| Summary: | The study area (Parangtritis) located in coastal aquifer at the southern part of
Yogyakarta Province, Indonesia bounded by Indian Ocean at the South, Opak River at
the West, and Tertiary of Limestone Rock at the East. Landuse is mostly covered by
agriculture, rice field and settlement where the population is estimated about 9, 386
persons in 2012 and the total surface is estimate around 9.46 km2. People in this area
commonly use groundwater for their domestic consumption as well as agricultural
purpose with the abstraction rate is increased every year. Consequently, groundwater
in this area is believed to be faced in many problem such as groundwater pollution,
land subsidence, and especially saline water intrusion.
This research titled �Coastal Aquifer Groundwater Modeling in the Southern Part of
Yogyakarta Area, Indonesia� aimed to understand the system of groundwater such as
hydrogeological conditions, groundwater flow patterns, system of unconfined aquifer
as well as to assess and predict saltwater intrusion by conducting numerical
groundwater model. Hydrological and hydrogeological data such as rainfall,
temperature, evapotranspiration, hydraulic conductivity and aquifer geometry had
been collected and applied into data input. Furthermore, conceptual was built to
simulate groundwater flow patterns as well as groundwater flow directions, and assess
groundwater balance in the study area.
The model was simulated in unconfined aquifer system where the aquifer thickness
varied from 30 to 40 meters. The material of the aquifer consists of sand varied from
fine to coarse grand size and fine gravel with hydraulic conductivities value equaled to
8.974 x 10-4, 1.794 x 10-3, and 1.337 x 10-3m/s at the northern, central, and southern
part of research area respectively. Initially, the maximum length of saltwater interface
is estimated about 205.1 m laterally and 40 m vertically associated to the location of
groundwater table equaled to 1m above sea level.
Comparing to observed head measured from 196 of dug wells, groundwater flow
model has been carried out with the Normalized of Root Mean Squared of 1.5%.
Direction of groundwater flow started from north to south. Groundwater table
elevation equaled to 5 m at the north and equaled 0 m at the south of research area
with hydraulic gradient is estimated about 2.45 x 10-3.
As the result of simulation in steady-state as well as two cases of prediction in five and
ten years later, the salinity is not potentially polluted to groundwater quality in this
study area. The reason of this fact due to the number of population in this area is low
while the groundwater resources is abundance.
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