1. Geological Engineering Department
Faculty of Engineering
Gadjah Mada University
Coastal Aquifer Groundwater Modeling in the
Southern Part of Yogyakarta Area
Presenter
Main Advisor
Co-Advisor
: Mr. Doung Ratha
: Dr. Doni Prakasa Eka Putra
: Dr. Ir. Heru Hendrayana
Thesis Final Exam
August 24, 2012
1

2. Agenda
1.
2.
3.
4.
5.
6.
7.
Introduction
Literature Review
Research Methodology
Characteristics of Research Area
Data Analysis and Evaluation
Model Application and Discussion
Conclustion
2

3. 1.
Introduction



Background
Research Objectives
Scope of Research Area
3

4. Introduction

Background
The research has been conducted in Coastal Zone of the
southern part of Yogyakarta Area.
People in reseach area are mainly use fresh water from dug
wells that abstracted from groundwater for thire daily needs
(deomestics and agrigculture)
Increasing of (population+agriculture) =>
increasing of groundwater abstraction =>
Degradation groundwater resources both in quantity &
quality (Subsidence, Seawater Intrusion…)
4

5. Introduction

Objectives of Research
The core objective of this research is to apply groundwater
model flow to support groundwater management and solve
such problems in study area in order to achieve 2 main
objectives:
1. To understand the groundwater system which
include hydrogeological conditions, groundwater flow
pattern, and the system of aquifer BY:

Simulate groundwater flow flow system

Understand groundwater balance in study area

Understand hydraulic interaction between river and
groundwater
5

6. Introduction

Objectives of Research (cont’d)
2. To predict and assess salt groundwater in study
area BY:

Estimate the present, offshore location of the interface in the
system

Assess if the interface system was stable prior to pumping

Determine the potential for intrusion or accelerated intrusion
based on current pumping or future projected pumping

Estimate the impacts of abstraction when the specific well locations
in study area increase abstraction rate or abstraction time
6

7. Introduction

Scope of Research area
Research Located in the Parantritis Beach, Southern part of Yogyakarta area, bounded by
Opak River at West and Indain Ocean at South, and
Tertiary Limstone Rock at the East.
Source: google earth, 2011
source: Google Earth (2011)
7

8. Introduction

Scope of Research area (cont’d)
Landuse Map of Study Area
The surface of research area is
approximately 9.46 km² which
is occopied 10 different
landuse.
8

9. 2.
Literature Review

Background theory

Previous research

Hypothesis
9

10. Literature Review

Background theory
•
Groundwater modeling
•
Groundwater in Coastal Aquifer





Coastal Aquifer Hydrogeology
Causes of Seawater Intrusion
Classification of Saline Water
Types of Seawater Intrusion
Estimate Seawater Interface
10

11. Literature Review
• Groundwater Modeling Definition
o Groundwater models is the valuable tools for
management of groundwater resources which are
represented of the reality of natural system and can
be used to monitoring, evaluating and forecasting
groundwater flow and transport.

12. Literature Review
• Coastal Aquifer
o In most coastal aquifer systems groundwater flows
naturally towards the sea driven by the head
potential created by inland recharge.
o Freshwater flow influences salinity stratification

13. Literature Review
• Types of Seawater Intrusion
Two types of seawater intrusions
1. Lateral encroachement from the ocean due to
excessive water withdrawals from coastal aquifer

14. Literature Review
Types of Seawater Intrusion (con’d)
2. Upward movement form deeper saline zones due to
upconing near coastal discharge/pumping wells

15. Literature Review

Previous Researches
Regional Geology & Hydrogeology
 Wates Formation
 Sand Dunes Formation
15

16. Literature Review
Regional Geology
Study Area

Referring to MacDonald & Partners (1984), study area located in Wate
Formation and Sand Dunes Geology.
16

17. Literature Review
Wates Formation

Consist of littoral sand and gravel

Thicknes range up to 30m

Classified as minor aquifer which limited
the permeability and storage (provided well
yield that can support potable supplied, but only limited
irrigation or industrial supplies)
[Mac Donald and Partners, 1984]
17

18. Literature Review
Sand Dunes Formation

Consist of fine to medium gravel & sands
overlying the Wates Formation.

Thickness ranges up to 42m

It is unconfined aquifer

Groundwater elevation 3.50 to 5.60m

Depth to groundwater table 0.50 to 4.15m
[Mac Donald and Partners, 1984]
18

19. Literature Review

Hypothesis
1. Aquifer in study area is unconfined with groundwater
flow directions are dominantly oriented from the north of
the hilly area seaward to the south. Depth of groundwater
table is shallow, and material of aquifer composts of Sand
varied from fine to coarse size and Gravels. Groundwater
quantity is defined as minor aquifer which is limited the
permeability and storativity
2. Groundwater beneath the study area is contaminated
by seawater intrusion resulting from development of
groundwater abstraction for the need of agriculture
aspect and development of tourism sector.
19

20. 3. Research Methodology
 Flow Chat of Research Methodology
 Flow Chat of Modeling Process
20

21. Research Methodology
Problems Definition
Flow Chat of
Research Methodology
Desk Study
Secondary Data
Literature Review
-Topographic map
- Land use map
- Regional geological map
- Hydrogeological data
- Meteorological data
- Existing borehole data
- Background study
- Previous study
Hypothesis
Model Preparation &
Running
Field Reconnaissance
StudyArea Determination:
- Topographical observation
- Landuse surveying
Work Plan
Model Result
Application
Detail Field Works
Parameter Measurements
Hydrogeology
Dug well location
 Water table
measurement
Pumping test
Hydrology
Model Calibration
Soils Sampling
Permeability
 Rainfall data
Porosity
 Runoff
Conclusion &
Recommendation
Texture
Evapotranspiration
 Distance of saline
water interface
Transmissivity and
hydraulic conductivity
Data Imput Optimization
21

22. Research Methodology
Flow Chat of Groundwater
Modeling Process
Define Purpose
Preparation & collection
Data
Understanding Natural
System
Develop Conceptual
Model
NO
NO
Model Calibration &
Validation
Sensitivity Analysis
Prepare Numerical
Model & Running
YES
Analysis Flow Model Error
& Verification
YES
Simulation Flow Modlel
22

23. 4. Characteristics of Research Area
 Hydrological Condition
 Hydrogeological Condition
 Groundwater Usage
 Groundwater Qualilty
23

24. Characteristic of Research Area

Hydrological Condition
Rainfall data were obtained from station of meteorology Bantul during
11 years
=> Average annual rainfall (Pundong Station)
= 1855.2 mm/year
=>Average monthly rainfall (Pundong Station)
= 154.6 mm
=>Average temperature
= 25.9 (c)
24

25. Characteristic of Research Area

Hydrological Condition
=> Evapotranspiration = 1330.8 mm/year
; A = 9.46 km2
=> Runoff = 310.5 mm/year
=> Groundwater infiltration = 214 mm/year
25

26. Characteristic of Research Area
 Hydrogeological Condition
Hydrogeological Cross
Section of Study Area
Based on geological map of Yogyakarta Province (scale: 1: 100 000) and some
of relevant studied the thickness of aquifer in study is approcimatly ranged
from 30 to 40m
26

27. Characteristic of Research Area
 Hydrogeological Condition (cont’d)
Groundwater Flow
Pattern of Study Area
Groundwater Table Measurement: 196 dug wells area measured. The depth of GW
varied from 0.5 to 5 m.
27

28. Characteristic of Research Area
River Measurement: There are 5 locations of river measurement were conducted to
identify: River stage, River Bed, River width, and Thickness of sediment.
Cross Section of River
in point of measurement
28

29. Characteristic of Research Area
 Hydraulic Conductivity
The value of hydraulic conductivity of study are determined based on Method Stug Test
of Hvorslev (1951):
29

30. Characteristic of Research Area
 Hydraulic Conductivity (con’t)
30

31. Characteristic of Research Area
 Hydraulic Conductivity (con’t)
31

32. Characteristic of Research Area
 Groundwater Usage (cont’d)
Population Growth: The growth of population could be calculated by logistic equation
or Verhulst (1847)
=> Nt = 9 041 x e ^ (0.0187 x 2) = 9 386 person
Groundwater Usage: Could be calculated by:
=> Vt = 9 386 person x 150 L/person/day = 1 407 831 L/day = 513 859 m3/a
32

33. Characteristic of Research Area
 Groundwater Quality (salinity)
The salinity of sall water in study area has been determined by the value of
TDS
33

34. Characteristic of Research Area
 Possibility of saltwater intrusion
34

35. 5. Data Analyis and Evaluation
35

36. Natural System
Conceptual Model
36

37. Data Analysis and Evaluation
Parameters Input
Groundwater Recharge = 213.9 mm/year
- Evapotranspiration = 1330.8 mm/year
-
-
Hydraulic Conductivity (KX= KY = K; KZ = 0.1K)
•K1
•K2
•K3
-
= 1.794 E-3 m/s
= 1.337 E-3 m/s
= 8. 974 E-4 m/s
Observed wells : 196 wells
Discretization (30 x 30 m)
- Model Boundaries ( Constand head, River, and No flow)
-
37

38. Uncalibrated Model Result
Data Analysis and Evaluation
Calculated GW table vs.
measured GW table
38

39. Calibrated Model Result
Data Analysis and Evaluation
Calibrated GW table vs.
measured GW table
39

40. Groundwater Mass Balance
Data Analysis and Evaluation
40

41. Data Analysis and Evaluation
Groundwater Flow Model Result
Groundwater Flow Pattern of Model Calculation
41

42. Data Analysis and Evaluation

Parameter sensitivity analysis (PSA)
The aim of sensitivity analysis is to estimate the rate of
change in the output of a model with respect to changes in
model inputs.
To test the thickness of aquifer within the research
whether is it correct or not
42

43. Data Analysis and Evaluation

Parameter sensitivity analysis (PSA)
Groundwater equipotential line
recharge variation
Groundwater equipotential line
of Hydraulic variation
=> Hydraulic parameter more sensitive than recharge
43

44. Data Analysis and Evaluation

Parameter sensitivity analysis (PSA)
Equipotential line of PSA 9 (10-20m)
PSA10 (20-30m) , PSA11 (40-50m)
are quite far from EPL of model result
(30-40m)
=> Aquifer thickness varied from 3040m is assumed correctly.
44

45. 6. Model Application and Discustion
 Application Groundwater Model
to Indentify the Decreasing of
Groundwater Table
 Application Groundwater Model
for Seawater Intrusion
45

46. Model Application and Discustion
 Application GW Model to Indentity the
Decreasing of WT
This application is used the model result to predict
decreasing of WT in the study area in next 5 and 10
years.
46

47. Model Application and Discustion
Changing of GW table in Case 1 and 2 of Prediction
47

48. Model Application and Discustion

Application GW Model for Seawater Intrusion
Intrusion of seawater is identified by calculating the
position of seawater interface by using the priciple
of Ghijben-Herzberg
and also the
formulation of lateral encroachment
48

49. Model Application and Discustion
49

50. 6. Conclusion
50

51. Conclusion and Recommendation
 Conclusion
-Based on observation head, the maximum head equaled to 5m while the
minimum head equaled to 0.5m. Hydraulic gradient is estimated equaled
to 2.45. Therefore, depth of groundwater within the study area is shallow
and groundwater direction in research area oriented from the north to
the south.
-The results of parameter sensitivity of aquifer thickness 30 to 40m
presented the lowest error than other cases, we can conclude that the
thickness of aquifer equaled to 30 to 40m is assumed correcly.
-Based on the value of hydraulic conductivity in three locations within the
research area that have been calculated by Slug Test Method equaled to
1.794 10-3, 1.337 10-3, and 8.974 10-4 m/s represented sand and fine gravel
material. Hence, the composition of aquifer in research area is surly sand
and fine gravel
51

52. Conclusion and Recommendation
 Conclusion (con’t)
-The initial of saltwater interface presented beneath the study area with
the maximum length of protrusion equaled to 205.1m horizontally and
equaled to 40m vertically from land surface.
- From the application of groundwater modeling shown that water table
can be dropped down due to the increasing of groundwater usage.
However, this changing is not relatively different from steady-state
condition because rate of groundwater abstraction still low compare to
abundance of groundwater resources in this area. The rate of
groundwater abstraction is limited due to the population density is low as
well as human activities such as industrial factories, hotels, and guesthouse
still low this area.
52

53. Thanks for your kind attention
53