Future Flood Management Strategies in Indonesia
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MATEC Web of Conferences 229, 01014 (2018) https://doi.org/10.1051/matecconf/201822901014 ICDM 2018 Future flood management strategies in Indonesia Ahmad Junaidi1, Nurhamidah Nurhamidah1,*, Darwizal Daoed1 1Civil Engineering Department, University of Andalas, Padang, Indonesia Abstract. Rapid developments in the catchments, such as deforestation and loss of swamp areas, and in the city, such us sealing off unpaved areas have resulted in higher runoff and deteriorated the river’s conveyance capacity. Critical flooding conditions occur in the city, particularly during heavy rainfall and high tidal flow. Inundation can be characterized as river, tidal, flash and urban flood. A number of flood defense measures have been implemented, designed for return periods of 15 to 50 years, and nonstructural measures within communities who live in flood-prone areas. However, strategies consisting of both structural and nonstructural measures should be developed, upgrade current flood defense practices in Indonesia to a higher safety level, complying with a return period of 50 to 100 years. An integrated and holistic approach is necessary to find solutions for flood management problems in Indonesia. Besides, a regional Water Resources Management plan should be developed, taking into account both flooding and water scarcity issues. The study at hand describes various flood management strategies, each compiled on the basis of different starting points, such as structural measures, non-structural measures, environmental considerations, etc. The implementation of strategies, or separate measures, should focus on priorities for areas most frequently affected. On the short term, efficiency and low-cost measures should be implemented, such as flood forecasting and early warming and flood proofing. In addition, planning of mid and long-term measures should commence on short notice. In the mid-term, larger scale and sustainable measures should be implemented in order to reach a safe level with return periods of 50 to 100 years in the future. Finally, however involving stakeholders and the local communities in planning, development, and implementation of strategies and measures are of utmost importance. 1 Introduction Malacca Strait. Pekanbaru is a center of government administration and economic activities. Pekanbaru is The increasing demand for land strongly influences the located about 160 km upstream of the Siak River. The land-use in a catchments area. The land-use changes Siak River is one of the biggest rivers in Riau Province. adversely affect areas that naturally absorb (flood) The Siak River crosses through Pekanbaru and flows waters such as; swamps, forest, etc. Settlement and other from west to the east. The right and the left side of the anthropogenic activities in these areas strongly influence river basin are occupied by an increasing number of the flooding charge, and the vulnerability to flooding people with various economic activities. The main damage [1-3] Population settlements and economic function of this river is navigation, which strongly activities increase rapidly in Indonesia, especially along supports the social-economic development of the region. the floodplains of the river. The societies surrounding the river work as traders and The flooding problems and accompanying damages traditional fisherman. might be the result of area cultivation and land-use changes without any control. In addition, it seems that increasing rainfall intensities in the upstream catchments of the river and in a city are contributing to the problem of flooding as well [4]. At the same time, the rising tide is dammed up as a result of a backwater in the river [5, 6]. These events cause the river to overflow and inundate the settlement areas in the floodplains and lower high lands. The study area is located on the middle of Sumatra island, where most areas are situated on the lowland, well known as Riau province. The capital of the province Fig. 1. Siak catchment area, Pekanbaru, Riau Province is Pekanbaru, which has a unique characteristic as influenced by two significant catchments; at the The Siak river has a total catchments area of upstream and downstream. The boundary of upstream 1,102,600 ha, while the catchments area up to Pekanbaru catchments is the hills, and the downstream boundary is (CA1) is 542,900 ha, 559,700 ha from Pekanbaru to the * Corresponding author: [email protected] © The Authors, published by EDP Sciences. This is an open access article distributed under the terms of the Creative Commons Attribution License 4.0 (http://creativecommons.org/licenses/by/4.0/). MATEC Web of Conferences 229, 01014 (2018) https://doi.org/10.1051/matecconf/201822901014 ICDM 2018 estuary (CA2), and the capital city of Pekanbaru is Affected residences : nearly 30,000 persons 63,220 ha. It figures out that the surface and subsurface Erosion along river banks : 400 m water flows of the capital city has been influenced from Victims :1 dead two directions of upstream and downstream. 2 The existing flooding condition The flood occurred along the river banks; however, Pekanbaru was also influenced by high intensities of rainfall, which also affected the catchments areas [7]. In addition, high tides inhibited the flow of floodwater downstream. Although the various efforts for an anticipation of the flood had been undertaken, i.e., constructing flood mitigation facilities, including water pumps the actual problems still could not be prevented. There were not enough facilities and infrastructure available, compared to the existing requirements. Fig. 2. Map of actual flooding areas at Pekanbaru The flood elevation reached up to 1.25 m, and the duration was longer than one week [8] [9] [16]. In figure 3, the flood elevations in one of the newer settlement areas are indicated. It was reported floods in Pekanbaru have begun to Fig. 3. Flood Elevations in Settlement Areas of Pekanbaru subside but still resulting over 10,000 people displaced persons since the occurrence on the 1st of December 2017 [10-11]. The evacuees are residing in various spots 2.1 Inundated areas allocated for evacuation and assisted by the office of the During floods, some areas in Pekanbaru are inundated Provincial Government. None of the victims have temporarily, others more permanently. This depends on expressed their willingness to return home, as some the magnitude and genesis of the flood and the houses are still flooded with water up to 1 meter. topography of the inundated area. In 2018, various areas were flooded in Pekanbaru during The average height of the water level in the flooded area the wet season with inundation depths of 10 to 150 cm of Pekanbaru in October 1985 was noted at the elevation [12-13]. of +4.60 m, in March 1988 +4.40 , in November 1994 Nowadays, annual floods are still taking place, +3.80 m and finally in December 2004 +3.80 m above mostly involving 3 sub regencies in 2 Regencies of sea level. The water level of the floods in Pekanbaru Pekanbaru. rises gradually; at the same time, flow velocities are The affected flooding area until December 2017 decreasing [9]. consisted of: The average duration of inundation in Pekanbaru is Flooding discharge : 2,642 m3/s 14 days. Nowadays, the sensitive and vulnerable regions Duration of inundation : 10 days are due to the unobstructed flood mitigation facilities Elevation of inundation : 0.5 - 1 m such as dikes, pumps and water gates. The sensitive and Length of affected roads : 16 km vulnerable regions are due to the uncompleted flood Affected schools : 3 units mitigation facilities such as pumps and water gates. Affected religious places : 8 units The relationship between flood elevation, inundated Affected rural/regencies : 3 regencies areas and return periods along the Siak River in 2 MATEC Web of Conferences 229, 01014 (2018) https://doi.org/10.1051/matecconf/201822901014 ICDM 2018 Pekanbaru are illustrated in Figure 4. This relation shows Figure 6-9 illustrate several locations in Pekanbaru that every year on average an area of approximately during and after the flood. 3,000 ha is inundated in Pekanbaru. Fig. 6. Houses during and after the Flood Fig. 4. The relation between water elevation, inundated area and return period Figure 5 shows that the areas of actual flooding are Fig. 7. Houses on stilts during and after the flood located in the center of Pekanbaru, in particular on the occupied settlements and public service areas. Usually, these floodings occur during heavy local rainfall and coinciding high tides. In the last decade the number of events in which intense local rainfall caused flooding of Pekanbaru has increased due to the increasing development of infrastructure, without considerating the impact on the hydrological system and the environment. Fig. 8. Public Health Service, Pekanbaru, during and after the flood Fig. 9. The Primary School SD 034 before and after the flood Fig. 5. Location of inundated areas in Pekanbaru 2.3 Organization of flood management in 2.2 Damages indonesia The damages caused by flooding are generally The formal institutions that are responsible for flood substantial and are characterized as follows: disaster mitigation and management in Indonesia and 1. The inundations that occurred in the densely Pekanbaru, consist of national, provincial, city and site- populated areas have resulted in destructions of specific level. The National Coordination Committee for houses and public infrastructures such as roads, hazard mitigation represents the coordinating institution, public health services, schools, and wells. which is responsible for the management of flood 2. These damages and destructions have disturbed hazards and victim relief [14]. The members of this socio-economic activities of the community in committee are from several ministries (Home Affairs, Pekanbaru. A significant number of students Social, Health, Public works, Settlement, and Regional have been vacated, and the majority of the Infrastructure, Finance and Transportation), Indonesian community in Pekanbaru have a refuge in the National Armed Forces, the Indonesian Police, and safer places.