Sediment As a Resource for Development of Eastern Nile Countries

Sediment as a Resource for Development of Eastern Nile Countries

By Dr. Mohammad Abdel·Fadil 1

Abstract Land and water are ecologically linked in a natural system called a catchment area, drainage basin, or watershed. From the smallest droplet to the mightiest river, water makes to shape the land, carrying sediment and dissolved materials that drain to watercourses and, in most cases, eventually to the sea.

Recently either in China, the watersheds of the Yel/ow River at loess plateau basin or in Eastern Nile Countries EN (Ethiopia·Sudan-Egypt), their main watershed areas, are of the world's mostly badly eroded ones. Due to the increasing problems of population and poverty, it is important to control erosion in these areas. China has already executed a project to overcome these problems in cooperation with World Bank into loess plateau region. The project outcomes show increase of agricultural products and incomes and reduce of erosion and sediment.

Into catchment's areas of EN countries, valuable farmland can be created due to construction of some small dams as warping dams through trapping eroded soil flowing down a gully during the flood season in the eroded areas. Not only would the dams conserve soil and water for local economic development, but they also help to reduce excessive sediment deposition in downstream gullies and rivers. Fully implemented a pilot project to construct some warping dams and using the suitable flushing sediment methods may provide a long-term solution to EN watershed and river's sediment problem. How best to utilize the pilot areas to make them attractive as financial investments under a market economy is a key issue to the success of the program.

Keywords: Key dam, warping dam, flushing-sediment, watershed, erosion, reservoir sedimentation.

Introduction

The Necessity for Watersheds Integration Land and water are ecologically linked in a natural system called a catchment area, drainage basin, or watershed. From the smallest droplet to the mightiest river, water works to shape the land, taking with it sediment and dissolved materials that drain to watercourses and, in most cases, eventually to the sea. It includes the land catches all the rain directed to a stream, river or lake, all the humans, plants and animals live in it, and all the things we have added to it as buildings and roads. In general, terms, a drainage basin can be divided into three main zones: an upper erosional zone of sediment production, a middle zone of sediment transport with simultaneous erosion and deposition, and a lower zone of sediment deposition. Flood control projects are more common in the middle and lower zones where the stream overflows frequently onto agricultural or urban land. The longitudinal profile of the stream system tends to flatten through time by degradation in the upper reaches and aggradation in the lower reaches. Figures (1 a. 1b) show drainage basin zones and some channel types through time [5].

1 Associate professor, Nile Water Sector, Ministry of Water Resources and irrigation, Cairo, Egypt EMail:[email protected]

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Figure (1 a); Drainage basin zones and some channel types

Figure (1 b); typical longitudinal stream profile through time

Everything we do affects our catchments - from washing clothes and growing food to larger-scale activities as mining, commercial farming, and building roads or dams. The reverse is also true: our catchments affects everything we do, by determining what kinds of plants we can grow, the number and kinds of animals that live there, and how many people and iivestock can be sustainably supported by the land. The most important truth about any catchment area is that we all live downstream from someone, and upstream from another. Anything dumped on the ground or released to the air in the catchment can end up in its rivers, lakes, or wetlands. A catchment's water may be made undrinkable by activities many kilometers away. To understand the water quality of a stream, one must look at the entire area it drains. Therefore, the catchments do not respect political boundaries, and in fact can encompass several cultural, national, and economic boundaries. What happens in one country's part of the catchment will affect water quality, quantity, or people who depend on it in the countries downstream

Physical Features of the Watershed and its Related Problems

A typical catchment is a network of smaller rivers or streams called tributaries, which link to each other, and eventually into a bigger river. Streams can be one of three types, depending on how often they carry water:~ • Ephemeral streams (small, temporary and not defined channels occur only during a rainstorm or after a flood), • Intermittent streams (generally flow only during the wet season), and • Perennial streams (flow year-round, well~defined channel and may have several smaller tributaries).

Analysis of the physical features of the catchment leads to understanding of stream catchment relationships and predicts the effects of human influences on different stream types. Slopes influence a catchment's drainage pattern, which very steep slopes coerce

2 rainwater to run off, and increases erosion. In addition, sun and wind affects on catchment area by temperature, evaporation, and transpiration that in turn affect on soil moisture and plants.

Most Eroded Watersheds

Recently. the most badly eroded watersheds in the world are; in china, the watersheds of the middle basin of the Yellow River (loess plateau region), and in Eastern Nile Countries EN (Ethiopia - Sudan - Egypt). Due to the increasing problems of population and poverty. it is important to conserve soil and water resources into these areas.

In 1993, China government in cooperation with the World Bank started executing a project for conservation of soil and water at the loess plateau basin. It was to increase the agricultural products, incomes and to reduce erosion, sediment through an efficient and sustainable use of land and water resources in the tributaries of the yellow river.

In 1999, the Nile basin countries launched an initiative to fight poverty and make socio economic development. EN countries initiate a regional integrated multipurpose program to ensure cooperation, and jOint action between them. They identified seven projects for efficient water management, optimal use of the resources, which include the integrated watershed management for their basins to reduce erosion and sediment.

Integrated watershed management in China

Yellow River and the problems of Loess plateau basin 2 The total drainage area of Yellow River (YR) is 795,000 km , and the total length is 5464 km. The annual average precipitation of the whole basin is 452 mm, which progressively reduces from 600 mm in the southeast to 200 mm in northwest (2). YR is suffering from deficient water resources, serious water and soil erosion, which has led to frequent basin wide drought and tremendous flood disasters in the lower reaches. The loess plateau in middle basin of YR is one of the world's most badly eroded regions, extending for an area of 430,000 km2 Figure (2). It contributes over 90% of the 1.6 billion tons of the total sediment carried by YR annually. To control sediment production and prevent flooding in the downstream densely population region, targeting was for the "severe eroded areas". That have annual erosion rates exceed 5000 ton/km2, for a total area 56000 km2, which contribute to 83% of the river's sediment load. Some areas have erosion rate 30000 tons!km2.

Figure (2): Yellow River and Loess Plateau Project, after [2]

3 Sediment Control through Multi-Purpose Dam The YR is well known as sediment-laden river so soil conservation work has been done on the area of its upper and middle reaches. Many large/medium-sized multi-purpose projects of Longyangxia, Liujiaxia, Sanmenxia, Xiaolangdi and Wanjiazhai etc on the main stream were completed. When the Sanmenxia dam located in Henan province in the YR's lower reaches was completed in 1960, sediment accumulation in its reservoir threatened to deplete its storage capacity in a few years. Consequently, the Sanmenxia dam was modified to include sediment-flushing facility to clear its reservoir from accumulated sediment. Roughly, 1/3 of Yellow River's annual flow was used for sediment flushing. Therefore, 3/4 of the total sediment flow was flushed to sea, leaving behind 1/4 of it, the coarse-grain sediment, to silt up the downstream river channel steadily. After thirty-some years of sediment accumulation, Sanmenxia dam's reservoir no longer had the capacity to temper a flood peak. Consequently, the Xiaolangdi dam was built downstream Sanmenxia dam to afford safety to the densely populated downstream region. This Dam is located at the exit of the last gully of the middle reaches of the Yellow River. This large-scale dam has several functions for sediment and flood control, hydropower production, maintenance of minimum flows of the Yellow River downstream reaches, irrigation downstream, and water supply. Even with sediment-flushing provision, the Xiaolangdi dam is expected to have a very limited useful life, if sediment deposition in the river remains unchecked.

Sediment Control through Land Utilization The region had probably irregular landform, some rocky terrains would be more uneven, and so it was necessary to devote an extensive labor in leveling the field before farming. The climate in the loess plateau is too dry to support a reasonable vegetation cover, and the loess soil is too loose to be protected from water erosion due to severe rainstorms during the monsoon season by such a sparsely covered surface. So the sediment-control program was based on limited goal of preventing eroded soil from leaving the gullies before it enters any drainage system. How best to carry it out differs as doing of; , • A comprehensive water and soil conservation program over the entire land surface as mentioned later and limiting human activities to prevent the destruction of forests and herding of sheep and goats, • On the other hand, simple proposals to stop sediment flows of the gullies and minor river tributaries, preventing them from reaching the major rivers. • The descriptions of these programs are: • Terracing the slopes, it is successful in south region where the climate is suitable for agriculture, as the fields are entirely rain fed and developed from top to down. • Utilizing the gullies; to prevent the undercutting of the gullies, small dams as Key dams, Check dams and Warping dams were added to slow down flood runoffs for tiny gullies. Its reservoirs were partially filled with sediment, and used for cultivating once the floodwater is drained. In more densely populated areas, the gullies are built up in steps with warping dams. • Cultivating the valleys; in some regions, valley floor is well-irrigated and cultivated by rice which eroded regions are left broaden valleys that being built up by sluicing silt coming down with floodwater.

Loess-Plateau Gullies Development project Erosion dissected the loess plateau into tens of thousands of steep gullies. Surface runoff drains very rapidly from the region, creating flood peaks to the downstream rivers during the flood season. To arrest the surface runoff in the gullies before entering the rivers, the following sediment retention structures were executed: • For uninhabited areas, government construct key dams, one for each sub watershed, providing environment for agricultural development. They are earth dams 30-50 m high with reservoir capacities about one million m3, hold up 200

4 year storm and take 30-year until silted up. However, after 10-15 years of sediment retention, reservoirs will be filled with sediment 20-30 m deep, creating 10-15 hectare (ha) of farmland that turned over to the local villages, while the government recovers no direct payment for its investment. Figures (3a,3b) show a typical dam system that is provided with a key dam large enough to protect downstream from floods. • Farmers by their own initiative build silt trappers, or warping dams as earth dams 3 10 meters high, wherever they can, back filling them with sediment in average 3-5 years, to create new farmland upstream it. • Government funded construction of Check dams to retain sediment near its source and protect gullies from getting deeper. They are small earthen dams, often serve one to a few families, and suffer from lack of funds due to its limited goal.

~ Figure (3a), shows a typical small earth Figure (3b), a typical project site, a series dam system of sediment plots and key dam

Hydraulic-fill Method for Small Earth Dam Construction It is low cost construction method (3) because the dam is formed with locally available material, which the soil is very porous and soft. Earth extraction is done with water jets, transportation by flow sludge, and compaction by drying. A little mechanical operation is needed, and consequently the cost is reduced which making economic success for the proJect. The method is shown in Figure (4). Mud sludge flows down from the side to fill the body of the dam, when the water is drained, the soil grains are pulling by surface tension and forming a well-compact earth structure. The diesel pump only is used to pump water up from the gully to create the mud sludge, and operate the water jet for soil extraction. Drainage of the core takes place as following: some of the water percolates horizontally into pervious shell, the remainder moves upward to the surface, allowing the centre of the dam to subside. The downward movement eventually develops arching in the core and prevents its full consolidation. The suitable SOil grain size for this method is fine and uniform.

5 Figure (4 ): dam under construction by hydraulic-fill method

Remarks on the Loess plateau project • Farmland improvement financed through loans from world bank • Terracing the hill slopes or warping the gullies increase in productivity of improved land and it is sufficient way to repay for the initial investment because the purchasing power of the local population is increased, raising also farmers' incomes, so it is economically feasible. • The potential in developing the gully floors with warping dams, take advantage of their low-lying positions and high soil-moisture contents to create high-yield farmland.

Eastern Nile Integrated Watersheds Management

The EN region is one of the varied landscapes ranging from rugged highlands of Ethiopia to wetland areas of Sudan·to desert in northern part of Sudan and Egypt. It includes three main tributaries from eastern basin of the Nile; Blue Nile, Atbara and Sobat as well as White Nile and main Nile. About 83% of the total water of the Nile comes from Lake Tana, 1,800 metres above sea level in the Ethiopian mountains. The lake flows over every summer providing for the flood that today is tamed by the dams of Sudan and southern Egypt (4).The climatic variations make the region subject to droughts and floods. Erosion in highland areas are exacerbated by deforestation, population growth, overgrazing, and use of marginal lands. It causes downstream sedimentation, which decrease the existing reservoirs lifetime, reduce the hydropower, erode bank slopes and damage habitat.

The Nile Basin Initiative NBI Strategic Action Program consists of the basin-wide Shared Vision Program, and two Subsidiary Action Programs, one of them in the Eastern Nile. The EN Subsidiary Action Program (ENSAP) has the objective to" ensure efficient water management and optimal use of the resources through the equitable utilization and no significant harm; ensure cooperation and joint action between the EN Countries seeking win-win goals; target poverty eradication and promote economic development, and to ensure that ENSAP results in a move from planning to action (7)".

The Project Identification Document (PID) for ENSAP has outlined seven potential areas of cooperation. One of them is the Integrated Watershed Management program (6). This pprogram will cover some selected sub-basins proposed from the EN countries in their TOR as shown later.

6 Sedimentation Problems in Egypt

Generally, construction of a dam on a river induces sedimentation at the upstream end of its impoundment. Figure (5) shows the longitudinal profile of the reservoir sedimentation (2). This profile is characterized by the formation of coarse-grained top-set (sand and/or gravel) and fore-set deposits and fine-grained (Silt and clay) bottom-set deposits. The fore set defines a front that gradually migrates downstream into the reservoir.

Figure.(5), Schematic diagram of the typical long profile of a reservoir, after (2)

Aswan High Dam that inaugurated in 1970, 7 km upstream the Aswan Old Dam has created one of the largest man-made reservoir called Lake Nasser and its Sudanese portion called Lake Nubia. Its total length is approximately 500 km, about 350 km in Egypt, and the rest 150 km in Sudan. The Lake lies between latitudes 21 and 24 north and longitudes 31 and 33 east covering an area of about 6,600 km 2 out of which 5,600 km 2 in Egypt at a storage level of 182 m AMSL Nasser lake areas in Sudan and Egypt are threatened by serious sand encroachment. It was reported that substantial amounts of sand are pouring yearly into Lake, decreasing its capacity, and changing its morphology. Remote sensing studies for Dongola region show that the rate of sand movement varies between 3 to 25 m/year depending on the size of the dune. Nevertheless, nothing has been done to mitigate the problem. Annually Egypt and Sudan monitor and analyze the deposited sediment in Nasser Lake. The results show that deposition is increasing.

Egypt proposed management framework in its TOR (9) covers the whole lake area in both Egypt and Sudan. It includes execution of complete hydrographic survey for the Lake to have bathymetric map with suitable contour interval. So, better and accurate estimation of sediment deposition volumes and their distributions will be easily obtained. Moreover. the Lake water levels versus its surface area and volume curves require updating. In addition to study of the organic matters contents and the degree of contaminants in different deposited sediments, particularly clayey soils.

Sedimentation Problems in Ethiopia Ethiopia comprises four sub-basins, namely Tekeze. Abbay, 8aro-Akobo and Mereb. It is located in the Horn of Africa and has one of the most rugged terrains in Africa. Its terrain is divided into five major formations: the western lowlands, the western highlands. the eastern lowlands, the eastern highlands and the Great Rift Valley of East Africa that bisects the central highlands into east and west. The highlands are deeply incised by major rivers, which originate in the highlands and flow to the lowlands, most of which eventually cross the international border into neighboring countries. The topography ranges from 160 to 4620 amsl, and about 60% of the country lies above contour line 1500 amsl, and the rainfall increases with altitude whereas temperature decreases.

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Deforestation in the Ethiopian highlands is speeding up, and the use of the land for cUltivation and grazing without adequate protection has dramatically increased soil erosion, which its annual rate is about 1 billion tons. The majority of it leaves the country as suspended matter. Downstream sedimentation is causing damage to crops and infrastructure, reducing the life of reservoirs, increasing the frequency and intensity of flooding, and deterioration of the land, water, forests, and biodiversity.

Therefore, there is a necessity for a watershed management technically feasible, socially acceptable. The proposed study area (7) is about 363974 km2 (32% of the country's' area). It is highly rugged with steep mountains and is divided into two units: • The western and south-western parts of the basin (46% of the area) as low as 400 amsl , and • The northern, eastern, central, and southern parts are above 1500 amsl. A distinct escarpment whose slope is very sharp and edges toward the west separate these two units and it is highly eroded. Figure (6) shows the tributaries of the eastern river Nile into Ethiopia and Sudan.

Ethiopia's TOR objective is to improve the standard of living of the populations residing within the study area, increase land productivity, reduce erosion and sediment transport, and decrease pressure on resources. The first assignment covers two of the four proposed sub-basins, 1) Tekeze -Setit-Atbara, 3) Baro/Akobo-Sobat and 2) Abbay-Blue Nile, 4) Mereb-Gash.

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Figure (6); tributaries of Eastern River Nile, after (12)

9 Sedimentation Problems in Sudan Sudan is traversed by 9 000 Km of the Nile and its tributaries. The Eastern Nile tnbutaries extend from those of Sobat in the south to those of Atbara in the north. It has a tropical sub continental climate. The annual rainfall ranges between 25 mm in the dry north and over 700 mm in the tropical rain in the south. The mean annual temperature ranges from 30°C to 40°C in summer and from 10 DC to 25 DC in winter. The rainy season is generally short extending for three to four months in most of the country. Potential eva po-transpiration ranges from 3000 mm in the north to 1700 mm in the extreme south

The banks of the Blue Nile are very steep and liable for bank failure and erosion. Atbara river has steep gradients and deeply incised in its substratum. The Dinder and Rahad rivers are characterized by erosion and sedimentation along their banks and bed. Sobat-Bara Akobo-Pibor, its landscape is flat with some depressions and suffers from floods and inundation. The Main Nile, from Khartoum to Aswan High Dam suffers from sedimentation, i)(lnk erosion. and sand encroachment. Over grazing of the grassland resulted in ueur(Juatiol1 of the watershed. EffiCiency of Roscircs, Scnnm and Khashm 01 Girbo darns and their reservoirs are reduced due to siltation.

Therefore, there is a need to address a comprehensive and integrated watershed management and the first assignment in Sudan's TOR (8) is going to cover two of the selected five sub-basins, 1. Seti!. Bahr salam and Atbara up to the confluence with the Main Nile; 2. Dinder and Rahad up to their confluence with the Blue Nile: 3 the Blue Nile, 4. Baro-Akobo-Pipor-Sobat, 5. Main Nile between Khartoum and Aswan, In addition to study sedimentation in reservoirs, off-takes of the pumps stations. bank erosion, and sedimentation by sand encroachment.

Results and Recommendations for EN Countries

The most Important truth about the catchment area of EN countries is that Sudan lives downstream from Ethiopia and upstream from Egypt. The eroded soils from Ethiopian's catchment area deposited through the reservoirs of Roseires. Sennar, Khashm el Glrba dams in Sudan and Aswan High dam In Egypt. From the pre-mentioned TORs of EI\j countries, careful management and protection of soil is necessary to preserve soil from erosion, and it is important to look at the entire area as one unit, which the catchments do not respect the political boundaries.

Generaily, the available methods of redUCing reservoir sedimentation are either by retention in the catchment area or by removing from reservoirs (10). Among the second methods, flushing sediment through outlet works within the dam body. However, this technique is only effective under certain favorable conditions and is not universally applicable which its efficiency depends on many factors. These factors are: sediment size, site conditions (Iength width- depth) to avoid the related structural damage. hydrology and sedimentology of the basin, shape and storage of reservoirs, drawdown (full- partial). outlets (level-discharge), operation considerations (water and power demands). and downstream impacts (1). Another method is to build secondary dam (as check dam or gravel basin) near the reservoir inlet to retain the bed load and clear its lake periodically to prevent its sedimentation. Another one is the reservoir dredging either from the shore or from a boat and use the removed material as dam Wier. Also according to Chinese experience at Loess Plateau region, the construction of small earth dams (key, warping, and check) by hydraulic-fill method; aiong steep gullies lead to preserve soil from erosion. and create farmland that improve the social and economic levels.

10 Hence, the most sediment of EN countries comes from the Abyssinian highlands through Blue Nile and Atbara River, it is highly recommended to start a pilot project through EN countries as following: • In Ethiopia, construction of some earth dams (key, warping, and check) along some tributaries of blue and Atbara rivers to control sediment movement. According to (11), the average gradient of the Blue Nile and Atbara river into Ethiopian boundaries is about 1.5 m/km. It is not suitable for dam construction except three sites. They are shown in circular shape in figure (6), (shafartac - kutai - demetcha) at junctions of Blue River with Uema - muger - demetcha) tributaries, in addition to some sites along SeUt, Bahr Salam tributaries of the Atbara River. The suggested project will decrease the sediment through Sennar, Roseires and Khashm el Girba dams. The proposed dam height is bout 30 meters with slopes 1 :4 to decrease the effect of hydro pressure on core and slopes and to increase the efficiency of the reservoir, which its estimated storage is about 0.5 km3. The proposed cross section is shown in figure (7), which can be easily constructed using hydraulic-fill technique. This project will lead to improve the economic and social standards.

• • Figure (7): the recommended key dam cross section • In Sudan, its reservoirs sedimentation problems must be investigated for Flushing sediment application. The world experience shows that the reservoir water levels should be lowered during flood season to flood control level. This condition provides the most effective conditions for sediment flushing that becomes effective when the depOSited sediment reaches the proximity of the dam and in most cases it Will be many years after commissioning. At that time the flow is carrying most of its sediment load. • As a Simple and effective solution for reservoir sedimentation, JFE holding company from Japan (13) developed a comprehensive technology based on the concept that the entire sediment transport region from the river basin to the shoreline forms a "sediment transport system". JFE proposes a hydro-pipe sediment removal technology as shown in figure (8) which dredges sediment from the dam reservoir and releases it into the downstream region. By combining sediment dredging pipe (hydro pipe) that uses the hydrostatic pressure to suck sediment from the reservoir, and sediment flush gate through dam body, this system enables efficient discharge of sediment over a wide area without large reductions in the dam water level.

Figure (8); hydro-pipe system dredging system. after (13)

• And for Egypt, Nasser Lake problem in Sudan and Egypt, it is recommended to study the application of the flushing-sediment technique through formation of density flow as that used for Xiaolangdi reservoir on the YR considering that there are some differences between the two dams in their engineering (design - hydraulic) and

11 operation policy. Density flow is a special flow pattern of high sediment laden rivers which its flow is going to submerge under the clear water due to large difference of their densities which is important to transport reservoir sediments as shown in figure (9). The method needs three major conditions: the big flow, the hyper-sediment load especially fine silts, and hydrodynamic process. It was used for the first time to formulate artificial density flow to flush sediment out of Xiaolangdi reservoir as mentioned in the Chinese experiment. Which the sediment was flushed through Sanmenxia reservoir and transferred the sediment-laden flow into Xiaolangdi reservoir; provide additional sediments and hydrodynamics for transportation. Hyper sediment undercurrent reached Xiaolangdi dam and released through its discharge tunnels.

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Figure (9); density current in a reservoir with: i-approach flow,2-delta,3-plunging point,4 floating debris,5-density current,6-clear water,7-sediment deposited,8-outlet,9-dam,A river,S clear reservoir-recirculation, after (10)

Flushing sediment through a reservoir was practiced successfully and found to be inexpensive in many cases. To satisfy the water demand and water consumed in the flushing operation, two models combining the reservoir simulation model and the sediment flushing model should be established (14).

According to the previous pilot projects through EN countries, it is clear that the resulted sediments can be used for development into different ways (creating farmlands along tributaries, reclaiming desert areas near reservoirs) which enhance the cultivation and increase the economic and social standards. Finally, for EN countries, Economic and Financial Analysis should be done for these pilot projects to assist in the identification and selection of the most favourable sediment management method. The success of the results will encourage the private sector into each country to invest in this field.

References

"Flushing of Sediments from Reservoirs", by: Dr W. Rodney White HR Wallingford, UK, ''http://www.dams.org/docs/kbase/contrib/opt184.pdf,'' "Yellow River: Geographic and Historical Settings", by George Leung's, "Yellow river home page", .. http://www.cis.umassd.edu/-gleung/geofo/ysh32en.html.. "Reclamation and Sediment Control in the Middle Yellow River Valley," Water International, March 1996,"Yellow river home page", ''http://www.cis.umassd.edu/-gleung/ geofol ysh32en.html" "12 reasons to exclude large hydro from renewable initiative" ,International rivers network, Berkeley, CA USA, "www.irn.org,,". "Engineering and design Channel Stability Assessment for Flood Control Projects", department of the army, u.s. army corps of engineers,1 000, oct., 1994. CECW-EH-D

12 Washington. DC 20314," http://www.usace.army.mil/inet/usace-docs/eng manuals/em1110-2-1418/toc.htm". "Strategic Action Program-Overview", Nile basin initiative, may 2001,Nile Water Sector, Egypt, [email protected] "Eastern Nile Subsidiary Action Program, IDEN - Integrated Watershed Management Project", Terms Of Reference For Egypt, Draft For Discussion - 15 April 2003, Nile Water Sector, Egypt, nwater@idsc,net.eg "Eastern f\lile Subsidiary Action Program, DEN - Integrated Watershed Management Project, Draft TORs For Sudan, Draft For Discussion - 15 April 2003, Nile Water Sector, Egypt, nwater@idsc,net.eg "Eastern Nile Subsidiary Action Program, IDEN - Integrated Watershed Management Project, Terms Of Reference For Egypt", Draft For Discussion -15 April 2003, Nile Water Sector, Egypt, [email protected] "Reservoir sedimentation", Dam Hydraulics, by: D.L.Vischer, W.H,Hager, 1996. "Nile basin encyclopaedia", by Hurst, Black. and Semica, Cairo, vol. 9, 1965 "National atlas of Ethiopia-drainage and river basins" by Ethiopian mapping authority. first edition,1998 "dam sediment removal.", Environmental Report 2003, JFE holding inc., Japan, .. http://www.jfe-holdings.co.jp/en/environment/pdf/2003/5o3.pdf, "Optimization of operation rule curves and flushing schedule in a reservoir", Fi-John Chang, Jihn-Sung Lai, U-Shan Kao, Volume 17, Issue 8, 2003. Pages 1623 1640, Copyright © 2003 John Wiley &Sons, Ltd