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Annex B. Water resources

Summary
B.1. General background
B.2. Rainfall patterns
B.3. Available flows at river basin level
B.4. Demand at the river basin level
B.5. Development potential at the river basin level

Summary

The three objectives of this preliminary assessment of water resources are to evaluate existing information and ascertain its usefulness and relevance, to prepare a preliminary balance of water resources, and to make recommendations for water management.

The available maps and rainfall and climatological information were reviewed to identify contour lines, the river network and watersheds. Existing rainfall and baseflow information were analyzed to approximate the hydrological probability of flow occurrence in 28 river basins.

The following information deficiencies prevented a more substantial analysis: there are few operational rain gauge stations, so that complete rainfall statistics are lacking; the equipment at climatological stations is not standard, so that information is inaccurate; flow controls are not systematically located, so that the hydrological information is incomplete and inaccurate; and the lack of a water usage inventory precluded the preparation of an exact balance of water resources.

The limited information available permits the following statements about supply and demand. The Central Water Authority (CWA) has 25 intakes and the installed capacity to supply 3.4 million gallons per day (mgd) on the island. The Castries-Gros Islet urban area takes 2.25 mgd, Vieux Fort takes .5 mgd and the remainder is supplied to the rest of the country. The daily per capita demand in urban and rural areas is 48 gallons. In the hotels, 120 gallons per person per day are required. Banana boxing plants, numbering approximately 100 in the country, require between 3 200 and 28 000 gallons daily, depending on plant size; the plants usually operate two days a week. One million gallons a day are required to irrigate 200 acres (5 000 mgd per acre); irrigation is usually required for five months in the year. Land classes I-III (U.S. Conservation Service Land Classification System) have the best prospects for irrigation. A total of 5 034 acres requiring 25.7 mgd have been identified in 7 basins as being suitable for irrigation (see Table B-6).

Detailed analyses of water supply and demand are made for the Marquis, Roseau, Vieux Fort, Canelles, Troumasse, Fond D'Or and Cul de Sac river basins. Recommendations for the use of surplus or provision for shortages are made.

B.1. General background

B.1.1. Objectives of the study
B.1.2. Evaluation of basic information

B.1.1. Objectives of the study

There are very few sources of reliable information on water resources in Saint Lucia, which prevents a detailed analysis of the existing conditions and precise projections of long-term trends of water availability. The main objectives of this preliminary assessment of water resources in Saint Lucia are to evaluate the existing basic information, to ascertain its usefulness and relevance and to prepare a preliminary balance of water resources at the national level. In doing so, the study formulates recommendations for water management and development policies and identifies project proposals for short-term action.1

1 Oelsner, J., "Saint Lucia, Water Resources," OAS Technical Report, Saint Lucia, May 1981 (mimeo).

The following sections concentrate on the results of the balance of water resources for the various watersheds and discusses their development potential, matching supply with foreseeable water demands for urban, tourism, industrial and agricultural development. The recommendations for institutional and legal development for water resource management are summarized in Chapter 7 of this report.

B.1.2. Evaluation of basic information

i. Cartography

The 1:50 000 map scale (Edition 3, DOS, U.K., 1980) was used as the basis for calculations and analysis. This map contains contour lines at intervals of 200 feet; the river network; main, secondary and feeder roads and tracks; elevation bench marks referring to ground level; identification of beaches, cliffs, swamps and mangroves; and other detailed geographic data. For specific purposes (forestry coverage, cultivated areas, etc.) the 1:25 000 map scale (Edition 3, DOS, U.K., 1974) was used.

ii. Rainfall measurements

During the 1930's, there were 34 rain gauge stations in operation in Saint Lucia. This number was reduced to the present 15 stations during the early 1950's. Only six of the original stations are still functioning. Table B-1 indicates the distribution of the precipitation gauge network by river basin and the continuity of the measurements taken.

TABLE B-1. PRECIPITATION GAUGE NETWORK*

Basin or area

Name of precipitation gauge

Continuity
Years Evaluation

Marquis

Marquis Estate

33-80 Good


Marquis Babonneau


58-80 Good

Fond D'Or

Cardi La Ressource

80-


La Caye


41-80 Good


Ressource


41-45


Border


34-49


Rabot


36-48 Good


Ford Doux


36-40

Dennery

Errard

35-


Prospect


33-48 Good

Fond Patience


51-80 Good


Fond Estate


72-80 Good

Troumasse

Mahaut

52-80 Poor


Troumasse Estate


33-69 Good


Quilesse


35-78 Good

Canelles

Edmund Forest

80-

Vieux Fort

Beause jour (V.F.)

33-80 Fair


Woodlands


33-54 Good


Retraite


33-42


Daubergour


33-34

Black Bay

Girand

33-48 Good


Black Bay


33-69 Fair

Piaye

Londonderry

33-60 Good

Balembouche

Morne Lezard

33-54 Good


Balembouche


41-70 Fair

Dorée

Park

33-68 Good

Choiseul

Fargue

48-79 Fair


Bath Nursery


50-80 Good


Belle Plaine


33-48 Good

L'Ivrogne

Union Vale

33-80 Good

Beausejour (Soufr.)

33-48 Good

Soufriere

La Perle (Soufr.)

33-50 Good

Ruby

33-48 Good

La Dauphine

33-40

Roseau

Roseau

33-80 Good

La Perle (Roseau)

33-

Mont D'Or

33-50 Good

Belair

33-54 Good

Vanard

33-54 Good

Cul de Sac

Soucis

33-54 Good

Crown Lands

33-51 Good

Ravine Poisson +

33-36

Barre de L'Isle

41-80 Good

Castries

Government House

45-80 Good

Bol. Gdns.

33-41

Barracks Vigie

33-42

Choc

Union

33-80 Good

Choc

33-44 Good

La Brelotte or D'Orange


Trouya

77-80

Corinth

33-53 Good

Northern Peninsula

Cap Estate

40-79 Fair

Reduit

33-40

Southern Peninsula

Moule-a-Chique

33-67 Good

Point Sable

33-38

* Stations used in the analysis of water resources. Stations which started to operate during the last months of 1980 are excluded.

+ Ravine is a term used locally for tributary river.

Source: Oelsner, J., "Saint Lucia, Water Resources," OAS Technical Report, Saint Lucia, May 1981 (mimeo).

iii. Climatological information

There are only four climatological stations in operation in Saint Lucia and all are located in the coastal zone: one at Union Agricultural Station, one at Roseau Agricultural Station (WINBAN), and one at each of the two airports, Vigie and Hewanorra. The equipment in the Union and Roseau stations is similar. Both have a Type A evaporation pan, Campbell heliograph, actinometer, maximum and minimum thermometers, rain gauge, hygrometer, rain recorder and wind meter. In both cases the evaporation pan requires certain adjustments to conform to international standards: no painting, proper ventilation and leveling. It would be desirable to take 3 daily recordings. In the interior of the island at elevations above 100 feet the only available climatological information is for rainfall.

iv. Hydrological background

A significant restriction for water resource development and planning is the absence of systematic flow controls. In the past, various institutions have made water flow measurements but no permanent systematic hydrological information has been gathered for a list of all flow measurements taken in Saint Lucia (see Table B-7, at the end of this annex). Data have not been consistently collected over time; deficiencies in the existing information give an inaccurate picture of the hydrological behaviour of the watersheds. Nevertheless, by using the available information and making complementary flow measurements, it was possible to obtain an approximation of the availability of water resources in the island and to make a preliminary balance for the most important watersheds.

The configuration of the country's watersheds is defined by the location of the major elevations, which form a spine (La Barre de L'Isle) that runs south-southwest to north-northeast in the center of the island. Rivers that flow radially to the north and east have less pronunced gradients than those that flow to the Caribbean coast. Most rivers are rather short, the longest being 15 to 18 km in length. Some rivers, like the Roseau, have well defined high, medium and low courses, which have gradients ranging from 1:50 in the high course to 1:680 in the medium course and 1:6 000 in the delta.

B.2. Rainfall patterns

The topography of Saint Lucia has an influence on rainfall patterns; there is high rainfall in the mountainuous interior, while lands at the extreme north and south of the island get less than half as much rainfall. Table B-2 contains data on the average rainfall for 28 river basins; these represent 72 percent of the country's surface, omitting the very small watersheds of the northern section of the country.

TABLE B-2. RAINFALL BY WATERSHED

Basin No.

Name

Drainage area

Rainfall

Volume (hm3)

acres

km2

in

mm

1.

Salles

890

3.6

60.23

1 530

5.51

2.

Esperance

2 273

9.2

70.07

1 780

16.38

3.

Dauphine

1 409

5.7

69.68

1 770

10.08

4.

Marquis

7 512

30.4

88.18

2 240

68.09

5.

Fond D'Or

9 711

39.3

97.24

2 470

97.07

6.

Dennery

4 645

18.8

90.55

2 300

43.24

7.

Praslin

1 977

8.0

85.43

2 170

17.36

8.

Fond

4 472

18.1

106.69

2 710

49.05

9.

Volet

1 779

7.2

79.13

2 010

14.47

10.

Troumasse

7 586

30.7

119.68

3 040

93.32

11.

Micoud

2 298

9.3

76.77

1 950

18.52

12.

Canelles

4 028

16.3

101.18

2 570

41.89

13.

Vieux Fort

7 240

29.3

91.33

2 320

67.97

14.

Black Bay

3 583

14.5

74.01

1 880

27.26

15.

Piaye

2 768

11.2

92.91

2 360

26.43

16.

Balembouche

1 334

5.4

83.46

2 120

11.44

17.

Dorée

2 743

11.1

111.81

2 840

31.52

18.

Choiseul

2 273

9.2

89.36

2 270

20.88

19.

L'Ivrogne

1 433

5.8

87.00

2 210

12.81

20.

Soufriere

3 954

16.0

109.84

2 790

44.64

21.

Canaries

3 410

13.8

108.26

2 750

37.95

22.

Grand Riviere de L'Anse La Raye

2 174

8.8

106.69

2 710

23.84

23.

Petite Riviere de L'Anse La Raye

1 661

4.7

88.18

2 240

10.52

24.

Roseau

11 861

48.0

120.47

3 060

146.88

25.

Cul de Sac

9 563

38.7

111.02

2 820

109.13

26.

Castries

1 137

4.6

90.94

2 310

10.62

27.

Choc

3 410

13.8

87.79

2 230

30.77

28.

La Brelotte

2 397

9.7

72.04

1 830

17.75

Note: See Table A-7 for land capability characteristics.

Source: Oelsner, J., "Saint Lucia, Water Resources," OAS Technical Report, Saint Lucia, May 1981 (mimeo). Table 8.

The evaluation of water resources for the main river basins based on yearly average values of rainfall presents severe constraints, given the small size of the watersheds (they never exceed 48 km2, 11 860 acres). The use of monthly values also presents limitations, but because of the scarcity of information. They were considered acceptable for this preliminary evaluation of water resources.

Statistical analysis shows that Saint Lucia receives a recordable level of rainfall every month. To identify the probabilities of occurrence of the recorded rainfall levels and to establish the normal distribution throughout the year, six stations were selected as representative of the rainfall regime at the most important locations and most significant elevations on the island: Barre de L'Isle, Troumasse, Marquis, Quilesse, Roseau and La Fargue.

Table B-3 contains the monthly values of rainfall (maximum, minimum and normal) for the selected stations but does not reflect the periods of drought, which can last up to 45 days, giving low run-off in watercourses due to the small size and lack of regulating capacity of the river basins. Some dry up completely during the dry season.

B.3. Available flows at river basin level

The analysis will concentrate on the 28 river basins identified in Table B-2. While no water flow measurement stations exist, in the past some measurements have been taken and stage statistics taken during the dry season at three stations (Petite Riviere du Vieux Fort, Grande Riviere du Vieux Fort at Woodland and at Boxing Plant) were converted to flow values. This information does not permit a precise identification of available flows and their reliability. It is also not possible to make a frequency analysis of monthly and daily flow values as required by the small size of the watershed. As a substitute, the available information was analysed to determine the minimum observed base flows for each watershed, correlating these values with the monthly rainfall data which would have given the flow. In this way an approximation of the hydrological probability of occurrence was obtained. For these purposes, metered discharge values were transformed into natural discharge values (values without alteration from upstream intakes). Table B-4 summarizes the results of this exercise, showing base flows per watershed with a high probability of occurrence.

B.4. Demand at the river basin level

No water usage inventory has been taken for Saint Lucia. Table B-5 summarizes current water intakes for different river basins; background information was obtained from the Saint Lucia Central Water Authority (CWA). The columns "CWA Maximum Intake" contain the maximum installed pump capacity.

Water diverted by CWA is used for both domestic and industrial purposes. Present water requirements are approximately 48 gallons/person/day (160 liters/second/person/day) in the rural and urban areas and 120 gallons/room/day (63 liters/second/room/day) for the hotels. Banana boxing plants consume between 3 200 and 28 000 gallons/day, depending on their size, and normally operate twice a week. It is estimated that some 100 boxing plants are currently in operation.2 Field packing technology, currently being introduced in Saint Lucia may change these estimates.

2 Madramootoo, C.A. and H.M. Sanchez, "A Coordinated and Unified Approach to the Development of Water Resources in Saint Lucia," Castries, December 1980 (mimeo).

TABLE B-3. MONTHLY RAINFALL PARAMETERS IN SELECTED RIVER BASINS

Source: Oelsner, J., "Saint Lucia, Water Resources," OAS Technical Report, Saint Lucia, May 1981 (mimeo), Table 9.

TABLE B-4. NATURAL BASE FLOWS DETECTED WITH HIGH PROBABILITY OF OCCURRENCE

Basin

Station

mgd

l/s

l/s

prob km

Observations %

Marquis1

Sorciere N°1

0.039

2

9.1

81


Sorciere N°2

0.005

0.3

0.48

83

Conserv. req.

Piton

0.017

0.9

2.8

65


Joseph

0.010

0.5

2.6

65


Louisie

0.011

0.6

1.8

65


Marquis

0.195

10

3.6

81


Babonneau

0.028

1

0.33

83

Conserv. req.

Roseau

Roseau 700 ft

0.98

52

3.7

84


Roseau a. jct.






Millet

2.93

150

8.3

90


Millet a. jct.






Roseau

0.98

43

5.0

90


Sarot2

3.62

163

5.0

90


Roseau Factory






(WINBAN)

4.44

233

5.9

89


Fond D'Or

Dernier, Ressource

1.98

104

8.4

98


Mabouya, Bona Vista

3.44

1.81

17.0

98


Bosquet D'Or

5.36

282

9.0

98


Mabouya, Fon D'Or

3.96

208

14.5

98


Praslin

Mamiku

0.85

45

6.2

86


Fond

Bridge

1.82

95

6.1

75


Troumasse

Boxing Plant

4.73

248

9.2

75


Cul de Sac

Geest pump

2.25

119

3.8

68


Ravine Poisson

0.26

13.7

2.8

75


Choc

Union

0.29

15

1.8

90


Dennery

St. Joseph Estate

1.37

72

5.6

86


Vieux Fort

Woodland

1.00

52.4

11.3

98


Boxing Plant

1.73

91.2

4.9

98


Petite

Above junction






Riviere

Grande Riviere

0.51

26.7

5.7

98


At junction ofPetite + Grande

2.25

118

5.1

98


1 Indicated are minimum recordings taken at different times. As shown in Table B-7, CWA abstracted on April 17, 1963, the most unfavourable or lowest combination which approximated 0.5 million gallons per day (mgd).

2 In the driest years, such as 1977 (January-May), the flow could decrease to 2.6 mgd (4.2 l/s/km2) as estimated by CWA.

Source: Oelsner, J., "Saint Lucia, Water Resources," OAS Technical Report, Saint Lucia, May 1981 (mimeo). Table 10.

There are currently 25 water intakes, of which the seven located in the Marquis basin, the three at Choc (2 wells and one surface intake), two at Cul de Sac and one at Roseau. All supply water to the Gros Islet-Castries urban corridor (see Table B-5). The CWA has the installed capacity to supply 3.4 million gallons per day (mgd) on the island: 2.25 mgd to the Gros Islet-Castries area, .5 mgd to Vieux Fort and the ramainder to the rest of the country.3

3 It should be noted that the figures refer to installed pump capacity at 100 percent efficiency. Some pumps, like those at Talvern and Marquis, are currently operating at 25 to 40 percent efficiency. See Hughes, P., Report on Available Hydrological Data for the Marquis Catchment Area and Possible Modifications to the Existing Hill-20 Supply System to Minimize Pumping Cost, Jamaica, June 1978 (mimeo).

It is estimated that about 500 acres (200 ha) are currently under irrigation, with an approximate consumption of water of 300 mgd. Assuming a high efficiency rate for irrigation, approximately 2.4 inches/month is required to irrigate one acre of land (150 mm-ha/month).4 On the average, 1 mgd are required to irrigate 200 acres; irrigation is required generally during the first 5 months of the year.5

4 Based on an evapotranspiration rate of approximately 6 inches per month.

5 Bannie & Partners, Saint Lucia, Water Resources Development Study; Stage III, Saint Lucia, June 1978 (mimeo); Madramootoo, C.A. and H.M. Sanchez, op. cit.

The areas with the best prospects for irrigation are those in land classes I to III which have non-erosive flat land: 0-5 percent slope, good soil depth, moderate to slow filtration capacity, moderate to high productive capacity and manageable clay texture (in some areas surface drainage may be required). A total of 5 034 acres (2 037 ha) of land have been identified as having the highest potential for benefitting from irrigation. For this purpose, a total of 25.17 mgd of water will be required (see Table B-6).

TABLE B-5. CURRENT WATER INTAKES

Basin

Location of intake

CWA max

intake

CWA min

intake

Irrigation

mgd

l/s

mgd

l/s

mgd

l/s

1.

Sallee








2.

Esperance








3.

Dauphine

Upstream bridge road







La Guerre - La Borne

0.5

3

0.02

1



4.

Marquis

Babonneau + Marquis

0.70

37

0.5

26

0.231

12

5.

Fond D'Or

Ravine Cochon + Ravine







Basin Noir

0.16

8

0.16

8

E


Ravine Saut

0.10

5

0.05

3

E


6.

Dennery








7.

Praslin








8.

Fond

Ravine Calfoure

0.04

2

0.04

2

E


9.

Volet








10.

Troumasse

Affluent near to Latille





0.092

5

11.

Micoud








12.

Canelles

At 1 000 ft a.s.l.

0.20

10

0.20

10

E


13.

Vieux Fort

Ressource + upstream







Chateau Bel Air

1.50

80

0.40

21

0.531

28

14.

Black Bay






E


15.

Piaye








16.

Balembouche






E


17.

Dorée


0.10

5

0.071

4



18.

Choiseul








19.

L'Ivrogne

French Canal, Deville Rv.


7


?

1

52

20.

Soufriere

3 Springs

0.15

8

0. 10

5

E


21.

Canaries


0.035

2

0.035

2



22.

Grande Riviere de L'Anse La Raye

Mt. Plaisant Estate

0.03

2

0.03

2



23.

Petite Riv. de L'Anse La Raye








24.

Roseau

Sarot

1.50

79

0.54

28

E


25.

Cul-de-Sac

Ravine Poisson

0.80

42

0.26

14

E


26.

Castries








27.

Union


0.25

13

0.25

13

E


28.

La Brelotte









TOTAL


4.7

296

2.6

139

0.88


1 A Coordinated and unified approach to the Development of Water Resources in Saint Lucia (1980).

2 WINBAN

E: Currently existing irrigation. Amount of water extracted is unkown.

Source: Oelsner, J., "Saint Lucia, Water Resources," OAS Technical Report, Saint Lucia, May 1981 (mimeo), Table 11.

TABLE B-6. IRRIGABLE LANDS AND WATER DEMAND IN SELECTED RIVER BASINS

Basin

Ha

Acres

mgd

Marquis

153

378

1.89

Roseau

539

1 332

6.66

Troumasse

121

299

1.50

Fond D'Or

473

1 169

5.84

Canelles

101

250

1.25

Cul de Sac

584

1 443

7.22

Vieux Fort

66

163

0.81

Total

2 037

5 034

25.17

Source: Oelsner, J., "Saint Lucia, Water Resources," OAS Technical Report, Saint Lucia, May 1981 (mimeo). Table 12.

B.5. Development potential at the river basin level

B.5.1. Marquis River basin
B.5.2. Roseau River basin
B.5.3. Vieux Fort River basin
B.5.4. Canelles River basin
B.5.5. Troumasse River basin
B.5.6. Fond d'Or River basin
B.5.7. Cul de Sac River basin

On the basis of the information in the preceding sections and considering existing water development projects, a basic evaluation of water resource development potential is presented for the most important and promising watersheds, including those of the Marquis, Roseau, Vieux Fort, Canelles, Troumasse, Fond D'Or and Cul de Sac. Lack of reliable information prevents a valid analysis of the other watersheds.

B.5.1. Marquis River basin

Currently CWA intakes draw off all available base flow of the Babonneau subbasin at points upstream of the junction with the Ravine Talvern and the base flow of the Marquis river upstream of its junction with the Ravine Chassin. Table B-5 shows that the installed capacity is approximately 0.7 mgd, and to date the most critical observed flow is 0.5 mgd (see footnote, Table B-4). Consequently, the available flows are those from other subbasins located downstream of CWA's intakes.

The existing information indicates that Marquis Estate is willing to irrigate 60 acres of land, demanding 0.3 mgd, apart from the 0.23 mgd that is currently used for irrigation of lands that form part of the 378 acres identified with irrigation potential in the river basin. Additionally, the Babonneau Poultry Cooperative will demand 0.3 mgd for its boxing plants, water for livestock and small farm irrigation. Therefore, water demand can be estimated at 0.6 mgd within the basin. To meet these demands, water regulation works will be necessary. Three possibilities are open in the short term:

i. Up to 0.327 mgd (17 l/s) might be obtained from the Babonneau River by using a collector canal or pipelines up to 9 km in length with intakes located on the left bank of the river at 175 feet and reaching Ravine Peauyane.

ii. Similarly, about 0.212 mgd could be obtained by collecting the affluence on the right bank of the Marquis river constructing a canal of 5 km with intakes installed at 150 feet.

iii. Water flows from the Dauphin River could be diverted to the Marquis watershed by means of a tunnel of 1 km starting in the Dauphin at an elevation of 200 feet and ending in the Ravine Peauyane, thus increasing its flow by.06 mgd.

These additional flows will meet demand during the dry season (January-May). To fully assess the feasibility of these proposals, the installation of flow measurement stations on the Marquis River at L'Hermitage and on the Dauphin River at 200 feet asl is recommended. It would be also desirable to re-establish the flow controls at the pumping and gravity intake stations on the Babonneay and Marquis rivers.

This study has established the limited water availability in the Marquis River basin, which depends heavily on the infiltration and ground storage capacity of the catchment areas of the rivers, creeks and springs currently in use. Efficient and equitable utilization of the water resources depends on a strict demarcation of the river basins. This is necessary for the Forestry Service to be given legal and financial power to assure the conservation of forest resources of the basins. This action will be of prime importance to the river basins that feed Sorciere N° 2 and the Babonneau intake, as observed in Table B-4.

B.5.2. Roseau River basin

Although the Roseau River basin has important land resources (more than 1 300 acres of irrigable land) its development has been hampered by a lack of sufficient water. At present, CWA takes 1.50 mgd from the Roseau River at Sarot; additionally, some 0.53 mgd are being extracted to irrigate lands in the lower parts of the basin. The minimum natural flow measured at Sarot is 3.62 mgd, but CWA estimates that in the driest years this flow can decrease even further, to 2.6 mgd.

In the near future, CWA is considering increasing the amount of water drawn at Sarot from the present 1.50 mgd to 2.1 mgd to meet future demands in Castries.6 The Saint Lucia Model Farms Resettlement Project will require additional water for irrigating 300 acres of bananas and vegetables, demanding an additional 1.5 mgd of water over current use.

6 Tourism alone will require 70 000 additional gallons per day over current needs in the next 5 years if it expands according to projections. See OAS, Tourism Development Program, "Five Years Development Plan of Tourism, Saint Lucia," Technical Document, October 1981 (mimeo).

Construction of a stationary reservoir located outside the Roseau River bed in the Cender de Feu valley is being considered to satisfy total projected demand. This reservoir will have an initial capacity of 196 mg (0.7 hm3, Alternative A) or 318 mg (1.4 hm3, Alternative B), to be increased at a later phase to 327 mg (1.5 hm3) or 451 mg (2 hm3), respectively. The dam would collect the water by gravity from the Roseau near its junction with the Millet River and simultaneously serve CWA's requirements at Sarot and the irrigation needs of the lower Roseau. The cost of the dam (1979 prices) would be EC$10 800 000 (Alternative A) or EC$20 100 000 (Alternative B). To ensure proper siting and design of the dam, a more detailed study of the hydrological behaviour of the basin is required. A permanent flow measurement control has been installed in the Roseau downstream from its confluence with the Millet.7 Further strong protection measures are needed at the head of the watershed.

7 As part of the EDF's Project of Technical Assistance to the Land and Water Use Unit of the Ministry of Agriculture.

An alternative to the construction of a dam is to increase the Roseau River's flow by transferring some of the flows available in the upper Troumasse basin. This alternative will be discussed in Section B.5.5.

B.5.3. Vieux Fort River basin

Originating in a well preserved forest area that has one of the highest rainfall levels, over 150 inches per year, the Vieux Fort River basin is formed by two principal rivers, the Petit Riviere du Vieux Fort and the Grand Riviere du Vieux Fort, the latter carrying up to three times the flow of the former.

Recently, CWA increased its pumping capacity to 1 mgd at the headwaters of the Grande Riviere du Vieux Fort upstream from Chateau Bel Air. There are several intakes for domestic, industrial and agricultural use nearby at the junction of the Petite and Grande Riviere, drawing an estimated 1.3 mgd. 8 Because the minimum natural base flow estimated from existing data is 2.25 mgd, any growth in demand in the future will have to be met through regulation works or by transferring water from other watersheds.

8 Great Northern Capital Corporation, "Water Resources Study for Vieux Fort Area," Castries, 1973; Madramootoo, C.A., and H. M. Sanchez, op. cit.

Future short-term demand for water will arise from the 40 acres of land to be irrigated as part of the development of the experimental livestock station at Beausejour, which will require 0.2 mgd.9 A similar amount will be required for irrigation, livestock and the operation of boxing plants in the Laborie-Augier area. Tourism development in the area is expected to demand an additional 0.05 mgd.10

9 Madramootoo, C.A., and H.M. Sanchez, op. cit.

10 OAS, Tourism Development Program, op. cit.

Including water demands for new industries and the growth of population, new demands for water will amount to 0.5 mgd within the next five years. In the long term it is estimated that up to 6.0 mgd will be required in the area; however, this projection assumes high population targets for the area (nearly 80 000 persons) and sharp increases in tourism and industrial development.11

11 Underwood, McLellen and Associates, Ltd. - UMA, 1973.

Construction of a reservoir on the Vieux Fort River upstream from Tourney is under consideration; it would supply between 6 and 7 mgd. At present, there is no justification for building such a facility. Instead, it is recommended that transferring water flows from the headwaters of the Canelles and/or Troumasse be studied as a viable low cost alternative. There is an urgent need to have flow control upstream from the existing intakes of the lower reach of the Vieux Fort or, alternatively, on the Petite and Grande Riviere du Vieux Fort.

B.5.4. Canelles River basin

Like the Vieux Fort, the Canelles River originates in one of the areas with highest rainfall in the country. Indeed, 36 percent of the total area of the Canelles basin is above 600 feet above sea level and receives nearly half of the watershed's inflow, equivalent to 3 510 mm (20.5 hm3).

According to the available background information, the forest cover of the headwaters area above the Grande Riviere du Vieux Fort at Woodlands has the same characteristics as exist over the 600 feet level in the Canelles basin. It seems that the geological characteristics are also the same.

A specific base flow at Woodland has been estimated at 11 l/s/km using flow data from 1975. This value is lower than the lowest value detected in 1971. From this figure, available flows of 1.25 mgd (66 l/s) can be estimated. Discounting the installed intake capacity by CWA, the availability is still 1 mgd.

To irrigate 250 acres of suitable land using the Canelles watershed, an estimated 1.25 mgd will be required. Other competitive demands on the waters of this watershed may arise from the need to supplement the flows of the Grande Riviere du Vieux Fort. There is the alternative of drawing 0.5 mgd (26 l/s) at an altitude of about 500 feet above sea level, diverting this flow by a pipeline or canal of 3 km to another branch of the Canelles river, and from there through a tunnel of 1.5 km (4 900 feet) to the Grande Riviere du Vieux Fort. Under these conditions it is probable that at least 0.5 mgd will be available to irrigate the 250 acres identified downstream.

No hydrological information is available for the Canelles basin. To obtain realistic figures it is recommended that a flow control be installed at the Canelles River near 200 feet asl, or close to the bridge which connects De Mailly with Desruisseau. Additionally, strict control is required to maintain the forest cover over 500 feet asl.

B.5.5. Troumasse River basin

According to the scarce background information available on this river basin, which records one of the highest specific flows during the low water period, the water resources of this basin are not being utilized at this time. Only recently has 0.09 mgd (5 l/s) been extracted from one of the branches of the Canelles River for irrigation purposes. According to the estimate shown in Table B-6, approximately 299 acres can be irrigated, requiring 1.5 mgd.

This basin has extremely favourable headwaters conditions for resource development. The area above 600 feet comprises 53 percent of the basin and receives 64 percent of the average yearly rainfall - 3 645 mm (50 hm3). Applying a rationale similar to the one used in Section B.5.4, it is possible to estimate an available base flow of 3.5 mgd or 185 l/s.

This allocation would be sufficient to cover the future demands envisioned by CWA for the Roseau at Sarot and also the requirements for the "Saint Lucia Model Farms" irrigation project. These requirements fluctuate between 2.1 and 3.6 mgd. Another alternative is to make use of all or part of these resources in the Vieux Fort River basin, which could double the available water upstream from Resource. A third alternative is for the two basins to share the resources in accordance with their requirements and priorities.

Water could be transferred from the Troumasse River basin to the Roseau River basin through a 1.9 km (6 200 feet) tunnel starting at 650 feet asl at the junction of the Quilesse Ravine and the Troumasse or through a combination of a canal or pipeline and a tunnel at a slightly higher elevation.

To transfer the water flow from the Troumasse to the Vieux Fort, the intake work should be located 650 feet asl. The flow would be transported through a canal or pipeline for 3-4 km to Ravine Noel, another branch of the Troumasse, and then through a tunnel of 9 km (3 000 feet) to the Canelles. This would increase the flow of the Canelles, which would then be diverted at 500-plus feet, as indicated previously (Section B.5.4).

It is recommended that a water measurement control be installed on the Troumasse River at Mahaut near the bridge and that the forest resources of the Troumasse headwaters, which at present are threatened with destruction, be preserved.

B.5.6. Fond d'Or River basin

This river basin is formed by the Derniere Riviere and Grande Riviere subbasins of the Mabouya River. Currently, the CWA is diverting 0.16 mgd of the Ravine Couchon and Ravine Basin Noir for domestic and industrial uses. Additionally, other intakes for irrigation are known to exist but neither the number nor the amount drawn is currently known. From the flow measurements for the dry season of the years 1979, 1980 and 1981, it is estimated that the available base flow in the Derniere Riviere subbasin is approximately 1.8 mgd and that the base flow of the Mabouya between the Bona Vista and Bosquet D'Or rivers varies between 3.4 and 5.4 mgd.

Together with the Roseau and Cul de Sac basins, the Fond D'Or basin contains the best agricultural lands in the country. It is estimated that up to 1 170 acres could be irrigated, demanding 5.8 mgd.

A reservoir fed with diversions located at 160 feet asl on the Ravine Coauchon and Derniere Riviere, with a capacity of 1.2 hm3 near the Grande Ravine, has been proposed to provide for future water demands.12

12 Bannie and Partners; Water Resources Development..., op. cit.

An alternative solution would be to consider construction of a 12 km collector canal on the left bank of the river at 50 feet asl starting at Mabouya near Thomazo. The canal could divert the flow of the Derniere Riviere after its junction with the Ravine Basin Noir and other creeks, before it arrives at the last branch of the Fond D'Or northeast of the Dennery Factory. This canal could be constructed in stages, starting at an intermediate point that could attend to the development of most of the favourable irrigation areas. This would permit amortizing the investments in shorter periods.

It is recommended that the following flow measurement stations be installed: Mabouya after its junction with the Thomazo river and the Derniere Riviere after its junction with the Petite Riviere. It will also be necessary to make a survey of all the existing irrigation intakes and to expand the defined protection limits of the tributary river basins, which are adequate but not ideal. It might be advisable to include some of the land situated between 200 and 800 feet.

B.5.7. Cul de Sac River basin

This river basin contains the largest single area of irrigable lands, 1 443 acres, which will demand approximately 7.0 mgd of water. Currently, the CWA has in operation an installed pump capacity capable of diverting 0.8 mgd at the headwaters, (13 percent of the basin area) of the Cul de Sac at Ravine Poisson. Taking this into consideration, it is evident that the available base flow can only meet 20 percent of the potential water demand. To fully develop the potentially irrigable land, one or more reservoirs will be required.13

13 Ibid.

TABLE B-7. FLOW MEASUREMENTS

TABLE B-7. FLOW MEASUREMENTS (cont. 1)

TABLE B-7. FLOW MEASUREMENTS (cont. 2)

TABLE B-7. FLOW MEASUREMENTS (cont. 3)

TABLE B-7. FLOW MEASUREMENTS (cont. 4)

TABLE B-7. FLOW MEASUREMENTS (cont. 5)

TABLE B-7. FLOW MEASUREMENTS (cont. 6)

TABLE B-7. FLOW MEASUREMENTS (cont. 7)

TABLE B-7. FLOW MEASUREMENTS (cont. 8)

TABLE B-7. FLOW MEASUREMENTS (cont. 9)

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