Flood Prevention in Champasack district, Champasak province

Transcription

1 Flood Prevention in Champasack district, Champasak province Prepared by Khamfeuane SIOUDOM,PhD Lecture and Deputy Head of Research & Post Graduate Faculty of Engineering, National University of Laos

2 Contents 1. The Characteristics of Flood in Champasack district 2. Reduction of Flood Damages in Champasack district 3. Flood Prevention Measures 4. Recommendation for Champasack district 2

3 1. The Characteristic of Flood in Champasack district Develop Quickly Huge Peak Flood - Characteristic of topography, Urbanization Sudden change of Weather Pattern Storm hit and heavy rainfall - the number of Storms be increased Flood develop in the all season 3

4 2. Reduction of Flood Damages Each hydro structure Basin wide Structural measures Structural _ non structural Measures Post-Flood Recovery Pre-Flood Preparation The Quicker response, The less damages 4

5 3. Flood Prevention Measures in Champasack district 1. Structural Measures - Operating Large Dike - Constructing Dike, levees, pumping stations 2. Non Structural Measures - Improving Operation of Dike - Flash Flood Forecast - Flood Risk Map - Expected Annual Damages(EAD) 5

6 Flash Flood Forecast 6

7 Flash Flood Guidance What is FFG? FFG is the amount of rainfall needed in a specified period of time to initiate flooding on small streams Where? FFG is computed for small engaged areas (grids, zones) 7

8 Flash Flood Guidance Forecast Lead Time? FFG is computed for 1-, 3-, and 6-hour durations Use? FFG use zone / small watershed 8

9 Improving Operation of Dike 9

10 Flash Flood Damage 10

11 Flash Flood System Atmospheric Rainfall Forecast Radar/Satellite Threshold Runoff Bank full Discharge Unit Hydrograph Estimations of Soil Moisture State FFG Computation Sacramento Model TOPMODEL 11

12 Threshold Runoff T.R q Q PR p A Where, Qp is bankfull flow [cms] qpr is unit hydrograph peak flow [cms/cm] Qp Computation (1) Manning s Formula (2) 2yr Flood Frequency qpr Computation (1) Unit Hydrograph 12

13 Flash Flood Forecast Model Rainfall Forecast Computed FFG Threshold runoff (R) is fixed in time FFG depends on current rainfall-runoff curve Comparison btw Rain Forecast & FFG Rain Forecast > FFG : FF Warning Rain Forecast < FFG : FF Notice Rain Forecast < < FFG : FF Cancel 13

14 Flood Risk Map 14

15 Flood Mapping Process Area of Flood Prevention 15

16 Flood Mapping Process 16

17 Expected Annual Damages (EAD) 17

18 Risk Analysis 1. Water Resources projects Many types of Uncertainties - Natural Environment : Variability of Rain, Stream flow - Engineered system : Reliability of pumps, gates, levees, dike - Economic values of Floodplain property : Probability distribution on Flood frequency 18

19 Risk Analysis 2. Uncertainty : A lack of Sureness synonym : Doubt, Dubiety, Skepticism -With respect to natural phenomena an outcome is unknown -With respect to a belief a conclusion is not proven -With respect to a course of action a plan is undecided Uncertainty can be described by Probability distribution 19

20 Expected Annual Damages 20

21 4. Recommendation for Champasack district 1. Construction Hydro structures, Riverbank protection or Dike - Upstream Tributaries - Small_Medium size 2. Non structural Measures - Service Real time Flood information to users (Flood Analysis model, Real time operation system) - Distribution of Flood Risk Map - Flash Flood Forecast 21

22 Bank full stage is river water level below overflow range. Flood-prone area gets inundated by river overflow. 22

23 Stream profile view (top). Stream plan view (middle). Stream crosssection (bottom). 23

24 Maintenance of equilibrium river meander geometry based on bank full flow, which is below flood overflow levels. 24

25 Design criteria for maintenance of equilibrium river meander geometry based on bank full flow level. Top: wavelength, amplitude Left: scour depth, radius of curvature 25

26 Meandering river at bankfull levels - e.g. River. Cut-off channels are not recommendable since meandering will reestablish again. 26

27 Causes and Reasonability occurs after reducing water level in Mekong River Assumption of Erosion Mechanism A) : Notch Formation Type B) : Undermining and Surface Mass Separation Type C) : Sliding Type Sheet Actually, Combination of above types, enforced by piping and residual pore pressure. Major Riverbank erosion occurs in Flood Recession Period. 27

28 Erosion Type A Top Soil Silty Clay /Sand Soil Mass Falling Down Notch Formation Silty Gravel layer 28

29 Erosion Type B Fissures Top Soil Soil Mass Separation/Fall Down Silty Clay/Sand Alternation of Gravelly Silt And silty clay 29

30 Erosion Type C Fractures Sediment Soil Sliding 30

31 Thank you for your attention.