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Page 1: FLOOD PROBLEM IN PADANG CITY: THE EFFECTIVENESS … · Ahmad Junaidi, Nurhamidah Civil Engineering, Andalas University, Padang Indonesia ABSTRACT Padang is the most significant natural

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International Journal of Civil Engineering and Technology (IJCIET) Volume 8, Issue 10, October 2017, pp. 1210–1219, Article ID: IJCIET_08_10_124 Available online at http://http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=8&IType=10 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication Scopus Indexed

FLOOD PROBLEM IN PADANG CITY: THE EFFECTIVENESS SOLUTION

Ahmad Junaidi, Nurhamidah

Civil Engineering, Andalas University, Padang Indonesia

ABSTRACT

Padang is the most significant natural disaster in Padang City besides earthquake,

storm surges, landslides and Tsunami from the perspective of population affected,

frequency, area extent and disruption to socio-economic activities. Padang City and

its surrounding alluvial lands still suffer from flood damage by frequent floodwaters.

The main problems of flooding in Padang City are caused by regular river flooding

and urban flash floods. Several engineering works have been implemented in the

rivers, in and near Padang City aiming at mitigating the impacts of the floods.

However, the city still faces problems with flooding during the rainy season. During

the flood on December 25, 2007, three people died and thousands of houses were

inundated. Flood problems in Padang City, present status of the ongoing management

measures, their effectiveness and future in improvement of flood protection and urban

drainage are described. Padang city has a history of vulnerability to floods. This

situation will worsen due to changes in land use, impact of land subsidence and of

climate change. Therefore an optimal urban drainage and flood protection will have

to be developed, that is based on the present and expected future conditions and will

be feasible from the economic point of view. Scenarios for efficient flood protection

and urban drainage systems in Padang city will be presented.

Keywords: natural disaster, flood vulnerable, flood protection, urban drainage

Cite this Article: Ahmad Junaidi and Nurhamidah, Flood Problem in Padang City: the Effectiveness Solution, International Journal of Civil Engineering and Technology, 8(10), 2017, pp. 1210–1219 http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=10

1. INTRODUCTION

We still may observe a rapid population growth, a significant increase in agriculture exploitation, urbanisation and industrialisation in lowland, flood prone areas. Due to this such areas become increasingly vulnerable for extreme weather conditions that will have their effect on the requirements for drainage and flood management. There are no indications that this tendency will change. In the rural areas we may observe improvements in agriculture production and an increase in the value of crops, farm buildings, water management facilities and infrastructure. Rapid urbanisation is especially ongoing in the emerging countries. Most of the areas are located in the flood prone zones. Due to urbanisation and industrialisation and the

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improvement in the standard of living, the value of property, buildings and infrastructure has significantly increased and will further increase in future. Especially in flood prone areas in South and East Asia we may observe a very rapid growth of urban areas. In order to cope with this growth for new urban areas very often reclamation has taken place of low-lying areas in the neighbourhood of the existing urban area. From a water management and flood protection point of view this implies removal of storage area, increase in urban drainage discharges and in the need for adequate flood protection (Schultz, 2001 and 2006).

Indonesia covers a land area of approximately 2 million km2 and has 237 (census in 2010) million inhabitants (Statistic Board of Indonesia, 2010). The occurrence of major floods is increasing, with casualties and substantial losses to the economy. This is caused by an increasing population, which results in rapid urbanisation, coastal and river basin degradation, encroachment of urban areas in ‘natural’ flood storage systems, reduction of natural retention for storm water runoff, and of potential diversion capacity. Moreover, higher population density and economic development increases the number of casualties and value of losses (Basuki, et al., 2005).

As an archipelago area, Indonesia has a number of cities in coastal areas. Some cities, especially in Java Island, have rapidly developed. Cities like Jakarta, Surabaya and Semarang are nowadays subject to frequent suffering due to floods. In these cities, polder development is done with up to date technology by project developers on the one hand and using simple technology by the local people on the other hand. Unfortunately, so far this development was often not carried out based on a well-balanced approach between resources utilisation and valuation of ecological functions as called for in the principles of conservation. As a result urban drainage and flooding problems, salinity intrusion in the groundwater and land subsidence have increased significantly, both in the urban areas themselves as in the surrounding areas (Joint working group, 2009).

2. FLOOD IN PADANG CITY

Padang City as a capital of West Sumatra plays a key role as the centre of political and economic activities, a strategic point for air and sea routes in the western part of the island of Sumatra, Indonesia. The city is increasingly industrialized as the centre of development on the island of Sumatra.

Flooding is the most significant natural disaster in Padang City-besides earthquakes, storm surges, landslides, and tsunamis-from the perspective of population affected, frequency, area extent and disruption to socio-economic activities. The main problems of flooding in Padang City are caused by regular river flooding and urban flash floods. Several engineering works have been implemented in the rivers, in and near Padang City aiming at mitigating the impacts of the floods. However, the city still faces problems with flooding during the rainy season.

During the flood of 25 December 2007, three people died and thousands of houses were inundated. Due to the development as outlined above, decreasing flood conveyance and the low design standard, the risk of flooding is increasing seriously in the area of Padang City. Moreover more and more people settle in the floodplains and the areas prone to flooding. This is mainly caused by the rapid population growth in the area. The risk of a large number of casualties has become very serious and, due to the economic development, the potential damage is high, especially in the area close to the coast. Therefore, reducing flood risk is an important concern for the government and the communities responsible for the rivers and urban drainage systems. To improve flood control and urban drainage different measures can be implemented to reduce the flood risk.

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2.1. Actual Conditions of Padang City

The provincial capital of West Sumatra, Padang City has been a trade centre since the 16th century. During the 16th and 17th centuries pepper was cultivated and there was trade with India, Portugal, the United Kingdom and the Netherlands. In 1663 the city came under the authority of the Dutch. This ended in 1942.

Padang City plays a key role as the centre of political and economic activities in the western part of Sumatra (Figure 1). It is also a strategic point for air and sea routes. Industries in Padang City and its environs are represented by agriculture and commerce, and the city is increasingly industrialized. The population influx from farming villages has activated commerce and economy. The city is rapidly expanding its urban districts through enhanced maintenance of roads and ports based on the master plan for urban development (Japan’s Official Development Assistance (ODA), 2005).

Figure 1 The area of Padang City (Public Works Service, 2007)

In 1945, the city had around 50,000 inhabitants. The population growth since then was largely a result of the migration to major cities as in so many developing nations(http://en.wikipedia.org/wiki/Padang, Indonesia). In 1981, the city had a population of 494,000, which resulted in an average population density was 765 persons/km2. In 2003, the population of Padang City had reached up to 765,000 and the population density increased to 1,101 persons/km2. The population of Padang City in 2007 was about 840,000 and the population density was about 1, 210 persons/km2. In Figure 2 the growth of the population in Padang City from 1998 – 2007 is illustrated.

Figure 2 Population growth in Padang City (Padang Municipality and statiscal board, 2010)

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Padang City has been suffering from flooding since the Dutch ages (1660). In 1797 Padang was inundated by a tsunami with an estimated flow depth of 5-10 metres, following a seaquake, estimated to have been 8.5-8.7 Mw (Moment Magnitude Scale). The shaking and flooding caused considerable damage and causalities. In 1833 another tsunami inundated Padang City with an estimated flow depth of 3-4 metres. This was the result of a seaquake, estimated to have been 8.6-8.9 Mw, which occurred off Bengkulu. The shaking and flooding caused considerable damage in Padang City.

The geographical characteristics often brought floods in the city, causing damage and influencing economic activities. The flooding was caused by the floodwater from Arau, Kuranji and Air dingin Rivers. The Flood prone areas are located in the middle and lower basins of these rivers. As a counter measure against the flood damage in 1903 a flood diversion channel was proposed intending to divert a part of the flood runoff of the Arau River and to prevent floods of the Kuranji River to attack Padang City. The construction works of the diversion channel and diversion structure at its head started in 1911 and were completed in 1918 (Figure 3). The flood diversion channel discharges directly into the sea. The capacity of the flood diversion channel has been increased in Phase 1 of the Padang Area Flood Control Project. This project started in 1991 and was completed in 2001.

Figure 3 Flood diversion channel

The most characteristic feature of the tropical climate is its uniformity with respect to temperature, solar radiation, humidity, wind speed and evaporation. The major climatic parameter that varies in time and space is rainfall. Factors that control the rainfall in Indonesia are equatorial double rainy seasons, monsoons and local influences (Van der Weert, 1994).

The historical past floods and flood plans are illustrated in Figure 4.

Figure 4 Historical flood and flood defences

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2.2. Floods and Characteristics

The river basins are situated in the heavy rainfall zone by the monsoon and characterized by the topographic features of river channels with a steep slope. Such heavy rainfall brings frequent inundation in low-lying areas of the basin while the rivers are not too long from the upstream area, if heavy rain falls in the mountain areas, the water stage rises rapidly in the middle reaches as well as in the lower reaches and the river water may overtop the river bank. From such topographic and hydrological features of the rivers, the duration of the floods is short, about 5 hours. Moreover, the debouching of river water during flooding is frequently aggravated by high tides. Most of flooding occurred in two periods of November to December and April to May.

In general, a distinction can be made between five different types of floods: river flood, coastal flood, flash flood, stagnant and urban floods, and lake floods. The floods in Padang City can be river flood, coastal flood, flash flood, stagnant and urban flood. The main problem of flooding in Padang City consists of regular river flooding, urban flash floods, and an inadequate urban drainage system (Anonymous, 1991). High intensity precipitation often occurs, causing flash floods from the upstream and stagnated flood at the downstream part.

Records of river flooding since 1972 are presented in Table 1. From Padang Area Flood Control Project, these are past records of the flooded area and damage caused by external overflow of Arau, Kuranji and Air Dingin rivers. Table 1 shows that the flood of 1972 caused the largest inundated area, followed by the flood of 1986. The flood of 2007 caused damage to

buildings and infrastructure of Padang City (Figure 5).

Table 1 The total inundated area and damage

Flood Inundated area

(ha)

Losses

(106 Rp)

Losses

(1,000 US$)

May 8, 1972 3,940

April 4, 1979 2,810

November 24, 1980 3,340

November 22, 1981 1,440 No record

December 26, 1982 1,280 11,325 5,660

November 1, 1986 3,450 30,502 15,300

November 20, 1988 680 6,030 3,020

February 2, 1992 780 6,890 3,450

June 2 ,1993 1,310 11,600 5,790

July 3, 2001 1,600

February, 2003 20

February 28, 2005 10

Sources: Public works; Padang Area Flood Project Phase II) US$ 1 ≈ Rp.2, 000 (1993)

The flood of November 1986, in particular, inundated an area of 3,450 hectares, causing severe damage to 6,100 houses and 31,000 people. In this context, a flood control plan was drawn up in 1988 in cooperation with the Japanese government. The Padang Area Flood Control Project Phase-1 was implemented between 1991 and 1996, aiming at the Arau River and the construction of a flood diversion both flowing through the old city area. The capacity of the flood diversion channel has been increased in 1997 (Japan’s Official Development

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Assistance (ODA), 2005). However, Floods are still common, even almost every year there is a big flood.

This is caused by a lack of functioning of the drainage channel and the high intensity of rainfall.

Figure 5 The flooding in 2007

2.3. Problem Defenition

Most of floods in Indonesia are due to overtopping of river banks and inundating adjacent lowland areas. Velocities of water overflowing over lowland areas depend on the terrain of the lands and the height of accumulated water in the river. Due to this, urban centres, commercial districts or agricultural areas can be inundated for a couple hours and even a couple of days (2-5 days).

From the perspective of population affected, frequency, areal extent and disruption to socio-economic activities flooding is the most significant natural disaster in Padang City besides earthquakes, storm surges, landslides, tsunamis and drought.

The Padang City flood management system can be categorized as a sectoral flood management system. There is no clear concept to cope with the floods and flood mitigation activities are only project oriented. The reduction of flooding and the susceptibility to flood damage is only focusing on structural measures. The lack of a management, operation and maintenance plan for urban drainage and flood protection makes it more complicated. For the maintenance are not enough budgets available for every year. In recent years, rapid development within the river basin has resulted in higher runoff and deteriorated river capacity. Nowadays, localised flooding in the urban area of Padang City is typically caused by inadequate functioning or clogging of the internal drainage system (Figure 6).There are several problems of urban drainage system in Padang City:

• All urban drainage systems are open drains, and not enough space is available for widening the drains (Figure 7);

• Many drainage channels are not well maintained;

• Substantial budget is needed to improve and maintain the drains.

The change in land use of Padang City also contributes to flooding. The city has expanded, and encroaches its surrounding swamps area. The increased deforestation, particularly in the upstream of rivers in Padang City has contributed to increased flooding and sedimentation in the lower part of the rivers (Figure 8).

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Figure 6 Drainage problems

Figure 7 Open urban drains

Figure 8 Deforestation upstream and sedimentation in the flood diversion channel downstream

2.4. Research Methodology

The methodology of this study consists of the following:

• At the beginning, a review of previous studies on urban drainage, flood protection and flood modelling will be done from available reports, journals, internet, etc.;

• Data collection, model selection and development, setting up scenarios, flood risk analysis, determination of potential flood damages, determination of appropriate ways to cope with flooding in the study area, conclusions and formulation of recommendations.

The key parameters that will be optimised are basically the total cost involved as by way of the example shown in the theoretical Figure 9.

Figure 9 Theoretical relation between cost for flood management and flood protection (Schultz, 2001)

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Under land use change scenarios, land subsidence and climate change, the optimisation package will be determined based on a risk-analysis method. The model will be largely based on rainfall-runoff modelling and numerical/flood modelling by applying the model (SOBEK Urban/Rural-1D/2D) coupled with a GIS system. Land use change (increase in population and value of public and private property) in the flood prone areas, land subsidence and climate change are three important phenomena which are linked to each other and have to be evaluated with support of integrated optimisation modelling.

Figure 10 Research methodology

2.5. Effectiveness of Flood Mitigasyion Measures

In general the Padang Area Flood Control project is very much effective in containing the external overflow due to over-topping from the rivers, so that it can be considered that the long-term objectives particularly the socio-economic and environment impacts have been sufficiently realized. Land areas that previously hardly can be used for economic activities are now free from flood and the many people who settled in the areas concerned can have a better live.

The problem of sand sedimentation at the mouth of the Air Dingin River according to the Deputy of the Project has been solved and there is no more sand blocking the flow of the Air Dingin River into the sea by constructing jetties along the end banks of the rivers using such technique that made it possible the sand be swept to sea the downturn the tide. Subsequently no more flood occurred in the surrounding settlements (Kusumo A. Martoredjo, 2005)

The flood that occurred during the rainy season of 2003 and 2004 are not due to the over-topping of the rivers but due to urban drainage channels that are not effective enough in channelling the surface water caused by the heavy rainfall at certain times only and hardly bring much damage to the Padang City since the flood subsidies within practically short time (Kusumo A. Martoredjo, 2005)

Increasing population and change in land use are contributing to the problem of flooding in Padang City. Flooding in Padang City is caused by the following factors:

• Over bank flow of floodwater of the river;

• Insufficient capacity of the drainage system (urban drainage);

• Backwater effects of flood water levels as a result of incoming tide. Regarding the urban area located between the Arau and the Kuranji Rivers, intensive inundation seems to be caused by the combination of two or more of the above mentioned;

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• The existing drainage systems of Padang City are not well maintained and poorly functioning.

After several cases of flooding in the period between 1959 and 1993, the Padang Area Flood Control Project was implemented which started in 1991 and finalized in 2001. The project should prevent flooding by widening the river channel, heightening the river embankment and improve the flood diversion channel and urban drainage system. However, the city still faces problems with flooding during the rainy season.

In the future the following measure should be taken to cope with flood in Padang city:

• Upper basin (elevation >25 m): Flood regulation by detention basin;

• Middle basin (elevation 5 – 25 m): Flood prevention by improvement of rivers and channel;

• Lower basin (elevation 0 – 5 m): Flood prevention by retention basin and urban drainage improvement.

Coping with floods in Padang City has been mainly focusing on structural measures. A flood early warning system is not available for the Padang City Area. In the future the area that has an elevation between 0-5 m above sea level still will most probably have problems of flooding. There is a lack of management system in Padang City; it means no clear concept to cope with flood.

The concept of Integrated Flood Management (structural and non-structural, measures such as retention measures, reforestation, flood plain regulation, river training works, urban drainage and a flood forecasting and early warning system) would increase the reliability to cope with flood in the future of Padang City.

The following recommendations are suggested for the local government of Padang city to cope with future flooding:

• The local government should increase the awareness of flooding of the people who are living in flood prone area.

• The local government of Padang city should consider implementing the combination and integration of structural and non-structural measures such as multipurpose retention area to cope with floods;

• It is strongly recommended to pay more attention to a specific policy of land use planning, taking into account additional space for flooded retention area;

• The general public and stakeholders should be involved to contribute to coping with floods in Padang City;

• The local government should enhance the operation and maintenance of the rivers and the urban drainage system of Padang City.

It is needed to continue with the development a comprehensive study to anticipate on the future (socio-economic and spatial) of Padang City, which should be related to the flooding issues and resulting in among of these, a flood modeling system of Padang City to be used by decision makers of the Local Government of Padang City.

ACKNOWLEDGEMENTS

The research of this paper was financially supported by Faculty of Engineering, Andalas University Padang, Indonesia, grant no: 021/UN.16.09D/PL/2017. I would like to express my deep gratitude to Prof. Dr. Ir. Bart Schultz and Dr. Ir. FX. Suryadi for their encouragement and useful critiques of this research work.

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