Flash Flood Risk Management â A Training of Trainers ... - ReliefWeb

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Flash Flood Risk Management: A Training of Trainers Manual Figure 14: Slope area method Session 13 Flood level Day Three Flow area = A Wetted perimeter = P Nature of the bed = n Slope = S Source: Shrestha (2008) where n is the Manning coefficient, R is the hydraulic radius, and S is the longitudinal slope (see Figure 14). The steps for estimating discharge using the slope area method are as follows: Step 1: Select as straight a section of the river with as uniform a slope, cross-section, and roughness as possible. Step 2: Conduct a detailed survey of the river reach, and estimate its Manning roughness coefficient, n. The Manning coefficients are given in Table 9. The highest flood mark should also be recorded. Step 3: Calculate the flow area A and determine the wetted perimeter P using the survey data. The longitudinal slope also needs to be taken into account. The hydraulic radius, R is calculated using R = A/P. The values obtained are used to calculate the flow velocity during the flash flood using the Manning equation. Then the discharge, Q, is calculated using Q = A x V. RM 13.4: Flood routing and calculating hydrographs at different locations Flood routing Flood routing is a procedure used to determine the time and magnitude of flow at a given point on a water course; it uses known or assumed flood parameters at one or more points upstream. The methods used to calculate the parameters are described above. Flood routing can provide information such as the impact of the flood at the locations of communities and settlements downstream of the catchment outlet. It is a highly technical procedure and various computer software programs are available to calculate this complicated flood routing. 86
Day 3 There are two types of routing, hydrologic and hydraulic routing. Both of these methods use some form of the continuity equation. Hydrologic routing. Hydrologic routing methods combine the continuity equation with some relationship between storage, outflow, and inflow. These relationships are usually assumed, empirical, or analytical in nature. An example of such a relationship might be a stage-discharge relationship. Session 13 Hydraulic routing. Hydraulic routing methods use the continuity equation in combination with other physical relationships that describe the physics of the movement of the water. The momentum equation is the one most commonly used. In hydraulic routing analysis, it is intended that the dynamics of the water or flood wave movement is more accurately described. Table 9: Values of the Manning coefficient Manning Typical appearance Manning Typical appearance n value n value Source: USGS (no date) 87
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Flash Flood Risk Management A Train
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Published by International Centre f
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Foreword The Hindu Kush-Himalayan (
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Acronyms and Abbreviations CFFRMC D
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Flash Flood Risk Management - A Tra
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Introduction Day 1 Session/Activity
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Day 1 Suggestions for the facilitat
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Day 1 Suggestions for the facilitat
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Day 1 Session 2 Flash Flood Hazards
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Day 1 Session 2 Resource Materials
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Day 1 RM 2.4: Flash floods in the H
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Day 1 in flash floods during the pe
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Day 1 Activity 3.2: Identifying the
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Day 1 Figure 4: Categorisation of f
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Day 1 Session 4 Flash Flood Hazard
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Day 2 Session/Activity Session 5: V
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Day 2 Activity 5.2: Flash flood ris
Page 43 and 44: Day 2 In a physically vulnerable zo
Page 45 and 46: Day 2 Step 2 Show the short video o
Page 47 and 48: Day 2 Session 6 Handouts Handout 6.
Page 49 and 50: Day 2 Figure 8: The four pillars of
Page 51 and 52: Day 2 • As a result of rapid cha
Page 53 and 54: Day 2 Session 7 Community-Based Fla
Page 55 and 56: Day 2 Step 4 Step 5 Discuss the dif
Page 57 and 58: Day 2 Figure 10: Framework for comm
Page 59 and 60: Day 2 • First-aid and health: Th
Page 61 and 62: Day 2 Session 8 Gender Perspectives
Page 63 and 64: Day 2 The CFFRMC also plays a role
Page 65 and 66: Day 2 Note to the trainer Clarify t
Page 67 and 68: Day 2 groups such as people with di
Page 69 and 70: Day 2 RM 9.3: Process of participat
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Page 73 and 74: Day 3 Activity 10.3: Strategies for
Page 75 and 76: Day 3 RM 10.2: Various strategies f
Page 77 and 78: disseminated. The South Asian tsuna
Page 79 and 80: Day 3 Session 11 Resource Materials
Page 81 and 82: Day 3 Geospatial Stream Flow Model
Page 83 and 84: Day 3 Activity 12.2: Concept and co
Page 85 and 86: Day 3 perspective means looking for
Page 87 and 88: Day 3 their livelihoods. Watershed
Page 89 and 90: Day 3 Session 13 Hazard-Specific Fl
Page 93: Day 3 where Q = discharge A = area
Page 97 and 98: Day 3 Box 13: Exercise on flood rou
Page 99 and 100: Day 3 Activity 14.4: Measures that
Page 101 and 102: Day 3 Figure 15: Types of landslide
Page 103 and 104: Day 3 occurs). In most documented c
Page 105 and 106: Day 3 Figure 21: Tsatichhu landslid
Page 107 and 108: Day 3 Estimating downstream floodin
Page 109 and 110: Day 3 Strand (1977) uses the same e
Page 111 and 112: Day 4 Session/Activity Session 15:
Page 113 and 114: Day 4 Session 16 Hazard-Specific Fl
Page 117 and 118: Day 4 Figure 25: Development of the
Page 119 and 120: Day 4 RM 16.3: Impacts of GLOF even
Page 121 and 122: Day 4 Supra or englacial drainage.
Page 123 and 124: Day 4 Briefing for the Field Trip T
Page 125: Days 5, 6, and 7 Field Trip
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Flash Flood Risk Management: A Trai
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