hydro-enhancement of lidar data to support floodplain modeling 2011 asfpm annual conference...

Hydro-enhancement of LiDAR Data to Support Floodplain Modeling

2011 ASFPM Annual ConferenceLouisville, Kentucky

May 18, 2011

Mark W. Ellard, PE, CFMAssociate, Water Resources

Edward C. Beute, PSM, CPVice President LiDAR Operations

Presentation Outline

Role of LiDAR in Watershed Modeling

Hydrological Representation of LiDAR

Issues with LiDAR & Modeling

LiDAR Data Collection & Classification Overview

LiDAR Hydro-enhancement

Modeling Results Impact

• Detailed Surface Representation

• Digital Data Source

• Easy to Update Incrementally (i.e., New Development, etc.)

• Easy to Take for Granted

Role of LiDAR in Watershed Modeling

Role of LiDAR in Watershed Modeling

Inundation

Calibration & Verification

Surface Storage & ConveyanceRepresentation

Hydrological Response – Rainfall Excess Estimation

Detailed Topographical Representation

Flood Model Foundation

• GIS Processing for Model Parameterization

– Catchment / Basin Delineation

– Storage Extraction

– Cross-section Extraction

– Flow Path Tracking

– Floodplain Inundation

Hydrological Representation of LiDAR

• Conditions in Florida that Cause Problems– Non-Dendritic Watersheds– Flat Topography– Thick Vegetation Obscures Ground Surface

• Misrepresentation of Storage– Lakes / Ponds – Initial Stages– Sloped Water Surfaces (rivers, canals, etc.)– Affects Estimates of Floodplain Depth

• Misrepresentation of Conveyance– Channels– Overland Flow– Inaccuracies in Floodplain Depth and Flow

Issues with LiDAR & Modeling

Issues with LiDAR & Modeling

Issues with LiDAR & Modeling

Issues with LiDAR & Modeling

Issues with LiDAR & ModelingSurvey Enhancement of Conveyance Features

(Ditches, Canals, etc.)

• Laser scanner, Survey Grade GPS Receivers, Inertial Measurement Unit (IMU), Aircraft

• Processing Computers, Proprietary Software• Collection is project specific which determines

altitude, ground speed, pulse rate repetition, and point density.

• Every project must have a boresite calibration flight

LiDAR Data Collection & Classification Overview

LiDAR Collection Process

LiDAR Data Collection & Classification Overview

• Data extraction• Processing of trajectory for position and orientation

of the sensor• Pre-processing data using proprietary software• Output data in LAS format in project specific

coordinates and units

LiDAR Data Collection & Classification Overview

LiDAR Processing

• Off The Shelf (TerraScan) or proprietary software• Automated Routines using a set of parameters

designed to model the bare earth ground and other useful information

• Terrain specific parameters• Allows for batch processing of a project

LiDAR Data Collection & Classification Overview

Classification Process

• Automated routines will correctly model most of the project

• Some conditions do not meet the criteria set up in the automated routines

• Labor intensive manual classification is necessary for the remainder

• It is labor intensive is necessary where conditions for automated routines are not met

LiDAR Data Collection & Classification Overview

Classification Process

Some common errors:Over filtering the data• data is smoothed showing no artifacts• valuable ground information is missing

Under filtering the data• data is noisy due to artifacts • Non-ground added to the ground

Modeling is compromised in both scenarios

LiDAR Data Collection & Classification Overview

Classification Process

LiDAR Hydro-enhancement

Original Data Enhanced Data

LiDAR Hydro-enhancement

LiDAR Hydro-enhancement Classifications as Delivered

Orange = Bare Earth

LiDAR Hydro-enhancement Classifications after Hydro-enhancement

Orange = Bare Earth

LiDAR Hydro-enhancement Classifications as Delivered

Orange = Bare Earth

LiDAR Hydro-enhancement Classifications after Hydro-enhancement

Orange = Bare Earth

LiDAR Hydro-enhancement

Classifications as Delivered Classifications after Hydro-enhancement

LiDAR Hydro-enhancement

Classifications as Delivered Classifications after Hydro-enhancement

LiDAR Hydro-enhancement

Classifications as Delivered Classifications after Hydro-enhancement

LiDAR Hydro-enhancement

• Examine the data for suitability by identifying holidays, voids, and point density

• Consider enhancement of data through reclassification to obtain additional ground points, identify structures and separate vegetation by height

• Supplement or create new 3D break lines using Direct Terrain Extraction techniques (QCoherent LP360, Cardinal Systems VrLiDAR)

LiDAR Hydro-enhancement

Points to Consider

Modeling Results ImpactAerial

Note Dense Vegetation Along

Channel

Modeling Results Impact

Original

Modeling Results Impact

Enhanced

Modeling Results Impact

Original

Modeling Results Impact

Enhanced

• Example Conveyance Feature

Modeling Results Impact

• Example Conveyance Feature

Modeling Results Impact

Modeling Results Impact

• Model Node Stage Impact• Higher Flood Risk Indicated

• 100 Year – 72 Hour Simulation: Time – Stage Plot

OriginalEnhanced

• LiDAR plays an Important Role in Current Floodplain

Modeling Efforts

• Proper Classification of Ground Points is Critical

– Properly Define Conveyance ways

– Properly represent Storage

• Hydro-enhancement Improves Surface Representation

• Better Representation Increases Model Accuracy

Conclusions

Thank You !Mark Ellard, PE, CFM Associate, Water Resources mellard@geosyntec.com

Thomas Amstadt, PE, CFM Professional, Water Resources tamstadt@geosyntec.com

Edward Beute, PSM, CPVice President LiDAR Operations e_beute@aca-net.com