ST2 - 1

令和４年度砂防学会研究発表会概要集

Assessment of Swa Dam Breach Using Empirical Formulas and Satellite Data
Pa Pa Shwe Sin Kyaw, Taro UCHIDA (University of Tsukuba)
1. Introduction
Though dams provide various benefits for livelihood, their failures also would deliver adverse
effects to localities in downstream. Myanmar, a country in Southeast Asia with an area of 615,678 km2
and 52 million populations, have already experienced several dam failures cases which leads to theneed of investigation of the dam breach and its consequences of inundation in the downstream areaand share such information with the stakeholders living in the downstream areas so that preventive
measures can be put in place to avert catastrophic damages. For example, the spillway collapsed eventof Swa Dam in Myanmar was happened recently in 2018, impacted a number of damaged todownstream societies. However, case studies of dam breach event in Myanmar is still limited.
Although there are several previous studies that have proposed disaster risk assessments for dam
failures (e.g., Froehlich, 2008), its effectiveness has not been fully verified for dam failure cases inMyanmar.
The objective of the study is to assess the dam breach event happened in Swa dam in order toanalyze the characteristics of the spillway breach, breach mechanisms and consequences on
downstream using simple approach such as empirical equations proposed by previous studies.
2. Material and Methods
2.1 Study area
Swa dam is located within Yedashe Township in
Bago Region, southern part of Myanmar (Map reference
94A/4 V645250) (Fig. 1). Location has average annual
rainfall of 2127 mm which gives average annual inflow 385
million m3. The dam was constructed in 1999 andcompleted in 2005. It is an earthen typed dam which has acatchment area of 1044 km2. Dam height is 29.57 m and it
is 2011.68 m in length. The dam has a total water volumeof 267 million cupid meter in its fully storage. The reservoir
area is 2792 ha and irrigation scheme is 14,164 ha. Spillway
type is Reinforced Concrete Bath tube (duckbill) which has
122 m crest length, 170.7 m long and spillway discharge is1486 m3/s.

MyanmarFigure 1. Location of study area

2.2 Data
Swa spillway collapsed at about 5:30 am in the morning of 29th August 2018. Spillway was overflowed
about 0.5 m water depth above the crest and water level was about 102.68 m which was about 4.1 m
to the crest of the dam embankment. Water levels during the event were recorded for two days byIrrigation and Water Utilization Management Department (IWUMD) of Myanmar. Field survey wasconducted after the flood and elevation contour map of study site after the breach was also preparedby IWUMD. After the failure event, technical teams by IWUMD investigated the spillway collapsesite to find the causes of the collapse and the factors that could effect on the stability of spillway.
3. Results
3.1 Topographic change－ 111 －From the topographic data, the maximum cross sectional
width of the breach is about 148.73 m, bottom width ofbreach is about 71.93 m and average breach width is 110.33
m. Height of Breach is about 26.28 m from the dam crest
RL- 107.28 m, as shown in Figure 2.

Outflow(m3/s)

3.2 Outflow Hydrograph
Figure 2. Cross section of breach (Blue before, Red after)
Maximum breach discharge occurred in spillway9000
8000
failure event was calculated which was about 7218.5 m3/s at
7000
102.68 m water level happened at 5:30 am in the morning
6000
5000
using observed water level recorded during the breach and4000
height-volume relationship of the Swa dam as shown in
3000
2000
Figure 3.
1000
5
6.5
8
9.5
11
12.5
14
15.5
17
18.5
20
21.5
23
24.5
26
27.5
29
30.5
32
32.9

0

4. Discussions & Conclusions
Time (hr)In this study, observed breach parameters and peakFigure 3. Calculated Breach outflow
discharge of Swa dam were compared with calculatedparameters by using empirical formulas from previous research. The most common empiricalequations were selected into consideration as shown in Table 1. It is found that the calculated resultsfrom MacDonald’s breach equations provided the highest values whereas the Bureau of reclamation
gave the lowest values in terms of average breach width, and peak outflow respectively. Froehlich’s
predictor equations provided the nearest values in average breach width while, Pierce’s method could
explain data in Swa dam for peak discharge.
From these results, it was confirmed that dam breach parameters and peak outflow of Swa damcase could be predicted if we can select an appropriable empirical formula. On the other hand,sufficient accuracy may not be obtained if an incorrect formula was selected such that peak flow rate
may be underestimated several times. In the future, we would like to consider the reason for the low
accuracy and how to select a suitable formula for dams in Myanmar.
Table 1. Comparison of calculated and observed breach parameters & outflow for Swa Dam
MacDonaldet al(1984)

Bureau ofReclamation(1988)

Soliman(2015)

Froehlich(1995a)

Froehlich(2008)

Pierce(2010)

SwaDamBreach average width (m)

349

67

168

169

155-

110.33

Breaching time Tf (hr)

2.62

0.73

2.28

4.01

3.56

-

2.5

Peak Outflow Qp (m3/s)

12489.72

5913-

8793.53-8269.157218.5

References;
T.C. MacDonald, J.Langridge-Monopolis, Breaching characteristics of dam failures, J.Hydraul. Eng., 110(5) (1984) 567586.
Bureau of Reclamation, Downstream hazard classification guidelines, ACER Tech. Memorandum Rep.No. 11, (1988),
Denver.
D.C. Froehlich, Embankment Dam Breach Parameters Revisited, ASCE Conf. New York (1995a) 887-891.
D.C. Froehlich, Embankment Dam Breach Parameters & their uncertainties, J. Hydraul. Eng., 134(12) (2008) 1708-172.
M.W. Pierce et al, Predicting peak outflow from breached embankment dams, J. Hydrol. Eng., 15(5) (2010) 338-349.
A. Soliman, Hydrological Impacts of Renaissance Dam Failure on the Downstream up to the High Aswan Dam, (2015)
Cairo University, Egypt.

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