Hydrological and Drainage Investigation Report
Short Description
Hydrological and Drainage Investigation Report...
Description
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
TABLE OF CONTENTS Page No.
Chapter 1 1.1 1.2 1.3 1.4 1.5
1.6
General ...........................................................................................................................1 Project Background ........................................................................................................1 Project Rationale .............................................................................................................1 Scope of Work .................................................................................................................2 Design Approach .............................................................................................................2 1.5.1 Agency Coordination .........................................................................................2 1.5.2 Field Reconnaissance Survey ..........................................................................2 1.5.3 Data Collection .................................................................................................3 1.5.4 Hydrologic Analysis ...........................................................................................3 1.5.5 Hydraulic Design ..............................................................................................3 1.5.6 Design Documentation ......................................................................................4 Contents of the Report ....................................................................................................4
Chapter 2 2.1 2.2 2.3 2.4
2.5
3.3
Available Information ...........................................................................................5
General ...........................................................................................................................5 Previous Study ................................................................................................................5 Topographic Map ............................................................................................................5 Field Reconnaissance Survey .........................................................................................5 2.4.1 General .............................................................................................................5 2.4.2 Existing Cross - Drainage Structure ..................................................................5 2.4.3 Field Observations ............................................................................................5 Basic Data Acquisition .....................................................................................................5 2.5.1 Rainfall Data .....................................................................................................6 2.5.2 Climatological Data ...........................................................................................6
Chapter 3 3.1 3.2
Introduction ..........................................................................................................1
Project Area Features ..........................................................................................7
The Project Route ...........................................................................................................7 Creeks Along the Project Road .......................................................................................7 3.2.1 Balante Creek ...................................................................................................7 3.2.2 Halang Creek ....................................................................................................7 Meteorological Characteristics .........................................................................................8 3.3.1 Air Stream .........................................................................................................8 3.3.2 Tropical Cyclones .............................................................................................8 3.3.3 Cyclone Tracks .................................................................................................8 3.3.4 Climate..............................................................................................................9 3.3.5 Rainfall ............................................................................................................10 3.3.6 Temperature ...................................................................................................10 3.3.7 Relative Humidity ............................................................................................11 3.3.8 Winds ..............................................................................................................11
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page i
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
Page No. Chapter 4 4.1 4.2 4.3 4.4 4.5
4.6 4.7
General .........................................................................................................................12 Catchment Parameters..................................................................................................12 Time Parameter.............................................................................................................13 Frequency Analysis .......................................................................................................14 4.4.1 Rainfall Analysis ..............................................................................................14 Runoff Analysis .............................................................................................................22 4.5.1 Basin Characteristics ......................................................................................22 4.5.2 Storm Rainfall .................................................................................................23 4.5.3 Design Storm Frequency ................................................................................24 4.5.4 Delineation of Catchment Areas ......................................................................27 Runoff Calculation .........................................................................................................27 Selecting Run Off to be Consider in this Project ............................................................29
Chapter 5 5.1 5.2 5.3 5.4 5.5
5.6 5.7 5.8
5.9 5.10
Hydrology Study and Analysis............................................................................12
Hydraulics ..........................................................................................................30
General .........................................................................................................................30 Design Standards ..........................................................................................................30 Design Criteria...............................................................................................................30 5.3.1 Design Flood Frequencies ..............................................................................30 Highway Hydraulics Structure........................................................................................30 Culvert Design Analysis .................................................................................................31 5.5.1 Inlet Control ....................................................................................................31 5.5.2 Outlet Control ..................................................................................................31 Manning’s Roughness ‘n’ For Culvert ............................................................................31 Sizing of Culvert (Closed Conduit) .................................................................................32 Open Channel ...............................................................................................................33 5.8.1 Hydraulic Considerations ................................................................................33 5.8.2 Hydraulic Design of Channels .........................................................................33 5.8.3 Open Channel Flow Equations ........................................................................33 5.8.4 Manning’s Roughness ‘n’ For Open Channel ..................................................34 5.8.5 Permissible Velocities for Unlined Channel .....................................................34 Open Channel Hydraulics ..............................................................................................35 Box Culvert ....................................................................................................................36 5.10.1 Existing Box Culvert ........................................................................................36
Chapter 6
Summary of Results...........................................................................................37
6.1 6.2
Flood Level and Depth ....................................................................................37 Drainage Along Viaduct and at Grade Surface ................................................ 41
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page ii
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
Page No.
List of Tables Table2.5.1a Table 2.5.1b Table 4.4.1.3.3a Table 4.4.1.3.3b Table 4.5.1.1 Table 5.6.1 Table 5.8.4.1 Table 5.8.5.1 Table 6.1.1
Computed Extreme Values of Precipitation (mm) ...........................................6 Intensity of Computed Extreme Values (mm/hr) .............................................6 Computed Extreme Values of Precipitation (mm) ......................................... 21 Intensity of Computed Extreme Values (mm/hr) ........................................... 21 Values of “C” For Use in Rational Formula ...................................................23 Manning’s “n” Values for Culvert ..................................................................31 Average Values of “n” for Manning’s Roughness.......................................... 34 Recommended Permissible Velocities for Unlined Channel ......................... 34 Flood Level and Depth .................................................................................37
List of Figures Figure 3.1.1 Figure 3.3.1 Figure 4.2.1. Figure 4.4.1.3.2a Figure 4.4.1.3.2b Figure 4.4.1.3.3a Figure 4.4.1.3.3a
Project Location .............................................................................................7 Climate Map of the Philippines and Frequency of Typhoons ..........................9 Catchment Area ...........................................................................................13 Rainfall Depth Duration Curve (27 years record) .......................................... 18 Rainfall Intensity Duration Frequency (27 years record) ............................... 19 Rainfall Depth Duration Curve (21 years record) .......................................... 21 Rainfall Intensity Duration Frequency (21 yrs record) ................................... 22
List of Annexes Annex A Annex B Annex C Annex D Annex E Annex F Annex G Annex H
Inventory of Existing Drainage Structures Rainfall Data from 1993 - 2013 Regression Analysis for Rainfall Intensity versus Rainfall Duration Equation of Data from PAGASA Regression Analysis for Rainfall Intensity versus Rainfall Duration Equation of Raw Rainfall Data from PAGASA Log Pearson Type III Distribution Calculation Hydraulic Analysis for Halang and Balante Creek Flood Depth Map Drainage Schedule
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page iii
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 1. INTRODUCTION 1.1
General
This report presents the updated technical information on the drainage, hydrological and hydraulic aspects of the Detailed Engineering Design and Construction Supervision of LRT Line 2 East (Masinag) Extension Project located along Marcos Highway. The report is one of a series of documents produced during the conduct of study and the detailed design of the LRT Line 2 East (Masinag) Extension Project. The required services are provided by the joint venture firms of Foresight Development and Surveying Co. in Joint Venture with Soosung Engineering Co. Ltd and Korea Rail Network Authority. This is prepared based on and in accordance with the scope of services stipulated in the Terms of Reference (TOR) and the Consultant’s appreciation of the project requirements. The findings and results of the field investigation and study will provide the necessary inputs to support the detailed design and construction supervision of the LRT Line 2 project and appurtenant drainage structures and its eventual construction. 1.2
Project Background
The Government of the Philippines plans to expand the mass transit system in the Manila Metropolitan area to solve the increasingly serious transportation problem. The LRT Line 2 Extension Project ("the Project") is a top priority project under DOTC's Manila Metropolitan Area Transportation Master Plan and cited in the Comprehensive Integrated Infrastructure Program (CIIP) of the National Economic Development Authority} (NEDA). Based on these plans, the Philippine Government in 2011 sought the assistance of the Japanese Government by requesting through Japan's Individual National Assistance for a complete preparatory study for LRT Line 2 East Extension to Masinag. The study will focus on the serious traffic congestion issue, air pollution and greenhouse gas reduction and climate change mitigation that will address the aims LRT Line 2 by the extension of LRT Line 2 to the east and to the west. After more than five years in operation, it has been observed that the LRT Line 2 system greatly contributed to the decongestion of the Recto Avenue-Legarda-Magsaysay-Aurora-Marcos Highway corridor. However, it has also been noted that passengers boarding/alighting at the existing Santolan Station are mostly from the eastern parts of Rizal (e.g. Antipolo, Cainta, Taytay, and other towns). Thus, the implementation of this project is being pursued to maximize the potential of the existing Line 2 alignment from Recto to Santolan. It is envisioned that the extension will attract 117,000 additional daily passengers in 2015. The LRT 2 East Extension Project is one of the identified priority projects included in the NEDA Comprehensive Integrated Infrastructure Program (CIIP) 2009-2013. This project involves the construction of a 4.2-km elevated rail extension from Santolan Station to Masinag in Antipolo City along Marcos Highway. Two (2) additional passenger stations to be located at Emerald near Sta. Lucia Mall and Masinag near SM Antipolo are to be constructed. 1.3
Project Rationale
To maximize the operations and capability of the existing LRT Line 2.To enable the commuters coming from the eastern side of Rizal to have easier access to faster mode of transportation. To enable more commuters to use public transport system to ease the road traffic and save on cost Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 1
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT of transport. To serve as vehicle in further economic development of the impacted area. To improve the operation aspects of the LRT operations with the use of automated system. To improve the facilities available to commuters and LRT employees. To have aesthetically and environmentally friendly facilities, structurally sound and cost efficient. 1.4
Scope of Work
The detailed design will basically consider the following objectives. • •
To undertake hydrology and drainage studies along the project alignment. To provide appropriate recommendations and design results such as sizes, length, elevations, alignments and locations of appropriate drainage structure such as culverts and bridge.
The following hydrologic and drainage undertaking is deemed necessary to carry out the required above scope of work. • • • • 1.5
To assess/evaluate the existing drainage structures along the project in terms of its workability and hydraulic adequacy. To delineate physical characteristics of watershed areas and carry out flood flow estimation of peak flow of major and minor waterways. To establish flood level for Railway vertical geometric design purposes; To undertake hydraulic analysis to determine the required waterway conveyance structures such as side ditches, sizes of pipes and box culverts cross-drainage. Design Approach
Railway drainage design is an integral component in the design of railway network. Drainage design for the project facilities must strive to maintain compatibility and minimize interference with existing drainage patterns, control flooding of the project surface for design flood events. The design of the project drainage facilities is a process which evolves as an overall railway design develops. The primary elements of the process include agency coordination, data collection and field investigation, hydrologic analysis, hydraulic design and final design documentation. Each of these elements is briefly described in the following: 1.5.1
Agency Coordination
Prior to the detailed design of railway drainage facilities, it is essential to coordinate with concerned line agencies and other local entities that have interests in project and drainage matters. The concerns of these agencies are generally related to potential impacts resulting from the project drainage. Other entities with interests in project drainage as well as storm drainage systems include local municipalities and developers. The local municipalities are generally aware of proposed development in the vicinity of the project which may impact drainage design. 1.5.2
Field Reconnaissance Survey
Field reconnaissance involved field review of information from maps and plans, ocular inspection and investigation of existing drainage structures, channels/structures condition and flood flow characteristics, type and extent of vegetation, the limit and extent of flooding condition and topographic features.
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 2
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT Inventory of existing drainage structures must be taken to include bridges spanning the roadway, cross drainage such as box and pipe culverts, roadside ditches, storm drainage systems and its appurtenant structures, etc. Whenever possible, interviews of residents along the stretch of the project alignment should be conducted especially for alignment situated along the floodplain areas. Information obtained such as the extent of depth of flooding, duration and direction of flood flow, available high water mark elevations and flooding history will have a considerable effect on the project vertical and geometric design. 1.5.3
Data Collection
The analysis and design of the hydrological and drainage aspects of the project cannot be successfully conducted without the availability of a wide range of secondary base data. This process involves assembling and reviewing technical data, background information, previous studies and relevant documents including the following information: • • • • • •
Watershed mapping identifying topographic features, watershed boundaries, existing drainage patterns and ground cover. Land use mapping identifying existing and expected future land uses. Soils maps identifying soil types and hydrologic soil groups. Flood histories and the extent of flooding including high water mark elevations. Descriptions of existing drainage facilities including sizes, shapes, materials, invert elevations information, age, condition, etc. Climatological and rainfall data.
The abovementioned data are further supplemented by primary data at the project site by means of actual site inspection/investigation of existing structures. 1.5.4
Hydrologic Analysis
The establishment of elevation along floodplains and the design of drainage structures are based on hydrological criteria which are predominantly estimates of flow and flood levels. The method of frequency analysis is undertaken to quantify the uncertainty inherent in hydrologic data. The objective of frequency analysis of hydrologic data is to relate the magnitude of extreme events to their frequency of occurrence or recurrence interval. The recurrence interval, which is also called return period, is defined as the average interval of time within which a hydrologic event of given magnitude is expected to be equaled or exceeded exactly once. The hydrologic data subject to frequency analysis are assumed to be independent and are gathered to provide inputs for the design of drainage and flood mitigating structures in the project area. The data are processed statistically and are analyzed and evaluated accordingly to come up with a design flow parameters based on designated return periods. These shall serve as inputs for the determination of flood level as well as the design of structures capable of withstanding the flow which passes through a specific point or reach of the river that could be expected near the proposed project’s site. 1.5.5
Hydraulic Design
The design of drainage structures consisting of bridges, pipes and box culverts and drainage canals/ditches on identified waterways is based on hydraulic principles used to economically carry out the selected design discharge. The hydraulic design opening to determine the span and elevation of major structures such as bridges will be designed using the HEC-RAS computer program. The sizes of drainage structures will be designed using Manning’s equation for open channel flow and further facilitated using nomographs.
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 3
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 1.5.6
Design Documentation
This process includes the preparation of documentation for the preliminary design plans related to the hydrology and drainage aspects of the project. Design documentation includes here to design report and its supporting hydrology and hydraulics analysis. 1.6
Contents of the Report
The report contains the following sections with a brief description of each chapter’s contents. •
Chapter 1: Introduction - Provides background information for the report and presents the scope of work performed including contents of the report.
•
Chapter 2: Available Information - Provides a description of data collected and field works performed during the course of study.
•
Chapter 3: Project Area Features - Provides general description of the project area’s physical and natural environment.
•
Chapter 4: Hydrology - Provides analysis of rainfall data and determination of design storm rainfall depths over the project area for a range of storm duration and conversion of the rainfall hyetographs to discharge at the proposed bridge crossing.
•
Chapter 5: Hydraulics - Discusses the relevant hydraulics design parameters and related calculations of the design floods using Manning’s equation for the proposed cross drainages.
•
Chapter 6: Summary of Results - Summarizes the flood study investigations and results of the hydrologic and hydraulic analyses conducted on the waterways.
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 4
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 2. AVAILABLE INFORMATION 2.1
General
This section outlines the different types of information utilized in the detailed design of road drainage including reference reports and documents as well as data, both previously available and collected specifically for this road project. 2.2
Previous Study
A previous study was conducted by Parsons Brinkerhoff and TCGI Engineers. The Detailed Engineering Design, Package 4, Marcos Highway (Evangelista to Masinag). The Drainage Structure Designed by Parsons Brinkerhoff and TCGI Engineers was considered in this project. 2.3
Topographic Map
Topographic maps of the project road were secured from National Mapping & Resource Information Authority (NAMRIA)in the scale of 1:50,000. 2.4
Field Reconnaissance Survey
2.4.1
General
The purpose of field inspection/investigation and inventory survey is to gain an understanding of site characteristics, identify exact locations and sizes of existing cross drains, present physical condition of existing drainage structures and its appurtenances, location and extent of flooding and other potential relevant data useful as inputs to the detailed design of the drainage structures. The site investigation provides an opportunity to obtain an appreciation of site topography, stream flow regime, flooding and channel condition, geology, road alignment and other equally important and necessary items of information which could not be obtained from other sources. From these on-site observations it is often possible to identify practical locations for improvements of the road alignment, condition and its appurtenant drainage structures. 2.4.2
Existing Cross - Drainage Structure
The inventory of existing drainage structures (box culverts, and pipe culverts) were obtained from actual site investigation, as shown in Annex A. 2.4.3
Field Observations
In order to identify actual flood and inundation conditions in the project road, interviews of residents along the whole stretch of the road were also undertaken to determine the extent or depth of flooding, duration and direction for the yearly as well as the largest flood experienced in the area. 2.5
Basic Data Acquisition
The update, analysis and design of the hydrological and drainage aspects of the project cannot be successfully conducted without the availability of a wide range of secondary base data. The data collected include climatological and rainfall data, climatological data and topographic maps.
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 5
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 2.5.1
Rainfall Data
The nearest rainfall station reckoned from the project site record is situated in Science Garden. Daily Rainfall From 1993 to 2013 is considered in this project. The RainfallIntensity-Duration-Frequency Data (27 years of record) was also obtained from PAGASA. Raw Rainfall Data from 1993 to 2013 is shown in Annex B and Tables 2.5.1a and 2.5.1b shows the Computed Extreme Values of Precipitation and Intensity of Computed Extreme Values respectively (based on 27 years of records). Table2.5.1a Computed Extreme Values of Precipitation (mm) (Based on 27 years of records) T
10
20
30
1
2
3
6
12
24
(yrs)
mins
mins
mins
hr
hrs
hrs
hrs
hrs
hrs
2
20.3
31.1
38.7
53
77.1
93.3
120.1
143.9
164.1
5
29.4
46.2
58.5
81.4
113.8
136.7
175.3
210.5
240.9
10
35.5
56.2
71.6
100
138.1
165.4
211.9
254.5
291.8
15
38.9
61.8
79
110.7
151.9
181.6
232.5
279.4
320.5
20
41.2
65.7
84.1
118.1
161.5
193
246.9
296.8
340.6
25
43.1
68.8
88.1
123.8
168.9
201.7
258
310.3
356
50
48.7
78.1
100.4
141.3
191.6
228.6
292.3
351.6
403.7
100
54.3
87.4
112.6
158.8
214.3
255.4
326.2
392.6
451
Table 2.5.1b Intensity of Computed Extreme Values (mm/hr) (Based on 27 years of records) T
10
20
30
1
2
3
6
12
24
(yrs)
mins
mins
mins
hr
hrs
hrs
hrs
hrs
hrs
2
121.8
93.3
77.4
53
38.5
31.1
20
12.0
6.8
176.4
138.6
117
81.4
56.9
45.6
29.2
17.5
10.0
10
213
168.6
143.2
100.1
69.1
55.1
35.3
21.2
12.2
15
233.4
185.4
158
110.7
76.0
60.5
38.8
23.3
13.4
20
247.2
197.1
168.2
118.1
80.8
64.3
41.2
24.7
14.2
25
258.6
206.4
176.2
123.8
84.5
67.2
43
25.9
14.8
50
292.2
234.3
200.8
141.3
95.8
76.2
48.7
29.3
16.8
100
325.8
262.2
225.2
158.8
107.2
85.1
54.4
32.7
18.8
2.5.2
Climatological Data
The nearest synoptic station for the project road is Science Garden. Climatological data were obtained such as daily rain fall, temperature, relative humidity and wind data.
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 6
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 3. PROJECT AREA FEATURES 3.1
The Project Route
The LRT Line 2 Extension Project is situated along Marcos highway from Santolan Station to Sumulong highway (Masinag) junction. The Project intercepts two (2) Creek namely Balante and Halang Creek. The two (2) creeks are the most important drainage system that crosses the project alignment. The project starts at K023+000 (Santolan Station) and ends at K027+200 (Sumulong Highway (Masinag) junction. The LRT Line 2 project location is shown in the Figure 3.1.1.
Figure 3.1.1 Project Location 3.2
Creeks Along the Project Road
3.2.1
Balante Creek
The Balante Creek has significant large watershed draining the area of Marikina city including Marikina Heights in the North. Balante Creek has a catchment area of 11.88 sq. km. (11880.00 hectares). 3.2.2
Halang Creek
Halang Creek drains the immediate area north of Marcos Highway as well as the southeastern area after Masinag Junction. Halang Creek has a catchment area of 4.55 sq. km. (455.00 hectares)
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 7
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 3.3
Meteorological Characteristics
3.3.1
Air Stream
The principal air streams, which significantly affect the area, are the southwest monsoon, northeast monsoon, and Pacific trade winds. The southwest monsoon originating from the north side of the Indian Ocean affects the area during the months of May to October. During this period the distribution of rainfall is influenced by the vertical situation of shear line between the South Pacific trade and southeast monsoon. The air mass is classified as equatorial maritime and is warm and very humid. The northeast monsoon, which affects the area from October to March, is most dominant during January and February. The North Pacific trade winds generally prevail during April and May whenever the northeast and the southwest monsoons are weak. In the Philippines, the northeast monsoon is associated with the dry season while the southwest monsoon is linked with the wet season. 3.3.2
Tropical Cyclones
Tropical cyclones are the most influential factors that bring considerable rainfall in the Philippines. There are three classifications of tropical cyclones, namely: depressions which have wind speed of 45 to 63 kph, storms which have wind speed of 64 to 119 kph and typhoons which have maximum speed of 120 kph or stronger. Typhoons usually occur from June to December with highest frequencies in July and August. The mean annual number of tropical cyclones that pass through the Philippine Area of Responsibility (PAR) is about 20. The cyclones originate in the region of Marianas and Caroline Islands in the Pacific Ocean usually between 125°E and 170°E. Their movements follow westerly or northwesterly course over the country and deposit substantial amount of rainfall. The most frequent disastrous typhoons generally occur during the months of October and November.1 Tropical cyclones are classified according to their intensity. The World Meteorological Organization (WMO) provides the following classification: Classification Tropical depression
Maximum Sustained Winds (kph) Up to 62
Tropical storm
62-88
Severe tropical storm
89-117
Typhoon
118 or more
Studies at selected stations in the Philippines have shown that 47% of the average yearly rainfall is due to tropical cyclones, 14% to monsoons and 39% to other weather disturbances such as thunderstorm, easterly waves, International Tropical Convergence Zone (ITCZ) and fronts. 3.3.3
Cyclone Tracks
Tropical cyclone tracks vary from year to year. In general, tracks during the months of January, March, April, and May are located over northeastern Mindanao and the Visayas. About 55 to 60 percent of tropical cyclones that form in the Pacific Ocean move westward. In February, about 80 percent of cyclones have westward movement but dissipate before reaching the east coast. In June, the track is across Luzon with 70 percent moving in a generally westward direction.
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 8
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT From July to October, the tracks are located over Northern Luzon, reaching its northwest position in the latter half of August. During this period, about 80 to 95 percent of the cyclones approaching from the east moves toward the west. The position of cyclone tracks shift southward around September and in November is located across Central Luzon with secondary tracks over northeastern Mindanao and Visayas. About 70 percent of cyclones during this month have generally westward movement. In December, the track is located across Southern Luzon and Northern Visayas. A secondary track passes through northeastern Mindanao and Visayas where about 80 percent moves toward the west. 3.3.4
Climate
The Climate of the Philippines is tropical and maritime. It is characterized by relatively high temperature, high humidity and abundant rainfall. The Philippine climate is classified into four types depending on rainfall distribution and pattern (Figure 3.3.1). The four climate types are described as follows: Type I:
Two pronounced seasons. Dry from November to April, wet during the rest of the year. Type II: No dry season with a very pronounced rainfall from November to April and wet during the rest of the tear. Type III: Seasons are not very pronounced, relatively dry from November to April, wet during the rest of the year. Type IV: Rainfall is more or less evenly distributed throughout the year. The project site is classified under Type I.
Figure 3.3.1 Climate Map of the Philippines and Frequency of Typhoons
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 9
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
3.3.5
Rainfall
The nearest rainfall station reckoned from the project road with considerable and reliable rainfall record located in Science Garden. Based on the 29-year record the area receives a total (average) of 2,574.4 mm annually. The rainfall is evenly distributed throughout the year. Highest monthly mean rainfall is about 504.2 mm in August. The months from June to September generally experience intense rainfall. The monthly average maximum rainfall values based on the record from PAGAGSA are shown as follows. Rainfall, mm Average
Month
3.3.6
Jan
18.5
Feb
14.6
Mar
24.8
Apr
40.4
May
186.7
Jun
316.5
Jul
493.3
Aug
504.2
Sep
451.2
Oct
296.6
Nov
148.8
Dec
78.7
Temperature
The temperature data for the project area are reckoned at PAGASA’s synoptic station located at Science Garden. The monthly mean, minimum and maximum temperature are shown as follows: Month
Max
Temperature, °C Min
Mean
Jan
30.6
20.8
25.7
Feb
31.7
20.9
26.3
Mar
33.4
22.1
27.8
Apr
35.0
23.7
29.4
May
34.7
24.7
29.7
Jun
33.1
24.6
28.8
Jul
31.9
24.1
28.0
Aug
31.3
24.2
27.8
Sep
31.6
24.0
27.8
Oct
31.6
23.5
27.6
Nov
31.4
22.7
27.1
Dec
30.5
21.6
26.0
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 10
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT Based on record, the mean monthly variation of temperature is relatively small with values ranging from 0.0 °C to 0.9°C. The mean annual temperature is about 27.7°C. January is the coldest month with a recorded temperature of 20.8°C while April is the warmest at 35.0°C. 3.3.7
Relative Humidity
The average annual relative humidity for the project area reckoned at the station is about 77.6%. The mean monthly values of the relative humidity range from a low of 67 percent to a high of 84 percent. The most humid months usually occur during July to November while the month of April is the least humid. The monthly relative humidity data for the project area is shown below.
3.3.8
Month
Rel. Humidity, %
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
76 73 69 67 72 79 83 84 84 83 82 79
Winds
The easterly winds generally affect the project area throughout the months except during the month of August where the prevailing wind direction is westerly. The average wind speed is about 2.0 m/s. The monthly normal and extreme wind speed and direction reckoned at nearest synoptic station are shown below: 1
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Normal Speed (mps) Direction 1 N 1 NE 1 SE 1 SE 1 S 1 SW 2 SW 2 SW 1 SW 1 N 1 N 1 N
Source: PAGASA
1
Period of Record: 1981-2010
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 11
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 4. HYDROLOGY STUDY AND ANALYSIS 4.1
General
This section discusses the various procedures used in estimating peak discharge to be conveyed across and along the project site. The study activities consist of familiarization on the present site conditions, field investigations, data gathering and hydrologic analysis. Relevant and important items noted during this study, are as follows: • • • 4.2
Recommended design storm frequency period Magnitude of the tributary (drainage) area The values of rainfall intensity obtained from the nearest relevant monitoring stations of PAGASA Catchment Parameters
The size of the watershed or catchment basin is the most important parameter affecting the determination of the total runoff. For given conditions, the peak flow at the proposed site is approximately proportional to the drainage area. The shape of a basin affects the peak discharge. Long, narrow basins generally give lower peak discharges than pear-shaped basins. A basin orientation with respect to the direction of storm movement can affect peak discharge. Storms moving upstream tend to produce lower peaks than those moving downstream. The mean elevation of a drainage basin is an important characteristic affecting runoff. Higher elevation basins can receive a significant amount of precipitation. The location of this divide and thus the perimeter of the basin is determined from the topographic maps in the available scale of 1:50,000. The delineated waterways crossing the project road is shown in Figure 4.2.1.
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 12
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
Figure 4.2.1 Catchment Area 4.3
Time Parameter
The main effect the slope has on water flow is the time of concentration, or the time it takes the rainfall to flow from the farthest point in the watershed to the point under consideration (bridge and culvert sites). Steep slopes cause a shorter time of concentration and, thus higher peak discharge than do flatter slopes. The time of concentration is a variable often used in computing surface runoff. The variable indicates the response time at the outlet of a watershed for a rainfall event, and is primarily a function of the geometry of the watershed. In flood hydrology, the time of concentration of a watershed is normally considered as constant, independent of the magnitude of the flood. The time of concentration is defined as the time required for a drop of water to flow to the watershed outlet from the most distant point in the watershed. It is influenced by surface roughness slope and flow patterns. Estimating the time of concentration for the watershed is expressed as; Tc = L1.15 /51*(H) 0.385 Where: Tc
=
time of concentration, the time required for storm runoff to travel from the most remote point of the drainage basin to the point of interest in minutes.
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 13
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT L
=
H
=
length of mainstream from the farthest point to the point of interest in meters. difference in elevation between most remote point and outlet in meters.
The minimum Tc for moderate slopes and paved is 10minutes, for areas which do not afford surface storage and are steeper than 1:10 is 5 minutes. Once the time of concentration Tc is estimated, the rainfall intensity (I), corresponding to a storm of equal duration, obtained from Rainfall Intensity-Duration-Frequency (RIDF) table or graph. 4.4
Frequency Analysis
Frequency analysis is concerned with estimating the relationship between an event and corresponding return period of that event. It is generally based on assumed (population) probability distributions and sample estimates of the population parameters. 4.4.1
Rainfall Analysis
4.4.1.1
Data Availability
The Rainfall Data Considered in this project is the raw Daily Rainfall Data from 1993 to 2013. The Raw data will be analyze to come up with Probable Rainfall Intensity and probable discharge at a given return period. Rainfall gauging stations are found available from the following locations. Rainfall Stations and Years of Record Sta. No./Location Science Garden. Quezon City
4.4.1.2
Coordinates Latitude 0
14 38’41.0”N
Longitude 0
121 02’31.0”E
Years of Record
Station Type
1993-2010
Synoptic
Rainfall Data
a. Maximum Yearly Rainfall Maximum Yearly Rainfall (mm) 1993
145.4
1994
131.2
1995
143.2
1996
104.4
1997
156.6
1998
137.2
1999
204.8
2000
267
2001
110.4
2002
246.4
2003
137.4
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 14
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT Maximum Yearly Rainfall (mm) 2004
135.6
2005
104.6
2006
159.6
2007
147
2008
125.6
2009
455
2010
122
2011
250.9
2012
391.4
2013
225.7
b. Maximum Monthly Rainfall Maximum Monthly Rainfall (mm) May Jun Jul Aug
Year
Jan
Feb
Mar
Apr
Sep
Oct
Nov
Dec
1993
0
1
11.6
12.2
1.4
109.2
145.4
79
94.6
118.2
89.6
32.4
1994
24.8
23.6
30
13
25.4
123.8
101.4
131.2
97.1
78.7
4
87.2
1995
16.1
5.4
1.8
3
61.2
64
74.8
115.8
143.2
58.2
70.8
49.4
1996
17
0
8.6
29.6
37
33.6
53.2
89.8
104.4
65.6
34.4
7.2
1997
4.2
25.3
1
14
156.6
35.7
80.4
145
47.5
56.7
34.4
6
1998
11.8
0
2.5
1.2
78.3
91
60
49
137.2
128.1
36.6
84.2
1999
10.2
3.4
20.3
38.5
48.8
40
103.2
196.2
204.8
152.1
46.6
36
2000
9.2
25.7
23.4
17.8
96.1
35
175.1
115.1
267
160.6
102.8
33.6
2001
19.8
35.8
5.3
17.2
48.8
49.5
107.4
110.4
34
57.8
39
30.2
2002
8.4
8.6
15.4
10
18.8
36
246.4
99.7
64.6
76
76.5
18.4
2003
1.4
5.2
5.2
20.6
137.4
55.6
38.4
100.2
120.2
52.2
30.4
5.4
2004
3.6
25
0
33.4
61.2
24
40.6
135.6
79
32.2
126.7
45.4
2005
8.4
7
9.8
16.8
65.2
85.3
54.6
59.6
86.9
104.6
34.6
12.9
2006
24.2
2.4
26.8
0
54.8
69.4
116.4
58.9
159.6
36.5
30.4
53
2007
1.4
24.1
15.3
14.6
107
21
42.4
147
53.5
78.6
65.4
26.3
2008
30.2
8
19.4
7.1
49.6
125.6
38.6
52.4
74.7
91.4
61.4
25
2009
22
7.8
37.1
40.4
86
75.7
153.5
93
455
79
15.5
6
2010
3
0
2.4
15.2
52.8
56.5
105.9
122
120.6
88.2
45
67
2011
51.5
0.2
16.6
1.2
75
250.9
99
109.5
121.2
70.7
105.6
58.4
2012
41
65
1.6
46.7
84.4
116.9
391.4
159.3
98.9
7.9
18
0
2013
13.7
61.7
55.3
45.6
61.6
78.7
84.4
225.7
148.8
80.8
27.2
34.8
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 15
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT c. Average Yearly Rainfall Ave Yearly Rainfall mm. 1993
7.06
1994
7.08
1995
8.74
1996
5.58
1997
6.07
1998
7.36
1999
9.14
2000
11.05
2001
6.24
2002
8.13
2003
5.98
2004
6.08
2005
6.47
2006
7.27
2007
6.27
2008
6.49
2009
9.62
2010
7.28
2011
8.61
2012
12.03
2013
9.62
d. Average Monthly Rainfall
Month
Jan
Feb
Mar
Apr
Ave. monthly rainfall May Jun Jul
Aug
Sep
Oct
1993
0.00
0.04
0.52
0.53
0.05
10.85
16.03
15.31
17.28
11.33
7.47
5.34
1994
1.59
0.88
1.36
1.00
5.96
14.06
25.79
11.14
14.22
5.02
0.26
3.65
1995
0.56
0.29
0.07
0.18
9.76
13.09
11.60
20.87
24.95
11.26
6.16
6.12
1996
0.63
0.00
0.34
2.68
3.73
4.75
12.90
10.96
16.18
8.93
5.40
0.42
1997
0.38
1.16
0.03
1.01
15.60
5.56
18.22
18.05
7.82
3.15
1.53
0.34
1998
0.56
0.00
0.17
0.05
6.00
9.64
6.46
8.81
20.61
15.70
5.97
14.3
1999
1.25
0.14
2.67
4.59
6.48
8.19
22.84
27.92
14.53
11.08
5.56
4.37
2000
0.56
1.31
3.34
1.25
19.10
5.91
32.36
16.78
20.14
17.32
8.50
6.06
2001
0.68
3.76
0.40
1.04
8.42
8.28
16.74
17.72
6.10
6.16
2.44
3.13
2002
0.27
0.48
0.70
0.68
1.60
6.14
42.27
14.34
14.21
7.79
7.83
1.21
2003
0.05
0.26
0.31
0.74
15.03
7.73
8.65
12.27
16.59
5.96
3.94
0.22
2004
0.19
1.26
0.00
2.95
6.66
7.15
10.83
22.13
10.28
2.79
6.82
1.94
2005
0.41
0.43
0.52
1.19
4.45
17.63
7.14
11.05
13.79
15.74
2.55
2.79
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Nov
Dec
Page 16
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
Month
Jan
Feb
Mar
Apr
Ave. monthly rainfall May Jun Jul
Aug
Sep
Oct
Nov
Dec
2006
1.82
0.24
2.53
0.00
5.57
11.12
21.37
10.00
22.25
6.85
2.96
2.48
2007
0.07
0.86
0.71
0.86
8.33
3.31
6.64
21.61
14.59
7.10
9.49
1.68
2008
1.52
0.82
1.25
1.18
8.45
12.05
7.27
13.88
14.92
8.05
6.26
2.26
2009
1.39
0.37
3.02
4.62
8.66
14.60
21.32
13.16
37.45
8.78
1.80
0.21
2010
0.16
0.00
0.08
0.67
2.00
11.85
13.24
20.26
12.89
13.34
8.48
4.42
2011
2.59
0.00
0.57
0.40
6.04
18.00
15.46
20.71
13.88
11.24
8.74
5.75
2012
1.33
4.43
6.31
0.07
10.57
10.44
28.59
44.75
24.54
10.94
0.89
1.55
2013
1.52
3.18
4.26
1.79
5.48
18.56
8.65
31.05
22.78
11.43
2.99
3.75
4.4.1.3
Design Storm Hyetograph
The process is undertaken in two stages, namely; (a) probable point rainfall frequency analysis, (b) rainfall intensity duration frequency (RIDF) analysis. 4.4.1.3.1 Probable Point Rainfall Frequency Analysis Probable rainfall analysis has two sub-parts, namely frequency analysis and selection of the best fit frequency distribution. Frequency Analysis This involves the fitting of theoretical frequency distributions to the annual maximum rainfall data. Two types of theoretical distributions are used in this study, namely Extreme Value Distribution (Gumbel), and Log Pearson Type III Distribution. 1. Extreme Value Distribution (Gumbel) This distribution utilizes the Fisher-Tippet extreme value function, which relates magnitude linearly with the logarithm of the reciprocal of the exceedance probability. Working equations are the following:
RTr = R + KTr ⋅ S KTr =
(YTr − Yn ) Sn
YTr = −(0.83405 + 2.3025 ⋅ log log Where:
RTr = R= S = KTr = YTr = Yn, Sn = n
=
Tr Tr − 1
)
Probable rainfall at return period Tr Mean of the annual maximum rainfall series Frequency factor at return period Tr Standard deviation of annual maximum rainfall series reduced variate at return period Tr reduced mean and reduced standard deviation number years of record
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 17
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT Reduced Mean and Standard Deviation n
Yn
Sn
n
Yn
Sn
n
Yn
Sn
0
0.49522
0.94963
21
0.52519
1.06938
31
0.53714
1.11588
10
0.49522
0.94963
22
0.52673
1.07547
32
0.53803
1.11927
11
0.49969
0.96753
23
0.52819
1.08115
33
0.53889
1.12245
12
0.50348
0.98327
24
0.52959
1.08648
34
0.53959
1.12557
13
0.50699
0.99712
25
0.53084
1.09143
35
0.54026
1.12849
14
0.51000
1.00951
26
0.53202
1.09615
36
0.54107
1.13127
15
0.51285
1.02055
27
0.53326
1.10048
37
0.54177
1.13391
16
0.51542
1.03058
28
0.53419
1.10471
38
0.54243
1.13649
17
0.51770
1.03972
29
0.53533
1.10860
39
0.54294
1.13900
18
0.51978
1.04806
30
0.53616
1.11238
40
0.54363
1.14130
19
0.52177
1.05575
20
0.52352
1.06282
4.4.1.3.2 Rainfall intensity duration frequency (RIDF) analysis This method determines the probability that rainfall of a given intensity and duration is equaled or exceeded. From this probability determination, the return period of time interval measured in years, over which a given storm event may be expected to occur again, can be predicted. The results of the analysis are presented in curves or graphs that will relate rainfall intensity of a given duration to the probable frequency of occurrence of said event. From these rainfall frequency curves, the relationship between rainfall intensity and duration for any pre- determined return period can be developed. Tables 2.5.1a and 2.5.1b shows the Computed Extreme Values of Precipitation and Intensity of Computed Extreme Values respectively. Figures 4.4.1.3.2a and 4.4.1.3.2b shows the Rainfall Depth Duration Curve and Rainfall Intensity Duration Frequency respectively as shown as follows: X=Rain fall Duration, Y= Rainfall Depth 600 500 2 yrs. 400
5 yrs. 10.yrs.
300
15 yrs 25 yrs.
200
50 yrs. 100 yrs.
100 0 0
200
400
600
800
1000
1200
1400
1600
Figure 4.4.1.3.2a Rainfall Depth Duration Curve (27 years record) Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 18
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
X=Rainfall Duration, Y=Rainfall Intensity 350 300 250
2yrs. 5yrs
200
10yrs 15yrs
150
25yrs 50yrs.
100
100yrs
50 0 0
200
400
600
800
1000
1200
1400
1600
Figure 4.4.1.3.2b Rainfall Intensity Duration Frequency (27 years record)
Regression Analysis Parameters of Rainfall Intensity versus Duration frequency Constants Yrs.
A
d
b
2
825.301
10
0.64239
5
1354.58
11.9
0.65959
10
1753.36
13.3
0.66948
15
1989.69
14
0.67441
25
2320.51
15
0.6822
50
2604.68
15.5
0.67489
100
3144.45
16.5
0.69248
Regression Analysis for Rainfall Intensity versus Rainfall Duration Equation of data from PAGASA is presented in Annex C. 2. Log Pearson Type III Distribution. (See Annex E for Calculation) This distribution belongs to the family of distribution suggested by Pearson with log transformation of rainfall data. The parameters used are the mean, standard deviation and skewness coefficient. The working equations are the following: Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 19
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
RTr = R + KTr ⋅ S KTr =
2 G
⋅ {[( Kn −
G 6
)⋅
G 6
+ 1]3 − 1}
Where:
RTr = R=
Log of probable rainfall at return period Tr
KTr =
Frequency factor at return period Tr
Mean of the log of rainfall series
S= Kn =
Standard deviation of the log of rainfall series
G =
Skewness coefficient of the series
P
=
Normal frequency factor (see table)
Probability Table for Normal Frequency Factor
Kn -3.71902 -3.29053 -3.09023 -2.87816 -2.57583 -2.32635 -2.05375 -1.95996 -1.75069 -1.64485 -1.28155 -0.84162 -0.52440 -0.25335 -0.17733 0.00000
P 0.99990 0.99950 0.99900 0.99800 0.99500 0.99000 0.98000 0.97500 0.96000 0.95000 0.90000 0.80000 0.70000 0.60000 0.57040 0.50000
Tr 1.000 1.001 1.001 1.002 1.005 1.010 1.020 1.026 1.042 1.053 1.111 1.250 1.429 1.667 1.753 2.000
Kn 0.00000 0.17733 0.25335 0.52440 0.84162 1.28155 1.64485 1.75069 1.95996 2.05375 2.32635 2.57583 2.87816 3.09023 3.29053 3.71902
P 0.50000 0.42960 0.40000 0.30000 0.20000 0.10000 0.05000 0.04000 0.02500 0.02000 0.01000 0.00500 0.00200 0.00100 0.00050 0.00010
Tr 2.000 2.328 2.500 3.333 5 10 20 25 40 50 100 200 500 1000 2000 10000
4.4.1.3.3 Rainfall intensity duration frequency (RIDF) analysis This method determines the probability that rainfall of a given intensity and duration is equaled or exceeded. From this probability determination, the return period of time interval measured in years, over which a given storm event may be expected to occur again, can be predicted. The results of the analysis are presented in curves or graphs that will relate rainfall intensity of a given duration to the probable frequency of occurrence of said event. From these rainfall frequency curves, the relationship between rainfall intensity and duration for any pre- determined return period can be developed. Tables 4.4.1.3.3a and 4.4.1.3.3b shows the Computed Extreme Values of Precipitation and Intensity of Computed Extreme Values respectively (based on 21 Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 20
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT years of records). Figures 4.4.1.3.3a and 4.4.1.3.3b shows the Rainfall Dept Duration Curve and Rainfall Intensity Duration Frequency respectively as shown as follows: Table 4.4.1.3.3a Computed Extreme Values of Precipitation (mm) (Based on 21 years of records) T
10
20
30
1
2
3
6
12
24
(yrs)
mins
mins
mins
Hr
hrs
hrs
hrs
hrs
hrs
2
23.0
35.2
43.8
60.0
87.3
105.6
136.0
162.9
185.8
5
30.7
48.3
61.1
85.0
118.9
142.8
183.1
219.9
251.7
10
36.9
58.4
74.4
104.0
143.5
171.9
220.3
264.5
303.3
25
45.7
72.9
93.4
131.2
179.1
213.8
273.5
329.0
377.4
50
53.1
85.2
109.5
154.1
208.9
249.3
318.7
383.4
440.2
100
61.3
98.7
127.2
179.3
242.0
288.4
368.4
443.3
509.3
Table 4.4.1.3.3b Intensity of Computed Extreme Values (mm/hr) (Based on 21 years of records) T
10
20
30
1
2
3
6
12
24
(yrs)
mins
mins
mins
hr
hrs
hrs
hrs
hrs
hrs
2
137.9
105.6
87.6
60.0
43.6
35.2
22.7
13.6
7.7
5
184.3
144.8
122.2
85.0
59.4
47.6
30.5
18.3
10.5
10
221.4
175.2
148.8
104.0
71.8
57.3
36.7
22.0
12.6
25
274.2
218.8
186.8
131.2
89.5
71.3
45.6
27.4
15.7
50
318.6
255.5
218.9
154.1
104.5
83.1
53.1
31.9
18.3
100
367.9
296.1
254.3
179.3
121.0
96.1
61.4
36.9
21.2
X=Rain fall Duration, Y= Rainfall Depth 600 500 2 yrs.
400
5 yrs. 10.yrs.
300
15 yrs 25 yrs.
200
50 yrs. 100 yrs.
100 0 0
200
400
600
800
1000
1200
1400
1600
Figure 4.4.1.3.3a Rainfall Depth Duration Curve (21 years record) Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 21
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT X=Rainfall Duration, Y=Rainfall Intensity 400 350 300 2yrs. 250
5yrs 10yrs
200
15yrs 25yrs
150
50yrs.
100
100yrs
50 0 0
200
400
600
800
1000
1200
1400
1600
Figure 4.4.1.3.3a Rainfall Intensity Duration Frequency (21 yrs record) Regression Analysis Parameters of Rainfall Intensity versus Duration frequency Constants Yrs.
A
d
b
2 5 10 25 50 100
890.5 1416.98 1825.49 2358.02 2935.59 3551.31
9 12 13.3 14 15.5 16.5
0.63455 0.65951 0.66988 0.67559 0.68567 0.69252
Regression Analysis for Rainfall Intensity versus Rainfall Duration Equation of Raw Rainfall data from PAGASA is presented in Annex D. 4.5
Runoff Analysis
Runoff is the amount of water that flows out of a watershed sub-area as a result of a storm event. This value is equal to the amount of rainfall that occurs on the area, minus the amount of rainfall that is infiltrated into the ground, intercepted by foliage, is lost through evaporation and evapotranspiration or is held in small depressions. 4.5.1
Basin Characteristics
1. Basin Area – the area of a drainage basin is the most important watershed characteristic affecting any surface runoff calculation. Determining the size of the watershed area that contributes to flow generation at the site of the drainage structure is the basic step in a
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 22
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT hydrologic analysis. This is regardless of the method used to evaluate flood flows, most frequently determined from field surveys, topographic maps or aerial photographs. 2. Slope – the slope of a drainage basin is one of the major factors affecting the rate of overland flow and time of concentration of rainfall runoffs. Steep slope tends to hasten the arrival of maximum discharge while flat slope has the opposite effect, at the point under consideration. The areas surrounding the site are predominantly rolling terrain. 3. Shape – the shape, or outline formed by the basin boundaries, affects the rate at which water is supplied to the main stream as it proceeds along its course from runoff source to the site of drainage structure. Long narrow watersheds generally give lower peak discharge than do fan or pear shaped basins. The areas irregular, long and narrow. Classification of “C” coefficient – any changes in C value will also cause increase or decrease in surface water runoff. Ground cover characteristics are another critical factor considered in runoff determination. The values of “C” coefficients, taking into considerations the above mentioned factors, are classified into 11 surface categories, as presented in Table 4.5.1.1. Table 4.5.1.1 Values of “C” For Use in Rational Formula Surface
4.5.2
Value Proposed
Concrete or asphalt pavement
0.9 – 1.0
Bituminous Macadam and DBST (sandy to clayey)
0.7 – 0.9
Gravel surface road and shoulder
0.3 – 0.6
Residential area – city
0.3 – 0.6
Residential area – town & village
0.2 – 0.5
Rocky surface
0.7 – 0.9
Bore clayey surface (faces of slips, etc.)
0.7 – 0.9
Forested land (sandy to clay)
0.3 – 0.5
Flattish cultivated areas (not flooded)
0.3 – 0.5
Steep or rolling grassed areas
0.5 – 0.7
Flooded or wet paddy
0.7 – 0.8
Storm Rainfall
As for long duration rainfall, the standard rainfall duration is an important factor to develop a model hyetograph, which will be used for the evaluation of flood runoff analysis within the drainage basin. In this case, mostly duration of rainfall was considered. Rainfall event characteristics which are considered important to any highway drainage design are: Intensity (rate of rainfall), in mm/hr • Duration (time rainfall lasts), minutes • Frequency (statistical probability of how often rainfall will occur) a return period
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 23
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 4.5.3
Design Storm Frequency
The rainfall intensity from which the frequency of recurrence is based, dictates the design frequency. Presented below are various selected standards to illustrate the principle. Cases
Design Storm Frequency
Bridge (MFWL)
1 in 50 years
Box culvert (Discharge)
1 in 25 years
Pipe Culvert (Discharge)
1 in 15 years
Embankment (HFL) Road Surface (Drainage)
1 in 10 years 1 in 10 years
Roadside Drainage (Ditches)
1 in 10 years
These design frequencies, which were used, are not totally dependent on economic consideration alone but also based on guidelines used in similar projects in the different regions of the country. The runoff model adopted in this context are the Rational Formula, which has been widely used in the Philippines for the design of the rural or urban drainage improvement project with an area less than or equal to 20 square km. and Unit Hydrograph for the areas greater than 20 square kms. The parameters necessary for the estimation using the said formula are as follows: 1. Rational Method Q = 0.278 CIA Where: Q C I A
= = = =
design discharge in cu.m/second coefficient of runoff (refer to Table 4.5.1.1) Rainfall intensity, in mm/hr Drainage Area, in (sq. km)
Rainfall Intensity is estimated based on the calculated rainfall depth and duration. The relationship between duration, intensity and frequency at any location maybe obtained from analysis of rainfall records obtained at the location. The rainfall intensity-frequency-duration data are useful in peak flow estimation of runoff. The general equation for rainfall intensity derived for the project area is: I = A / (tc + d)b Where: I
=
Tc = A,d,b =
average rainfall intensity in mm/hour for the selected frequency and for a duration equal to the time of concentration. storm duration, in minutes constants depending on the frequency of occurrence and usually derived by analytical method.
Table 1.4.1.2 Regression analysis parameters of rainfall intensity versus duration frequency represent values of constants of a given return period. Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 24
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
For large basin area, equation is express as follows: C = C1A1 +C2A2 + --- / A1 + A2 + --The equation represents the percent of water which will run off the ground surface during storm. The remaining amount of precipitation is lost to infiltration, transpiration, evaporation and depression storage. •
Time of Concentration “Tc” Equation is express as follows: Tc = L1.15 /51*(H) 0.385 Where: Tc = L
=
H =
time of concentration, the time required for storm runoff to travel from the most remote point of the drainage basin to the point of interest in minutes. length of mainstream from the farthest point to the point of interest in meters. difference in elevation between most remote point and outlet in meters.
The minimum Tc for moderate slopes and paved is 10minutes, for areas which do not afford surface storage and are steeper than 1:10 is 5 minutes. Once the time of concentration Tc is estimated, the rainfall intensity (I), corresponding to a storm of equal duration, obtained from Rainfall Intensity-Duration-Frequency (RIDF) table or graph. 2. Unit Hydrograph Peak floods of rivers or stream with catchments areas larger than 20sq. km. may be computed using the Snyder Method and U.S. Soil Conservation Services (SCS) Method – Unit Hydrograph – principle. Existing bridge with long span or wide riverbed, with drainage area of more than 20 sq km. may be hydrologically analyzed by the more accurate unit hydrograph method in order to determine more accurately the new bridge opening and safe span. The instantaneous unit hydrograph for each individual watershed may be derived from a dimensionless graph prepared by the basin physiographic characteristics of respective project sites as inputs. For each watershed, the 50-year rainfall values at intervals equal to D the duration of excess rainfall in hours ranging from 1/4 to1/5 of basin lag time may be derived from designed rainfall intensity curves. The increments will be computed and rearranged into a pattern that would yield maximum run-off. The results of this analysis give the effective rainfall values to be used in the computation of the flood hydrograph. For relatively small size watersheds along the project roads, adjustment factors for area and duration may not be applied to the rainfall data furnished by PAGASA, i.e. point rainfall is assumed equal to area rainfall. In the absence of specific base flow data for each river or stream, mean monthly flows from July to October which are generally the wet months in the country from stream Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 25
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT gages in the vicinity of the may be considered for analysis. The ratio of base flow to peak run-off (as suggested by Te Chow in “Applied Hydrology”) is 0.01 at the start of the storm while the maximum possible ratio is 0.10. For each bridge site the roughness coefficient n should be estimated in the field using Manning values for various bed conditions. The “n” values of all bridge sites along each project road may be averaged and applied in the design of minor drainage structures. The final step in the SCS Method is the computation of the flood hydrograph. This requires the application of the convolution or superposition methods in order to determine peak discharges. The method involves computing “Lg” (time to peak run-off) and “tr” (duration of rainfall) by the modified Snyder’s Formula. The parameter Lg and tr given by the following: Lg = 0.6865 Ct (L x Lca / S1/2)0.38 This is the lag time from midpoint of unit rainfall duration, tr, to peak of unit hydrograph, in hours tr = Lg / 5.5, unit rainfall duration in hours Where: L
=
Lca = S Ct
= =
distance along longest water course from point of interest to watershed divide, km distance along watercourse from point of interest to intersection of perpendicular from centroid of basin to stream alignment, km harmonic mean slope of the main river or stream coefficient representing variation of catchments slopes and storage
In the absence of hydrologic records of nearby basins of similar characteristics as the basins under study, the coefficient Ct has to be assumed, e.g. Ct
=
1.2 for mountainous drainage areas
=
0.70 for foothill drainage areas
=
0.35 for valley drainage areas
Compute for the time to peak, (tp) in hours. tp = Lg + ½ tr, in hour Compute for the unit peak discharge (qp) in cms/sec per one millimeter depth of rainfall in the basin. qp = (0.278(Cp) (D.A)) / tp Where: Cp = D.A. = tp =
basin coefficient ranging from 0.60 to 0.80 Drainage Area in sq. km. time to peak, in hours
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 26
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT Compute for the time base, (tb) in hours tb = 2.67 (tp), in hours Plotting the rainfall depth – duration curves and using the dimensionless graph, the runoff is given by the Convolution method as follows: j
Qj = Σ R(i) U (j-i+1) i=1
Where: Qj= run-off at time j, cms R (i) = excess rainfall during time j-i+1 U (j-i+1) = unit graph ordinate, cms 4.5.4
Delineation of Catchment Areas
The drainage areas of each waterway were delineated from the scale 1:50,000 topographic map produced by the NAMRIA which is basically the main source of information necessary in the determination of the watershed area. The drainage areas were determined with the aid of AutoCAD software. Delineation of the drainage watershed is done by connecting the high points that enclosed the limit of drainage area. The continuous line defined is then allowed to intersect with the road alignment, using the latter as the final line of closure. The delineation of each waterway drainage areas is presented in Figure 4.2.1. 4.6
Runoff Calculation
The method use in the computation of the discharge of the two creek namely Balante and Halang creek is Rational method because the catchment area is less than 20 sq. km. 1. Using RIDF data from PAGASA (27 years of record, 1983-2010)
HYDROLOGICAL CHARACTERISTICS OF WATERSHEDS AND RELATED DISCHARGES PROJECT: LRT Line 2 Extension Project BASIN
NAME OF
WATERSHED
NO.
CREEK
AREA
1. 2.
Balante Creek Halang
WATERSHED
ELEVATION
A
A
ΔH
UP
ha
km2
m
1188.00
11.880
18.4
27.8
455.00
4.550
21.1
30
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
LENGTH
AVERAGE
TIME OF
OF STREAM
SLOPE
CONCEN.
Ls
S
Tc
m
m/m
mins
9.40
7616.00
0.00242
185.98
8.90
5222.00
0.00404
114.31
DN
Page 27
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
BASIN
NAME OF
RAINFALL INTENSITY
RUNOFF
NO.
CREEK
FOR RETURN PERIOD OF
COEFF.
2-year
5-year
10-year
15-year
25-year
50-year
100-year
mm/hr
mm/hr
mm/hr
mm/hr
mm/hr
mm/hr
mm/hr
C
1
Balante Creek
27.80
41.41
50.63
55.84
62.29
72.55
79.51
0.40
2
Halang
37.25
55.71
68.24
75.33
84.15
97.61
107.60
0.50
2.
BASIN
NAME OF
DISCHARGE
NO.
CREEK
Q 5-year
10-year
25-year
50-year
100-year
m3/s
m3/s
m3/s
m3/s
m3/s
1.00
Balante Creek
56.48
66.89
82.28
95.85
105.04
2.00
Halang
36.37
43.16
53.22
61.74
68.05
Using RAW RAINFALL DATA FROM PAGASA (21 years of record, 1993-2013)
HYDROLOGICAL CHARACTERISTICS OF WATERSHEDS AND RELATED DISCHARGES PROJECT: LRT Line 2 Extension Project BASIN
NAME OF
WATERSHED
NO.
CREEK
AREA
WATERSHED
ELEVATION
A
A
ΔH
ha
km2
m
UP
DN
LENGTH
AVERAGE
TIME OF
OF STREAM
SLOPE
CONCEN.
Ls
S
Tc
m
m/m
mins
1.
Balante Creek
1188.00
11.880
18.4
27.8
9.40
7616.00
0.00242
185.98
2.
Halang
455.00
4.550
21.1
30
8.90
5222.00
0.00404
114.31
BASIN
NAME OF
RAINFALL INTENSITY
RUNOFF
NO.
CREEK
FOR RETURN PERIOD OF
COEFF.
2-year
5-year
10-year
25-year
50-year
100-year
mm/hr
mm/hr
mm/hr
mm/hr
mm/hr
mm/hr
C
1.00
Balante Creek
31.37
43.32
52.60
65.77
77.22
89.78
0.45
2.00
Halang
41.96
58.27
70.91
88.76
104.39
121.50
0.50
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 28
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
4.7
BASIN
NAME OF
DISCHARGE
NO.
CREEK
Q 5-year
10-year
25-year
50-year
100-year
m3/s
m3/s
m3/s
m3/s
m3/s
1.00
Balante Creek
64.39
78.18
97.75
114.77
133.43
2.00
Halang
36.85
44.84
56.14
66.02
76.84
Selecting Run Off to be Consider in this Project
In selecting Run Off to be considered in the Detailed Drainage Design of this project, we need to consider the latest rainfall occur. Among the two alternatives that were used to determine the Runoff, the calculated Runoff using the raw rainfall data from 1993 to 2013 is more reliable. This data includes the rainfall occur in four (4) consecutive days. This happened on August 18,19,20, and 21, their respective rainfall are as follows, 174.8,108.8,225.7 and 166.1mm. This event rarely happens. From the raw rainfall data, it only happens once in 21 years. The two (2) alternatives are reliable in computing probable rainfall intensity, therefore, in this alternatives, we will consider whichever is larger. Runoff used in this project is presented table below; BASIN
NAME OF
DISCHARGE
NO.
CREEK
Q 5-year
10-year
25-year
50-year
100-year
m3/s
m3/s
m3/s
m3/s
m3/s
1.00
Balante Creek
64.39
78.18
97.75
114.77
133.43
2.00
Halang
36.85
44.84
56.14
66.02
76.84
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 29
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 5. HYDRAULICS 5.1
General
This document outlines and discusses the procedure of various hydraulic analyses in assessing to determine and understand how different drainage facilities can be integrated to provide complete drainage control. It also discusses the design standard and criteria adopted for the design. 5.2
Design Standards
The following references were heavily relied on during the design process: 1. DPWH Design Guidelines, Criteria and Standards 2. AASHTO Highway Drainage Guidelines 3. HDS 4 – Introduction to Highway Hydraulics 5.3
Design Criteria
5.3.1
Design Flood Frequencies
One way to select the design flood frequency is through the concept of economics by establishing the least total expected cost for the structure. This concept considers the capital cost, maintenance costs, and the flood hazard costs that are incurred due to damage by a range of flooding events. The flood frequency that generates the least total expected cost for the life of the project would be the one chosen for the design of the structure. The following design flood frequency: Structure Bridge Box culvert Pipe Culvert Pavement Road Surface Ditches 5.4
Design Flood Frequency 1 in 50 years 1 in 25 years 1 in 15 years 1 in 10 years 1 in 10 years 1 in 10 years
Highway Hydraulics Structure
Highway hydraulics structure, perform the vital function of conveying, diverting, or removing surface water from the highway right of way. One type of drainage facility will rarely provide the most satisfactory drainage for all sections of a highway. Therefore, the designer should know and understand how different drainage facilities can be integrated to provide complete drainage control. They should be designed to be commensurate with risk, construction cost, importance of the road, economy of maintenance and legal requirements. Based on the study the drainage facilities adopted for this project are classified into two major categories: 1. Cross Drainage – involves the conveyance of surface water and stream flow across or from the highway right of way. This is accomplished by providing a culvert to convey the flow from one side of the roadway to the other side or past some other type of flow obstruction.
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 30
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 2. Open Channel – is a conveyance in which water flows with a free surface. The term is generally applied to natural and improved watercourse, median swales, ditches, roadway channels, curb and gutter flow, and others. 5.5
Culvert Design Analysis
Outlet control analysis was done to minimize excessive velocities at outlet and to design the headwater depth. Each proposed cross-culvert were analyzed as to whether inlet or outlet control condition. 5.5.1
Inlet Control
Inlet Control –occurs when the culvert barrel is capable of conveying more flow than the inlet will accept. A culvert flowing in inlet control has shallow, high velocity flow categorized as “supercritical”. For supercritical flow, the control section is at the inlet of the barrel. 5.5.2
Outlet Control
Outlet Control – occurs when the culvert barrel is not capable of conveying as much flow as the inlet opening will accept. A culvert flowing in outlet control will have relatively deep, low velocity flow termed “subcritical” flow. For sub-critical flow the control is at the outlet of the culvert. The tail water depth is either critical depth at the culvert outlet or the downstream channel depth, whichever is higher. 5.6
Manning’s Roughness ‘n’ For Culvert Table 5.6.1 Manning’s “n” Values for Culvert Type of Culvert Concrete Pipe Concrete Box
Wall Description Smooth Walls Smooth Walls
Manning (n) 0.010-0.013 0.012-0.015
Corrugated Metal pipes & Boxes, annular or Helical Pipe (Manning n values with barrel size) Refer to Figure B-3
2-2/3 by ½ inch Corrugation 6 by 1 inch corrugations 5 by 1 inch corrugation 3 by 1 inch corrugations 6 by 2 inch structural plate corrugation 9 by 21/2 inch structural plate corrugation
0.022-0.027 0.022-0.025 0.025-0.026 0.027-0.028 0.033-0.035 0.033-0.037
Corrugated Metal Pipe, Helical 2-2/3 by ½ inch corrugations 0.012-0.024 corrugations and Full Circular Flow Smooth Walls 0.012-0.013 Spiral Rib Metal Pipe NOTE: The values indicated in this table are recommended Manning “n” design values. Actual field values for older existing pipelines may vary depending on the effects of the abrasion, corrosion, deflection, and joint conditions. Concrete pipe with poor joints and deteriorated walls may have “n” value of 0.014 to 0.018. Corrugated metal pipe with joint and wall problems may also have higher “n” values, and in addition may experience shape changes which could adversely affect the general hydraulic performance of the culvert. Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 31
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
5.7
Sizing of Culvert (Closed Conduit)
Design capacity is determined by the use of the Bernoulli’s energy balancing equation. Sizing of Culverts was done by aid of AutoCAD Land Development Desktop software. There are two (2) controls of flow in culvert namely: 1. Flow with Outlet Control For tail water (TW) elevation equal to or greater than the top of the culvert at the outlet, set ho culvert height type equal, D or TW and find HW by the following equation. HW = H + ho – LSo Where: HW H
-
vertical distance in meters from culvert invert to the pool surface. head loss in meters
H = 1 + K (29 LN² / R 1.33) V² / 2g ho
=
So L
= =
vertical distance in meters from culvert invert at outlet to control point on hydraulic grade line. slope of the barrel culvert length in meters
For tail water (TW) elevation less than the top of the culvert at the outlet, use the following equation of find HW: HW = H + ho – Lso Where: ho dc D
= = =
(dc + D) /2 or TW, whichever is greater critical depth culvert height
2. Flow with Inlet Control For Unsubmerged it operates as a weir flow, the headwater is in low condition. A weir is an unsubmerged flow control section where the upstream water surface elevation can be predicted for a given flow rate. The Equation is express: HWi/D = Hc/D + K (Q/AD0.5)M– 0.5S2 HWi/D = K (Q/AD0.5)M Submerged it operates as an orifice flow, the headwater submerging the culvert entrance. An orifice is an opening, submerged on the upstream side and flowing freely on the downstream side, which functions as a control section. The Equation is express: HWi/D = c (Q/AD0.5)2 + Y-0.5S2 Where: HW i D Hc
= = =
headwater depth above inlet control section invert, m interior height of culvert barrel, m specific head at critical depth (dc + Vc2/2g), m
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 32
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT Q = discharge, cms A = full cross section area of culvert barrel, sq m S = culvert barrel slope, m/m K, M, c, Y = constant Notes: 1. Equation for (unsubmerged) apply up to about Q/AD0.5 = 1.07 2. For beveled inlets use +0.7S instead of -0.5S as the slope correction factor 3. Equation for (submerged) applies above about Q/AD0.5 = 1.22 5.8
Open Channel
5.8.1
Hydraulic Considerations
The hydraulic design of open channel consists of developing a channel to carry the design discharge under the controlling condition as follows: 1. Adding freeboard as needed 2. Determining the type of channel protection required to prevent erosion. 3. Provide channel linings to increase the hydraulic capacity of the channel by reducing the channel roughness. The hydraulic capacity of a drainage channel is dependent on the size, shape, slope and roughness of the channel section. For a given channel: • • •
The hydraulic capacity becomes greater as the grade or depth of flow increases. The channel capacity decreases as the channel surface becomes rougher. A rough channel can sometimes be an advantage on steep slopes where it is desirable to keep flow velocities from becoming excessive high and reduce the flow velocities
Open channel designs which lower the water surface elevation can result in excessive flow velocities and cause erosion problems. A planned rise in water surface elevation can cause: • • 5.8.2
Objectional flooding of the road surface and adjacent properties. An environmental and maintenance problem with sedimentation due to reduced flow velocities.
Hydraulic Design of Channels
Open channel hydraulic design is of particular importance to highway design because of the interrelationship of channels to most highway drainage facilities. The hydraulic principles of open channel flow are based on steady state uniform flow condition. 5.8.3
Open Channel Flow Equations
The Equations of open channel flow are based on uniform flow conditions. The Equation was adopted:
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 33
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 3. Manning’s Equation – assuming uniform and turbulent flow conditions, the mean flow velocity in open channel can be computed as: V = (R2/3 S1/2) /n Where: V n S R A Wp 5.8.4
= = = = = =
mean velocity, m/sec Manning coefficient of roughness (Table 5.8.4.1) channel slope, m hydraulic radius, m = A/Wp cross sectional flow area, m2 wetted perimeter, m
Manning’s Roughness ‘n’ For Open Channel Table 5.8.4.1 Average Values of “n” for Manning’s Roughness Type of Channel
n value
Unlined Channel: Clay Loam Sand Gravel Rock, Grouted Riprap Lined Channels: Portland Cement Concrete Air Blown Mortar (troweled) Air Blown Mortar (untroweled) Air Blown Mortar (roughened) Asphalt Concrete Sacked Concrete Pavement and Gutters: Portland Cement Concrete Asphalt Concrete
0.023 0.020 0.030 0.040 0.014 0.012 0.016 0.025 0.018 0.025 0.015 0.016
Depressed Median: Earth (without Growth) Earth (with Growth) Gravel/ Riprap 5.8.5
0.040 0.050 0.055
Permissible Velocities for Unlined Channel Table 5.8.5.1 Recommended Permissible Velocities for Unlined Channel Permissible Velocity (m/sec) Type of Material in Excavation Section
Intermittent Flow
Sustained Flow
Fine Sand (Non colloidal)
0.8
0.8
Sandy Loam (Non colloidal)
0.8
0.8
Silt Loam (Non colloidal)
0.9
0.9
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 34
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT Permissible Velocity (m/sec) Type of Material in Excavation Section
5.9
Intermittent Flow
Sustained Flow
Fine Loam Volcanic Ash Fine Gravel Stiff Clay (Colloidal)
1.1 1.2 1.1 1.2
1.1 1.1 1.1 1.2
Graded Material (Non colloidal) Loam to Gravel Silt to Gravel Gravel Coarse Gravel Gravel to Cobbles (Under 150mm) Gravel & Cobbles (Over 200mm)
1.5 1.7 1.8 2.0 2.1 2.4
1.5 1.7 1.8 2.0 2.1 2.4
Open Channel Hydraulics
An important factor in flood analysis is to estimate characteristics of the flow during flood times. In order to do this, cross-sections of waterways are identified and representative cross sections of the river channel are obtained by actual field survey. Mean bed slope of the stream is obtained from actual survey of the waterway cross sections. For a river or waterway where conventional stream gauging data are not available, the average velocity for a given stage-height can be estimated using the Manning’s formula. The Manning’s formula is essentially an empirical formula, based upon field observations and laboratory measurements. This formula states that in steady uniform flow: V = R2/3 S1/2/n and, Q = A R2/3 S1/2/n Where: V Q R S n A P
= = = = = = =
average velocity, m/s discharge, m3/s hydraulic radius, A/P slope of the energy line Manning’s roughness coefficient cross-sectional area, m2 wetted perimeter, m
The use of the above equation to estimate the peak discharge for a flood in which various characteristics of the flow have been measured is often called the slope-area method. The hydraulic slope of the river based on field survey is given as follows; In reality, the value of n is highly variable and depends on a number of factors. The factors that exert the greatest influence upon the coefficient of roughness include the surface condition, vegetation, channel irregularity, variation of channel cross-sections and obstruction. Typical n values that can be used in the project design are given below:
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 35
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT Values of Manning’s Roughness Coefficient, n Floodplains
Range
Pasture, short grass, no brush
0.030 – 0.035
Cultivated land – no crop
0.030 – 0.040
Cultivated land – nature field crops
0.045 – 0.055
Man-made channels and ditches Earth, straight and uniform
0.017 – 0.025
Dredged
0.025 – 0.033
Lined – smooth concrete
0.012 – 0.018
Lined – grouted riprap
0.017 – 0.030
Asphalt pavement
0.013 – 0.016
5.10 Box Culvert A box culvert may be defined as a drainage structure or conveyance structures and are generally constructed to allow the continuation of a stream flow thorough a roadway. The design of box culvert requires assessment of the characteristics of the waterway flowing through it. For this, it is necessary to understand the factors that govern stream runoff, water surface levels, scour and channel stability and hydrodynamic forces acting on the bridge. In general, the presence of a box culvert in many locations cause the natural stream channel to be somewhat constricted. Such case may reduce severely the area through which the water must pass, particularly when the stream is at flood stage. In such event, the velocity of the water through the box culvert opening may be considerably increased, with resultant danger to the box culvert structure through scour at inlet and outlet headwalls, and the elevation of the water upstream side may be increased subjecting the area above the culvert site to possible flooding. It is therefore axiomatic that the box culvert must be designed to pass the flow occurring at flood stage without excessive velocity and without damage to property located above the culvert crossing. 5.10.1 Existing Box Culvert Runoff at waterways crossing the roadway comes from intense rainstorms associated with tropical cyclones or widespread and prolonged heavy rainfall associated with monsoonal depressions. The hydrological characteristics of the study area is analyzed and estimated through several approaches and techniques. The Rational Method is used to estimate the peak runoff of Balante and Halang Creek. Station
Drainage Area (sq. km)
Slope (m/m)
Balante
24+962
11.88
0.01119
Time of Concentration (min) 103.09
Halang
25+892
4.55
.00596
98.45
Sites
Flood Level For the box culvert crossing Marcos Highway, the design flood levels of 5, 10, 25, 50, and 100 year return period were estimated using the HEC-RAS. The cross section at box culvert site was used to derive the elevation and discharge relationship. Mean bed slope of the Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 36
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT stream was obtained from the waterways topographic map by scaled measurement of distances between known spot elevations along the box culvert site survey. In this study, two (2) cases of hydraulic analysis were performed. Case 1. Balante and Halang Creek was analyst w/out dredging Balante Creek. Case 2. Balante and Halang Creek was analyst w/ Balante Creek Dredged Downstream. Result of this two case of hydraulic analysis presented in Table 6.1.1 Flood Level and Depth. Hydraulic Analysis using HEC-RAS is presented in Annex F. 6. SUMMARY OF RESULTS 6.1. Flood Level and Depth From the Hydrology and Hydraulic Analysis of the LRT Line 2 Project, Several Flood depth ware obtained. The 5, 10, 25, 50, and 100 year return period were computed using HEC-RAS 4.0. The computed maximum Flood level is located in K025+000. The design of the surface drainage at the built-up areas will basically involve the proper collection of storm runoff, its conveyance and disposal to the nearest discharge point. Computed flood level and depth at various locations along Marcos Highway using the two (2) cases of hydraulic analysis is presented below in Table 6.1.1. Flood Level and Depth. (All units are in meters). Table 6.1.1 Flood Level and Depth CASE 1. WITHOUT DREDGING OF BALANTE CREEK 24+200
24+400 Emerald Station
24+300
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
10.616 10.616 10.616 10.616 10.616
10.37 10.98 11.21 11.38 11.57
-0.25 0.36 0.59 0.76 0.95
10.24 10.24 10.24 10.24 10.24
10.37 10.98 11.21 11.38 11.57
0.13 0.74 0.97 1.14 1.33
10.10 10.10 10.10 10.10 10.10
10.37 10.98 11.21 11.38 11.57
0.27 0.88 1.11 1.28 1.47
24+500
24+600
24+700
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.84 9.84 9.84 9.84 9.84
10.37 10.98 11.21 11.38 11.57
0.53 1.14 1.37 1.54 1.73
9.76 9.76 9.76 9.76 9.76
10.37 10.98 11.21 11.38 11.57
0.61 1.22 1.45 1.62 1.81
9.93 9.93 9.93 9.93 9.93
10.37 10.98 11.21 11.38 11.57
0.44 1.05 1.28 1.45 1.64
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 37
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 24+800 Return Period (Yrs.) 5 10 25 50 100
Balante Creek 24+890
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
10.31 10.31 10.31 10.31 10.31
10.37 10.98 11.21 11.38 11.57
0.06 0.67 0.90 1.07 1.26
10.40 10.40 10.40 10.40 10.40
10.37 10.98 11.21 11.38 11.57
0.00 0.58 0.81 0.98 1.17
10.01 10.01 10.01 10.01 10.01
10.37 10.98 11.21 11.38 11.57
0.00 0.00 0.00 1.37 1.56
25+100 Return Period (Yrs.) 5 10 25 50 100
25+000
25+200
25+300
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
9.77 9.77 9.77 9.77 9.77
10.37 10.98 11.21 11.38 11.57
0.00 0.00 1.44 1.61 1.80
9.37 9.37 9.37 9.37 9.37
10.37 10.98 11.21 11.38 11.57
0.00 1.61 1.84 2.01 2.20
9.67 9.67 9.67 9.67 9.67
10.37 10.98 11.21 11.38 11.57
0.00 0.00 1.54 1.71 1.90
25+400
25+500
25+600
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.99 9.99 9.99 9.99 9.99
9.06 9.32 9.58 9.77 10.01
0.00
9.78 9.78 9.78 9.78 9.78
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.00 -0.01 0.23
9.51 9.51 9.51 9.51 9.51
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.07 0.26 0.50
-0.22 0.02
25+700
Halang Creek (25+790)
25+900
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.03 9.03 9.03 9.03 9.03
9.06 9.32 9.58 9.77 10.01
0.04 0.30 0.56 0.74 0.98
8.73 8.73 8.73 8.73 8.73
9.06 9.32 9.58 9.77 10.01
0.34 0.60 0.86 1.05 1.29
8.88 8.88 8.88 8.88 8.88
9.06 9.32 9.58 9.77 10.01
0.18 0.44 0.70 0.89 1.13
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 38
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 26+000
26+100
26+200
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.31 9.31 9.31 9.31 9.31
9.06 9.32 9.58 9.77 10.01
0.00 0.01 0.27 0.46 0.70
9.61 9.61 9.61 9.61 9.61
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.00 0.16 0.40
9.47 9.47 9.47 9.47 9.47
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.11 0.30 0.54
26+300
26+400
26+500
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.42 9.42 9.42 9.42 9.42
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.16 0.35 0.59
9.51 9.51 9.51 9.51 9.51
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.07 0.26 0.50
9.52 9.52 9.52 9.52 9.52
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.06 0.25 0.49
26+600
26+700
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.62 9.62 9.62 9.62 9.62
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.00 0.15 0.39
12.52 12.52 12.52 12.52 12.52
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.00 0.00 0.00
CASE 2. WITH DREDGING OF BALANTE CREEK 24+200
24+400 Emerald Station
24+300
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
10.616 10.616 10.616 10.616 10.616
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.00 0.00 0.304
10.24 10.24 10.24 10.24 10.24
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.00 0.28 0.68
10.10 10.10 10.10 10.10 10.10
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.00 0.42 0.82
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 39
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT
24+500
24+600
24+700
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.84 9.84 9.84 9.84 9.84
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.27 0.68 1.08
9.76 9.76 9.76 9.76 9.76
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.35 0.76 1.16
9.93 9.93 9.93 9.93 9.93
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.18 0.59 0.99
24+800 Return Period (Yrs.) 5 10 25 50 100
Balante Creek 24+890
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
10.31 10.31 10.31 10.31 10.31
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.00 0.21 0.61
10.40 10.40 10.40 10.40 10.40
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.00 0.12 0.52
10.01 10.01 10.01 10.01 10.01
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.00 0.51 0.91
25+100 Return Period (Yrs.) 5 10 25 50 100
25+200
25+300
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
9.77 9.77 9.77 9.77 9.77
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.34 0.75 1.15
9.37 9.37 9.37 9.37 9.37
9.47 9.52 10.11 10.52 10.92
0.00 0.15 0.74 1.15 1.55
9.67 9.67 9.67 9.67 9.67
9.47 9.52 10.11 10.52 10.92
0.00 0.00 0.44 0.85 1.25
25+400 Return Period (Yrs.) 5 10 25 50 100
25+000
25+500
25+600
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
9.99 9.99 9.99 9.99 9.99
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.00 0.00 0.02
9.78 9.78 9.78 9.78 9.78
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.00 0.00 0.23
9.51 9.51 9.51 9.51 9.51
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.07 0.26 0.50
Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 40
HYDROLOGICAL AND DRAINAGE INVESTIGATION REPORT 25+700
Halang Creek (25+790)
25+900
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.03 9.03 9.03 9.03 9.03
9.06 9.32 9.58 9.77 10.01
0.04 0.30 0.56 0.74 0.98
8.73 8.73 8.73 8.73 8.73
9.06 9.32 9.58 9.77 10.01
0.34 0.60 0.86 1.05 1.29
8.88 8.88 8.88 8.88 8.88
9.06 9.32 9.58 9.77 10.01
0.18 0.44 0.70 0.89 1.13
26+000
26+100
26+200
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.31 9.31 9.31 9.31 9.31
9.06 9.32 9.58 9.77 10.01
0.00 0.01 0.27 0.46 0.70
9.61 9.61 9.61 9.61 9.61
9.06 9.32 9.58 9.77 10.01
0.00 0.00 -0.03 0.16 0.40
9.47 9.47 9.47 9.47 9.47
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.11 0.30 0.54
26+300
26+400
26+500
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.42 9.42 9.42 9.42 9.42
9.06 9.32 9.58 9.77 10.01
0.00 -0.10 0.16 0.35 0.59
9.51 9.51 9.51 9.51 9.51
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.07 0.26 0.50
9.52 9.52 9.52 9.52 9.52
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.06 0.25 0.49
26+600
26+700
Return Period (Yrs.)
Road Elev.
Flood Elev.
Flood Depth
Road Elev.
Flood Elev.
Flood Depth
5 10 25 50 100
9.62 9.62 9.62 9.62 9.62
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.00 0.15 0.39
12.52 12.52 12.52 12.52 12.52
9.06 9.32 9.58 9.77 10.01
0.00 0.00 0.00 0.00 0.00
The corresponding Flood Depth Map for the 5-years, 10-years, 25-years, 50-years and 100years return period is shown in Annex G. 6.2 Drainage Along Viaduct and at Grade Surface. Schedule of Drainage Structures is Presented Annex H. Consultancy Services for the Civil Works of the LRT Line 2 East (Masinag) Extension Project
Page 41
View more...
Comments
