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Transcript of Floodplain_Analysis_of_Cagayan_de_Oro_River_Basin
River Basin 1. To assess flood frequency for the assessment of flooding potential of Cagayan de Oro City.
2. To build hydrologic model for the Cagayan de Oro River Basin
3. To analyze the floodplain using steady flow one-dimensional model.
4. To prepare flood inundation map
5. To evaluate the potential non-structural mitigation option Project location: Motivation: A Master Thesis Presentation by
KELVIN MABAO-WAREM Precipitation frequency Analysis: Hydrologic Model Hydraulic Model Objectives: Precipitation Frequency Analysis Hydrologic Model Hydraulic Model Inundation Map Precipitation Data: Probable Point Rainfalls Rainfall-Intensity-Duration-Frequency Curve Design Precipitation Hyetograph Alternating Block Method HEC-HMS Hydrologic Engineering Center-HYdrologic Modeling System Tool Description -Simulates precipitation-runoff processes of a watershed system -Components of hydrologic cycle such as precipitation, evapotranspiration, infiltration and runoff are computed
using deterministic mathematical modeling -A watershed model is built by separating the hydrologic cycle into manageable pieces and constructing boundaries around them.
-HEC-HMS uses separate model to represent each component of the runoff process. These models compute the volume of the precipitation that falls
on the ground which infiltrates on pervious surfaces, how much volume runs off the pervious surface and volumes runs off off the
impervious surfaces and the time runoff starts. Models that compute runoff volume; Models of direct runoff; Direct runoff models describes what hapens as water that has not infiltrated or been stored on the watershed Models of Baseflow; Baseflow models simulate the slow subsurface drainage of water from the system into the channels Models of Channel Flow; These routing models simulate 1-dimensional
open channel flow SCS Curve Number Loss Model The Soil Conservation Service (SCS) Curve Number (CN)
model estimates precipitation excess as a function of cumulative precipitation, soil cover, landuse, and antecedent moisture. Curve Number -It is essentially a coefficient that reduces the total precipiation to runoff potential, after "losses"-evaporation, absorption, surface storage.
-The higher the CN value the higher the runoff potential will be SCS UH -Emperical model based on traditional unit hydrograph. -These empirical models attempt to establish a causal linkage between runoff and excess precipiation without detailed consideration of internal process -assumes that the watershed UH is a single-peaked hydrograph Muskingum-Cunge -The model is based upon solution of the continuity equation and diffusion form of momentum equation
-A physically-based routing model Hydrologic Model Building There are several ways of developing watershed networks in HEC-HMS:
-Manually in HEC-HMS GUI
-Combination of two in which watershed networks are created in HEC-HMS while its properties are derived from GIS. HEC-GeoHMS -Uses ESRI's ArcGIS for Desktop Basic and the Spatial analyst to develop modeling inputs for HEC-HMS. It is capable of creating background map files, basin model files and a grid cell model file from ana existing Digital Terrain model (DTM) and other corresponding datasets for developing hydrologic model. Stream- Length, slope, downstream connection
Watershed-Area, slope, curve number, lag time Topographic data are need to develop the watershed properties.
-Geospatial datasets usch as those Digital Elevation Model HEC-GeoHMS Processing DEM needs to be processed first before it can be used in HEC-GeoHMS. ArcHydro Tools or Spatial Analyst can be used for preprocessing and creating layers discussed below: Watershed Characteristics Hydrologic Parameter Estimation SCS Curve Number Method as the loss model The production of curve number grid file requires landuse and soil classification Landsat ETM + Band 7,4,2 and 8 Landcover/Landuse derived from NDVI using thematic bands 4 and 3 Soil type CURVE NUMBER Routing Method Muskingum-Cunge parameters: derived from DEM:
-side slope Transform Method -Lag time, the length of time between the centroid of rainfall
excess and the peak flow of the resulting hydrograph were
computed using the CN LAG Time function in GeoHMS.
-37.5% of the runoff volume occurs before the peak flow and the lag time can be approximated by taking 60% of the time of concentration. Meteorologic Model Control Specifications Simulation Runs HEC-RAS Hydrologic Engineering Center-River Analysis System Tool Description HEC-RAS is an integrated system of software designed for interactive use in a multi-tasking. multi-user network environment. The system comprises the graphical user interface (GUI), separate hydraulic analysis components, data storage and management capabilities, graphics and reporting facilities. Capable of performing 1-D analysis for:
Steady flow water surface profile
Unsteady flow simulation
Movable boundary sediment transport computation
Water quality analysis Hydraulic MOdel Building There are several way to build a hydraulic model in HEC-RAS:
1. Do a physical survey and collect river geometry data manually
2. USe geospatial datasets like DEM and develop geometric data in GIS
3. Use both physical survey data ang geospatial datasets derived from DEM HEC-GeoRAS Preparation of TIN GeoRAS Preprocessing Simulation Results GeoRAS Post Processing RAS GIS Import file had to be exported to GeoRAS
-Stream network, cross section data, bank station data will be read and shapefiles are automatically created. Based on the water surface elevation attached to each cross section, a waters surface TIN is created Floodplain delineation then will use this water surface TIN and terrain model to calculate the floodplain boundary and inundation depths. The floodplain delineation method rasterizes the water surface TIN and compares it to the DTMGrid. The floodplain is calculated where the water surface is higher than the terrain grid. inundation depth grid is the result from the water surface and terrain grid comparison APPLICATIONS CONCLUSION RECOMMENDATION FOR FUTURE WORKS