Trade-off assessment in the Senegal River Basin

ICID

Saskatoon 2018

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Amaury Tilmant

Jasson Pina

The Senegal River basin▪ Located in western Africa

▪ Drainage area = 337000 km2

▪ Shared by four countries: Guinea, Mali, Mauritania and Senegal

▪ Traditional uses:• transportation (navigation)• food production: fisheries + flood recession agriculture

▪ More recently: hydroelectricity

▪ Significant year-to-year variability of river discharges:• exposes water users to a high hydrological risk

▪ Significant development potential in the basin. Coordination through the river basin authority: OMVS

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The Senegal River basin

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By Bourrichon (https://creativecommons.org/licenses/by-sa/3.0)]

020406080

100120140160180200

Volume (hm3)

4.5 km3

Artificial flood (AF)

HEM for the Senegal River basin▪ As river basins develop it becomes more and more relevant

• To seek efficient allocation policies• To understand the linkages between

• Economic sectors• Water users• Water users and their biophysical and social environment

▪ In the Senegal River basin, the following hydro-economic principles apply:• Water should be used where and when its user value is the

greatest• Water should be stored in reservoirs upstream • Water for consumptive uses should be withdrawn downstream

▪ How to find the balance between these principles?

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Hydro-economic modelling (HEM)

Débits naturels

Diversion

Réservoir existant

Centrale hydroélectrique existante

Zone irriguée et flux de retour

Légende

34.1 Débit naturel annuel [km3]

1.3

Pertes annuelles [km3]

1. Balassa

2. Koukoutamba

6. Manantali

15. Moussala

16. Gourbassi

9. Maréla

8. Boudofora

10. Badoumbé

GouinaFélou

Falémé

Bafing

Bakoye

03

06

1920

N,P

23. Diama

Sénégal

2122232427

4. Boureya

5. Bindougou

GUINÉE

MALI

SÉNÉGAL

MAURITANIE

Débit environnemental

N,PN,PN,PN,P

N

P Pêche

Navigation

Lac de Guiers & Lac Aftout

P

OcéanAtlantique

Renforcement de la Gestion des Ressources en Eau Transfrontalières sur le Bassin du Fleuve Sénégal

25-26

3.

7.

3.

11.

12.13.

14.17.18.19.20.21.22.24.

Réservoir (2de génération)

Centrale hydroélectrique(2de génération)

Réservoir (3ème génération)

Centrale hydroélectrique (3ème génération)

▪ Maximizes expected net benefits from hydropower generation and irrigated agriculture

• Constraints: M&I uses, artificial flood (eflows), navigation

▪ Up to 10 reservoirs / 12 hydropower plants

▪ 11 irrigation demand nodes / 52 crops

Débits naturels

Diversion

Réservoir existant

Centrale hydroélectrique existante

Zone irriguée et flux de retour

Légende

34.1 Débit naturel annuel [km3]

1.3

Pertes annuelles [km3]

1. Balassa

2. Koukoutamba

6. Manantali

15. Moussala

16. Gourbassi

9. Maréla

8. Boudofora

10. Badoumbé

GouinaFélou

Falémé

Bafing

Bakoye

03

06

1920

N,P

23. Diama

Sénégal

2122232427

4. Boureya

5. Bindougou

GUINÉE

MALI

SÉNÉGAL

MAURITANIE

Débit environnemental

N,PN,PN,PN,P

N

P Pêche

Navigation

Lac de Guiers & Lac Aftout

P

OcéanAtlantique

Renforcement de la Gestion des Ressources en Eau Transfrontalières sur le Bassin du Fleuve Sénégal

25-26

3.

7.

3.

11.

12.13.

14.17.18.19.20.21.22.24.

Réservoir (2de génération)

Centrale hydroélectrique(2de génération)

Réservoir (3ème génération)

Centrale hydroélectrique (3ème génération)

▪ Maximizes expected net benefits from hydropower generation and irrigated agriculture

• Constraints: M&I uses, artificial flood (eflows), navigation

▪ Solved using Stochastic Dual Dynamic Programming (SDDP)

▪ Generic HEM coded in MATLAB + efficient Gurobi solver

Scenarios - Senegal River basin

▪ Development scenarios represent alternative levels of water resources’ commitment in the basin

▪ Management scenarios reflect alternative allocation policies between competing uses

• Food security: flood recession agriculture, fisheries and irrigation

• …

• Energy security: hydropower generation

Baseline2015

2 reservoirs2 hpp74 kha5.9 million inhabitants

Mid-development2030

5 reservoirs6 hpp255 kha9.7 million

Full-development2050

10 reservoirs12 hpp402 kha16.8 million

Hydropower generation

▪ Annual energy generation

Baseline2015

2 reservoirs2 hpp74 kha

Mid-development2030

5 reservoirs6 hpp255 kha

Full-development2050

10 reservoirs12 hpp402 kha

Cultivated area – flood recession agriculture

Baseline2015

2 reservoirs2 hpp74 kha

Mid-development2030

5 reservoirs6 hpp255 kha

Full-development2050

10 reservoirs12 hpp402 kha

Marginal value of water

10

9

86

5

4

2

1

1817

14

16

15

2322 21 20

19

13

12

10

Diama

Félou

Gouina

Boureya

Balassa

Moussala

GourbassiBoudofora

Manantali

Bindougou

Koukoutamba

M A L IM A L I

M A U R I T A N I AM A U R I T A N I A

S E N E G A LS E N E G A L

G U I N E AG U I N E A

-1800000

-1800000

-1500000

-1500000

-1200000

-1200000

-900000

-900000

-600000

-600000

12

00

00

0

12

00

00

0

14

00

00

0

14

00

00

0

16

00

00

0

16

00

00

0

18

00

00

0

18

00

00

0

20

00

00

0

20

00

00

0

Legend

ROR

Reservoir

nodes

River

Water value

$/1000m3

0.00

0.01 - 0.03

0.03 - 5

5 - 6

6 - 19

19- 33

Water accounting (2030)

▪ Short-run values and costs (million US$/y)

River basinservices

Production Storage

HydrologicCommodity-

based

RunoffInfiltration...

M&I usesHydropowerAgricultureNavigation...

Surface and groundwater reservoirs

Guinea Mali Senegal Mauritania

Fisheries 0.4 0.6 3.6 8.4

Irrigation 17.4 3.0 187.7 78.2

Hydropower 199.3 142.9 2.8 0.0

Evaporation -4.7 -5.8 -0.4 0.0

Storage services 57.4 35.6 3.6 0.0

Natural inflows 117.0 29.6 1.1 0.0

-50

0

50

100

150

200

250

300

350

400

Val

ue

an

d c

ost

(m

illio

n U

S$/y

)

Indicators

▪ Satisfaction level = degree to which one objective is achieved in a particular scenario (compared to the max achievable performance in the corresponding “best” scenario)

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Indicator Scale & units « best » management scenario

Flood recession ag Flooded area (ha) Food security

Energy Energy (MWh) Energy security

Navigation Probability of exceeding min flow (-) Navigation

Fisheries Fish catch (T) Food security

Trade-off (2030)

▪ The thick lines = the average performance of a particular scenario

▪ Thin lines = performance for a particular hydrological year → give an indication of the year-to-year variability

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Basin-wide net revenues (2015, 2030, 2050)

14

0 50 100 150 200 250 300 350 400

Hydropower

0

50

100

150

200

250

300

350

400

450

500

Irri

ga

tio

n a

nd

fis

he

rie

sNet revenues (million USD)

Guinea

Mali

Senegal

Mauritania

Basin

Baseline

Energy

Food

Full dev. wo flood

Full dev. w flood

Conclusions and recommendations

▪ Future developments of the basin will exacerbate the existing trade-offs between competing uses

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Hydropower

Flood recession agricultureFisheriesEcology

HydropowerNavigation

Flood recession agricultureFisheriesEcology

Irrigated agriculture

Baseline2015

Full-development2050

Conclusions and recommendations

▪ Future developments of the basin will exacerbate the existing trade-offs between competing uses

▪ Inter and intra-country trade-offs

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Mali

MauritaniaSenegal

MauritaniaSenegal

MauritaniaSenegal

Mali, Guinea,

MauritaniaSenegal

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Baseline2015

Full-development2050

Conclusions and recommendations

▪ Food production sector more vulnerable to hydro-climatic variability

▪ The performance of the Senegal river system can be significantly improved through the coordinated operation of the multireservoir system

▪ Impact of climate change on trade-offs has yet to be carried out

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