Study on Dam Risk Assessment as a Decision-Making Tool to Assist Prioritizing Maintenance of Embankment Dam in

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3. Water Resources Engineering and Management

Study on Dam Risk Assessment as a Decision-Making Tool to Assist Prioritizing Maintenance of Embankment Dam in

Indonesia

Edy Anto Soentoro¹, Arie Bayu Purnomo² & Sri Hetty Susantin³

1Water Resources Engineering Research Group, Faculty of Civil and Environmental Engineering, Institut Teknologi Bandung (ITB)

Email: [email protected], [email protected]

2Master’s program in Water Resources Management, Faculty of Civil and Environmental Engineering, Institut Teknologi Bandung (ITB)

Email: [email protected]

3Hydraulic Structure and Geotechnical Experimental Station, Center for Water Resources Research and Development (Puslitbang Sumber Daya Air), Ministry of Public Works

Email: [email protected]

Abstract. Dam failure can cause a big disaster in its downstream river, including lost of life and property damages. Dam risk assessment is used to assess the potential of dam failure based on its failure modes and consequences. Since the budgets for dam’s maintenance activities in Indonesia is limited, it is needed a method that can be used as a decision-making tool to make priority of dams maintenance activities. This study applied three dam risk assessment methods (i.e., Modified Andersen, Modified ICOLD and FEMA methods) on six dams for case study. The methods are then compared based on their techniques, requirements, and results. Since each method has its advantage and disadvantage, selection for the most appropriate method should be handed over to the user. It is recommended that dam maintenance should be done completely for the whole components of a dam. In case of many dams have safety problems, meanwhile maintenance budget is limited so that balance on the budget should be done, the FEMA method can be used to assist prioritizing on dam maintenance. Through this decision, the budget can be allocated appropriately to ensure dam safety as well as dam’s function to generate benefits for people.

Keywords: dam safety, decision-making tool, priority, risk assessment.

1 Introduction

Dam failure can cause a big disaster on its downstream river, including lost of life and property damages. Maintenance of a dam is a very important activity to ensure that dam safety is well maintained, and it can be operated normally to provide benefits over the effective life of the dam. In Indonesia, budget for dam’s maintenance activity is allocated in Operation & Maintenance (O&M) activities, and the budget for maintenance is very limited.

The Government has limited annual budget for O & M of many dams in Indonesia, in which budget for dam’s risk assessment is also included on it. Due to condition above, priority

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allocation of maintenance budget for dams based on their risk of failure is needed. This paper explores dam risk assessment as a decision making tool to assist prioritizing maintenance of embankment dam due to limited budget.

2 Literature Review

Dam Risk Assessment is a risk analysis where the loads, the dam’s failure mode and the consequences are presented in a consistent manner within a probabilistic framework.

According to Cyganiewicz and Smart (2000), a general risk equation is:

𝑅𝑖𝑠𝑘 = [𝑃𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝐿𝑜𝑎𝑑 ] 𝑥 [

𝑃𝑟𝑜𝑏𝑎𝑏𝑖𝑙𝑖𝑡𝑦 𝑜𝑓 𝐴𝑑𝑣𝑒𝑟𝑠𝑒 𝑅𝑒𝑠𝑝𝑜𝑛𝑠𝑒

𝐺𝑖𝑣𝑒𝑛 𝐿𝑜𝑎𝑑

] 𝑥 [𝐶𝑜𝑛𝑠𝑒𝑞𝑢𝑒𝑛𝑐𝑒𝑠 𝑜𝑓 𝐺𝑖𝑣𝑒𝑛 𝑅𝑒𝑠𝑝𝑜𝑛𝑒 ]

Dam risk assessment is also considering all aspects of risks that quantitatively can be taken into account in the risk assessment process. The result will be combined with the other factors that are important to determine appropriate actions to maintain or even to restore a particular dam as the final decision. Such factors include dam operations, economics, public participation, water usage and legal requirements.

Dam risk analysis can be divided into three categories: standards, qualitative and quantitative-based approach. The range and level of details vary between categories and within the category, providing options to assessor to match the context of the policy that will be taken. One type of assessments does not need to be superior than the other, but the most important factor, the selected method should be appropriate with the policy and in accordance with the principles of scientific analysis. Three types of dam risk assessment methods according to ICOLD (2005) are as follow:

 Standards-based approach. Standards-based approach does not explicitly carry out risk analysis. Consideration of risk is demonstrated by classifications that reflect the natural hazards of the dam, the impacts of a dam failure, the design load, and the safety coefficient.

 Qualitative approach. A qualitative approach considers the risk more explicit than the standard approach, but without stating the uncertainty in the form of probabilistic. The simplest technique is by indexing and ranking scheme that takes into account security and the consequences of dam failure. Failure Mode and Effect Analysis (FMEA) is one of the first method applied for dam risk assessment by using qualitative approaches widely. Interpretation of results of FMEA requires a measure that describes the severity, importance, criticality, potential of occurrence, etc.

 Quantitative approach. Including in quantitative approaches are reliability analysis method (reliability as First Order Second Moment), Monte Carlo Simulation, and full integration method. Complete quantitative risk analysis will need the following things:

(a) complete identification of the physical properties of the system and the natural conditions that lead to the response of the system, and (b) complete list of failure mechanisms. Output of quantitative risk analysis approach is the complete measure of risk including a complete mathematical specification of the uncertainty in the estimation of probabilities.

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There is no method available to perform a complete quantitative risk analysis of dam, since some of the logic of scientific uncertainties are not known (e.g., internal erosion risk, the probability of dam failure and loss of life). However, a critical understanding of dam safety can be obtained by combining the elements of a standards-based approach, qualitative risk analysis and quantitative risk analysis. So, dam risk analysis is carried out within the limits of acceptable scientific norms and procedures related to quality assurance. In general, the method chosen will be suitable if:

 Scientifically valid and fits with the system and risk assessment purposes,

 The result could provide important information for decision-making process, such as information about the nature of the risk, probability of occurrence and whether the risk can be controlled,

 The method can be used by various practitioners, and it is traceable, repeaTable and verifiable.

This study examines three dam risk assessment methods: Modified Andersen, Modified ICOLD and FEMA methods, in which the first two methods above have been applied in Indonesia. The purpose of this study is to provide alternative methods of dam risk assessment that associated with the availability of data, time for assessment, human resources and budget provided in order to make prioritize of maintenance activities of embankment dam accordingly, effectively and efficiently. Then, the most appropriate method based on the constraints above can be used as a standard decision making tool in prioritizing of maintenance activities of embankment dam in Indonesia.

2.1 Modified Andersen Method

The method is also called the Risk Indexing Method, which has been modified and used by the Puslitbang Sumber Daya Air to determine the level of earth-fill/rockfill dam safety in Java (Puslitbang SDA, 2006). The method was originally introduced by Andersen et al (2001) and it includes probabilistic concept even though the values of the probability is still deterministic. It uses forms that should be filled in to calculate the Risk Index and Dam Safety level. The first step is to calculate the Dam Importance (Idam), then calculate the Dam Relative Importance (RI). From there it can be calculated Total Risk Index (IRtot) and Dam Safety level (Naman). From the value of Naman, dam then classified into 4 classes namely satisfactory, enough satisfactory, less satisfactory and unsatisfactory. This method requires expert judgment to determine the dam relative importance (RI) for the values obtained from field inspections. Modification has been done by Puslitbang Sumber Daya Air where dam stability and instrumentation data reading are included in the method. More details of the method can be seen in the Puslitbang SDA (2006).

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2.2 Modified ICOLD

Modified ICOLD method is adapted from ICOLD (1989) on the selection of seismic parameters for large dams. The method has been used by the Directorate General of Water Resources (DGWR) to conduct a risk assessment on “Dam Operational Improvement and Safety Project Program” (DGWR, 2008). As in the Modified Andersen method, the method also uses forms that should be filled in. This method still uses a deterministic concept in risk assessment.

Risk assessment criteria can be divided into two groups, factors of the dam itself and factors related to the dam itself. Factors of the dam itself cover reservoir capacity, dam’s height, the availability of data on construction and maintenance, observation data from instrumentation that has been installed, the level of work done on previous safety evaluation due to deficiencies on flood-related, stability from static and earthquake loads. Factors related to the dam cover potential downstream damages as result of possibility of the dam failure, the business risks, and the evacuation requirements (number of people) to save the people living on downstream. The dam risk values are determined from values obtained from technical data and from assessor’s estimations. The values of the risk than can be arranged into four risk classes, namely, extreme, high, moderate and low. More details of the method can be seen in the DGWR (2008).

2.3 FEMA Method

FEMA method was developed by the US Federal Emergency Management Agency (FEMA), a federal agency in charge of disaster and emergencies in the United States. This method is used as a standard-based approach method and a preliminary assessment. The dam risk is determinate based on failure probabilities of dam’s elements (e.g., earth-fill/rock-fill embankment, spillway, outlet tower and conduit) due to the load that cause dam’s failure (e.g., flood, piping, static and earthquake loads).These elements are given specific criteria for determining the probability that assessor determines the probabilities based on these criteria based on technical data or condition of the dam at the time of assessment. Magnitude of lost of life potential (LLP) is obtained by estimating the number of people affected by dam failure. The risk value of each element of the dam is determined by multiplying the failure probability magnitude with the LLP. The sum of risk value of each element of the dam is the total risk value. The risk value of each element and the total risk value of dam are then classified into three classes, they are: priority A, B and C, in which the priority A is the highest risk. More details about this method can be found in FEMA (2008).

3 Methodology

The methodology of this study is to compare the results of dam’s risk assessments using the three methods mentioned above. The criteria for comparison are such as the assessment process, probability concept, assessment tools, infrastructures that are assessed, data and information, time available to get data, human resources to assess the risk, budget, and maintenance priorities. The comparison process is carried out in two stages, first to compare

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the results of FEMA and Modified ICOLD, and second, to compare the results of Modified Andersen and modified ICOLD. The first comparison is assessing the Sermo and Sempor dams based on data in year of 2004, 2008 and 2012 using FEMA and Modified ICOLD methods. The second comparison is assessing Sermo, Sempor, Wadaslintang, Tempuran, Penjalin and Ketro dams based on data in year of 2004. Flowchart of assessment measures used in the three methods are shown in Figure 1, 2 and 3 in the next page. The method of comparison and their results can be seen in Table 1.

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Figure 1 Modified Andersen method Figure 2 Modified ICOLD method Figure 3 FEMA method

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Table 1. Method of Comparison of Dam Risk Assessment: Modified Andersen, Modified ICOLD and FEMA

Method Assessment tool

Infrastructur e

Assessment process

Probability

concept Risk

Data and informa

tion

Time required

Assessoro r Expert needed

Cost Ouput Maintenance priority Modified

Andersen

1. Dam importance factor (Idam) worksheet 2. Relative

importance (RI) worksheet 3. IRtot and

Namanwork- sheet

Embank ment dam

1. Calculate dam importance factor (Idam) 2. Estimate

physical condition by

inspection (CF) 3. Calculate

Total Risk Index (IRtot)

amd dam safety level

(Naman)

Use in failure mode

probability (P[Cj|Mi]) and physical

probability (P[Mi|F]).

The probabilistic

is still deterministic

Only count dam condition

e.g.

overtopping, surface erosion, piping and slope stability

Dam initial condition,

dam technical

data, instrumentati

on data, statistic and dynamic data

to do stability analysis, and

site inspection

data

Relative ly time consu

ming

Senior dam engineer

must be involved

Relativ ely expen

sive (expert

s and inspecti

on compo

nent)

Total risk index (IRtot)

and dam safety level

(Naman)

Maintenance priority arrange based on Naman. Dam with low Naman

gets higher priority and vice versa.

Modified ICOLD

1. Main worksheet to calculate

risk score 2. Additional worksheet to estimate physical deficiencies

All type of dams

1. Calculate physical deficiencies 2. Estimate risk

score and calculate total

risk

No probability

concept is used

Consider dam condition and condition beyond the

dam, e.g., evacuation requirement, business risk due to dam failure, and downstream development

Dam technical

data, inspection

data

Relative ly fast (rapid assessm

ent)

Senior dam engineer

can be inlvolved

or junior dam engineer

will be enough

De pend

on inspecti

on compo

nent and expert compo

nent

Risk score and risk classifica

tion

Maintenance priority arrange based on risk score.

Dam wih higher risk

score gets higher priority

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Table 1 Method of Comparison of Dam Risk Assessment: Modified Andersen, Modified ICOLD and FEMA (continued)

Method Assessment tool Infrastructur e

Assessment process

Probability

concept Risk

Data and informa

tion

Time required

Assessoro r Expert

needed

Cost Ouput Maintenance priority FEMA

Workhseet on Microsoft Excel

Embank ment dam, for another type can be seen in FEMA (2008)

Started by estimate magnitude of

failure probability,

estimate consequences, risk classification

and ended by priority making

Subjektive probability is used

Risk is declared in probability which the multiplication

of failure probability

and consequences

Dam technical

data, surveillance

data, inspection data (if any),

previous research (if

any), hydrologic

data, demographic

data, etc.

Relative ly fast

Junior dam engineer is enough

Relativ ely low

Total risk score, each

element risk score

Maintenance priority not only based on total risk score but also on element risk score so that priority making can be

arranged easier.

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3. Water Resources Engineering and Management y = 0,000794x + 0,040305

R² = 0,950086

1,E-06 1,E-05 1,E-04 1,E-03 1,E-02 1,E-01 1,E+00

40 45 50 55 60 65 70 75 80 85 90

FEMA

Modified ICOLD

Modified ICOLD vs FEMA

extrem

Priority A Priority B Priority C

moderate high

4 Result and Analysis

4.1. Comparison of Modified ICOLD vs. FEMA method

The results of dam risk assessment risk scores and risk classes based on each method used.

Comparison of risk score using Modified ICOLD and FEMA methods on Sermo and Sempor dams (year of data: 2004, 2008 and 2012) are shown in Table 2.

Table 2 Comparison of risk score of Modified ICOLD vs. FEMA

Dams Years Modified ICOLD FEMA

Risk Score Risk Class Risk Score Risk Class Sermo

2004 45 Moderate 7,70 x 10^-2 Priority A

2008 46* High* 7,90 x 10^-2 Priority A

Sempor

2004 49 High 7,70 x 10^-2 Priority A

2008 66* High* 9,30 x 10^-2 Priority A

Source: result of calculation, and *) based on data from DGWR (2008)

Figure 4 Risk Score Comparison between Modified ICOLD and FEMA in linear regression

From Figure 4, coefficient of determination (R²) is 0.9501 (close to 1.00) and coefficient of correlation is 0.9747, which means that the results of the risk assessment are strongly related to each other, or both methods were highly correlated. From the values above, the correlation between the results of the two methods are almost perfect.

In FEMA method, it is found that the LLP value of Sermo and Sempor dams are the maximum value (i.e., 1000) due to dense population at downstream of the dams. This condition results in both risk score of dam’s element and the total risk score will tend to be in priority A, regardless of its failure probability magnitude.

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3. Water Resources Engineering and Management y = 0,1441x + 39,4149

R² = 0,6978

0 10 20 30 40 50 60 70

0 20 40 60 80 100 120 140

Modified ICOLD

Modified Andersen

4.2. Comparison of Modified Andersen vs. Modified ICOLD method

Comparison of risk score using

Modified Andersen and Modified ICOLD

methods on Sermo and Sempor dams (year of data: 2004) are shown in Table 3.

Table 3 Comparison of risk score of Modified Andersen vs. Modified ICOLD

Dams Modified ICOLD * Modified Andersen**

Risk Score Risk Class Risk Index Naman Safety Class

Sermo 45 Moderate 49,61 89,50 Satisfactory

Sempor 49 High 34,05 89,19 Satisfactory

Wadaslintang 61 High 115,06 86,65 Satisfactory

Ketro 50 High 97,31 76,83 Satisfactory

Tempuran 40 Moderate

14,63 72,91 Satisfactory

enough

Penjalin 50 High 95,26 82,36 Satisfactory

Source : *) result of calculation, and **) based on data from Puslitbang SDA (2006)

Figure 5 Risk Score Comparison between Modified Andersen and Modified ICOLD in linear regression

From Figure 5, coefficient of determination (R²) is 0.6978 and coefficient of correlation is 0.8353 (relatively closed to 1.00), which means that the correlation between the methods is very strong. Results on Table 6 showed that moderate and high risk classes on Modified ICOLD method are still included in safe category on Modified Andersen method. It is an anomaly because of the high risk values should not result in satisfactory level of safety. High risk value should produce an unsatisfactory safety level or less satisfactory. However, the Modified Andersen method itself has anomalies at the lowest risk index: Tempuran dam at satisfactory enough level of safety, and at the highest risk index: Wadaslintang dam at satisfactory level of safety.

For anomaly happened on Tempuran dam, the Modified Andersen method only see the condition of the dam only, and the calculation does not take into account other conditions

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beyond the dam (e.g., evacuation requirement, business risk due to dam failure, and downstream development) as they are used in the calculation on the Modified ICOLD method. Moreover, there is no direct correlation between the value of the risk of Modified ICOLD and the safety level (Naman) of Modified Andersen method. For anomaly occurred on Wadaslintang dam, it happened because the Modified Andersen method determines the safety level (Naman) by taking into account the importance of the dam (Idam) in a particular form that cause the high value of Idam will result in high value of Naman as well. In the result of assessment, Idam of Wadaslintang dam is the highest among other dams, and this condition causes Naman of the dam falls into the level of safety class as satisfactory although the risk index is the highest.

4.3. Proposed Modification on FEMA method

An adjustment on the FEMA method is proposed in order to make results of the method became more represent the real condition of dams in Indonesia. Modifications are made by adding two criteria, dam’s instrument and Government Ordinance Number 37 year 2010 for the following reasons:

1. Dam’s instrument criteria is not included in the criteria of FEMA method, meanwhile majority of dams in Indonesia are old and they are lack of installed necessary instrument or device to measure the dam’s condition. On the other hand, most of dam in the US are already installed with necessary dam instrument. Data obtained from the instrument will increase alertness about dam safety to the dam managers as well as to the risk assessor.

So it is important and necessary to add dam’s instrument criteria for application of FEMA method in Indonesia.

2. Concepts of dam O&M (Operation & Maintenance) in Government Ordinance Number 37 year 2010 should be included in criteria, since the regulation is the basis for dam management in Indonesia. By adding this criterion, it can be as the benchmark for assessing standard compliance of dam O&M activities. Compliance of dam O&M activities will influence the risk of failure and safety of a dam.

The proposed criteria and probabilities magnitudes are shown in Table 4 and 5.

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3. Water Resources Engineering and Management Table 4 Proposed criteria and probability magnitude of dam’s instrument

Failure mode descriptions Probability

magnitude

Modified ICOLD Risk Class 1. a. Most of the instrumentation is damaged

b. Irregular instrumentation monitoring c. Data evaluation instrument is not running

d. Untrained observers

10^-3-1 Extreme 2. a. Half of instrumentation are working

b. Monitoring instruments performed on a regular schedule c. Data evaluation instrument performed well

a. Poorly trained observers

10^-4 High

3. a. There are at least water pressure, deformation and seepage instrumentation

b. Most of the instruments work well

c. Monitoring instruments performed on a regular schedule d. Data evaluation instrument performed well

e. Trained observers

10^-5 Moderate

4. a. Complete instrumentation i.e., water pressure and earth pressure instrument, seepage instrument, deformation

instrument and seismicity instrument b. All instruments work well

c. Monitoring instruments performed on a regular schedule d. Data evaluation instrument performed well

e. Trained and experienced observers

10^-6 Low

Table 5 Proposed criteria and probability magnitude of O&M activities according to Gov. Ordinance No. 37 year 2010

Failure mode descriptions Probability

magnitude

Modified ICOLD Risk Class 1. Availability of 0 - 1 point from number 4 criteria 10^-3-- 1 Extreme 2. Availability of 2 - 3 point from number 4 criteria 10^-4 High 3 Availability of 4 - 5 point from number 4 criteria 10^-5 Moderate 4. Availability of 6 or 7 points from these criteria

a. Dam management plan

b. The existence of Dam Management Unit (DMU) c. Available-to-date Reservoir Operations pattern d. Available Guidelines O & M cutting edge e. Available Operating Permit Dam f. O & M Dam held properly

g. Emergency Action Plan-to-date availability

10^-6 Low

4.4. Test on Modified FEMA method

Implementation of modifications criteria on the FEMA method is performed on Sermo

and Sempor dams based on data in year 2012. Results of additional criteria assessment

are shown in Table 6. These results are then compared with the initial risk score before

the modification and Modified ICOLD risk score in the same year as shown in Table 7.

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Table 6 Risk Score of Sermo and Sempor dam at 2012 using Modified FEMA method (additional criteria are applied)

Dam Additional Criteria Element of Risk Score

from Additional Criteria Total Risk Score

Sermo Instrumentation 2 x 10^-3

8,20 x 10^-2

G.O. 37 2010 5 x 10^-3

Sempor Instrumentation 1 x 10^-2

9,50 x 10^-2

G.O. 37 2010 1 x 10^-2

Table 7 Comparison of Risk Score Comparison among FEMA, Modified FEMA and Modified ICOLD

Dams FEMA Modified FEMA Modified ICOLD

Sermo 7,50 x 10^-2 8,20 x 10^-2 44

Sempor 7,50 x 10^-2 9,50 x 10^-2 45

4.5. Findings

There are some findings of the study as below:

 In the FEMA method total risk value (or score) is the sum of risk value of each element of dam, meanwhile the range of risk class levels of total risk value and those of risk value of each element are the same. By this condition, if a dam has risk value on elements of the dam, total risk class level of the dam will likely fall in to priority A.

 FEMA method uses maximum value (i.e., 1000) of lost of life potential (LLP) when it is applied to dam risk assessment in Indonesia (e.g., Sermo and Sempor dams), due to dense population at downstream of dam. It will result in a large value of the total risk score and class level of priority A, whatever result of Modified ICOLD Method either moderate or high.

 Modified Andersen method only considers condition of dam alone, and it does not care of conditions beyond of the dam as the Modified ICOLD does (e.g., evacuation requirements, potential downstream damage, business risk as a result of dam failure).

By this condition, result of dam risk assessment of Modified Andersen method which is in “satisfactory” of safety class level, result of the Modified ICOLD could be in “high”

risk class level (e.g., Wadaslintang dam). The Modified ICOLD risk classes and Modified Andersen safety level is not directly.

 Risk Index Value of Modified Andersen Method is not directly comparable with Naman

of a dam, however, a high risk index and a huge Idam will result in a higher Naman (e.g.

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case on Wadaslintang dam). It happens because the calculation of Naman is not only depends on the risk index, but also relies on the importance level of dam (Idam).

 Since each method has has its advantage and disadvantage, it cannot be concluded that one method is better than other methods. The three methods can be an alternative choice for dam risk assessment in Indonesia. The selection of the appropriate method is handed over to the user based on following principal criteria:

a. Modified Andersen method requires data and information in the form of baseline dam, dam technical data, monitoring data from installed instrument, static and dynamic material parameters for stability analysis of influencing earthquake and field inspection. Dam risk assessor should be a senior expert in dam engineering. It requires a relatively long time to collect and analyze data, and a relatively expensive cost in the presence of experts in the field inspections. Priority of maintenance is based on the value of Naman , in which a dam with a low of Naman gets a higher priority of maintenance. Modified Andersen method is recommended to use if risk factors come from conditions beyond the dam can be sipped for consideration

b. Modified ICOLD method requires data and information in the form of dam technical data, field data either from field inspection or complete of secondary data supplement. Dam risk assessor can be either senior or junior dam engineer. The method is suitable for rapid assessment, since the time required for getting data is relatively fast. Costs required for this method can be costly depending on the presence or absence of low-skilled expert component and field inspections. Maintenance priority is based on dams risk score, in which a dam with a high risk value gets a high priority of maintenance. Modified ICOLD method is recommended to use a rapid dam risk assessment is needed.

c. FEMA method requires data and information in the form of dam technical data, field data, previous research data (if any), hydrological data, demographic data, and so forth. Dam risk assessor needed is just a junior dam engineer. The time required is relatively fast, but it not as fast as that of the Modified ICOLD method. It is required a relatively small cost since there is no component of senior experts. Total risk score of dam risk is the sum of risk value of each element of dam, so that selection of maintenance priority can be based on either the highest risk of a dam as one unit, or the highest risk of dam’s element due to very limited maintenance budget. FEMA method is recommended to use one want to know the level of risk of each dam element that facilitates allocation of limited maintenance budgets.

 Selection to use the most appropriate dam risk assessment should also consider the available resources, such as time and fund available to get field data, information and secondary data that are ready at that time, level of expert needed for assessment, dam maintenance priorities, and the results of risk assessment from each method.

5 Conclusion

Dam risk assessment can be used as decision-making tool to assist prioritizing maintenance of embankment dam in Indonesia by rank them to find the highest risk of dam failure. There are three dam risk assessment methods that have been examined in this study, however, it cannot be

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concluded that one method is better than other methods, since each method has its advantage and disadvantage. The three methods can be an alternative choice for dam risk assessment in Indonesia. Selection for the most appropriate method should be handed over to the user based on criteria such as: data and information required for each method, time and budget available to get data, level of expert needed to assess the risk, dam maintenance priorities, and the results of risk assessment from each method.

As a decision-making tool to assist prioritizing maintenance of dam in Indonesia, a dam risk assessment will rank dams based on its risk score and risk class. Then the highest risk dam should be prioritized in dam maintenance. It is recommended that maintenance or even restore of an embankment dam should be done completely as one unit of dam to ensure its safety as well as its function to generate benefits. In case of many dams have safety problems, meanwhile the maintenance budget is very limited, and a balance of spending in maintenance should be done. In this case, the Fema method can be used as decision-making tool to assist prioritizing dam maintenance, since the method provides risk score of each element of dam.

Through this decision, is expected that limited maintenance budget can be allocated accordingly, effectively and efficiently to ensure dam safety as well as dam’s function to generate benefits for people.

6 References

[1] Andersen, G.R., et. al., 2001, Risk Indexing Tool to Assist in Prioritizing Improvements to Embankment Dam Inventories, Journal of Geotechnical and Geoenvironmental

Engineering, Vol. 127, No. 4, April, 2001.

[2] Cyganiewicz, J.,M.,Smart, J.D., 2000, USBR’s Use of Risk Analysis and Risk Assesment in Dam Safety Decision Making, the 20^Th ICOLD Conference, Beijing, China.

[3] DGWR (Directorate General of Water Resources), 2008, Project Implementation Plan for Dam Operational Improvement and Safety Project.Directorate General of Water Resources, Ministry of Public Works, Indonesia, Jakarta.

[4] FEMA (US Federal Emergency Management Agency), 2008, Risk Prioritization Tools for Dam Users Manual, Available at: http://www.fema.gov/ library/ viewRecord.

do?id=3296. (accessed: Januari 2013).

[5] Government of Indonesia, 2010, Government Ordinance of Republic of Indonesia number 37 year 2010 on Dam.

[6] Government of Indonesia, 2007, Law of Republic of Indonesia number 7 year 2007 on Water Resources.

[7] Harrald, J.R., Tanali, I.R., Shaw, G.L., Rubin, C.B., Yeletaysi, S. 2004, Review of Risk Based Prioritization/ Decision Making Methodologies for Dams, George Washington University. Washington DC.

[8] ICOLD (International Commission on Large Dams), 2005, Risk Assesment in Dam Safety Management, AReconnaisance of Benefits, Methods and Current Applications, Buletin No. 130. Paris, France.

[9] ICOLD (International Commission on Large Dams), 1989, Selecting Seismic Parameters for Large Dams.Buletin No. 72. Paris. France.

[10] Puslitbang SDA, 2006. Tingkat Keamanan Bendungan di Jawa, Volume II, Jawa Tengah. Bandung.