DEPARTMENT OF PUBLIC WORKS AND HIGHWAYS JAPAN INTERNATIONAL COOPERATION AGENCY MANUAL ON FLOOD CONTROL PLANNING MARCH 2003 Project for the Enhancement of Capabilities in Flood Control and Sabo Engineering of the DPWH MANUAL ON FLOOD CONTROL PLANNING Table of Contents MESSAGE ................................................................................................................. VII FOREWORD............................................................................................................. VIII ACKNOWLEDGEMENT............................................................................................... X CHAPTER 1 INTRODUCTION ...................................................................................1 CHAPTER 2 FLOODING IN THE PHILIPPINES.........................................................4 2.1 Topography......................................................................................................4 2.2 Climate ............................................................................................................6 2.2.1 Hydrologic Region.....................................................................................6 2.2.2 Annual Rainfall Distribution .......................................................................9 2.3 Rvers in the Philippines ...................................................................................9 2.4 Flood Damage...............................................................................................11 CHAPTER 3 FLOOD CONTROL PLANNING...........................................................14 3.1 Necessity of Flood Control Plan ....................................................................14 3.2 Design Flood Frequency................................................................................14 3.3 Procedures for the Formulation of Flood Control Plan ...................................16 CHAPTER 4 DESIGN DISCHARGE.........................................................................20 4.1 Procedure in the Determination of the Design Discharge...............................20 4.2 Catchment Area.............................................................................................21 4.3 Reference Point.............................................................................................22 4.4 Specific Discharge.........................................................................................22 4.5 RUNOFF MODEL..........................................................................................24 4.5.1 Rational Formula.....................................................................................24 4.5.2 Unit Hydrograph Method.........................................................................34 48CHAPTER 5 FLOOD CONTROL ALTERNATIVES AND DESIGN DISCHARGE DISTRIBUTION...........................................................................................................48 5.1 Design Discharge Allocation..........................................................................48 5.1.1 Flood Control Measures..........................................................................48 5.1.2 Allocation Procedure in Flood Control Planning ......................................50 5.2 Modeling of Discharge allocation to Flood control facilities/measures............52 5.2.1 Runoff Model for Alternatives ..................................................................52 5.2.2 Modeling of Effect by Flood Control Facilities..........................................52 5.3 Design Discharge distribution ........................................................................56 CHAPTER 6 RIVER CHANNEL IMPROVEMENT ....................................................58 6.1 Goal of River Channel Improvement..............................................................58 i 6.2 River and Segment........................................................................................58 6.2.1 Classification of River Segment ..............................................................58 6.2.2 River Characteristics Corresponding to River Segment ..........................60 6.3 Existing River Channel ..................................................................................75 6.3.1 River Characteristics...............................................................................75 6.3.2 Flow Capacity .........................................................................................84 6.4 River Channel Planning .................................................................................86 6.4.1 Planning Procedure ................................................................................86 6.4.2 Improvement Stretch...............................................................................86 6.4.3 River Channel Route...............................................................................87 6.4.4 Water Level Computation........................................................................88 6.4.5 Alignment..............................................................................................110 6.4.6 Longitudinal Profile ............................................................................... 111 6.4.7 Cross-Sectional Plan ............................................................................113 GLOSSARY OF TERMS ...........................................................................................118 REFERENCES .........................................................................................................123 ii List of Tables Table 2.1 18 Major River Basins....................................................... 9 Table 2.2 Summary of Typhoon and Flood Damage......................... 11 Table 2.3 Destructive Tropical Disturbance and Corresponding Casualties................................................. 12 Table 2.4 List of River Basins with Records of Most Casualties........ 13 Table 3.1 Sample of Design Flood Frequency ................................ 15 Table 3.2 River Cross-Sectional Survey Interval............................... 18 Table 4.1 Constant for Regional Specific Discharge Curve............... 22 Table 4.2 Runoff Coefficient Used in the Philippines ........................ 26 Table 4.3 Runoff Coefficient Applied for Metro Manila ...................... 26 Table 4.4 Percentage of Land Use Category (Example)................... 27 Table 4.5 Kraven’s Formula.............................................................. 29 Table 4.6 Computation of Direct Runoff by Unit Hydrograph Method................................................... 37 Table 4.7 Design Hyetograph by Alternating Block Method .............. 42 Table 5.1 Flood Control Measures.................................................... 48 Table 5.2 Allocation of Target Discharge (Example)......................... 51 Table 6.1 Classification of River Segment and its Characteristics..... 60 Table 6.2 Type and Cause of Bank Erosion...................................... 68 Table 6.3 Interval of Cross Sectional Survey .................................... 98 Table 6.4 Values of Manning’s Roughness Coefficient “n”................ 100 Table 6.5 Location of Primary and Secondary Tidal Gauge .............. 102 Table 6.6 Recommended River Width .............................................. 113 Table 6.7 Minimum Required Freeboard for Dike ............................. 114 List Figures Figure 2.1 Topography ...................................................................... 5 Figure 2.2 Climatological Map............................................................ 7 Figure 2.3 Mean Annual Rainfall........................................................ 10 Figure 4.1 Design Discharge Estimation Method ............................... 20 Figure 4.2 Illustration to Read Specific Discharge.............................. 23 Figure 4.3 Example of Land Use Category ........................................ 27 ii i Figure 4.4 Inlet and Outlet Points of Rational Formula....................... 28 Figure 4.5 Sample River with Contour Lines...................................... 30 Figure 4.6 Computation of Unit Hydrograph....................................... 36 Figure 4.7 Runoff Model for San Juan River Basin ............................ 38 Figure 4.8 Design Hyetograph by Alternating Block Method .............. 42 Figure 4.9 SCS Unit Hydrograph ....................................................... 43 Figure 4.10 A Triangular Unit Hydrograph .......................................... 44 Figure 4.11 Concentration Time for Residual Subbasin ....................... 45 Figure 4.12 Baseflow........................................................................... 46 Figure 4.13 Lag and Attenuation due to Channel................................. 46 Figure 5.1 River Improvement............................................................ 47 Figure 5.2 Reduction of Flood Peak Discharge by Dam/Retarding Basin ................................................... 50 Figure 5.3 Comparative Cost Analysis of Alternatives (Example)....... 51 Figure 5.4 Runoff Basin Model........................................................... 52 Figure 5.5 Typical Discharging by Dam ............................................. 53 Figure 5.6 Simple Outflow Structure of Dam ...................................... 53 Figure 5.7 Composition of Outlet Flow and Spillway Flow.................. 55 Figure 5.8 Flood Control by Retarding Basin ..................................... 56 Figure 5.9 Design Discharge Distribution