Flood Hazard Mapping in San Juan River Basin PDF

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Chapter 1 INTRODUCTION Humanity is currently confronted with a catastrophic phenomenon known as “global warming”. The United States Environment Protection Agency (US-EPA) defines it as the “rise in global average temperature near the earth’s surface that is caused mostly by increasing concentrations...

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Chapter 1 INTRODUCTION

Humanity is currently confronted with a catastrophic phenomenon known as “global warming”. The United States Environment Protection Agency (US-EPA) defines it as the “rise in global average temperature near the earth’s surface that is caused mostly by increasing concentrations of greenhouse gases in the atmosphere”. Greenhouse gases act like a blanket around the Earth, trapping energy in the atmosphere and causing it to warm. This phenomenon is called the ‘greenhouse effect’ a natural and necessary phenomenon to support life on Earth. However, the buildup of greenhouse gases can change Earth's climate and result in dangerous effects to human health and to ecosystems.

The

earth’s

average

temperature has risen by -17.0°C over the past century, and is projected to rise to as much as -11.4°C over the hundred air

next one

years. Global average

temperature

increased

Source : PAGASA, 2011

by

0.7°C since 1906 and the strong

Fig. 1.1 Global Warming showing the increase in mean temperature caused by the Greenhouse Effect

temperature increase since 1975 is unprecedented.

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Small changes in the average temperature of the planet can translate to large and potentially dangerous shifts in weather and climatic patterns. Climatic change, an aftermath of global warming, is characterized by extreme shifts in temperature, precipitation, wind patterns, and other atmospheric conditions (EPA, 2012).

In the Philippines, an increase of 0.6°C from 1951-2010 in the mean temperature due to the so called enhanced greenhouse effect is projected to persists for the next 60 years (Fig 1.2). For the year 2020 and 2050, there is a projected increase of 1ºC to 2ºC and it is very alarming to

know

that only after 2050 that the temperature increase will start to diverge. Greenhouse gases already in the atmosphere

remain

stationary and will take 30 to 40 years for

a

stabilized

atmosphere (Fig 1.3).

Source : PAGASA, 2011

Fig. 1.2 Mean temperature increase of 0.65°C from 1951-2010

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Source : PAGASA, 2011

Fig. 1.3 Projected annual mean temperature of the Philippines

Increasing scientific evidences point to potential devastating effects of global warming to many aspects of human life, including water supplies, agriculture, power and transportation systems, the natural environment, and peoples’ health and safety. Increases in the warming and acidity of oceans threaten aquatic life. For example, the meltdown of glaciers damages the habitat of some animals and contributes to rising sea levels that imperils shoreline habitation. Intense droughts also result in severe heat waves that are adverse to people, animals and plants. Given these, preventing the disastrous consequences of global warming and extreme climatic changes has been recognized as one of the most onerous challenges to world leaders, scientists, business firms, and planners of today.

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In the Philippines, one of the most challenging effects of global warming and climatic change is the occurrence of increased number of typhoons and huge volumes of rainfall which trigger flooding in many residential and agricultural areas of the country. The effects of climate change on the severity of changes in rainfall patterns in the Philippines are shown in Figure 1.4. Heavy daily rainfall (exceeding 300mm) events will continue to increase. As such, the changing pattern is slowly being felt in various parts of the country,

thus

the

abnormal

effects,

flooding, which is projected to be more

Fig. 1.4 Philippines’ Projected Frequency of Extreme Rainfall

devastating and destructive.

The PAGASA Hydrology and Meteorology Division (HMD) defines floods as an abnormal, progressive rise in the water level of a stream that may result in the overflowing of water from its normal confines subsequently resulting to inundation of the areas which are not normally submerged to water.

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Dangerous levels of flooding have been hitting numerous areas of the country in the recent years, resulting in the devastation of communities, damages to agriculture and physical assets, loss of lives and properties, displacement of families, and disruption of social, economic, and political activities of the nation. According to the 2011 Philippine Disaster Report of the Citizens’ Disaster Response Center (CDRC), flood topped the list of the five (5) disasters in 2011 with 121 reported incidents or 28% of the total number of disaster events monitored in the same year.

Flooding affects agriculture in very significant ways. Being an agricultural country, much of the crops grown in the food basket of the Philippines rely heavily on irrigation, dams and reservoirs. The moisture retention capability of soil is an important consideration in choosing the land to cultivate for agricultural production. Lands that are frequently submerged to rain water lose soil fertility, thus making them unsuitable for agricultural production. This is one of the reasons why agricultural planners maintain close coordination with weather and climate forecasters and with agencies involved in the management of water resources, disaster preparedness and management, and flood mitigation. Getting enough information allows agricultural planners to be aware of weather disturbances and enables them to revise plans for agricultural development. Despite such awareness and efforts to coordinate, agriculture continues to be generally vulnerable to the devastating effects of flooding. According to the Bureau of Agricultural Statistics of the Philippines - Department of Agriculture, Typhoon “Ketsana” more

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popularly known as Typhoon “Ondoy” devastated the agricultural sector over an alarming figure of 126,721 hectares of rice-farming land, which affect almost 3% of the country's annual expected rice production. Added to this, Ondoy devastated some 1,374 hectares of corn plantations. (GMA, 2009)

More importantly, the effects of flooding to communities and people are also a matter of great concern. Flood ranked as second in the list of disasters that affected the most number of people in 2011, recording a total of 4.6 million victims in various parts of the country.

The occurrence of flood is precipitated by many factors. Overflow flooding occur when waterways have exhausted their capacity to hold and channel water to its location while inland flooding is caused by inadequate drainage and/or high water level in the main channel. The saturation of the holding capacity of floodplains, streams, and river basins are among the natural causes of flooding. Under such a situation, tropical cyclones which bring excessive volume of rainfall easily result to flooding. There are about 19 to 21 tropical cyclones entering the Philippine Area of Responsibility (PAR) every year, an important reality that has to be recognized in dealing with the issue of flooding.

Human activities have a lot to do with aggravating the vulnerability of certain areas to flooding. Dumping of garbage and encroachment of river banks diminish the

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holding capacity of river basins while deforestation loosens the soil, resulting in the depletion of its capacity to hold water.

In the urban areas, the problem on flood

management is compounded by the land-use conversions that impair the natural soil retention and absorptive capabilities of the environment. Encroachment into natural waterways and drainage of sediments, garbage and siltation, and increase in run-off in developed areas with cemented pavement also significantly contribute to uncontrolled land degradation.

The seriousness of the flooding situation has prompted various sectors of society to collaborate in developing effective flood prevention and risk mitigation strategies. In recent years, the Philippine government has tried numerous schemes to mitigate the adverse consequences of flooding. Such approaches are classified as structural or nonstructural (or a combination of both). Structural measures are direct countermeasures against flooding and are aimed at: (a) increasing the water discharge capacity such as widening of waterways, dredging and excavation, or a combination of all of them; (b) reducing and controlling the peak discharge of flood, such as dam and retarding basin; (c) preventing inland flooding such as revetment, spur dike, and cut-off channel; (d) preventing harmful degradation of riverbed such as groundsill; and (e) preventing the obstruction against river flow and or conserving the good condition of the river in order to keep the flow of water uninterrupted such as sabo works and regular maintenance.

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Non-structural approaches are preventive and remedial in nature. Preventive approaches include flood plain management, watershed management, and public awareness programs. Remedial approaches are like flood forecasting and warning systems, flood fighting and relief operation. It is based on the premise that disaster preparedness and evacuation plan greatly minimizes threats to both life and property. Here, the basic tool is ‘information’ and ‘how’ it can be disseminated effectively and promptly to the affected residents and the disaster management teams. This is the essence of the approach called Flood Hazard Mapping or FHM which is the subject of this study.

FHM is a non-structural approach that aims to enable communities to cope with the hazards of flooding. The FHM approach has three main components, namely: (a) advanced identification of flood-prone areas and locating of such areas in a Flood Hazard Map; (b) advanced designation of evacuation sites in times of flooding; and (c) the dissemination of information to the people about the flood-prone areas and the evacuation sites, including its location, route, and the dangerous spots to be avoided. Flood Hazard maps shows the geographical delineation of the areas subjected to the effects of flood hazard, the degree of exposure to the physical social and the built environment, further accentuating the hazard prone of the area. The information about flood-prone areas includes the depths and other information that are useful in predicting the seriousness of the flooding. The FHM is based on a premise that the provision of advanced information to the people will enable them to plan for the appropriate course of action before the

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crisis begins. For example, a family who knows that its house is erected in a flood-prone site may consider raising the foundation of the abode or quickly access the evacuation site if warranted by the situation.

The FHM approach demands the participation of many agencies at different levels. Through its Coordinating Council, the barangay provides information on their flooding experiences, describing the depth of the flood, volume of rainfall, and other factors that contribute to the inundation of the place, such as creeks, blocked waterways, or malfunctioning drainages. The information is streamed up to the Municipal or City Coordinating Council which provides additional statistical data and other details on the flood prone areas. On the basis of the enriched data, the Municipal or City government adopts and implements policies on local flood management. The combined information from the barangay and municipal councils is forwarded to the Provincial Coordinating Council which collates the data and adopt and implement policies that affect the flood management policies of municipalities and influence policy making on floods at the national level.

The national flood mapping preparations are done with the use of

information from the barangay, municipal, city and provincial levels. The national flood mapping information is disseminated back down to the barangay level. The barangays are expected to undertake full dissemination of information to its constituents. At the center of all these actions at the national level is the National Disaster Coordination Committee which is headed by the Office of the Civil Defense of the Department of

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National Defense. It works with other lead agencies of government such as the Department of Public Works and Highways and the Department of Science and Technology, through PAGASA. The body of knowledge generated in the entire process is used for FHM and for other structural and non-structural flood mitigation strategies of government. Figure 1.5 encapsulates in graphic form the process through which FHM operates.

Fig. 1.5 Flow of Flood Hazard Mapping Dissemination

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In the Philippines, specifically at the National Capital Region (NCR), the flow of warning information dissemination originates from the lone meteorological authority or the agency that is mandated to provide a timely issuance of forecast, warning and bulletins - the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA). The warning/information is transmitted to the National Disaster Risk Reduction Management Council (NDRRMC) and spread out, up to the lowest disaster management level - the Barangay Disaster Risk Reduction Management Council (BDRRMC). During worst-case scenarios of flooding, the NDRRMC may recommend to the President to declare a state of calamity at specific affected areas or the whole region(s) as the case may be. The illustration/flowchart of how the warning is disseminated is presented below:

Fig. 1.6 Flowchart of Information/Warning on Natural Hazards

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There are six national government agencies, including the affected LGU(s), which are involved in the Flood Management and Control in Metro Manila. They are the NDRRMC-OCD, DOST -PAGASA, MMDA, DPWH and the DENR.

Every disaster arising within the Philippine Area of Responsibility (PAR) is addressed by the concerned agencies. The PAGASA is the agency responsible for the formulation of typhoon and flood warnings and advisories. On the other hand, the NDRRMC is the highest policy making, coordinating and supervising body at the national level in terms of ensuring the protection and welfare of the people during disasters or emergencies. The issuance of volcanic hazard warning is under the directive of the Philippine Institute of Volcanology and Seismology (PHIVOCS). The suspected nuclear radiation issue that stemmed out due to the Tsunami and earthquake of 8.9 magnitude of the Richter Scale that occurred in Japan in 2011, feared most of its neighboring Asian countries. This was readily addressed by the quick response of the Philippine Nuclear Research Institute (PNRI).

As such, there is no dedicated agency that is mandated to solve the flooding problems. The NDRRMC, PAGASA and LGUs concerned may collaborate to address problems on flooding. Yet the long-term planning for an effective flood mitigation programs always take a back seat since there are no policies or national programs for flood-related risk prevention and preparedness.

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The use of flood hazard mapping became popular during the early ‘70s. It became a vital component for land use planning especially in flood-prone areas. Easily-read, rapidly-accessible charts and maps which facilitate the identification of areas at risk of flooding are some of the distinguishing features of the application. It also helps prioritize mitigation and response efforts (Bapulu, G.V. and Sinha, R, 2005).

Flood hazard maps are designed to increase awareness of the likelihood of flooding among the public, local authorities and other organizations. They also encourage people living and working in flood-prone areas to find out more about the local flood risk and to take appropriate action. Among the numerous documented success stories about the growing popularity on the use of flood hazard mapping is described in the review of literature.

1.1

Statement of the Problem

This study will answer the question: “How effective is flood hazard mapping project in terms of identification of flood-prone area, designation of evacuation sites, and dissemination of information in providing an alternative solution to flooding problems?”

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1.2

Objectives of the Study

1.2.1

Assess the Flood Hazard Mapping Project in terms of relevance on identified flood-prone areas and to the needs of target beneficiaries;

1.2.2

Determine the impact of using Flood Hazard Mapping in improving the responsiveness of the community to warning and evacuation;

1.2.3

Assess the effectiveness of the Flood Hazard Mapping with regard to achievement of project’s objectives;

1.2.4

Assess the efficiency of the project in providing alternative option for the prevention of loss to lives and property;

1.2.5

Assess the sustainability of the project by determining whether the project is able to become a channel for the adoption by recipients or beneficiaries and;

1.2.6

Recommend policy and program for future flood disaster preparedness and management projects like development of a Disaster Management and Development Program.

1.3

Significance of the study

This study is expected to come up with findings and recommendations that could inform policy and decision making with regard to the use of Flood Hazard Mapping for

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flood prevention and management.

For the LGUs, the identification of frequently-

flooded areas using Flood Hazard Mapping as a predictive tool is a modern breakthrough in flood mitigation and could be considered as an option in selecting the flood control and mitigation program that suits their particular context.

This project does not mean to undermine potentials for expansion of business initiatives in the area. Rather, it seeks to provide a credible analysis that could inform decision making on the productive use of the concerned areas. Its results are potentially helpful for the business sector because they can provide indications on whether there is a need for investors to defer their plans to do business in the concerned localities. The study may also generate insights that are helpful to business firms in adopting flood mitigation plan for existing business establishments and physical properties on those critically mapped areas. This will avert potential business loses arising from floods.

In regard to the outcomes of the project, the assessment envisions to come up with information that would show whether the target beneficiaries, being already aware of their exposure to flood hazard, have adopted the evacuation scheme and were empowered enough to sustain it. The results would also be useful to local barangays in the development of disaster management and development program.

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Furthermore, this study hopes to identify lessons learned from its planning phase to implementation stage including the sustainability measures that could be adopted and replicated by proponents of similar undertakings, like Flood Hazard Mapping projects. Such future endeavors could project higher possibility of success, as stakeholders and beneficiaries are now properly informed with the right directions. Problems identified can be offered with solutions or recommendations so that they may be avoided in similar future endeavors. The insights drawn from this study could also serve as tool that could be adopted by other LGUs in dealing with flood-related challenges.

Overall, a number of flood mitigation projects, structura...