ALCOM's Surface Water Body Database for SADC1

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more than just a list of dams, lakes and    swamps

1 Southern African Development Community <>

2 Aquatic Resource Management Programme for Local Communities


Lieven Verheust
Small Reservoir Fisheries Specialist
ALCOM2

Introduction

Since 1992, ALCOM has been gathering information on surface water bodies (SWBs) from all countries in the SADC Region. In the past four years, this work has evolved from a compilation of a list of dams to what is now probably the most complete and accurate database on all surface water bodies at the SADC Region level and, for a number of countries, even at the national level.

More than 14,000 water bodies have been inventoried in eleven countries and more data are being added daily. Database fields include geographical, administrative, meteorological, socio-economic, physical and chemical data as well as data on the use of the water body, presence of plant and animal species and fishing activity. Additional, supplementary information is generated by linking to other existing databases with other fields, using uniform identifiers.

Since 1996, the SWB database has been integrated in a geographical interface which has enabled a multitude of applications in various disciplines: hydrology, agriculture, fisheries, health, environment or general development. Besides the SWB digital map, which holds the point data for all geo-referenced water bodies, the database is now also adding polygon data for a number of water bodies as well as polygons of all watersheds in SADC.

Sources of data

The database incorporates data from different disciplines and different countries, collected from a number of governmental and non-governmental organizations as well as from literature and existing databases:

Information and grey literature from:
- national water departments or hydrological services;
- national fisheries departments;
- national departments and organizations involved in irrigation;
- development organizations.
Official literature on :
- fisheries water physico-chemistry;
- hydro-electric installations.
Hardcopy and digital maps on:
- hydrological boundaries (lakes, dams, rivers and catchments);
- administrative boundaries; and
- land use.
Databases (international and/or national) on:
- reservoirs; - fisheries; and
- hydrology.
Field work from:
- ALCOM; and
- other NGOs and GOs


For Zimbabwe alone, the information in the core fields (name, geographical references and size) was compiled from more than 10 different sources. Information on other specialised fields is gathered from specific literature, much of which is classified as "grey" literature. Continuous contacts with the different sources of information is also ensuring a regular update on new information from these sources. New dams are still being constructed, new research is being conducted, fisheries statistics are being collected continuously and the new information is entered in the database when it becomes available.

A number of fields are generated by overlaying the geographical co-ordinates of water bodies with digital maps such as climatological, topographic, hydrological, geological, pedalogical and administrative maps. A meta-database contains the data sources for each individual entry so that sources can be retraced easily and contacted for verification or supplementary information.

Conditions for inclusion of Surface Water Bodies in the database

Both reservoirs and natural water bodies larger than one hectare (ha) are included in the inventory. Since most of the SWBs in SADC are reservoirs, a number of the data fields (e.g. dam wall data) are only valid for these water bodies. The following conditions have to be met for a water body to be included in the inventory:

1. situated within the physical boundaries of SADC (only mainland at the moment);
2. if seasonal, appearing regularly (appearing at least once every 10 years);
3. some geographical references (village, district,...) or co-ordinates known; and
4. stagnant water (rivers are not yet included) with a surface area bigger than 1 ha.

Data fields included in the main database

The main database includes more than 95 fields subdivided in geographical, administrative, meteo-rological, socio-economic, physical and chemical data as well as data on the use of the water body, presence of plant and animal species and fishing activity. A list of the fields included in the main database and the number of current entries in each field are given in Table1.

Linking to other existing databases with different fields (such as databases with time series on fish production) provides more details on water bodies and the geographical entity to which these water bodies belong (districts, provinces, countries,etc.). Calculation of other variables (such as Morpho Edaphic Index), overlay with digital maps (such as elevation, temperature, rainfall,etc.) and modelling provide additional information on each water body.

Collected data

At present, data from eleven countries have been collected (Table 2). Supplementary data are still expected from Botswana, South Africa (only big reservoirs included at the moment), Tanzania, Zambia and Zimbabwe.

Integration into a geographical interface and GIS (Geographic Information System)

Entries with latitude and longitude data have been integrated in a geographical interface. The integration of the database into a GIS is used to generate more data and to enable studies that require geographical analysis. It is possible to zoom into a certain area of SADC and click on displayed points or polygons (water bodies) to get more information about these bodies (Figure 1). One can also display one water body or a set of water bodies based on their characteristics from the database. This has been made possible using a combination of two simple and affordable software packages in the Windows environment by a transfer of unique identification numbers of the database program to the mapping program and vice versa.

Application of the database as a decision support tool

Modules are being developed in the database to function as a decision support tool for policy-makers, government services and non governmental organizations. Applications are numerous and only a limited number of them are described below. Note that most of the described modules are still in the planning or development phase.

Hydrology

Planning of new dams

GIS analysis of water availability versus demographic pressure can determine areas which have a critically low domestic water supply. Combined with the potential of the watersheds (river characteristics), priorities can be established for construction of new dams and estimates made on the required capacity of these dams. In Figure 2, land-use maps overlaid with maps of water bodies show a relatively low number of dams in communal areas compared to commercial farmland.

Monitoring of filling and drying of dams

Since the catchments of all geographically positioned dams can be determined relatively easily in combination with a DEM (Digital Elevation Model), it is also possible to determine rainfall in the catchment of individual dams by

Table 1 Characteristics and summary statistics on main fields in the SWB database

Nr.

Field name

Field description

No. of entries

1

SADC ID

SADC Database Identification Number

14,240

2

Nat ID

National Database Identification Number

14,240

3

Nat_Index

Index in national database (if applicable)

12,450

4

Name

Name of the water body

4,525

5

Latitude

Latitude (in decimal degrees)

11,442

6

Longitude

Longitude (in decimal degrees)

11,442

7

Grid_Ref

Map grid reference

11,719

8

Map_Nr

Map number

11,286

9

Coord_South

Coordinates south (in any format

798

10

Coord_East

Coordinates east (in any format)

798

11

UTM_Zone

UTM zone number

0

12

UTM_Coord

UTM coordinates

0

13

Rivername

Name of the main river(s) which feed(s) the water body

1,054

14

Sub-catchment

Name of the sub-catchment

99

15

Main catchment

Name of the main stream catchment

0

16

Division

Division in which the water body is situated (if applicable)

10,560

17

District

District in which the water body is situated

12,617

18

Province

Province or Region in which the water body is situated

9,667

19

Country

Country in which the water body is situated

14,240

20

International

Is the water body shared by different countries?

13,715

21

Owner

Unit which controls the water body or name of owner

1,011

22

Ownertype

Type of ownership

884

23

Surf. area

Full supply surface area

9,342

24

Capacity

Full supply capacity

9,418

25

Maxdept

Maximum depth

600

26

Meandepth

Mean depth

8,478

27

Catch. area

Catchment area of the water body

443

28

pH

Average pH value of surface water

347

29

Conductivity

Average conductivity of surface water

350

30

Transparency

Average Secchi Disk value

349

31

Alt_min

Altitude - Min of range

646

32

Alt_max

Altitude - Maximum of range

646

33

Permanence

Is the water body permanent or seasonal?

647

34

Rainmin

Mean annual rainfall - minimum of range

598

35

Rainmax

Mean annual rainfall - maximum of range

598

36

Soiltype

Main soil type of the catchment of the reservoir

1

37

Type

Type of water body (Lake, Swamp or Reservoir)

3,305

38

Constr_Yr

Construction year of the dam

2,690

39

Wallheight

Height of the dam wall

768

40

Condition

Dam wall condition

572

41

Siltation %

Estimated percentage of dam silation (volume %)

565

42

Breached or silted

Is the dam breached or completely silted?

304

43

Fenced

Is the damwall fenced ?

1

44

Access

Access by road

432

45

Dist.vill

Distance from the nearest village

73

46

Main use

Main use of the water body

555

47

Domestic

Is the water body used for domestic water supply?

246

48

Irrigation

Is the water body used for irrigation?

6,560

49

Livestock

Is the water body used for livestock watering?

323

50

Municipal

water Is the water body used for municipal water supply?

280

51

Bricks

Is the water body used for brick construction?

6

52

Industry

Is the water body used for industrial purposes?

97

53

Fishing

Is the water body used for fishing?

69

54

Other use

Any other use of the water body?

1,717

55

Fish

Presence of any fish in the water body

51

56

Stocked

Was the water body stocked with fish ?

24

57

Microph.bream

Presence of microphageous tilapia (bream)

241

58

Macroph.bream

Presence of macrophageous tilapia (bream)

98

59

Clarias

Presence of Clarias sp.

193

60

Labeo small

Presence of small Labeo sp.like L. cylindrus,...

28

61

Labeo big

Presence of Big Labeo sp. like L. capensis, umbratus, altivelis,...

5

62

Barbus small

Presence of small Barbus sp. like B. paludinosus,...

86

63

Barbus big

Presence of big Barbus sp. like B. holubi, marequensis,...

3

64

Carp

Presence of carp (common, chinese,...)

50

65

Eel

Presence of Anguilla sp.

1

66

Bass

Presence of Micropterus sp.

31

67

Tigerfish

Presence of Hydrocynus vittatus

1

68

Lepomis

Presence of Lepomis macrochirus.

8

69

Lungfish

Presence of Protopterus sp.

1

70

Other fish

Presence of other non-determined fish species

20

71

Crocs

Presence of crocodiles

394

72

Hyacinth

Presence of water hyacinth (Eichornia crassipes)

7

73

Hook and line

Presence of hook and line fishing

403

74

Traps

Presence of trap fishing

0

75

Sport

Presence of sport fishing

0

76

Gill net

Presence of gill net fishing

0

77

Seine nets

Presence of seine net fishing

0

78

Fisherfolk

Number of net fishers

53

79

Nets

Number of gill nets used (1 net = 100m2 mounted)

16

80

Boats

Number of boats/canoes/vessels

45

81

Catch/yr

Total yearly fish catch

75

82

Comments

Any observations or comments on data collection or water body

3,077

83

Date

Date of record (visit to water body)

11,174

84

Lat/Long generation

Source of the Lat/Long date

10,750

85

Source of data

Source of Data

11,713

86

Orig_ID

ID in original database

525

87

Orig_Ref

Reference source in original database

525

88

Dupe_ID

SADC ID of possible duplicate record

0

89

Main_ID

SADC ID of water body where this water body belongs to

0

90

Nat region

Natural region (if applicable, currently Zimbabwe only)

447

91

Hydrozone

Hydrozone (if applicable, currently Zimbabwe only)

10,564

92

Subzone

Subzone (if applicable, currently Zimbabwe only)

10,551

93

Locality

Locality (if applicable, currently Zimbabwe only)

10,413

94

ZimOT

Ownertype (used in Zimbabwe database only)

10,566

95

ZimDT

Division Type (Zimbabwe only)

10,562

96

Reliability

Reliability of Source data (ZAR data only)

503

Table 2. Number of entries per country for 3 important fields

using cold cloud cover data. When rainfall data is plugged into a run-off model (overlaying vegetation, soil and topographic data), the inputs of water into the dam can be calculated on a weekly basis, which allows monitoring of filling and drying of dams. Reservoirs or other water bodies which are not readily accessible can be evaluated in this way.

Environment and ecology

Monitoring of aquatic pests and aquatic exotics

Presence of aquatic pests such as water hyacinth is being entered in the database. Potentially, these organisms can reach any other water body downstream and it is thus important to forecast their potential spread to permit timely preventive measures (Figure 3). The same applies to fish or other animal aquatic organisms that have been introduced into certain catchments.

Wildlife

Important sanctuaries for aquatic wildlife can be entered as part of the geographic database to identify possible dangers of introduction of species in the watersheds above these sanctuaries. The availability of a map layer with these sanctuaries facilitates decision making on the introduction of exotic species.

Irrigation

Analysis of potential for irrigation

Since there is already a field for the use of the water body for irrigation, it is quite easy to add the information on the surface area under irrigation. This will help in assessing the extent of utilization of water bodies for irrigation purposes.

Fisheries and aquaculture

Choice of the right species to stock

The generation of fish species maps, based on catchment areas, will provide information on which fish species are already present in the catchment of a selected water body. This information can then be combined with the climatological and physical data of the water body to determine the optimum species of fish to use for stocking and to forecast fish production potential (see below).

Determination of fisheries potential

Important factors for fish production such as temperature, growing season and water conductivity are generated through the GIS. One can then predict fisheries potential, MSY

and optimum fishing pressure through modelling. This can be done by the input of soil data (determining conductivity and nutrients), physical water body data (such as depth, shoreline and surface) and climatological data, into fish production estimation models.

Health

Monitoring of water borne diseases such as bilharzia

Presence of bilharzia in water bodies can be entered in the database to help monitor the spread of this disease. Combining data on bilharzia with data on endemic fish species facilitates decisions on the stocking of macro-phytophageous and/or malacophageous fish species for snail control.

Monitoring of water borne diseases such as malaria

Combining data on the permanence of a water body, population density and climatic conditions will help define high risk areas for malaria, as well as priority areas for the stocking of fish to limit the number of mosquito larvae.

General development and food security

The fact that water is a prime factor in food security is widely recognised; however, it is not enough to monitor rainfall alone to predict harvests. Water storage is an equally important factor which influences food production. The module which monitors filling and drying of dams can be used to make early warning systems more complete in predicting shortfalls of harvests.

 

 

Figure 1. Information about a water body displayed on a clickable map

 

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Figure 2: Distribution of dams in Zimbabwe in relation <>to land use

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Figure 3: Watersheds affected by water hyacinth in Zimbabwe

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Future of the database

Just like most databases, the SWB SADC database is very dynamic. Dams are continuously being constructed and related information added to the database. More information is being collected to complete fields for registered water bodies and fields are being added when there is a demonstrated need. New databases are also being linked to the main database as necessary.

A number of data in time series require monthly or yearly inputs from the different SADC member countries. This underlines the need for an integration of the database management in a strong SADC structure that is able to fulfil these tasks.

Finally the database has to be accessible to all interested parties to perform queries and analyses. Part of these queries could be satisfied by making a part of the database available on a WWW server where a simple search instrument could provide users with information on a selection of water bodies. HTML (Hyper Text Markup Language) also provides a graphic clicking interface which allows users to zoom into the geographical area of interest. The same interface can be used on WWW and on a local network. ALCOM has already made some information available on WWW and plans to make a large part of the database available later this year. More specialised queries and requests for analysis should be directed to the database management team which should be able to respond to all demands through the decision support module of the database.

Figure 4. Coverage of the SWB database
  • Excellent coverage
  • Relatively good coverage
  • Basic coverage

For additional information, contact: ALCOM SWB database management team
e-mail (Harare, Zimbabwe): alcom@ harare.iafrica.com
Fax: 00263-4-736847

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