Development of WEB-GIS program for River Basin Management in Indonesia

Ahmad Munir and Juni Astuti
Department of Agricultural Engineering Hasanuddin University-Jl.
Cokroaminoto University Makassar –Indonesia
E-mail:amunir@unhas.ac.id




Abstract
In Indonesia, the national government has to spend a large amount of money in order to conserve water quality. Since the regional autonomy is being involved, management of watershed becomes important issue. Because of many watersheds are occupied by more than one regional authority, therefore it is very hard to optimize watershed management. A computer program for river basin management have been developed in order to assist inter-region watershed management. The purpose of this paper is to describe the procedure and profile of an WEB-GIS program for the purpose of optimizing river basin management in term of minimizing erosion and sedimentation rate. The system was developed using Java, PHP and HTML and some supporter program such as MySQL, SVG Vew and ArcInfo were used to develop spatial database. Input data for the model consists of five spatial data: erosivity factor, erodibility, length-slope factor, land cover factor and conservation factor. All spatial data were being converted into geospatial format.

1. Introduction
During the recent decades in Indonesia, rapid exploitation of natural resources has increased pollution rate that has affects on ecosystems. This problem is reflected in increasing annual cost estimates on damage to water quality due to erosion rate through agricultural sources that range from $2.2 billion to $7 billion. Since the regional autonomy is being involved, management of watershed becomes important issue. Because of many watersheds are occupied by more than one regional authority, therefore it is very hard to get an ideal integrated management for optimizing water resources. The purpose of this paper is to describe the procedure, general feature and pplication of WEB-GIS program for River Basin Management in order to optimize water management in term of minimizing erosion and sedimentation rate. Web-GIS System Development The Web-GIS system for river basin managemen was developed using PHP and Html programming language. The system employs PHP, Java and HTML. It is mainly supported with Open Scalable Vector Graphics Map Server (Open SVGMap Server). This software is a free and an open source set of scripts that run on a web server, it was developed by Nedjo Roger, will dynamically generate vector map files from spatial data in a database. The scripts are in the PHP scripting language and are designed for use with a MySQL database. The input data to run the simulation consist of erosivity, erodibility, length slope factor, land cover factor and conservation factor. The data were generated in scaleable vector graphic (SVG) format, with attribute data in the form of Javascript arrays. The input and output file can be viewed through the Internet Explorer web browser with the SVG Viewer (a free browser plug-in from Adobe). Also included in the OpenSVGMapServer software distribution is a script that will export geospatial data and associated formatting information from the desktop GIS software application ArcView into a MySQL format suitable for use with OpenSVGMapServer. The software requires no special software on the web server beyond the free, open source, and broadly available MySQL database and PHP scripting. Development of Geospatial Data The Web-GIS program was applied at the Mamasa river basin, the main basin where the Garugu dam is located. The dam-site is located 250 km from the city of Makassar, on South Sulawesi, Indonesia (Fig. 1). The Mamasa River runs through the South and West Sulawesi Provinces that are occupied by four district (Kabupaten) authorities (Polewali-Mandar, Mamasa, Pinrang, and Toraja). Total area of the basin is about 108,072 ha (1,080 km2) which is positioned at 60 m to 2,873 m above sea level. The slopes of the basin vary between 15% - 45 %. Due to the soil structure of the region, the risk of landslides in the basin is high. Land use within the basin consists of dry-land and mixed agriculture (cocoa, coffee, and other tree crops), secondary forest, dry-land agriculture (maize, upland rice, and vegetables) and settlements. The run-off flows into the Mamasa River, which has a total length of 127 km. Geographically, the Mamasa River Basin is located on the coordinates of 119°13’ - 120°21’ East Longitude and 2°43’ - 3°46’ South Latitude. According to the government, the basin is located in 2 provincial regions, i.e. the West Sulawesi Province and the South Sulawesi Province. The West Sulawesi Province consists of the Mamasa District and the Polewali Mandar (Polman) District, whereas the regions of the South Sulawesi Province include a part of the Pinrang District and the Tana Toraja District. The river basin supplies all the water to the Garugu Dam for generating electricity in South Sulawesi Indonesia. Input data for the computer program are: geospasial data of erosivity, erodibility, and the slope-length, land cover and conservation factors.


Fig. 1. Location of Mamasa River Basin


The annual rainfall amounts in the Mamasa River Basin shows variability between the three stations. The averages of annual rainfall during the period 1988 – 2005 are 4644 mm, 2952 mm, and 2414 mm for the Sumarorong, the Minake and the Mamasa Stations, respectively. Each step of geospasial calculation was processed in the web server. Erosivity factors were established using the method proposed by Bols (1976). Isoerodent maps were developed from data for the Sumarorong, Minake and Mamasa meteorological stations. Erodibility factors were developed from land-based surveys that were conducted by the Institution for Rehabilitation and Conservation, South Sulawesi.

The soil in the basin consists of Ultisol and Alfisol-ordos (USDA, 1992). Udults and Udalfs-ordos are the common soil types found in the basin. The soil can be grouped into the following: Typic Tropudults (Podsolik), Typic Tropudalfs (Meditran) and Typic Hapludults (Brown Forest). Generally, the basin soil contains less clay and therefore has a low water holding capacity. Due to these properties, the soil is susceptible to erosion. Length and slope factors were developed using digital elevation models that were generated using IDRISI and SURFER programs. Steep slopes dominate the topography in the basin, and slopes between 25 and 40% occupy 40% of the drainage basin. The slope-length factor varies between 0.39 and 21.44.

Land cover data were generated from satellite imagery SPOT4. The data was interpreted using ERDAS software. It was found that the drainage basin is dominated by forest and arable land, with some parts of the drainage basin occupied by mixed agriculture (paddy fields and dryland agriculture). Historically, soil and water conservation projects have not been conducted in the basin, and it is estimated that no conservation practices are applied on more than 50% of the drainage basin.

Small areas of the drainage basin are managed using traditional conservation techniques (e.g. terracing). These small conservations regions are considered in the erosion simulation. In the web server, erosion rates is computed using Universal Soil Loss Equation (USLE) method (Wischmeier & Smith, 1978). Sedimentation due to surface erosion (SEP) is computed using SEP = E . SDR, where E is erosion rate (t ha-1 year-1) and SDR is sediment delivery ratio computed using the formula described by Roehl (1962) 20 . 0 36 - × = A SDR , where A is drainage area (km2). Sedimentation rate (m3 km-2 year-1) was computed using a density of the soil of 1200 kg m-3.

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