Appendix B2 Progress report on groundwater field work at WCNP ENV-S-I 2004-006 INTERACTIONS BETWEEN GROUNDWATER AND SURFACE WATER: ASSESSMENT OF THE LANGEBAAN LAGOON AS A STUDY AREA I. Saayman, C. Colvin, J. Weaver, L. Fraser, J. Zhang, S. Hughes, G. Tredoux, A. Hön, D. Le Maitre, F. Rusinga, and S. Israel Issued by: Division of Water, Environment and Forestry Technology, CSIR P O Box 395, Pretoria 0001 March 2004 Page - 2 Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 Table of Contents 1. Motivation ......................................................................................................................... 1 2. Background to Groundwater – Surface Water Interactions ....................................... 1 2.1 Climate ....................................................................................................................... 1 2.2 Geology ...................................................................................................................... 2 2.3 Cultural Influences ..................................................................................................... 2 3. Methodology/Approach ................................................................................................... 2 4. Study Site Description ...................................................................................................... 4 4.1 Bio-physical Environment.......................................................................................... 4 4.2 Regional Hydrology and Hydrogeology .................................................................... 5 4.3 Vegetation .................................................................................................................. 6 4.4 Conservation status .................................................................................................... 6 4.5 Salinity tolerances ...................................................................................................... 7 5. Initial Conceptual Model ................................................................................................. 7 6. Results of Initial Field Work and Discussion............................................................... 12 6.1 Study area ................................................................................................................. 12 6.2 Geophysics Results .................................................................................................. 12 6.2.1 6.2.2 6.2.3 6.2.4 7. 8. Introduction ..................................................................................................................... 12 Field methods .................................................................................................................. 13 Results and preliminary interpretation ............................................................................ 14 Areas of uncertainty and lessons learned ........................................................................ 19 6.3 Remote Sensing ........................................................................................................ 20 6.4 Chemical Sampling .................................................................................................. 21 Data Inventory/Availability ........................................................................................... 23 7.1 Reports and papers: .................................................................................................. 23 7.2 Maps: (Hard copies) ................................................................................................. 24 7.3 GIS data: ................................................................................................................... 25 7.4 Berg River Monitoring data ..................................................................................... 25 7.5 Borehole data: .......................................................................................................... 25 References ....................................................................................................................... 26 Page - 3 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 List of Figures Figure 1: Geology of the Langebaan Lagoon area (Reaper, 1995) ............................................ 5 Figure 2: Conceptual model of Groundwater Discharge to the Langebaan Lagoon .................. 9 Figure 3: Scenarios to explain the distribution of fresh and saline water at Oosterval ............ 10 Figure 4: Relation between slope, geology and the fresh water/salt water interface ............... 11 Figure 5: Plotted resistivity data for the initial resistivity profile at Geelbek. The two data points in red were the only bad data points that were removed. ...................................... 15 Figure 6: Resistivity profile 1 at Geelbek traversing from saline water vegetation to fresh water vegetation. .............................................................................................................. 16 Figure 7: National Groundwater database listed boreholes in study area. ............................... 21 List of Tables Table 1: Seasonal salinity ranges in selected parts of the Langebaan Lagoon (Flemming, 1977) ............................................................................................................................ 5 Table 2: Field measurements from reconnaissance borehole sampling at Langebaan. .......... 21 Page - 4 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 1. Motivation The South African National Water Act (no. 36 of 1998) prioritises the allocation of water to meet basic human needs and the requirements of the environment, and recognises groundwater as part of the water cycle. Water Resource managers are therefore required to understand the contribution that groundwater makes to a surface water system and its role in sustaining ecosystems, before an allocation may be made from that groundwater resource. The scientific tools required to develop such an understanding, however, is largely lacking or non-existent. A number of Water Research Commission (WRC) funded projects are underway or have been recently completed to address the need for methodologies/approaches that quantify the contribution of groundwater to rivers (Xu, et al., 2003), and to assess the degree of ecosystem dependence on groundwater (Colvin, in progress). This project is funded through the WRC Aquifer Dependent Ecosystem project (1337) CSIR’s parliamentary grant, and aims to: Test methodologies to characterise the interactions between groundwater and surface water systems and coastal ecosystems; Establish an integrated approach within the CSIR Groundwater Group when tackling groundwater studies; Build capacity within the CSIR Groundwater Group, which can be applied to future research studies. 2. Background to Groundwater – Surface Water Interactions The interaction between groundwater and surface water takes place when and where groundwater emerges at the surface or discharges to a surface water body, or where surface water passes into groundwater. In many settings the flow of streams or rivers and water logged conditions in wetlands and vleis during periods of little or no rainfall is maintained through the discharge of groundwater. Surface water systems on its part represent important zones of recharge to groundwater, especially in arid and semi-arid settings (Lerner, 1990). Where groundwater and surface water occur in close association, it is the elevation of the groundwater table relative to the surface water level that controls the direction and quantity of flow in or out of the surface water system. The relation between these two systems is in part influenced by climate (discharge volumes and patterns), geology, (aquifer properties and changes in topography), and cultural activity (like landuse, groundwater abstraction and the damming of rivers) (Lerner, 1996, Van Niekerk, et al., 1995, Xu, et al., 2002). Changes in these factors along the reach of a river will influence the relative elevation of the water table, and so dictate the type and extent of the groundwater/surface water interaction. 2.1 Climate Different climatic zones are characterised by typical groundwater/surface water relations. Humid and temperate regions for instance are characterised by high water tables and perennial rivers. Seasonal changes in the water table may result in perennial rivers being seasonal in their upper reaches. Ephemeral rivers on the other hand are more common in arid and semi- Page - 1 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 arid regions. In such regions rivers are typically perched, though such systems may switch between being perched and connected as water table elevations change seasonally, or in response to recharge events (Lerner, 1996). The greater depth of groundwater in arid and semi-arid settings also results in saturated flow typically making a much smaller contribution to stormflow discharge than in humid–temperate regions (22% in a semi-arid catchment vs. 40 to 80% in humid-temperate catchments – Sandström, 1996). 2.2 Geology In all settings, the rate of exchange between groundwater and surface water will be dictated by the hydraulic gradient between the two systems and the hydraulic conductivity of the intervening soil, rock and bed sediments. Variations in hydraulic conductivity will also influence the rate and location of groundwater discharge or recharge. Even in largely homogonous systems, the hydraulic conductivity will dictate the location of the groundwatersurface water interaction. An example is the numerical model presented by the U. S. Army Corps of Engineers (1999) of groundwater discharge to a seepage lake. The model shows that the higher the hydraulic conductivity of the aquifer that underlie the lake, the more likely it is that inflow through the lake bottom will be reversed to outflow. 2.3 Cultural Influences Human activities commonly affect the distribution, quantity, and chemical quality of water resources. Where groundwater resources are exploited, groundwater pumping can result in a change in the rate and direction of groundwater flow. This has the ability to decrease flow in streams that are hydraulically connected to aquifers, either by reducing leakage of groundwater to the stream or by inducing leakage from the stream into the subsurface (U. S. Army Corps of Engineers, 1999). Controlled or altered discharge to streams and rivers also has the ability to induce surface water recharge to aquifers or to limit groundwater discharge to streams. In most settings agriculture is the biggest groundwater user, but also impact water resources through the modification of landscapes. This in turn results in a modification of the infiltration and runoff characteristics of the land, which in turn affects recharge to groundwater, the delivery of water and sediment to surface water bodies, and evapotranspiration (Winter, 1998). The application of fertilizers, herbicides and pesticides to agricultural land also results in the contamination of water resources. Other sources of water resources contamination include waste disposal sites, cemeteries, and discharges from waste water treatment plants, industrial facilities and stormwater drains. 3. Methodology/Approach The interrelated nature of systems where interactions between surface water and groundwater occur, requires the input of a multi disciplinary team, which would typically include hydrogeologists, geochemists, geophysicists, hydrological/hydrogeological modellers, botanists, and remote sensing specialists. The CSIR is in the fortunate position of having specialists in all of theses fields. The project leadership identified persons within the CSIR (and in particular the Groundwater Group), which had these skills, and invited them to project Page - 2 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 planning meeting. During this meeting the approach to be followed was discussed, and possible study sites identified. The study sites that were identified during the planning meeting (nine sites were identified), and the criteria which the study team viewed as significant for the selection of a research site was passed on to a MBA study group at the University of Stellenbosch, who had agreed to use an ‘Analytical Hierarchy Process” to rank the sites in terms of their suitability, relevance and practicality. Their analysis found that the Zeekoevlei and Langebaan Lagoon sites scored highest when evaluated in terms of the stated criteria. Following review of the results of the analytical hierarchy exercise, the study team decide on the Langebaan Lagoon as their preferred study site, as: 1. The Langebaan Lagoon is recognised as an area of high ecological significance, which is threatened by human activity; 2. The west coast is semi-arid, with very little surface water run-off and a high reliance on groundwater for water supply; 3. Use of the Langebaan Lagoon as a study site makes possible cooperation and research partnerships with the WRC funded “Aquifer Dependent Ecosystems” project, the National Parks Board, and the University of Stellenbosch (Botany Department). Once the Langebaan Lagoon was selected as the research study site, permission was obtained from the National Parks Board to do research within the West Coast National Park (Appendix 2), the area visited on the 12th and 13th of January 2004 to familiarise team members with the area. A workshop was held subsequent to the study visit during which the study team formulated their conceptual understanding of hydrogeological system and developed a number of tasks to test its validity. The outputs of the hydrological system conceptualisation (sketched cross sections and plans) is presented in section 5. The work-plan to test the validity of the conceptual model comprised the following: Analysis of remote sensing images so that the distribution of freshwater vegetation on the edge of the lagoon may be delineated; Geophysics using multi-electrode resistivity imaging to delineate the contact between fresh groundwater and saline/brackish lagoon water; A drive-peizometer survey, along the edge of the lagoon where the remote sensing analysis and geophysics indicated the discharge of freshwater, so that groundwater samples may be obtained for lab analysis; A survey of existing boreholes and an assessment of their suitability for groundwater sampling, so that the chemical/isotopic character of the Langebaan Lagoon may be defined. An inventory of existing data of the study area, and an evaluation of its suitability for the construction of a numerical groundwater flow/discharge model. The results of and progress made on each of these tasks are presented in Section 6. Page - 3 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 4. Study Site Description 4.1 Bio-physical Environment The Langebaan Lagoon covers an area of approximately 57 km2 and lies within the 187 km2 West Coast National Park, which was proclaimed in 1985. The Langebaan Lagoon has been classified as a wetland of international importance in terms of the Ramsar Convention (1975), mainly because it supports more birdlife than any other wetland in South Africa (Reaper, 1995). The high conservation status of the West Coast National Park results in part from the large areas of the highly threatened Lowland fynbos (or Strandveld) that it protects, while the lagoon plays host to a wide variety and large number of bird species. Three veld types can be discerned in the Langebaan area; West Coast Strandveld, Coastal Renosterveld and Cape Macchia (Reaper, 1995). Halophytic vegetation is found along the edge of the Langebaan Lagoon. The area is essentially semi-arid with an average annual rainfall of about 260 mm, half of which occurs during the months May to July. The low rainfall and the highly permeable and unconsolidated nature of the geology limit surface runoff. Annual temperatures range from an average winter low of 5°C to an average summer high of 34°C. The Saldanha Bay and the Langebaan Lagoon formed as a result of dramatic sea-level changes during the Cenozoic era, which resulted in the development of barrier sand dunes along the coast. These dunes were later (during the Tertiary - ±9000 years ago) submerged and washed away. The Donkergat Peninsula remains as a remnant of the barrier dune system. It has remained intact thanks to the outcrop of resistant Cape Granite at its headlands. The geology of the area consists of Cape Granite (here known as the Darling Granites), which forms the areas’ geological basement, The Granite is covered by unconsolidated marine sand, deposited by numerous marine transgressions and regressions during the Tertiary and Quaternary periods. Extensive calcrete sheets are found in and around the lagoon. These are believed to be the fossilised remains of oyster beds. Outcrops of these sheets have been found under all the salt marshes at Langebaan Lagoon (Reaper, 1995). The Langebaan Lagoon forms the southern extension of Saldanha Bay, from which it is separated by Skaapeiland. From Skaapeiland to Geelbek (on the southern edge of the lagoon), the lagoon measures 14.5 km. At its widest point it is approximately 4.0 km, and has an average depth of 1 – 2 metres. During tidal fluctuations partial exchange of water occurs with Saldanha Bay (half the lagoon water passes into the bay), with little direct exchange of coastal water from the Atlantic (Shannon and Stander, 1977). The water clarity and shallow nature of the lagoon result in relatively high water temperatures (14°C in winter to 25°C in summer). This results in higher evaporation rates and consequently higher salinities than in Saldanha Bay and the coastal waters. Table 1 presents a comparison of winter and summer salinity at various parts of the Lagoon (Flemming, 1977) Page - 4 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 Table 1: Seasonal salinity ranges in selected parts of the Langebaan Lagoon (Flemming, 1977) Station Mount Kraalbaai Bottelary Churchhaven Geelbeck Salt Marsh Creek (Geelbek) 4.2 Winter 33 32 30 32 33 22 Summer 34 34 34.5 35 36.5 48 Regional Hydrology and Hydrogeology Most of the hydrogeological investigations have focussed on understanding and developing the Langebaan Road aquifer (Timmerman, et al., 1986, Weaver, et al., 1997, etc.). The Langebaan Road aquifer lies in the Cenozoic deposits in the area between the Berg River, the Langebaan Lagoon, Darling and Hopefield. The aquifer is bound by the Berg and Sout rivers to the east and north, a zero flow boundary between Langebaan and Hopefield in the south, the Vredenburg headland in the north west and Saldanha Bay in the west. The major aquifer types that occur in the Langebaan Road aquifer are: The Langebaan Limestone of the Bredasdorp Formation, which is typically unconfined, and varies in thickness from 10 to 20 m. The Sand and Gravel deposits of the Elandsfontein Formation, which is between 40 and 60 m thick. The Elandsfontein coarse sand and gravel aquifer is in places confined by the Elandsfontein clays and peats, which may be up to 20 metres thick. Figure 1: Geology of the Langebaan Lagoon area (Reaper, 1995) Page - 5 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 Generally groundwater flows in a westerly direction from Hopefield. From Langebaan Road a portion of the water flows in a northerly direction towards the Berg river, while the remaining portion continues its westward migration to Saldanha Bay. Artesian boreholes occur in the vicinity of Langebaan Road. Groundwater quality in the aquifer is variable. (Timmerman, 1985a & b, and Weaver, et al., 1997) A few small, seasonal streams enter the lagoon but there is no other surface runoff. The hydrogeology of the area is quite complex with different formations having different properties (Weaver and Wright 1994). The Elandsfontein primary aquifer unit probably discharges into the lagoon and the overlying dune areas are also likely to store groundwater which could discharge into the southern end of the lagoon (Weaver and Wright 1994). 4.3 Vegetation The terrestrial vegetation is a mixture of west coast dune thicket and sand-plain fynbos whose composition is strongly controlled by the different soil sources: unconsolidated and consolidated aeolian sands, limestones and granites (Boucher and Jarman 1977). The granite and limestone communities are particularly rich in rare plant species. These communities grade into freshwater marshes dominated by Phragmites and Typha and then into salt marshes characterised by varying abundances of Arthrocnemum (Salicornia), Juncus kraussii, Chenolea, Limonium, Spartina and a mixture of other sedges and shrubs (O’Callaghan 1994). The marsh supports a very rich fauna of algae, molluscs and crustaceans and is a nursery ground for many fish species (Barnes 1998). The freshwater wetlands are characterised by a high water table (Boucher and Jarman 1977). There do not seem to have been any studies which have examined the role of groundwater in the salt marsh but groundwater discharge sustains the freshwater marshes (Boucher and Jarman 1977; Christie 1981; O’Callaghan 1994) which probably would not be sustained by rainfall alone. The groundwater is very likely to have some influence on the salt marsh as well, for example the distribution of Juncus kraussii (O’Callaghan 1994; Reaper 1995). The potential role of groundwater in this ecosystem will be investigated in the near future as part of a research project being conducted by the authors. Although the lagoon is not a traditional form of estuary, its mixture of fresh and salt water habitats qualifies suggests that it is functioning as an estuary and that groundwater is an important component of the hydrology. This hypothesis is supported by the estuarine character of the zooplankton at the southern end of the lagoon (Grindley 1977) and similar north-south increases in dissolved silica (and phosphorus) although nitrogen concentrations decrease (Christie 1981). 4.4 Conservation status Langebaan lagoon was proclaimed a Ramsar wetland in 1998 and is recognised as an internationally important bird area (IBA No 105, Barnes 1998). It forms part of the West Coast National Park. More than 250 bird species have been recorded in the park and the highly productive salt marsh regularly supports to more than 35 000 birds of a range of species, particularly 15 species of Palearctic wader and other waterbirds. Many of these species are classified as globally or nationally threatened. Other species make use of the freshwater marsh and adjacent terrestrial vegetation, including Marsh Harrier (Circus ranivorus), Black Harrier (C. maurus), Red-chested Flufftail (Sarothrura rufa) and African Rail (Rallus caerulescens) and various reptiles and amphibians. Page - 6 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. 4.5 March 2004 Salinity tolerances There have been few studies of the effects of salinity on South African salt marsh and freshwater marsh species. Studies by Adams (UPE) found that Phragmites is tolerant of salinities of 3 ppt (‰) for up to 3 months. Studies of Phragmites australis from mediterranean France found that seed germination was reduced by salinity levels above 10 ‰ from 90-100% in freshwater to 5-60 % at 25 ‰ (Mauchamp and Mesleard 2001). Seedling growth decreased with increasing salinity: 50% decrease at 7.5 ‰ compared with freshwater and 7-100 % mortality occurred at 15 and 20 ‰. Salt tolerance in P. australis has been shown to involve an energy dependent sodium exclusion mechanism (Lissner et al. nd). Plants from warmer environments salt tolerance had growth rates which were 20-100% higher, especially at salinities ranging from 0.5-2.0%, largely because of an improved energy balance and better osmoregulation. Most emergent plants do not survive salinities of more than 5 g/l, an exception is Phragmites which can survive up to 12 g/l (Anon nd). Other relatively salt tolerant aquatic or marsh plants such as Triloglochin can tolerate up to 10 g/l. Typha's maximum salinity tolerance is apparently lower than that of Phragmites with an absolute max 17g/l versus 20g/l under cool climatic conditions (find reference#). The general opinion is that differences in distribution of Phragmites and Typha species are due more to their different tolerances of inundation rather than salinity. Based on the literature and the healthy looking reeds (Phragmites) and Typha nearby the site, salinities probably do not exceed 5 g/l for long periods, and higher salinities only occur for short periods. Apparently Phragmites can survive with only 0.3 m of freshwater above much more saline water. As the salinity of the lagoon water are high, at least seawater, the vegetation indicates that there must be substantial freshwater inflows. This would also accord with observations by Reaper (1995), O’Callaghan (1993, 1994), and Boucher and Jarman (1977). Coral Birrs (Gauteng Environment) told us that there is a fresh water spring on Jutten Island (near Saldanha) and springs and freshwater pools in the saltmarshes. The WCNP staff know where these are located. 5. Initial Conceptual Model A workshop was held on the 15th of January, during which team members formulated their conceptual understanding of the Langebaan Lagoon/Groundwater system based on their observations during the field visit and research presented in the literature. The initial conceptual model that was developed during the workshop formed the basis of the data acquisition phase of the project. The discussions and relevant issues were captured in the form of sketches. These largely capture the consensus thinking within the group, and highlight areas of uncertainty. Sketches 1 and 2 (Figure 2): Regional Model. The area is underlain by two aquifer systems, which are separated by a largely impervious clay layer. 1. Groundwater from the unconfined aquifer discharges to the lagoon. There is little or no interaction between the lagoon and the deeper confined aquifer. 2. Groundwater from both the shallow and deeper aquifer units discharges to the Langebaan lagoon. Page - 7 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 Areas of uncertainty: Does the clay layer occur continuously across the whole area? Experiences at the Langebaan Road Aquifer system suggest that there may be “windows” in the clay layer (Weaver, et al., 1997). Sketch 2 (Figure 2) shows a scenario in which the clay layer is absent in parts of the lagoon, so that water from the deeper aquifer discharges to the lagoon. Understanding the connectivity between the aquifers and the extent to which each contributes discharge to the lagoon will provide valuable input to design of groundwater abstraction models and assessments of environmental impact. Does groundwater in the deeper aquifer discharge to the sea, or is the aquifer pinched out between the clay layer and bedrock? What is the quality of water beneath the lagoon? and if it is salty, Where will the fresh water – salt water interface occur in the shallow and deep aquifers? Sketch 3 (Figure 2): The distribution of freshwater vegetation is controlled by shallow calcrete lenses that forces shallow circulating groundwater to the surface. Areas of uncertainty: The relationship between the calcrete layers and groundwater discharge is unclear. The shallow nature of the calcrete layers makes it unlikely that they will be the major factor controlling groundwater discharge. Even if a relationship is found between the two, whether this is a major factor controlling groundwater discharge will have to be tested. Calcrete may simply be controlling topography in the tidal zone. Sketches 4 to 6 (Figure 3): Plan layout of the Oosterval area, with cross-sections of two models that explain the local hydrology, based on the vegetation distribution. Page - 8 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. REGIONAL MODEL E March 2004 1 W RAIN 1 (a) Where is the interface? 1 (b) Is there an interface? T T T S S 1a 1b CLAY L LAGOON ATLANTIC OCEAN ?SALTY? ? 2 Clay 3 typha Standing fresh water calcret e Clay Figure 2: Conceptual model of Groundwater Discharge to the Langebaan Lagoon Page - 9 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. T N T M M M M M M M M M M M M T T T T T T T TT T T T T T T T T M T T T T March 2004 T T T T T T T ROAD S T T F F F Start of Boardwalk F F F T F F M F F F- Fynbos T- Typha S- Salt Marsh M- Mud Flats F F F F F F F F S N Evaporite 1 T T T calcrete N 2 S Layer of fresh water Evaporation Figure 3: Scenarios to explain the distribution of fresh and saline water at Oosterval Page - 10 - Fresh Saline calcrete Evaporation Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 Saline Windflat Lagoon Windflat N S Granite Hills Symbols Granite Calcrete Evaporite E Water Bodies i.e. Lagoon and Ocean Inter face Granite SAND Sand Clay lenses Figure 4: Relation between slope, geology and the fresh water/salt water interface Page - 11 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 6. Results of Initial Field Work and Discussion 6.1 Study area The study area is located about ½ km north-east of the Geelbek farm complex, near the bird hide and the walkway which connects it to the shoreline. The nearshore environment comprises low dunes which grade into a gently sloping terrace with a shallow layer of saline sand. This environment supports a salt marsh habitat described as the Limonium-Disphysma (salt-bush) form by Boucher and Jarman (1977). This community indicates highly saline conditions. There appears to be little leaching of the salts by the rainfall. This terrace may be inundated by extreme tides (spring highs?) and probably gets some marine water inundation from overtopping waves when there are strong winds from the north-west. The bird hide itself is located in a belt of the Spartina-Triloglochin (salt marsh sedge) form which fringes the shoreline of the lagoon. The shoreline itself is marked by a narrow strip of the invasive European sedge species Schoenoplectus (Scirpus) triqueter which extends to below the high tide line. There are also localised patches of the Juncus kraussii-Nidorella and Typha capensis (bullrush) vegetation types in the area below the step. Just to east of the walkway, and crossing it near the shoreline, is a clear boundary in the vegetation associated with a step or drop of about 0.15 m in the ground level. The vegetation on top of the step is the salt marsh and below the step it is the Spartina-Triloglochin and Typha, clear evidence of an abrupt reduction in salinity below the step. To the east of the walkway the sedge and bulrush vegetation is replaced by Phragmites australis (fluitjiesriet) marsh. Further east the Phragmites extends right to the shoreline of the lagoon with just a narrow strip of Schoenoplectus between it and the saline lagoon water. 6.2 Geophysics Results 6.2.1 Introduction Resistivity is a non-invasive geophysical tool that can provide cost-effective answers to geological problems. The Lund imaging system is a completely automated resistivity data acquisition system. A pseudo-section of apparent resistivity data is acquired that shows both lateral and vertical changes in resistivity along the profile. The inversion software RES2DINV has revolutionised the inversion of such a complex data set and the interpretation of the resistivity data has been optimised. The software output is a true resistivity pseudosection that can be directly related to geological changes. The bulk resistivity of different geological units varies mostly because of changes in either salinity of the pore fluid or changes in porosity. The resistivity method can thus be applied very effectively to delineate changes in water quality, for e.g. to delineate the interface between the fresh water and the saline water in the coastal zone/lagoonal areas. It can also be applied to distinguish between different lithologies, if there is a variation in either porosity or salinity of the pore fluid. Page - 12 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 The resistivity technique was proposed as a tool for providing information for research questions relating to the interaction between aquifer water from the Elandsfontein aquifer and the lagoon at Langebaan. The vegetation around the lagoon varies from terrestrial to fresh water to salt marsh vegetation. These changes in vegetation can probably at least in part be attributed to groundwater flow regimes. Some of the potential hypotheses for the differing vegetation around the lagoon will be tested using the Lund imaging system and includes the following: The saline vegetation is underlain by calcrete and the fresh water discharge from the aquifer does not reach the rootzone of the vegetation. The fresh vegetation is underlain by calcrete, preventing fresh rainwater from infiltrating, thus keeping a freshwater lens on top. A combination of above – where groundwater flow can be delineated. 6.2.2 Field methods The Lund imaging system, consisting of the SAS1000 resistivity unit, the ES464 switching unit, multi-core cables and electrodes, was used for the acquisition of resistivity data in the study area. The Lund imaging system is completely automated and pre-designed protocols are used to optimise data coverage for specific profiles for e.g., for groundwater flow regimes, data quality and resolution/coverage must be excellent. Multi-core cables with a two metre electrode spacing were used to improve data coverage and quality at shallow depths. The Wenner array was used for all profiles. The field procedure involved rolling out the multi-core electrical cables in the pre-selected areas. The electrodes are then inserted next to the electrode take-outs on the cables. Where possible the electrodes were pushed into the ground to minimise disturbance of soil around the electrode and thus maximising electrode contact. The electrodes were then connected to the electrode take-outs on the multi-core cables using the earthing cables. This is also the opportunity to ensure that electrode grounding is optimum, ensuring good quality data. The cables are then plugged into the ES464, which is connected to the SAS1000. The SAS1000 is then connected to the battery and the system started. Quality control during the acquisition phase starts with an “electrode test”, which checks the grounding of all the active electrodes. Electrodes that are not properly grounded can then be investigated and re-checked. Generally, more than 90 % of the electrodes must be active – i.e. properly grounded. In the saline conditions next to the coast a pass rate of 100% is expected and were achieved. A further quality control measure associated with the Lund imaging system is the leastsquares error. The resistivity data are acquired using at least two stacks (maximum of six stacks to optimise data quality, total acquisition time and battery power). The least squares error in the measured resistivity reading is displayed and saved as a standard deviation. This error is saved in the data file and can be seen by converting the field data to the ABEM Multipurpose Protocol (.AMP) file format. The data quality can be assessed by looking at the general error percentage. The number of data points with an error in excess of 5% should be minimal. These erroneous data points can be removed from the data set. Unfortunately for the initial trial survey, the standard deviation error of more than 60 % of the data was above 5%. This was attributed to an equipment error and the resistivity unit had to be repaired, causing further delay. Page - 13 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 The data were inverted using the RES2DINV software. The resistivity pseudo-section is automatically plotted and the only pre-processing done was to erase obviously erratic data points. The data was then automatically inverted using the finite element inversion technique. The apparent resistivity pseudo-section (field data) is displayed with the inversion starting model and the inverted true resistivity sections. The true resistivity pseudo-sections are used for the interpretation of the resistivity data. Quality control for the inversion process occurs through the least-squares error that is calculated for the inverted true resistivity pseudo-section. This RMS (Root-Mean-Square) error should ideally be below 10%. The RMS error for the Geelbek profile is ~ 8%. 6.2.3 Results and preliminary interpretation Plans for detailed geophysical surveying at the Langebaan Lagoon study site had to be reassessed when the electrical imaging equipment that were to be used during the study became unavailable due to a breakdown. The equipment was in use in Mozambique until December 2003 after which it had to be sent to Sweden for repairs. Some geophysical surveying could however be attempted in February and March 2004. The rest of the resistivity data were acquired in April 2004. The first data set was acquired near the Geelbek bird hide, traversing from salt marsh vegetation to fresh water vegetation. The salt marsh area is flat and then “steps down” into the fresh water vegetation. There is a small drop (~10 – 15 cm) in ground elevation from the salt “flats” into the fresh water vegetation. The fresh water vegetation stands in lagoon water all the time because of this change in elevation. The tide was coming in during the actual acquisition phase of the profile and the general change in water level could be closely observed. The water level increased by about 20 cm in the fresh water vegetation, with the end of the profile covered in about 0.5 m of water during peak tide. The zone just above the root zone of the saline vegetation was washed – the saline marsh was water logged, but not flushed. The salt marsh vegetation most probably gets flushed at spring tides only. The repair of the resistivity unit did wonders for the data quality. The data are of excellent quality with less than 1% of the data with an error of above 5%. The raw data are shown in Figure 5 with the bad data points highlighted. Page - 14 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 Figure 5: Plotted resistivity data for the initial resistivity profile at Geelbek. The two data points in red were the only bad data points that were removed. The data were initially inverted using a vertical/horizontal ratio of 1:1, i.e. the elongation of structures in the horizontal or vertical direction was ignored. The data was then inverted using a vertical/horizontal ration of 2:1, assuming strong horizontal layering. This was done to attempt to delineate any thin horizontal lenses for e.g. calcrete lenses under the salt marsh vegetation. However, the latter data inversion did not significantly re-align structures to warrant the use of the increased horizontal ratio for the inversion – the inversion was not more meaningful using a greater horizontal flatness. The inverted data are shown in Figure 6, with the vegetation types indicated above the profile. Also note that all resistivity profiles acquired in this area have been rescaled to the same resistivity, for comparison. Page - 15 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. Salicornia (saline) Juncus (fresh) Typha (fresh) March 2004 Phragmites (fresh) 18/03/04 13:25 Barrier zone Top sandy/silty lagoon sediments Aquifer sand Figure 6: Resistivity profile 1 at Geelbek traversing from saline water vegetation to fresh water vegetation. The data shows a low resistivity layer at the top underlain by a high resistivity zone. The low resistivity top layer varies slightly from very low resistivity under the salt marsh vegetation to higher under the fresh vegetation. This correlates with what is observed in the field. The saline vegetation is surrounded by pools of hypersaline water (very low resistivity) and the fresh water vegetation stands in fresher (brackish) water (low resistivity). The water salinity also seems to decrease the further you progress into the fresh water vegetation – the further you are away from the lagoon. This is probably because the lagoon water reaches this far into the flats at spring tide. The resistivity of the layer underlying the fresh water vegetation is very high and this changes laterally into a lower resistivity zone under the salt marsh vegetation. This seems almost to form a vertical barrier zone in the subsurface between the fresh water vegetation and the salt marsh vegetation. The data are not conclusive and the controls on the vegetation in this area cannot be defined from the resistivity data. However, it does seem that it is most probably a significant change in the properties of the underlying (aquifer) sand. This change could be a change in porosity – a lower porosity sand underlying the salt marsh – or even a change in lithology, i.e. a facies change – for e.g. clay in the sediments underlying the salt marshes. The control on the vegetation could then be: the fresh water vegetation in underlain by sandy material with a higher hydraulic conductivity that acts as an aquifer discharging groundwater into the fresh water vegetation area. This continual fresh groundwater discharge allows mixing with the higher salinity lagoon water and thus lowers the electrical conductivity of the water enough to allow fresh water vegetation to grow. The lateral change in properties of the subsurface sediments forms a barrier (dam) wall for this groundwater, pushing the groundwater up in the fresh water vegetation zone, but preventing it from discharging in the saline marsh area. The elevation changes can also account for part of the control on the vegetation. The lower elevation around the fresh water vegetation allows wet conditions for the fresh water vegetation. The saline vegetation might be just above mean sea level preventing groundwater discharge on the flats. Some geological control should be acquired for the resistivity data in the form of auger holes. Changes in sand coarseness or lithology should be closely observed. These should be located to confirm lateral changes in the soil properties. Page - 16 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 The second profile was acquired closer to the Geelbek visitors centre and traversed from terrestrial vegetation to salt marsh vegetation. The profile line started at the line of bluegum trees lining the road to Geelbek. The elevation decreases slowly from the start of the line to the salt marshes where the elevation flattens out. This part of the salt marsh is further away from the lagoon – the marsh vegetation will probably only be inundated during spring tides. No tidal variation was observed here while doing the survey. Tidal data will be correlated with the data. The inverted resistivity data are shown in Figure 7. The shallow resistivity below the salt marsh (and a bit onto the terrestrial side) is low. This grades laterally into a higher resistivity. This correlates well with observed conditions. The saline conditions (salt marsh) will result in a low resistivity that will increase laterally away from the flats due to less salt. The shallow low resistivity zone on the terrestrial vegetation is either tidal variation or more likely saline patches on the surface. The discontinuous shallow low resistivity layer is underlain by a layer of higher resistivity. Similar to the previous profile, this is probably the sandy aquifer material with fresher water. The resistivity changes across this profile are not significant, with an average resistivity between 7 and 50 Ω.m. There is a lower resistivity barrier, similar to the first profile’s, where the vegetation changes from terrestrial to saline. However, the change in resistivity is not that significant, mostly because the variation in resistivity is smaller. This is thus not necessarily expected to be a real feature controlling the vegetation. It should however be further investigated. It is important to note that the shallow lower higher resistivity zone at the start of the profile might be due to the drying out of the soil due to the abstraction of groundwater by the bluegums. Saline patch Terrestrial Saline reeds with saline veg in between Saline Aquifer sand 20/04/04 10:28 Barrier zone? Top sandy/silty lagoon sediments Bluegum abstraction? Figure 7: Resistivity profile 2 at Geelbek traversing from terrestrial vegetation to saline water vegetation. The possible control on vegetation along this profile is expected to be elevation changes. The terrestrial vegetation grows on the higher elevation sandy area above the neap high tide mark. The saline vegetation then grows on the salt flats. The general lower resistivity as opposed to that of the first profile could be an indication of lower porosity. This in turn can indicate less groundwater discharge, preventing fresh water vegetation. Alternatively, the fresh water vegetation might not grow here because the elevation does not drop enough to form flooded conditions. Page - 17 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 The third resistivity profile was acquired closer to the road – on the far side of the Geelbek bird hide. The profile started on the terrestrial vegetation and then crossed into fresh water vegetation. The elevation decreases from the start of the profile, and then flattens out at around -26 m, then it drops of again slightly after +5 m along the profile. The fresh water vegetation was in water all the time. The tidal variation was not obvious, but it seemed high during the data acquisition phase. Tidal data will be acquired to correlate. This profile line was further away from the lagoon and the tidal influence here is probably minimal, in terms of both water level and salinity. The inverted data are shown in Figure 8. The data correlates well with the observed conditions. The shallow low resistivity data layer is indicative of the wetter and more saline conditions in the fresh water vegetation. Note that the general resistivity of this top layer is higher than on the other resistivity profiles. This is probably because this profile was acquired further away from the lagoon and the tidal influence in minimal. The general salinity of the water is probably lower than the fresh water vegetation on the first profile, but this should be confirmed. The high resistivity patch at about –50 m along the profile is a small sand dune – the high resistivity indicative of the dry sand. The resistivity of the lower layer is approximately the same as that of the previous profile. There are also no significant changes in the resistivity of this layer. The control on the vegetation does not seem to originate from the subsurface. The control on the vegetation is most probably elevation again. The terrestrial vegetation grows on the higher sandy areas above the neap high tide. The fresh water vegetation grows where the elevation has dropped below mean sea level, where the vegetation is constantly flooded. The tidal influence is minimal and some fresh water discharge occurs; the salinity of the water is low enough for the fresh water vegetation to grow. Terrestrial Juncus with salicornia in between Typha (fresh water) Top sandy/silty lagoon sediments Aquifer sand 22/04/04 10:28 Figure 8: Resistivity profile 3 at Geelbek traversing from terrestrial vegetation to fresh water vegetation. The data for the fourth resistivity profile were acquired at the northern end of the lagoon, traversing from saline vegetation to terrestrial vegetation. The saline vegetation grows on a “salt flat” and then the elevation increases gradually from about –30 m. From about +7 m along the profile the elevation increases more rapidly. The tidal variation was not observed during data acquisition, but tidal data will be acquired for future correlation. The interpreted resistivity data can be seen in Figure 9. The general resistivity variation correlates well with observed surface conditions. The low resistivity at the start of the profile relates to the salt flats with associated saline vegetation. The resistivity increases laterally as Page - 18 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 the terrain changes from salt flats to higher elevation sandy dune area. The high resistivity after the centre of the line is typical of the saline sand. It is important to note that this profile is the only profile where some sort of a salt water/fresh water interface can be seen (this has been indicated on Figure 8). The saline interface is more pronounced here than in the other profiles most probably because the hydraulic conductivity of the subsurface material is not that high. The groundwater flow related to the higher hydraulic conductivity normally pushes the saline interface further out to sea, and it cannot be observed on the resistivity sections. Also note that the low resistivity zone extends into the terrestrial area; this is similar to the second profile and indicates either neap high tide influences or saline soil that extends this far. The vegetation control in this area seems to be elevation changes again. The saline vegetation grows on the salt flats and the terrestrial vegetation grows above the neap high tide mark. Salicornia + sparabolis (saline grass?) Terrestrial Top dry sand Top sandy/silty lagoon sediments Saline interface? Aquifer sand 23/04/04 09:40 Figure 9: Resistivity profile 4 at the northern end of the park traversing from saline water vegetation to terrestrial vegetation. 6.2.4 Areas of uncertainty and lessons learned The controls on the vegetation around the lagoon cannot be conclusively derived from the resistivity data. It does however clarify some areas of uncertainty and then it also created some other areas of uncertainty: There is no evidence of any sort of horizontal calcrete or clay layers controlling the saline vegetation and/or terrestrial vegetation. The vegetation seems to be controlled by elevation changes: the terrestrial vegetation grows above the average high tide mark and or neap high tide mark. One of the uncertainties arising from this is that the position of the neap high tide mark should be investigated to see if some of the terrestrial vegetation gets flooded during neap high tide. The saline vegetation grows on the flats where the vegetation is mostly in wet conditions but not covered by water all the time – gets inundated by the tides every now and again. The uncertainties arising from this are: firstly, how did the flats form – some geologic process (stream weathering, etc.) or some lithologic process (i.e. calcrete lenses preventing rapid weathering). Secondly, the vegetation control should have something to do with the physiology of the plants (apart from obvious specialisations to adapt to saline conditions) – does the saline vegetation need to sometimes dry out a bit (considering it does not grow at elevations where it can be submerged for long periods of time). The fresh water vegetation grows in the areas lower than the salt flats where the root zone in permanently submerged. There should also be fresh groundwater discharge to allow mixing with the saline lagoon water to decrease salinity to acceptable levels for the fresh water species. Page - 19 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 In terms of general geophysics lessons learned: the initial geophysics fieldtrip produced data with a high error. A subsequent field trip was undertaken on 5 February to ascertain whether this was the result equipment failure or human error. During the field trip the following became apparent: Always check background voltage using a multi-meter. This background voltage should be corrected for by the LUND system itself. However, significant voltage variation can result in large errors and negative readings. When the voltage varies significantly it is important to increase the input current significantly to improve signal to noise ratio. In the Langebaan case, the background voltage was stable at around 47 mV, but spikes did occur occasionally. One spike for e.g. caused a negative reading, which was ratified by re-measuring. In the coastal zone, the natural background self-potential drops off towards the coast. This causes fairly significant potential lines parallel to the coast, which will influence resistivity data when acquired perpendicular to the coast. Once again the LUND system should be able to correct for this error, but the current should be increased to improve signal to noise ratio. Also to overcome significant voltage and self-potential (which can be classified as sources of noise), the data acquisition time and delay time between cycles should be increased to ensure that true direct current is used for surveying. In general, the LUND manual error codes should be kept handy to prevent unnecessary data loss due to errors that could be corrected for in the field. In the coastal zone, input current should be at least 500 mA – this is to improve signal to noise ratio. You will need two 12V batteries since one can supply a maximum of 200 mA. Always check the cables using the cabletest option on the LUND system before even going to the field. This test takes a while, but it is worthwhile. Check the switching unit as well, using the ES464 test on the LUND system. Resistivity interpretation is ambiguous and groundtruth is necessary for control. Hypothesis should always be tested and background information needs to be applied where necessary. 6.3 Remote Sensing Remote sensing satellite and aerial photographic images was to be used to generate map high resolution vegetation maps of the study area. This was meant to generate a detailed georeferenced map of the study area on which areas of interest could be delineated. However, due to time constraints the detailed remote sensing analysis could not be performed. The GIS component was able to import data from the National Groundwater Database (NGDB) of the Department of Water Affairs and Forestry. Boreholes and wells in the immediate area of the Langebaan Lagoon listed in the NGDB is shown in Figure 7. Page - 20 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 Figure 7: National Groundwater database listed boreholes in study area. 6.4 Chemical Sampling Limited hydrogeochemical sampling has been carried out in areas of interest around the Lagoon. The sites sampled are listed in the table below and shown in the map above. Initial results show predominantly of Na-Cl type water groundwater with a highly variable salinity in the vicinity of the lagoon. There is a poor correlation in borehole position and data with existing information from the National Groundwater Database, making these data of questionable value. Table 2: Field measurements from reconnaissance borehole sampling at Langebaan. Sampling of Wells in the West Coast National Park Field Parameters Sample ID W/Level (M) Depth (M) Electrical Conductivity pH Temp (mS/m) deg C Geelbek Well 1 -1.26 4.28 260 7.48 21 Geelbek Well 2 1.30 4.64 205 Geelbek Well 3 -1.64 4.64 416 7.78 21 Geelbek Well 4 -1.91 3.73 Point 178 -1.41 3.49 Oesterwal Borehole 174 6.58 27 Oesterwal Well -2.00 3.00 1659 7.95 20 Oesterwal Well 3 -1.46 2.04 665 20 Andrag Well 1.00 9.00 199 7.94 22 Roadworks Borehole 85 7.64 23 Churchhaven Well -2.20 -2.50 503 8.01 22 Page - 21 - Colour Clear clear Clear Odour None None None Slight Yellow H2S Slight Yellow None clear none Clear none clear none clear none Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 Langebaan Water Chemistry 80 80 60 Sampling Site 60 40 Andrag Well Churchhaven Geelbek well Geelbek Well Oesterwal Borehole Oesterwal Well Roadworks borehole 40 20 20 Mg SO4 80 80 60 60 40 40 20 20 80 Ca 60 40 20 20 Na 40 60 80 HCO3 Figure 8: Piper Trilinear Plot of Groundwater Quality at selected boreholes at Langebaan Lagoon. Page - 22 - Cl Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 7. Data Inventory/Availability 7.1 Reports and papers: Geology Coles, S. K. P., and Van Den Bossche, J. L., 2003, Brief Operations/Cruise Report for the Langebaan Marine Magnetometer Survey 9Ignimbrite Project) Conducted on behalf of the University of Stellenbosch Geology Department 9Surveyed 6 June 2003), Report No. 2003-0158, Marine Geoscience Unit, Council for Geoscience. Scheepers R. and Poujol M., 2002, U-Pb Zircon age of Cape Granite Suite ignimbrites: characteristics of the phase of the Saldanian magmatism, South African Journal of Geology, volume 105, p 163-178 Leygonie, F. E., 1975, The granites of Langebaan, Cape province (in Afrikaans), M.Sc. Thesis (unpubl.), University of Stellenbosch, 97 p. Van der Walt G. N., 2003, Geophysical Investigation of the Postberg Ignimbrite Succession and Surrounding Rocks. Honours Thesis, University of Stellenbosch Hydrogeology Bertram W E., 1985 Hidrosensus in die weskusvlakte tussen velddrif, yzerfontein, Atlantis, Darling en Hopefield. Tegniese verslag No. Gh3371. Direktoraat: Geohidrologie, Kaapstad Du Toit I. M. and Weaver J., 1995, Saldanha steel project: groundwater investigations, CSIR report no. 27/95, Stellenbosch Timmerman K M G, 1986, Hydrocensus in the area of between Darling, Malmesbuey and Mamre, Directorate of Geohydrology, Cape Town Timmerman L.R.A., 1985a, Preliminary report on the geohydrology of the Langebaan and Elandsfontein aquifer units in the lower Berg River region, Report GH3373. DWAF, Cape Town Timmerman L.R.A., 1985b, Possibilities for the development of groundwater from Cenozoic sediments of lower Berg river region. Report Gh3374. DWAF, Cape Town Timmerman L.R.A., 1987a, PhD Thesis: Regional hydrogeological study of the lower Berg river area, Cape Province, South Africa, Volume I, State University Ghent Timmerman L.R.A., 1987b, PhD Thesis: Regional hydrogeological study of the lower Berg river area, Cape Province, South Africa, Volume II, State University Ghent Page - 23 - The work of Timmerman (1985, 1986, and 1987) gives the most comprehensive overview of the area’s geology and hydrogeology. Building on the work of Timmerman, Weaver, et al. (1997) provides a further assessment of the area’s hydrogeology. These assessments are however, largely focussed on describing and assessing the state of the Langebaan Road Aquifer Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. Geology Timmerman L.R.A., 1987c, PhD Thesis: Regional hydrogeological study of the lower Berg river area, Cape Province, South Africa, Volume III, State University Ghent Timmerman L.R.A., Timmerman K M G and Candoolaeghe M A C, 1986, Proposal for the development of a departmental production wellfield in the Langabaan road primary aquifer unit, Directorate Geohydrology, Cape Town Weaver J. and Talma S., 2000, Langebaan road wellfield isotope data from the new boreholes, Report no. ENV/S-C 2000-082, Stellenbosch, South Africa Weaver J. and Fraser L., 1998, Langebaan road aquifer: Drilling and testing of new wellfield, Report no. ENV/SC98042, Stellenbosch, South Africa Weaver J., Van der Voort I., Hön A., Conrad J. 1997, Langebaan road aquifer unit –water supply project, Report no. ENV/S-C97015, Stellenbosch, South Africa Woodford A C., 1999, South African National Parks: Langebaan road aquifer system: review of reports outlining the hydrogeological conditions, exploitation potential and proposed development f the Langebaan road aquifer system. T&P report no. 990195. Toens & Partners CC.: Geological, Hydrogeological, civil Engineering &Environmental Consultants. , 8 Lester Road Wynberg, 7800 Botany Reaper, M. B. S., 1995, A study of the relationship between environmental conditions and saltmarsh zonation at Langebaan Lagoon, M.A. Thesis (Unpubl.), University of Cape Town. March 2004 system. Zoology 7.2 Maps: (Hard copies) Maps of the Langebaan area can be found in Timmerman (1985a, b, 1986, 1987a, b, c, and Timmerman, et al., 1987). These illustrate the geology, thickness contour of geological formation, hydrochemistry (water type, water class, hardness, hydrochemical subareas), hydraulic conductivity, recharge area, and modelled water level contour, vegetation map. Also available are: Langebaan road aquifer: monitoring network, DWAF Langebaan road aquifer: clay thickness, CSIR Langebaan road aquifer: aquifer thickness, CSIR Langebaan road aquifer: EC, CSIR Page - 24 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. 7.3 March 2004 GIS data: DEM data for the lower Berg River and digital aerial photography of the Langebaan Lagoon (1999) is available on CD from the Western Cape Nature Conservation Board. Topography information in CGM file format is available from DWAF. The CSIR has elevation contours and the ability to build a DEM and to do other topographic analysis. Coverages are also available for: Coastline - 1: 50 000 contours - 1: 50 000 roads - 1: 50 000 rivers - 1: 50 000 waterbodies - 1: 50 000 wetlands - 1:250 000 Landcover - 1:250 000 Satellite Imagery Landsat ETM+ satellite data November 1999 Landsat 4/5 Satellite Mosaic circa 1990 - 28.6m Pixel/Ground Resolution - 28.6m Pixel/Ground Resolution Also available in digital form are scanned 1:50 000 topo-sheets. 7.4 Berg River Monitoring data GIS data which covers sub-catchment G10 (low Berg River) is available. Time series data is available for rainfall, river flow, dam levels, and some groundwater abstraction. Tides Tides: we have tidal constituents at Saldanha Port -> can be used to generate tidal levels for any time period in Saldanha Bay. The tides in the lagoon are howver somewhat different. The Delft3D computer model can be used to simlate the corresponding tidal levels at any location in the lagoon. Model is already set up, but would need to be run for a particular time and location (1 days work). Air temperature, pressure and wind: 1994 -2003 measured at Port Control in Saldanha Bay. Need permission to use from NPA. NB: wind has a significant impact on water levels in lagoon - this can also be simulated with Delft3D model. An example of Delft3D model of Saldanha Bay/Langebaan Lagoon attached (animated gif format - play with e.g. internet explorer) 7.5 Borehole data: The National Groundwater Database contains records of 486 boreholes data in the 1:50 000 topographic map sheets 3318AA and 3318AB, with information on: borehole locations, altitude, water level, borehole yield, lithology, recharge, and land use etc. Timmerman’s documents give some borehole log, and pumping test graphs Page - 25 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 8. References Anon nd. The nature of salt-affected natural ecosystems. Information Step B3. Tools for improved management of dryland salinity in the Murray-Darling Basin. National Dryland Salinity Programme, Murray-Darling Commission. Downloaded from www.ndsp.gov.au/salinity/tools/index.html Barnes, K.N. (1998) The important bird areas of southern Africa. BirdLife South Africa, Johannesburg. Bonell, M., 1998, Selected challenges in runoff generation research in forests from the hillslope to headwater drainage basin scale, Journal of American Water Resources Association, 34 (4), 765-785. Boucher, C. and Jarman, M.L. (1977) The vegetation of the Langebaan area, South Africa. Transactions of the Royal Society of South Africa 42, 241-272. Boulton, A. J., 2000, River ecosystem health down under: Assessing ecological condition in riverine groundwater zones in Australia, Ecosystem Health, Vol 6. No. 2, pp 108-118. Boulton, A. J., 2001, Twixt two worlds: taxonomic and functional biodiversity at the surface water/groundwater interface, Records of the Australian Museum Supplement no. 64. Buttle, J. M., 1994, Isotope hydrograph separation and rapid delivery of pre-event water from drainage basins, Prog. Phys. Geogr., 18, 16-41. Christie, N.D. (1981) Primary production in Langebaan lagoon. In Estuarine ecology with particular reference to southern Africa (ed. J.H. Day), pp 101-115. A.A. Balkema, Cape Town. Clark, I., and Fritz, P., 2001, Environmental Isotopes in Hydrogeology, Lewis Publishers, New York. Dawson, T. E., and Ehleringer, J. R., 1998, Plants, Isotopes and Water Use: A CatchmentScale Perspective, In: Kendall, C., and J. J. McDonell (eds.), Isotope Tracers in Catchmet Hydrology, Elsevier Science, Amsterdam, pp 165-202. Grindley, J.R. (1981) Estuarine plankton. In Estuarine ecology with particular reference to southern Africa (ed. J.H. Day), pp 117-146. A.A. Balkema, Cape Town. Kendall, C., Mast, M. A., and Rice, K. C., 1992, Tracing watershed weathering reactions with ∂13C, In: Y. K. Kharaka, and A. S. Meast, Water-Rock Interactions, Proceedings of the7th International Symposium, Utah, pp 569-572. Lerner, D. N., 1990, Recharge in arid and semi-arid regions. Lerner, D. N., 1996. Surface water - groundwater interactions in the context of groundwater resources. Keynote address to Water Research Commission Workshop on Groundwatersurface water issues in arid and semi-arid areas, Mabalingwe Lodge, Pretoria, South Africa, 15-16 Oct. 20 pages. Page - 26 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. March 2004 Lissner, J., Schierup, H-H., Comín, F.A. and Astorga, V. nd. Effects of climate on the salt tolerance of the common reed (Phragmites australis). Abstract Number:524. Mauchamp, A. and Mesleard, F. (2001) Salt tolerance in Phragmites australis populations from coastal Mediterranean marshes. Aquatic Botany 70: 39-52. McDonnell, J. J., Bonell, M., Stewart, M. K. and Pearce, A. J., 1990, Deuterium variations in storm rainfall: Implications for stream hydrograph separation, Water Resources Research, Vol. 26, 3, pp 455-458. Midgley, J. J., and Scott, D. F., 1994, The use of stable isotopes of water (D and 18O) in hydrological studies in the Jonkershoek Valley, Water SA, Vol. 20, No. 2, pp 151 – 154. O’Callaghan, M. (1994). The saltmarsh vegetation at Langebaan lagoon. Bothalia 24: 217222. O'Callaghan, M.G. 1993. Salt marshes of the Cape (South Africa): vegetation dynamics and interactions. Ph.D. Thesis, University of Stellenbosch. Reaper, M. B. S. (1995) A study of the relationship between environmental conditions and saltmarsh zonation at Langebaan Lagoon, M.A. Thesis (Unpubl.), University of Cape Town. Rodhe, A., 1987, The origin of streamwater traced by oxygen-18, PhD Thesis, department of Physical Geography, Division of Hydrology, Univ. of Uppsala, Rep. Ser. A41. Saayman, I. C., Scott, D. F., Prinsloo, F. W., Moses, G., Weaver, J. M. C., and Talma, S., 2003, Evaluation of the application of natural isotopes in the identification of the dominant streamflow generation mechanisms in TMG catchments, Water Research Commission, WRC Report No. 1234/1/03. Sandström, K., Hydrochemical deciphering of streamflow generation in semi-arid east Africa, Hydrol. Processes, 10: 703-720. Shannon, L.V. and Stander, G.H. (1977) Physical and chemical characteristics of the water in Saldanha Bay and Langebaan lagoon. Transactions of the Royal Society of South Africa 42, 441-459. Sklash, M. G., and Farvolden, R. N., 1979, The role of groundwater in storm runoff, J. Hydrol., 43: 45-65. Steward, M. K., and McDonnell, J. J., 1991, Modeling base flow soil water residence times from deuterium concentrations, Water Resour. Res., 27, 2681-2693. U. S. Army Corps of Engineers, 1999, Groundwater Hydrology: Engineering and Design, Engineer Manual, 1110-2-1421. Weaver, J and Wright, A. 1994. Specialist study of groundwater. Appendix 5. Saldanha Steel Project Phase 2 Environmental Impact Assessment. Report EMAS-C94017D, Division of Water Environment and Forestry Technology, CSIR, Stellenbosch. Woessner, W. W., 2000, Stream and fluvial plain ground water interactions: rescaling hydrogeologic thought, Ground Water, 38, No. 3: 423-429. Page - 27 - Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. Plates Plate 1: Salt water vegetation near the edge of the lagoon, with tall trees that must be accessing freshwater at depth. Plate 2: Freshwater vegetation (Typha) alongside saline vegetation. The coast (lagoon) is about 1 km away. Page - 28 - March 2004 Interactions between Groundwater & Surface Water: Assessment of the Langebaan Lagoon as a Study Site. Plate 4: Close-up view of freshwater vegetation (Typha) alongside saline vegetation. Plate 3: View of Langebaan Lagoon from a granite hill. Page - 29 - March 2004 Appendix 1: ‘Analytical Hierarchy Process’ – Decision Support Systems Page – A-1 -