Resource Directed Measures for Protection of Water Resources: Groundwater Component
WATER RESOURCE PROTECTION POLICY IMPLEMENTATION
RESOURCE DIRECTED MEASURES FOR PROTECTION OF WATER RESOURCES
SECTION D:
PROCEDURE FOR THE DESKTOP AND PLANNING ESTIMATE DETERMINATION OF
THE GROUNDWATER RDM
Senior Authors: Carel Haupt, WSM (Pty) Ltd
Roger Parsons, Parsons and Associates Specialist Groundwater Consultants
Editor:
Guy Pegram, Pula Strategic Resource Management
Version 1.0
Date:
24 September 1999
M:\f_rdm_october\groundwater\version 1.0\gw_sectionD_draft.doc
Department of Water Affairs and Forestry, South Africa
Version 1.0: 24 September 1999
D/1
Resource Directed Measures for Protection of Water Resources: Groundwater Component
Section D:
Procedure for the Desktop and Planning Estimate
Determination of the Groundwater Component of
Resource Directed Measures
D.1 Preamble
The Department of Water Affairs and Forestry (DWAF) initiated the Water Resources Situation Study (WRSS)
to provide a broad overview of national and provincial water requirements and water resources available to meet
these requirements. This information is to be used to assist decision making related to long-term water resource
planning. The study covers the whole of South Africa, but information will be collated on a quaternary
catchment basis. Available information is being used and will facilitate reconnaissance level estimates being
made of both water requirements and available resources.
The WRSS formed the basis of both the Desktop and Rapid Reserve Determination methods. These are
preliminary methods used to set the Reserve (as defined in the National Water Act, Act No. 36 of 1998). By
definition, Reserve determinations using the Desktop and Rapid methods should take approximately 2 hours and
2 days to complete respectively. Further, such estimates would typically have ‘very low’ to ‘low’ levels of
confidence.
It was recognised at the outset of the WRSS that water resources comprise both surface and groundwater. WSM
(Pty) Ltd were appointed to develop methods and tools to facilitate quantification of groundwater resources
(Haupt, 1999). The procedure described below is based on this work and is used for both the Desktop Reserve
Determination (DRD) method and the Rapid Reserve Determination (RRD) method.
D.2 Process of Reserve Determination
The DRD and RRD methods differ from Intermediate Reserve Determinations (IRD) and Comprehensive
Reserve Determinations (CRD) methods in that the generic seven step process of Reserve determinations is not
closely followed (DWAF, 1999 – Volume 2). The main purpose of the DRD and RRD methods for determining
the groundwater component of the Reserve is to quantify how much groundwater could be abstracted without
impacting the Reserve using readily available information.
Quaternary catchments were assumed to be significant water resources and therefore formed the basis of
preliminary Reserve determinations. No process is specified for demarcation geohydrological regions or
homogeneous response units. Similarly, no formal resource classification system is used. As very rapid tools, it
was assumed no groundwater management corrective actions are required. In those instances where
groundwater systems have been impacted, a CRD assessments will probably be required.
The proposed process requires generic, conservative Resource Quality Objectives (RQO’s) be set (see Section
D4). Though recognised that groundwater monitoring is required as part of the Reserve determination process,
no monitoring requirements are specified by the DRD and RRD procedure. It was assumed this aspect will be
addressed by the general authorisation and permitting processes.
D.3 Method
D.3.1
Basis
Both DWAF and the Water Research Commission (WRC) recognised the need to prepare geohydrological maps
of the country. A set of national maps were prepared by Vegter (1995) while DWAF concentrated on preparing
a series regional scale maps. These maps in turn led to preparation and publication of the national groundwater
harvest potential map of the Republic of South Africa (Seymour, 1995, Baron et al., 1998).
Department of Water Affairs and Forestry, South Africa
Version 1.0: 24 September 1999
D/2
Resource Directed Measures for Protection of Water Resources: Groundwater Component
As these maps represent the best available national assessment of groundwater resources in the country, it was
decided to base the groundwater component of the WRSS on these data sets (Haupt, 1999).
It was also recognised that total water resources are not equivalent to a simple addition of available surface and
groundwater resources nor does base flow account for all groundwater resources. As limited or no baseflow
occurs in the drier western parts of South Africa, groundwater resources are both significant and important in
these areas.
A spreadsheet was developed by Haupt (1999) in which the sustainable volume of abstractable groundwater in
each quaternary catchment was determined. This volume, referred to as the groundwater portion, is similar to
the groundwater allocation used in the IRD method discussed in Section E. Because of the low level of
confidence of the estimate, the estimates are conservative. The series of steps followed in determining the
groundwater portion are briefly described below.
D.3.2
Calculation Procedure
The procedure used by Haupt (1999) to determine the groundwater portion of each quaternary catchment is
recorded below to allow practioners the opportunity to evaluate both the methodology and the resultant
assessment. To allow for comparison, the groundwater portion of the catchments used to test the IRD method
(Section G1) are presented in Table 1.
STEP1: Determine harvest potential of each quaternary catchment
The harvest potential of each quaternary catchment was determined using information from the groundwater
harvest potential map (Seymour, 1995; Baron, et al., 1998). Quaternary catchment boundaries were overlain on
the harvest potential map and the harvest potential of each quaternary catchment calculated. It is important to
recognise harvest potential is based on both recharge and aquifer storage criteria, with the limiting criterion
being used to quantify the harvest potential of an area.
STEP2: Determine the exploitation potential
Because of economic and environmental considerations, it is not possible to abstract all groundwater recharged
or stored in an aquifer system. The hydraulic conductivity of groundwater systems plays a major role in
determining how much water can be abstracted. As regional information on hydraulic conductivity is not readily
available, borehole yield information from the National Groundwater Database (NGDB) and the Water Services
Database (WSDB) were used to determine the borehole yield factor (Table D1) as a strong relationship exists
between borehole yield and hydraulic conductivity.
Table D1: Determination of the Borehole Yield Factor
Average
Borehole
Yield
(L/s)
>3.0 L/s
1.5 - 3.0 L/s
0.7 - 1.5 L/s
0.3 - 0.7 L/s
<0.3 L/s
Borehole
Factor
Yield
0.7
0.6
0.5
0.4
0.3
The average borehole yield for each quaternary catchment was determined and, using Table 1, the borehole yield
factor determined. The harvest potential of each catchment (Step 1) was then multiplied by the corresponding
borehole yield factor to obtain an exploitation potential. Exploitation potential is a measure of the volume of
groundwater that realistically can be abstracted from the catchment.
STEP 3: Determine base flow contribution
In some areas groundwater contributes to the base flow of rivers (effluent river) while in other areas surface
water recharges groundwater systems (influent river). If this relationship is not understood, it results in ‘double
Department of Water Affairs and Forestry, South Africa
Version 1.0: 24 September 1999
D/3
Resource Directed Measures for Protection of Water Resources: Groundwater Component
accounting’ when determining the total water resource available for abstraction. To avoid this problem it was
decided to subtract groundwater contribution to base flow from the harvest potential (Haupt, 1999).
STEP 3a: Determine base flow
Determine the 75th percentile of MAR of a catchment from WR90 daily flow duration curves.
STEP 3b: Determine the base flow factor
Divide the base flow of a catchment by it’s harvest potential.
STEP 3c: Determine the corrected base flow


If the base flow factor is less than 1, accept the determined base flow (Step 3a) as the corrected base flow.
If the base flow factor is greater than 1, then divide the determined base flow (Step 3a) by the base flow
factor and record the quotient as the corrected base flow
STEP 4: Determine the groundwater portion
The groundwater portion is determined by subtracting the corrected base flow (Step 3c) from the harvest
potential (Step 1). The groundwater portion of a catchment is then considered to be the annual volume of
groundwater that can be abstracted from a catchment on a sustainable basis without impacting the Reserve.
D.3.3
Groundwater Portion Spreadsheet
The spreadsheet (Table 2) in which the groundwater portion of each quaternary catchment will be recorded is
currently being finalised (Haupt, 1999). Determination of the groundwater component of a DRD will merely
require looking up in the spreadsheet the groundwater portion of the relevant catchment. A similar process is
used when undertaking a RRD assessment, but a geohydrologist with local knowledge may be consulted
regarding surface – groundwater interaction, present status and related issues. No geohydrological fieldwork
will be possible.
It must be recognised the spreadsheet is in its early stages of development and refinements will be required. In
the eastern parts of the country which experience higher rainfall and where harvest potential is limited by storage
(Seymour, 1995; Baron, et al., 1998) the groundwater portion appears inappropriate. Poor understanding of
surface-groundwater interaction and the assumption that storage is a limiting factor in high rainfall areas (i.e.
where the base flow factor is greater than 1) contribute to this. This problem needs to be addressed.
D.4 Resource Quality Objectives
RQO’s are set to ensure the integrity of the Reserve remains intact and provide resource management guidelines
and performance specifications. Catchment specific conditions need to be considered when setting RQO’s. The
timeframe allowed for the DRD and RRD methods, however, will in many cases preclude consideration of site
specific information. The following generic RQO’s, therefore, are set as guidelines:



the regional groundwater level in a quaternary catchment may not decline over the long-term;
groundwater quality may not deteriorate and must remain in its ambient state; and
groundwater abstraction may not impact river and spring flow, riparian or terrestrial vegetation nor land
stability.
If any of the above conditions are apparent in a quaternary catchment, the preliminary Reserve determination
methods are invalid and a CRD assessment may be required.
Department of Water Affairs and Forestry, South Africa
Version 1.0: 24 September 1999
D/4
Resource Directed Measures for Protection of Water Resources: Groundwater Component
D.5 Conclusion
A methodology for quantifying the groundwater component and setting generic RQO’s as part of the DRD and
RRD methods of determining the Reserve is proposed. The groundwater portion of a quaternary catchment is
obtained from a spreadsheet currently being developed as part of the WRSS (Haupt, 1999). Though the
spreadsheet was based on best available information, it still requires continual development and refinement. It is
recommended a formal process be initiated to compare all estimates of the groundwater component of the
Reserve to facilitate improvement of the DRD and RRD methods.
Department of Water Affairs and Forestry, South Africa
Version 1.0: 24 September 1999
D/5
Resource Directed Measures for Protection of Water Resources: Groundwater Component
References
Baron, J., Seward, P. and Seymour, A., 1999: The groundwater harvest potential map of the Republic of South Africa;
Technical report Gh 3917, Directorate of Geohydrology, Department of Water Affairs and Forestry.
Department of Water Affairs and Forestry, 1999: Resource directed measures for protection of water resources.
Volume 1: Integration Manual Version 1.0, Department of Water Affairs and Forestry, Pretoria.
Haupt, C., 1999: Water resources situation study - groundwater evaluation; document in preparation for the
Department of Water Affairs and Forestry, WSM (Pty) Ltd, Pietersburg.
Parsons, R.P., 1999: Intermediate Reserve determination method – a guide for quantifying the groundwater
component; Beta Version report prepared for the Department of Water Affairs and Forestry, Parsons and Associates,
Somerset West.
Seymour, A., 1995: Explanation report for the groundwater harvest potential map of South Africa 1995, with notes on
secondary aquifer system classification; Unpubl. provisional report, Department of Water Affairs and Forestry,
Pretoria.
Vegter, J.R., 1995: An explanation of a set of national groundwater maps; Report TT 74/95, Water Research
Commission, Pretoria.
Department of Water Affairs and Forestry, South Africa
Version 1.0: 24 September 1999
D/6
Resource Directed Measures for Protection of Water Resources: Groundwater Component
Table D2: Groundwater portion of selected quaternary catchment using the DRD method.
QUATERNARY
CATCHMENT
AREA
(km2)
HARVEST
POTENTIAL
(x 106 m3/a)
BASEFLOW
(x 106 m3/a)
CORRECTED
BASEFLOW
(x 106 m3/a)
GROUNDWATER
PORTION
(x 106 m3/a)
Pienaars River
A23B
A23C
A23F
A23G
A23H
A23J
817
493
566
954
1061
933
13.98
9.04
10.42
21.38
20.69
17.11
7.65
1.86
2.38
11.21
4.83
3.83
7.65
1.86
2.38
11.21
4.83
3.83
6.32
7.18
8.04
10.17
15.86
13.28
A23 total
Atlantis
4824
92.62
31.76
31.76
60.85
G21B
Graaff-Reinet
307
14.33
0.64
0.64
13.69
N13A
554
6.20
1.53
1.53
4.67
Note:
This table excludes Step 2 as exploitation potential (as defined by Haupt, 1999) as no direct relevance to quantification
of the Reserve is evident.
The catchment used for N13A is larger than that used for the IRD case study (554 against 430 km 2).
Department of Water Affairs and Forestry, South Africa
Version 1.0: 24 September 1999
D/7