aquatic weeds management upstream new naga hammady...

Eighteenth International Water Technology Conference, IWTC18 Sharm ElSheikh, 12-14 March 2015

264

AQUATIC WEEDS MANAGEMENT UPSTREAM NEW NAGA HAMMADY

BARRAGES

Hosam Ibrahim1, Emam A. Osman

2, T.A. El - Samman

3, and Mahmoud Zayed

4

1 Prof., Deputy director of Channel Maintenance Research Institute (CMRI), National Water

Research Center (NWRC), Kanater El-Khairiea, Kalubeia, 13621, Egypt,

[email protected].

2 Researcher, CMRI, NWRC

3 Prof., CMRI, NWRC.

4 Assistant Researcher, CMRI, NWRC.

ABSTRACT

In order to control high floods through the main Nile River stream, High Aswan Dam "HAD" was

constructed in 1968. This led to reduce the maximum annual flow discharge downstream of Old Aswan

Dam "OAD" from 911 million m3/day in 1964 to 275 million m

3/day in 2002. Accordingly, enormous high

aquatic weed infestation spots have been generating which caused many problems along the river and

various irrigation channels. Therefore, many human activity fields and economic interests have been

affected such as water losses, retardation of flow, obstruction of gates and intakes, interference with

navigation, health hazards and alteration of water physical-chemical characteristics.

Consequently, the present research was planed to investigate the aquatic weed problems upstream the

new Naga Hammady barrages which is located on the Nile River at km 362.700 downstream "OAD". The

intake structure of the installed hydropower plant suffers from severe infestation of submerged aquatic

weeds upstream the barrage which breakdowns the power plant operation for several hours daily. To

overcome such difficulty, specific barriers and trash rack upstream the old and new Naga Hammady

barrages were designed and constructed to control the floating and submerged aquatic weeds.

Several field measurements that cover a study reach of 38 km upstream the new barrages were conducted.

Apply remote sensing and GIS technologies, each of the intensity, percent of infestation, and the moving

trend of submerged aquatic weeds were identified over the study reach. Therefore, detailed design criterion

for weed control device was established. Using the collected data and based on the analysis of field and

laboratory studies, appropriate solutions were designed and constructed to prevent submerged aquatic weeds

from reaching the hydropower plant intake structure which consequently led to enhance the generated

hydroelectric power by 26% in July 2014. Moreover, to remove the deposited aquatic weeds on the trash

rack, the appropriate maintenance program for the proposed barriers was recommended.

Keywords: Aquatic weeds, Management program, Remote sensing and GIS, Barrier design

1- INTRODUCTION

Infestation of aquatic weeds can be considered as major negative effect of "HAD" and its mitigation by

means of research, testing and introduction of various control methods, management and maintenance are

enormously recommended. The annual high flood discharges - before "HAD" construction – tend to flush

aquatic weeds from the main Nile River stream and the branched irrigation channels. As most of the

sediment is trapped in Nasser Lake after "HAD" construction, water releases have become clear and free of

suspended solids. This in turn encouraged weed growth due to water surface fluctuations and deeper

penetration of sunlight in water. Consequently, numerous problems were emerged such as water losses by

transpiration, changes in water quality, health hazards, interference with navigation waterway and the

concern problems with the accumulation of aquatic weeds in the intakes of hydro powers and pumps. The

latter influence can be considered as the most important inconvenience problem along the Nile River main

stream. An example for that is the loss in the generated electric power which was reduced in 2011 by 38%


265

due to blocking the frontal inlet of the hydropower plant by aquatic weeds. For this reason, mitigating the

aquatic weed problems upstream the new Naga Hammady barrages would be considered during the present

paper.

A detailed study for solving aquatic weeds problems upstream the new Isna barrages was conducted by

the Channel Maintenance Research Institute "CMRI" by Hosam Ibrahim et al (2004) [4]. In this study, the

aquatic weeds infestation was monitored along enough river reach for one year, and then the required

barriers for mitigating the aquatic weed problems was designed and implemented. Additional study was

carried out by "CMRI" (2011) [2] to monitor the submerged aquatic weeds infestation along 38 km of the

Nile River upstream the new Naga Hammady barrages which is the subject of the present paper. In this

study, the produced hydraulic characteristics by Chow, V.T. (1959) [3] were applied for several cross

sections allover the study reach.

The recent developments in computer hardware and software allow for integrating remote sensing "RS"

and geographic information systems "GIS" to assist sustainable development and management of water

resources in easy, flexible and accurate way. With this in mind, the submerged aquatic weed infestation was

identified within the study reach which extends for 38 km upstream the new Naga Hammady barrages. The

aquatic weed monitoring method was applied and the percentage of infestation was evaluated in the study

reach. This revealed that Ceratophyllum demersum weed is the dominant species with the highest infestation

at the shoreline of the main stream, and the shoreline bed material was characterized by clay loamy soil.

This type of weed constrained water flow by blocking the frontal inlet of the hydropower plant and

consequently caused serious problems. Remote sensing and GIS technologies were applied to distinguish

and map the distribution of aquatic weeds within the studied reach.

Several experimental investigations were carried out concerning the parameters that affect the magnitude

of the drag forces exerted by moving fluid on floating circular cylinder placed across a channel. Change of

drag coefficient with the Froude number and the relative depth of the approaching flow was examined by

Hsieh, T. (1966) [5], Khalil, M.B. (1969) [6], and Ko, S. C. et al, (1972) [7]. These concluded that drag

coefficient CD depended mainly upon Froude number irrespective of Reynolds number.

FD = ½ ×CD × ρ × V2 × Ls ×b……………………………………………..………………(1)

Where:

FD is the drag force:

CD is the drag coefficient (dimensionless);

Ls is the submerged length,

b is the unit breadth;

V is the maximum measured water velocity at cross section;

ρ is the mass density of water.

On the other hand, there is acting pressure on the barriers due the floating aquatic weeds which is mainly

consists of "Water Hyacinth". This impact was estimated as shearing force due to the accumulated weeds in

front of barrier which was evaluated by Ali, R.M. (2000) [1] as follows:

Fτw = (V*w)2 . ρ /g ………………………………………………………………………….(2)

Where:

Fτw is shear force;

V*wis shear velocity;

ρ is mass density of water;

g is the acceleration due to gravity;


266

The above mentioned 2 equations were used for design weed control barriers upstream new Naga Hammady

barrages. Hence, the aim of this study is to investigate, design, and construct specific weed control system of

barriers and trash rack upstream the old and new Naga Hammady barrages respectively.

2- DESCRIPTION OF THE STUDY AREA The new Naga Hammady barrage was constructed on the main Nile River stream at Km 362.700

downstream of "OAD" and at 3.2 km downstream the existed one. Its total length is 325 m and consists of a

first class navigation lock, low head hydropower plant provided with 4 bulb-turbines and sluiceway which is

equipped with 7 radial gates of 17 m width and 13.5 m height each. At normal operation - except for high

flood discharge – the water surface level upstream the new barrage is maintained at (65.90) m. The

Hydropower plant structure is adjacent to the spillway on left bank of Nile river. It consists of four bulb

turbines each bulb turbine designed to generate 16 Mega watt, design head 5.7 m, design discharge 320

m3/sec/unit, and started to be connected to the Egyptian electricity network in Feb 2008. The average

generated power for each bulb turbine in July 2011 was 9.88 Mega Watt, there was a reduction in the

generated power 38% from blocking the frontal inlet of the hydroelectric power plant by aquatic weeds. The

impending aquatic weeds from the upstream urges to close the hydropower plant for several hours daily and

consequently release the total discharge from the spillway only without electric generation. The selected

study reach is located along 38 km upstream the new barrages which comprises several islands located in the

studied reach which determinate two sub courses water as shown in Figure (1). To facilitate the planed field

works, the main studied reach was divided to five smaller sub-reaches as shown in Table (1) and Figure (2)

while the located islands within the Study reach are listed in Table (2).

Figure (1): The Selected Study Reach


267

First reach Seond reach

Fourth reach

Fifth reach

Third reach

Table (1): Sub-Reaches Boundaries

Reach

No.

Distance (km) Area

(m2)

Length

(km) From

(km)

To

(km)

First 324.500 330.500 2854079 6.000

Second 330.500 335.200 2853917 4.700

Third 335.200 347.000 2854126 11.800

Fourth 347.000 359.500 2854696 12.500

Fifth 359.500 362.500 2855181 3.000

Total monitored length (km) 14271999 38.000

Figure (2): Location of the Five Sub-Reaches

Table (2): Located Islands within the Study Reach

No Island name Island location

Distance (km) Island length

(m2) From

(km)

To

(km)

1 El Akool island First reach 324.500 328.300 3.800

2 El Hamodia island First reach 326.000 330.300 4.300

3 El Shawaria island Second reach 330.800 335.000 4.200

4 El Kanawia island Third reach 337.500 341.500 4.000

5 El Sahel island Fourth reach 346.900 348.700 1.800

6 El Kalh island Fourth reach 348.000 352.000 4.000

7 El Wasta island Fourth reach 358.000 359.400 1.400

Total islands length (km) 23.500

3- METHODOLOGY

To achieve the objective of the present study for controlling the accumulated aquatic weeds upstream the

hydropower trash rack, extensive field measurements were carried out to detect the hydraulic characteristics

of the study reach which can be summarized as follows:


268

Survey and monitor aquatic weeds infestation allover the entire reach of 38 km length upstream the new

Naga Hammady barrages.

Measuring longitudinal velocity profiles along ten cross sections located upstream the new and old Naga

Hammady barrage by using electro magnetic current meter. Velocity measurements for each cross

section were carried out at 1.0 and 2.0 m depths from water surface. Locations of the velocity measuring

cross sections are shown in Figures (3 and 4). The plotted locations in those Figures are the distances

(km) upstream El-Roda gauge station which is located at 927.000 km downstream "OAD".

Figure (3): Locations of Measured Velocities and Submerged Weeds Infestation between the New and Old

Barrages


269

Figure (4): Locations of Measured velocities and submerged Weeds Infestation Upstream Old Naga Hammady

Barrages

Using Echo Sounder, seventy cross sections were surveyed to detect the percentage of the submerged

weeds infestation along the study reach.

Using weed sampling device, intensity of moving submerged aquatic weeds along the upper flow layer

up to 4.0 m under water surface level were measured in the study sub-reaches.

Using floating wood pieces, the moving trend of submerged aquatic weeds were identified in the studied

reaches.

4- RESULTS AND DISCUSSIONS

4-1 Field Measurements Results

The attainable results from the conducted measurements can be summarised as follows:

4-1-1 Velocity distribution

The measured velocity profiles and aquatic weeds infestations showed that the maximum stirred submerged

weeds are within the main flow stream through about 4.0 m depth under water surface. More over, water

velocity distributions along cross section (2) at km 361.300 downstream "OAD" - which is located at 1.400

km upstream the new Naga Hammady barrages – are shown in Figure (5). This showed that the measured

velocity at 1.0 m depth (V1) is higher than that at 2.0 m depth (V2). While Table (3) lists the main variations

between the measured flow velocities at 1.0 and 2.0 m respectively for the measured 10 cross sections

allover the study reach. This revealed that the measured velocity at 1.0 m is much higher than that at 2.0 m

depth which obviously is due to the existence of the submerged aquatic weeds. Moreover, Table (3) also

listed that the overall average of the measured flow velocity at 1.0 m depth is about 0.825 m/s which is about

2.1 times that at 2.0 m depth which is about 0.392 m/s as listed in Table (3).


270

R. Bank

Figure (5): Measured Velocity Profiles at 1.400 km Upstream the New Barrages

Table (3): Variations in the Measured Velocities

Sec.

No

Distance

Downstream

"OAD"

(km)

Reach

No.

Distance

Upstream the

new barrages

(km)

Mean velocity variation (m/s)

At 1.0 m flow

depth

At 2.0 m flow

depth

1 350.000 Fourth 12.700 0.85 0.67

2 351.300 Fourth 11.400 0.85 0.57

3 354.500 Fourth 8.200 0.82 0.58

4 355.000 Fourth 7.700 0.73 0.21

5 355.500 Fourth 7.200 0.83 0.43

6 356.000 Fourth 6.700 0.80 0.42

7 357.000 Fourth 5.700 0.83 0.42

8 358.500 Fourth 4.200 0.79 0.15

9 361.300 Fifth 1.400 0.83 0.25

10 362.300 Fifth 0.400 0.82 0.22

Main Average flow velocity (m/s) 0.825 0.392

4-1-2 Aquatic weeds survey

The attainable results for the monitored aquatic weeds through the entire five study sub-reaches along

seventy cross sections by using the Echo Sounder are listed in Table (4). In this Table, the total infested

area by submerged aquatic weeds on the right and left shoreline along each sub-reach was determined. This

revealed that the total infested area by submerged aquatic weeds on the right and left shoreline of the studied

reaches is 2256000 m2 as shown in Table (4).


271

Table (4): Infested Areas on Both Shorelines

No Reach Distance (km) Mea

n

River

width

(m)

Infested

area on

right

shoreline

(m2)

Infestation

Percent

Infested

area on

left

shoreline

(m2)

Infestation

Percent

(%)

From

(km)

To

(km)

1

First

324.500 326.000 - - - - -

2 326.000 330.500 700 600000 19 % - -

3 Second

330.500 331.500 500 1000 0.2 % 20000 4 %

4 331.500 335.200 575 12000 0.6 % 370000 17.4 %

5

Third

335.200 339.000 510 60000 4.2 % 17000 1.2 %

6 338.000 341.500 580 57000 2.8 % 6000 0.3 %

7 341.500 345.500 450 400000 22.2 % 8000 0.5 %

8 345.500 347.000 610 76500 8.4% 6500 0.7 %

9

Fourth

347.000 348.000 810 10000 1.2 % 12000 1.5 %

10 348.000 349.000 810 10500 1.3 % 15000 1.8 %

11 449.000 350.000 810 14500 1.8 % 18000 2.2 %

12 350.000 351.000 870 9500 1.1 % 74000 8.5 %

13 351.000 352.000 870 10500 1.2 % 76000 8.7 %

14 352.000 353.000 630 4500 0.7 % 25000 4 %

15 353.000 354.000 630 5500 0.9 % 25000 4 %

16 354.000 355.000 430 5500 1.3 % 80000 18.6 %

17 355.000 356.000 500 7500 1.5 % 60000 12 %

18 356.000 357.000 500 8500 1.7 % 60000 12 %

19 357.000 358.500 700 7500 0.7 % 60000 5.7 %

20 358.500 359.500 800 8000 1 % - -

21 Fifth 359.500 362.500 700 8000 3.8 % 7000 3.3 %

Sub-Total Infested Areas 1316500 939500

Total Infested Area 2256000

Moreover, the total infested areas by submerged aquatic weeds on the shoreline of the seven located islands

within the five sub-reaches were monitored as listed in Table (5).

Table (5): Monitored Infested Area on the islands Shoreline

No Island name Island

location

Distance (km) Infested

area

(m2)

From

(km)

To

(km)

1 El Akool island First reach 324.500 328.300 298000

2 El Hamodia island First reach 326.000 330.300 68000

3 El Shawaria island Second reach 330.800 335.000 1112500

4 El Kanawia island Third reach 337.500 341.500 720000

5 El Sahel island Fourth reach 346.900 348.700 560000

6 El Kalh island Fourth reach 348.000 352.000 1505000

7 El Wasta island Fourth reach 358.000 359.400 195000

Total infested area on the islands shoreline 4458500

This showed that the total infested area by submerged aquatic weeds on the shorelines of the seven islands is

4458500 m2 as shown in Table (5). The mean percentage of infestation was 0.29 % by ditch bank weeds

while no floating weeds were detected along the entire reaches. It can be concluded from the monitoring

investigation that the studied reaches has been suffering from a remarkable amount of the aquatic weeds

infestation.


272

4-1-3 Submerged weeds intensity

The intensity of moving submerged aquatic weeds was measured along the upper 4.0 m layer depth under

water surface in the study reach by using weed sampling device. The device consists of 4.0 m rode length

which is fixed on floating cylinder hollow to control the device balance and float on the river flow surface.

There are two movable light rods 1.0 m length each which are installed on the long rod, each light rod was

supplied with several bolts 0.1 m length for capturing the moving submerged weeds at different water

depths.

Submerged weeds intensity was identified by using the device at four different water depths from water

surface of 0.5 m, 1.0 m, 2.5 m, and 4.0 m in turn for thirty minutes time at each water depth. The device was

examined in different locations along cross sections (1 and 2) as shown in Figure (3) directly upstream the

new barrages, and cross section (5) directly upstream the old barrages. The captured submerged weeds

around the bolts were collected and weighted for each water depth. The collected weight of weeds in thirty

minutes directly upstream the new barrage was 1450 gram at water depth 0.5 m and 650 gram at 1.0 m water

depth while no weeds were detected at 2.5 m and 4.0 m. While the collected weight of weeds in thirty

minutes directly upstream the old barrages was 1400 gram at 0.5 m flow depth and 475 gram at 1.0 m water

depth while no weeds were detected at 2.5 m and 4.0 m depth.

The huge amount of moving submerged weeds with river flow was estimated by 25 tons per day directly

upstream the new barrages, and 23 tons per day directly upstream the old barrages which are accumulated at

the hydropower plant intake structure and trash rack. It can be concluded that, the submerged weeds in the

studied reach moved with river flow along the upper layer of water surface (2.0 m depth).

4-1-4 Submerged weeds moving trends

The moving trend of submerged aquatic weeds was identified in different locations of the study area by

using pieces of floating woods. Movement of six floating pieces were monitored from upstream El-Wasta

island at km 357.500 downstream of "OAD" to the old barrages by using surveying device as shown in

Figure (6). The floating pieces were placed at equal distances between right bank and left bank of the river

stream. The first, second and third floating pieces tracks (1), (2) and (3) directly moved toward the old

barrages between the right bank and El-Wasta island. The fourth floating piece track (4) moved directly

toward the old barrages between the left bank and El-Wasta island. While the fifth and sixth floating pieces

track (5) and (6) directly moved toward the old barrage navigation lock between the left bank and El-Wasta

island. This concluded that, 67 % of the floating weeds moved toward the old barrage, and 33 % moved

toward the old barrages navigation lock.

Movement of the five floating pieces were then monitored in the third sub-reach from upstream El-kalh

island at km 349.000 downstream of "OAD" to the end of the island at km 351.000 by using surveying

device as shown in Figure (7). The floating pieces were placed at equal distances between left bank and El-

kalh Island. The first and second floating pieces tracks (1) and (2) directly moved toward the shoreline of El-

Kalh island. The third, fourth and fifth floating piece tracks (3), (4) and (5) directly followed the stream

flow. It can be concluded that, 60 % of floating aquatic weeds in the study reach moved directly with the

stream flow, and 40 % of floating aquatic weeds in the study reach moved toward the shoreline of El-Kalh

Island.


273

Old Naga HamadeBarrage

Track1

Track3

Track2

Track4Track6

Figure (6): Aquatic Weeds Track Lines within the Second Sub-Reach Directly

Upstream the Old Barrages

Track1

Track 2Track 3Track 4Track 5

Figure (7): Tracks of Aquatic Weeds at El-Kalh island.

4-2 Monitoring by Using "RS" and "GIS"

Monitoring and classifying aquatic weeds were additionally carried out through the entire length of the

study reaches by using Remote Sensing "RS" and "GIS". Submerged and ditch bank aquatic weeds

infestations were identified in the reaches. The evaluation showed that the floating aquatic weeds have not


274

found allover the entire studied area. For the submerged aquatic weeds the Moriophyllum spicatum and

Ceratophyllum demersum were the dominant species.

While for the ditch-bank aquatic weeds, the Hycoscyamus muticus and Rumex dentatus were the dominant

species. The current study focuses on the acquisition of satellite images (LANDSAT Thematic Mapper) of

the studied area. Landsate satellite image with global positioning system "GPS" and geographic information

system "GIS" technologies were used to distinguish and map the distribution of submerged and ditch bank

aquatic weeds in the study reaches in the following sequences:

Spot 5 imagery was used with medium accuracy from 1 to 5 m for detecting and classifying the aquatic

weeds.

Arc Gis 8.1, ERADS imagine and AutoCAD were used to prepare, digitize and analyze the images for

layout the maps.

Three methods for detecting and classifying the images were used as follows:

A- Supervised and unsupervised classifying method.

B- Band ratio by Band calculation.

C- NDVI (Normalized different vegetation index).

The process of these images and the implementation and application of "RS" were carried out to

estimate the aquatic weeds infestation. Table (6) shows the water surface area for the five studied

reaches, the infested area by submerged and ditch bank weeds, and the percentage of infestation for

each reach. The total infested area by submerged and ditch-bank weeds was estimated by 2854536 m2,

the submerged weeds 1901247 m2, and the ditch bank weeds 953289 m

2. The total water area for the

studied area was 14271999 m2, the total infested area by submerged and ditch-bank weeds was 2854536

m2, and the results revealed that the percentage of submerged and ditch-bank weeds infestation was

20.0% in August 2011. Also Figure (8) show the satellite images for the study area from new Naga-

Hammady barrages to 38.0 kilometer upstream the barrages in August 2011.

Table (6): Monitored Infested Areas

Reach

No.

Distance (km) Area

(m2)

Infested

area

(m2)

Infeststion

intensity

From

(km)

To

(km)

First 324.500 330.500 2854079 799713 28.02 %

Second 330.500 335.200 2853917 503431 17.64 %

Third 335.200 347.000 2854126 706111 24.74 %

Fourth 347.000 359.500 2854696 813874 28.51 %

Fifth 359.500 362.500 2855181 31407 1.10 %

Total infested area 14271999 2854536 20.00 %


275

Figure (8): Infested Area by Submerged and Ditch Bank Weeds in August 2011

4-3 Weed Control Utilities

To overcome the current problem, which has an environmental impact, some assured utilities have to be

introduced. Using the available knowledge in this field, the basic technical data were used, and the famous

approaches and special techniques had been applied to analyze, suggest, and design such works. With this in

mind, the breakdown problem of the new Naga Hammady barrages hydropower plant for several hours daily

can be considered due to the following causes:

The infested weeds are extended along the river far upstream the new barrages, and every where along

the shallow depths and island sides within the study reach.

The traveling aquatic weeds are moving with the stream, crossing old Naga Hammady barrages and its

navigation lock then directed towards the intake structure of the hydropower plant with water current.

The problem is mainly due to the moving aquatic weed peaces within the upper 2.0 m under water

surface.

Breakdown of the hydropower plant is gradually occurred cumulatively in accelerating trend, which

requires complete protection upstream the new barrages.

Therefore, successive weed traps and weed control lines might be necessarily arranged along the upstream

reach to increase the hydroelectric power plant operation efficiency. To control the aquatic weeds in the

studied reach in an efficient manner, a compound system of barriers and racks have been designed and

constructed, which consists of the following units:

1. Upstream reach barriers; which consist of simple floating buoys with submerged trash racks as

shown in Figure (9). Buoys would be fixed to the river bed by using concrete blocks and attached to

river banks by stiff cables. The first barrier would be located at km 361.300 downstream "OAD" on the

left river bank with total length of 100 m between the new and old barrage as shown in Figure (10). The

second barrier would be installed at km 358.500 downstream of "OAD" between the river right bank

and El-Wasta island with 230 m total length upstream the old barrages as shown in Figure (11). The

third barrier would be located at km 351.300 on the west bank of El-Kalh island with 100 m total

length. The barrier should fulfill its purpose if sufficient maintenance and attention have been taken

place.

2. The old Naga Hammady barrages sliding trash racks; would be installed in the frontal maintenance

groves of the old barrage piers to a certain depth to prevent weeds peaces from passing the opening


276

vents of the barrages. The racks have been designed in an efficient angle to collect weeds, and rigid

enough to resist the working pressure as shown in Figure (12). Moreover, the possible rack side effects

had been studied and minimized (such as the generated upstream heading up and the resulted flow

velocity distribution).

Figure (9): Detailed Design of the Upstream Reach Barriers at km 361.300, km 358.500

and km 351.300 Downstream of "OAD"

A

B

E K

L

D

C

N

W.L. W.L.


277

Figure (10): Proposed Barrier Location at km 351.300 Upstream the New Barrage

Figure (11): Proposed Barrier at km 358.500 Upstream the Old Barrages


278

L150X150X15

L150X150X15

L150X150X15

L150X150X15

L150X150X15

[ 280

[ 280

كرة ب

PL 330 x 330 x10 mmPL 330 x 330 x10 mm

PL 410 x 500 x12 mmPL 410 x 500 x12 mm

[ 280

[ 280

Figure (12): Proposed Old Naga Hammady Barrage Trash Rack


279

If the proposed barriers system is installed in a complete way (with all components working together in a

harmonic manner), and exerting sufficient active maintenance efforts, the system will be capable of

controlling the aquatic weeds upstream the hydropower plant with high efficiency.

5- SYSTEM DESIGN

To achieve final practical design of the control system components, detailed design have been carried

out, and the following concepts have been taken into consideration.

5-1 The Upstream Reach Barriers

The barrier units had been designed and constructed in a specified shape as shown in Figure (9) to suite

its purpose and all the required calculation and stresses checks have been carried out. The buoyancy of the

barrier units was checked with the proposed buoy unit shape. Loads on submerged trash racks according to

weeds existence and water current have been considered. Fixation devices have been designed in order to

hold the barrier considering all the probable loads, the required fixing anchorage blocks, and mooring

utilities (wires, chains, and locks). All related items such as river bed material frictional capacity with

anchorage blocks, water current velocity, and shear stress have been sufficiently considered.

The developed barrier is a buoy system, each unit provided with labors walk, and a frontal inclined trash

rack (for 2.2 m depth). Buoys are built from steel sections and filled with foams to save buoys from sinking.

The buoy units are anchored to each other and to anchorage blocks on the river bed, which are responsible

for barrier fixation. The barrier units were designed to fulfill all the following requirements:-

1. Preventing weeds > 20 cm from passing to the intake structure of the hydropower plant.

2. Sustaining weeds load and water pressure on it (shear, drag and hydrostatic forces).

3. To be held completely by the anchorage blocks on the river bed considering all loads on the barrier, and

the blocks’ frictional resistance on the bed material.

4. Validating safety for the barrier by using side anchorage between buoys units, and for the labors by

using labor walks for maintenance availability.

The barrier units have been suggested and designed in a specified shape, which consists of the following:-

1. Floating unit (A).

2. Frontal trash-rack, which prevent weeds and defend the intake from aquatic weeds & debris (B).

3. Anchorage block (C).

4. Chain for connecting floating unit with anchorage blocks (D).

5. Pocket in the floating unit can be filled with sand for adjusting the barrier unit balance (E).

6. Top maintenance walk path for maintenance workers (k).

7. Hand - rail,

8. Safety utilities likewise; extra side anchorage, safety handrails, and buoy’s inner foam filling (L).

5-2 Old Naga Hammady Barrages Trash Racks

Trash racks are normally selected to prevent some debris from passing through the old barrage vent, and

the rack type varies according to the design target. The used racks were designed and constructed specially

to prevent the weeds of big size from reaching the hydropower plant, and meet new Naga Hammady barrage

requirements. The tight steel trash racks were installed in the frontal maintenance groves of the old Barrage

piers, to a certain depth to prevent weeds from passing the barrages opening vents. The racks are firm

removable and vertically adjustable (with changeable water levels) with an efficient angel to easy collect

weeds, and made rigid enough to resist the working pressure. Designation process had considered the

working loads existed on the racks resulting from hydrodynamic forces (shear with weeds and rack bars),

and hydrostatic forces resulting from the small expected head difference. Rack was adapted to lie in a

certain angel of inclination, and allow for easy weed collection. The rack dimensions are 3 m height and 6 m

width for each vent as shown in Figure (12). Finally probable hazard had been studied to ensure safety of


280

old Naga Hammady barrages with the maximum expected Heading-up resulting from entire rack blockage

by weeds.

6- MAINTENANCE PROGRAME

Removal of the aquatic weed in Nile River is commonly executed by means of mechanical equipments.

However, the current maintenance programm can be considered ineffective for controlling the aquatic weeds

upstream the old and new Naga Hammadi barrages. Although there are a nubmer of harvesters, more than 4

harvesters, exist upstream the old barrages, but they are out of order for long time and not in use. Those

conditions lead weeds to grow and spread of weeds upstream the two barrages and threaten the hydropower

plant operation as well as the existing hydraulic structures. For these reasons it is recommend to use

floating units loaded with mechanical equipments. Two aquatic weeds harvesters and two floating hydraulic

excavators are required for maintaining the studied reach (left, right shorelines and for the shoreline of the

existed islands). While barrires and trach rack are recommended to be manually maintained by using hand

tools and small boat. Dry weeds are later loaded into truck and transferred to the dumping locations. Labors

included are harvester driver and assistant, crane operator, truck driver loader driver and two manual labors.

The proposed maintenance program for the body of barriers and trash racks are as follows:

Buoy body routine maintenance must be frequently carried out using anti-rust and anti foaling paints.

Using the buoy crane, the rack will be tilted in an oblique angle, and drop the stuck weeds on the

barrier deck, which could be removed later using some maintenance boats.

Trash racks must frequently check for damage, accidents, or destroying safety by submarine check.

Trash racks must be left up using the same frontal maintenance crane and cleaned using water jet to

remove weeds, debris and stuck bodies.

7- CONCLUSIONS

1. The applied method for solving the aquatic weeds problems upstream the new Naga-Hammady barrages

can be considered as a practical example for treating such difficulty. Several field measurements and

"RS" as well as "GIS" were carried out to assist development of particular solution for the problem

which revealed the following:

The infested weeds are extended along the river far upstream the new barrages, and every where

along the shallow depths and island sides within the study reach.

The traveling aquatic weeds are moving with the stream, crossing old Naga Hammady barrages

and its navigation lock then directed towards the intake structure of the hydropower plant with the

stream flow.

The problem is mainly due to the moving aquatic weed peaces within the upper 2.0 m layer under

water surface level.

Breakdown of the hydropower plant is gradually occurred cumulatively in accelerating trend,

which requires complete protection upstream the new barrages.

2. To control the aquatic weeds in the study reach, a compound system of barriers and racks have been

designed and constructed, which consists of the following:

The upstream reach barriers; each barrier consists of a compound floating buoy units, provided

with submerged trash rack extended to 2.2 m under water surface. The first barrier would be

located at km 361.300 on the left river bank with 100 m length between the new and old barrage.

The second barrier would be located at km 358.500 betwen the right river bank and El-Wasta

island with 230 m total length upstream the old barrages. Third barrier located at km 351.300 on

the west bank of El-Kalh island with 100 m total length.

Sliding trash racks at old Naga Hammady barrages which would be installed in the frontal

maintenance groves of the old barrages piers.


281

3. It is also recommend to use loaded floating units with mechanical equipments. Two aquatic weeds

harvesters and two floating hydraulic excavators are required for maintaining the study reach (left,

right shorelines and for the shoreline of the existed islands). While the proposed barrires and trach

rack are recommended to be manually maitained by using hand tools and small boat.

4. Satisfactory and active maintenance program must be followed to maintain all the system elements

performance with optimum efficiency.

5. The implemented solution for the aquatic weeds problems upstream each of old and new Naga-

Hammady barrages led to enhance the generated hydroelectric power from the new barrages by 26%

in July 2014 which recorded an average decline of 38% in year 2011.

REFERENCES

Ali, Reda M.(2000), “Hydraulic characteristics of open channels with floating weeds”, M. Sc.

Thesis, Faculty of Engineering, Ain Shams University, Cairo, Egypt.

Channel Maintenance Research Institute (2011), “Aquatic weeds management upstream New Nagh

Hamady Barrage”, Delta Barrage, Cairo, Egypt.

Chow, V.T. (1959), “Open – Channel Hydraulic.” McGraw-Hill, New York.

Hosam Ibrahim, Mohamed Bakry, and Sherif Saad, (2004), "Designing Barriers For Solving Aquatic

Weeds Problems Upstream New Esna Barrage," World Conference on “ Energy For Sustainable

Development: Technology Advances & Environmental Issues”, 6-9 December, Cairo, Egypt.

Hsieh, T., (1966), “Resistance of cylindrical piers on open channel flow”, Jour. of Hyd. Div., proc.,

ASCE., Vol. 90, Hy l, January, pp. 161-173.

Khalil, M. B., (1969), “Resistance and behaviour of a cylinder placed on bed of an open flow”,

submitted to the Bulletin of Science and Technology, Assiut University for publication.

Ko, S. C., and Graf, W. H., (1972), “Drag coefficient of cylinders in turbulent flow”, Jour. Of Hyd.

Div., proc. ASCE., Vol. 98, No. Hy. 5, May, pp. 897-912.

aquatic weeds management upstream new naga hammady...

Documents