DAMS AND HYDROPOWER DEPARTMENT

NEW ESNA PROJECTWATER LEVEL REGULATION SYSTEM

Novembre 1996

SOGREAH

; ‘ 5 w

Paper for the Internationa’ Workshopon Regu’ation of Irrigation Canals

(April 22-24, 1997 - Marrakesh - Morocco)

INGENIERIE

NEW ESNA BARRAGE (EGYPT)WATER LEVEL REGULATION SYSTEM

P. JEI-IANNOhydraulics enç’in eer

P. BERNARDproject nianagel

C. ODEYERhydra UI! CS eligin eel.

SOGREAH IngCnierie (France)

I. INTRODUCTION

‘Fhe Nile, the worlds longest river (6800 km) has the oldest and moSt complete series of hydrological data in existence.

For more than 7000 years, the Egyptians have done their utmost to control and limit its floàds which are a sourCe of life but cab at thesame time be devastating.

It was at the start of the 19th century that the Egyptians began to build embankments with the aim of impounding water and barragesto raise the water level, hence guaranteeing supplies to the irrigation canals that are the mainstay of their agriculture.

The barrage at Esna, a town situated 700 km to the south of Cairo, is one of the structures built on the Nile in Upper Egypt. tts maibpurpose is to control the river’s discharge and to raise the upstream water level sufficiently to supply the irrigation canal networkswithout having to pump water or carry out extra excavation work.

In all, three barrages of this type were built along the Nile downstream of Aswan, namely Esna (1908, overhauled in 1945), NagaHammadi (1930) and Asyut (1902, overhauled in 1934), raising the head between 2.5m and 5m.

With the growing need for water to satisfy agricultural demand in the Governorate of Qena, the changes in irrigation practices and theincrease in the amount of land under cultivation, the existing barrages could no longer cope and were becoming outdated.

The road crossing the Nile across the old Esna barrage had been designed for live loads of less than 20 tonnes, whereas nowadays theyreach nearly 70 tonnes.

There is also anew factor, that of the tourist boats sailing between Luxor md Aswan. They are now so numerous and large that lockoperations have become difficult and too lengthy.

For all these reasons, the Ministry of Public Works and Water Resources decided that it was necessary to construct a new barrage.

One of the attractive points of the project is the energy generated by the hydropower plant associated with the barrage (installedpower 00 MW)

2. TFIE OLD ESNA BARRAGE

mis barrage is one the oldest irrigation structures in the country. It was built in 1908 near the towii of Esna, 167 km to the north ofAswan dam and about 60 km from Luxor. The aim was to raise the water level and provide water supplies by gravity to the irrigationcanal network.

The barrage is 900 m long and was equipped with 120 gates (gate width: 5m) and a navigation lock (80 m long and 16 iii wide).

3. TI-IL NEW ESNA BARRAGE

The New Esna barrage was commissioned in 1994. It is located 1200 in downstream of the old structure. The main reasons that led tothe construction of the new barrage were the following:

— the possibility it affords of raising the water level to the height required for irrigation,

- saving 1.5 thousand million cuhic meters of water that formerly spilled through the barrage each year; this was needed to keep the(lillerence between upstieam and downstream levels within reasonable limits, for reasons of stability of the structure.

— use of the water saved to reclaim new agricultural land.

— product on of electricity (634 GWh/year),

— development ol navigation, by replacing the old lock with a new one that is sut ticiently wide and long to accommodate two largetourist ships at the samc time,

— improvement in trat tic, hy constructing a new road across the barrage crest.

4. GENERAL DESCRIPTION Ol TI-IE STRUCTURES

‘l’he complete engineering services, from prel mi nary design studies through to preparation of tender documents were carried 0111 bySOGREAI I troni 1984 to 986.

New Esna barrage comprises tour maui structures: the navigation lock, a liydropowcr plant, a flood spillway and a rocktillembank ment.

The main characteristics of the structures are the following:

a) navigation lock:

— length 150 in, width I 7m, draught 3 in,

— locking cycle: about 25 minutes.

b) hydropower plant:

• 6 bulb units, 6.25 in diameter, . .

output 6 x 13MW.

e) flood spillway:

• regulation level: 79m, . .

• design flood discharge: 7000 m3ls,crest length: 173m,

• 11 radial gates (12 in wide x 12.9 m high).

d) rockfill embankment

• made of gravelly material, with a central core of quarry run.

e) irrigation intakes

• the New Esna barrage allows for irrigation of 125 000 ha.

5. WATER LEVEL REGULATION

5.1 Introduction

The aim of the water level regulation system is to maintain the water level in Esna reservoir witlun a range 01 selected values, in orderto ensure proper operation of the irrigation intakes and power plant.

The “physical” variables of the regulation system are mainly:

- the inflow discharge (almost equal to the flow released by Aswan, less the discharge diverted through the irrigation intakes),

- the discharge liowing through the power plant,

- the discharge (or gate opening) of the spillway,

- the water level in the reservoir.

Provided that irrigation needs are satisfied, one of the objectives of the regulation system is to divert the maximum discharge throughthe power plant, with a quasi constant upstream water level, in order to ensure proper operation of the irrigation intakes.

Taking into account the fact that inflow is regulated by Aswan dam, there are no rapid variations in discharge, and level regulation inrelation to inflow variations poses no problent.

The main problem was that of designing a regulation system able to cope with total load rejection by the power plant (Q= 1800 m3/s).

In the event of load rejection, and in order to avoid overspill at the barrage, the spillw:iy gates must be manocus red. 1-lowever, if thegates are opened too quickly, the stilling basin md associated protection may be damaged, and in irtit icial 110011 will be createddownstream of the barrage, which could cause damage along the river banks and emmd:inger people and boats downstream.

On the other hand, if the gates are opened too slowly, the water level in the reservoir rises too I ir md nily damage the structures as aresult of overspill.

‘l’he aim o the s udy was to exam ne whether it was ioss I hi e to open the gales slow! y enough wit hon I excessively ra sing the waterlevel in the reservoir. The maximum permissible rise in level is 70cm.

This study was carried out in 1992 in the lrarnework of quality control. It did not included all the aspects of the regulation andprovides only indications to the constructor in the way to achieve its regulation system.

This study was carried out with the help of a simulation systeni, allownig to desci he correctly the hydraulic phenomena in thereservoir (unsteady fows, surges etc.), associated with a steerine interface allowm: to simulate the operation of the water levelregulation system.

It should be noted that the hydraulic phenomena in the reservoir are conipl cater! (large upsurges in front of the posver plant, reflectionin the reservoir and, generally speaking, two-dimensional effects) and, in this case, a study with the help of a simulation systemappeared necessary.

5.2 Hydrodynaniic simulation system

The simulation system used is the CARIMA system, developed by SOGREAH.

CARIMA is a modelling system which simulates unsteady flOw (e.g. flood wave propagation, water transportation for irrigation, tidepropagation) in rivers, estuaries and open channels, including loopecf river networks.

The basic equations used for unsteady flow are those of BurrO Dc Saint Venant The simulation is mainly one-dimensional, flow in theflood plains being represented without inertia.

The numerical method for solving the equations is the Preissmann Scheme, developed by SOGREAII. This method is now of commonuse in different software, developed by French of foreign companies or universities.

The CARIMA system simulates flow in looped river networks, including the main hydraulic tèatures, for example: weirs, barrages,bridges, special head losses, automatic regulation gates, fuse plugs , etc. Of course, pressure flow can he simulated using the “Preissmanndouble slot” method.

With regard to regulation studies, the CARIMA system has been used with success tor different barrages or canals all over the world, forexample for:

- the Rhone barrages in France (for the CNR),

- the large Kirkuk irrigation canal in traq,

- the Bini hydropower project in Cameroon

5.3 Steering interface

The steering interlace is the CASCADE system, developed by the LHF (Laboratoire d’Flydraulique de France, a subsidiary ofSOGREAII and of Grenoble Science University).

This interface, connected to the CARIMA system, simulates any hydraulic system including regulation.

The purpose of the steering interface is to otter the user of the CARIMA/CASCADE system the general framework for defining aspecific behaviour at a number of sites in his river or canal model (programmed in the control niodules), antI allowing the controlmodules and hydraulic simulator to communicate during the unsteady flow simulation.

In practice, the regulation modules are included in the CARIMA/CASCADE system. During the simulation run, the hydraulicsimulator (CARIMA) solves the unsteady flow equations in a normal way at each calculation time step. At regular intervals (i.e. at eachregulation time step), the simulation is partially interrupted and regulation modules are activated.

Just as on the prototype, the regulation procedure has access to water levels and discharges at different locations of the hydraulicnetwork. These values are taken into account to force a discharge, a water level or the operation of hydraulic devices, for example gates,at the regulation points

A number of regulators have already been programmed in the CASCADE system, for example PID regulatorN. constant upstream Waterlevels, AVIO or AVIS gates, sector or flat gates, etc. Special regulators (not included in the above list) can easily he programmed in theCASCADE system.

5.4 Special features of the Esna regulation system

4. I I lydraulic representation of the Nesv Lsn:i prEj.ct

The hydraulic model represents:

- the Nile over a distance of 100 kin upstreani of the barrage,

- the Nile over a distance of 20 km downstream of the barrage,

— the precise geonietry of the reseivoir iii the vicinity iii the barrage and power plant.

Ihe general layout of the project is presented on lig. I In oider to repiesent surge propanatioli and ret lection correctly upstream of thepower plant and generally in the reservoir. repiesentation of the reservoir by rneaiis of a looped network was dupted as shown inFit!. 2. in order to represent the two—dimensional Ilows in the reservoir properly

5.4.2 Modelli.pgghition

1 lie general modelling network is shown on lig. 2.

II can be noted that:

— go we r is represe n tcd as a function Q:=l ( t ) , ta k tip in to aecou itt the Sl) a I features of the power plant,

— spi llway discharge is calculated as a function of the upstream water level (P1 formulation).

Ott the prototype, the water levels are detected m three different locations in the reservoir: two in front of the power plant (points WL Iand WI 2) and one I 50 in upstream of the power p1 atit (point WL3)

In the sintulation this’ ieference level (WR) was calculated as a balancin of these three diffetent levels (calculated by the sitnul:itor):

WR 0.05 x WP1 + 005x WP2 + 0.9*Wp3

These coefficients were selected due to the fact that the water level 150 rn tipstrearn of the structures is really less affected than levels infront of the power plant, tn the event ot swift power plant discharge changes (in tour minutes, the effect of sss ill changes in local levelsis elttriinatecl).

Different formulations of the regulation procedure were tested. In the present paper, only a classical P1 regulator formulation isptesetited. This is:

Q = p *(y_cons )+ K cons)5dt

to

where:

- Q is the discharge to be drawn off by the power plant or the spillway,- Y is the water level,- cons is the target water level,- K is the proportional term,- Ki is the integral term,- t0,t is the time,- dt is the regulation time step.

lly differentiation and discrettsation. the formula becomes:

DQ= K’(Y-Y)+ Ki(YYcons)

where:

- DQ: change of (lischarge to be drawn off during the comitig regulation step,- Yp: water level at the previous regulation step.(The CARIMAJCASCADE simulation being of discrete type, the formulation has a differential form).

The (ithet features of regulation were the following:

- calculation time step: l5s,

- regulation time step: 240s (4 minutes),

- ncutr,il hand of the target level (green zone): t).02m (rio action if the difference betweeti reference level and target level is less than2cm, in absolute value),

— yellow zone: 0.05m; if the difference between reference level :ittd target level is higher than Sctti. the P and I coefficients are ch:ingecl,in order to restore the level quickly to almost the target level,

- seitsitivity (liseharge of the spillway. 90 m3/s (if spillway discharge is less than 990 m3/s) and .30 m3/s (if spillssay discharge is morethan 990 m3/s): no action if the discharge variation calculated by the regulation procedure is less thiiri this value,

time necessary for starting activation of the spillway gates after load rejection: 12 mm,

limit of discharge changes :iccepted at the power plant for load acceptance two values were tested: 5 and 1.5 m3/s/s.

The aim of the neutral hand of the target level and sensitivity discharge of the spiliway is mainly to limit gate and turhine manoeuvres,

in order to minimise equipment wear.

Furthermore, in some cases, calculation ol the real discharge through the spill way can take into account gate openings, upstream waterlevel and downstream water level.

6. MAIN RESULTS

The main simulations were carried out with an initial power plant discharge of I 800 ni3/s and ii tot:tl ulistreani discliaigc ot 2500 in3/s.

Different regulation parameters and general conditions were tested. Only few conhgurations of simulation conditions are presentedhere.

6.1 Case of a single load rejection

In the case presented, the power plant discharge varies from 1800 m3/s to 0 in about 3 mm, in two steps, as shown on Fig. 3.

In order to make it easier to understand the results, the sensitivity discharge of the spillway was fixed it zero in this simulation. For theother simulations, the sensitivity discharge was taken into account.

The main results of the simulation (run ret’, no. 9) are summarised on Figs. 3 to 5.

On Fig. 5, water levels in front of the power plant displays two quick peaks, due to the two surges generated by the two closures of thepower plant. Upstream of the power plant, the surges are almost absorbed by the reservoir and the peak level is limited (see water level150 in upstream of the power plant, Fig. 4) or negligible (see water level downstream Old Esna, Fig. 5).

This explains why it was decided to calculate the reference water level mainly from that measured 150 in upstream of the power plant(see subsection 5.4.2).

Fig. 3 and 4 show that:

— the regulation is stable and the target level is reached in about one. hour,

- the maximum rise in water level is less than 40cm, which corresponds easily to the fixed objective,

the maximum discharge downstream of the barrage is 2900 m3/s. which rcpresents in iucrcasc of 400 nO/s in comparison with theinitial discharge.

In fact, arm increase in discharge after a load rejection is unavoidable: As the closure of the power plant is almost instantaneous, and as itis not possible to open the spillway gates quickly, there is an accumulation of water upstream of the barrage. Consequently, asupplementary discharge is necessary to empty the reservoir partially and reach the target level.

6.2 Case of load rejection followed by load acceptance

In the case presented (rtin ref. 13), the discharge from the power plant varies iS shown on Fig. 9 (load rejection Irom 1800 m3/s to zeroin about 3 mi lollowed by a load acceptance from zero to 1800 m3/s in 6 mi beginning one hotir after load rejection).

The main results of the simulation are summarised on Figs. 6 to 9.

The simulation carried out shows that the regulation is stable and that the surges generated by gate amid turbine manoeuvrmng do notrepresent a hindrance for proper operation of the regulation system.

The effect of the sensitivity discharge can be seen on Figs. 9 (discrete variations of the spillway discharge), and on Fig. 8, where theeffects of small surges generated by the discontinuous gate manoeuvring can be observed on water levels near the power plant (forexample from time0.4h to lh).

With regard to the water level drop due to load acceptance, this remains well within acceptable limits (drop 01 I 0cm).

The main problem is the maximum discharge released in this case, which reaches 3770 in3/s (initial discharge: 2500 rn3/s), I.e. anincrease of some 1200 m3/s in 5 to 6 mm. It is not certain that such in increase would be acceptable br the river, the population andnavigation downstream,

it should be noted that, in the case of this simulation, the load acceptance took plicc in the niost adverse conditions, i.e. when thespillw:iy discharge was close to a maxmmnuni. A significant decrease in spillway discharge takes place at least 2 hours alter load rejection.

Consequently, it appears difficult to limit the downstrcam discharge by trying to improvc the regulation lormulation md parameters.

The variation in power plant discharge occurs 1.4 times laster than that of the spmllway at the beginning of the load acceptance. thespillway gates cannot be manoeuvred quickly enough to limit the downstream discharge

A second simulation sas carried out (run ref. 19), assuming a slower variation in power plant discharge (1.5 in3/s/s, i.e. load acceptancelasting 20 mm).

The iesults ire shown on Fins 10 md I I In this case, the inaxoitum downstream discharnc is loitited to 2)0() m3Is, which is moleieee pta h Ic

7. CONCLITSIONS

Ihe sinmul:itions carried 0111 show that it is possible to linut watei level rise in the reservoir hv regulating the spiliway gates with aclassical P1 procedure.

In the event of load rejection lol owed by load acceptance, the study shows I hat it is necessary to increase the load acceptance, in orderto avoid an artifIcial flood downstream ol the barrage.

REFERENCI S

p SauviigeV(LI-IF): CASCADE / steering interlace and control modules. Users manual . September 1990

I’.Meillancl, P. Jehanno and P. Bernard (SOGRIiAI-I): New Esna Prolect. Water level regulation system. Report to Ministry of PublicWorks and Waler Resources. October 1992

iA. Cunge5 (LHF), F.M. Holly (Iowa State Univ.) and A. Verwey (lIl-IE, Delft): Practical aspects of computational hydraulics.Pitman. 1980.

C) pres’iousl’ SOGREA I-I stall.

-9 -s

Cl-) H m 0 C-)

—I

0 z

-9 -h C) m z m I 0 C -4

SPILLWAYQ = f(WLI ,WL2 ,WL3)

U/S LIMIT

o : ID CALCULATION POINT

D REGULATION POINT

WL: WATER LEVEL MEASUREMENT

WL2

WL1

POWER PLANTQ= F(t)

D/S LIMIT

Fig 2 TOPOLOGY OF THE MODEL

W L3

D C

DOWNSTREAM DISCHARGE

POWER PLANT DISCHARGE

UPSTREAM DISCHARGE

20 40 6} FO 00 70 40 60

Fig 3 : RUN 9 (LOAD REJECTION)

70900

WATER LEVEL 150m U/S

THE POWER PLANT

0 40 60 00 00 0 *0 60 %2 11*7

Fig 4 RUN 9 (LOAD REJECTION)

WATER_LEVELS

0/S OLD ESNA

U/S THE POWEI? I’LANF

70 411 00 00 00 I 20 *0 60 I3 71*1

Fig5 RUN9 (LOAD REJECTION)

Fig 6 : RUN 13 (LOAD REJECTION AND LOAD TAKING)

I79400

71739

19 I0

19.00

17971

79.7(7

19 74Drn

79 70_

7 9.I0

79(00

.67016 1*1

OIl .4”

DISCHARGES

DOWNSTREAM NEW ESNA

UPSTREAM

10 40 67 IV (10 I’0 .0.60100 100 II.,)

LEV0L

:::

,

Fig 7 RUN 13

LOVEL

WATER LEVEL 150rn U/S

THE POWER PLANT

(LOAD REJECTION AND LOAD TAKING)

79 80

79 70_

79 50_

“-‘0-

79-40

0930

79 20.

79 0

7070

WATER LEVELS

u/s OLD ESNA

U/S

THL POWER PLANT

40 00 0 00 00 40 I 00 I&7

Fig 8 : RUN 13 (LOAD REJECTION AND LOAD TAKING)

0

POWER PLANT

015107101467

ZIQO

0 SPILLWAY

— 0 UPSTREAM

1

‘ooj

I I

00 40 00 SO 00 10 (40 60 (00 774414.1

9 : RUN 13 (LOAD REJECTION AND LOAD TAKING)Fig

OISCh4flCi (,,3,.)

DISCHARGES

DOWNSTREAM NEW ESNAUPSTREAM

FIg 10: RUN 19 (LOAD REJECTION AND LOAD TAKING)

O POWER PLANI

U SPTLLWAY

O UPSTREAM

/

-- - -- —

——— - - — -— --— —

70 1/) 11 flO 00 20 00 60 80 00

FIg 11: RUN 19 (LOAD REJECTION AND LOAD TAKING)