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1. RESULTS AND DISCUSSION
Morphometric Characteristics of Maragondon River Watershed
Maragondon River Watershed is the biggest of the six major river systems in
Cavite Province. Table 1 shows the Morphometric characteristics of the Maragondon
river watershed. They include watershed shape, watershed relief, and channel
morphology.
Perimeter. Watershed perimeter is the outer boundary of the watershed that
enclosed its area. It is measured along the divides between watersheds and maybe
used as an indicator of watershed size and shape.
The perimeter of Maragondon river watershed is 89 kilometers and it has the biggest
perimeter of the six major river watersheds in the province. In that way, if the ground
can no longer absorb the water it will flow into the adjacent rivers and when the rain
continues to increase, it will cause flooding.
Area. The area of watershed is also known as the drainage area, and it is the
most important watershed characteristic for hydrologic analysis and defined as the
area contained within the vertical projection of the drainage divide on a horizontal
plane. Maragondon river watershed has an area of 334.713 square kilometers. As
the size and shape of a river's drainage basin dictates how much precipitation the
river can receive and how quickly it will arrive. A large drainage basin indicates that
the river's catchment area is very huge, which will result in significant water collection
and increased outflow.
Bifurcation ratio. Defined as the ratio of the number of streams of any given
order to the number of the streams in the next lower order. The lower the bifurcation
ratio value, the higher the flood hazard in the discharge area. The bifurcation ratio of
MRW is 1.93, thus it means that the watershed and communities within the
watershed are vulnerable to flooding.
2. Gravelius form factor. The ratio of the average width to the axial length of
the basin. Form factor indicates the flow intensity of a basin of a defined area
(Horton, 1945). This ratio helps to understand whether the basin has a circular of
elongated geometry. The smaller the value of the form factor, the more elongated will
be the basin and low runoff will generate with long runoff duration, whereas rounded-
shape watershed with high value of form factor experiences high runoff with short
time of concentration and is highly sensitive to flooding. (Waikar and Nilawar 2014).
The form factor of Maragondon river watershed is 0.2641, indicating elongated basin
with lower peak flows of longer duration than the average.
Elongation ratio. Defined as the ratio between the diameter of a circle with
the same area as the watershed and the maximum length of the watershed. A basin
with a smaller elongation ratio discharge more runoff and vice versa. Values of
elongation ratio generally vary from 0.6 to 1.0 over a wide variety of climatic and
geologic types. Elongation ratio values close to unity correspond typically to regions
of low relief, whereas values in the range 0.6–0.8 are usually associated with high
relief and steep ground slope (Strahler 1964). These values can be grouped into
three categories namely (a) circular (>0.9), (b) oval (0.9-0.8), (c) less elongated
(<0.7). The elongation ratio of Maragondon river watershed is 0.5801. Therefore, the
area is slightly sensitive to flooding.
Circulation ratio. It is expressed as the ratio of the basin to the area of a
circle having the same perimeter as that of the basin. Circulation ratio (Rc) values
approaching to 1 indicates that the basin shapes are circular and the low value
indicates that the basin is elongated and not structurally controlled (Babu, et al.,
2014). The circulatory value specifies the form of the basin, as the circulatory ratio
rises, the basin's shape becomes more rounded and flooding at the outflow point is
more likely due to short flow duration (Bogale, 2021). Thus, the area is elongated due
to its value of 0.5310.
3. Basin length. The distance traveled by the surface drainage and sometimes
more appropriately labelled as hydrologic length. The basin length indicates whether
flooding during rainfall is more likely or less likely. Long basin length indicates lower
chances of flooding during rainfall, whereas short basin length indicates higher
chances of flooding. Therefore, the area has a lower chance of flooding as it has a
total of 35.6 kilometers.
Basin relief. Basin relief is the elevation difference of the highest and lowest
point of the basin. It determines the slope and indicates high or low runoff and
sediment transport. The longer the slope length, the greater the volume of water, flow
speed, and inertia force. The highest elevation of MRW is 0.695 kilometers and the
lowest elevation is 0.003 kilometers. Thus the basin relief of MRW is 0.692
kilometers.
Relief ratio. Defined as the ratio of the total basin relief to the maximum basin
length. Relief ratio measures the overall steepness of a drainage basin and is an
indicator of the intensity of erosion process operating on slope of the basin (Schumm,
1956). The relief ratio of Maragondon river watershed is 0.0194.
Relative relief. The ratio of the maximum basin relief to the perimeter of the
basin. Relief refers to the difference in height between the highest point and the
lowest point on land. When rain falls, the surface runoff can move very quickly from
mountainous or hilly areas to low lying areas making these low lying areas more
prone to flooding. Maragondon river watershed has relative relief of 0.007809.
Elevation. It is the distance above sea level. The higher your flood elevation,
the less likely it is that your property will flood. The lower or more negative the
elevation, the higher the risk of a flood (Bettersworth, 2022). The highest elevation in
MRW measuring of 0.695 kilometers and 0.003 kilometers for lowest elevation.
Slope. Watershed slope reflects the rate of change of elevation with respect
to distance along the principal flow path. The bigger the amount of water, flow speed,
and inertia force, the greater the slope length. In other words, the larger the distance
4. from the watershed line, the greater the kinetic energy of the flow, and therefore the
higher the velocity of the flow, resulting in an increase in flood vulnerability (Yongmei
et al. 2011). Maragondon river watershed has a highest slope measuring of 23.8o
and
0.493o
for lowest slope.
Sinuosity index. Is the channel length between two points on a river, and
valley length is the straight line distance between the same two points. The sinuosity
index of MRW with a dimension of 0.9266. The sinuosity index of the river channel
was influenced by morphological changes in the river channel caused by flood
events. The severity of flood in a channel is also determined by river characteristics
such as sinuosity (Susware N. K, et al 2021).
Stream order is a measure of the relative size of streams. The stream order
of MRW is 4. When flooding occurs, high order streams take longer to reach flood
stage than lower order streams, and the flood lasts longer.
Stream number. Is a positive whole number used in geomorphology and
hydrology to indicate the level of branching in a river system. The total stream
number in MRW has a total 169 streams and with a total stream length of 348.8110
kilometers. The number of tributaries that feed into a river influences the chance of
flooding. If a river has a large number of tributaries, the river's discharge will be much
higher because a large amount of water will enter it from the tributaries. After heavy
rain, the flow will climb even more, increasing the likelihood of flooding, particularly at
confluences (where a tributary meets the river), where discharge is maximum.
Table 1. Morphometric characteristics of Maragondon River Watershed (CvSU-PGC,
2019)
PARAMETER DIMENSION
A. Watershed-shape
Perimeter (P) 89 km
Area (A) 334.713 k
Gravelius Form Factor (GF) 0.2641
Bifurcation Ratio (BR) 1.93
Elongation Ratio (ER) 0.5801
Circulation Ratio (CR) 0.5310
5. Basin Length (BL) 35.6 km
B. Watershed Relief
Basin Relief 0.692 km
Relief Ratio 0.0194
Relative Relief 7.809x10-3
Elevation
Highest Elevation 0.695 km
Lowest Elevation 0.003 km
Slope
Highest Slope 23.8o
Lowest Slope 0.493o
C. Channel Morphology
Sinuosity Index 0.9266
Stream Ordering 4
Stream Number 169
Total Stream Length 348.8110 km
Areas and Communities that are Vulnerable to Flooding
On map 1, it shows the areas and communities within the watershed that are
vulnerable to flooding. There are two vulnerable areas that have been identified as
low-lying areas, namely Barangay Poblacion 1B and Barangay Bucal 3B. This
Barangay are vulnerable to flooding because they are located in low elevation and
near in the river.
Quantitative Correlation Between Morphometric Characteristics and
Incidence of Flooding
Impacts of Flooding to the Vulnerable Communities Inside Maragondon River
Watershed
Based from the flood vulnerability assessment there are two areas that are
vulnerable to flooding, namely Barangay Poblacion 1b and Barangay Bucal 3b. The
population size in Barangay Poblacion1B is 1500 and 627 in Barangay Bucal 3B. The
participants of this study are those communities that are located in vulnerable areas
and those who experienced flooding in the area. In selecting the participants the
researchers used Cochran’s formula. Out of 1500 population in Barangay Poblacion
1b only 306 individuals and 239 individuals in Barangay Bucal 3b out of 627
populations to answered the survey question.
6. Table 2 shows the demographic profile of participants in Barangay Poblacion
1b includes age, sex, civil status, size of the family, educational attainment, major
occupation and position in the barangay (LGU and DRRMO only).
Age. There were 124 (23%) participants on each of these age group between
57 to 64 years old. There are 119 (22%) participants were on each of these age
group between 41 to 48 years old. There were 116 (21%) of the participants were on
of these age group between 49 to 56 years old. There were 85 (16%) participants
were on these age group between 65 to 72 years old. There were 51 (9%)
participants were on these age group between 73 to 80 years old. There were 35
(6%) participants were on these age group between 33 to 40 years old. There were
15 (3%) participants were on these age group of 25 to 32 years old. Based from the
ages of the participants 25 years old is the youngest and 80 years old is the oldest.
Sex. There were 545 participants in Barangay Poblacion 1b and Barnagay
Bucal 3b and majority of the participants were female with a population of 294 (54%)
and the remaining 251 (46%) were male.
Civil status. There were 274 (50%) participants were married, 98 (36%)
participants were single, 38 (7%) participants were separated and 35 (6%)
participants were widow. Based from the civil status of the participants mostly were
married and least were widow.
Size of the family. The size of the family of the participants ranges from 2 to
10 members. There were 273 (50%) participants had 5 to 7 members, 199 (37%)
participants had 2 to 4 members, and 73 (13%) participants had 8 to 10 members.
Based from the family size of the participants the majority have 5 to 7 members in the
family and participants with a family size of 8 to 10 members had the least number of
family members.
Educational attainment. Table 2 shows that 126 (23%) of the participants
were elementary graduates, 104 (19%) participants were High school graduates, 101
(19%) participants were High school level, 77 (14%) participants were college level,
7. 47 (9%) participants were elementary level, 45 (8%) participants were college
graduate vocational graduate respectively. Based from the educational attainment of
the participants the majority were elementary graduates and an educational
attainment of college and vocational graduates had a least number of participants.
Major occupation. There were 139 (26%) participants were housewife, 92
(17%) participants were construction workers, 76 (14%) participants were farmer, 74
(14%) participants were drivers, 65 (12%) participants were barangay/DRRMO
officers, 42 (8%) participants were jobless, 30 (6%) were vendor/business owners,
and 5 (1%) participants were teacher. Based from the major occupation of the
participants mostly were housewife and least were teachers.
Position in the barangay. Based from the major occupation there were 65
(12%) participants were barangay and DRRM officers. There were 15 (23%)
participants were barangay police, 14 (22%) participants were DRRM office, 13
(20%) participants were barangay councilors, 9 (14%) participants were barangay
health workers, 8 (12%) participants were barangay maintenance, 2 (3%) participants
were barangay captain, barangay secretary and barangay treasurer respectively.
Table 2. Demographic profile of participants in Barangay Poblacion 1b and Barangay
Bucal 3b
CHARACTERISTICS FREQUENCY PERCENTAGE
Age
25 – 32
33 – 40
41 – 48
49 – 56
57 - 64
65 – 72
73 – 80
15
35
119
116
124
85
51
3
6
22
21
23
16
9
9. Fisherman
Farmer
Driver
Vendor/Business owner
Barangay/DRRM officer
Housewife
Jobless
Position in the Barangay
DRRM Officer
Barangay Captain
Barangay Councilor
Barangay Health Worker
Barangay Secretary
Barangay Treasurer
Barangay Police
Barangay Maintenance
22
76
74
30
65
139
42
14
2
13
9
2
2
15
8
4
14
14
6
12
26
8
22
3
20
14
3
3
23
12
Table 4 shows the impacts of flooding in Barangay Poblacion 1b and
Barangay Bucal 3b. Based from the 545 participants, there were 534 (98%)
participants experienced loss and damages of their houses, 360 (66%) participants
experienced loss and damages of their poultry, 346 (63%) participants experienced
the loss and damages of their boats, 322 (59%) participants experienced loss and
damages of their fish farm, 311 (57%) participants experienced loss and damages of
their stores/shops 267 (49%) participants experienced loss and damages of their
agriculture and crops, 60 (11%) participants experienced the loss and damages of
their piggery, and 49 (%) participants experienced the loss and damages of their goat
10. farm. Based from the impact of flooding in Barangay Poblacion 1b and Barangay
Bucal 3b mostly experienced the loss and damaged of their houses and goat farm
had the least number of loss and damaged.
Table 4. Impacts of flooding in Barangay Poblacion 1b and Barangay Bucal 3b
LOSS/DAMAGES FREQUENCY PERCENTAGE
Houses
Boats
Fish farm
Stores/shops
Poultry
Agriculture/crops
Piggery
Goat farm
534
360
346
322
311
267
60
49
98
66
63
59
57
49
11
9
*multiple responses
Table 6 shows the support of LGU to affected residents in Barangay
Poblacion 1b and Barangay Bucal 3b. There were 533 (98%) received relief goods,
518 (95%) received financial/cash assistance, 256 (47%) received rescue response,
65 (12%) received clothes, and 44 (8%) received beddings. Mostly of the participants
received relief goods as support of their Local Government Unit and the least support
that the participants received were beddings.
Table 6. Support of LGU to affected residents in Brgy. Poblacion 1b and Barangay
Bucal 3b
SUPPORT OF LGU FREQUENCY PERCENTAGE
Relief goods 533 98
11. Financial/Cash assistance
Rescue response
Clothes
Beddings
518
256
65
44
95
47
12
8
*multiple responses
Recommended Mitigation Measures to Control and Minimize the Effects of
Flooding to the Vulnerable Communities
Table 8 shows the mitigation measures to minimize the effects of flooding in
Barangay Poblacion 1b and Barangay Bucal 3b. There were 476 (87%) on proper
waste disposal, 445 (82%) on unclogging of drainage system, 275 (50%) on
construction of retaining walls, 109 (20%) on evacuation response, 99 (18%) warning
sign of flood and landslide prone areas, 52 (10%) typhoon information dissemination,
and 43 (8%) on conducting training and seminars. Based from participant responses
it is visible that the LGU of Maragondon, Cavite prioritized proper waste disposal and
segregation, and unclogging of drainage system.
Table 8. Mitigation measures to minimize the effects of flooding in Brgy. Poblacion 1b
MITIGATION MEASURES FREQUENCY PERCENTAGE
Proper Waste Disposal
Unclogging of Drainage System
Retaining Walls
Evacuation Response
Warning sign (flood and
landslide)
Typhoon Information
Dissemination
Training and Seminars
476
445
275
109
99
52
87
82
50
20
18
10
12. 43 8
*multiple responses
RECOMMENDATION
1. Allocate additional funds on flood prevention program and projects
2. Enhanced emergency warning system
3. Upgrade and add the equipment present for better flood response
4. Canal lining
5. Improve the construction quality of flood related infrastructure
6. Relocation of informal settlers who generate solid waste that causes flooding
7. Stop the strong political connections in providing assistance and relief operations.
8. Implement semiannual training and seminars for both government officials and
residents.
13. SUMMARY, CONCLUSION, AND RECOMMENDATION
SUMMARY
CONCLUSION
RECOMMENDATION
Babu, K. J., Sreekumar, S., & Aslam, A. (2014). Implication of drainage basin
parameters of a tropical river basin of South India. Appl Water Sci 6. 67 – 75.
Retrieved from https://rdcu.be/cZyJ3
