An Assessment for designing a seawall to mitigate coastal erosion and flooding

1. AN ASSESSMENT OF PUROK 2, BAYBAYON, MABINI, BOHOL
FOR DESIGNING A SEAWALL TO MITIGATE COASTAL EROSION
AND FLOODING

2. INTRODUCTION
STATEMENT OF THE PROBLEM
OBJECTIVES
SCOPE AND LIMITATION
CHAPTER 4
CHAPTER 5
The Earth’s rising temperature has caused
the rise of global sea level together with the height
of waves. This increase is affecting a lot of places all
over the world and is causing problems to people
living in low lying areas.
A portion of Barangay Baybayon in the
municipality of Mabini is a place near the coast in
the province of Bohol that is experiencing flooding
during high tide. Aside from global warming, the
2013 Bohol earthquake also catalyzed Barangay
Baybayon’s further exposure to coastal flooding due
to the shoreline which moved closer to the
residential houses. Furthermore, people migrated
coastward due to population growth and
urbanization.

3. INTRODUCTION
STATEMENT OF THE
PROBLEM
OBJECTIVES
SCOPE AND LIMITATION
CHAPTER 4
CHAPTER 5
FINDINGS
As the sea level rises and coastal flooding has
been a natural occurrence, some features of the
coast have been eroded and seawater reaching the
nearby residences has been experienced during
high tide in Purok 2 of Barangay Baybayon, Mabini,
Bohol. This study seeks to assess the topography
and coastal exposure of the area and evaluate the
necessity of seawall construction in the location.
Thorough analyses of the data gathered enabled
the researchers to come up with an action plan and
recommendations for designing a seawall that will
mitigate coastal erosion and flooding.

4. INTRODUCTION
STATEMENT OF THE PROBLEM
OBJECTIVES
SCOPE AND LIMITATION
CHAPTER 4
CHAPTER 5
FINDINGS
CONCLUSIONS
The study aims to achieve the following objectives:
1. to gather the actual topographical and
coastal data from the location by
determining the:
1.1. tide height
1.2. land elevation
2. to determine the features of the coast that
can be eroded when flooding occurs;
3. to evaluate the necessity of seawall
construction and gather information from
the respondents for flood risk analysis such
as:
3.1. flood hazard information
3.2. exposure information
3.3. vulnerability information; and
4. to recommend an action plan based on
the results of the study.

5. INTRODUCTION
STATEMENT OF THE PROBLEM
OBJECTIVES
SCOPE AND LIMITATION
CHAPTER 4
CHAPTER 5
FINDINGS
CONCLUSIONS
RECOMMENDATIONS
This study is focused on the assessment of Purok 2,
Baybayon, Mabini as to whether the place is in need of a seawall
based on the results of analyses of the gathered data during high
tide and rising sea level through:
1. surveying and on-site observation; and
2. satellite imaging of the surface of the earth and
tide chart.
The researchers also gathered flood hazard information,
exposure information, and vulnerability information from the
respondents with the use of a questionnaire. It is subdivided into:
1. profile of the respondents;
2. brief description of the house;
3. experience in residing in the area;
4. feature of the coast that can be eroded; and
5. frequency/intensity of coastal flooding effects and
opinions on seawall construction.

6. INTRODUCTION
STATEMENT OF THE PROBLEM
OBJECTIVES
SCOPE AND LIMITATION
CHAPTER 4
DATA PRESENTATIONS, RESULTS AND
DISCUSSIONS
FINDINGS
CONCLUSIONS
RECOMMENDATIONS
ACTION PLAN
This chapter includes the
presentation, analysis, and interpretation
of data. The researchers studied the
topographical and coastal data and
assessment on the necessity of seawall
construction.
Introduction
CHAPTER 5

7. Table 4.1. Recorded Tide Heights and Elevation of Sea Level
Coastal Data and Topographical Surveying
Time
Tide Height (TH) @ Mean Sea Level
(m)
Actual Height of Tide @ BM (m) Elevation of Benchmark (BM) @ 0.00 (m)
Final Elevation of Sea Level with Respect
to BM
October 16,2022
12:00 0.45 0.4 0.05 0.4
1:00 0.48 0.4 0.08 0.4
2:00 0.5 0.46 0.04 0.46
3:00 0.56 0.5 0.06 0.5
4:00 0.45 0.41 0.04 0.41
October 23,2022
7:00 0.78 0.74 0.04 0.74
8:00 0.89 0.84 0.05 0.84
9:00 0.99 0.94 0.05 0.94
10:00 0.98 0.95 0.03 0.95
11:00 0.9 0.84 0.06 0.84
October 24,2022
7:00 0.76 0.71 0.05 0.71
8:00 0.92 0.85 0.07 0.85
9:00 0.995 0.95 0.045 0.95
10:00 0.97 0.93 0.04 0.93
11:00 0.83 0.77 0.06 0.77

8. STAFF SETUP DISTANCE (m)
B.S.
(m)
I.S.
(m)
F.S.
(m)
RISE (+) FALL (-) R.L. REMARKS
Elevation with reference from maximum
tide height
0 2.6 0.00 BM ---
1 0+00 2.55 0.05 0.05 -0.90
2 0+15 2.24 0.31 0.36 -0.59
3 0 + 35 1.77 0.47 0.83 -0.12
4 0 + 40 1.68 0.09 0.92 -0.03
5 0 + 45 1.58 0.1 1.02 0.07
6 0 + 50 1.46 0.12 1.14 0.19
7 0 + 55 1.33 0.13 1.27 0.32
8 0 + 60 1.25 0.08 1.35 0.4
9 0 + 65 1.14 0.11 1.46 0.51
10 0 + 69.29 1.51 1.05 0.09 1.55 CP 0.6
11 0 + 73.91 1.5 0.01 1.56 0.61
12 0 + 80 1.49 0.01 1.57 0.62
13 0 + 90 1.49 0 1.57 0.62
14 0 + 95 1.53 -0.04 1.53 0.58
15 0 + 98.97 1.52 0.01 1.54 0.59
16 1 + 05 1.55 -0.03 1.51 0.56
17 1 + 10 1.56 -0.01 1.5 0.55
18 1 + 14.14 1.48 1.6 -0.04 1.46 CP 0.51
19 1 + 20.73 1.47 0.01 1.47 0.52
20 1 + 25 1.45 0.02 1.49 0.54
21 1 + 27.98 1.52 1.48 -0.03 1.46 CP 0.51
22 1 + 30 1.52 0 1.46 0.42
23 1 + 35 1.61 -0.09 1.37 0.35
24 1 + 40 1.68 -0.07 1.3 0.32
25 1 + 50 1.68 0.03 1.3 0.35
26 1 + 52.38 1.65 0.03 1.33 Last Reading 0.38
Table 4.2. Topographic Survey of Land Area Affected by Flooding

9. Tide Height and Elevation with Respect to Benchmark
Time Height of Tide Staff Set-up Distance Elevation
October 16, 2022 0 ---
12:00 0.4 1 0+00 -0.90
1:00 0.4 2 0+15 -0.59
2:00 0.46 3 0 + 35 -0.12
3:00 0.5 4 0 + 40 -0.03
4:00 0.41 5 0 + 45 0.07
October 23,2022 6 0 + 50 0.19
7:00 0.74 7 0 + 55 0.32
8:00 0.84 8 0 + 60 0.4
9:00 0.94 9 0 + 65 0.51
10:00 0.95 10 0 + 69.29 0.6
11:00 0.84 11 0 + 73.91 0.61
October 24,2022 12 0 + 80 0.62
7:00 0.71 13 0 + 90 0.62
8:00 0.85 14 0 + 95 0.58
9:00 0.95 15 0 + 98.97 0.59
10:00 0.93 16 1 + 05 0.56
11:00 0.77 17 1 + 10 0.55
18 1 + 14.14 0.51
19 1 + 20.73 0.52
20 1 + 25 0.54
21 1 + 27.98 0.51
22 1 + 30 0.42
23 1 + 35 0.35
24 1 + 40 0.32
25 1 + 50 0.35
26 1 + 52.38 0.38

10. 3D Presentation of the Location at Maximum Tide Height during the Observation

11. Date Time Maximum Tide Height
Month of December 2022
December 24, 2022 10:52 PM 2.28 m
December 25, 2022 11:39 PM 2.3 m
December 27, 2022 12:27 AM 2.25 m
Month of January 2023
January 22, 2023 10:59 PM 2.32 m
January 23, 2023 11:48 PM 2.33 m
January 25, 2023 12:33 AM 2.24 m
Month of February 2023
February 19, 2023 10:12 PM 2.16 m
February 20, 2023 11:01 PM 2.22 m
February 21, 2023 11:45 PM 2.18 m
Month of June 2023
June 6, 2023 11:22 AM 2.15 m
June 7, 2023 12:08 PM 2.15 m
June 8, 2023 12:57 PM 2.09 m
Month of July 2023
July 4, 2023 10:33 AM 2.16 m
July 5, 2023 11:24 AM 2.22 m
July 6, 2023 12:14 PM 2.21 m
Month of August 2023
August 2, 2023 10:36 AM 2.2 m
August 3, 2023 11:26 AM 2.24 m
August 4, 2023 12:13 PM 2.17 m
Table 4.3 Top 3 Upcoming Spring Tides per Month in Year 2022-2023

12. 3D Presentation of the Location at Maximum Tide Height on upcoming King Tides

14. Items Frequency (𝒇)
Percentage
(%)
Rank
Property 16 69.6 2
Beach/Mudflat 1 4.35 3
Footpath 21 91.3 1
Waterway 1 4.35 3
Table 4.4. Features of the Coast that Can be Eroded

15. Items Frequency(𝒇) Percentage(%) Rank
Never 2 8.70 4
Less than 30 cm 8 34.78 1
30 cm – 1 meter 7 30.43 2
1.1 m – 1.5 m 4 17.39 3
1.6 m – 2.0 m 2 8.70 4
Above 2.0 meters 0 0 5
Table 4.5. Highest Level of Coastal Flood Experienced

16. Items Frequency(𝒇) Percentage(%) Rank
1. Materials
Wood 8 34.78 2
Concrete 3 13.04 3
Half-concrete 12 52.17 1
1. Size and Design
Elevated from the Ground 7 30.43 2
Bungalow 13 56.52 1
Two-storey house 3 13.04 3
Three-storey or higher 0 0 4
Table 4.6. Characteristics of the Houses in the Affected Area

17. Items Frequency (𝒇)
Percentage
(%)
Rank
1. Approximate distance of the house to the shoreline
1-3 meters 11 47.83 1
4-6 meters 4 17.39 3
7-9 meters 0 0 4
10 or more meters 8 34.78 2
1. Approximate no. of years
Less than one year 1 4.35 6
1-10 years 7 30.43 1
11-20 years 1 4.35 6
21-30 years 5 21.74 2
31-40 years 2 8.7 5
41-50 years 3 13.04 4
More than 50 years 4 17.39 3
Table 4.7. Approximate Distance and No. of Years Residing in the Area

18. Items Frequency (𝒇)
Percentage
(%)
Rank
1. Household size
1-3 members 13 56.52 1
4-6 members 4 17.39 3
7-9 members 6 26.09 2
10 members and above 0 0 4
1. Main Source of Income
Fishing 7 30.43 1
Skilled Workers 1 4.35 5
Daily Workers 4 17.39 3.5
On-Call Jobs 1 4.35 5
Small Business 5 21.74 2
Work from Home 1 4.35 5
Dependent on Pension/Remittance 4 17.39 3.5
Table 4.8. Profile of the Respondents

19. Items Frequency (𝒇)
Percentage
(%)
Rank
Visible Cracks 15 65.22 1
Moss Build-up 5 21.74 4
Steel Corrosion 7 30.43 3
Wood Deterioration 11 47.83 2
Others: Washed-out Kitchen 1 4.35 5
Table 4.9. Observable Damage on Houses

20. Statement
N (1) R (2) S (3) O (4) A (5)
WM DV Rank
F WF F WF F WF F WF F WF
1. The coastal flood reaches inside my house. 2 2 2 4 9 27 7 28 3 15 3.04 S 6
2. The coastal flood negatively affects my day-to-day life and activities. 2 2 2 4 5 15 7 28 7 35 3.65 O 2
3. The flooding ruins my properties. 2 2 5 10 3 9 6 24 7 35 3.48 O 3
4. The coastal flood causes negative impacts to my livelihood. 5 5 3 6 1 3 9 36 5 25 3.26 S 4
5. We are advised to evacuate whenever there are typhoons due to the
disaster vulnerability of our area.
0 0 0 0 1 3 2 8 20 100 4.83 A 1
6. Transportation within our area is hard. 3 3 7 14 8 24 5 20 0 0 2.65 S 8
7. There are strong waves reaching the coast. 4 4 3 6 10 30 2 8 4 20 2.96 S 7
8. The color of the water changes (turns muddy or brownish) during high
tide.
3 3 2 4 11 33 4 16 3 15 3.09 S 5
COMPOSITE MEAN 3.40 O
Table 4.10. Frequency/Intensity of Coastal Flooding Effects

21. INTRODUCTION
STATEMENT OF THE PROBLEM
OBJECTIVES
SCOPE AND LIMITATION
CHAPTER 4
CHAPTER 5
SUMMARY, FINDINGS, CONCLUSION AND
RECOMMENDATIONS
FINDINGS
CONCLUSIONS
RECOMMENDATIONS
ACTION PLAN
Introduction
This chapter contains
the summary, findings,
conclusions and
recommendations
formulated by the
researchers based on the
gathered data and results.

22. INTRODUCTION
STATEMENT OF THE PROBLEM
OBJECTIVES
SCOPE AND LIMITATION
CHAPTER 4
CHAPTER 5
FINDINGS
CONCLUSIONS
RECOMMENDATIONS
ACTION PLAN
After the on-site observation and survey to the
respondents and having gathered, analyzed and
interpreted the data, the researchers found out that:
1. The results of the actual topographical and coastal
data in terms of:
 tide height
 land elevation
2. the main feature of the coast that can be eroded is
footpath.
3. the results of the flood risk analysis in terms of:
 flood hazard information
 exposure information
 vulnerability information

23. STATEMENT OF THE PROBLEM
OBJECTIVES
SCOPE AND LIMITATION
CHAPTER 4
CHAPTER 5
FINDINGS
CONCLUSIONS
RECOMMENDATIONS
ACTION PLAN
The following are the conclusions based on the findings:
1. The low topography of the area compared to the height of tides
proves the presence of flooding.
2. There is visible evidence of erosion may it be on properties or on
the surroundings.
3. The occurrence of coastal flooding is frequent and the degree of
its consequences on the local population is bothersome.
4. A seawall is necessary to alleviate the difficulties encountered by
the local residents as a result of frequent flooding in the area.

24. OBJECTIVES
SCOPE AND LIMITATION
CHAPTER 4
CHAPTER 5
FINDINGS
CONCLUSIONS
RECOMMENDATIONS
ACTION PLAN
Future researchers may undergo the following
recommendations for the improvement of the study:
1. Use advance instruments such as total station
and the like to make further accurate surveying
and topographical elevation results.
2. Lengthen the duration spent observing the tide
height to fully validate the idea that the area is
prone to flooding and coastal erosion.
3. Render 3D elevation of the area to further
visualize the tide height and the affected area more
likely to experience flooding.

25. SCOPE AND LIMITATION
CHAPTER 4
CHAPTER 5
FINDINGS
CONCLUSIONS
SUMMARY
ACTION PLAN
Proposed Action Plan for Seawall Construction
Areas of Concern Objectives Time Frame Strategies Persons Involved Remark
1. Awareness on the
topography of the
land
Inform all concerned
persons about the
topography of the land
December 2022
Presentation of the data to
the Barangay officials of
Baybayon, Mabini
Government officials
Possibility of constructing a
seawall
1. Awareness on the
perception of the
residents on seawall
construction
Inform the government
officials of the insights of
the residents based on the
survey
December 2022
Presentation of the results
of the survey to the
Barangay officials
Government officials
Promote the advantages of
seawall construction
1. Dissemination of
information on the
hazards caused by
living in flood-prone
areas
To broaden the knowledge
of the residents of the
possible risks of flooding
to their health and safety
December 2022
Conducting symposium on
flood hazards to the
residents
Residents and government
officials
Additional knowledge to
the residents and barangay
officials to reinforce the
need for seawall
1. Identifying the key
design parameters in
designing a seawall
To determine the initial
design of the seawall
needed for the area
January 2023
Acquire DPWH seawall
design to serve as reference
for possible seawall
construction
Researchers,
DPWH Engineers
Orient the researchers on
the project plan of a
seawall