Asian Physics Symposium 2015 Institut Teknologi Bandung, 19-21 Aug 2015 Author: Dasapta Erwin Irawan, Prihadi Sumintadireja, Ahmad Darul, Anggita Agustin, Arif Nurrochman, and Deny Juanda Puradimaja Preliminary hydrogeological study of the spring belt at three stratovolcanoes has been carried out to predict major hydrogeological boundaries in the stratovolcano system. We used hydrogeological map and 2D finite-element, 2D, computer program to fit the groundwater flow net with the location of spring belt. The spring belt ranges from 250 to 650 masl at Gunung Ciremai, 500-750 masl at Gunung Gede, and 200-400 masl at Gunung Karang-Pulasari. In the first experiment, we set the geological boundaries and topographical features as fixed boundary, which returns slightly different spring belt in the model. Therefore we need to adjust the geological properties to be able to match the spring belt position. Several scenarios using different thickness and permeability have been applied to the model. We find rock thickness has more control to groundwater flow net, where as permeability values have less sensitive role to such flow net. Each volcanoes showed distinct variations of two parameters has occurred on many directions, controlling radial groundwater flow with different hydraulic gradient. Role as recharge area has not applied to entire part of highlands, because of impermeable lava. Anomalies needed careful on-field focussing to get the complete picture of hydrogeology system of strato volcano.

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Hydrogeological boundaries of stratovolcanoes
| Asian Physics Symposium 2015
Irawan, DE., Sumintadireja, P., Darul, A., Agustin, A.,
Nurrochman, A., and Puradimaja, DJ.
Institut Teknologi Bandung
Aug 20, 2015 (version1)

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Introduction
Methods
Preliminary results
Closing

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Introduction

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Problem
• Hydrogeological system in volcanic area still has many
questions, in terms of:
• What is the dominant control to the groundwater flow
• The nature of groundwater spring zone
• How long is the average residence time in the system

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Important role of volcanoes
• Water tower for the lowlands
• Conservation

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Location

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Location2

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Location3

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Location4

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Geological history

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Methods

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Tools
• Preliminary results, computer scale,
• Using free program: Topodrive and ParticleFlow from
USGS,
• It runs on Windows (off course), Mac and Linux.

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Model specifications
• 2D, finite elements
• Boundary condition:
• upper boundary: topography
• lower boundary: Tertiary sediments
• left and right boundary: no flow

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Data
• Groundwater spring survey, mainly to identify the spring
zone:
• Gunung Ciremai: step wise 250 - 650 masl, 750 - 1250 masl,
1300 - 1500 masl
• Gunung Karang-Pulasari: 200 - 400 masl
• Gunung Gede: 500 - 750 masl

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Preliminary results

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Flownet

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Flownet2

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Flownet3

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Discussions
• The model still couldn’t mimic the spring zone perfectly,
• Another question arise? Which parameter plays dominant
control to the system,
• We did some tryouts of sensitivity test.

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Discussions2
Parameter Sensitivity
Depth to lower boundary High
Thickness of the aquifer Low
Intercalation layers High
Hydraulic properties Low

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Closing

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Future directions
• Hopefully we can develop our own model, based on the real
data,
• It can be the basis of a more quantitative approach to
predict spring emergence,
• More tools to support the model: water quality using
multivariate analysis (cluster, PCA, decision tree)

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Acknowledgements
• Research funding: ITB
• Field team: a group of very dedicated undergrad students

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Thank you
• This slides are made by R-Markdown syntax using
LATEXbackend
• Slides pdf are available at My Slideshare repo
• Codes are available at My Github repo
• @dasaptaerwin