DETERMINATION OF RECHARGE AREA USING GIS-AHP METHOD IN MOUNT WELIRANG, PACET AND TRAWAS DISTRICT, EAST JAVA

• Main Author: Mikail Hakim Padmanagara, M
• Format: Final Project
• Language: Indonesia
• Subjects: Geologi, hidrologi & meteorologi
• Online Access: https://digilib.itb.ac.id/gdl/view/78882
• Institution: Institut Teknologi Bandung

The research area is located on the northern slopes of Mount Welirang, in the Pacet and Trawas Districts. This area is a Nature Conservation Area managed by the Raden Soeryo National Forest Park. It encompasses the Arjuno-Welirang Geothermal Working Area, overlapping with land designated for conservation, production, and forest preservation purposes. These forests are suspected to be recharge areas for springs utilized by the community for clean water and tourism purposes. The aim of this research is to understand the hydrogeological conditions, particularly delineating the recharge areas. The research methodology employed includes the analysis of geological conditions, hydrogeochemical analysis of spring water, and an assessment of potential recharge areas. Geological condition analysis and hydrogeochemical analysis of spring water are used to understand the geological conditions that control the hydrogeological system, particularly the recharge areas. Recharge areas are delineated based on field observations and GIS-AHP analysis. The GIS-AHP analysis integrates five criteria, namely lithology, land cover, lineament density, drainage density, and slope. These five criteria are assessed to control the potential for recharge in study area. Based on the results of data processing and analysis, the primary geological factors controlling hydrogeology in the research area are lithology and geological structure. The spring outputs originate from local groundwater flow patterns with minimal water-rock interaction and springs located close to their recharge areas. Weighting using the AHP method yielded the following percentage weights for the criteria: lithology (31%), land cover (12%), lineament density (23%), drainage density (13%), and slope (21%). The delineation of recharge areas using the GIS-AHP method resulted in four classifications with their respective percentage areas: very low (5%), low (47%), high (40%), and very high (8%). Areas with high recharge potential are influenced by lithology with high infiltration rates, such as tuff and tuff breccia, areas with the presence of intensive fractures and faults as pathways for infiltration of water, and relatively gentle slopes (0°-8°) that support rainwater retention. The development of the Working Area (WKP) is recommended to be focused on the areas around the central eruption point of Mount Welirang and the vicinity of the Padusan hot springs. This is due to the predominantly low distribution of potential infiltration values in these areas.