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International Network on

Sustainable Water Management i n D e v e l o p i n g C o u n t r i e s

SWINDONex)(ceed

International Network on

Sustainable Water Management i n D e v e l o p i n g C o u n t r i e s

SWINDONex)(ceed

Control and Mitigation of Drinking Water Intake Problems along Nile River

Gamal A. Sallam, Ass. Professor Head of Hydraulic Structures Department

Nile Research Institute, National Water Research Center

Intake structures are constructed to withdraw water from rivers, lakes, and other bodies of water for communities and industries. Intakes usually are combined with pumping stations to deliver water to reservoirs and treatment plants. Intake location and design must account for phenomena that could affect performance and endanger the structure; such as sedimentation, scour, and waves. Intakes are designed depending on, amount of water to be diverted, amount of silt carried by the river, and geomorphology of the river.

Drinking water stations

3812 well stations 817 compact stations

153 candidate stations 21 desalination units

Production of drinking water / day

25 million m 3/ day

The subscribers in the service of drinking water

12 million subscribers

Number of population is about 90 million.

Aswan

Nasser LAKE

The Nile River is regarded as the longest river in the world. It is 6,853 km long. The Nile is an "international" river as its water resources are shared by eleven countries, namely, Tanzania, Uganda, Rwanda, Burundi, Congo-Kinshasa, Kenya, Ethiopia, Eritrea, South Sudan, Sudan and Egypt. In particular, the Nile is the primary water source of Egypt and Sudan

Water management in Egypt depends on a complex set of infrastructure along the entire length of Nile River. The key element of this infrastructure is the Aswan High Dam. The dam stores (90 billion cubic meter) more than one and a half the average annual flow of the Nile River (55.5 billion cubic meter) per year. thus Aswan High Dam providing a high level of regulation compared to other regulated rivers in the world. Downstream of the Aswan Dam, there are seven barrages to increase the river's water level so that it can flow into irrigation canals. Egypt depends for 97% of its water supply on the Nile. Rainfall is minimal at 18 mm per year, occurring mainly during autumn and winter time.

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Water Resources in Egypt

Type of Water Resources

Quantity in billion m³ per year

Nile River 55.5

Precipitation 1.8

Fossil Groundwater 1

Sea Water Desalination 0.1

Sum 58.4

Reuse of Spilled Water Resources

Groundwater Extraction 2.3

Wastewater Reuse 2.9

Agricultural Drainage Reuse 7.5

Sum 12.7

It is forecasted that in 2025 the population of Egypt will increase to about 100 million, leading to a decrease in per capita water availability from 800 to 600 m3 per year assuming that total water availability remains constant. Developments in the riparian countries could reduce water availability to Egypt. Seawater desalination, which already is used in some resorts on the Red Sea, is likely to become an increasingly important source for water supply in coastal areas of Egypt. Brackish water desalination for irrigation may also become an important source.

Sediment

Control

Water

Treatment

Structures Source

1.Sluice Gates

2. Lateral

3.Bend

4.Bottom

5. Combined

1.Floating

2.Submerged

3.Tower

4.Shore

5.Pier

1.Lateral

2.Frontal

3.Bottom

4. Overhead

1. River

2. Canal

3. Reservoir

4. Lake

A river intake consists of a conduit provided with a gravity well. The conduit is supported on pillars 1-2m above the bottom to prevent entry of silt. Also it is kept 1m below the top surface to avoid entry of floating particles. Velocity should be kept less than 0.15 m/s to prevent entry of small fish. River intake structure should be constructed a way from the point of sewage disposal or industrial waste water disposal. River intakes are need screens to exclude large floating matter. The bottom of the river intake must be sufficiently stable.

Unprotected river intake protected river intake

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Pumped river water intake

Movable River intake

Intake tower Water intake through hinged tubes

Bank river intake using infiltration drains Pumping station in embankment water abstraction in the river bed

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Pumping station mounted on floating platform in the river Intake using side channel and screen

The main function of intakes is to : provide highest quality of water from a source. protect pipes and pumps from damaging or clogging by wave action, and floating bodies.

Intake Pipe

To WTP

to town service Water system

Changing the river flow path from time to time. Sediment and Erosion problems. Flow regime variation: changing the flow rate changing the water level The presence of tributary disturbing and complicating the flow pattern Orientation problems Navigation problems Water quality (Pollution problems ) Effect floods and wave to the structure Erosion of the embankment damaging the suction pipes.

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Sediment clogging the intake pipes The water treatment processes could suspended because the raw water turbidity is high

Source of pollution at front of water intake

In general, raw water quality is influenced by both natural and human use factors. Important natural factors include wildlife, climate, topography, geology and vegetation. Human use factors include point sources (e.g., municipal and industrial wastewater discharges) and non-point sources (e.g., urban and agricultural runoff, including agrochemicals, livestock or recreational use). Water quality problems related to water are muddy and polluted water. Water quality control is a very important consideration in withdrawal from water body. By decreasing the contamination of the source water, the amount of treatment required is reduced. This may reduce the production of treatment by-products and minimize operational costs .

Hazards that should be taken into consideration include: sewage discharges industrial discharges chemical use (agricultural pesticides) human access (e.g., recreational activity) wildlife and livestock; inadequate buffer zones and vegetation, soil erosion and failure of sediment traps storm water flows geology (naturally occurring chemicals) climatic and seasonal variations (e.g., heavy rainfalls, and natural disasters. lack of alternative water sources unsuitable intake location

The performances of some water intakes systems along Nile River are not as per desired level, some of these intakes have problems. In some cases, the raw water turbidity is high, the quality of raw water is poor especially for river direct intake systems. Some of the intake systems are clogged with suspended materials; pointing to deficiencies in their designs. At times the water treatment processes are suspended because the incoming raw water is turbid to be treated. Moreover, there is a need for measures in place to divert excess sediments and all eroded materials at river intakes, especially in the rainy season. The main objectives are: 1. For future intake installations: to be designed for best hydraulic performance in relation to; river

flows and processes, channel shifting, sedimentation, scour, and waves. In addition to give the best water quality, maximizing pump performance, minimizing maintenance costs and increasing the long-term lifespan of pump stations.

2. For the existing water intakes: control and mitigate losses of the existing water intakes.

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The basic criteria for selection of intake locations are: An intake should be located on a stable reach without frequent wandering of a flow path. The concave bank of a bend is an ideal location for an intake because it can divert relatively clear water with low sediment concentration. An intake on a straight reach is usually not favorable for preventing sediment from entering it. An intake should be as far as possible from the confluence of a tributary to avoid disturbing and complicating the flow pattern in front of the intake. Heavy water currents should not strike the intake directly. Intake should be located at such a situation where sufficient quantity of water remains available under all the circumstances.

It should not be located in navigation channels.

Flood waters should not be concentrated towards the intake.

Intake should be located on up stream side of the town. Water will not be contaminated on this side due to sewage disposal of the city.

Site should be well connected by good type of roads.

In spite of all the effort and precautions, problems may still be there due to natural causes. Temperature, seasonal variations in quantity and quality, wind currents etc. may affect the stability and safety of the intake works.

Intake should be sufficiently heavy so it will not be washed away by heavy water currents.

Intake should be designed to withstand all the expected forces.

The foundation of the intake should be taken sufficiently deep, this will avoid overturning of the structure.

Strainers in the form of wire mesh should be provided on all the intake inlets.

protection inlet against damages (navigation, floods).

raw water quality considerations (avoid coarse floating materials and fish).

Pump stations that operate with unsuitable approach flow hydraulics can suffer damage from cavitations, vibration, and may be unable to meet design requirements. Focused analysis using physical and computer models provide key information for optimal pump design, thus improving performance, reducing maintenance costs, and increasing the lifespan of equipment.

Whether water is drawn from surface or underground sources, it is important that the characteristics of the local catchment or aquifer are understood and that the scenarios that could lead to water pollution are identified and managed. The extent to which potentially polluting activities in the catchment can be reduced may appear to be limited by competition for water and pressure for increased development in the catchment. However, introducing good practice in containment of hazards is often possible without substantially restricting activities, and collaboration between stakeholders may be a powerful tool to reduce pollution without reducing beneficial development.

Effective resource and source protection includes : promoting awareness in the community of the impact of human activity on water quality. registration of chemicals used in catchments. specific protective requirements for chemical industry. control of human activities within water resources. control of wastewater effluents. regular inspections of water resources. diversion of local storm water flows. watershed management from polluting activities. proper well construction, including casing, sealing and wellhead security. proper location of wells. security from access by animals. security to prevent unauthorized access and tampering. use of available water storage during and after periods of heavy rainfall. appropriate choice of off-take depth from reservoirs.

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It is strongly recommended to: Using the mobile-bed physical models to finalize intake locations, orient structures to minimize sedimentation and scour, and design river training structures.

Using the numerical 3-D (computational fluid dynamics) modeling as a hydraulic design-aid tool to replace or complement physical modeling. Using maps, images, and field inspection to assess suitability of intake locations, based on river morphology and processes including, erosion, and sedimentation. Also, using Field studies and measurements to evaluate performance of existing and newly constructed intakes.

The steel bridge carry the intake pipes at Neda water intake, which is located in sohag governorate

Sediment was collected at front of Neda water intake pipes Intake using side channel on the east side of Nile River

Using barrels at front of side channel to prevent entry of floating materials Assuit water intake on the west side of Nile River

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Assuit water intake on the west side of Nile River Matai water intake located on the River Nile down stream Assuit Barrage (at Km. 200 South of Cairo), It experienced chronic problems with bed sediment buildup at its intake.

Sedimentation problem is relatively common along the Nile River. Matai water intake located on the River Nile down stream Assuit Barrage (at Km. 200 South of Cairo), It has a problem of sedimentation at its intake. The reason for that is the highly variable flow regime (flow rates; usually vary between very low (60 million.m3/d) and very high (275 million.m3/d) during a year. The consequence of the variable flow regime is significant variations of the river morphology. So far the application of design engineering could not prevent all sedimentation problems of such intakes.

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The hydrographic and land survey of the River Nile at Matay water intake site have been carried out.

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Distance (m)

Level

(m)

SEC-7

EastWest

Max. W.L (33.15)

Bed Level (2006)

Bed Level (1995)Total 29 m2/m/year

Sediment

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• Matai water intake is badly located; There are 2 islands at the front of the intake. The river bed at the west side upstream the intake is much higher (30.50 MSL), where it goes above the minimum water level (29.74 MSL). • The withdrawing intake's flow directs the suspended materials towards the intake, which causes silt accumulation at the front of water intake. • The extending of steel bridge, which caries the intake's inlet pipes for a long distance (about 50 m across the river), causes the accumulation of bed sediment around it at the front of water intake. • The variability of flow regime of the River Nile post construction of the High Aswan Dam where the discharges decrease dramatically. Also, vary of flow rates between very low and very high in a season. • Dredging the River Nile for navigation purposes is considered the main factor for sediment problems at the front of the intakes along the River Nile.

• The first solution and the most common one is the periodic dredging, that can be done by removing the sediment at front of the water intake, by means of dredging system which is dedicated to the water intake. The total accumulated sediment at front of water intake for a period 10 years is about 70000 m3. The capital cost to dredge this volume of accumulated sediment is about 2,100000 L.E.

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intake location

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•The second alternative is changing the location of the intake pipes. The new proposed location is to the west side of the River Nile down stream the water intake. The estimated capital cost of this alternative is approximately about 5,000000 L.E. This including (pipes cost, steel bridge construction, and pipes installation).

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The third alternative is the sediment control modifications by "guide-wall" extending partially across the river. This submerged guide-wall would function to concentrate flow past the intake, such that the discharge of flow water will be available at the intake under all river flow conditions. The estimated capital cost of this alternative is approximately about 4,000000 L.E. It includes (field data collection, physical model, mathematical model, and guide wall construction).

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The intakes on the River Nile, especially reach 4 (down stream Assuit to Upstream Delta Barrages) are more exposed to sedimentation problems. Matai water intake has a history of consistent problems with river sediment buildup in front of the intake structure. Sediment at pump intakes causes problems to pumps with consequent high operating costs and undesired interruption in water supply. So, there is a need for effective removal of sediment at River Nile intakes. Sedimentation problems in some cases could be minimized through the modification of intake structure for more effective designs with due regard to local hydraulic and sediment dynamics/morphology. In cases of well designed intakes, still some degree of sedimentation is bound to occur. In such cases an effective sediment removal system would help to control localized sedimentation at the intake.

Comparing between the three alternative solutions, to solve the sediment problem at Matai water intake, I would recommend the first solution for the following reasons:

1. The first solution (i.e. periodic dredging at front of the water intake) is more effective, less in cost and the least in adverse impact on the River Nile characteristics.

2. While the second solution (i.e. changing the location of the intake pipes) is high in cost, beside that the new proposed location could be aggregated in the future.

3. Nevertheless, the third solution (i.e. submerged-wall extending across the River Nile for a long distance) is likely to create safety problems for sailing boats and ships in the Nile. It would –as well- change the River Nile characteristics.

International Network on

Sustainable Water Management i n D e v e l o p i n g C o u n t r i e s

SWINDONex)(ceed

International Network on

Sustainable Water Management i n D e v e l o p i n g C o u n t r i e s

SWINDONex)(ceed