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

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

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

ASCII- Input lidar file format

Text file format– Simple– Large file size

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

Loading Data: LAS To Multipoint Tool

LAS = industry standard file format for lidar

•Multipointsused for efficiency•Filter options

-By class-By return

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

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.

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.

Point to Raster Post-process: Void FillingPoint

Con(IsNull([pt2ras]), FocalMean([pt2ras], Rectangle, 3, 3, DATA), [pt2ras])

Terrain to Raster

Quality•Supports ancillary data

(breaklines, water bodies, etc.)

•True interpolation•Can handle large datasets

DEM with breaklines: Phase I, Louisiana

LIDAR Project

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)

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

Flow Accumulation map

DEMFill Sink

Flow directionFlow Accumulation

Stream Definition

Catchment GridDrainage lineOutlet

SoilLand use

Curve Number

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

Mitigation measures

Identification and removal of obstruction in drains

and rivers

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

Regrading and lowering the drain and river beds

optimally

Creation of additional storage beyond project

area

Prevention of unscrupulous dumping of

solid waste in waterbodies and

waterways

Encouraging Artificial recharge and

Rainwater Harvesting