Nile River Flood Control: Egyptian Experiences
By
M.B.A.Saad
Ph.D. Hydraulic Engineering
Emeritus Professor, Hydraulics Research Institute
Coordinator of National Water Resources Plan
Tel.00 20 2 3544 94 92, Fax. 00 20 2 3544 9492
E mail bahaa@mwri.gov.eg
Ebahaa@mwri gov egAndE-mail mohamed.bahaasaad.saad@gmail.com@gMailing Address: El Shorouk City, Postal Cod 11837, B.O
Box 82, Egypt

Area:
1000,000 Km2Population:
79 Million Capita

Total CultivatedArea:
8 Million Acres

Egypt water withdrawal more than 40% of theavailable fresh water1. Introduction
1 1 Th1.1
The HydrologicalH d l i l Features
F toff TheTh Nile
Nil RiverRiBefore
B fand After the High Aswan Dam*The Nile is the longest river in the world andextends for approximately 6800 km.
*The maximum discharge for the Nile before theconstruction of the High Aswan Dam (HAD) was
14000 m3/s which occurred in the year 1878/79,*Meanwhile the minimum discharge was 274
m3/s which occurred in the year 1913/14.

Lengtth in Km

The River Nile is the longestriverRiver NameDrainaage Area in 10000 Km2The Nile Discharge is not the biggest

River Name

1870
1875
1880
1885
1890
1895
1900
1905
1910
1915
1920
1925
1930
1935
1940
1945
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005

N a tuu r a l fl o w (B C M )Natural Yield of the Nile River for Years Through 1870 to 2007

160

140

120

100

80

60

40Date*In high water years, catastrophic floods inflicted
didisastrousthharm on agriculture,
i lt
iindustry,d t anddddwellings
lli
offlower Egypt, while in low water years, some lands wereexposedd tto severe droughts.
dht*The regulation of these varying natural flows had been
carriedi d outt iin steps:
tth construction
thetti
off leveeslalonglththeriver course to prevent flooding,b ildi off barrages
buildingb
across theth riveri
tot raisei theth watert
to command levels, and later on, some annual storage
projects
j t were executedt d ini ththe riveribbasin.
iMajorcontrolHydraulicstructurest tacross theNile in
Egypt

*The
The first of these storage projects was the old Aswan
Dam. This did not offer complete control of the Nilewaters The amount of flood water discharging to the seawaters.
between August and October in a normal-flow year was 32
km3, a little above one third of the total average yearlysupply.
1 2 Need for the High Aswan Dam (HAD)
1.2
In 1968 the High Aswan Dam was constructed to save theexcess water from high-flood
high flood years to be consumed in theyears of low floods.
This guaranteed the annual average of 84 km3 of water
needed for the present use and the future arable land
expansion.
expansion

In one of the most severe droughts which continued formyear 1979 to year 1988, water availability to Egypt wassecured from HAD reservoir. In addition, to protect Egypt
from high floods.

1 3 Description of HAD
1.3*HAD was completedpin 1968. It's heightg is 111 m.
between the bed level and the roadway level. The lengthof HAD is 3600 m including
g the two wings.
g It wasconstructed of granite stone and sand with a core of
puddle clay,
py, connected to a horizontal impervious
playery in
the upstream to prevent water seepage.
seepage A vertical cut-off
curtain below the core havingg a depth
p of 210 m ppenetrated thesedimentary layer to the bedrock.

*AA diversion channel was excavated on the eastern bankleading to the hydrohydro--power main tunnels.
tunnels The 6 tunnels deliver
the water to the generating units,units and there are bypasses which
direct the surplus water out of the power station. The capacityof the power station is 2.10 million kW.
* An emergency gated spillway of crest of length 288m. isconstructed on the left bank to pass the flow when it reaches its
maximum level.
*The total reservoir storage capacity was estimated at 162 km3at water level of 182 amsl, including: 90 km3 for live storage,
31 km3 for sediment deposition
deposition, and 41 km3 for flood
protection.

Max. Level

Flood Storage

Toshka Level

U.S Level

Li Storage
LiveStD.S Level

Dead Storage

Schematic of the HAD

1.4
1
4 System of Controlling Upstream
Water Level of HAD
To control the water surface elevation upstream
HAD duringd ring high floods to not e
exceedceed themaximum elevation of +182 amsl, the surplus
pwater could be directed through the bypasses
out of the power station(The total dischargeof these tunnels is 11000 m3/s.) or (and)through the emergency gated spillway to theriver downstream.
downstream

2.Reasons for Toshka
P j t
Project
Practical experience showed that degradation
occurs at low rates and causes no great danger
as longg as the discharges
g flowingg downstream
HAD are kept within the limits of the actualrequirements.
requirements

Discharges exceed the actualrequirements should be released in theriver course, the downstream reaches ofthe barrages would be subjected totangible increase in degradation rates ofthe river channel. This can be avoided
if the extra discharges could be released
upstream of HAD, into Toshka
DDepression.
iSt di aboutStudies
b tTToshka
hkj
demonstrated its efficiencyy inProject
fulfilling the required purpose.

3. Toshka Project Description
The excess flood water passes out of lake Nasser via Khor
Toshka to the Toshka depression. Three hydraulic structures
are constructed within the project to control the water level in thelake,, to measure the discharge spilled to the Toshkalake
Depression and to maintain the channel stability.
stability These worksare: Uncontrolled Spillway, Toshka Channel, and an Ogee
Weir.

3.1. Khor3o Toshka
os a
It is a natural waterway leading to the Nile. It extends
in the north west towards Lake Nasser. Its length is 72
km form the axis of the River, but its width isconsiderably variable, ranging from 1.0 km to 10.0 km.
The area of Khor Toshka covers about 132 km2,confinedcoed by contour
co tou line
e 185
85 m a
amsl
amsl.
s

Lake Nasser & Toshka Depression

Landsat Image in April 2001

Main Basins in Toshka Depression

3.2 The Uncontrolled Spillway
It is a sill made of p
plain concrete with downstream dryy
pitching. The level of the sill is 178 m. amsl, and its
lengthg is 750 m. It allows the excess flood water toflow freely when its level exceeds 178 m. amsl.
3.3 Toshka Channel
Toshka channel starts just DS of the sill with a bed level
178m.amsl which is the same as the sill crest level. The
length of the channel to the depression isapproximatelypp
y 22 km. The channel width is 750 m at
the beginning and then decreases to be 440 m at thebridge
g located at distance of km 3 across the channel.
Downstream of the bridge the channel width is 350 m
and it continues till km 20.5. The longitudinal
gbed
slope of the channel is 15 cm /km.

The channel section has been designed to make possible
the maximum released discharge
g is 250 million m3 /dayy(2894 m3/s) at water level of 182.73 m amsl in the lake
3.4 The Ogee Weir

An Ogee weir with crest level 176m was constructed near
the end off Toshka channel (at( km 20.5),) to measure theexcess passed discharge and to maintain the stability oftheh upstream channelhl cross sections.
sections
iAlAlso,thishi weiri isifunctioning as a drop structure as the bed level at its
upstream isi 175 m amsll andd at its
i downstream
disi 172.5172 5
m. amsl.
amsl Downstream of the weir, the channel is much
more steeptandd theth bed
b d materialt i l isi weakk sandd stonet
which is also erodiable.

Longitudinal Section along the Study Area
182
180

Q = 150.85 M.m 3 /day
(178.0)Bridge178(176.0)(175.0)176

Ogee Weir(172.5)

174

170-20

Khour Spillway Canal
20.5 km

Khour Toshka
17 km

172-15-10-50510Distance (km)Khour Toshka

Plan View of the Study Area

152025303 5 Toshka Depression
3.5The Toshka Depression is a huge, wide
depression in the western desert at the left
side of the Nile. Its entrance at the end ofKhor Toshka at a distance of 72 km from theNile some 250 km south of the HAD.
Nile,HAD It
covers an area of 6000 km2, at level 180amsl.
l TheTh topographic
thi studies
t di relatedl t d tot thisthiproject indicated that the depression isbounded by mountainous escarpments.

4. Benefits of Toshka Spillwaypy
Toshka spillway is considered to be a projectcomplementary
py to HAD. Its objective
jis mainly
y to achieve
full control of discharges released to the Nile course
downstream of HAD,HAD, Consequently,
qy, it will fulfill the followinggbenefits:-Preventing
g the increase of the degradation
grates in theRiver course, to protect the constructions erected on theriver from overall degradation.
g-Increasing the capacity of protection against the dangersof highg floods.
-Increase the live storage capacity up to the level of 178
m amsl instead of 175 m amsl.
-Feeding of the groundwater reservoir south of the New
Valley, to raise its safe yield .

5. Role of Toshka Project in the Management ofFloods of the years (1998/1999) and(1999/2000)
Flood water reached Toshka Spillway for the firsttime in the year 1996,
1996 and the amount of water
spilled to the depression was 0.5 km3. In the year
1998/99 the depression received 14.1 km3for theyear (1999/2000).
(1999/2000)
The following Table and Figure shows the monthly
variation of water level upstream HAD with the following
terms:- inflow upstream HAD- amount of water spilled to Toshka depression- amount of water spilled to the sea.

Aug., 9Se 8p.
,9O 8ct., 9N 8ov.,
D 98ec., 9Ja 8n.
,9Fe 9bM ., 9ar 9ch
Ap , 99
ril,
M 99
ay,
Ju 99
ne,9Ju 9ly,99US W
Water Leevel of HAAD (m)
182

181

180

179

178

177

176

175

174

Water LevelToshka Discharge
Q (7)-(6)Q in at HAD (5)+(7)+(9)Discharrge 10 m

93109876543210

6.Future
6Future Plan for Increasing the Spillway
Capacity
The capacity of Toshka Spillway may need to be
increased to limit the outflow from Lake Nasser into
the river downstream
downstream.
Through the flood of year (1998/1999),(1998/1999) the Ogee weir wascalibrated and the discharge was related to the water headpwater level of HAD.
above the weir crest,, or to the upstream
The results of the calibration are the following two equations:
1 569
Q = 2.012 BH1.569
Q = 519.84 h - 93028

This calibration indicates that the maximum
discharge of the channel will be about 137
million m3/day (1586 m3/s) at a water levelof 182 m amsl, instead of 250 million
m3/day (1894 m3/s) which was thed idesigned
d discharge.
di hTh t leads
Thatl d tto theth needdto investigategthe ppossible methods forincreasing the discharge capacity.

Many alternatives
Mltti
were proposedd anddtested by
y a mathematical model ((WENDY1-D) developed by Delft Hydraulics todetermine the corresponding dischargethat can be passed through the channel.
The optimum solution was a combination
between deepening and widening the bed
width of the Toshka channel. Also, it
involves replacing the Ogee weir withcontrol structure having a lower floorlevel.

7. Summaryy and Conclusions*For the safety of HAD against over topping and to protect theNile River bed against degradation in case of surplus
di hdischarge
isi tot beb released
ld DS ththe HAD
HAD, Toshka
T hk spillway
ill
was constructed to pass this surplus water to maintain theriver discharge at a level which is required for meeting thewater demands of Egypt.
*Toshka spillway
py p
proves its function during
g the last two
successive floods where more than 27 Milliard m3
were passed through it.
*Th Ogee*TheO
weir
i was calibrated
lib t d andd theth obtained
bt i d results
lt
revealed that the maximum discharge of the spillway at awater level in the lake of 182 amsl is about 1546 m3/s
which is much less than the original design discharge((2894 m3/s).
)

*A one-dimensional model was employed based on thettpographic
hi andd hydrographich dhi datad t forf theth 17 km
k lengthlth off
Khor Toshka in addition to 20.5 km length of the channel.
Th modelThed l was formulated
fl t d byb using
i WENDY program
which was developed by Delft Hydraulics.
M
Many
alternatives
lt
ti
for
f enlargement
lt off Toshka
T hk canall
capacity were tested using the mentioned numericalmodel
d l tot findfi d outt theth mostt economici andd efficientffi i talternative.
*Th mostt optimum*Thetisolution
l ti appears tot beb a sortt offcombination between deepening and widening thechannelhl bed,b d ini addition
dditi tot replacingl i theth OgeeOweir
i withitha simple control structure having a lower floor level.