هيدروليكي

1. A Sustainable Drainage System Design in Brgy. 82 Marasbaras-
Villa Dolina Subdivision, Tacloban City
A Research Study Presented to the Civil Engineering Faculty,
Eastern Visayas State University, Tacloban City
In Partial Fulfillment of the Course Requirements for the Subject
CE 563 (Water Resource Engineering)
JEFFREY H. BELOY
ABSTRACT
Drainage plays a relevant and important consideration in planning roads and building structures to
avoid damage due to runoff, in other words, to avert the accumulation of water on the surface that can lead
to flooding. As a fundamental principle, drainage has to be designed properly to efficiently and safely
convey the runoff within its corresponding catchment area. One of the many barangays in the City of
Tacloban where the researchers have chosen to conduct the study is in Brgy.82 Marasbaras-Villa Dolina,
Tacloban City. Due to the rising development of house buildings and other structures in the area, some of
the drainage systems facilities are difficult to meet the current storm water runoff because of the land-use
change, hence leads to inundation. This prompted the researchers to embark into finding ways on how to
alleviate flood and logging of water in the area. Thus, the main objective of the study was to design a
sustainable drainage system of adequate capacity to control flood water from overflowing to the roads and
households and to evaluate the adequacy of the existing drainage systems whether it is enough to carry
rainwater or not. This in turn can greatly help the residents of the subdivision to be spared from flooding.
Moreover, Quantum Geographic Information System (QGIS), being one of the best GIS tool in the free and
open-source community was used by the researchers to delineate the catchment area and its sub-catchments,
and compute the runoff. Rational Method was used to compute for the peak discharges. The use of the
rational method in the calculation of the design peak discharges for the catchment resulted in a 10-year
return period for a maximum peak discharge was 1.604 𝑚3
/𝑠. Ultimately, manning‘s equation was used to
compute for drainage facility cross sectional dimension. Results showed that out of the twenty-six (26)
sewers, two (2) cross-sectional dimensions prevails the design of the drainage system obtained from a 10-
year return period. Thus, the existing drainage system is inadequate to convey corresponding runoff. The

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result recommends the locality of the need to widened or replaced the culverts for the existing drainage
systems and construct additional drains in order to greatly improve the water quality and to give a better
quality life to every individual.
INTRODUCTION
Water is vital for sustaining life, promoting development and maintaining environmental safety.
Without which, life could never exist. However, it can be invasive when it flows. Flood is an example of a
phenomena in which water can be of great nuisance to human life. It is basically an overflow of water which
submerges the land that is normally dry. In some residential areas, the occurrence of flooding can cause a
lot of negative effects. It brings risk and inconvenience to individuals living in that certain locality. This
type of natural disaster can cause damage to properties including vehicles, houses, and other infrastructures.
Flood is not just a disastrous calamity, but it can also be harmful to health.
Flooding of urban areas is one of the major problems that the world is facing, as cities grow and
the amount of impermeable surfaces increase generating more surface runoff. Existing storm water drains
are mostly not capable of dealing with such increases in runoff, therefore, greater volumes of water are left
on the surface. The cause of flooding in most areas can be attributed to the increased runoff emanated from
land-use change i.e. increase in impermeable surfaces. As well as, lack of any maintenance or upgrade of
the drainage system indicates that the system can no longer uphold the runoff volumes.
Tacloban, a first class highly urbanized city in the Philippines, lies along the typhoon corridor. It
has a population of approximately 250,000 making it the most populated city in Eastern Visayas. Dumping
of garbage in waterways, rapid industrialization, and poor maintenance of drainage system are amongst the
many motives of flooding which are well-evident in Tacloban. Due to urban development, green lands are
replaced by impervious roofs, roads and parking lots, which reduce the capacity of the surface to absorb
water that increases the velocity of flow and decreases the concentration time of surface runoff. In that way
has worsened flooding in every part of Tacloban.
One of the many barangays in Tacloban City facing this kind of seemingly usual issue is at
Barangay 82, formerly Marasbaras. Barangay 82 is situated at the southern portion of Tacloban, 3.6
kilometers away from the downtown area and shares a common border with the following barangays,
Barangay 80, Barangay 81, and Barangay 96. It has a population of 1,229 as determined by the 2015 census.
Thus, represented 0.51% of the total population of Tacloban City. Barangay 82 is located at roughly

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11.1913, 125.0033, in the island of Leyte. At these coordinates, the elevation is estimated 16.70 feet or 5.10
meters above mean sea level. Figure 1 shows the satellite views of Brgy. 82 Marasbaras, Tacloban City.
There is an existing drainage system in some parts of Brgy. Marasbaras specifically in Villa Dolina,
but shows gap to its functionality because during heavy rainfall, the water starts overflowing especially in
an area where the elevation is low. Instead for the water to be drained through inlets or drain holes, the
water tends to build up quickly which causes flood. This pressing event brings risk to the community upon
entering and leaving the subdivision. The proper maintenance of the drainage system is also a major factor
to its functionality but is not given that much attention and importance. Drainage structures can be less
sufficient when contained with granular materials caused by erosion and other unwanted materials like
garbages can potentially lead to clogging and among these, are more factors in question. The explicit cause
of flood is rainwater and runoff, now the situation only becomes drastic when what’s left to a drainage
structure’s capacity to work is hindered by its functionality. Hence, a study is needed in order to investigate
the hydrological factors responsible for flooding the specified area to be able to come up with recommended
improvements.
One of the solutions developed by people to limit flooding was through directing water to an outlet.
Hence, the drainage system (Carulasan et al., 2012). Drainage systems are used as prevention for the
accumulation of water that can lead to flooding. It is intended and designed to drain the observed excess
rainwater and groundwater from impermeable surfaces such as paved streets, sidewalks, parking lots,
footpaths, and roofs (Chauhan, 2013). However, as time pass, most of these systems reduce its functionality
and capacity for transferring the runoff flow, and their level of service reduces due to improper maintenance,
inappropriate design, and structural deterioration.
Figure 1. Satellite views of Brgy.82 Marasbaras-
Villa Dolina, Tacloban City
STUDY AREA

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Barangays should adopt the drainage system in order to regulate the flow of water inside or around
the property and convey water to a suitable outlet. Not considering an effective and sustainable drainage
system may cause all sorts of problems to develop. This is why it is important that every barangay pays
attention to any drainage issues.
The topographic, hydrologic and manmade conditions of an area are the primary contributors of
surface runoff. Considering the geographic placement, the land area of Barangay 82 is of low elevation
which can be a contributing factor to cause flood in the locality. Rainwater runoff from higher elevation of
various surfaces contributed all throughout the catchment area seeking the nearest outlet, plus the
hydrologic conditions of Barangay 82 being in a tropical country all add up to a greater volume of runoff
in the lower elevation. All of these factors are of high potential in generating runoff which explicitly causes
flood.
Having the study area considered, the researchers will be using the Rational Method was adopted
in the study. Moreover, an innovation was the application of GIS in the process. In determining the peak
discharge, rational method was used. JICA and DPWH asserts that the conception behind the Rational
Method is that if a rainfall of intensity (begins instantaneously and continues indefinitely, the runoff rate
will increase until the time of concentration (when all of the watershed is contributing to the flow at the
outlet point or point under consideration. Needhidasan & Nallanathel (2013) used the Rational Method on
designing a storm water drainage system in India.
With the aid of technological advancement, the use of GIS in hydrologic studies is now gaining
pace. The application of GIS in the field of hydrology was used in the computation of storm water drainage
network (Desai and Patel, 2014), demarcation of drainage network for watersheds (Pragati, D et al., 2012),
drainage patterns and systems (Guilbert and Zhang, 2013), hydrologic models (Simões, 2013), groundwater
potential (Rocha, Garcia, & Ribeiro, 2011, and water quality (Lubrica, 2013).The study aimed at evaluating
the adequacy of the existing drainage system of the area and suggest improvements in assuaging the
drainage problem. Specifically, the study revealed, area contributory to the storm run-off, corresponding
peak discharges, and the evaluation of the adequacy of existing drainage systems.
The primary goal and objective of this study are to prevent flood through improving the drainage
system and minimize the improper disposal of garbage which is the greatest factor of excessive flowing of
water. Objectively, the study aims to answer the following questions: (1) What are the physiographic
characteristics of the study area in terms of: (a) Topography-Catchment Area, (b) Rainfall Intensity
Duration Frequency: (2) What is the profile of the ground cover in terms of: (a) Land use (Runoff
Coefficients); (3) What is the total flow generated in terms of peak runoff.

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MATERIALS AND METHODS
The researchers will use the evaluation design approach. This type of method is suitable for the
study since it attempts to describe, explain and interpret the present state of the existing drainage system in
the locale. Trochim (2006) situates the evaluation research method as a research approach enclosed within
a larger planning-evaluation cycle.
The study involved contour map, and peak rainfall intensity as inputs while list of extent of
catchment area and section of the drainage conduit will be the outputs. The processes to meet the outputs
were performed through ocular inspection, GIS, maps, Rational Method and Manning‘s Equation. The
materials utilized in this study were GIS and Microsoft Excel. Quantum GIS (QGIS) version 2.18.28 was
used in plotting maps and performing computations. In plotting the Rainfall Intensity Duration Frequency
Curve, Microsoft Excel was used. Pictures were also taken to document the lack of drainage systems at the
area of study.
In achieving the objectives required for this research, the researchers will utilize Geographic
Information System, an instrument which best suits the needs in gathering relevant information. GIS is a
computer-based software that is used for capturing, storing, analyzing, managing and visualizing all kinds
of geographic or spatial data. This technology is an asset in providing a base for spatial information which
will help in advancing our understanding of hydrological processes by providing tools for spatial analysis
of the physiographic and manmade profiles which is needed for computations. Data from GIS will be
automatically and graphically presented which will provide convenience for the researchers in the analysis
of data.
The researchers gathered information through site observation and interviews. Other hydrological
data such as 30-year rainfall data in Tacloban City, which will be considered for the locale and will serve
as secondary data, was gathered from Engr. Marvin Jade Genoguin.
The analysis performed in order to evaluate and design efficiently a sustainable drainage system
was through Rational Method, which is one of the most commonly used methods for the calculation of peak
flow for small areas. Rational Method is limited to a catchment area of 200 acres (809,371.28 𝑚2
) or less
(Federal Highway Administration, 2009, and Wright, 1996, and AASHTO, 2012, and DPWH, JICA, 2003).
Based on preliminary computations, the contributory catchment area of the study is less than 200 acres
(809,371.28 𝑚2
). In order to determine the area of the catchments, the researchers used GIS to create the
land cover map and contour map of the area of study.

6. 6
Figure 2 shows the methodology utilized in the study. The outlined red text boxes are the three (3)
main parameters in calculating for the peak discharges, that is 𝑄 = 𝐶𝑖𝐴. The figure illustrates that
determining the capacity or adequacy of the existing drainage facilities utilized the combined support of
GIS and Microsoft Excel. Several online plugins such as satellite map and contour map, and measurement
tools to compute the area of the catchment can be found and used in the GIS software. The land cover map
or ground cover profile was delineated in the software to obtain the corresponding runoff coefficients
covered by every sub-catchment. To create the land cover map, the researchers digitized the catchment area
from the satellite map according to actual land use.
In determining the runoff coefficients for every sub-catchment, the criteria of Schaaka, Geyer and
Knapp runoff coefficients on the different types of development or area was used. The use of weighted
average values to simplify the determination of runoff coefficients was adapted. Furthermore, where a
GIS
EXCEL
Drainage System Design
Land Cover Contour Map
Type of Surface Catchment Area, A
Run-off Coefficient, C
Peak Discharge
Q= (Σ CA)i
Manning’s Equation
Design Dimension
Time of
Concentration, 𝑡𝑐
RIDF
Rainfall Intensity, i
Σ CA
Composite Runoff
Coefficient, CA
DEM Satellite Map
Sub-catchment Area
Adequacy
Figure 2. Research Methodology

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drainage area is composed of sub-areas with different runoff coefficients, a composite coefficient for the
total drainage area is computed by dividing the summation of the products of the sub-areas and their
coefficients by the total area: 𝐶𝑜𝑚𝑝𝑜𝑠𝑖𝑡𝑒 (𝐶) = ∑ 𝐶(𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙 𝑎𝑟𝑒𝑎𝑠)𝐴(𝑖𝑛𝑑𝑖𝑣𝑖𝑑𝑢𝑎𝑙 𝑎𝑟𝑒𝑎𝑠)/𝐴(𝑡𝑜𝑡𝑎𝑙 𝑎𝑟𝑒𝑎).
For the rainfall intensity (i), the aid of Microsoft Excel was used to plot the graph of Rainfall Intensity
Duration Frequency curve. RIDF curves show the rainfall intensity (in mm per hour) against the duration
of the rains (in minutes) for specific return periods. Return periods are storms having variations represented
by a numerical value. The smaller the value of a design storm the lesser its intensity but the higher its
probability of occurrence. It explains that a curve with a return period of one (1) year will exhibit the worst
storm that will on average occur every year, a curve with a return period of two (2) years is the worst storm
that can be expected in a 2-year period, and so on. To conceive which return period to take from the RIDF
curves, the 𝑇𝑐 or time of concentration has to be calculated. The time of concentration is the time it takes
for rainwater to reach the outlet from the most remote point of the catchment area. In this study, this time
will be considered as the duration of a rainfall or storm event. The Kerby-Kirpich approach was used to
compute for the time of concentration (𝑇𝑐). This method requires only a few input parameters, is easy to
apply, and produces readily interpretable results. After computing for 𝑇𝑐, we look for the rainfall intensity
on the chosen curve, at the duration of a storm equal to the time of concentration which we calculated. After
the intensities are obtained, the peak discharge (Q) can be computed. Using the computed peak discharge
and the other parameters available, the cross sectional dimension follows the computation. The efficient
cross-sectional dimension was determined from the computed discharge using Manning‘s Equation, 𝑣 =
(1/𝑛)(𝑅)2/3
(𝑆)1/2
. Moreover, the computed design dimension will be compared in order to find out the
adequacy of the existing drainage facilities. In order for the drainage systems to be efficient, the capacity
and the cross-sectional dimension of the existing drainage must be larger than that of the theoretical.
ANALYSIS
Physiographic Characteristics of the Study Area
The topography is defined by the downloaded Digital Elevation Model covering a large area
including the northern part of Leyte and some parts of Samar and Biliran such that to manage this data
specifically for the study area, a reduced DEM was extracted. The DEM was clipped or cut to an extent
intended just for the study area. Figure 3 shows the extent of the DEM.
Figure 4 shows the generated catchment area and contour lines. The catchment area is 24.719
hectares as calculated in QGIS which was automatically generated through running the processing tool
r.watershed or the Watershed basin analysis program on the DEM. The contour lines provide the analysis

8. 8
of the flow paths in the catchment area taking into consideration the existing structures on the possible flow
paths.
Figure 5 shows the modified catchment area and its sub-catchments. Sub-catchments are delineated
to approximate the actual contributing area for a certain drainage through analyzing the contour lines
likewise of existing structures since it affects the flow of runoff. The modified catchment area is 168897.095
m2
(16.89 ha. or 41.735 acres). A total of 26 sub-catchments are delineated and labeled from 1 to 26 as
shown in Figure 5. Their corresponding equivalent areas are shown in Table 1.
The land use of the study area is classified as a residential and commercial zone. The type of land
has different ground covers, hence will result in different runoff coefficient values (C). Figure 6 shows the
shapefile layers showing the profile of the ground cover in terms of C values.
DEM
The Study Area
Figure 3. Digital Elevation Model Figure 4. Catchment Area and Contour Lines
0.15
0.15
0.15
0.7
0.7
0.7
0.7
0.7
0.7
0.9
0.9
0.9
0.9
0.1
0.1
0.9
0.15
0.15
0.15
0.85
0.85
0.85
0.85
0.85
0.8
5
0.15
Figure 5. Modified Catchment Area and
its Sub-catchments with Labels
Figure 6. Ground Cover Profile
(Selected Runoff Coefficient)

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Figure 7 shows the layout of the existing water drainage line in Villa Dolina Subdivision. As
observed by the researchers through the conducted ocular inspection in the locale, only the major roads of
the subdivision have installed culverts with diameter of 0.500 m. While road gutters serve as the drainage
line of minor roads. The entire existing drainage network eventually discharges into the Burayan creek or
to the public storm drain outfall.
Rainfall Intensity Data
Figure 8 shows the Rainfall Intensity Duration Frequency curve obtained from PAGASA. Based
on the estimated time of concentration and the different storm events, the corresponding rainfall intensities
(i) for the whole catchment were plotted and determined. Based on the figure as shown below, it displays
that in a 100-year period, there is a probability that an intensity of 250 mm/hr. will occur.
Figure 9 shows the Rainfall Intensity Duration Frequency curve performed by the researchers using
EXCEL. Based on the estimated time of concentration and a 10-year return period were used by researchers
so as to be more sustainable and efficient. The corresponding rainfall intensities (i) for the whole catchment
were plotted and determined. The intensities obtained in every sub-catchment are shown in Table 1.
Figure 7. Existing Water Drainage Line in Villa Dolina Subdivision

10. 10
10 mins 20 mins 30 mins 1 hr 2 hrs 3 hrs 6 hrs 12 hrs 24 hrs
2 years 107 80.8 67.1 42.8 29.8 23.5 14.5 8.7 5
5 years 145.6 110.2 91.4 57.4 40.3 31.7 19.6 11.7 6.7
10 years 171.1 129.6 107.5 67.1 47.3 37.2 23 13.7 7.9
15 years 185.5 140.5 116.5 72.5 51.2 40.2 24.9 14.9 8.5
20 years 195.5 148.2 122.9 76.3 54 42.4 26.3 15.7 8.9
25 years 203.3 154.1 127.8 79.3 56.1 44 27.3 16.3 9.3
50 years 227.2 172.4 142.8 88.3 62.6 49.1 30.5 18.2 10.3
100 years 250.9 190.4 157.8 97.3 69.1 54.2 33.6 20.1 11.4
0
50
100
150
200
250
300
INTENSITY
DURATION
RIDF CURVE
2 years 5 years 10 years 15 years
20 years 25 years 50 years 100 years
Peak runoff
The maximum runoff is acting on the outlet of the catchment area as shown in Figure 10 where the
largest area contributes during the time of concentration and where excessive surface runoff occurs. The
0
50
100
150
200
0 100 200 300
RAINFALL
INTENSITY
(mm/hr)
DURATION (min.)
10-YEAR RETURN PERIOD
Figure 9. Rainfall Intensity Duration Frequency (RIDF) Curve of a 10-year Return Period
Figure 8. Rainfall Intensity Duration Frequency Curve for Tacloban City

11. 11
maximum runoff is defined by the Rational Formula Q = CiA. The ground cover profile was processed in
QGIS with the aid of digitizing tools such that values for each respective contributing drainage area was
automatically calculated in the attributes table. With its corresponding values for runoff coefficient C and
the values for rainfall intensity are given in Table 1, the peak flow of runoff based on a 10-year storm event
return period was estimated.
Using the attribute table of GIS, the peak discharges for a return period of ten (10) years for sub-
catchments 1 to 26 were obtained and are shown on Table 1. The maximum discharge attained from the
table was 1.604 𝑚3
/𝑠 of sub-catchment 20, while the minimum discharge was 0.069 from sub-catchment
1.
Table 1 shows the parameters used to compute for the peak discharge. The runoff coefficient (C)
was computed as a weighted average of the land use with respect to its area. On the other hand, the rainfall
intensity was computed as a function of the time of concentration (𝑡𝑐) for a sustainable return period of ten
(10) years.
Using the RIDF curve, the rainfall intensities for a 10-year return period were calculated based
from the computed time of concentration. Thus, resulting to varying values of the rainfall intensity as found
in Table 1. The values of the total area drained were derived through analyzing the sub-catchments’
direction of flow considering its elevation towards other sub-catchment as it contributes to the flow of that
particular sub-catchment. The composite runoff coefficient of every sub-catchments was acquired by
multiplying the area of sub-catchment and the runoff coefficient. At the same time, the summation CA was
computed by following the same analysis being done in the total area drained section, this time pertaining
to the composite runoff coefficient data values.
Figure 10. Location of Peak Flow

12. 12
Table 1. Sub-Catchment Parameters, Calculated Discharge and Cross-Sectional Dimension
The peak discharge in Table 1 was calculated by multiplying the intensity and ∑ 𝐶𝐴. Using
Manning’s equation, the theoretical drainage cross-section dimension was solved. The value of Manning’s
Roughness Coefficient considered all throughout the sewers was 0.0014. It was found out that the governed
computed maximum design dimension was 0.630-m and 0.654-m in diameter or approximately 0.700 m-
∅. Comparing the cross-sectional dimension of the existing drainage facilities which has a diameter of 0.500
m in Table 2 was discovered to be inadequate.
Sewer
Ground
Elevation
Area Length (m)
Slope
(m/m)
Runoff
Coefficient, C
Time of
Concentration
(min.)
Intensity
(i)
Total Area
Drained
Composite
Runoff
Coefficient
ΣCA
Design
Discharge, Q
Computed
Diameter,
m
1 70 8518.875 131.99 0.011 0.308 39.205 94.60 8518.87 2627.88 2627.88 0.069 0.230
2 70 7437.169 162.67 0.012 0.485 36.221 98.45 7437.17 3608.74 3608.74 0.099 0.261
3 70 19113.335 154.10 0.008 0.250 38.046 96.27 19113.33 4786.87 4786.87 0.128 0.307
4 70 24696.820 70.72 0.029 0.241 26.570 115.05 24696.82 5944.08 5944.08 0.190 0.281
5 70 9974.186 131.85 0.015 0.406 23.163 122.55 34671.01 4051.01 9995.09 0.340 0.397
6 70 858.808 59.58 0.023 0.623 14.516 152.12 54643.15 534.94 15316.90 0.647 0.464
7 70 513.681 31.18 0.013 0.763 8.171 171.10 62594.00 392.15 19317.79 0.918 0.589
8 70 764.405 22.21 0.027 0.668 1.133 171.10 71877.28 510.29 22455.96 1.067 0.543
9 70 1099.549 59.02 0.021 0.709 6.570 171.10 72976.83 779.10 23235.06 1.104 0.579
10 71 2351.020 56.16 0.015 0.421 20.224 129.05 2351.02 989.83 989.83 0.035 0.169
11 70 1911.077 59.58 0.027 0.524 19.209 132.72 4262.10 1001.52 1991.35 0.073 0.199
12 70 1214.479 57.62 0.018 0.684 7.108 171.10 74191.31 830.65 24065.70 1.144 0.601
13 69 1087.486 57.03 0.025 0.703 6.640 171.10 75278.79 764.84 24830.54 1.180 0.572
14 70 1846.007 64.33 0.027 0.560 16.137 145.20 6108.10 1034.31 3025.66 0.122 0.240
15 70 872.202 58.80 0.023 0.765 6.268 171.10 6980.31 667.17 3692.83 0.176 0.285
16 68 1190.105 61.93 0.021 0.722 6.995 171.10 76468.90 859.79 25690.33 1.221 0.596
17 70 981.692 46.87 0.022 0.713 6.448 171.10 77450.59 699.89 26390.22 1.254 0.600
18 68 1156.924 61.73 0.024 0.758 7.009 171.10 8137.23 877.15 4569.97 0.217 0.307
19 69 1305.314 57.86 0.025 0.609 1.287 171.10 77656.35 794.29 27184.51 1.292 0.593
20 68 1012.071 114.59 0.028 0.482 9.524 171.10 89823.51 487.73 33741.77 1.604 0.630
21 71 1918.303 43.82 0.032 0.782 10.208 170.28 1918.30 1499.56 1499.56 0.071 0.191
22 68 9099.415 81.93 0.014 0.554 27.804 112.20 9099.41 5042.77 5042.77 0.157 0.298
23 67 6921.384 102.45 0.032 0.866 2.742 171.10 16020.80 5993.65 11036.42 0.525 0.403
24 66 18727.070 55.73 0.024 0.319 27.353 113.20 18727.07 5966.72 5966.72 0.188 0.290
25 71 34530.287 53.08 0.014 0.441 28.769 110.25 34530.29 15226.72 15226.72 0.466 0.449
26 70 9795.433 225.11 0.020 0.639 17.025 142.33 79073.59 6261.28 38491.14 1.522 0.654
(𝒎𝟐
) (𝒎𝟑
/𝒔)
(𝒎𝒎/𝒉𝒓)

13. 13
Figure 11 shows how water will move depending on its own slope and elevation. The shaded
portion above shows the flood prone area of the locality. As seen, water remains stagnant at its lower
elevation since there is no adequacy of drainage for its outflow. For overcoming of water clogging and
flooding problems in this area, it is proposed to sustainably design a drainage system of adequate capacity;
so as to dispose of the floodwater, safely to the Burayan Creek.
RESULTS AND DISCUSSION
Flooding is a serious problem in Villa Dolina Subdivision that impacts the life of the residents.
Flood is observed on the location of peak flow during heavy rainfall which slowly subsides and will
eventually be drained. The drainage problem is caused by a decreased drainage capacity of the drainage
structures which is because of the presence of granular materials and unwanted wastages. Proper and
adequate drainage system is the key element to eliminate serious flooding in many areas.
Based on the methods used, the watershed and its characteristics were established, including its
catchment basin boundary, land cover characteristics, hydraulic parameters, and the peak discharge. The
catchment basin was delineated using the available DEM, and the catchment boundary as shown in Figure
4.
Figure 11. Drainage Water Flow (Based on the available data)

14. 14
The use of GIS technology in delineating catchment network increased the accuracy of determining
the flow paths and the catchment and sub-catchment boundaries. The output derived from this study is very
much helpful in the preparation of the hydrologic and hydraulic data to be used for the modeling and
analysis of catchment.
The catchment area is a composite watershed having different runoff coefficient values ranging
from 0.1-0.9 due to its type of ground surfaces from clayey soils to roofs and pavements. The extent of the
catchment area is 168,897.095 m2
and is divided into 26 sub-catchments. The sub-catchments’ area are
presented in Table 1. The time of concentration governing the whole watershed is 39.205 minutes while the
lowest time of concentration is 1.287 minutes. The use of average values was adopted to simplify the
determination of runoff coefficients.
The rainfall intensities were plotted from the RIDF curve of a 10-year return period. The peak
runoff obtained from a 10-year return period was tabled and has been found out that the maximum peak
discharge was 1.604 𝑚3
/𝑠 which will be considered at the outfalls. In computing for the cross-sectional
dimension of the drainage system, Mannng’s Equation was adapted. The assignment of roughness
coefficient for every sub-catchment are all equal, with an equivalent value of n = 0.0014 (for cement-
concrete pipe).
Having gathered all the necessary information, it has been found out that the actual existing 0.500-
m design diameter in the Villa Dolina subdivision is lesser than the computed theoretical design diameter
of 0.700-m. Thus, the capacity of the existing drainage is not enough to convey peak discharges or runoff
especially in the critical volume where discharge water will meet and gather. Since the computed theoretical
design diameter is greater than the existing design diameter, current culverts are necessary to be widened
or replaced. Upon recommendation, a trench or open drain is introduced to sustain the functionality of the
drainage systems in the locale to effectively convey the observed excessive runoff taking into consideration
the peak discharge of sub-catchment 20 and sub-catchment 26 from a 10 year return period. It will serve as
a substitute to the present gutter along the main roads. Through the initiative, a drainage design layout was
prompted. Figure 12 shows the recommended sustainable drainage design system in Brgy 82, Marasbaras-
Villa Dolina Subdivision. The laid out drainage system will greatly reduce flooding in the area. This will
eventually translate into improved conditions in the barangay, thus improving the social and economic
development of the people in the area.
It is likewise recommended to organize sensitization programs towards enlightening residents on
the need to keep drains located in their communities clean and not use them as refuse dump places.
Residents in the area have to be responsible and disciplined enough not to carelessly dump garbage

15. 15
anywhere or wherever it is that is appropriate. It is often essential that community members must at least
participate in maintaining drains. Providing support for clearing the drains from debris or wastes would
lessen the effect of flooding. Indeed, the best solution is for community members themselves to take
responsibility.
The key to sustainability is maintaining a balance between development and environment
conservation and drainage is one factor to help the community keep balance. Good drainage practices
optimize the development while conserving environmental quality. Implementing policy guidance,
planning techniques and management methods must be the topmost priority of every locality to eliminate
the effect of flooding. It is important to give authorities sufficient means and executive power to promote
installation of sustainable drainage systems.
Figure 12. Recommended Sustainable Drainage Design System in Brgy.82, Marasbaras-Villa
Dolina Subdivision, Tacloban City
Villa Dolina Subdivision
Brgy.82 Marasbaras, Tacloban City
Coordinates: 125.004766,11.192541
Scale: 1:6,033

16. 16
RECOMMENDED DRAINAGE DESIGN
A culvert is a structure that transport
water from one area to another or
transmit rainwater runoff underneath,
along or away, commonly from one
side of a road to the other side. It is
usually embedded in the soil. The type
of culvert to be used in the design
within the vicinity of Villa Dolina is
concrete pipe culverts while for the
national roads is a box culvert. These
two common types of culvert structures
will be used to transport water drainage
without the obstruction of debris
outside the environment.
A trench drain (also referred to as channel,
open drain, line drain, slot drain, linear drain
or strip drain) is a specific type of floor drain
containing a dominant trough- or channel-
shaped body. It is essentially a gutter that is
placed into the ground. An open drain is
used for the rapid evacuation of surface
water or for the containment of domestic and
solid wastes. Trench/Open Drain will be
designed where it has steel grating at its ends
so as to not easily cause clogging in the
drainage system. In addition, it is essentially
important that the involvement of every
household in conserving and sustaining the
cleanliness of drains so as not to cause any
water-borne diseases or threats to their
health.
TOP VIEW
SIDE VIEW
3-D VIEW
REINFORCED CONCRETE PIPE CULVERT
SIDE VIEW
3-D VIEW
VIEWS OF OPEN/TRENCH DRAIN

17. 17
The existing 0.500-m diameter culvert in Villa Dolina is
used in the design including its existing Catch basins.
However, is not adequate to convey peak discharges for a
10-year rainfall intensity. The computed theoretical
diameter dimension is 0.700-m, hence, a need to resize the
culvert is required. In addition, to primarily minimize the
problem of the sudden impacts of flooding, open drains are
introduced and replaced with the existing gutters. The
researchers think that this may seem to be one of the best
approaches to achieve a sustainable subdivision.
CROSS-SECTIONAL DIMENSION OF PIPE
CULVERT TO CATCH BASIN
DETAILED VIEW CONNECTION OF OPEN DRAIN
TO CATCH BASIN TO CONCRETE CULVERT

18. 18
REFERENCES
DIAZ-NIETO J, BLANKSBY J, LERNER
DN, SAUL AJ. 2008. A GIS approach to explore
urban flood risk management. Proceedings of the
11th International Conference on Urban
Drainage; 2008 August 31 - September 5;
Edinburgh, Scotland, UK. Retrieved from
https://web.sbe.hw.ac.uk/staffprofiles/bdgsa/11t
h_International_Conference_on_Urban_Drainag
e_CD/ ICUD08/pdfs/653.pdf
GENOGUIN, MARVIN JADE. 2020. 28-Year
Daily Rainfall Data 1990 - 2020.
FUENTES X. 2004. Land Cover 2004-07.
[PhilGIS] Philippine GIS Data Clearinghouse.
Retrieved from http://philgis.org/thematic-
maps/land-cover
ZHOU Q. 2014. A review of sustainable urban
drainage systems considering the climate change
and urbanization impacts. Licensee MDPI, Basel,
Switzerland. Retrieved from
www.mdpi.com/2073- 4441/6/4/976/pdf
Dela Rama-Liwanag et al. 2016: Catchment
Parameter Estimation and Maximum Discharge
Calculation. Philippine Journal of Science Vol.
147 No. 2, June 2018.
Ghani. A. A, Zakaria, N. A, Chang. C.K, and
Ainan. A, (2008). Sustainable Urban Drainage
System (Suds): Malaysian Experiences. In: 11th
International Conference on Urban Drainage,
Edinburgh, Scotland, UK 2008.
The Hydrometeorological Data Applications
Section (HMDAS). 2019. Rainfall Intensity-
Duration Frequency Analysis Data for Tacloban
City. Hydro-Meteorology Division, PAGASA.

19. 19
DOCUMENTATION
Flood occurrence after tremenduous
excessive rain in the main entrance of Villa-
Dolina due to low-lying elevation
Presence of debris in the drainage system
Stagnant water in the existing catch basin
along Derniere St.
Presence of sediments in the drainage
system caused by erosion

20. 20
Figure 13. FLOOD HAZARD MAP OF TACLOBAN CITY
Source: Mines and Geosciences Bureau (MGB), City Planing Development Office
The location of the project is considered to be low-moderate flood susceptibility.
Area of Study

21. 21
INDEX

22. 22
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5 10 15 20 25 30 35
Rainfall
Intensity
(mm/hr)
Return Period (yrs)
FREQUENCY ANALYSIS
24-hr Rain Intensity
Intensity Duration Frequency Analysis of the 24-hr Rain Intensity from 1990-2018 for Tacloban City
The IDF Analysis
for Tacloban City
displayed above
presents that the
highest intensity
brought by a 30-
year return period is
approximately 0.55
mm/hr.