Department of Water Affairs and Forestry
Upper Vaal Water Management Area

LEEU TAAIBOSCHSPRUIT FORUM

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1. Water Quality Objectives

The LeeuTaaibosch Forum or LTF tasked the Technical Committee to formulate and propose Water Quality Objectives (WQOs) for the Catchment. The Technical Committee therefore convened a working session on 25 February 2003 in order to set these WQOs. This meeting was attended by various stakeholders, which are represented on the Technical Committee.

 

 1.1 Water Quality Objectives in context

 The WQOs, once adopted by the LTF, will provide the basis or guideline against which to compare in-stream water quality. It is important to note that these in-stream objectives cannot be enforced within the Catchment on their own. Instead, the Department of Water Affairs and Forestry (DWAF) will use these objectives to determine the assimilative capacity of the watercourse, with the inclusion of the qualities specified by the Reserve. The Reserve specifies the quantity and quality of water required to sustain the health of the ecosystem and basic human needs. DWAF will then use the assimilative capacity and Reserve to calculate waste load allocations when issuing Water Use Licenses in terms of Section 21 of the National Water Act, 1998 (Act 36 of 1998). In this way DWAF will use the in-stream objectives to calculate actual discharge quality limits when issuing licenses in terms of Section 21(f) of the National Water Act, 1998 (Act 36 of 1998).

 

1.2 Methodology

There are five basic steps involved in determining appropriate and realistic WQOs for a Catchment:

1.      Identify water users

2.      Determine the needs of these users

3.      Determine the Catchment Background or Reference Condition

4.      Determine the status of the watercourse

5.      Determine the desired condition

 

  • Determine water users

 Within the LeeuTaaibosch Catchment, we have the following users:

        Aquatic ecosystem

        Agriculture

        Recreation and domestic

        Industrial

        Mining

Rand Water services the Greater Sasolburg area and therefore no water is abstracted for drinking. However, it is important to note that water is abstracted from the Vaal River downstream of this Catchment for purification and drinking.

 

  • Determine the needs of the water users

 The needs of all of these water users have been determined by the Department of Water Affairs and Forestry and published as Water Quality Guidelines for all of the above users. For the purposes of this exercise, the Target Water Quality Guidelines for full contact recreation and irrigation were used to ensure that the needs of the most sensitive users in terms of recreation and agriculture were considered.

 

  •  Determine the Catchment Background

 Limited data is available on the Catchment Background of some of the watercourses within the Catchment. The main sources of data used to determine the background was monitoring data collected by DWAF and Rand Water at the Taaiboschspruit weir, which is upstream of Sasolburg town and also most impactors. Historical data was also considered for the Taaiboschspruit and Leeuspruit where available.

 

  • Determine the status of the watercourse

 Considerable data is available on both the Taaiboschspruit and Leeuspruit within the Catchment itself. Both Rand Water and DWAF conduct routine monitoring at strategic points within the Catchment and this monitoring indicates various hot spots within the Catchment. A strategic point for consideration in both watercourses is the point just before they confluence with the Vaal Barrage. This provides a good indication of the overall effects and impacts of the entire Catchment, especially when compared to the Catchment background quality.

The Technical Committee elected to evaluate the water quality data statistically in order to provide a sound scientific basis for this process. The 25th, 75th and 95th percentile were determined using data from 1997 2003, and 1999 - 2003 in some cases. This provided a good impression of the variability in the data and allowed the committee to obtain a realistic impression of the current status of the water quality in these watercourses.

 

  • Determine the desired condition

 The last step of this exercise involved determining the actual WQOs for both the Leeuspruit and the Taaiboschspruit. The WQOs set for the Vaal Barrage were used as a starting point. Then the Target Water Quality Guidelines were considered for each water user. All of this was then compared to the Catchment Background quality and current status of each watercourse. The stakeholders around the table then negotiated until agreement was reached on each variable.

In most cases, the WQOs proposed for the Leeuspruit were identical to the Taaiboschspruit. It is however important to note that the quality of the Leeuspruit was considered on its own and the concentrations for each variable negotiated in the same way as with the Taaiboschspruit.

 

1.3 Proposed Water Quality Objectives

 The Technical Committee elected to align the WQOs for this Catchment with those set by the Vaal Barrage Catchment Executive Committee for the Vaal Barrage. This alignment was done by considering the WQOs for the Vaal Barrage when setting the actual WQOs for this Catchment, as well as using the same tiered structure for the objectives.

 

The proposed Leeuspruit and Taaiboschspruit objectives therefore are set out as in a tiered structure:

  •  Catchment background

This is the baseline for the catchment and therefore acts as reference to the catchment.  This tier aims to describe the ideal status of the catchment, taking cognisance of all the natural impactors on the catchment

  • Management target

This is the target for the Catchment and takes into account the ideal status, as well as the needs of all water users and the current status of the river.

  • Interim target

Tier three is an interim goal between the maximum value and the management target level.  Its primary aim is to identify progression from the status quo (existing concentrations in the catchment) or the unacceptable status to the management target level.

  •  Unacceptable

Concentrations of water quality variables above the limits set for tier three were considered unacceptable and were therefore labeled as the maximum concentration levels for the respective water quality variables. 

 

Table 1:            Proposed Water Quality Objectives for the Taaiboschspruit

Parameter

Unit

Catchment background

Management target

Interim target

Unacceptable

Physical determinant

Electrical Conductivity

mS/m

40

60

70

> 80

pH

pH units

8.0

7.0 8.5

7.0 9.0

< 6.5 ; > 9.0

Suspended solids

Mg/l

27

50

90

155

Macro determinants

Aluminum

Mg/l

0.15

0.5

1

> 5

Ammonia

Mg/l

0.25

0.5

1

> 1

Chloride

Mg/l

50

60

75

> 80

Copper

Mg/l

 

0.006

0.006

0.05

Fluoride

Mg/l

0.4

0.7

1

> 1

Iron

Mg/l

0.4

0.5

0.8

> 1

Manganese

Mg/l

0.1

0.1

0.17

> 0.2

Nitrate

Mg/l

0.15

2.5

3

> 4

Sodium

Mg/l

30

50

70

> 70

Sulphate

Mg/l

40

80

100

> 200

Phosphate

Mg/l

0.2

0.5

1

> 3

Boron

Mg/l

0.1

0.1

0.1

> 0.3

Biological determinant

Faecal coli

Counts/ 100ml

100

126

200

> 500

Organic determinants

Chemical Oxygen Demand

Mg/l

< 10

10

20

> 30

Phenol

Mg/l

 

0.01

0.1

> 0.1

 

Table 2:            Proposed Water Quality Objectives for the Leeuspruit

Parameter

Unit

Catchment background

Management target

Interim target

Unacceptable

Physical determinant

Electrical Conductivity

mS/m

40

60

70

> 80

pH

pH units

8.0

7.0 8.5

7.0 9.0

< 6.5 ; > 9.0

Suspended solids

Mg/l

30

50

90

100

Macro determinants

Aluminum

Mg/l

0.15

0.5

1

> 5

Ammonia

Mg/l

0.25

0.5

1

> 1

Chloride

Mg/l

50

60

75

> 80

Copper

Mg/l

 

0.006

0.006

0.05

Fluoride

Mg/l

0.4

0.7

1

> 1

Iron

Mg/l

0.4

0.5

0.8

> 1

Manganese

Mg/l

0.1

0.1

0.17

> 0.2

Nitrate

Mg/l

0.15

2.5

3

> 4

Sodium

Mg/l

30

50

70

> 70

Sulphate

Mg/l

40

80

100

> 200

Phosphate

Mg/l

0.03

0.1

0.4

> 1

Boron

Mg/l

0.1

0.1

0.1

> 0.3

Biological determinant

Faecal coli

Counts/ 100ml

100

126

200

> 1 000

Organic determinants

Chemical Oxygen Demand

Mg/l

< 10

10

20

> 30

Phenol

Mg/l

 

0.01

0.1

> 0.1


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