Groundwater monitoring in the Orange-Fish River Basin, Namibia: Recommendations towards establishing a monitoring system
EAW Tordiffe April 2010
General Editor Desert Research Foundation of Namibia (DRFN)
Report Editor Carole Roberts & Sharon Montgomery
Suggested citation
Tordiffe, EAW. 2010. Groundwater monitoring in the Orange-Fish River Basin, Namibia: Recommendations towards establishing a monitoring system. Report produced by GeoHydro Consultants Namibia and Karst Hydrogeological Consultants Namibia for the Ephemeral River Basins in Southern Africa (ERB) Project, Desert Research Foundation of Namibia (DRFN): Windhoek.
Distribution Desert Research Foundation of Namibia (DRFN) 7 Rossini Street, Windhoek West PO Box 20232, Windhoek Namibia
Download: www.drfn.org.na/erb/index.html
This series of reports presents findings from research carried out in the Ephemeral River Basins Project – ERB. The project, implemented in three ephemeral river basins in southern Africa – one each in Namibia, Botswana and South Africa – is funded by the Norwegian Ministry of Foreign Affairs through the Royal Norwegian Embassy in Pretoria.
Groundwater monitoring in the Orange-Fish River Basin, Namibia: Recommendations towards establishing a monitoring system April 2010
Report prepared for the ERB Project by EAW Tordiffe of
KARST HYDROGEOLOGICAL CONSULTANTS
Namibia cc.
Registration No. CC/2008/4338
Tel. +264 (61) 234526 PO Box 80050 Fax. +264 (61) 239086 Olympia
Project Partners
Desert Research Foundation of Namibia (DRFN) Carole Roberts (ERB in Southern Africa Project and ERB-Namibia Co-ordinator) PO Box 20232, Windhoek, Namibia Tel: +264 (0)61 377500 Fax: +264 (0)61 230172 Email: [email protected]
Harry Oppenheimer Okavango Research Centre (HOORC) Dr Dominic Mazvimavi (ERB-Botswana Co-ordinator) Prof Moses Chimbari P/Bag 285, Maun, Botswana Tel: +267 6861833 Fax: +267 6861835 Email: [email protected]; [email protected]
Surplus People Project (SPP) Harry May (ERB-South Africa Co-ordinator) PO Box 468, Athlone 7760, South Africa Tel: +27 (0)21 4485605 Fax: +27 (0)21 4480105 Email: [email protected]
Agriculture Research Council, Range and Forage Unit, University of Western Cape Igshaan Samuels P/Bag X17, Bellville 7535, South Africa Tel: +27 (0)21 959 2305 Email: [email protected]
Plant Conservation Unit, Department of Botany, University of Cape Town Simon Todd University of Cape Town, Rondebosch 7701, South Africa Tel: +27 (0)21 6502440 Fax: +27 (0)21 6504046 Email: [email protected]
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Ephemeral River Basins in Southern Africa Project
Ephemeral River Basins (ERB) in Southern Africa is a project that promotes the sustainable, equitable and improved utilisation of water and other natural resources in ephemeral river basins in southern Africa through the process of integrated water resource management (IWRM). Although IWRM is accepted – internationally and regionally – as the approach promoting sustainable management of water resources and the river basin is considered the ideal unit over which to apply it, the basin management approach has not been widely tested and implemented in ephemeral river basins in southern Africa.
The ERB in Southern Africa Project, however, explores the potential and options for basin management in three ephemeral river basins in southern Africa – the Boteti, an outflow of the Okavango Delta, in Botswana, the Buffels, a westward-flowing ephemeral river in the Northern Cape, in South Africa and the Fish River Basin, a tributary of the Orange River, in Namibia.
Despite being ephemeral, all three river basins are essential water resources in their areas. The three basins have different biophysical and socio-economic characteristics and are managed under different legislative, policy and institutional arrangements. Together, they thus provide good examples to explore the potential and options for basin management in ephemeral rivers and on which to base a comparative analysis for wider application.
The purpose of the project is met by five main activities: Sensitising managers and users of natural resources to the concepts of IWRM and basin management Assessing the potential for the application of integrated basin management Establishing appropriate forums for promoting IWRM in the three basins Documenting the biophysical and socio-economic status of the three basins Documenting best practices, lessons learnt and case studies as a comparative analysis for wider application.
This is one of many reports emanating from the ERB in Southern Africa Project. For more information on the project, visit our website at http://www.drfn.org.na/erb/index.html
The project is funded by the Norwegian Ministry of Foreign Affairs and co-ordinated by the Desert Research Foundation of Namibia (DRFN). Work in the Boteti River Basin is being led by the Harry Oppenheimer Okavango Research Centre (HOORC), in the Buffels by the Surplus People Project (SPP) and in the Fish by the DRFN.
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Acronyms and abbreviations a annum Ca 2+ calcium ions
CaCO 3 calcium carbonate Cl - chloride
CO 2 carbon dioxide DWAF Directorate of Water Affairs and Forestry F- fluoride GIS geographic information system GPS global positioning system GROWAS National Groundwater Database
H2CO 3 carbonic acid - HCO 3 bicarbonate km kilometre(s) km 2 square kilometre(s) m metre(s) m3 cubic metre(s) mamsl (metre(s)) above mean sea level MAWF Ministry of Agriculture, Water and Forestry mg/ l milligram(s) per litre Mg 2+ magnesium mm millimetre(s) Mm 3 mega cubic metre(s) (10 6 m 3) N$ Namibia dollar(s) Na + sodium - NO 3 nitrate OFBMC Orange-Fish Basin Management Committee OFRB Orange-Fish River Basin pH acid/alkaline content RWL resting water level 2- SO 4 sulphate
Sy specific yield TDS total dissolved solids VAT value-added tax
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Contents
Acronyms and abbreviations ...... iv
1. Introduction ...... 1 2. Geology and its groundwater potential...... 1 3. Geomorphology ...... 5 3.1 Nama-Karoo Basin ...... 7 3.2 Karas Mountains ...... 8 3.3 Gamchab Basin...... 8
3.4 Orange River Canyon...... 8 4. Groundwater monitoring ...... 8 4.1 General concepts of groundwater occurrence ...... 11 4.2 DWAF groundwater level recorders ...... 14 4.3 NamWater groundwater production schemes ...... 22 4.4 Conclusions ...... 36 5. Groundwater quality...... 36 6. Proposed limited hydrocensus ...... 41 6.1 Ownership of the monitoring...... 41
6.2 Groundwater level monitoring ...... 42 6.3 Groundwater quality monitoring...... 46 6.4 Rainfall monitoring...... 48 6.5 Flood gauging ...... 48 6.6 Springs...... 49 6.7 Training ...... 50 6.8 Cost estimate ...... 50 7. Conclusions ...... 52
8. Recommendations...... 53 References...... 54
Appendix 1: Chemical analyses of groundwater samples from NamWater production schemes ...... 55
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Orange -Fish River Basin, Namibia
vi Ephemeral River Basins in Southern Africa
1. Introduction
According to a report by Bockmühl (2009), the Orange-Fish River Basin (OFRB) drains an extensive area of approximately 120,000 km 2 in the southern part of Namibia, with only seven monitoring boreholes distributed over the entire area (i.e. on average, one monitoring borehole for every 17,000 km 2). These monitoring boreholes are equipped with analogue chart recorders that measure the groundwater level in the boreholes on a continuous basis, while the recorder charts have to be replaced on a monthly basis by personnel of the Geohydrology Division in the Ministry of Agriculture, Water and Forestry (MAWF).
During the 7th Orange-Fish River Basin Stakeholders’ Meeting held at Keetmanshoop, 19–21 August 2009, the issue of groundwater monitoring in the OFRB was discussed in some detail and the value of such groundwater monitoring was clearly demonstrated.
After discussing the need for, and current shortcomings of, proper groundwater monitoring in the OFRB by a selected Working Group, a proposal was put forward to the meeting that a limited groundwater hydrocensus of the OFRB be undertaken with the aim of extending the groundwater monitoring system. The importance of community involvement in such monitoring, under the supervision of dedicated government personnel, was also discussed. Training of people identified and willing to participate in such a monitoring programme, would be necessary.
Subsequent to the meeting, Karst Hydrogeological Consultants Namibia (KHGC) was appointed on 15 December 2009 by the DRFN to compile this desk study aimed at formulating an outline of procedures to be followed during the execution of a limited groundwater hydrocensus that could lead to the establishment of a groundwater monitoring system in the OFRB.
The purpose of this study is thus to present the essential issues regarded as necessary for consideration during the hydrocensus, the procedures that should be followed to upgrade the current groundwater monitoring system, as well as a time and cost estimate to conduct the hydrocensus.
2. Geology and its groundwater potential
The main geological units in the OFRB are presented in Table 1, indicating their dominant rock types, relative ages, groundwater occurrence and distribution.
Groundwater occurrence and its dynamics depend largely on the type and nature of the geological formations present in any given area. Swart (2008) has described the geology of the OFRB in some detail, showing the occurrence of older rock types along the southern, western and north-western margins of the basin. Because of the complex distribution of the different rock units, he produced several individual maps showing the distribution of each major unit separately.
1 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Table 1: Geological units within the OFRB, relative ages, groundwater occurrence and distribution
Age Name Dominant rock types Groundwater Distribution (Ma) occurrence Primary pores, good 0–30 Alluvium River sand and gravel Riverbeds potential Primary pores, sand, Patches in the south 30–65 Kalahari Group Sand, clay, calcrete fractures in calcrete Brukkaros Caused fracturing of From Brukkaros to Carbonatite, crater intruded rocks north of Gibeon sediments c. 75
Kimberlite Kimberlite pipes Kalkrand basalt, Kalkrand, Fractures, moderate 180 dolerite (dykes and Keetmanshoop, potential sills) Grünau Pores in sandstone; Eastern margin; Karoo Ecca shale, sandstone fractures, moderate south-west of Sequence potential Karasburg 250–300 Eastern margin; Dwyka tillite, glacial Fractures; saline Keetmanshoop and in deposits the south Fractures in Shale, sandstone with sandstone; limestone beds of limestone; Dominant over entire 530–550 Nama Group fractures and subdivided in various OFRB cavities, moderate subgroups potential Damara Folded metamorphic Outside of OFRB >500 Not applicable Sequence rocks Dyke swarms, c. 717 Gannakouriep Locally fractured Noordoewer doleritic Folded metamorphic North and north- 1,200– Sinclair Fractures and faults, sediments and eastern margins of 1,400 Sequence low potential volcanics OFRB Karas Mountains; 1,400– Namaqua Fractures and faults, Gneiss, granite southern OFRB and 1,800 Complex low potential around Aus Rehoboth Folded metamorphic North and north- 1,420– Sequence Fractures and faults, sediments and eastern margins of 1,670 low potential volcanics OFRB Elim Formation 1,700– Orange River Granite, gneiss, Fractures and faults, Extreme southern 2,000 Group amphibolite low potential margin; Rosh Pinah
The older rock units around the margins of the basin comprise the Orange River Group (highly deformed and metamorphosed amphibolites, metasediments and associated intrusive rocks), the Elim Formation and Rehoboth Sequence (sedimentary and volcanic rocks) and the Sinclair Group (rift fill sediment and mafic and felsic volcanic rocks). Since these rock-types are restricted to the basin margins, they are not considered to play any major role in the regional groundwater dynamics. However, they may be important at a local scale.
2 Ephemeral River Basins in Southern Africa
An extensive part of the southern OFRB is underlain by highly deformed rocks of the Namaqua Metamorphic Complex, comprising a major component of the Karas Mountains. Outcrops are also found to the east of Karasburg and extend southwards to the Orange River.
The predominant rock-types within the basin comprise sedimentary cycles of the Nama Group which is subdivided into the subgroups indicated in Table 2.
Table 2: Stratigraphic subdivision of the Nama Group
Group Subgroup Formation Rock types Aquifer type
Gross Aub Red shale & sandstone Secondary/Primary
Red shale & purple Nababis Secondary/Primary sandstone
Fish River Red/purple quartzitic Breckhorn Secondary sandstone
Red/purple coarse Stockdale quartzitic sandstone; Secondary conglomerate
Green shale & Vergesig Secondary/Primary green/red sandstone
Red shale & sandstone Nama Nomtsas Secondary/Primary with some limestone Schwarzrand Greenish shale & Urusis sandstone; blue Secondary/Primary limestone
Green shale, sandstone Nudaus Secondary/Primary & quartzite
Blue/green shale, sandstone; Zaris Secondary/Primary pink/grey/black Kuibis limestone
Grey quartzite & Dabis Secondary/Primary dolomitic limestone
For those who have no geological background it should be noted that the Kuibis Subgroup occurs at the base of the Nama Group while the Fish River Subgroup occurs at the top of the Group. The distribution of outcrops of the respective subgroups of the Nama Group within the OFRB is indicated in Figure 1 below.
Generally the bedding in the Nama Group is near to horizontal although slight dips toward the east are not uncommon due to tilting and uplift of the crust.
3 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Due to diagenetic processes and recrystallisation, the Nama sediments have largely lost their primary porosity and are therefore dependent on secondary porosity for their groundwater- bearing properties. Faults, joints and fractures (in the clastic sediments such as sandstone, quartzite and shale), as well as solution cavities in the carbonate rocks (such as limestone and dolomite), often reveal good groundwater-bearing properties.
Fish River Subgroup
Schwarzrand Subgroup
Kuibis Subgroup
Figure 1: Distribution of the Nama Group in the Fish River Basin Adapted from: Swart (2008)
When considering the establishment of a groundwater monitoring system within the Nama Group, it is important to take note of the fact that two sub-basins of sedimentary deposition are recognised by Grotzinger (2000), namely the northern Zaris Basin and the southern Witputs Basin, which are separated by the Osis Ridge (Figure 2). It may well be possible that some hydrogeological differences exist within each of these sub-basins.
The north-eastern and eastern borders of the OFRB are underlain by outcrops of the Karoo Sequence, which were deposited later, above the Nama Group, and comprise sedimentary successions followed by the final outflow of basaltic lavas in the northern parts. At the base
4 Ephemeral River Basins in Southern Africa of the Karoo Sequence are the glacial deposits of the Dwyka Formation, deposited directly on the Nama Group, which are in turn overlain by sandstone and mudstone layers of the Ecca Group. The base of the Ecca Group consists of shale, sandstone and mudstone of the Prince Albert Formation, followed by black carbonaceous mudstone and shale of the Whitehill Formation. Weathering of the black shale results in a white discolouration, showing these deposits as prominent white bands in the field.
The final stages of the Karoo deposition culminated in the extensive outflow of basaltic lava revealing prominent outcrops around Hardap Dam and extending north of Kalkrand and under the Kalahari sediments to the east. These lava deposits are also locally termed the Kalkrand Formation. Part of this phase of Figure 2 : The Osis Ridge separating the basaltic intrusion was the emplacement of Zaris and Witputs basins Source: Swart (2008) dolerite sills and dyke swarms into the Karoo sediments. Of particular note are the extensive dolerite sills around Keetmanshoop and those stretching from around Karasburg, south-west to Noordoewer.
From a groundwater point of view, it should be noted that water in the Dwyka Formation is inclined to be very saline and unsuitable for human or animal consumption. This tendency appears to be consistent in the Dwyka throughout southern Africa and may be attributed to the amount and variety of decomposable rock fragments found in the tillite (Bond, 1946; Tordiffe, 1978). The sandstone beds in the Ecca Group tend to present good primary aquifers. Fractures, joints and faults in the Karoo Sequence often yield reasonable secondary aquifers. The contact zones along dolerite dykes are often indurated and fractured so that they contain fair amounts of groundwater.
Post Karoo diatremes, pipes and dykes of Kimberlite are scattered throughout the basin, although at least 42 are concentrated in the Gibeon area. The Brukkaros structure, which has a volcanic form and rises some 600 m above the surrounding plains, also formed at this time.
The Kalahari Group, which covers large portions of the rest of Namibia, only occurs as isolated patches in the basin. These calcretised deposits are of little hydrogeological significance within the OFRB.
3. Geomorphology
Undoubtedly, the geomorphology of the OFRB does have an influence on the groundwater movement within it. Recharge of the groundwater from rainfall is, for example, greatly
5 Towards establishing a groundwater monitoring system: Orange-Fish River Basin influenced by the rate of run-off of the surface water. In the escarpment areas, where run- off is at its highest, little or no groundwater recharge takes place, whilst in the flat-lying areas, where the run-off rate is low, there is more time for the rainwater to infiltrate the geological environment.
It should be stated here that apart from the geomorphology, other factors such as the nature and intensity of rainfall, geology and vegetation cover play an equally important role in groundwater recharge.
Swart (2008) has described in some detail the following four main geomorphological zones in the OFRB based on the general landform, slopes and underlying geology: • The Nama-Karoo Plains • The Karas Mountains • The Gamchab Basin • The Orange River Canyon area
From a groundwater perspective, the focus will be mainly on the Nama-Karoo Plains and the Gamchab Basin. The distribution of the various geomorphological zones is illustrated in Figure 3.
Figure 3 : Landform map sho wing the main geomorphological features in the Orange-Fish River Basin (Source: Swart (2008), adapted from Mendelsohn et al. (2002))
6 Ephemeral River Basins in Southern Africa
3.1 Nama-Karoo Plains
As previously discussed, the predominant rock formations within the OFRB comprise successive alternating sedimentary beds of shale, quartzitic sandstone, mudstone and carbonate rocks of the Nama Group with younger rocks of the Karoo Sequence in the east. These almost-horizontal sedimentary beds form a rather featureless landscape constituting the Nama-Karoo Plains with only Brukkaros providing a break in the monotony.
A large block of Nama sediments measuring 290 km in length and 75 km at its widest in the north, tapering down to 25 km wide in the south, occurs between the Fish and the Konkiep rivers in the centre of the basin (Figure 4). This block is represented by a large dome structure south-west of Mariental, which is called the Hudup Dome by Swart (2008). The dimensions are reported to be 44 km x 34 km, rising some 200 m above the surrounding rocks and may play a significant role in the local groundwater flow pattern. According to Swart (2008) the block appears to have formed by faulting, with more uplift in the west causing deeper incision of the rivers. The upper portions of the Fish River appear to postdate the formation of the block as the river flows north before turning east and eventually south around it, suggesting that the river flow direction is controlled by the uplift of the block.
Other smaller domes have been recorded in these northern parts of the basin suggesting some large magmatic activity below them.
Figure 4: Uplifted Nama block showing Hudup Dome in centre of OFRB Source: Swart (2008)
7 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
A number of north-west to south-east faults dissect the Nama Group in particular, whilst in the far north of the basin other faults occur with a north-south trend (or ‘strike’) that are the extension of a series of major faults, of which some may even be responsible for the springs and thermal boreholes encountered at Windhoek and Gross Barmen.
It is also believed that the Fish River Canyon caused by incision of the Fish River, is controlled by uplift of the crust through faulting.
3.2 Karas Mountains
It is believed that the Karas Mountains were formed by normal faults sometime after the end of the deposition of the Nama Group and at the start of the Dwyka glaciation.
3.3 Gamchab Basin
To the south of the Karas Mountains lies a set of large, broad, gently sloping valleys with their drainage directed towards the Orange River. Sedimentary rocks of the Karoo Sequence deposited on the older rocks of the Namaqua Metamorphic Complex prevail in the area and are often covered by thin calcrete layers of the Kalahari. Sills of dolerite also occur in the area. The area is covered with sparse grass and few trees, except in the watercourses.
3.4 Orange River Canyon
The Orange River has incised a meandering course over 700 m deep into the metamorphic bedrock.
4. Groundwater monitoring
Boreholes are the only practical mechanism for evaluating the response of groundwater levels within any given area to discharge (natural and artificial) and recharge (mainly from rainfall) over an extended period of time. Water levels in boreholes are measured from a fixed point above the ground level of the hole. Since the elevation of such a fixed point (in metres above mean sea level; mamsl) can be determined by various survey methods, the water level (mamsl) can be calculated at any given time when it is measured (Figure 5).
8 Ephemeral River Basins in Southern Africa
Figure 5 : Measuring level of groundwater in a borehole
For example, if: • Surveyed ground level of borehole = 852 mamsl, • Collar height of borehole above ground = 0.35 m, and • Measured depth from top of collar to water level = 12.24 m, then • Groundwater level = (852 + 0.35) – 12.24 = 840.11 mamsl
Different methods are used to accurately measure the depth to the groundwater level in a borehole:
• Many farmers measure the depth only when they extract the pipes from the hole for repairs and maintenance and see at what depth the pipes are wet. This is a rather inaccurate and unreliable method.
• Others lower a rope with a weight at the end down the hole and then measure the depth up to the wetted part of the rope. This is also not a reliable method since farmers only do this when they encounter problems and pull pipes. • The most commonly used method to accurately measure the depth to the water level in a borehole is to lower an electronic probe connected to a ruled electric cable down the hole. As soon as both electrodes become submerged the electric circuit is completed and a signal light glows on the device at the surface. With such a handheld dipper, water levels can be measured up to an accuracy of 1 cm. It is also possible to train unskilled personnel to operate such devices in a relatively short time (Mazambani, 2008). They can also be manufactured locally at relatively low costs, although commercial devices may be more accurate where the depth to the groundwater level exceeds 30 m. However, to be effective, continuous water level readings need to be maintained otherwise important data between measurements could be lost.
9 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
• In order to gain continuous water level readings on some monitoring boreholes, the Department of Water Affairs and Forestry (DWAF) has installed analogue groundwater level recorders in the basin. These are clockwork operated devices that record the calibrated water level on a rotating chart. The disadvantage of these recorders is that the charts have to be replaced every month or three months, depending on the model. Vandalism of these recorders has also been reported from time to time, since the housing in which the recording device is mounted is painted in an obvious red and yellow colour for easy identification. These devices are systematically being replaced with digital continuous recorders.
• Digital continuous recorders now used by the DWAF, are suspended on a wire cable at a suitable depth below the water level. The device records hydrostatic water pressure above the probe, which is converted to the water level. When the recorded data are to be downloaded electronically, the probe has to be withdrawn from the borehole. Every time the probe is removed or installed, calibration has to be done with the handheld device described above. The advantage of such devices is that they have no moving parts and data need only be downloaded when necessary or at least once every six months. A laptop computer is needed to download the data, thus requiring relatively skilled personnel. Vandalism of such devices is sometimes a problem and therefore special protection caps have to be fitted to the monitoring boreholes.
Why measure groundwater levels at regular intervals? The reason is that the water level in a single borehole represents the groundwater regime of a given area around such a borehole. For example, a steady decline in the groundwater level over time would indicate that the outflow of groundwater (natural and artificial) from the surrounding aquifer system exceeds the inflow into the system by a calculable volume. Recharge to the aquifer system will be indicated by a steady rise in the groundwater level, i.e. the inflow exceeds the outflow. Quantification of groundwater resources around the monitored borehole(s) therefore becomes possible.
Apart from being able to quantify groundwater resources through sound groundwater level monitoring, it is also important to determine changes in the chemical quality of the groundwater with time. This is particularly necessary after a significant recharge event or when the groundwater levels have declined to critically low levels, which need to be predetermined for each aquifer system according to its sustainable storage capacity. Such critical parameters can only be determined by means of a full-scale groundwater quantification project, yet to be undertaken by DWAF. Use could be made of electronic probes to determine certain chemical parameters in the field to some degree of accuracy. Unfortunately none of the monitoring boreholes serviced by DWAF are equipped with such devices and it also has not been the standard practise to collect any groundwater samples for chemical analysis during the monitoring process. NamWater, however, collects and analyses water samples from their production schemes on a regular basis. The collection of groundwater samples at selected time intervals, before and after the rainy season, should therefore be considered as part of the groundwater monitoring process. Such water samples could be collected from operating borehole(s) close to the selected monitoring borehole.
The distribution and location of the existing groundwater monitoring stations serviced by DWAF as well as the groundwater production schemes operated by NamWater within the
10 Ephemeral River Basins in Southern Africa
OFRB are presented in Figure 6. The nearest rainfall stations to these groundwater monitoring points are also shown.
4.1 General concepts of groundwater occurrence
All geological formations consist of solid mineral particles and open voids between the particles. The open voids constitute the space in which groundwater can be contained within the rock. This space determines the porosity of the rock and is expressed as a percentage or fraction of the volume. Where the individual mineral particles are loosely packed together (such as sand, gravel and recent alluvial riverbed deposits), the voids are termed primary porosity and the aquifers within such material below the groundwater table, are called primary aquifers . As an example, one can consider a container filled with round marbles of the same size; the voids between the marbles will be about 40% (0.4) of the total volume of the container.
The gravels and sands deposited in the riverbeds of the basin can form such primary aquifers, provided that they are deep and extensive enough to contain significant volumes of groundwater. Within the OFRB such aquifers are rather limited in extent and depth to sustain continued groundwater abstraction in large quantities over an extended period of time. Examples of these aquifers occur in the riverbeds of the Fish River at /Ai-/Ais and the Orange River at Oranjemund. Recharge to these aquifers is normally due to seasonal flood events in the rivers.
Other examples of primary aquifers are those in the sands of the Kalahari Group and to some extent in the consolidated sandstones of the Karoo Sequence and Nama Group. In such cases, groundwater recharge to the unconfined aquifer is directly from the infiltration of rainwater through the unsaturated zone above the groundwater table. As certain water requirements have to be met within the root zone of plants and in the rest of the unsaturated zone before any rainwater reaches the groundwater table below, only a very small percent (<4%) of the total annual rainfall ever reaches the saturated groundwater regime.
Sandstone, mudstone and shale are formed when the loose mineral particles in the various sediments are cemented together by calcium carbonate or silica that chemically precipitates out of the water in the pore spaces. During such a cementing process the total volume of original pore spaces (primary porosity) is considerably reduced, as in the case of the sandstone in the Karoo Sequence and Nama Group. However, fractures and faults occur within these rocks, due to crustal movements that take place, thus creating secondary pore spaces , which are called secondary porosity .
Igneous rocks (formed from the crystallisation of molten magma) and metamorphic rocks (formed by the re-crystallisation of previously existing rocks of various origins) have practically no primary porosity , but they can also be fractured and faulted to obtain limited secondary porosity . Aquifers that occur in such fractured environments (an interconnected network of micro and macro joints and fractures) are called either fracture aquifers or secondary aquifers .
11 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Another type of secondary porosity is developed along fractures and contact zones in limestone, where the groundwater moving through such fractures dissolves the limestone to form cavities. Such cavities are called karstic cavities, and aquifers related to them are called karstic aquifers. Secondary or fracture aquifers predominate in the OFRB, whilst a few karstic aquifers are located in the limestone of the Nama Group.
Figure 6 : Map of the OFRB showing DWAF monitoring r ecorders, NamWater schemes and related rainfall stations
Where the secondary aquifers are unconfined (open to the atmospheric pressure at the ground surface above) recharge from rainfall takes place exactly as in the case of the primary aquifers. It is, however, also possible that large faults can extend over long distances (several tens of kilometres), where rainfall in one place can affect the groundwater level at another place where it has not rained.
12 Ephemeral River Basins in Southern Africa
A confined aquifer is encountered where a porous rock formation underlies an impervious geological formation (normally a clay layer) that prevents the underlying pore spaces from having direct contact with the overlying atmospheric conditions. In such cases rainfall directly above the aquifer has no effect on the recharge to the aquifer. Recharge would therefore only take place from rainfall in the area where such porous rocks are exposed at the surface as outcrops. A typical example of such a confined aquifer is the Auob Sandstone Member underlying the impervious Rietoog Member of the Karoo Sequence in the Stampriet Artesian Basin east of the OFRB.
Most groundwater systems (aquifers) are not static, since there is always an amount of water flowing into and out of the system. The ease with which the water flows through a rock depends on the nature of the interconnected pore spaces and is called the permeability of the specific rock type. Water flows more easily through large openings than through fine openings. Therefore a fine-grained clay layer, although it may have a high porosity, has a very low permeability in comparison to coarse sand or gravel with a lower porosity. The rate that water flows through any given rock type is quantified as the transmissivity (m/day) through unconfined aquifers and hydraulic conductivity (m 2/day) through confined aquifers. These quantities are constant values for any given rock type at any given locality.
In the following section, various recordings of the decline and rise of groundwater levels at specific recording stations will be discussed and compared with available rainfall data near the given point. A steady decline in the groundwater level at a given station indicates that more groundwater flows out of the system than into it. This does not necessarily mean that no recharge from rainfall takes place over the given period of time, but rather that the total outflow exceeds the total inflow. The inflow can therefore be natural inflow from an adjoining system plus recharge from rainfall and outflow can be the natural outflow from the system plus all the groundwater abstracted by pumping. A steady rise in the groundwater level over a given time indicates that more water flows into the system than out of it. Such rises are often correlated with high recharge from extraordinary rainfall events.
The advantage of long-term groundwater level monitoring at any given borehole is that a general trend in the decline or rise in the levels over time can be determined and associated with what can be regarded as natural outflow and inflow into the local groundwater system. Any sudden decreasing trend in the water levels would indicate over-abstraction from surrounding boreholes, whilst under-utilisation of an aquifer would be indicated by a rise in water levels or by water levels remaining constant with time.
13 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
4.2 DWAF groundwater level recorders
Data on only five analogue groundwater monitoring recorders in the OFRB could be found in the DWAF groundwater database (GROWIS). The relevant data regarding the location of these stations, including the station at Aus which is outside but adjacent to the OFRB, are presented in Table 3.
Table 3: Co-ordinates of DWAF groundwater recorders and related rainfall stations
DWAF groundwater monitoring recorders Rainfall stations
Station Lat. Long. mamsl WW No. Station Lat. Long.
Klein Aub -23.79086 16.63920 1,550 82975 Klein Aub -23.82 16.67
Kalkrand -24.25113 17.54476 1,188 21219 Kub Sud -24.23 17.50
Bethanien -26.49537 17.13503 1,013 10601 Bethanien -26.50 17.15
Karasburg -28.03 18.75 Bondels Dam -27.99843 18.69355 955 8680 Narugas -28.12 18.73
Karasburg -28.03 18.75 Dreihuk Dam -28.09904 18.61222 885 12782 Narugas -28.12 18.73
Aus -26.64801 16.55999 1,507 12769 Aus -26.68 16.32
It should be noted that these stations are located in the geomorphological features presented in Figure 3 as follows: Rehoboth Highlands (Klein Aub), Nama-Karoo Plains (Kalkrand, Bethanien), Gamchab Basin (Bondels Dam, Dreihuk Dam) and Namib Plains (Aus). These stations are clearly inadequate to fully represent the geohydrological character of the respective geomorphological features.
In order to gain some perspective on the groundwater level response at each of these stations they will be discussed briefly in relation to the available rainfall data. At this point it should be noted that although the rainfall data at some of the stations extend over a considerable period of time, only a relatively small period corresponds with the time that the groundwater levels are recorded.
4.2.1 Klein Aub (WW82975)
Klein Aub is located on quartzite, conglomerate and argillite, known as the Klein Aub Formation in the upper part of the Sinclair Sequence (Upper Mokolian to lower Namibian age: 920 Ma). The station falls within the Rehoboth Highlands at the northern extreme of the OFRB.
14 Ephemeral River Basins in Southern Africa
Figure 7 illustrates the problems encountered when there is inconsistency between the rainfall data and the recorded groundwater levels. Although the rainfall data dates back to 1966/67, it only continues to 1984/85, thus limiting the scope of comparison with groundwater level data to the ten years from 1975/76 to 1984/85. A high rainfall event was recorded during the 1978/79 year (457.9 mm) and this is reflected to some extent by a small rise in the groundwater level. The decline in rainfall from 1978/79 to 1980/81 is also reflected in the decline in groundwater levels from about 1,527.10 to 1,522.91 mamsl (4.19 m). This represents a considerable outflow of groundwater over the two-year period.
Figure 7 : Groundwater levels at Klein Aub with corresponding rainfall data
The next significant recharge event appears to be in December 1985, but unfortunately the rainfall records extend only to June 1985 and therefore correlating data have been lost or are currently missing.
Significant groundwater recharge events took place in July/August 1988 as well as March 1989, where the groundwater levels rose to a maximum of 1,528.63 mamsl. However, from this time to November 1993 (1,514.77 mamsl) a steady decline in the groundwater levels is observed, with only the occasional recharge episode in between. This indicates a decline in the groundwater levels of 13.86 m over about three years.
15 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Since November 1993 there appears to have been a steady, but fluctuating, rise in the groundwater levels, with significant peaks in February 1997 (1,526.79 mamsl) and July 2006 (1,529.58 mamsl). Unfortunately no comparisons can be made with corresponding rainfall data, except that it is known that exceptionally high rainfall events were recorded during the 2006 rainy season throughout Namibia.
It may be concluded that the groundwater regime around Klein Aub and in the Rehoboth Highlands of the Fish River Basin is a dynamic one that readily responds to recharge and outflow. More groundwater monitoring stations should be identified and operated in this part of the basin.
4.2.2 Kalkrand (WW21219 and WW10479)
Kalkrand is located on basalt of the Kalkrand Formation covered by relatively thin layers of calcrete, which is probably related to the Kalahari Group. The Kalkrand Formation represents basaltic lava flows with minor beds of red sandstone of the late Karoo Sequence (Jurassic age: 180 Ma). Both boreholes are within the Nama-Karoo Plains, but represent only the basaltic Karoo environment.
A great advantage of this site is that two monitoring boreholes, a DWAF recorder and a NamWater production borehole, can be compared with rainfall data over a considerably longer time period than the previous case. According to the co-ordinates, the borehole WW21219 is several kilometres to the east of WW104779, and also in the downstream flow direction of the perceived groundwater gradient. For this reason, their combined groundwater level responses will be discussed here and not in separate sections.
In this case, the groundwater level monitoring at WW21219 started in February 1984 and has continued to the present, while the available rainfall data at Kub Sud dates back to 1911 and continued up to the 2003/04 rainy season. With such regular data it is almost impossible to believe that rainfall recordings have not continued to date. Rainfall data submitted for relevant stations should therefore be verified during the hydrocensus.
It should be noted that borehole WW21219 was drilled to a depth of 70 m, while the groundwater level was only at a depth of 4 m below surface.
At this stage it is important to note that only the rest water levels in borehole WW10479 are recorded. In the NamWater production boreholes it is standard procedure to measure both the pumping water level (while the pump is operating) as well as the rest water levels (some time after the pump is switched off - normally just before it is switched on).
Figure 8 illustrates that from 1984 to 1998 (14 years) the groundwater levels continued to decline in both the DWAF monitoring borehole (WW21219) and the NamWater production borehole (WW10479). In the monitoring borehole (WW21219) the decline was 1.97 m, whilst in the production borehole (WW10479) it was only 1.41 m. Within this period some minor fluctuations are observed which could be related to minor groundwater recharge events from rainfall. Such events are to be expected in the shallow aquifer where the groundwater levels are only four metres below ground surface.
16 Ephemeral River Basins in Southern Africa
Figure 8: Groundwater levels at Kalkrand with corresponding rainf all data
17 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
The significant rainfall event during the 2000/01 rainy season (419 mm) caused the groundwater levels to rise by some three metres in both boreholes. The subsequent decline in rainfall from 2000 to 2004 is also reflected in the decline in water levels in both boreholes.
From May 2001 to January 2005 the groundwater level in the monitoring borehole (WW21219) declined by 1.98 m. Over these 43 months the decline rate would be 0.046 m/month. Assuming that the influence area around the borehole is a conservative 1 km 2 (1,000,000 m 2), the related dewatered rock volume would amount to 46,000 m 3/month. A conservative
specific yield (S y) for the basaltic rock in which the aquifer occurs, is assumed to be 1% or 0.01, which means that the groundwater dewatering would amount to a volume of only 460 m3/month. According to the NamWater production figures from borehole WW10479, 117,601 m 3 were abstracted over this period of 43 months, which amounts to an abstraction rate of 2,735 m 3/month, suggesting that the bulk abstraction from WW10479 had very little influence on the outflow of groundwater at WW21219. If the groundwater abstraction at WW10479 had had any influence on the water level decline at WW21219, the dewatering volume at the latter borehole would have exceeded 3,000 m 3/month.
Unfortunately, due to insufficient rainfall data, one cannot assess the recharge events suggested in the monitoring borehole (WW21219) in 2006 and 2009. However, it is known that good rainfall (above average) was experienced during those seasons. Should exceptionally high rainfall have been recorded at Kub Sud during this period, a similar rise in groundwater levels as those recorded in 2000/01 would be expected. Such a rise is clearly indicated in the levels of WW21219.
4.2.3 Bethanien (WW10601)
Bethanien is located on sandstone, black limestone and shale of the Kuibis Subgroup which occurs at the base of the Nama Group (late Namibian age: 650 Ma). The monitoring borehole is situated in the south-western margin of the Nama-Karoo Plains and just east of the Konkiep River. The borehole was drilled into shale and quartzite to a depth of 42 m, striking a fracture between 30 m and 39 m.
The groundwater level fluctuations observed in borehole WW10601 at Bethanien are typical of those encountered in riverbed alluvials, where recharge is mainly from seasonal flood events in the river, indicating that the fracture zone which was struck in the borehole intersects the river, thus receiving recharge from the flood events. However, the high rainfall events of 1985/86 (151 mm), 1987/88 (181 mm) and 1988/89 (174 mm), are reflected by high elevations in the groundwater levels in the borehole. Other exceptionally high groundwater levels were encountered in April 2000 and May 2006, but unfortunately no rainfall data are available to show any correlation.
Another observation that can be made is the continued decline in groundwater levels from May 1989 to January 1993 (4.92 m), while since then there has been a steady average rise in the groundwater levels until December 2009.
18 Ephemeral River Basins in Southern Africa
Figure 9 : Groundwater levels at Bethanien with corresponding rainfall data
4.2.4 Bondels Dam (WW8680), Dreihuk Dam (WW12782) and Gabis (WW16389)
Since the groundwater monitoring stations at the Bondels Dam and Dreihuk Dam are in close proximity to each other and since the NamWater production borehole (Gabis) is at the Dreihuk Dam, it is considered reasonable to discuss the groundwater level responses in these three boreholes together (Figure 10).
The two rainfall stations at Karasburg and Naruchas are also in close enough proximity to each other and therefore it was decided to compare the average rainfall recorded at these two stations with the corresponding groundwater levels of the three boreholes.
Borehole WW8680 is located inside the Bondels Dam to the west of Karasburg, with the result that enhanced recharge takes place immediately when the dam fills up with rainwater. Tillite of the Dwyka Formation (Karoo Sequence) is dominant in the area and is intruded by a prominent dolerite sill that occurs widely around the Karasburg area. The borehole was drilled in shale and sandstone of the Dwyka Formation down to 42.6m, after which granite of
19 Towards establishing a groundwater monitoring system: Orange-Fish River Basin the Namaqua Metamorphic Complex was encountered down to 106 m. Groundwater was struck at 24 m and occurs above the granite.
Figure 10 : Groundwater levels at Bondels Dam, Dreihuk Dam and Gabis with corresponding rainfall data
20 Ephemeral River Basins in Southern Africa
Both the DWAF monitoring borehole (WW12782) and NamWater's Gabis production borehole (WW16389) are located behind the wall of Dreihuk Dam. These two boreholes are also located in the Dwyka Formation and close to its contact with the underlying granite gneiss of the Namaqua Metamorphic Complex. The boreholes are located almost in the centre of the Gamchab Basin.
Rainfall records related to groundwater level monitoring periods show a high rainfall event for the area during the 1985/86 rainy season (256.75 mm). This event is, however, reflected by only a slight rise in the groundwater level at the Bondels Dam (WW8680). Considerably lower groundwater levels are recorded at this borehole from 1987 to 1993, but this trend is not as obvious at the Dreihuk Dam (WW12782) and Gabis (WW16389). A considerable rise in groundwater levels is observed at the Bondels Dam between June 1994 and June 1997, which is also observed to a lesser extent in the other two boreholes. Unfortunately the available rainfall data does not extend beyond the 1993/94 rainy season. Of particular interest, however, are the conspicuously low groundwater levels from 2002 to 2005 and the considerable rise in these levels in all three boreholes during the 2006 rainy season.
4.2.5 Aus (WW12769)
Aus is located outside the Fish River Basin in the Namib Plains to the west of the Great Escarpment. Borehole WW12769 is located a few kilometres to the east of Aus at Schakalskuppe and was most probably drilled into a fault in the granitic rocks of the Namaqua Metamorphic Complex.
Figure 11 shows very little fluctuations in the groundwater levels in borehole WW12769 in relation to the rainfall data which extends from 1974 to 1991. The two conspicuous declining troughs (each extending over a period of two years) shown at their lowest levels in January 1978 and March 1994 are the result of a nearby production borehole that pumped water to supply road and railway construction operations at the time. The result of each of the pumping operations shows a clear dewatering of the aquifer, since the groundwater levels never recovered to their original levels before pumping resumed. A continued decline in the groundwater levels, although slight, can be observed in the borehole.
The two peaks recorded on the chart are attributed to recording errors, since they are represented by only one measuring point each.
In this case, one may conclude that no groundwater recharge occurs at Aus from any direct rainfall events. The 2006 rainfall event seems, however, to have had a slight influence on the recharge, but this event has not been recorded in the current data.
21 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Figure 11 : Groundwater levels at Aus with corresponding rainfa ll data
4.3 NamWater groundwater production schemes
Rest water level (RWL) data were found on a total of 14 groundwater production schemes operated by NamWater within the OFRB (see Figure 6, above, and Table 4, below). Nine of the schemes are located within the Nama-Karoo Plains and five within the Gamchab Basin.
Since the rest water level trends at the Kalkrand and Gabis Schemes have already been discussed in the section on DWAF recorders, they will not be repeated here.
It should also be noted that other data on the monthly production figures and pump water levels are available from the basin management office, but it is not intended to discuss such data at this point.
22 Ephemeral River Basins in Southern Africa
Table 4: Co-ordinates of NamWater groundwater schemes and related rainfall stations
Namwater production schemes Rainfall stations
Station Lat. Long. mamsl WW No. Station Lat. Long.
Schlip -24.0321 17.1086 1,340 24610 Kub Sud -24.23 17.50
Kalkrand -24.2522 17.2515 1,185 10479 Kub Sud -24.23 17.50
Gibeon -24.7405 17.8883 1,086 27524 Hardap -24.50 17.87
Kriess -25.0041 18.1615 1,182 21806 Gibeon -25.03 17.77
Maltahöhe -24.8100 16.9900 1,340 32651 Maltahöhe -25.70 17.50
Tses -25.8848 18.1057 948 24550 Tses -25.88 18.13
Gainachas -25.7626 17.7102 970 24765 Berseba -25.98 17.78
Berseba -25.9898 17.9891 930 23138 Berseba -25.98 17.78
Kosis -26.7117 17.3111 940 24599 Bethanien -26.50 17.15
Grünau -27.6557 18.3539 1,184 23404 Blanksdam -27.78 18.30
Ai-Ais -27.9005 17.5070 204 32413 Ai-Ais -27.93 17.50
Karasburg -28.03 18.75 Gabis -28.0990 18.6129 898 16389 Narugas -28.12 18.73
Ariamsvlei -28.1210 19.8400 773 22548 Ariamsvlei -28.12 19.83
Warmbad -28.2500 18.7494 698 10042 Warmbad -28.45 18.73
4.3.1 Schlip (WW24610)
Schlip is located on green shale and green and red sandstone of the Vergesig Formation at the top of the Schwartzrand Subgroup of the Nama Group. The site lies to the north of the Fish River and close to the Goma-Aib River (a tributary of the Fish) within the northern extremes of the Nama-Karoo Plains, but outside the uplifted Nama block (described in Section 3.1 and illustrated in Figure 4).
The fluctuating trend in the rest water level of borehole WW24610 (Figure 12) is typical of that encountered from regular flood events in the river. Kub Sud is the nearest rainfall station to Schlip and there appears to be no correlation between the rainfall data at this station and the rest water levels in the borehole. The peaks recorded in the rest water levels in September 1991, February 1992, July 2003 and September 2003 are all single points making such recordings rather suspect.
It would be expected that the exceptionally high rainfall (419 mm) recorded during the 2000/01 rainy season would have reflected some rise in the groundwater levels at Schlip, but this is not the case.
Data from run-off gauging in the rivers may be of some help in this case and therefore the acquisition of such data should be considered as part of the proposed hydrocensus.
23 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Figure 12 : Rest water levels at Schlip with corresponding rainfall data
4.3.2 Gibeon (WW27524)
Gibeon is located on tillite and subordinate shale of the Dwyka Formation, which forms the basal part of the Karoo Sequence and overlies the red shale and sandstone of the Gross Aub Formation (Fish River Subgroup; upper Nama Group).
The borehole WW27524 occurs in the Nama-Karoo Plains and is located on the eastern banks of the Fish River some 40 km upstream from Gibeon, but outside the uplifted Nama block. Saline groundwater in the Dwyka Formation around Gibeon is the reason why the options of north-west striking faults farther north were considered.
Since the borehole is closer to Mariental than Gibeon, it is better to compare the groundwater level response with the rainfall data at Hardap. Unfortunately the rainfall data at Mariental extend only from 1899 to 1980, which do not cover the period of rest water level monitoring at borehole WW27524.
The recorded rest water levels in the borehole show a high in September 1989, followed by a subsequent low between December 1992 and February 1996. This trend corresponds well with a high rainfall peak during 1987/88 (249 mm) at Hardap and a subsequent decrease until 1994/95. During the 1996/97 rainy season, the rest water levels appear to have risen considerably to the highest peak in May 2000. It is known that the whole of Namibia
24 Ephemeral River Basins in Southern Africa experienced exceptionally high rainfall during the 1999/00 rainy season as indicated in the rainfall data at Hardap (546 mm). Extensive flooding in and around Mariental was also recorded during 2000. Unfortunately the rainfall data do not extend beyond 2000/01 to make any further comparisons.
Figure 13 : Rest water levels at Gibeon with corresponding rainfall data at Hardap
4.3.3 Kriess (WW21806)
The farm Kriess 219 is located to the east of the Asab River and is situated on Kalahari sediments (<50 m thick) which cover shale, mudstone and sandstone of the Prince Albert Formation (Auob and Nossob Members) in the Ecca Group of the Karoo Sequence.
The borehole occurs in the eastern Karoo portion of the Nama-Karoo Plains.
Gibeon would be the nearest rainfall station to compare rainfall data with trends in the rest water levels in the borehole, but the rainfall data at this station are insufficient for any logical comparisons.
25 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Generally the rest water levels appear to remain reasonably constant with a slight drop in December 1994 to July 1999, due to increased abstraction.
A high peak is observed in July 2000, due to the high rainfall over that period, but soon after this the levels declined, until July 2003 when the groundwater seemed to have stabilised to a constant level.
Figure 14 : Rest water levels at Kriess
4.3.4 Maltahöhe (WW32651)
Maltahöhe is located on red shale and sandstone of the Stockdale Formation at the base of the Fish River Subgroup (Nama Group). The borehole WW32651 occurs in the northern part of the Nama-Karoo Plains and on the north-western edge of the uplifted Nama block.
Unfortunately the rainfall data extend only up to 1997, while the groundwater monitoring data only start from 1996.
However, there appears to be a consistent rise in the rest water levels up to April 2000 with a sharp peak in May 2001. Since then, the rest water levels dropped and fluctuated at a steady rate until October 2007. There was a conspicuous rise in April 2008 that continued until April 2009.
26 Ephemeral River Basins in Southern Africa
Figure 15 : Rest water levels at Maltahöhe wi th corresponding rainfall data
Tses (WW24550)
Tses is located on tillite of the Dwyka Formation at the base of the Karoo Sequence. The borehole WW24550 is situated on the banks of the Tses River within the eastern boundaries of the Nama-Karoo Plains.
Periods of high rainfall were recorded in 1987/88 (215 mm), 1996/97 (194 mm), 2003/04 (187 mm) and 2005/06 (182 mm). These periods seem to have had very little effect on the groundwater rest levels in the borehole. Due to the fluctuating nature of the rest water levels, it would appear that recharge to the aquifer is as a result of flood events in the Tses River, rather than from direct rainfall.
27 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Figure 16: Rest water levels at Tses with corresponding rainfall data
4.3.5 Gainachas (WW24765)
Gainachas is located to the north of the Brukkaros Crater, on red shale and sandstone of the Gross Aub Formation in the upper layers of the Fish River Subgroup (Nama Group). The borehole WW24765 occurs within the Nama-Karoo Plains and is also located in the uplifted Nama block.
Rainfall records at the nearest station at Berseba extend over a considerable length of time to coincide well with the groundwater rest levels recorded in the borehole from 1984 to 1999. However there is a gap in the rainfall data between 1999 and 2003 (a period when high rainfall was known to occur over most of Namibia).
28 Ephemeral River Basins in Southern Africa
Figure 18: Rest water levels at Berseba
Figure 17: Rest water levels at Gainachas with corresponding rainfall data at Berseba
From 1984 to 1993, the rest water levels remained consistent within a range of one metre of fluctuation. During this period a high rainfall event was recorded during the 1987/88 season (231 mm) which is not clearly reflected by any rise in the rest water levels in the borehole. From 1993 to March 1995 the rest water levels dropped by a considerable two metres in relation to a decline in rainfall to a low of 25 mm in 1995. Since then a steady rise in the rest water levels is observed to March 1999, with a conspicuous rise of about two metres in April 2000. Unfortunately no rainfall data are available for this period.
4.3.6 Berseba (WW23138)
Berseba is located to the south of the Brukkaros Crater, on red shale and sandstone of the Gross Aub Formation in the upper layers of the Fish River Subgroup (Nama Group). The borehole WW23138 occurs within the Nama-Karoo Plains and is also located in the uplifted Nama block. The borehole is drilled to a depth of only 42 m and encountered some calcrete followed by sandstone.
Unfortunately the rainfall records at Berseba do not cover much of the time when rest water levels were recorded in the borehole, since these recordings only started in 1998.
29 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Figure 18: Rest water levels at Berseba
However, during 2000, the rest water levels rose by more than one metre, reaching a peak in September 2000. After this the levels gradually dropped to fluctuate within one metre until June 2005. In May 2006 to November 2006, the rest water level rose to a peak of more than one metre, after which it declined to fluctuate within a one metre boundary until 2009.
4.3.7 Kosis (WW24599)
Kosis is located to the south-east of Bethanien on black limestone, green and red shale and sandstone of the Schwatzrand Subgroup of the Nama Group in the south-western part of the Fish River Basin. Borehole WW24599 is drilled to a depth of 59 m into black limestone, sandstone and shale and is located at the south-western edge of the uplifted Nama block in the Nama-Karoo Plains. Of particular interest is the fact that the groundwater target is a fault with a north-west to south-east trend that cuts across the Konkiep River.
The available rainfall records at Bethanien cover a large part of the rest water level records at Kosis up to 1998. High rainfall events for the area, exceeding 100 mm/a, are recorded as follows in relation to the groundwater level data: 1983/84 (107 mm), 1984/85 (102 mm), 1985/86 (151 mm), 1987/88 (181 mm), 1988/89 (174 mm), 1992/93 (113 mm) and 1996/97 (125 mm).
In 1989 the rest water levels rose by more than five metres, following high rainfall events during 1987/88 and 1988/89. After this the levels show a continued decline, with some slight recharge in July 1990, November 1992 and June 1997. These slight rises are marked by slightly higher rainfall during the 1990/91, 1992/93 and 1996/97 seasons. From April 1989 to December 1998, however, the total decline in rest water levels was 19.78 m. Thereafter, until May 2002, a continued rise of 18.82 m in rest water levels is observed with another peak in May 2006. It can therefore confidently be concluded that the aquifer at Kosis is directly influenced by rainfall events that exceed 100 mm/a.
30 Ephemeral River Basins in Southern Africa
Figure 19: Rest water levels at Kosis with corresponding rainfall data at Bethanien
4.3.8 Grünau (WW23404)
Grünau is located on gneiss and meta-sedimentary rocks of the Namaqua Metamorphic Complex within the Gamchab Basin.
The relevant rainfall data at Blanksdam date back only to 1998 and continue, with some gaps until 2006.
Rest water levels clearly show considerable fluctuations with time. Since groundwater production started in borehole WW23404 in 1986 the rest water level shows a steady decline of 16.18 m until December 1989. Thereafter it retains a constant low level until August 1992, when it rises sharply by more than ten metres by September 1993. After this, the level declines gradually until May 1995 and retains a constantly low level until August 1998. From 1986 to 1994 the average monthly production from the borehole was 375 m 3 and then declined to an average of 202 m 3/month from 1995 to 1998.
31 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
It is only since the 1998/99 rainy season that rainfall data are available at Blanksdam, but the sudden rise in rest water levels of 15.95 m from August 1998 to May 2000 can hardly be correlated with the available rainfall data (Figure 20). However, production from the borehole was drastically reduced to an average of 143 m 3/month from 1999 to 2005.
Figure 20: Rest water levels at Grünau with corresponding rainfall data at Blanksdam
From May 2000 to July 2004 the levels decline by at least seven metres and then rise by ten metres to April 2006. The rise in rest water levels in 2006 may be attributed to a delayed groundwater recharge event caused by the recorded rainfall events of the 2003/04 (95.9 mm) and 2004/05 (151.5 mm) rainy seasons.
32 Ephemeral River Basins in Southern Africa
4.3.9 Ai-Ais (WW32413)
Ai-Ais is located within the Fish River Canyon on granitic rocks of the Namaqua Metamorphic Complex. Although it is regarded to be in the western part of the Gamchab Basin, borehole WW32413 was drilled in the alluvial beds of the Fish River.
Figure 21 : Rest water levels at Ai -Ais with corresponding rainfall d ata
Rainfall data extend only from 1990 to 1997 at Ai-Ais. However, it is obvious that recharge to the riverbed alluvium is not dependent on local rainfall, but rather on flood events in the river. The erratic fluctuations in the rest water levels therefore reflect the typical recharge events from run-off in the Fish River.
It would therefore be better to compare the groundwater level response to run-off data in the river than with rainfall data of the area.
4.3.10 Ariamsvlei (WW22548)
Ariamsvlei is located on sandstone and shale of the Kuibis Subgroup at the base of the Nama Group. Borehole WW22548 occurs in the western margins of the Gamchab Basin.
33 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Figure 22 : Rest water levels at Ariamsvlei with corresponding rainfall data
Rainfall data cover a reasonable period of time that coincides with the rest water level data (Figure 22), although it extends only until 2002.
It can be noted that high rainfall for the area (>150 mm) occurred during 1987/88 and 1988/89. This maintained a relatively high rest water level in the borehole, which however, started to decline gradually by 5.83 m until December 1998. This decline in groundwater levels coincides with a decline in rainfall over this period. From December 1999 to February 2002 a rise of 3.77 m is observed in the rest water levels. During this period the rainfall gradually increased to reach a high of 258 mm in the 2000/01 season. Since then the rest water levels have maintained a constant fluctuation of within two metres.
34 Ephemeral River Basins in Southern Africa
4.3.11 Warmbad (WW10042)
Warmbad is located on grantitic rocks of the Namaqua Metamorphic Complex and borehole WW10042 is located within the Gamchab Basin. According to a borehole completion report that was done by geologist Roy Miller in August 1969, the following rock-types were intersected at the given depths: 0–70 m (gneiss), 70–73 m (weathered gneiss), 73–94 m (quartz – fault zone), 94–104 m (weathered gneiss), 104–107 m (quartz – fault zone).
Figure 23: Rest water levels at Warmbad with corresponding rainfall data
Unfortunately the available rainfall data at Warmbad that can be correlated with the rest water levels in the borehole only extend from 1990 to 1995.
The rest water levels show a gradual decline until August 1996. It would appear that the recorded rainfall events in Figure 23 had no significant effect on the rest water levels. From August 1996 to January 2000 a sharp decrease in the rest water levels (3.5 m) is observed, after which the levels rise gradually within some fluctuating limits.
The rainfall data at Warmbad are insufficient to make any objective correlation with, or conclusions about the groundwater levels.
35 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
4.4 Conclusions
Borehole WW10601 at Bethanien is the only DWAF groundwater level recorder that shows no correlation with the local rainfall records, since recharge appears to be mainly from flood events in the Konkiep River. An attempt should therefore be made to obtain run-off gauging data in the river.
With the exception of rest water levels in the NamWater production boreholes at Schlip, Tses and Ai-Ais, which seem to be recharged by run-off water in the rivers, the other 11 production boreholes reveal changes in rest water levels that could be influenced by local rainfall events. Data from these boreholes can therefore be useful in future calculations of outflow and inflow into the respective aquifers. The effect of abstraction should, however, not be ignored when making the outflow calculations.
The value of groundwater level monitoring at Rosh Pinah and Oranjemund should not be ignored, since groundwater level fluctuations may be caused by other sources than direct rainfall.
Although there appears to be a sufficient and well-distributed set of rainfall stations over the entire OFRB to evaluate mean parameters such as the mean annual rainfall trend and five- year mean moving averages at each station, the available data at many of the stations are insufficient to make proper correlations with the groundwater level trends. Most of the data end at early dates and do not continue to the end of the groundwater level monitoring periods. A process should therefore be developed to keep the rainfall data up to date at those stations that are close to the groundwater monitoring stations.
In conclusion, it is obvious that the 20 groundwater monitoring stations (six DWAF recorders and 14 NamWater production schemes) within the OFRB are hardly adequate to make any reasonable assessment of the groundwater dynamics within the basin or even in parts thereof. More boreholes within the basin should be identified and possibly equipped with groundwater level monitoring devices from which data can be downloaded at specific intervals. Such monitoring boreholes should be spaced closely enough to each other so that reasonable deductions from the borehole data can be compared. Furthermore, the distribution of such monitoring boreholes should be more evenly spaced than at present, so that the main geological and geomorphological domains within the basin are sufficiently represented for statistical analysis. In this regard a starting point may be to select future monitoring boreholes as close to the existing rainfall monitoring stations as possible.
5. Groundwater quality
Bockmühl (2009) quite rightly states that the chemical, physical and biological quality of groundwater is of pertinent importance. Unfortunately very little, if any, ongoing groundwater quality monitoring is conducted within the basin. Most of the groundwater quality data date back to a once-off exercise in the 1970s when groundwater quality maps of Namibia were compiled.
36 Ephemeral River Basins in Southern Africa
However, since 1997, water samples have been collected regularly for chemical analysis at the NamWater schemes. Details of such analyses are presented in Appendix 1, since it would take up too much space to insert each chart for every scheme in this document. However, Table 5 summarises the chemical character of the groundwater at each scheme.
It may be helpful first to briefly discuss the basic concepts of changes in groundwater chemistry in relation to rainfall and groundwater level fluctuations, before embarking on a discussion of the more obvious chemical changes observed at some of the NamWater schemes.
Water (including groundwater) contains positively charged cations + and negatively charged anions - as dissolved chemical components in various concentrations; these are normally expressed in milligrams per litre (mg/ℓ). Salts of such components are inclined to precipitate in the soils and rocks within the unsaturated zone above the groundwater table during dry periods, due to evaporation and evapotranspiration of plants. When sufficient rain falls on the ground so that enough water is available to percolate down to the groundwater table, many of these salts are dissolved again and carried to the groundwater regime (saturated zone). Such an event would then result in a temporary increase in total dissolved solids (TDS) of the groundwater. However, a continued downward flow of water, after most of the salts have been leached out, may result in dilution and therefore cause the TDS to decline suddenly after a while.
Another important aspect to consider is that rainwater falling through the air dissolves small
amounts of carbon dioxide (CO 2) to form carbonic acid (H 2CO 3), which dissolves calcium 2+ carbonate (CaCO 3), thus enriching the groundwater with calcium (Ca ) and bicarbonate - (HCO 3 ). As a general rule it may be expected that recently recharged groundwater has a typical calcium-bicarbonate chemical character. Exceptions to this rule do exist, particularly in the case of limestone environments. Slight rises in the pH (acid/alkaline content) of the water can cause the calcium carbonate to precipitate out of solution.
+ - 2- Chemical substances such as sodium (Na ), chloride (Cl ) and to some extent sulphate (SO 4 ) do not easily precipitate once dissolved in the groundwater. This also applies to other minor - - (but critical) anions such as nitrate (NO 3 ) and fluoride (F ). When these chemical components are dominant in groundwater, it generally indicates stagnant conditions or, in some cases, old water. Once again it must be emphasised that there are exceptions to this rule.
Magnesium (Mg 2+ ) is a cation with an intermediary solubility between calcium (Ca 2+ ) and sodium (Na +). Generally the magnesium concentrations in the groundwater of the OFRB are 2- lower than those of the other two main cations. High concentrations of sulphate (SO 4 ) in some of the analyses may indicate the presence of decomposed organic material in the adjacent sedimentary rocks or the presence of weathered sulphide minerals in the host rocks of the groundwater. Groundwater that circulates deep in the earth’s crust along major faults may also have high concentrations of sulphate.
37
Table 5: Summary of groundwater chemical data: NamWater schemes
Cations Anions WW TDS Place pH mg/ℓ mg/ℓ No. mg/ℓ + ++ ++ - - = - - Na Ca Mg Cl HCO 3 SO 4 NO 3 F
Ai-Ais 32413 7.5-8.3 1179-2318 230-500 213-478 92-217 185-440 312-386 290-810 0.5-3.7 0.6-3.5
Ariamsvlei 22548 7.3-8.1 1099-3136 162-420 175-925 117-629 235-880 244-388 134-670 5-51 0.2-1.7
Berseba 23138 7.2-8.2 635-695 116-136 138-208 88-100 46-59 338-414 40-78 3-10 0.3-0.6
Gabis 16389 7.7-8.4 507-752 132-228 55-113 33-75 34-82 214-402 59-226 0.5-3.2 1-3.5
Gainachas 24765 7.4-8.3 576-639 86-102 175-223 79-96 37-56 330-364 30-49 1.3-10 0.2-0.6
Gibeon 27524 7.4-8.3 845-908 164-206 168-195 75-92 107-124 282-326 140-173 8-12 0.3-0.6
Grünau 23404 7.6-8.2 565-815 81-97 113-283 108-158 78-147 216-338 48-73 2.8-10.3 0.6-2.0
Kalkrand 10479 7.8-8.2 647-694 155-172 105-123 58-71 50-70 252-304 103-125 4-5 1.4-1.9
Kosis 24599 7.1-8.3 1211-1338 139-169 450-600 142-167 198-245 324-370 182-315 11-37 0.4-1.0
Kriess 21806 7.9-8.6 706-756 210-230 50-58 54-67 48-68 368-432 53-76 3-4 0.6-0.8
Maltahöhe 32651 7-8 772-902 89-111 223-290 150-196 55-90 378-412 37-73 19-36 0.3-1.4
Schlip 24610 7.3-7.8 384-573 29-50 145-248 71-96 21-42 218-296 21-43 3-10 0.1-0.4
Tses 24550 7.7-8.4 760-1146 195-363 83-238 17-54 76-154 232-426 162-320 0.6-8 0.3-1.1
Warmbad 10042 7.5-8.3 1461-1675 230-360 305-510 54-75 340-460 162-174 340-520 3.8-5.8 0.8-2.7
Ephemeral River Basins in Southern Africa
- Other anions of particular importance to human health, in particular, are nitrate (NO 3 ) and fluoride (F -). Nitrate can occur naturally in high concentrations in groundwater, but in most cases these are caused by pollution from stock pens, fertilisers and sewage pits. Drinking water in which the concentrations of nitrate exceed 20 mg/ℓ is classified as Group C (according to Namibian health standards) and is regarded as a danger to young babies in particular. High concentrations of fluoride normally occur in groundwater within granitic environments, and are a problem particularly within the southern parts of the Basin. Drinking water in which the concentrations of fluoride exceed 2 mg/ℓ in water is classified as Group C (according to Namibian health standards) and is considered to pose a danger to human bone structure.
The characteristic cation and anion concentrations in the groundwater at the different NamWater schemes are presented in Table 6.
• Groundwater samples from the schemes at Schlip, Maltahöhe, Gainachas, Berseba, Kosis and ++ - Grünau have a Ca /HCO 3 character, indicating direct recharge from rainfall, as discussed above. - • Due to the Na+/ HCO 3 character of the samples from Kalkrand and Kriess, it may be assumed that cation exchange has taken place, suggesting that the groundwater has travelled over some distance through the bedrock along fault systems. - • At Gibeon and Tses, the groundwater has a Na+, Ca++/ HCO 3 character, suggesting that cation exchange has taken place in combination with direct recharge from rainfall. 2- • However, it is also noted that significant amounts of SO 4 occur in the groundwater at Tses, Kosis, Ai-Ais and Gabis, suggesting the possible deep circulation of some of the groundwater through fault zones, although the presence of decomposing sulphide minerals cannot be ruled out. - 2- • The groundwater at Ariamsvlei and Warmbad has a predominant Cl and SO 4 character, which could suggest stagnant conditions, but the warm to hot springs at Warmbad (34 o C) o 2- and Ai-Ais (66 C) could account for the high SO 4 content of the groundwater at these latter two localities, indicating deep circulating water along major fault zones.
Some obvious changes in the groundwater chemistry at each of the NamWater schemes are summarised in Table 6 and compared to the rest water levels (RWL) during a specific year. Unfortunately much of the rainfall data were not recorded (N/R) during the corresponding years, so that comparisons could not be made for all schemes.
In the Nama-Karoo Plains, the groundwater at Maltahöhe is known to contain excessive quantities of nitrate.
According to the hydrogeological map of Namibia (Christelis and Struckmeier, 2001) the Nama- Karoo Plains in the area around Gibeon and to the east of the road to Tses contains saline groundwater in the Dwyka Formation. Another area to the north-west of Keetmanshoop is also marked as saline groundwater in the Dwyka Formation. A large part of the Gamchab Basin is also marked with areas of groundwater with high salinity. The granitic area around Warmbad is also known to have groundwater with high fluoride.
39 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Table 6: Changes in chemical components with changes in rest water level at NamWater schemes
Scheme Main ions Year Rain (mm) RWL Chemical change
++ - ++ - - Schlip Ca HCO 3 2006 N/R Normal TDS, Ca , HCO 3 , NO 3 increase
+ - Kalkrand Na HCO 3 2003 132 Down pH and TDS increase - - 2004 60 Down NO 3 and F slight increase Gibeon Na+ Ca ++ 2000 546 Up TDS increase - - HCO 3 2005 N/R Normal NO 3 increase 2008 N/R Normal TDS increase + - Kriess Na HCO 3 2000 546 Up pH increase - 2003 41 Down TDS, NO 3 increase - 2004 N/R Normal pH, NO 3 increase 2008 N/R Normal TDS increase Maltahöhe Ca ++ Mg ++ 2000 N/R Up pH increase - ++ ++ - HCO 3 2008 N/R Up pH, TDS, Ca , Mg , NO 3 increase ++ ++ - 2009 N/R Up pH, TDS, Ca , Mg , NO 3 increase ++ = Tses Na+ Ca 2002 129 Down pH, TDS, Na+, HCO 3, SO 4 increase = = HCO 3 SO 4 2003 22 Down pH, TDS, Na+, HCO 3, SO 4 increase 2005 97 Normal pH, increase - 2007 N/R Down TDS, NO 3 increase 2009 N/R Normal pH, TDS increase ++ - - Gainachas Ca HCO 3 2000 N/R Up Marked decrease in NO 3 Fluctuating pH and TDS Berseba Ca ++ Na + 2000 N/R Up Marked decrease in F - - HCO 3 Fluctuating pH and TDS
++ Kosis Ca HCO 3 2000 N/R Up pH and TDS increase = - SO 4 2002 N/R Up Rise in NO 3 ++ = 2004 N/R Down Steady rise in TDS, Ca , SO 4 ++ - - Grünau Ca HCO 3 2000 N/R Up pH, TDS, NO 3 , F increase 2003 N/R Decline pH increase 2006 14 Up ++ - 2009 N/R Normal pH, TDS, Ca NO 3 increase ++ ++ = - Ai-Ais Na+ Ca 2004 N/R Down TDS, Na+, Ca , SO 4 , NO 3 increase = - SO 4 2006 N/R Up pH, TDS, F increase
+ - - - Gabis Na , HCO 3 2000 N/R Up HCO 3 , F increase = + ++ = - SO 4 2005 N/R Down TDS, Na , Ca , SO 4 , NO 3 increase 2006 N/R Up No obvious changes Ariamsvlei Ca ++ Mg ++ 2000 156 Down pH increase - = ++ ++ - = - Cl SO 4 2004 N/R Up TDS, Ca , Mg , Cl , SO 4 , NO 3 increase ++ ++ - = - 2005 N/R Up TDS, Ca , Mg , Cl , SO 4 , NO 3 increase Warmbad Ca++ Na + 2000 N/R Down No significant change - = Cl SO 4 2006 N/R Normal pH, TDS increase 2008 N/R Normal pH rising
No groundwater quality monitoring seems to be taking place in the irrigation area at Hardap and Naute. This is of particular importance, since there is the potential of groundwater pollution
40 Ephemeral River Basins in Southern Africa due to the application of fertilisers and pesticides on the irrigated lands. Special attention should also be given to the monitoring of other potential pollution areas such as sewage systems, cattle kraals, etc.
From the discussions above it is clear that a greater effort is needed to focus on groundwater quality monitoring in the basin in future.
6. Proposed limited hydrocensus
The term “ limited ” is used here, since it is perceived that the hydrocensus will only be focussed on the identification and establishment of suitable groundwater monitoring stations as discussed above. Other data collection, such as water use and stock counts, which are normally included in a hydrocensus, will not be addressed. This may, however, be an opportunity to gather other important information, such as names of persons to be trained in monitoring.
It is assumed that DWAF will remain the custodian of the GROWAS Database on which all relevant groundwater data in the basin are stored and processed. Should this assumption be accepted, then clear procedures must be devised to ensure that all relevant groundwater data collected within the basin by persons other than DWAF staff, are entered and stored in the GROWAS system. This would imply that DWAF has the responsibility of regularly evaluating the data received and reporting such evaluations to the Orange-Fish Basin Management Committee (OFBMC) on a prescribed basis. The same should apply to run-off gauging data in the main river systems within the basin.
6.1 Ownership of the monitoring
In order to ensure that the hydrocensus is not simply a once-off exercise to be filed in the archives as a forgotten report, it is imperative that some official institution takes ownership of the process once it is approved and implemented. Since the issue at stake here is water resource related, it is clear that the obvious ownership should rest with DWAF (Directorate: Resource Management) in the Ministry of Agriculture, Water and Forestry. The major role players within DWAF are expected to be the Divisions of Geohydrology, Hydrology and Water Environment. Within this context, it is assumed that the Geohydrology Division will take the leading role, since most of the work will be groundwater related. An obvious assumption is that the Hydrology Division is always in close contact with the Namibian Meteorological Office to obtain rainfall data from official gauging stations within the basin. Tasks related to the implementation and control of the monitoring programme should therefore be assigned to specific personnel within each of the above divisions in order to establish sound and ongoing communication.
The OFBMC, however, would be the main forum to motivate the need for positive action and to ensure that the implemented process continues in future so that local stakeholders are well informed of the results on an ongoing basis.
41 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
6.2 Groundwater level monitoring
From the above discussions it is clear that, in spite of the existing six groundwater level recorders monitored by DWAF and the 14 groundwater production schemes operated by NamWater in the OFRB, more groundwater monitoring stations need to be identified and utilised in order to enable the continued evaluation of groundwater behaviour within the basin.
To illustrate this argument, the uplifted Nama block between the Konkiep and Fish rivers (see Section 3.1 and Figure 4), covering an approximate area of 14,500 km 2 could be used as an example. Currently there are only three groundwater monitoring stations within this block, i.e. Gainachas, Bethanien and Kosis. Other monitoring stations may be close by, but they are all located outside the block. For all practical purposes, the recorder at Bethanien can also be regarded as outside the western margins of the block, thus leaving Gainachas to represent the central part and Kosis the southern part of the block. Groundwater fluctuations in these two boreholes could hardly be regarded as representative of what happens in the entire block. If, however, a total of ten monitoring boreholes were evenly distributed over the entire block and they all showed an average rise of 0.5 m within the same given time, it would be possible to calculate the total volume of groundwater that caused such a rise within the block. Assuming that the specific yield (S y) of the Nama sediments is a conservative 1% then the average rise of 0.5 m in the groundwater levels over the entire block would amount to:
Volume of groundwater = 14,500 x 10 6 x 0.5 x 0.01 = 72.5 Mm 3
Similar calculations can be done for different parts of the basin with reasonable confidence, provided that the groundwater monitoring network has a representative distribution of stations. Other important quantifications can then also be made in order to understand the hydrogeological regime of the basin with greater confidence.
It stands to reason that while a large number of closely spaced monitoring stations would be ideal, they would be impractical and costly to operate and control. However, considering the extent of the basin (120,000 km 2), the distribution of one monitoring borehole in every quarter- degree square (15’ x 15’; ±625 km 2; one 1: 50,000 topographic map) could be sufficient. Figure 6 has been subdivided into such blocks to indicate the ones that currently have no monitoring stations. Should such a distribution density be regarded as essential, at least 140 additional monitoring boreholes throughout the basin would have to be identified. The minimum requirement would be one borehole in every half-degree square, which would reduce the number to 40 boreholes that need to be identified. Since the distribution of rainfall stations appears to be fairly even throughout the basin (see Figure 24), it may be worthwhile to consider identifying new monitoring boreholes close to these stations. There are at least 35 such stations, which are not close to current groundwater monitoring boreholes.
42 Ephemeral River Basins in Southern Africa
Figure 24: Rainfall map of the OFRB showing distribution of rainfall stations Source: Adapted from Mendelsohn et al. (2002)
43 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Once a decision has been taken regarding the affordability and required density of new groundwater monitoring stations that would meet the objective to properly evaluate the groundwater behaviour within the basin, suitably qualified personnel should be commissioned to undertake a hydrocensus of existing boreholes within each desired block (either one suitable borehole on each 1: 50,000 topo map, or one suitable borehole within every four adjoining 1: 50,000 topo maps). Figure 25 indicates that there are more than enough existing boreholes within the Basin to choose from. Unfortunately the information on the GROWAS database at DWAF gives no indication of the current status of these boreholes, i.e. whether they are being used by the owner or whether they may be in disuse due to collapse or because they have dried up.
For the above reasons a number of boreholes on one selected farm or area should be identified and visited in order to determine their current condition. A priority should then be allocated to each pre-selected borehole in the respective blocks, and if the first borehole (Priority 1) is found suitable for groundwater level monitoring purposes, the others selected in that area may be ignored. Should the Priority 1 borehole, not be found suitable, the next priority borehole should be considered etc., until a suitable one is found for the specific block.
At all times the farm owner (or responsible person) should be approached and contacted beforehand, since he/she may have greater knowledge of the situation and could provide substantial assistance. If the borehole is privately owned by a commercial farmer, formal written approval and agreement to use it for groundwater monitoring purposes would have to be obtained.
Suitable boreholes should comply with the following: • It should not be an operating borehole.
• A production borehole should be close-by for water sampling (±1 km).
• Access to the borehole should be easy (preferably close to public roads; no locked gates or other obstacles).
• The borehole should be clear of any blockages above the groundwater level (free of tree roots and other obstacles).
• There must be a reasonable open depth of water between the water level and the bottom of the borehole to allow for groundwater level fluctuations (±5 m).
• If the borehole does not have a protruding stand-pipe, it should be possible to install one so that a digital logger can be installed.
• The owner must be willing to allow the borehole to be used for monitoring purposes (if there is any sign of reluctance by the owner to allow this, it is best to abandon all other possibilities on the property).
From the above discussion it is clear that the co-operation of the owner of the borehole should be negotiated. It may even be possible that some owners could be willing to take groundwater level measurements themselves and provide the data to a central point within the given area.
Apart from recording the groundwater levels, it may also be possible to encourage owners to provide regular rainfall data as an integral part of the groundwater monitoring programme. For
44 Ephemeral River Basins in Southern Africa this reason regular feedback on the groundwater response in a given area should be on the agenda of every local farmers’ association within the basin.
In the communal areas, it would be necessary to involve local personnel of the Directorate of Water Supply and Sanitation Co-ordination (DWSSC) in DWAF. Experience has shown that there are many government owned boreholes in the area that are not in use and that could be used as monitoring boreholes, e.g. at Goab Drift, Ukos and Amas. The local population within the rural communal areas should, however, be educated and informed about the importance of protecting the monitoring boreholes.
Even though very little rainfall occurs at Rosh Pinah and Oranjemund, groundwater level monitoring in this part of the basin should not be ignored. It has been reported that such monitoring of existing boreholes takes place at Rosh Pinah as part of the waste and effluent disposal permit conditions, but the data are not transmitted to the Geohydrology Division of DWAF for inclusion in the GROWAS Database. These monitoring boreholes should be visited during the hydrocensus and a proper communication process must be established to ensure that the necessary data reach the correct destination for evaluation and processing. Boreholes in the alluvium beds of the lower Orange River, used to supply water to Oranjemund, are also being monitored. This aquifer is recharged by flood events in the river and therefore the monitoring of the boreholes and river flow should form an integral part of the groundwater monitoring in the basin.
From the above discussion it is clear that at least 140 topographical maps (1: 50,000), showing the localities of the existing boreholes in the basin, would have to be investigated at the Geohydrology Division (DWAF). This could be done either on their GIS system (preferable) or on the hard copies. A number of potentially suitable boreholes can then be selected within the predetermined area, according to their accessibility from the roads and a map can be printed showing only the selected boreholes. It is estimated that three working days would be sufficient to select such boreholes and the respective farms or areas in which they are located.
Once the potential monitoring boreholes have been selected it will be necessary to compile a programme to visit the farms (or places) where they are located, so that the owners can be contacted and notified in advance of the intended visit. It may take some time to contact the first few farmers, but once the process is in operation and becomes known within the community, the exercise has been perceived to become easier. Community involvement will therefore be of utmost importance during such contact procedures and the assistance of personnel within the two regions will be necessary. Local farmers’ associations could also be used to sensitise members to the intended hydrocensus. It is therefore anticipated that five working days will be needed to compile the visiting programme and to contact the first farmers (owners). The contact process thereafter will, however, continue until the end of the field visits and adjustments to the programme may be necessary from time to time.
Considering the time to be spent discussing the need for the hydrocensus with each selected borehole owner as well as the travelling time to each farm (place), it is estimated that no more than three boreholes may be found suitable for monitoring purposes in the field in one day. This implies that should it be decided to select 140 additional monitoring boreholes, at least 47 working days will be needed, while 13 working days may be necessary to select 40 additional monitoring boreholes.
45 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
The distance to be travelled during the site visits is estimated to be between 7,000 km and 10,000 km , depending on the number of monitoring stations to be selected.
Equipment that will be needed during the hydrocensus will include the following:
• Maps that include the access roads, farm boundaries and boreholes
• Hand-held GPS
• Water level dipper • Sterile sample bottles
• A suitable wrench to unscrew end plugs on boreholes
• A consent form to utilise the selected borehole for monitoring purposes, to be signed by the owner once agreement has been reached on the suitability of the borehole
• Whoever is to undertake the hydrocensus must be provided with a document of authorisation by the Ministry of Agriculture, Water and Forestry
• A notebook and pencil, together with a prepared questionnaire regarding existing boreholes for monitoring, rainfall data, springs, etc.
6.3 Groundwater quality monitoring
The groundwater quality monitoring of the boreholes operated by NamWater at the 14 schemes within the basin should continue. However, a system must be established to ensure that the analytical data are transferred to the GROWAS database of DWAF on a regular basis for comparison with groundwater level changes in the basin.
Obviously groundwater quality monitoring is also being done at Rosh Pinah and Oranjemund and the same conditions would apply to these institutions.
No groundwater quality monitoring is being done on a regular basis at the groundwater level recorders operated by DWAF or in the irrigation area at Hardap.
During the proposed hydrocensus, operating boreholes that are close to the existing groundwater level recorders of DWAF should be identified and water samples for chemical analysis must be taken from them. They should then be marked as groundwater quality recorders so that water samples can be taken at prescribed intervals. At the same time, operating boreholes close to the newly identified groundwater level monitoring boreholes discussed in Section 6.2 above should be identified and water samples taken from them. It is not perceived that any additional time, travelling and costs, other than already assumed in Section 6.2, would be needed to conduct this exercise.
46 Ephemeral River Basins in Southern Africa
Figure 25: Distribution of existing boreholes in the OFRB
The situation at the Hardap and Naute Irrigation Schemes will need special attention. A potential pollution risk exists from the application of fertilisers and pesticides. Boreholes may exist within the schemes that can be used for groundwater quality monitoring, but the possibility also exists that special boreholes would have to be drilled to ensure their proper representative distribution over the irrigation areas. During the hydrocensus, the schemes will have to be visited and an assessment must be made concerning the availability of existing potential monitoring boreholes as well as the need to drill new boreholes. It is suggested that
47 Towards establishing a groundwater monitoring system: Orange-Fish River Basin two working days be set aside for such an assessment. Distances to be travelled during such an exercise are estimated at about 700 km .
Once the groundwater quality monitoring stations have been identified and accepted, it is suggested that a regular groundwater quality monitoring programme be implemented. Generally, the minimum requirement would be the collection and analysis of two groundwater samples per annum – one before the rainy season (August to September) and one after the rainy season (April to May). However, the situation at the Hardap Irrigation Scheme may be dictated more by irrigation practices than the rainy season itself.
6.4 Rainfall monitoring
From the discussions and charts presented in Section 4, it is clear that rainfall data correlate well with fluctuations in the groundwater levels at most of the existing monitoring stations in the basin. The groundwater quality is also affected by the rainfall to some extent. In order, therefore, to assess the effect of rainfall on the groundwater regime, it is essential that the rainfall at or near the groundwater monitoring stations is measured regularly and the data transmitted to the responsible persons and institutions.
Although it is possible to install automatic rain gauging equipment at each groundwater monitoring station, such equipment is expensive and subject to vandalism. The best option remains to rely on the goodwill and co-operation of the local farmer or other responsible person to measure the rainfall and send the data through to a local central point. There is the possibility of absentee farmers, however, and in such cases special or alternative arrangements would have to be made. During the hydrocensus, the borehole owner can be provided with a prepared sheet on which he/she can record the rainfall data. Such a sheet should also contain a contact number and address to which the data can be transmitted. In some cases it may even be possible to show willing persons how to enter such data on computer spreadsheets and produce rainfall charts.
Where the groundwater monitoring stations are at or close to rainfall stations that have previously been recording rainfall data, the person conducting the hydrocensus should try and obtain all missing data and encourage the owner to continue recording the rainfall. Virtually all the rainfall data recorded above are incomplete or extend only to a certain date (2004), which means that the relevant stations would either have to be visited, or the data may be obtained telephonically. A special effort must be made to discuss the issues with the Meteorological Office and establish some working relationship with relevant personnel at the office. Visiting the rainfall stations could be included in the time allocated for the hydrocensus in Section 6.2.
6.5 Flood gauging
Although it is perceived that flood gauging takes place when necessary in the Fish River upstream of the Hardap Dam, and in the Löwen River upstream of the Naute Dam, it is uncertain whether any formal gauging of this nature takes place in the main river systems downstream of these two dams. From the discussions above it is clear that in some cases recharge to the aquifers does take place from such flood events. Therefore a flood gauging process should be
48 Ephemeral River Basins in Southern Africa introduced in order to gather relevant data that can be correlated to the groundwater level fluctuations.
During the hydrocensus, suitable sites to install flood gauging plates at bridges and/or weirs should be identified, should they not already exist. Clear recommendations should then be made in the report emanating from the hydrocensus regarding the need for installation of such gauging plates as well as the flood monitoring process that is to be followed. Local personnel could be used and motivated to record the flood events when they occur.
6.6 Springs
There are 58 springs recorded on the GROWAS database of DWAF in the basin (Figure 26). Only a few occur in the Fish River, while most of them occur in clusters in the north, to the west of Mariental and upstream of the Naute Dam. Quite a number are also located in the area around Karasburg and Warmbad. Most of the springs are not perennial, but flow only after some significant rainfall events.
The significance of the springs in relation to groundwater is that they indicate areas of natural discharge. Monitoring the flow of each spring on a regular basis would be ideal to calculate the outflow of groundwater from the respective aquifers, but such an exercise would be costly, since gauging weirs would have to be constructed at each spring. The Hydrology Division within DWAF should be encouraged to become more active and involved in this regard. Figure 26: Distribution of springs in the OFRB
It may be worth sampling the water flowing from some of the springs on a regular basis in order to determine any changes in groundwater quality. For this reason it is suggested that some of the springs in the Fish River and at least one spring in each cluster be visited during the hydrocensus. This may mean that about ten springs could be visited and sampled. The time and costs to do this could be included in those indicated in Section 6.2.
6.7 Training
Once the hydrocensus is complete, an ongoing groundwater monitoring programme must be implemented in the basin. This task is perceived to rest mainly with the Geohydrology Division in DWAF. Although it may be possible for DWAF to install some automatic digital water level
49 Towards establishing a groundwater monitoring system: Orange-Fish River Basin probes in a limited number of monitoring boreholes, much time and cost could be saved by involving the local community with many of the monitoring tasks. The advantage of such community involvement would be a direct interest in what is happening to the groundwater situation in the basin with the result that they take ownership of the groundwater monitoring in their area.
Persons interested in participating in such a monitoring programme should therefore be identified during the hydrocensus. Training in the procedures to be followed during the groundwater monitoring programme would include:
• Basic borehole construction and design, emphasising monitoring boreholes • How to measure a water level in a borehole
• How to record the water level and what to do with the data once recorded
• How to take a groundwater sample and how to mark the sample bottle
• When to take groundwater samples and where to send them
• How to measure rainfall, record it and where to send the data
• How to construct your own water level monitoring device.
It is assumed that a maximum of four hours (a morning or afternoon) may be necessary to conduct such training, which would include some practical exercises and motivational lectures.
Such training could be done as a once-off event at one central point within the basin. However, considering the distances some less privileged persons would have to travel, it may be regarded more advantageous to have the training sessions at three or even more different places.
For budgetary purposes it is anticipated that three man days would be needed to conduct such training and at least 3,000 km would be travelled.
6.8 Cost estimate
The cost estimates (excluding 15% VAT), as presented in Table 7 below, are based on rates approved by Treasury for the appointment by government institutions of hydrogeologists who are Consultant Members of the Namibia Hydrogeological Association.
The costs assume that all the work will be done by a Hydrogeological Consultant, but in reality it may be decided that personnel in the Geohydrology Division of DWAF should also be involved. Travel costs could be reduced considerably, for example, should transport be provided by DWAF.
Furthermore, it may not be necessary for the consultant to be involved in the full 13 days of visiting and selecting suitable boreholes for groundwater monitoring. After spending a few days with the DWAF personnel in the field, they could be left to continue the exercise on their own.
50 Ephemeral River Basins in Southern Africa
Table 7: Time and cost (N$) estimates for limited hydrocensus in the OFRB
Item Days km Rate Cost Select and investigate monitoring boreholes Personnel Select boreholes to be visited (consultant) 3 3,680 11,040 Contact borehole owners (technician) 5 1,440 7,200 Visit sites to select 40 boreholes (consultant) 13 3,680 47,840 Travel & subsistence Expected kilometres to be travelled 8,000 6 48,000 Daily vehicle allowance 13 353 4,589 Camping allowance 13 350 4,550 Sub-total 123,219
Groundwater quality monitoring Personnel Visit Hardap Irrigation Scheme (consultant) 2 3,680 7,360 Travel & subsistence Expected kilometres to be travelled 700 6 4,200 Daily vehicle allowance 2 353 706 Camping allowance 2 350 700 Sub-total 12,966 Training Personnel Training of groundwater monitoring teams 3 3,680 11,040 (consultant) Travel & subsistence Expected kilometres to be travelled 3,000 3.36 10,080 Daily vehicle allowance 3 353 1,059
Camping allowance 3 350 1,050
Sub-total 23,229
Reporting Personnel Report on a monitoring programme (consultant) 10 3,680 36,800 Total 196,214
51 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
The estimated costs for equipment to be used during the hydrocensus or for the groundwater monitoring are presented in Table 8.
Table 8. Estimated costs (N$) of groundwater monitoring equipment
Item Cost per item No. Total cost
Digital loggers 15,000 46 690,000
Borehole caps 700 46 32,200
Cables 1,000 46 46,000
Dip meters 5,000 10 50,000
Homemade dip meters 500 20 10,000
Water sample bottles 10 100 1,000
Rain gauges 50 20 1,000
Total 830,200
7. Conclusions
From the above discussions it is concluded that: • The Nama-Karoo Plains and the Gamchab Basin form important geomorphological features within the Orange-Fish River Basin that control the groundwater behaviour.
• With the exception of a few, all aquifers in the basin should be regarded as secondary aquifers. • The Nama Group within the Nama-Karoo Plains form the most promising groundwater bearing properties while the Karoo Sequence is an important groundwater target in the Gamchab Basin.
• The Dwyka Formation (Karoo Sequence) produces highly saline groundwater in most places. • A good correlation exists between rainfall events that exceed 250 mm/a and recharge to the aquifers. Recharge to the aquifers is also enhanced by flood events in the main rivers.
• For continuity and sound control, one government institution such as DWAF in the Ministry of Agriculture, Water and Forestry should take full ownership of the monitoring programme.
• The current six groundwater level monitoring stations operated by DWAF and the 14 groundwater schemes operated by NamWater in the basin are not sufficient to evaluate the groundwater response in the whole basin.
• Although there appear to be sufficient rainfall stations that are well distributed over the entire basin, the data from these stations are incomplete.
52 Ephemeral River Basins in Southern Africa
• Groundwater quality monitoring in the basin is limited only to that done by NamWater at the various schemes. The irrigation schemes at Hardap and Naute could potentially present a pollution threat to the groundwater from fertilisers and pesticides. • Flood gauging in the main river systems below the Hardap and Naute Dams is insufficient and needs to be better implemented.
• There are 58 springs in the basin that occur in the rivers or occur in clusters at places.
8. Recommendations
It is recommended that:
• The groundwater monitoring system within the Orange-Fish River Basin is extended by implementing the LIMITED Hydrocensus as described in Section 6 of this report
• The Directorate of Resource Management, DWAF, is tasked by the Ministry of Agriculture, Water and Forestry to supervise and control the upgrading of groundwater monitoring in the OFRB • Personnel from DWAF (both Geohydrology and DWSSC) are involved in the proposed hydrocensus
• NamWater and DWAF continue with their current groundwater monitoring in the basin
• More emphasis is given to groundwater quality monitoring in the basin – especially at the Hardap Irrigation Scheme • Attention is given to upgrading rainfall gauging in the basin
• Flood and flow gauging in the main rivers is upgraded
• More attention is given to the monitoring of springs in the basin
• The community is encouraged to become more involved in the groundwater monitoring in the basin.
53 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
References
Bockmühl, F. 2009. A hydrogeological review of the Orange-Fish River Basin. Report produced for the Ephemeral River Basins in Southern Africa (ERB) Project, Desert Research Foundation of Namibia (DRFN): Windhoek.
Bond, GW. 1946. A geochemical survey of the groundwater supplies of the Union of South Africa. Geological Survey of South Africa, Memoir 41, 208pp.
Christelis, G and W Struckmeier (Eds). 2001. Groundwater in Namibia: An explanation to the hydrogeological map . Ministry of Agriculture, Water and Rural Development: Windhoek.
Grotzinger, JP. 2000. Facies and Palaeoenvironmental setting of thrombolite-stromatolite reefs, Terminal Proterozoic Nama Group (ca. 550-548Ma), central and southern Namibia, Communications of the Geological Survey Namibia , 12: 221-233.
Mazambani, C. 2008. Community-based groundwater monitoring in the Omusati and Kunene regions. Project report for BTech, Polytechnic of Namibia.
Mendelsohn, JM, A Jarvis, C Roberts and T Robertson. 2002. Atlas of Namibia: A portrait of the land and its people. David Philip: Cape Town, 200pp.
Swart, R. 2008. An earth science review of the Orange-Fish River Basin. Report produced for the Ephemeral River Basins in Southern Africa Project, Desert Research Foundation of Namibia (DRFN): Windhoek.
Tordiffe, EAW. 1978. Aspects of the hydrogeochemistry of the Karoo Sequence in the Great Fish River Basin, Eastern Cape Province, with special reference to the groundwater quality. University of the Orange Free State, PhD – Thesis, unpublished, 307pp.
54 Ephemeral River Basins in Southern Africa
Appendix 1: Chemical analyses of groundwater samples from NamWater production schemes
Ai-Ais ...... 56 Ariamsvlei...... 58 Berseba...... 60 Gabis...... 62 Gainachas ...... 64 Gibeon...... 66 Grünau...... 68 Kalkrand...... 70 Kosis ...... 72 Kriess ...... 74 Maltahöhe...... 76 Schlip ...... 78 Tses ...... 80 Warmbad...... 82
55 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Ai-Ais (WW32413)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO mg/ℓ + + ++ ++ - - - = - 2 Na K Ca Mg Cl F HCO 3 SO 4 NO 3 11/10/1997 7.6 2318.2 490 10 477.5 216.67 440 0.6 384 810 0.5 43 10/11/1999 7.5 1782.2 435 9 230 145.83 315 2.1 350 575 0.8 42 28/09/2000 8 1835.8 490 8 212.5 133.33 330 0.9 386 605 1.4 44 20/11/2002 7.6 1681.7 415 8 347.5 133.33 295 2.7 362 515 1.4 44 18/04/2003 7.5 1179.2 410 7 450 133.33 280 2.3 366 730 2.2 41 02/10/2003 8 1916.2 500 9 392.5 158.33 380 2.5 312 730 3.66 38 13/06/2004 7.7 1976.5 475 7 437.5 162.50 390 2.4 326 710 2.4 41 02/08/2005 7.7 1641.5 360 8 345 129.17 260 2.4 354 490 2.1 39 29/05/2006 8.3 1275.0 230 5 280 100.00 185 3.5 354 290 1 45 21/09/2007 7.5 1795.6 420 8 342.5 133.33 340 2.2 340 520 <0.5 45 05/11/2008 7.7 1581.2 260 5 275 137.50 200 2.2 360 350 1 68 01/07/2009 8 1303.2 300 7 245 91.67 186 2.6 346 330 0.7 47
56 Ephemeral River Basins in Southern Africa
57 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Ariamsvlei (WW22548)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 21/01/1997 8 1159.1 208 8 175 250.00 260 0.2 244 255 15 30 13/10/1997 7.3 1099.47 189 7 275 116.67 240 0.2 294 134 5 29 21/09/1998 7.3 1742 270 6 450 275.00 500 1 336 280 14.4 28 28/10/1999 8 1155.08 193 6 295 120.83 275 1.7 294 146 7.5 28 20/09/2000 8.1 1136.99 230 6 295 129.17 290 0.7 288 156 8.2 27 20/11/2002 7.9 1214.71 203 6 342.5 150.00 275 1.7 310 180 9.6 21 08/05/2003 7.6 1188.58 162 5 387.5 133.33 235 1.4 388 159 9.2 24 21/10/2003 7.6 1244.86 230 6 360 154.17 315 1.5 306 175 10.4 26 16/06/2004 7.4 2726.9 347 9 925 533.33 780 0.9 364 670 43.4 26 05/08/2005 7.9 3135.6 420 12 875 629.17 880 1 346 520 50.8 22 13/10/2005 7.5 1191.93 205 5 365 150.00 295 1.5 300 164 8.6 27 12/06/2006 7.6 1601.3 200 7 500 345.83 430 1.4 312 250 12.4 25 14/09/2007 7.7 1211.36 199 6 342.5 120.83 255 1.6 296 167 8.2 28 06/11/2008 7.5 1314.54 206 6 352.5 154.17 290 1.1 296 165 10.4 26
58 Ephemeral River Basins in Southern Africa
59 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Berseba (WW23138)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO mg/ℓ + + ++ ++ - - - = - 2 Na K Ca Mg Cl F HCO 3 SO 4 NO 3 25/09/1997 7.6 688.09 116 5 177.5 95.83 48 0.3 398 50 3 33 22/10/1998 8.2 676.7 126 3 180 91.67 58 0.6 396 49 7.3 34 25/10/1999 7.5 693.45 127 6 187.5 100.00 59 0.6 398 54 8 34 14/09/2000 8.2 635.16 126 3 137.5 95.83 55 0.4 338 49 8.1 34 23/10/2002 7.6 688.76 124 3 190 87.50 49 0.5 388 54 8.7 31 21/05/2003 7.7 682.06 126 2 187.5 91.67 51 0.5 388 66 8.7 33 29/10/2003 7.4 696.8 133 2 190 91.67 50 0.5 394 55 8.5 33 21/05/2004 7.6 690.77 136 3 207.5 95.83 50 0.5 394 78 8.7 33 24/05/2005 8.2 667.99 126 2 207.5 95.83 47 0.5 414 52 9.7 32 01/12/2005 7.5 667.32 128 3 185 87.50 58 0.5 394 63 8.6 31 17/05/2006 7.8 686.08 120 2 190 91.67 48 0.4 392 40 7.8 31 16/05/2007 7.9 669.33 125 2 192.5 91.67 53 0.5 384 49 5.6 32 11/10/2007 7.2 671.34 123 2 175 87.50 48 0.4 372 53 9.1 34 09/04/2008 7.5 665.31 116 2 197.5 95.83 49 0.5 378 50 5.9 31 08/10/2008 7.5 681.39 118 2 197.5 95.83 46 0.4 378 51 7.7 51 07/05/2009 7.7 688.76 121 3 202.5 91.67 52 0.5 380 56 8.4 34 05/11/2009 8.1 695.46 125 2 187.5 91.67 47 0.5 394 47 8 37
60 Ephemeral River Basins in Southern Africa
61 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Gabis (WW16389)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 30/06/2009 8.1 568.16 146 1 67.5 41.67 54 2.5 232 101 0.5 31 07/11/2008 8 507.19 132 1 60 33.33 46 2.5 214 95 2.5 28 09/08/2005 8.1 726.28 228 2 112.5 70.83 82 2.2 284 226 3.2 26 14/06/2004 7.8 596.97 163 1 70 45.83 47 3.1 252 153 1.9 26 13/10/2003 7.8 568.16 169 1 62.5 41.67 45 3.1 252 120 0.6 28 15/04/2003 8.3 523.94 141 1 55 33.33 36 2.7 242 110 0.5 26 27/11/2002 8 536.67 150 2 55 37.50 41 3.3 254 87 1.1 28 17/04/2001 ------3.1 - - - - 02/10/2000 8.2 607.02 165 5 70 75.00 34 2.2 402 59 0.7 25 10/02/2000 7.9 653.25 178 2 77.5 54.17 51 3.5 304 132 0.5 30 10/11/1999 7.8 669.33 172 2 80 58.33 59 2.7 278 148 1.1 27 09/06/1999 ------3 - - - - 24/09/1998 7.7 751.74 189 2 97.5 75.00 66 1.9 290 210 1.6 28 07/10/1997 8.1 686.75 183 4 80 62.50 42 0.8 286 177 0.5 30 30/12/1996 8.4 751.07 202 3 62.5 66.67 70 1 254 215 1.3 32
62 Ephemeral River Basins in Southern Africa
63 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Gainachas (WW24765)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 25/09/1997 8.1 577.54 88 2 175 95.83 39 0.2 336 30 8.1 30 22/10/1998 8 606.35 92 4 190 83.33 51 0.6 352 34 8.6 30 25/10/1999 7.8 629.8 98 4 192.5 87.50 51 0.6 350 45 9.7 33 29/10/1999 7.5 628.46 101 4 195 91.67 56 0.5 360 42 9.9 31 23/10/2002 7.8 607.02 93 3 190 83.33 52 0.4 364 40 1.3 18 21/05/2003 8 618.41 100 3 202.5 83.33 49 0.4 356 47 8.1 26 29/10/2003 8.2 594.29 99 3 205 83.33 43 0.5 348 45 8.7 25 21/05/2004 7.4 631.81 102 4 220 87.50 51 0.4 348 49 9.8 30 24/05/2005 8.3 580.89 99 3 210 83.33 37 0.6 362 43 8.9 21 01/12/2005 7.5 577.54 94 3 190 79.17 53 0.5 344 44 9.7 27 16/05/2007 7.7 575.53 93 3 187.5 79.17 43 0.4 336 34 5.1 28 11/10/2007 7.4 582.9 87 3 197.5 83.33 37 0.4 340 35 8.3 24 09/04/2008 7.6 631.14 89 3 222.5 91.67 55 0.4 336 44 7.4 27 08/10/2008 7.6 585.58 86 3 200 83.33 38 0.4 330 33 8.7 46 07/05/2009 7.8 639.18 91 4 220 87.50 51 0.5 342 42 10 28 05/11/2009 8.2 603.67 94 3 192.5 83.33 39 0.4 346 32 8.7 34
64 Ephemeral River Basins in Southern Africa
65 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Gibeon (WW27524)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 16/08/2000 8.3 907.85 185 3 172.5 87.50 120 0.3 322 158 8.1 31 15/11/2002 7.7 856.93 199 3 180 83.33 119 0.5 324 154 10.3 29 17/09/2003 8.1 886.41 206 3 167.5 75.00 112 0.6 322 140 9.1 27 20/08/2004 7.8 858.94 164 2 195 91.67 110 0.6 326 155 9.5 27 18/10/2005 7.7 844.87 190 3 170 79.17 107 0.6 324 173 11.6 30 01/09/2006 8 870.33 198 2 180 83.33 121 0.6 320 158 8.77 29 16/06/2008 7.4 903.16 199 3 170 83.33 120 0.6 312 155 8.3 28 10/06/2009 7.9 864.97 195 3 180 87.50 124 0.6 282 164 9 31
66 Ephemeral River Basins in Southern Africa
67 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Grünau (WW23404)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 30/12/1996 8.2 565.48 83 5 112.5 108.33 93 0.6 216 56 5.6 37 13/10/1997 7.6 692.11 81 6 205 120.83 86 0.6 316 53 2.8 35 23/09/1998 7.6 668.66 86 1 220 120.83 101 1.8 320 58 6.8 37 10/11/1999 7.7 653.25 82 4 205 116.67 86 2 324 53 5.9 35 29/09/2000 7.8 729.63 94 5 250 141.67 113 1.7 338 55 9.7 35 22/11/2002 7.9 672.01 85 3 222.5 125.00 83 1.9 330 53 6.7 31 03/10/2003 7.8 645.21 89 4 225 120.83 78 1.7 332 53 5.41 30 16/06/2004 7.6 663.97 82 2 217.5 116.67 82 1.8 328 48 6.1 31 03/08/2005 7.8 660.62 96 3 232.5 125.00 87 1.7 336 54 5.9 31 14/09/2007 7.8 797.3 97 4 260 158.33 147 1.7 284 73 10.3 36 05/11/2008 7.9 798.64 87 3 257.5 133.33 130 1.8 318 60 7.9 31 28/06/2009 8.1 814.72 95 4 282.5 150.00 137 1.8 330 62 6.7 35
68 Ephemeral River Basins in Southern Africa
69 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Kalkrand (WW10479)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 16/06/2009 7.9 659.28 157 2 110 66.67 65 1.7 252 125 4.6 40 17/06/2008 7.7 694.12 169 3 110 62.50 67 1.6 286 124 3.8 38 15/09/2006 7.8 686.75 165 2 115 62.50 63 1.6 292 107 4.57 36 14/10/2005 7.8 646.55 158 2 105 58.33 50 1.5 300 117 4.8 39 18/08/2004 8.2 669.33 155 2 122.5 62.50 62 1.8 302 124 5.4 36 16/09/2003 7.9 689.43 172 3 110 62.50 64 1.6 298 110 4.8 35 12/11/2002 7.8 659.28 157 3 122.5 62.50 61 1.4 304 108 4.8 36 23/08/2000 7.9 661.29 164 5 110 70.83 70 1.9 292 103 4.2 39
70 Ephemeral River Basins in Southern Africa
71 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Kosis (WW24599)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 29/10/1997 7.3 1329.28 160 3 500 166.67 245 0.4 364 265 11 26 22/10/1998 7.1 1211.36 156 3 450 154.17 225 0.8 368 250 12.3 - 01/11/1999 7.5 1234.14 155 3 475 162.50 210 1 370 265 21.6 27 15/09/2000 8.3 1216.72 147 2 462.5 158.33 205 0.9 360 245 23.2 27 22/10/2002 7.9 1244.86 153 2 572.5 158.33 200 1 350 260 36.8 25 22/05/2003 8 1280.37 156 2 550 162.50 200 0.9 342 300 34.3 26 29/10/2003 7.2 1307.17 155 2 600 166.67 215 1 346 315 32.2 26 26/05/2004 7.6 1337.99 169 2 587.5 166.67 215 1 348 290 32 26 24/05/2005 7.8 1228.78 157 2 537.5 166.67 198 0.9 338 265 31.9 25 02/12/2005 7.3 1333.3 157 2 585 150.00 210 1 342 315 29.5 24 08/04/2008 7.3 1272.33 139 1 537.5 141.67 227 1 324 182 28.8 25
72 Ephemeral River Basins in Southern Africa
73 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Kriess (WW21806)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 16/08/2000 8.6 721.59 210 5 55 66.67 68 0.8 430 60 2.5 30 18/11/2002 8 721.59 225 2 55 58.33 62 0.6 430 53 3.8 28 15/09/2003 7.9 756.43 230 3 55 62.50 63 0.6 426 66 3.4 27 16/08/2004 8.6 736.33 220 2 57.5 58.33 52 0.7 432 76 3.7 28 18/10/2005 8 706.18 219 2 52.5 54.17 48 0.8 430 64 3.3 30 01/09/2006 8.1 722.26 223 2 50 58.33 57 0.7 422 64 3.14 29 20/06/2008 7.9 752.41 210 3 52.5 58.33 61 0.7 418 65 2.7 29 09/06/2009 8 711.54 210 2 50 62.50 65 0.7 368 68 3.3 31
74 Ephemeral River Basins in Southern Africa
75 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Maltahöhe (WW32651)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 18/03/1998 7 779.88 89 11 222.5 150.00 66 0.3 398 44 21.9 29 16/08/2000 8 837.5 102 14 277.5 183.33 85 1.3 398 61 24.3 29 12/11/2002 7.5 803.33 102 12 280 175.00 73 1.1 412 59 27.5 26 17/09/2003 7.3 815.39 107 13 247.5 166.67 63 1.2 406 60 23 25 18/08/2004 7.3 808.02 102 12 260 158.33 67 1.2 402 68 24.8 24 19/10/2005 7.4 771.84 104 12 250 154.17 55 1.3 410 56 29.3 27 15/09/2006 7.5 805.34 101 12 252.5 150.00 61 1.1 408 37 19.3 26 18/06/2008 7.4 901.82 103 13 285 179.17 82 1.4 378 64 35.7 26 02/06/2009 7.9 885.74 111 13 290 195.83 90 1.2 386 73 31.7 28
76 Ephemeral River Basins in Southern Africa
77 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Schlip (WW24610)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO mg/ℓ + + ++ ++ - - - = - 2 Na K Ca Mg Cl F HCO 3 SO 4 NO 3 29/05/1997 7.6 383.91 29 3 145 70.83 21 0.1 234 21 2.9 30 25/08/2000 7.8 388.6 30 4 180 79.17 35 0.43 218 23 5.7 27 18/11/2002 7.5 416.07 32 2 185 79.17 32 0.3 228 41 3.3 26 16/09/2003 7.3 473.02 34 2 202.5 87.50 30 0.3 274 28 3.4 26 14/10/2005 7.6 434.16 34 2 210 79.17 22 0.4 272 43 3 28 15/09/2006 7.7 560.79 42 3 247.5 95.83 38 0.3 296 29 9.9 28 16/06/2008 7.3 502.5 38 3 225 87.50 34 0.3 294 35 3.1 27 16/06/2009 7.6 519.25 50 3 220 95.83 42 0.3 286 40 5.5 31
78 Ephemeral River Basins in Southern Africa
79 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Tses (WW24550)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 24/09/1997 8.1 868.32 195 1 177.5 54.17 76 0.3 382 167 3.6 19 22/10/1998 8.2 1006.34 290 3 127.5 29.17 102 1.1 388 275 2.9 16 25/10/1999 7.8 984.9 280 5 142.5 41.67 95 1 400 260 1.3 17 14/09/2000 8.3 890.43 210 2 165 50.00 104 0.6 300 205 8.3 20 23/10/2002 8.4 1141.68 363 2 105 20.83 123 0.9 426 320 0.6 14 21/05/2003 8.3 1043.19 345 2 82.5 25.00 119 0.8 368 270 0.8 16 29/10/2003 7.9 1146.37 360 2 115 25.00 130 0.9 434 280 0.6 15 21/05/2004 8.1 850.23 245 2 130 29.17 113 0.8 264 205 6.2 14 24/05/2005 8.3 944.03 224 2 237.5 41.67 154 0.5 232 250 6.7 12 01/12/2005 7.7 989.59 297 2 160 29.17 114 0.8 402 255 3.5 15 18/05/2006 8.2 760.45 203 2 122.5 20.83 87 0.7 248 162 8 12 16/05/2007 7.6 946.04 240 2 207.5 37.50 106 0.7 382 200 4.6 17 11/10/2007 7.7 1088.75 265 2 172.5 33.33 132 0.7 388 208 1.8 15 09/04/2008 8 875.69 240 2 102.5 16.67 87 0.8 294 174 14.2 12 11/10/2008 7.8 913.88 215 2 202.5 37.50 85 0.7 362 169 4.6 26 07/05/2009 7.8 896.46 245 4 152.5 29.17 91 0.8 330 193 6.5 19 05/11/2009 8.3 1055.25 265 2 202.5 41.67 112 0.8 422 194 2.9 20
80 Ephemeral River Basins in Southern Africa
81 Towards establishing a groundwater monitoring system: Orange-Fish River Basin
Warmbad (WW10042)
TDS Cations (mg/ℓ) Anions (mg/ℓ) Date pH SiO 2 mg/ℓ + + ++ ++ - - - = - Na K Ca Mg Cl F HCO 3 SO 4 NO 3 30/12/1996 8.3 1460.6 295 7 400 58.33 420 0.8 164 380 3.8 20 22/09/1998 7.7 1601.3 345 4 312.5 75.00 460 2.3 172 340 5.1 24 09/11/1999 7.8 1594.6 350 4 307.5 54.17 430 2.5 174 360 4.8 20 18/09/2000 7.9 1561.1 360 6 305 62.50 430 2.2 174 390 4.4 23 19/11/2002 7.8 1601.3 345 4 382.5 54.17 405 2.4 168 405 5.3 18 14/04/2003 7.8 1608 310 3 450 54.17 360 2 168 520 4.8 20 29/09/2003 7.6 1534.3 350 4 405 58.33 420 2.1 168 465 4.74 19 14/06/2004 7.7 1634.8 338 3 407.5 54.17 435 2.5 166 351 5.8 21 10/08/2005 8.1 1608 330 4 415 54.17 380 2.1 168 440 5.4 20 24/06/2006 7.7 1661.6 230 3 510 62.50 340 2.7 170 350 3.7 22 19/09/2007 7.5 1675 345 5 370 54.17 386 2 162 380 5.26 22 05/11/2008 7.8 1608 330 4 410 58.33 440 2.3 166 350 5.2 21 30/06/2009 8 1567.8 340 4 367.5 54.17 370 2.5 168 380 5 23
82 Ephemeral River Basins in Southern Africa
83