25 Prediction of the sea level was done for 2010, 2030, and 2100. The 1900 used
as a baseline year measurement; so that the value at 2.1 meter of 2010 for example, is the rising of the sea from 1900. The projection was divided into common and
extreme conditions. Common condition is the sea level in general climate while extreme condition is the sea level in the extreme climate condition namely in the
transition period of El Nino-La Nina. Thus prediction of sea level especially in year period of El Nino and La Nina, range in between common and extreme condition.
The formula of common condition
t
SLCC
and extreme condition
t
SLEC
of sea level projection can be seen as follows:
LS TWL
HW MSLM
SLCC
t t
+ +
+ =
2
t t
t
HEL LS
TWL HWex
MSLM SLEC
+ +
+ +
=
3 Where:
t
MSLM : Global Mean Sea Level in t year observed data according IPCC model
projection.
HW
: Average of high wave data.
HWex
: Maximum value of high wave data.
TWL
: Average range between maximum and minimum of tides data.
LS
: Land subsidence data.
t
HEL
: Sea level in t El Nino and La Nina transition period. To define level inundation, the value of HW has to multiply by 30, because
wave energy to push sea water up to the mainland is decrease about 30 due to hit the material which stand on the coastline area.
The value of sea level relatives has resulted and use as guidance to specify the level of inundation in year observation. Then in same time, the data resulted was
overlaid with the topographic map RBI map, to make a vulnerable map that possible to be displayed and geo-processed using Arc-view software.
3.4.3 Fieldwork
Field survey was conducted in July 2010 and December 2010 according to the tidal data prediction by Indonesian Navy tidal report in Surabaya city. The
fieldworks were intended to get information about tidal flood and to observe the
26 condition related to the research, to conduct interviewed to the local residents, and to
record the occurrence of tidal flood throughout 2010. Tidal flood observation was based on the existing vulnerable hazard map which has been made. The condition of
tidal flood in Surabaya can be seen in appendix 8. Flood impact might reduced by high sedimentation of Surabaya. According to
the interview of local expert and survey, the sedimentation in Surabaya reaches 3 km per year. It was the fact that the predominant soil type of Surabaya is clay-sand
alluvial from sedimentation formation. Several effort by local government to reduce the impact of the flood in Surabaya nowadays are: reforestation program,
small dam in Northern Surabaya Dupak, build paving road and managed the water channel along road side in Northern.
Figure 3.3: Efforts to Reduce Flood Impact
Figure 3.4 shows tidal flood and normal condition where has surveyed in Pabean cantikan sub-district. In Pabean cantikan sub-district, inundation level
ranging 0 to 30 cm.
27 Tidal Flood
Normal
Figure 3.4: Surveyed Area of Tidal Flood Condition
28
3.4.4 Processing and Reporting Phase
The reporting phase is finalizing phase of the research including discussion, i.e., writing, do some revision, consultation to the supervisor, co-supervisor and the
expert, also all activity for thesis report accomplishment. This phase also describe about the risk prediction of losses which caused by floods.
According UN 2004, risk is defined as the probability of harmful consequences, or expected losses deaths, injuries, property, livelihoods, economic
activity disrupted or environment damaged resulting from interactions between natural or human-induced hazards and vulnerable conditions. Risk can be expressed
as follows: Risk = Hazard x Vulnerability
. 3 In this study the risk assessment is calculation of physical losses tangible
damage from landuse types which was extracted from the Google Earth image. The risk assessment considered by vulnerable map that is resulted from previous phase
pre-processing. In this research, the risk estimation is only limited to the tangible damage or physical direct damage caused by tidal flood.
The method of risk damage calculation is:
V H
R Σ
=
4 Where:
R
= Risk damage currency unit per unit area,
H Σ
= total cost damage per unit area, and
V
= Vulnerability value. UN, 2004 Hypothetical prices of the landuse types were assigned based on previous of
hazards flood report and on personal experience of the author in field survey. In this research, land use was divided into four classes because majority land use in
Northern and Eastern Surabaya where located in range 0 ~ 6 km to the coastline are dominated by embankment zone fish and salt ponds, residential, and warehouse
building. So that only those four landuse type will be classified and calculated. The vulnerability value for estimation embankment zone was derived from
interviews to the fish farmer local resident. The cost damage can be calculated easily when the tide has reach more than 2 m high, because average height of main
embankment is 2 m. In the embankment zone, it assumed that the 100 loss total loss occurs when the tide reach 3 m high. The potential of wave energy to break the
embankment are not considered.
29 Table 3.1 presents the vulnerability values in relation to four different water
depth inundation level intervals: 10 cm, 10–50 cm, 50–100 cm and 100–150 cm from Coto 2002. Meanwhile the embankment vulnerable value was derived from
author assumed according survey.
Table 3.1: Vulnerability values for different landuse categories, in relation to four different water depth inundation level intervals
Landuse type Vulnerability values
10 cm 10-50 cm
50-100 cm 100-150 cm
Extremely Low Very Low
Low Moderate
Residential 0.01
0.15 0.5
0.8 Warehouse Building
0.2 0.4
0.5 Embankment
0.25 0.5
1 Commercial
0.1 0.4
0.6 0.8
Agricultural field 0.05
0.1 0.2
Farm 0.01
0.1 0.2
0.25 Farm for crop
0.3 0.45
0.5 0.55
Source from Coto 2002
The water depth inundation level in 2010, 2030 and 2100 were classified into: a.
Extremely low; areas with inundation level from 0 to 10 cm. b.
Very low; areas with inundation level from 10 to 50 cm. c.
Low; areas with inundation level from 50 to 100 cm. d.
Moderate; areas with inundation level from 100 to 150 cm. e.
High; areas with inundation level from 150 to 250 cm. f.
Very high; areas with inundation level from 250 to 400 cm and g.
Extremely high areas with inundation level 400 cm. The classifications of inundation level were established from the combination
class inundation level created by Coto 2000 and the predicted sea level in 2010 to 2100. The classified value expected could comprise the inundation level within 2010
to 2100. Compared with sea level in 2100 where predicted rise up to 400 cm, the sea level rise prediction in 2010 0 to 50 cm in categorized into low level.
Hypothetical loss prices of the landuse types were assigned based on previous hazards flood report by Bappenas 2007 and based on personal experience of the
author in field survey and some articles. The reference of cost damage parameter was obtained from the heavy damage value of each landuse type.
30 In residential area the cost value of heavy damage is 20 million rupiahs per
unit, while light damage in residential area is about 5 million rupiahs per unit, and warehouse building is about 200 million rupiahs per unit Bappenas, 2007.
According to survey, usually the resident builds a dike after occurrence of the floods in the inundation of 10 cm depth, and it is reference to the low vulnerable value for
residential. Total costs to build dikes per house approximately achieve 200 thousand rupiahs. The embankment is dividing into fish and salt, where for in fishshrimp
embankment the harvest price, is about 4.5 million per hectare per farming season 6 months Bappenas, 2000. Meanwhile in salt embankment, the harvest price is about
300 thousand rupiahs per hectare per farming at every 3 days Purbani, 2003. The detail of conversion amount of unit of each landuse type in one hectare
can be illustrated as follows: a. Residential area; the assumption per hectare of residential area are filled by
100 houses. Every house has size about 60 square meters so that for housing complex fill in area about 6000 square meter, and the rest area about 4000 square meter is
using for terrace and collector road. b. Warehouse; the warehouse criteria in this study is defined as more than
one-story building which has an area exceeding 500 square meters and is used as commercial properties. The assumption of general building size is 500 square meter
for each building and the rest about 5000 square meter for collector road and parking area, so that in one hectare will be consist of 10 buildings.
c. Embankment; the embankment usually has already been divided per plot in hectare area.
31
3.5 Sea Level Projection Component
