gi 476 design project – first review
DESCRIPTION
TRANSCRIPT
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GI 476 DESIGN PROJECT – First Review
DEM analysis for Flood management of Lidar data
Creation of a custom geoprocessing tool in ArcGIS
Bharathkumar S, Delvin N Diance, Jayakrishnan V & Kabil K
Under the tutelage of
Asst. Prof. Dr.K. Thirumalai Vasan
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Overview• Definition of Objectives• The problem of flooding in urban
areas• Study and collection of different Lidar
file formats• Creation of Python script tool for
iterative loading of the Lidar data into ArcGIS and for creating lidar tiles
• Study of ArcGIS supported formats for processing Lidar data
• Creation of a modelbuilder tool for automating the analysis
• Study of available mathematical flow models and required thematic layers for the analysis
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Definition of objectives• To create a custom geoprocesing tool
to automate the procedure of – Performing flood analyses using
hydrological – Creation a quick response tool that
simulates the flood area extent– Preparation of flood hazard maps and
evacuation maps based on more accurate flow models and utilities
using Lidar data and other thematic layers in ArcGIS
•To propose structural changes and mitigation measures for a highly urbanized city like Chennai to manage flood effectively
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ASCII- Input lidar file format
Text file format– Simple– Large file size
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Point File Information Tool
Inputs files (LAS and ASCII) and folders of files and outputs a polygon feature class.
Each output record includes-Polygon of file’s data extent-Source filename-Point count-Point spacing estimate-Z min-Z max
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Loading Data: LAS To Multipoint Tool
LAS = industry standard file format for lidar
•Multipointsused for efficiency•Filter options
-By class-By return
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Loading Data: ASCII 3D To Feature Class Tool
•Points, lines, polygons•Recommendations:
-Use ASCII as ‘open’ format for breakline data (otherwise shapefile)
-Use LAS for lidar points
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Point to Raster Tool
Used after points are loaded into geodatabase
•More detailed assessment than Point File Information
•Based on actual points loaded(i.e., filtered by class code or return) rather summary of entire file.
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Point to Raster Tool
Fast•Rasterizebased on multipoint
vertex z•Not true interpolation•Doesn’t support breaklines•Data gaps•Arguably works best with
1streturn data because there are fewer and smaller data voids to deal with.
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Point to Raster Post-process: Void FillingPoint
Con(IsNull([pt2ras]), FocalMean([pt2ras], Rectangle, 3, 3, DATA), [pt2ras])
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Terrain to Raster
Quality•Supports ancillary data
(breaklines, water bodies, etc.)
•True interpolation•Can handle large datasets
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DEM with breaklines: Phase I, Louisiana
LIDAR Project
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Surface Difference Tool
Subtract lidarbased ground surface from modeled (e.g., HEC-RAS) water surface
•Output polygons used to delineate floodplain•Optional output of depth surface(s)
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Literature review: Flood Forecasting
• Flood forecasting can be done using hydrological stream flow models
• These models use rainfall, topography, soils and land cover to model stream flow
• The FEWSNET SFM was developed to use satellite rainfall estimates and rainfall forecasts to– model streamflow– estimate when streamflow exceeds bankful– highlight subbasins at risk of flooding (from above)
• Can give up to a few days flood warning
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Flow Accumulation map
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DEMFill Sink
Flow directionFlow Accumulation
Stream Definition
Catchment GridDrainage lineOutlet
SoilLand use
Curve Number
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Mathematical Flow model
HEC-HMS, HEC-RAS, MIKE21 Validation
Selection of Thematic Layers
Flow Model
Artificial Ground water
recharge
Selection of
Mitigation technique
s
Flood risk
zonation
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Mitigation measures
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Identification and removal of obstruction in drains
and rivers
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Continuous removal of sandbar obstruction at sea mouths of the
estuaries to the required bed level for avoiding the breaking of waves that would reduce the littoral drift
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Regrading and lowering the drain and river beds
optimally
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Creation of additional storage beyond project
area
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Prevention of unscrupulous dumping of
solid waste in waterbodies and
waterways
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Encouraging Artificial recharge and
Rainwater Harvesting