RAINFALL RUN-OFF MODEL OF THE NASIPIT
CATHCMENT USING HEC-HMS SINGLE
BASIN MODELLING
In Fulfilment of the Requirement for the BS Civil Engineering 3
CE 3107 - Hydrology Class
by:
BENSIG, Hezron Donald M.
GOSIACO, Pierre Kendrick L.
JERUSALEM, Jel Ruben Gorios R.
A Case Study Presented to
Engr. Jonah Lee I. Bas, MSCE
DECEMBER 2020
1
TABLE
I.
CONTENTS
OF
CHAPTER I
INTRODUCTION
II.
III.
IV.
1.1
Introduction
.................
1
1.2
Background of the Study
.................
2
1.3
Research Objectives
.................
3
1.4
Scope and Delimitation
.................
3
CHAPTER II
METHODOLOGY AND MATERIALS
2.1
Research Design
.................
4
2.2
Calculation of Parameters
.................
6
CHAPTER III
PRESENTATION , DATA ANALYSIS AND INTERPRETATION
3.1
Simulation Graphs and Summary
.................
8
3.2
Description of the Hyetograph
.................
15
3.3
Discussion of the Results
.................
16
CHAPTER IV
CONCLUSION AND RECOMMENDATION
4.1
Conclusion
.................
18
4.2
Recommendation
.................
18
.................
19
REFFERENCES
2
APPENDIXES
.................
20
Appendix A: Subbasin Areas, Initial And Calculated Parameters
Appendix B: Elevation of Subbasins and Junction
Appendix C: Delineation of the Basin
Appendix D: Curve Number Grid for Nasipit Catchment
LIST OF TABLES
i.
Global Summary
.................
8
ii.
Subbasin 1 Summary
.................
9
iii.
Subbasin 2 Summary
.................
10
iv.
Subbasin 3 Summary
.................
11
v.
Junction 1 Summary
.................
12
vi.
Junction 2 Summary
.................
13
vii.
Sink 1 Summary
.................
14
LIST OF FIGURES
i.
Nasipit, Dona Rita and USC-TC Catchment . . . . . . . . . . . . . . . . .
2
ii.
Curve Number Grid for Nasipit Catchment . . . . . . . . . . . . . . . . .
7
iii.
HEC-HMS Model Basin Model
.................
7
LIST OF GRAPHS
i.
Subbasin 1 Hydrograph and Hyetograph
.................
9
ii.
Subbasin 2 Hydrograph and Hyetograph
.................
10
iii.
Subbasin 1 Hydrograph and Hyetograph
.................
11
iv.
Junction 1 Hydrograph and Hyetograph
.................
12
v.
Junction 2 Hydrograph and Hyetograph
.................
13
vi.
Sink 1 Hydrograph
.................
14
vii.
Sink 1 Hyetograph
.................
15
3
INTRODUCTION
Hydrological Models are amongst the very essential tools in water resources management
due to its capacity to facilitate the understanding of the physical process of an existing and
operating catchment. Moreover, hydrological modelling allows the monitoring of data, the
prediction of system response to changes, as well as the evaluation for possible alternative. Thus,
these tools allow the control and monitoring of the quality and quantity of water resources, through
the generated run-off hydrograph and hyetograph from a rainfall event [1],[2],[3].
Cebu City, being one of the Philippines’ highly urbanized areas, is a city with a booming
economy, thus, it was always subjected to numerous developments and projects overtime. In order
as to accommodate to the growing number of construction projects, the utilization of previously
unused land becomes vital. Most of these lands were mainly used mainly for mixed residential,
institutional and other commercial and industrial purposes. However, this process has created a
dramatic change in the natural landscape of these areas, including natural catchments and
watersheds. Unfortunately, numerous places have been developed with poor water management
and flood control systems. Additionally, these development sites are situated at the path of the
natural drainage and junctions. Over time, the effect of the lack of planning and development of
the areas have been observed and felt. Hence, during the wet season, floods often occur because
of a combination of heavy rainfall and urbanized or paved areas, thus, accumulating and producing
floods at low-lying areas [4].
1
BACKGROUND OF THE STUDY
Located at Talamban and Banilad in the Northern District of Cebu City; the Nasipit
Catchment (Fig 1), is one of the major catchments in city. This 6-hectare catchment is traversed
by Gov. M. Cuenco Avenue and intersects along the road segment [5].
Before mitigation systems have been constructed, prior to the year 2009, flood waters at
Gov. M. Cuenco could reach up to 1 meter above the road surface despite the 4000 m3 lagoon
which functions as a flood retention basin from the upstream. Hence, to lessen the flooding on the
area, the University of San Carlos - which is one of the contributors of the water runoff going to
Gov. M. Cuenco Avenue, constructed within its property a series of three small dams and 19
retention ponds for temporary storage of the surface runoff [5]. Through the construction of these
flood control system, flooding with due the university has been reduced as well as in the road
segment. However, flood water reaching up to less than a foot it still evident along the road
segment, especially during heavy rains.
2
OBJECTIVES OF THE STUDY
This study aims to create a rainfall-runoff model of the rainfall data, collected on July 22,
2019 from 2:50:30 PM until 4:12:21 PM of the same day, using HEC-HMS, to analyze and
simulate the complete hydrologic processes of the dendritic watershed system of the Nasipit
Catchment.
Specifically, this study aims to: (1) show the hydrographs of the catchment; (2) identify
the peak discharge of the said rainfall data; (3) identify the total duration of the hydrograph (in
hours), and; (4) identify the cumulative precipitation, soil infiltration, excess precipitation,
precipitation loss and direct run-off of the rainfall data.
SCOPE AND DELIMITATION
SCOPE
This study mainly deals with the analysis of the rainfall data collected on July 22, 2019 from
2:50:30 PM until 4:12:21 PM, using HEC-HMS.
DELIMITATION
The researchers, however, placed an emphasis on the Nasipit Catchment. Furthermore, the
researchers also utilized their forehand knowledge in calculating the slope, maximum potential
retention, initial abstraction and lag time. As for the basis of the estimation of other model
parameters - including the curve number and delineation, existing studies on the area conducted
by the faculty members of the Department of Civil Engineering of the University of San Carlos,
have been utilized. Lastly, routing methods and baseflow were not included in the simulation of
results for this study.
3
METHODOLOGY
AND MATERIALS
Processed data from similar studies were prepared in the assumption of parameters used in
the hydrologic modelling. The Nasipit Catchment was delineated using AutoCAD 2020 with the
study of Lalisan, C & Fornis, R. (2020) as the reference basis for delineation. The loss model used
in the study is the SCS Curve Number Loss Model since necessary data is readily available and it
is applicable for multiple sub-basins which are composed of different land uses and soil types.
Based on the study of Lalisan, C & Fornis, R. (2020), the sub-basins the Nasipit catchment which
is composed of tree-covered area, less-dense residential, and a small portion of mixed residential
and commercial is composed of curve numbers 45, 77, and 89, respectively. The average curve
number for each sub-basin was approximated using AutoCad 2020, where the weight of area
covered for each curve number is obtained. The same software is used to approximate the average
imperviousness covered by using the information given in Table 1.1 and land use description based
on the study of Lalisan, C & Fornis, R. (2020). The initial abstraction for each subbasin used is
based on the standard assumption that it is equivalent to 20% of the calculated potential maximum
retention after run-off began.
The transform model used in the study is the SCS Unit Hydrograph Model because it only
requires an accessible parameter which is lagtime and is also ideal for ungaged watersheds. The
initial parameters required which involve distance measurement (flow length and watershed
length) in order to calculate the lagtime is obtained using the software AutoCAD 2020. The
difference in elevations within the watershed is obtained by using a free topographic map in Cebu
City published online. The lagtime is then calculated using the formula from the SCS Method
developed by Mockus in 1961.
4
In regards to the baseflow of the study, according to a paper published by the Japan
International Cooperation Agency, the general area of the watershed is characterized by a regime
with no sustained or stable base flow, thus there is a need of the utilization of hydrological
equipment or apparatus in order to determine the stream’s baseflow parameters in order to further
be able to further develop a generalized baseflow for them.
[6]
However, since several of the
baseflow parameters are not readily available and due to the incapability of the usage of
hydrological measurement devices especially in this pandemic scenario, the data of other related
studies are to be used for the analysis of the study. According to one study entitled: “Estimation
of the Reduction in Flood Peak and Flood Volume Due to Rooftop Rainwater Harvesting for NonPotable Use” (Borgonia, K., and Fornis, R., 2020), with the same catchment area of this study,
due to the urban nature of the watershed and the dry weather climate, the baseflow level of the
stream can be considered as very insignificant. Though in reality, there will always be very
minimal baseflows, however, in regards to the baseflow parameter of the study, the baseflow
volume discharge is to be neglected. [7]
The average slope was determined based on the average watershed definition by the
“Vicaire” website. The source defines the slope as the product of the equidistance between two
consecutive contour lines and the total length of the contour lines, divided by the area of the
watershed.[8] However, the experimenters utilized a different approach in which instead of
obtaining the distance between the contour lines, they obtained the exact elevations of two different
points from “topographic-map.com”, then obtained their difference and divided the difference with
the horizontal length in between them. [9] This method was conducted as it provides a more nearly
accurate slope compared to the prior one.
5
Calculation of Parameters:
a. Subbasin 1
•
Ave. Curve No. (CN) = (0.8473)(77) + (0.1527)(45) = 72.11
•
Maximum Potential Retension (S) =
•
Initial Absttraction (Ia) = 0.2𝑆 = 0.2(3.87)(25.4) = 19.65 mm
•
Imperviousness = (0.8473)(65) = 55.07 %
•
Lag Time =
1000
𝐶𝑁
−10=
1000
72.11
−10 = 3.87 in
𝐿0.8(𝑆+1)0.7 (5024.93)0.8(3.87+1)0.7(60)
= 40.32 mins
1900√𝑦
1900√4.7
b. Subbasin 2
•
Ave. Curve No. (CN) = (0.2436)(77) + (0.7564)(45) = 52.80
•
Maximum Potential Retension (S) =
•
Initial Absttraction (Ia) = 0.2𝑆 = 0.2(8.94)(25.4) = 45.41 mm
•
Imperviousness = (0.2436)(65) = 15.83 %
•
Lag Time =
1000
1000
−10=
−10 = 8.94 in
𝐶𝑁
52.80
𝐿0.8(𝑆+1)0.7 (1969.07)0.8 (8.94+1)0.7(60)
1900√𝑦
1900√9.04
= 22.64 mins
c. Subbasin 3
•
Ave. Curve No. (CN) = (0.1151)(89) + (0.8849)(45) = 50.06
•
Maximum Potential Retension (S) =
•
Initial Absttraction (Ia) = 0.2𝑆 = 0.2(9.98)(25.4) = 50.68 mm
•
Imperviousness = (0.1151)(85) = 15.83 %
•
Lag Time =
1000
𝐶𝑁
−10=
1000
50.06
−10 = 9.98 in
𝐿0.8(𝑆+1)0.7 (2923.79)0.8 (9.98+1)0.7 (60)
1900√𝑦
1900√9.90
6
= 31.82 mins
Figure 2. Curve Number Grid for Nasipit Catchment
Figure 3. HEC-HMS Basin Model
7
PRESENTATION, DATA ANALYSIS
AND DATA INTERPRETATION
In this chapter, presented are the results of the hydrologic simulation of the basin model
representing the Nasipit Catchment using HEC-HMS software. Included in the results are the
following: (1) global summary for each hydrologic element; (2) hydrographs and hyetographs; (3)
summary of results for each subbasin model element. Detailed analysis for the resulting
simulations are further discussed after the presented graphs and tables. The following are as
follows:
Table No. 1
Global Summary
Table No. 1 shows the peak discharge in m3/s for the different hydrologic elements as well
as their time of occurrence. Further, it also shows us the total amount of volume collected of each
element during the time of occurrence of the peak discharge. As shown in the results, Subbasin 1
having the largest area is also the greatest contributor of the discharge in the sink.
8
Graph No. 1
Hydrograph and Hyetograph of Subbasin 1
Summary of Results for Subbasin 1
9
Graph No. 2
Hydrograph and Hyetograph of Subbasin 2
Summary of Results for Subbasin 2
10
Graph No. 3
Hydrograph and Hyetograph of Subbasin 3
Summary of Results for Subbasin 3
11
Graph No. 4
Hydrograph at Junction 1
Summary of Results for Junction 1
12
Graph No. 5
Hydrograph at Junction 2
Summary of Results for Junction 1
13
Graph No. 6
Hydrograph at Sink 1
Summary of Results for Sink 1
14
Graph No. 7
Hyetograph of Sink 1
Description of the Hyetograph
Graphs No 1-3 shows us the hydrographs and hyetograph at the different subbasins of the rainfall
data of the Nasipit Catchment last July 22, 2019. Since there is only one precipitation gage in the
meteorological model, the three hyetographs have the same precipitation volume in terms of depth
(mm). However, since the three subbasins have varying areas, the precipitation volume in terms
of 1000 m3 will vary with respect to the area of the subbasin. The precipitation losses for each
subbasin also vary due to the different infiltration capacity based on the calculated parameters
applied in the loss model. Among the three hyetographs, the hyetograph for Subbasin 1 has the
least precipitation loss, followed by Subbasin2, and lastly Subbasin 3.
15
Discussion on the Resulting Values
Table No. 1 shows the summary of the peak discharge for each hydrologic element, the
time of peak discharge as well as the volume of the discharge of the rainfall data.
Originally, the peak discharge and volume at different subbasin vary at different time.
However, sink 1 as the last point of intersection of these three subbasins should also experience a
peak rainfall close to the time of occurrence of the three subbasins’ peak rainfalls.
The results showed that the peak discharge of the rainfall was 13.4 m 3/s at 15:58. Moreover,
the entire rainfall lasted for 1.283 hours (approximately 1 hour and 16 mins), which started from
02:55:30 PM of July 22, 2019 until 04:12:41 PM of the same day.
Due to the difference in area of each subbasin, type of soil as well as the slopes, difference
in the cumulative precipitation, soil infiltration, excess precipitation, precipitation loss and direct
run-off is expected. As shown in the summary of the different subbasins, the cumulative
precipitation or the precipitation volume of subbasins 1 to 3 are 73.7 m 3/s, 19.3 m3/s and 24.8 m3/s,
respectively. These results tell us that subbasin 1 having the largest area among the three is also
expected to receive the highest volume of rainfall. It has to be noted that the volume in this unit
varies due to the difference in areas of each subbasin. However, if we base the volume in terms of
depth (mm) , all three subbasin produces a depth of the rainfall of 60.40 mm.
However, due to soil infiltration, precipitation loss and direct run-off, losses of the volume
of the precipitation were expected. From the three subbasin, subbasin 2 has the least loss of 13.7
m3/s, followed by subbasin 3 of 22.2m3/s, and lastly with subbasin 1 of 26.6 m3/s.
16
Graph No. 7
Precipitation Volume vs Loss Volume and Excess Volume
50
y = 0.8209x - 13.801
R² = 0.977
45
VOLUME (M3/S)
40
35
30
25
y = 0.1791x + 13.801
R² = 0.6689
20
15
10
5
0
0
10
20
30
40
50
60
70
80
PRECIPITATION VOLUME (M3/S)
Loss Volume
Excess Volume
Linear (Loss Volume)
Linear (Excess Volume)
Graph No. 7 above shows us the relationship of the precipitation volume or the Loss
Volume (which includes soil infiltration, precipitation loss and direct-runoff) and the Excess
Volume (or the precipitation volume) against the Cumulative Volume or the Precipitation Volume.
As shown in the graph, as the precipitation volume increases, both the loss volume and the
excess volume also increases for all the three subbasins. These results tell us that both the loss and
excess volume varies directly with the precipitation volume.
17
CONCLUSION AND RECCOMENDATIONS
Indeed, Hydrological Models allows us to visualize the operation of catchments such as
the Nasipit Catchment. This research was conducted to create a rainfall-runoff model of the rainfall
data, collected on July 22, 2019 from 2:50:30 PM until 4:12:21 PM of the same day, using HECHMS, to analyze and simulate the complete hydrologic processes of the dendritic watershed
system of the said catchment.
Generally, precipitation volume, discharge and losses vary per subbasin, due to the
difference in the infiltration capacities. However, these amount of water flows through one exit
point where it accumulates. From the results, the peak discharge of the rainfall data is 13.4 m3/s
which occurred at around 15:58 which produced a volume of 55.3 m3/s. Further, the rainfall lasted
for about 1. 238 hours, which started from 02:55:30 PM of July 22, 2019 until 04:12:41 PM of the
same day. Moreover, the cumulative precipitation or the precipitation volume of subbasins 1 to 3
are 73.7 m3/s, 19.3 m3/s and 24.8 m3/s, respectively or 60.40 mm for all the three subbasins.
However, due to several factors, losses of the volume of the precipitation were expected, thus
subbasins 1 to 3 experienced a loss of 26.6 m3/s, 13.7 m3/s and 22.2 m3/s, respectively.
Nonetheless, this rainfall data is just a representation of among the many other rainfall that
occurs in Nasipit. As mentioned, often times when heavy rainfall hits this area, several factors such
as pavements limit the infiltration of the rain water into the soil. As a result, lower areas experience
flooding which could reach up to 1 foot. Hence, to resolve this issue, it is recommended to
construct flood control systems such as minidams which have been constructed by USC-TC within
its perimeter. Specifically, it is recommended to construct more of these flood control system in
other area of the Gov. Cuenco Avenue where mostly these rain water meet.
18
REFERENCES
[1]
Cirilo, J. (2020, April 27). Development and application of a rainfall-runoff model for
semi-arid regions. Retrieved December 10, 2020, from
https://www.scielo.br/scielo.php?script=sci_arttext&pid=S2318-03312020000100219
[2]
Birkel, C., & Barahona, A. (2019). Rainfall-Runoff Modeling: A Brief Overview.
Retrieved December 10, 2020, from https://www.sciencedirect.com/topics/earth-andplanetary-sciences/rainfall-runoff modelling
[3]
Zeeuw, J.W. de (1973). Hydrograph analysis for areas with mainly groundwater runoff.
In: Drainage Principle and Applications, Vol. II, Chapter 16, Theories of field drainage
and watershed runoff. p 321-358. Publication 16, International Institute for Land
Reclamation and Improvement (ILRI), Wageningen, The Netherlands.
[4]
Rainwater catchment urban agriculture in Cebu (PH). (2018, November 22). Retrieved
December 10, 2020, from https://www.hogeschoolrotterdam.nl/samenwerking/samenw
erkingsportfolio/rainwater-catchment-urban-agriculture-in-cebu-ph/
[5]
Lalisan, C. L. L., & Fornis, R. L. (2020). Attenuation performance of runoff storage
basins within a moderate to steep slope urban catchments in cebu, philippines. HIGHENERGY PROCESSES IN CONDENSED MATTER (HEPCM 2020): Proceedings of
the XXVII Conference on High-Energy Processes in Condensed Matter, Dedicated to
the 90th Anniversary of the Birth of RI Soloukhin. https://doi.org/10.1063/5.0014958
[6]
Japan International Cooperation Agency. Supporting Report on Hydrology(2020).
Retrieved 22 December 2020, from
https://openjicareport.jica.go.jp/pdf/11210879_02.pdf
[7]
Borgonia, K. M. M., & Fornis, R. L. (2020). Estimation of the reduction in flood peak
and flood volume due to rooftop rainwater harvesting for nonpotable use. HIGHENERGY PROCESSES IN CONDENSED MATTER (HEPCM 2020): Proceedings of
the XXVII Conference on High-Energy Processes in Condensed Matter, Dedicated to
the 90th Anniversary of the Birth of RI Soloukhin. https://doi.org/10.1063/5.0014516
[8]
VICAIRE - Module 1A - Chapter 2. (2020). Epfl.Ch. https://echo2.epfl.ch/VICARE
/mod_lachapt2/text/htm?fbclid=IwARS30aXAqUczelQL 3e1t6oR_XL29vbik87c1AOm3FoAXGVNOd56d-_dos
[9]
Cebu City topographic map, elevation, relief. (2020). Retrieved December 10, 2020,
from https://en-gb.topographic-map.com/maps/lpd7/Cebu-City
19
APPENDIX
20
APPENDIX A : Subbasin Areas, Initial And Calculated Parameters
Table No. A1
Summary of the Initial Parameters per Subbasin
2
Area (km ):
Flow Length (ft):
Slope (%):
Subbasin 1
1.22
5024.93
4.70%
Subbasin 2
0.32
1969.07
9.04%
Subbasin 3
0.41
2923.79
9.90%
Table No. A2
Percent Area per Subbasin CN
Percent Area (%):
CN 45
CN 77
CN 89
Subbasin 1
15.27
84.73
0.0
Subbasin 2
75.64
24.36
0.0
Subbasin 3
88.49
0.0
11.51
Table No. A3
Calculated Parameters per Subbasin
Parameter
Ave. Curve No. (CN)
Maximum Potential
Retension (S)
Initial Absttraction (Ia)
Imperviousness
Lag Time
Subbasin 1
72.11
Subbasin 2
52.80
Subbasin 3
50.06
3.87 in
8.94 in
9.98 in
19.65 mm
55.07 %
40.32 mins
45.41 mm
15.83 %
22.64 mins
50.68 mm
15.83 %
31.82 mins
21
APPENDIX B : Elevation of Subbasins and Junctions
Image No.1
Elevation of Point SB 1 of the Catchment Area
Image No.2
Elevation of Point SB 2 of the Catchment Area
22
Image No.3
Elevation of Point J1 of the Catchment Area
23
APPENDIX C : Delineation of the Basin
APPENDIX D : Curve Number Grid for Nasipit Catchment
24