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Water Resources
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Pergau Reservoir Information System (PRIS) For Mapping and Sedimentaion Studies:
A Study on the Development of the Reservoir Database
Database Development
The use of a reservoir database linked to a GIS will considerably enhance the possibilities of satisfying users need through the capabilities of data processing and analysis, automated data sources and data acquisition techniques that have been used in the development of the Pergau Reservoir database.
Figure 1. Data Sources and Data Acquisition Techniques
Data Sources
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Aerial Photographs
Considering the size of the study area, this kind of data was found very suitable in achieving the necessary data for input to the reservoir database. The acquisition of aerial photographs was performed in April 1996. A total of 52 aerial photographs covering the entire reservoir and downstream area to Batu Melintang. The aerial photographs covering the entire reservoir and downstream area to Batu Melintang. The aerial photographs were taken with large format metric camera (230mm x 230mm). The camera used is a superwide angle lense cameraa with 88.32 mm focal length. The average flying height (H) is approximately 1000m. since that the project area is located in a very undulating terrain, the highest point is 925 m and the lowest point is 130 m above mean-sea-level. The average photo scale obtained is 1:25,000.
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Existing Map
As the study area low in development activity, land changes are not too critical. Therefore, the use of existing map as one of the data sources in the study was found very suitable and economic. The property and landuse boundaries were digitized from both of these maps in order to convert into digital format.
The Data Acquisition Techniques
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GPS Surveying
GPS surveying technique has been utilized to establish Ground Control Points (GCP) for photo control and hydrographic surveying activity. Five Ashtech dual frequencies GPS receivers were used in the field surveys. The survey was designed so that a network capable of generating centimeter level accuracy for both horizontal and vertical are satisfied. In order to check the network consistency, ties to at least three GPS First Order Stations has been made. For the etermination of heights above mean-sea-level, ties also has been made to the existing leveling benchmarks located near the study area. The network is incrementally built and adjusted on a daily basis. Finally, the adjusted coordinates given in the WGS84 system are transformed into the local geographic coordinate (Kertau) system and eventually to the plane coordinate (Cassini) system.
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Integrated Hydrographic -GPS surveying
Hydrographic surveying is performed over the impounded area of Pergau Reservoir. Random data collection pattern has been adopted for the hydrographic surveying of the Pergau Reservoir area. Depth measurements was recorded using the echo-trace and adjusted with the tide value observed during the process. The hydrographic system used has the capability to integrate both the sounding and GPS positioning data through a notebook computer carry on-board the boat. Differential correction of the GPS positions was accomplished by establishing a base station atop the Pergau dam area.
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Photogrammetric Mapping
A modified Wild B8 analytical plotter using ADAM Technology Software was used to produce the topographical map. The analytical plotter has the capability to allow stereo-
digitizing of the stereo-model of the aerial photographs. The ground control points obtained from the GPS surveying were used to orient Photogrammetric models before stereo-digitizing can be performed. The digital data obtained from the stereo -digitizing was incorporated with the reservoir bathymetric data to produce the complete digital topographic map. All the digital data was exported to AutoCAD software for editing purpose. The combination of both reservoir and hydrographic techniques generates the most accurate representation of the reservoir and downstream topographical information.
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Manual Digitizing
The existing property map (cadastral standard sheet) and landuse map have been transformed into the digital from by digitizing technique. The result of the digitizing process was incorporated into the digital topographic database as a different layer.
Database Contents
Generally, the data that entered into the database are of two types; spatial data and associated non-spatial attribute from by digitizing technique. The result of the digitizing process was incorporated into the digital topographic database as a difference layer.
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Positional Data
The spatial data that represent the geographic position of features has been stored in vector dataset. It contains a digital representation of the study area map, defines as a series of line(arc) and points (nodes) which combine to from a sequence of map units. Each map unit was defined by one or several polygons. The dataset have been structured in eitht major layers, reservoir and land contours, rivers, spot heights, roads, landuse and property polygons.
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Attribute Data
The non-spatial attribute data provide the descriptive information. Parts of the attribute data in this study were structured in tale's from. The relational database was used. The attribute data would be fed later into the reservoir information system as polygons identifiers and establish the linking between the graphic and alphanumeric database. At the moment, the attribute data consist of type and area of landuse type (landuse table) and river ID length, road ID and length, Point ID and slope (topographic table).
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