INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH VOLUME 9, ISSUE 01, JANUARY 2020 ISSN 2277-8616 768 IJSTR©2020 www.ijstr.org Geospatial Simulation Placement Of Sediment Retaining Buildings In The Mamasa River Basin Sjaid S Fais Assagaf, Eddy Agus Muharyanto, A Sudarman Abstract: Sediment Review (BPS) uses erosion simulations using geospatial simulations. The amount of erosion was analyzed using a gener al version released by the soil (USLE) using ArcGIS software version 9.2. Sources of data and maps obtained from relevant agencies. A satellite imagery map for the Mamasa watershed area obtained on 28 July 2009 was obtained from LAPAN. Data input is initiated by digitizing analogue maps and satellite imagery maps, where georeferenced processes have previously been made to rectify maps so that they become digital maps. The resulting digital map consists of USLE thematic maps (erosivity maps, erodibility maps, long slope maps, and land cover maps). The USLE thematic map is then overlaid resulting in an erosion map. The amount of erosion was obtained from the calculation of USLE attribute data. Sediment rates are calculated using the NLS formula (Sediment Release Ratio). The location and number of BPS are based on sediment rate and distribution. The results showed that erosion rates with very high criteria occurred on farmland and plantations. While the highest sediment rate occurred in Leko-01, Merang and Malobo-Lalaki Sub Watersheds. As many as 26 BPS points are scattered in 16 Sub Watersheds in the upstream, middle, and downstream areas of the Mamasa watershed. Keywords: erosivity, erodibility, rectification, thematic, Sediment Retaining Buildings ——————————  —————————— 1. INTRODUCTION The Mamasa watershed is geographically located at 119 ° 13 '-120 ° 21' BT and 2 ° 43 '-3 ° 46' LS. The Mamasa watershed area includes the administrative area of Mamasa Regency with an area of 83,352 ha (79%), the Pinrang Regency with an area of 21,160 ha (20%), and the Tana Toraja Regency with an area of 705 ha (1%). The total area of the Mamasa watershed ± 105,217 ha has S. Mamasa as the main river with a length of ± 117 km stretching from the north (Mamasa Regency) to the south (Pinrang Regency). S. Mamasa as a media to drain water is the critical and poor condition. This can be seen from the hydrograph indicator of river discharge, namely the ratio of the minimum river discharge that occurs in the dry season and the maximum discharge that occurs in the rainy season above 1:50. The standard size of river flow fluctuation is considered to be good if the minimum and maximum discharge ratios are below 1: 15. Another indicator for assessing the hydrological characteristics of flooding of a river is the measurement of water availability (specific discharge), especially in the dry season. The Mamasa River has a water availability of only 3.2 m3 / sec / km2 in the dry season, whereas in the rainy season, the availability of water is 6.6 m3 / sec / km2. The results of research on 10 major rivers in Indonesia show the specific value of river discharges in the dry season ranged from 4-10 m3 / sec / km2 and 10-80 m3 / sec / km2 in the rainy season[1]. The results of monitoring of the Mamasa watershed condition carried out by the Regional Environmental Impact Management Agency (Bapedalda) of South Sulawesi Province in 2002 showed that the forest area was only 39.57% of the area of the Mamasa watershed. The function of forests as water catchment areas in the Mamasa watershed is decreasing from year to year. Most of the forest land inside the protected area of the Mamasa River has been damaged and converted to agricultural cultivation. The amount of erosion that occurred in 1986 reached 60 tons/ha/ year with an area of erosion reaching 56%, whereas in 2002 erosion reached 784.8 tons/ha/ year. An increase in erosion of ± 300% in a period of 20 years. Land damage is a major cause of erosion and is a serious threat to the Mamasa watershed. As a result of continuous erosion, silting up along the river flows to the Bakaru reservoir, which is located downstream of the watershed. Silting problems have threatened the continuity of the service life of Bakaru Hydroelectric Power Plant so that it can disrupt regional electricity supply[2]. The sedimentation rate in 2006 of ± 800,000 m3 / year caused a decrease in the flow of water entering the Bakaru hydropower plant. The decrease in inflow caused the Bakaru hydropower production capacity to drop dramatically from a normal capacity of 126 MW to an average of only 20 MW. In an effort to improve and restore the conditions of the Mamasa watershed, proper identification and mapping of the problem are needed. One of the efforts made through this research is how to identify the rate of erosion and sediment. The erosion and sediment rates were analyzed using the USLE Equation. The use of the USLE formula because it is commonly used and easily obtained by input data variables, and the results of the analysis can be improved when using the geospatial model. Geospatial simulation is an erosion calculation model using the Geographic Information System (GIS) application program. The role of GIS in the field of infrastructure and natural resources has made it easier to manage and store a database of a location or object so that mapping and analysis of problems can be carried out appropriately[3]. The use of GIS in this research is to identify and analyze the number and locations of Sediment Retaining Buildings appropriately. Besides that, the use of GIS for mapping land degradation or erosion prevention can provide information on land management and forms of conservation appropriately. One form of soil and water conservation in the Watershed is by implementing a Sediment Retaining Building that serves to accommodate a number of sediments so that it does not cause the overflow of sediment volume out of the river channel during floods. Sediment containment buildings can also control the rate of sediment downstream which can threaten and disrupt the functioning of infrastructure that is downstream. ————————————————  Sjaid S Fais Assagaf, Universitas Iqra Buru, Indonesia. Email: sjaidfaisuniqbu@gmail.com  Eddy Agus Muharyanto, Universitas Iqra Buru, Indonesia. Email: edyagus.uniqbu@gmail.com  A Sudarman, Universitas Iqra Buru, Indonesia. Email: sudarma.uniqbu@gmail.com