data we could not run such a simulation but knowing that 80 % of the total discharge occurs during the rainy season, the optimum period for reservoir impounding seems to be between July and October when the reservoir can fill up to 95 % of its total storage capacity.
According to our water balance calculation, even at full energy production and securing a minimum downstream flow of 55.5 km3 yr-1, the reservoir can store annually up to 19 km3, representing more that 150 % of its capacity. This imply that the reservoir can operate at the maximum capacity even for a lower water inflow down to 65 km3 yr-1, supporting additional water storage upstream Merowe, increased irrigation scheme or drought periods.
68
5.2 Sedimentary aspects
One of the major issues of the Merowe Dam Project is related to a large volume of sediment expected to be annually trapped behind the future dam which will result in limited lifetime of the project to only 150 yr. Subsequent impacts are the increased lifetime of the AHD, downstream erosion along the Nile lower course and a general transgression of Nile Delta associated with local subduction favoring salt water intrusion and loss of large fertile agricultural areas.
An average suspended solids concentration of 1.7 g l-1 and an annual water flow of 84 km3 yr-1 imply an incoming suspended solids load of 143x106 t yr-1. Based on one order of magnitude drop in water velocity due to river impounding at Merowe, we predict a sediment retention capacity in the reservoir as high as 92 % of the suspended solid incoming load. Therefore, up to 130x106 t yr-1 will be annually deposited in the reservoir, corresponding to an average sediment flux of 164 kg m-2 yr-1. Using a sediment density of ~ 1.56 g cm-3, the annual volume of the sediment expected to be accumulated in the reservoir corresponds to 84x106 m3 yr-1, equivalent to an average sedimentation rate of 10.5 cm yr-1.
At this deposition rate, Merowe Reservoir will loss its dead storage capacity of 4.1 km3 in less than 50 yr, whereas the total storage capacity of 12.4 km3 will be lost in about 150 yr.
The main volume of the sediment is expected to accumulate in the upper stretch of reservoir, where, as in the case of AHD, a new delta is likely to form in relatively short time after impoundment. The sediment is expected to move gradually towards the dam. This situation is anticipated to extend at least over the half lifetime of the reservoir when the entire dead storage capacity and 50 % of its active capacity has been already lost. Therefore, the “special sluices” of the Merowe Dam and “particular operation rules” expected by the EIAR (2002) to “reduce the reservoir sedimentation” will not play any important role in the first decades. In conclusion, over the first 50 years period, the total
69
storage capacity of the Merowe Reservoir will be diminish with 34 % and not 17 % as predicted by the EIAR (2002).
High sedimentation deposition especially in the upper reach of the reservoir together with long anoxic periods of the deep waters is expected to smother the benthic organisms of the new forming lake.
With more that 90 % reduced sediment load below the dam the sediment accumulation along the river will be diminished and river bed and banks will be eroded. Induced scouring of the river channel downstream may result in lowering the river level with possible influences on the adjacent aquifers water tables. Moreover, no natural flooding below the dam will heavily impact the traditional recession farming along the river course. Together with the AHD, the Merowe Reservoir is expected to increase the general erosion of the Mediterranean shore and to accelerate the transgression of Nile Delta, favoring salt water intrusion over the large fertile agricultural areas.
5.3 Water quality and geochemistry
The onset of water column thermal stratification is expected in the Merowe Reservoir. Thermal stratification will depend on external driving forces as hydro-meteorological conditions, location, wind induced surface forces, etc and internal properties such as lake morphometry, light absorption and the theoretical water residence time. Using an empirical dependence of reservoir stratification and residence time, we predict a temperature difference between surface and 30 m below of about 10-12 °C. Therefore, starting in spring, the water column of the Merowe Reservoir may become stratified extending over the entire reservoir length. During the flood period, the thermal stratification may be destructed, especially on the upper stretch of the reservoir. With a length of 200 km, the lower stretch of the reservoir, especially the areas in front of the dam or the side bays are anticipated to be less affected by the flood. However, the
70
overturn due to the changes in climatic conditions during the winter period will allow convective mixing between the surface and the deep waters of the reservoir.
Thermal stratification, high light penetration, increased water temperature in the epilimnion and relatively high riverine nutrient supply will maintain high rates of primary production up in the eutrophic level.
With an approximated average rate of 370 g C m-2 yr-1, in-situ primary production is expected to produce annually between 130’000 and 300’000 t C yr-1. We consider that 20 % of the organic carbon produce in-situ within the reservoir will be accumulated at the lake floor. With high sedimentation rates, half of the total accumulated carbon is expected to be rapidly buried in the sediment of the reservoir. Therefore, the other half (between 13’000 and 30’000 t C yr-1) represents the potential sedimentary organic carbon available for greenhouse gas production. Under expected anoxic conditions below the sediment/water interface, decomposition of organic matter will result mainly in CH4 production which will be exported to the atmosphere. During transport towards the surface, a fraction of the CH4 is expected to be oxidized and converted to CO2. Stratified water column in the Merowe Reservoir will result in storage of both CO2 and CH4 in the hypolimnion. During turnover periods, especially in the winter, convective mixing will release rapidly the accumulated gas to the surface.
We also expect that another 20 % of the total organic carbon production (26’000 to 30’000 t C yr-1) will undergo bacterial decomposed within the water column which will result in oxygen consumption and CO2 production. As the supply of dissolved oxygen from atmosphere will be limited by stratification, constant oxygen consumption will lead to a gradual decreased in dissolved oxygen concentration and even total oxygen depletion in the deepwater.
Therefore, both CO2 and CH4 will be produced during decomposition of organic matter within the Merowe Reservoir. As the CO2 and CH4 fluxes reaching the surface depends upon a large number of factors, we limit out estimation to only the potential organic
71
carbon for greenhouse gas production. Therefore, the available organic carbon for greenhouse gas production in the sediment is expected to range annually between 13’000 and 30’000 t C yr-1. This will be supplemented by between 30’000 to 60’000 t C yr-1 from the water column. The values are actually expected to be much higher if considering that annually, about 400’000 t C yr-1 with an upstream origin will be accumulated to the sediment of the reservoir and contributing with half to the total greenhouse gas potential.
Using a simplistic mass balance approach we estimated that the internal processes within the Merowe Reservoir will retain annually up to 8 % of the inflow load. Therefore, the nutrient concentration in the reservoir will be dependent on the input and to a lesser extent on primary production or sedimentation.
Pollution and eutrophication of the reservoir could create public health hazard for people drinking water or eating fish from the reservoir.
Together with water stratification, low oxygen concentration is expected to have high impact on life conditions of the organisms of the reservoir possible causing fish mortality when oxygen depletion will temporally affect the entire reservoir water body.
Additionally to the quality of water discharges which are likely to contain high levels of nutrient, organic matter and hydrogen sulfide, the impacts of bottom water release from the reservoir could be related to coldwater pollution and anoxic conditions. As bottom release, the temperature of the outflow water will be lower in summer than it would be under natural conditions. Therefore, coldwater pollution together with low dissolved oxygen concentration in the discharged water during the summer are expected to impact the downstream fish population. However, the oxygen content in the water downstream would tend towards natural values by re-oxygenation. On the other hand, the water temperature is expected to need a longer distance before reaching the normal values. Therefore, if the downstream impacts on the biological productivity generated by the low oxygen concentration will be limited to relatively short distance, large temperature changes are expected to induce higher impacts.
72
5.4 Ecology and health-related impacts
Based on present conditions and water quality of the Nile River, strong eutrophication of the reservoir is anticipated. The input of relatively large amounts of nutrients will induce an increase of biological productivity. Plankton, benthic organisms and fish will benefit and the biomass will increase rapidly. As a result, the reservoir is considered to have positive effect on the lake species as these fishes may find suitable habitats and food whereas the river species are expected to show a decline.
The migratory species which usually swim to the upstream reaches of the river or tributaries for spawning will be blocked by the dam. No fish ladder is fore seen.
Conditioned by the daily and weekly flow variability, reduced downstream spawning areas will have negative impacts on both lotic and lentic fish populations. Nutrient retention in the reservoir may also lead to a decrease of the downstream aquatic productivity resulting automatically in a decrease in fish yield downstream.
Flood events act as biological triggers for reproduction in some fish species. As the natural distribution and timing of downstream flow regimes will be destructed, the impact on the spawning of those fish species is expected.
Due to rapidly changes in the daily and seasonal flow downstream of the dam site, only aquatic organisms tolerant to flow fluctuations and to sudden changes in temperature and dissolved oxygen will prevail. Aquatic organisms will be more affected by the sudden temperature and oxygen changes than by rapid flow increases.
The initial period of increased biomass is generally expected to be followed by stabilization in fish productivity, as the environmental conditions of the lake are expected to reach a steady-state. Therefore, benefiting from newly formed reservoir, commercial fishing could be initiated after a period of few years after impoundment.
73
Stagnant water and exposure of large area of the river bed can create perfect breeding condition for mosquitoes, vectors of malaria and yellow fever and the water flea, host of the guinea-worm. As malaria was endemic in Sudan in 1942 resulting in about 100’000 deaths, precautionary measures should be considered.
The reservoir water quality may also be less adequate for human consumption under high annual drawdown of dry periods due to reduced dilution, eutrophication and pollution, as well as the presence of decaying vegetation.
The presence of stagnant water around the construction site due to excavation, ditches or other activities may induce good breeding conditions for anopheles in the immediate area and generate malaria among the construction personal or local population if not managed properly. It cannot be fully excluded that anopheles will find favorable conditions in the upper reaches of the reservoir, specially during the seasonal receding of the water level which will expose the annual drawdown zone and favor the creation of temporary shallow stagnant pools in some areas.
Although it is not necessary expected to trigger dramatically health problems, the arid conditions and the characteristics of the reservoir area with large seasonal water level fluctuations seems to justify a cautious approach.
74
6. The Lahmeyer report
6.1 International standards
The environmental impact assessment report should be seen as guidance, identifying at the beginning the environmental issues resulting from the project implementation, estimating their extent and providing a basis for deciding whether or not a project should be carried out. Among the goals of the EIAR, the report should contribute to the sustainability and viability of such projects by foreseeing conflicts and deficiencies as well as reparation and mitigation costs. Such a report should propose at the end a few tools to help the decision makers to minimize negative impacts. There are several published guidelines such as the report by the World Commission on Dams (WCD, 2000) or the Operational Policies of the World Bank (www.worldbank.org, which provide specific requirements for establishing an EIAR for a large dam project. No reference is made, however, to such international standards in the Merowe Dam report.
6.2 Important deficiencies
The EIAR (2002) was not made available for public review. Therefore a chance was missed for involving major stakeholders and the general public in a discussion of the quality of the information and the assessments of the report. In addition, it seems that no formal peer review of the report was carried out by qualified environmental assessment specialists, prior to the submission to the Sudanese Government.
It does not appear that Lahmeyer have carried out any specific technical studies for evaluating potential impacts. No reference is made in the report to such studies.
75
Key environmental issues such as reservoir sedimentation, irrigation, water quality, downstream ecological impacts resulting from hydropeaking were not addressed adequately, as specified below.
6.2.1 Sedimentation
We predict that an annual sediment volume of approximately 84x106 m3 yr-1 will be accumulated in the Merowe Reservoir. As this value is extremely high compared to the total storage of 12.4x109 m3, the reservoir is expected to lose its total capacity (dead and active) in less than 150 yr. For comparison, the dead storage capacity (20 % of the total reservoir volume) of the AHD will be lost in 360 yr whereas it will take another 1’000 yr until the reservoir will lose its active capacity (55 % of the total volume). Therefore, sedimentation represents a major issue for the Merowe Dam Project and more detailed information should be acquired.
On page 4-6, the EIAR (2002) made the following statement: “…the future reservoir will trap 100 % of the river bed load and much of its suspended load”. On page 2-2, the EIAR specifies potential mitigation strategies: “The dam design incorporates special sluices and particular operation rules to reduce the reservoir sedimentation and to reduce the capacity losses over 50 yr period to 17 % of the original active capacity (83 % will still remain active)”.
The proportion of bed load to suspended load varies from river to river. In general, large rivers at lower elevations are less steep and therefore the proportion attributable to bed load is small (Meade et al., 1990). This is the case for the Nile River for which the bed load transport does not represent an issue. The issue here is represented by the suspended load.
According to EIAR (2002), the volume of sediment annually retained in the reservoir will correspond to 28x106 m3 yr-1. Using the conversion factor of 1.56, this annual volume is equivalent to a sediment mass of 44x106 t yr-1. Compared to the inflow load of 143x106 t
76
TSS yr-1 calculated from a water flow of 84 km3 yr-1 and a TSS concentration of 1.7 kg l-1, the sediment retention capacity of the reservoir would correspond to only 30 % of the incoming sediment load.
Compared to our estimated retention of 90 % of the incoming load for a residence time of approximately two months, the EAIR (2002) assumption is based on unknown or unshared data and represents a factor of 3 lower retention. This low retention contradicts existing experience with large dams such as the Iron Gates Reservoir (Teodoru and Wehrli, 2005) and the AHD. No technical information is given to sustain the claim that “special sluices” and “particular operation rules” can indeed ensure the transport of the suspended load for 200 km along the Merowe Reservoir.
6.2.2 Hydrology
Long hydrological time series and their interpretation is often a matter of controversy. The EIAR (2002) does not specify the source of the hydrological data on which the average annual runoff and its variability were based.
Peak operation of the hydropower scheme will create daily water level fluctuations between 2.6 and 4.9 m below the dam. This hydropeaking will have significant impacts on small-scale irrigation pumps and ferry landing sites expected to occur over a small distance of only 20 km downstream the dam. Further consequences for the local population and the riparian morphology and ecology are not discussed in any detail. Good practice in large dam design would require a serious evaluation of mitigation measures such as a small dam to limit the amplitude of these daily level fluctuations.
6.2.3 Irrigation
The Merowe Dam is described as a multi-purpose project for hydropower production and irrigation. At the completion of the EIAR in April 2002, the irrigation component was still studied at pre-feasibility level “although two irrigation intakes on the right and left
77
bank of the river (2x150 m3 s-1) have been incorporated in the dam structure design” (EIAR, 2002; page 2-1).
According to our calculations, the proposed irrigation scheme would lead to an annual abstraction of up to 7.4 km3 yr-1. As this diversion would represent 9 % of the river flow, the irrigation scheme should be assessed in the report together with the operation rules, a plan for limiting salinization of irrigated land, and total water allocation within Sudan. Such an important aspect should not be ignored simply due to the fact that the plans are still in limbo.
6.2.4 Water quality
No database on water quality parameters was presented by the EIAR (2002). The general prediction that “no significant change of water quality is expected to occur, neither immediately after impounding nor in the long term” disregards long-term observations on reservoirs in arid areas. The optimistic assessment was based on the following assumptions (EIAR, 2002; page 4-4)
(1) “Remarkable very little biomass exists within the reservoir area – 25,000 t of readily degradable and 9,000 t of slowly degradable biomass”;
(2) “Very short residence time of only two months”;
(3) “Annual draw-down of the reservoir which will tremendously reduce reservoir depth, length and volume”;
(4) “Operation of bottom outlet and low water intake level”.
Based on the water residence time and the local climate, we demonstrate that strong water column stratification, with temperature differences between the surface and the deep waters of several °C will occur during the summer period.
Moreover, it seems that the Lahmeyer report disregards in-situ reservoir production. Low primary production rates will produce between 320’000 and 750’000 t of organic matter
78
per year, which is one to two orders of magnitudes more than the existing biomass in the reservoir area before flooding. In addition, inflow organic matter will be degraded within the reservoir.
6.2.5 Greenhouse gas
The report assumes that greenhouse gas emissions were limited to the degradation of existing biomass in the reservoir area. A “total emission of some 600,000 t of CO2” was predicted by the EIAR (2002) on page 4-4. “Since anaerobic decomposition would not occur, due to the continual exchange of water within all parts of the reservoir, no methane would be produced”, so that “…greenhouse gas emissions from the Merowe project are considered to be non-significant”.
These predictions contradict the current scientific knowledge. Even in the absence of anoxic bottom water, high sedimentation rates in the reservoir and therefore high burial efficiencies will result in prevalence of anoxic condition within the sediment. Therefore, during decomposition of organic matter, both CO2 and CH4 will be produced within the sediment of the Merowe Reservoir. As the CO2 and CH4 fluxes released from the reservoirs depend on a large number of factors, we limited the evaluation to the total carbon available for greenhouse gas production. Our calculations showed that annually, between 40’000 and 90’000 t C yr-1 will be available to be converted into CH4 by organic matter decomposition within the water column and the sediment. Considering the large fraction of organic matter input via total suspended solids, the available carbon will be actually much higher, between 250’000 and 300’000 t C yr-1. These simple estimates show that monitoring of the water column for oxygen and greenhouse gases is of high priority for a sound assessment of reservoir performance.
6.2.6 Fishes
Concerning the fish populations, the EIAR (2002) considered the Merowe Dam Project having no significant impacts on fish fauna, being “…mainly limited to changes in the
79
future reservoir” (page 4-7) due to the fact that “…no endangered species have been reported and there is no evidence of fish migration other that local movements in the Main Nile river” (page 4-7).
The report disregards the fact that the present fish population of Lake Nubia consists of several migratory fish. Several species like Barbus bynni, Barbus perine, Labeo coubi, Labeo horie and Laboe niloticus which belong to Cyprinidae family are migratory fish. The ecological assessment is based on incomplete species lists and disregards the life cycle of the different species involved. The isolation of a very large fish population on the 700 km river stretch between Aswan and Merowe represents a dramatic fragmentation of one of the largest river systems in the world and requires a much more careful and detailed monitoring and assessment.
6.3 Recommendations for mitigating negative impacts
6.3.1 Recommendation on reservoir level operation
In general, the operation policy of a dam is to “refill” the reservoir volume during the high flow, which in the case of Merowe is represented by the summer period between June and October and to have the reservoir full at the beginning of the following dry season. In the course of autumn, winter and spring, the water levels will usually decrease progressively due to the water release for energy production and/or irrigation demands and evaporation.
The seasonal fluctuation in the Merowe Reservoir of between 800 km2 at maximum level and 350 km2 at low stand imply that more than 450 km2 of reservoir floor will be exposed to aeolian transport and soil-forming conditions. Therefore, it should be considered that, in order to minimize the environmental impacts, the operation policy should be done in such a manner to reduce the exposure of the reservoir sediment. This would represent a
80
substantial advantage in terms of environmental impacts of the aquatic life and landscape as well as the water losses.
Daily operation scheme of the dam will create downstream water level fluctuations ranging between 2.6 and 4.9 m with significant impacts on small-scale irrigation pumps and ferry landing site. A retention dam at the outlet of the power station could mitigate such negative side effects of hydropeaking. Therefore, the feasibility of a small second dam downstream Merowe, to equalize the daily fluctuations, should be included.
6.3.2 Recommendation on sedimentation
Our predicted annual sediment retention of up to 90 % of the river incoming load is expected to accumulate in the upper stretch of the reservoir, where a new delta will form in relatively short period. The simplest appropriate solution for reducing the sediment retention in the Merowe Reservoir is increasing the discharge during the summer period as 80 % of the annual sediment load occurs with the flooding between July and October.
For a precise estimation of the incoming sediment load, TSS measurements over a full annual cycle should be carried out. A detailed sediment management plan should address the problems of reservoir sedimentation and provide detailed measures and operation rules to mitigate the impact on the reservoir lifetime.
6.3.3 Recommendations on water quality
The water quality in the Merowe Reservoir will mainly depend on the inflow and on the pollution in the catchment area, and to a lesser extent on internal processes. Of particular importance are the summer temperature variations, the flood and the return of water from irrigated areas.
Mitigation measures for reservoir water quality generally focus on maintenance of water quality upstream by treating the sewage of large upstream cities and by preventing water
81
stratification and oxygen depletion. This can be done by limiting the water residence time and designing optimal water intakes for the power plant. The position of the intake influences the nutrient content, oxygen conditions and fish population in the reservoir and downstream. An intake located in the hypolimnion will help to minimize the stratification in the reservoir and assist the transport of oxygen to greater depth. Therefore, the intake should be made flexible to “mix” and maintain a minimum O2 level. A flexible solution will also help in the future to mitigate unforeseen problems.
82
References
Abu Zeid M (1987) Environmental Impact Assessment for the Aswan High Dam. Water Research Center, Ministry of Irrigation. In: Biswas A. and Q. Geping (Eds) Environmental Impact Assessment for Developing Countries (pp 168-190). London
Abu Zeid M, Charlie WA, Sunada DK & Khafagy A (1995) Seismicity induced by reservoirs: Aswan High Dam. Water Resources Development 11: 205-213
Adams RD (1983) Incident at the Aswan Dam. Nature 301: 14
Ahmed AM, Mohammed AA, Springuel I & Elotify AM (1989) Field and Laboratory Studies on Nile Phytoplankton in Egypt. 3. Some Physical and Chemical Characteristics of Aswan High Dam Lake (Lake Nasser). Internationale Revue Der Gesamten Hydrobiologie 74: 329-348
Aleem AA & Samaan AA (1969) Productivity of Lake Mariut, Egypt. Part I. Physical and chemical aspects. Internationale Revue Der Gesamten Hydrobiologie 54: 313-355
Ali MM, Hamad AM, Springuel IV & Murphy KJ (1995) Environmental-Factors Affecting Submerged Macrophyte Communities in Regulated Waterbodies in Egypt. Archiv fur Hydrobiologie 133: 107-128
Aly AIM, Froehlich K, Nada A, Awad M, Hamza M & Salem WM (1993) Study of Environmental Isotope Distribution in the Aswan-High- Dam Lake (Egypt) for Estimation of Evaporation of Lake Water and Its Recharge to Adjacent Groundwater. Environmental Geochemistry and Health 15: 37-49
Balba AM (1979) Evaluation of Changes in the Nile Water Composition Resulting from the Aswan High Dam. Journal of Environmental Quality 8: 153-156
Bastviken D, Cole J, Pace M & Tranvik L (2004) Methane emissions from lakes: Dependence of lake characteristics, two regional assessment, and a global
83
estimate. Global Biogeochemical Cycles 18: 1-12, GB4009, doi: 4010.1029/2004GB002238
Bratrich C, Truffer B, Jorde L, Markard J, Meier W, Peter A, Schneider M & Wehrli B (2004) Green hydropower: a new assessment procedure for river management. River Research and Applications 20: 865-882
Benuning KRM, Talbot MR & Kelts K (1997) A revised 30'000-year paleoclimatic and paleohydrologic hystory of Lake Albert, East Africa. Paleogeography, Paleoclimatology, Paleoecology 136: 259-279
Coelho PEFP (1987) Seismicity around Brazilian dam reservoirs. Environmental Geology and Water Science 10: 149-158
Duchemin E, Luccote M, Canuel R & Chamberland A (1995) Production of the greenhouse gases CH4 and CO2 by hydroelectric reservoirs of the boreal region. Global Biogeochemical Cycles 9: 529-540
Eldardir M (1994) Sedimentation in Nile High Dam Reservoir, 1987-1992, and sedimentary futurologic aspects. Sediment. Egypt 2: 23-39
El-Hinnawi EE (1980) The state of the Nile Environment: An Overview. Water Supply & Management 4: 1-11
El-Hussain IW & Carpenter PJ (1990) Reservoir induced seismicity near Heron and El Vado Reservoirs, Northern New Mexico. Bulletin of the Association of Engineering Geologists 27: 51-59
Elraey M, Nasr SM, Elhattab MM & Frihy OE (1995) Change Detection of Rosetta Promontory over the Last 40 Years. International Journal of Remote Sensing 16: 825-834
Entz BAG & Latif AFA (1974) Report on surveys to Lake Nasser and Lake Nubia (1972–1973). Aswan, Lake Nasser Development Center Project (RPA/UNDP/FAO) Working paper (6).
Entz BAG (1980a) Sedimentation Processes in the Reservoir Lake Nasser-Nubia during 1965-1974 and Future Aspects. Water Supply & Management 4: 63-66
84
Entz BAG (1980b) Ecological aspects of Lake Nasser-Nubia. Water Supply & Management 4: 67-72
Failer E (2004) The Merowe Dam Project, Sudan. The biggest water resource project in Africa. 7th German-Arab Business Forum 2004 2nd-4th June, Berlin. http://www.dihk.de/inhalt/themen/international_neu/regi...oad_2/irak_ws5_3.pdf
Fanos AM (1995) The Impact of Human Activities on the Erosion and Accretion of the Nile Delta Coast. Journal of Coastal Research 11: 821-833
Finger D, Schmid M & Wüest A (2005) Downstream effects of hydropower operation on riverine particle transport and subsequent effects on downstream lakes. Water Resources Research (accepted)
Friedl G & Wüest A (2002) Disrupting biogeochemical cycles - Consequences of damming. Aquatic Sciences 64: 55-65
Friedl G, Teodoru C & Wehrli B (2004) Is the Iron Gate I reservoir on the Danube River a sink for dissolved silica? Biogeochemistry 68: 21-32
Frihy OE, Dewidar KM, Nasr SM & El Raey MM (199 Change detection of the northeastern Nile delta of Egypt: shoreline changes, Spit evolution, margin changes of Manzala lagoon and its islands. International Journal of Remote Sensing 19: 1901-1912
Galy-Lacaux C, Delmas R, Couadio G, Richard S & Gosse P (1999) Long-term greenhouse gas emissions from hydroelectric reservoirs in tropical forest regions. Global Biogeochemical Cycles 13: 503-517
George CJ (1972) The role of the Aswan High Dam in changing the fisheries of the southeastern Mediterranean. In: Farvar MT & Milton JP (Eds) The careless technology: ecology and international development (pp 179–18. Natural History Press for the Conservation Foundation and the Center for the Biology of Natural Systems, Washington University, Garden City, New York
Hakanson L & Jansson M (1983) Principles of Lake Sedimentology. Springer-Verlag, Berlin Heidelberg
85
Harrison GP, Whittington HW & Gundry SW (1989) Climate change impacts on hydroelectric power. Proceedings of 33rd Universities Power Engineering Conference (UPEC '9, Edinburgh, September 1998, pp. 391-394. available at http://www.see.ed.ac.uk/~gph/publications/GPH-Upec98.pdf
Harrison GP & Whittington HW (2001) Impact of climatic change on hydropower investment. Proceedings of the 4th International Conference on Hydropower Development (Hydropower '01), 19-22 June 2001, Bergen, Norway, pp. 257-261. Available at http://www.see.ed.ac.uk/~gph/publications/Hydro01.pdf
Hilal MH & Rasheed MA (1976) Some chemical changes in properties of the Nile water after the construction of the High Dam. Egyptian Journal of Soil Science 16: 1-8
ILEC (2005) Promoting Sustainable Management of the World's Lakes and Reservoirs. World Lakes Database. http://www.ilec.or.jp/eg/index.html
Kebeasy RM, Maamoun M & Ibrahim EM (1991) Aswan Lake induced earthquakes. Bull. Intern. Inst. Seism. Earthq. Engin. 19: 155-160
Kinawy SMA (1974) Hydrography and nutrient salts in the water of Lake Edku, Egypt. M.Sc. Thesis, Alexandria University
Kotob M & Mottoleb MM (1981) Effect of Aswan High Dam on the regime of the river downstream Esna barrage. High dam side effects research institute, Cairo.
Latif FA & Rashid MM (1972) Studies on Tilapia nilotica from Lake Nasser. 1: Macroscopic characters of gonads. Bull. Inst. Ocean. Fish. 2: 215-238
Latif FA & Rashid MM (1983) Reproduction of Tilapia nilotica. Asw. Sci. Tech. Bull. 4: 207-223
Latif AFA (1984) Lake Nasser, the new man-made lake in Egypt (with reference to Lake Nubia). In: Taub FB (Eds) Ecosystems of the World 23, Lakes and Reservoirs (pp 385-410). Elsevier Publishing Co., Amsterdam, Oxford, New York, Tokyo
Meade RH, Yuzyk TR & Day TJ (1990) Movement and storage of sediment in rivers of the United States and Canada. In: Wolman MG & Riggs HC (Eds) Surface Water Hydrology: The Geological Society of America (pp 255-280). Boulder, CO
86
Meade RB (1991) Reservoirs and earthquakes. Engineering Geology 30: 245-262
Mohamed YA, Van der Hurk BJJM, Savenije HH & Bastiaanssen WGM (2005) Hydroclimatology of the Nile: results from a regional climate model. Hydrology of earth System Sciences 9: 263-278
Mohammed AA, Ahmed AM & Elotify AM (1989) Field and Laboratory Studies on Nile Phytoplankton in Egypt. 4. Phytoplankton of Aswan High Dam Lake (Lake Nasser). Internationale Revue Der Gesamten Hydrobiologie 74: 549-578
Nixon SW (2003) Replacing the Nile: Are anthropogenic nutrients providing the fertility once brought to the Mediterranean by a great river? Ambio 32: 30-39
Rashid MM 1995 Some additional information on limnology and fisheries of Lakes Naser (Egypt) and Nubia (Sudan). In: CIFA Technical Paper, No. 30. Rome, FAO. 1995. 134p
Rosenberg DM, Bodaly RA & Usher PJ (1995) Environmental and social impacts of large scale hydroelectric development: who is listening? Global Environmental Change 5: 127-148
Rosenberg DM, Berkes F, Bodaly RA, Hecky RE, Kelly CA & Rudd JWM (1997) Large scale impacts of hydroelectric development. Environmental Reviews 5: 27-54
Roskar J 2000 Assessing the water resources potential of the Nile River based on data, available at the Nile forecasting center in Cairo. Hidrometeorological Institute of Slovenia UDC: 556.53 (282.263.1) 36. Ljubliyana, http://www.zrc-sazu.si/giam/zbornik/roskar_40.pdf
Rzoska J & Talling JF (1966) The development of plankton in relation to hydrological regime in the Blue Nile. Journal of Animal Ecology 55: 637-662
Saad MAH (1976) Studies on the nature and composition of the sediment of two Egyptian lakes found under different local conditions. Limnologica 11: 1-8
Saad MAH (1980) A limnological study on Lake Nasser and the Nile in Egypt. Water Supply & Management 4: 81-92
87
Sadek MF, Shahin MM & Stigter CJ (1997) Evaporation from the reservoir of the High Aswan Dam, Egypt: A new comparison of relevant methods with limited data. Theoretical and Applied Climatology 56: 57-66
Said R (1993) The Nile River: geology, hydrology and utilization. Pergamon Press, Oxford, UK. 320 p.
Siegenthaler U & Sarmiento JL (1993) Atmospheric carbon dioxide and the ocean. Nature 356: 119-125
Selim MM, Imoto M & Hurukawa N (2002) Statistical investigation of reservoir-induced seismicity in Aswan area, Egypt. Earth Planets Space 54: 349-356
Shalash S (1982) Effects of sedimentation on the storage capacity of the Aswan High Dam reservoir. Hydrobiologia 92: 623-639
Simpson DW (1976) Seismicity changes associated with reservoir loading. Engineering Geology 10: 123-150
St. Louis LV, Kelly CA, Duchemin E, Rudd JWM & Rosenberg DM (2000) Reservoir surfaces as sources of greenhouse gases to the atmosphere: a global estimate. BioScience 50(9): 766-775
Stanley DJ (1996) Nile delta: Extreme case of sediment entrapment on a delta plain and consequent coastal land loss. Marine Geology 129: 189-195
Stanley DJ & Wingerath JG (1996) Nile sediment dispersal altered by the Aswan High Dam: The kaolinite trace. Marine Geology 133: 1-9
Straskraba M & Mauersberger P (198 Some simulation models for water quality management of shallow lakes and reservoirs and a contribution to ecosystem theory. In: Mitsch WJ, Straskraba M & Jorgensen SE (Eds) Wettend Modelling (pp 153-176). Elsevier, Amsterdam
Talling JF (1980) Some problems of aquatic environments in Egypt from a general viewpoint of Nile ecology. Water Supply & Management 4: 13-20
Teodoru C & Wehrli B (2005) Retention of sediments and nutrients in the Iron Gate I Reservoir on the Danube River. Biogeochemistry 76: 539-565
88
Woodward JC, Macklin MG & Welsby DA (2001) The Holocene fluvial sedimentary record and alluvial geoarchaeology in the Nile Valley of northern Sudan. In: Madday D, at al. (Eds) River Basin Sediment Systems: Archives of environmental change (pp 327-355). Rotterdam, Balkema
WCD 2000 Dams and development. A new framework for decision-making. The report of World Commission on Dams. ISBN: 1-85383-798-9 356. London and Sterling, VA. http://www.dams.org//docs/report/wcdreport.pdf
89
|
|
 
|
|
|
|
|
| العنوان |
الكاتب |
Date |
| عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 03-30-06, 02:39 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | على محمد على بشير | 03-30-06, 02:57 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Tragie Mustafa | 03-30-06, 03:18 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 03-30-06, 04:12 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | على محمد على بشير | 03-30-06, 04:23 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | على محمد على بشير | 03-30-06, 04:27 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | كبسيبة | 03-30-06, 03:56 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | abdalla BABIKER | 03-30-06, 05:08 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | قلقو | 03-30-06, 05:57 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Hani Arabi Mohamed | 03-30-06, 06:21 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | محمد مختار جعفر | 03-30-06, 07:42 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 03-30-06, 10:15 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | الأمين عثمان صديق محمد | 03-30-06, 10:29 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 03-30-06, 12:16 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | كبسيبة | 03-30-06, 01:30 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 03-30-06, 01:55 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Mannan | 03-30-06, 06:09 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Elmoiz Abunura | 03-30-06, 11:07 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | حسن الجيلى سعيد | 03-31-06, 03:02 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 03-31-06, 03:56 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | wadaldeem | 03-31-06, 11:36 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 03-31-06, 04:18 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Mannan | 04-01-06, 02:21 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-01-06, 03:13 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | wadaldeem | 04-01-06, 08:09 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عبد الوهاب المحسى | 04-01-06, 09:49 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عبد الوهاب المحسى | 04-01-06, 10:11 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Tragie Mustafa | 04-01-06, 01:48 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-02-06, 03:29 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عبد الوهاب المحسى | 04-02-06, 06:16 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | معتصم الطاهر | 04-02-06, 06:45 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-02-06, 04:43 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عبد الوهاب المحسى | 04-02-06, 06:21 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عبد الوهاب المحسى | 04-02-06, 06:23 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عبد الوهاب المحسى | 04-02-06, 06:41 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-03-06, 02:06 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | banadieha | 04-03-06, 02:44 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | banadieha | 04-03-06, 04:02 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عادل فيصل راسخ | 04-03-06, 06:29 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-03-06, 09:15 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | مهيرة | 04-03-06, 09:58 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عبد الوهاب المحسى | 04-03-06, 03:08 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-04-06, 03:28 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-04-06, 09:34 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عبد الوهاب المحسى | 04-06-06, 05:04 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | adil amin | 04-07-06, 10:06 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-15-06, 05:57 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-16-06, 05:16 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-17-06, 04:56 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | عبد الوهاب المحسى | 04-20-06, 03:14 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-21-06, 09:58 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-22-06, 09:43 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-23-06, 12:40 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 04-24-06, 12:49 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Nazar Yousif | 05-05-06, 05:04 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | adil amin | 05-05-06, 10:05 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | الأمين عثمان صديق محمد | 05-05-06, 05:08 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 05-06-06, 12:34 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 05-05-06, 06:19 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Suad I. Ahmed | 05-06-06, 01:34 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 05-07-06, 11:05 AM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 05-09-06, 04:28 PM |
| Re: عاجل : شبكة الانهار الدوليه تطالب بوقف العمل في خزان مروي | Asskouri | 05-22-06, 05:42 AM |
|
| |
عبد الوهاب المحسى
فيس بوك
تويتر
انستقرام
يوتيوب
بنتيريست