flood mapping via hec-ras model and arcgis

PowerPoint Presentation

Flood Studies in Lower Mekong River Cambodia via HEC-RAS and ArcGISBy: KIM Lengthong

Advisor: Dr. LY Sarann

2015-2016

Institute of Technology of Cambodia

Department of Rural Engineering

Good afternoon professors, lecturer and everyone here. Thank for coming.My name Kim LengthongPresent my research thesis on the topic Flood studies at Lower Mekong river Cambodia under supervived Dr. Ly Sarann

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OutlinesIntroductionMaterials and MethodsResults and DiscussionsConclusions and Recommendations 2Flood Studies by using HEC-RAS

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Why flood studies?

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Source: National Committee of Disaster Management, 2015 Objectives of the studyEvaluate HEC-RAS model performanceProduce flood maps from 2000 to 2013 at peak flow Produce 10-years flood return period mapAssess the critical result from map

Flood Studies by using HEC-RAS

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4LocationFrom Chbar ampov to Korkir Thom commune, Kean Svay(approximate 50 km)

Data collection

DEM 30m cell size from STRM 18 cross sections (ADCP measurement on 24th May 2015)Manning roughness (n)

Study AreaFlood Studies by using HEC-RAS

Discharge

5Water level in 2009, 2010 and 2012 were missing.

Flood Studies by using HEC-RAS Lower Mekong River at Koh Norea Q = 976.147(H-0.428)1.494 Available discharge and water level at Koh Norea Station

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Pre-Process

Post-Process

HEC-RAS 4.1

RAS-Geometry

Water Surface Profile

1.Edit and Enter Manning Value

2. Input river flow data

3.Steady flow withsubcritical RUNArcGISModel FrameworkFlood Studies by using HEC-RAS

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Results of inundated area were evaluated by fit values: F1 and F2 (V. Moya Quiroga et al., 2016)

- A is the total flooded area that predicted correctly by model- B is the total area that over predicted by the model - C is the total area that is under predict by the model

Water Level was evaluated by index error (Moriasi et al.,2007)

7Model Performance Evaluation

Satisfactory criteria: NSE > 0.50 and RSR < 0.60, PBIAS = [-25%;25%] The satisfactory value:F1 and F2 > 0.5Flood Studies by using HEC-RAS

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Model Simulation Performance Rating8

Simulated output on 24th August 2008 Observed flood on 24th August 2008Source: UNOSAT,2008F1= 0.86F2= 0.74

1st Note: Affected area from simulation is greater except in Sambour commune.


9NSE = 0.992101PBIAS = 0.234619 RSR = 0.088878

2nd Note: The water level from simulation is less than observation except 2005, 2006 and 2007 .The result from HEC-RAS flow came out of bank earlier than actual and the water surface elevation is a bit lower than in real situation (Goodell & Warren, 2006).


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Results from 2000-2013Flood Studies by using HEC-RASVideo Playback

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From 2000 until 2013, the affect area ranged from 1,400 to 8,000 hectares (excluding river area 4600 ha), while water level fluctuated from year to year. Flood Studies by using HEC-RAS

1210-years return period flood mapThe inundated area was about 8000 hectares and flood depth range from 0.05 mm to 11 m (at the bottom of river). The 10-years return period inundation map is really important for planning, development project, and industries. Flood Studies by using HEC-RAS

Now we move to 10-year return period flood map. Its is the map that expressed the greatest flood that occurred in this location. Based on above map, we could get the affected area along the river was around 8000 hectares while the flood depth was ranged from 0.05 mm to 11 meters. These result would be useful for development project, planning, and also investment since they know the maximum flood so they can take the affected into their decision making for their project. 12

13ConclusionsBased on results of model evaluation, HEC-RAS model is capable flood studies for Mekong river and produce flood mapThe affected area for the both sides of river was ranged from 1,400 to 8,000 hectares while flood depth varied from year to year.

RecommendationsHigh resolution of DEM is recommended At place water level and more surveying cross-sections are neededThe study should account with islands along the riverHEC-HMS or SWAT should be used to simulate surface runoffHEC-RAS version 5.1 is recommended for future study


Thank you for your attention14