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A Technical Guide for Wine Producers
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RECENT ARTICLES | WYNBOER HOME
Geographic Information Systems: an aid in development planning
John Wooldridge1 and Hein Beukes2
1. ARC Infruitec-Nietvoorbij, Stellenbosch
Key words: design, garden, geographic information systems, heritage, planning.
Abstract
Geographic Information Systems (GIS) are widely used for municipal and engineering planning purposes, but are rarely used at farm level. This article illustrates how GIS may be used to facilitate the planning of a development project, using the Heritage Garden as an example.
Geografiese Inligting Stelsels (GIS) word wyd gebruik vir munisipale en ingenieurswese beplanning, maar word selde op plaasvlak gebruik. Hierdie artikel illustreer hoe GIS gebruik kan word by die beplanning van 'n ontwikkelingsprojek, met die Gedenktuin as voorbeeld.
Introduction
Geographic Information Systems (GIS) are computer programmes which reference information in terms of its geographic location, ie latitude, longitude and altitude. The information can be stored, manipulated in various ways, including statistical analysis, and displayed in map form. Because of their speed and accuracy, and their user-friendly pictorial output, geographic information systems are used in many countries for purposes as diverse as maintaining records of the locations of property boundaries, power lines and buried pipe lines and, increasingly, disaster management. However, the uses of GIS are not restricted to planners and engineers. In combination with precision farming methods and remote sensing, GIS is potentially a powerful agricultural management tool. This is especially the case in vineyards where terroir considerations link vine performance and wine style to a variety of GIS-definable environmental factors, such as slope and aspect. Nevertheless, GIS is used in very few South African vineyards at present, probably because the agricultural and land-use planning and management applications and capabilities of GIS have not been widely publicised. To address this, the present article describes the use of GIS as an aid in concept development and planning, these being the critical first stages in the execution of any project. Because of its relative complexity the Heritage Garden is used as an example.
Objective
In the 1970's a c. four hectare, partially wetland site on the ARC Infruitec campus in Stellenbosch was extensively landscaped and developed as a garden. Plants and artefacts of cultural and scientific interest were added, and the garden evolved into a cultural heritage site. Changes are now desirable, to enable the Garden to be used for a range of educational and demonstration purposes, whilst retaining its role as a heritage site. Planning such changes necessitates the consideration of many alternatives, each with plus and minus points, and associated costs. Achieving the best balance is greatly facilitated by the use of GIS, since GIS enables plans and proposals to be modelled and visually presented, often in three dimensions and viewable from any direction. It is therefore possible to assess the overall appearance, potential and impacts of the project before resources are committed.
In most applications, GIS is used to display such forms of information as satellite or air survey imagery and maps showing the positions of vineyards, buildings, pipelines and roads. Over this base a variety of additional information can be overlaid. This may take the form of soils and geological maps, altitude, slope direction, solar radiation intensity and other landscape-related climatic factors. Since scale is variable, it is possible for features as small as a single vine to be identified, and its yield or other salient features recorded in a spread sheet, whilst retaining the facility to zoom to a full-farm, or larger, perspective. Although the most widely utilised output from GIS is an image, statistical analysis and presentation in graphical or tabular form is also possible. Since dimensions such as areas, lengths and volumes can be determined from the GIS imagery, it is easy to estimate such requirements as lengths of irrigation pipe, numbers of vines, or even the volumes of soil involved in dam construction, road building or landscaping. It is also possible to portray differences in yield or other plant parameters across an area of land or, with the help of soil analysis and crop factors, to calculate fertiliser, lime and water requirements.
Relationship to surroundings
The position of an area of land relative to surrounding landscape features may be critical from a terroir viewpoint, notably as regards mesoclimatic factors. Three dimensional (3-D) GIS-generated landscape models are useful for assessing landscape effects. Figure 1 shows that the Garden is situated in a depression at the mouth of the Jonkershoek valley, the axis of which runs from north west to south east. The Garden therefore lies directly in the path of the prevailing summer wind from the south-east. Because the valley has a venturi-like effect, the wind velocity in the region of the Garden is high. Conversely, although the landscape to the northwest of Stellenbosch is undulating, there are no mountains to screen the area from rain-bearing winds from the north-west in winter.
Base map and 3D imagery
A prerequisite for planning is an accurate site map. An adequate and inexpensive plan of the Garden was created by scanning a decades-old map and digitally warping the image to fit a reasonably recent, rectified, air survey photograph (Fig. 2). Features that were installed after the survey were subsequently added using a combination of direct measurement and co-ordinate data from a global positioning system. Interpolation between spot height and contour data enabled a 3-D image of the Garden to be generated (Fig. 3).
Physical features
As previously intimated, the purpose of a base map is to provide planners with a scale representation of the site onto which ideas may be drawn or projected. This process enables beneficial landscape features to be used to the greatest advantage. It also enables costly alterations, such as earthwork, to be minimised. Figure 3 shows that the Garden consists of a two-part landscape in which a plateau looks southward over a lowland area. These features respectively correspond to the 14 m (upper) and 7 m (middle) terraces of the Eerste River (Söhnge and Greef, 1985). The plateau and lowland are respectively underlain by coarse, sandy boulder gravel intermixed with clay from the decomposed granite of the underlying Stellenbosch pluton, and by gravely clay overlying phyllite (altered fine grained sedimentary rock) of the late Precambrian Tygerberg formation. Soil texture and parent rock type therefore change, though gradually, with altitude. Across the garden there is a trend toward decreasing altitude, and increasingly wet soil conditions, from north east to south west. Along much of the northern border of the garden the plateau and lowland are separated by an escarpment-like slope. Below the existing car park and southern access road the angle of this slope was artificially steepened by bulldozing material cut from the granite terrace during excavation of the foundations of the neighbouring building southwards toward the terrace margin. Only to the north east does the land slope at a natural angle. The lake is also an artificial feature. Since it does not lie at the lowest point in the landscape it acts as a reception point for drainage water from only a part of the garden. The land to the south west of the lake is appreciably lower than the lake surface, and is prevented from flooding in winter only by the presence of an artificial drainage system. This discharges into a deep ditch parallel to the southern boundary fence.
Zonation within the Garden
Together with soils and climatic data (not shown), the 3-D image was used to subdivide the garden into zones, and to tentatively assign positions to buildings and paths (Fig. 4). Since the long axis of the Garden is approximately aligned with that of the Jonkerskoek valley, the best views are along the length of the Garden toward the south-east. Developments in the Garden must preserve this line of sight, but must also provide shelter for plants that are susceptible to wind damage.
Highest and smallest of the planting zones is the plateau which adjoins the car park. The gravely landfill in this area is well drained and forms suitable soil for deciduous fruit trees. Also limited in area is the steeply sloping land above the lake. This forms an attractive lawn, although its steeper extremities are better suited to rockeries and trees. The gently sloping land adjacent to the eastern boundary is subject to surface water movement in winter, but is mostly sufficiently well drained for mountain fynbos species and most medicinal plants, and for deeper-rooted plants that are intolerant of protracted water-saturated soil conditions. An earth-walled dam lies across the foot of the slope. Although this receives surface run-off, the dam wall is unsealed and water seeps through the base of the wall, creating super saturated conditions on part of the low-lying land to the west. South-east and south of the lake the local topography is undulating, mainly as a result of earlier landscaping to create flower beds and the dam wall. Soil textures in this region reflect depth of excavation and range from coarse sandy clay loam where topsoil was deposited to sandy clay in the hollows. Whereas the raised areas are generally well drained, the depressions become saturated during rains. These varied soil conditions are potentially advantageous, since they enable an unusually wide variety of plants to be grown in close proximity to one another.
Though grass covered, the lake margins are excessively wet in areas where surface runoff collects. However, a study of the contours suggests that this problem can be rectified by linking the depressions with open channels, thereby creating decorative waterways (Fig. 4). From Figures 1 and 2 it is apparent that the slope of these channels is sufficient to maintain water flow during summer. Water will be supplied to the heads of these channels using hydraulic ram pumps located in the main supply channels. Since these pumps use no power other than that which is inherent in the flowing water, and can be easily home built, they are ideal for rural use.
With the exception of an artificial mound occupied by olive trees, the area between the lake and the southern and western boundary fences is low lying, and slopes gently down toward the south-west. As previously noted, this area is artificially drained. Although the ditches and drains prevent the south western corner of the garden from reverting to its original wetland character, they nevertheless conflict with the sentiment of many environmentalists that wetlands should be conserved and protected. From the imagery it appears likely that excess drainage can potentially be controlled, thereby facilitating a return to wetland conditions.
The southern, and part of the eastern boundary fences, will be bordered by an irregular strip of forest containing plant species that are indigenous to the Stellenbosch area. Where possibly, plant heights and textures will be varied, creating open cell-like enclosures (Fig. 5), each traversed by a path and containing a sculpture or other artefact, and dedicated to a specific cultural theme, plant selection or scientific development. The position of each plant group, tree and artefact will be recorded in the GIS database, together with information concerning its origin, cultural significance and uses.
Further uses of GIS database
Perhaps the most valuable aspect of GIS databases is that they evolve and diversify with time. Rather than become redundant, their function changes. During planning, the primary needs are for simulations to facilitate the placing of buildings and services, and for such parameters as areas, lengths, slopes, volumes and numbers of vines or trees to be calculated for costing purposes. However, as the garden develops, the database will increasingly be used a repository for information about the garden, and for data obtained from instruments placed in the garden. Some of this information will be made available to visitors. Other information will be used for research and demonstration purposes. The inclusion in the database of cultural and technical information concerning plants and artefacts will facilitate and support of the garden's role as a heritage site. The database will also facilitate routine management by keeping track of visitor utilisation patterns, water use, maintenance, and costs. Eventually, the GIS database will be extended to include the ARC farms at Helderfontein and Nietvoorbij.
Conclusions
From the example of the Heritage Garden cited in this article it is apparent that GIS can be used to investigate the possibilities, and plan the development of almost any area of land, at cost levels that need not significantly exceed that of the time involved.
For further information contact John Wooldridge (wooldridgej@arc.agric.za) or Hein Beukes (beukesh@arc.agric.za).
Reference
SÖHNGE, P.G. & GREEF, G.J., 1985. A town founded on alluvial gravel terraces: engineering geology of Stellenbosch. In: A.B.A. Brink (ed.), Engineering Geology of Southern Africa. Building publications, Pretoria, 4, 234-240.
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