Estimating Water Volumes in

High Plains Playa Lakes

GIS image classification and analysis

Playas in Texas

• Dominant hydrological

feature of High Plains

• ~20,000 mapped playas

• Important source of

groundwater recharge

• Stop-over points for

migratory waterfowl

• Used for irrigation, forage,

and grazing

• Over 50 years of studies

Playa Features

• Wetland area

defined by soil,

plants, and

hydrology

• Many playas lie

within larger

topographic

depression

• Water area varies

seasonally

Topographic depression

Water area

Wetland area

TWDB Playa Project

BackgroundContinued drawdown of High Plains Aquifer threatens

agricultural economy of the Texas Panhandle

Project Objectives1. Determine volume and distribution of playa water

resources

2. Determine timing and magnitude of recharge under current conditions

3. Assess playa modification strategies to increase recharge

Objective 1: Determine Volume and

Distribution of Playa Water Resource

Two strategies:

• Field monitoring

– Instrument and survey

selected playas

• Remote sensing

– Estimate water

resource region-wide

Field Monitoring

PROs

• Tailored to project objectives

• Continuous observations

• Access to subsurface

• Ground-truth remote/indirect

observations

CONs

• Time consuming

• Expensive

• Continual maintenance,

recalibration

• Access agreements

• Extensive QC and data

management

Field Monitoring

Remote Sensing

PROs

• Data available for free

• Regional coverage

• 30-year archive of imagery

• Work with desk-top tools

CONs

• Clouds

• Limited resolution

• Limited frequency of

observations

ESTIMATING PLAYA WATER

VOLUME

USING REMOTE SENSING AND

GIS METHODS

ESTIMATING WATER VOLUME

A 3-Part Process

1. CLASSIFY WATER AREAS IN PLAYAS USING REMOTE

SENSING METHODS

2. OBTAIN PLAYA WATER SURFACE ELEVATION AND BASIN

TOPOGRAPHY USING GIS METHODS

3. ESTIMATE PLAYA VOLUME USING GIS METHODS

PART 1

CLASSIFY PLAYA WATER AREAS

CLASSIFY PLAYA WATER AREAS

EVALUATE AVAILABLE RS IMAGERY

• 21 Types of Remotely-Sensed Imagery were evaluated

• 17 were eliminated due to: lack of current data, wrong

scale, or simply not a good fit for the type of mapping

inherent to the project

• 4 selected for further consideration: Landsat-4, with

the Thematic Mapper sensor (TM), Landsat-5 TM, and

Landsat-5 Multi-Spectral Scanner (MSS), Landsat-7

EVALUATE AVAILABLE RS IMAGERY (cont.)

× Landsat-4 TM, decommissioned June 2001. (need current data)

�Landsat-5 TM: improved spectral separation and

geometric fidelity, greater radiometric accuracy and

resolution than the MSS sensor. Used to monitor

changes in land surface over periods of months to

years—a near perfect fit for this project!

× Landsat-5 MSS: Landsat-5 TM better fit for this project.

× Landsat -7: The Scan Line Corrector (SLC) in the ETM+ instrument

failed in 2003; good data from 1999 – 2003.

CLASSIFY PLAYA WATER AREAS

Obtain Landsat-5 TM Image

Readily available from

landsat.gsfc.nasa.gov OR

glovis.usgs.gov

User friendly GUI allows

obtaining by coordinates,

satellite row/path, or by

interactively selecting an

area of interest.https://glovis.usgs.gov

CLASSIFY PLAYA WATER AREAS

Obtain Landsat-5 TM Image

CLASSIFY PLAYA WATER AREAS

Evaluate TM Spectral Bands

Band Wavelength, µm Characteristics

1 0.45 to 0.52 Blue-green. No MSS equivalent. Maximum penetration of water,

which is useful for bathymetric mapping in shallow water. Useful for

distinguishing soil from vegetation and deciduous from coniferous

plants.

2 0.52 to 0.60 Green. Coincident with MSS band 4. Matches green reflectance peak

of vegetation, which is useful for assessing plant vigor.

3 0.63 to 0.69 Red. Coincident with MSS band 5. Matches a chlorophyll absorption

band that is important for discriminating vegetation types.

4 0.76 to 0.90 Reflected IR. Coincident with portions of MSS bands 6 and 7. Useful

for determining biomass content and for mapping shorelines.

5 1.55 to 1.75 Reflected IR. Indicates moisture content of soil and vegetation.

Penetrates thin clouds. Good contrast between vegetation types.

6 10.40 to 12.50 Thermal IR. Night time images are useful for thermal mapping and for

estimating soil moisture.

7 2.08 to 2.35 Reflected IR. Coincides with an absorption band caused by hydroxyl

ions in minerals. Ratios of bands 5 and 7 are potentially useful for

mapping hydrothermally altered rocks associated with mineral

deposits.

CLASSIFY PLAYAS WATER AREAS

Landsat-5 TM Subscene, SE Quadrant, Floyd County

(October 15, 2010)

Composite and Detail Views of Enlarged Landsat-5 TM Subscene,

SE Quadrant, Floyd County (October 15, 2010)

Single, Band-5 Selected

• Initial evaluation indicated

single-spectral Band 5

classification provided best

results with minimal

processing

• Grid cells with a value of ≤60

indicate water area

• Field verification scheduled

Landsat-5 TM, Band 5

CLASSIFY PLAYA WATER AREAS

CLASSIFY PLAYA WATER AREASField Verification - 11 May 2011

• Scheduled to coincide with

Landsat-5 image acquisition

• Cloud-free day

• Visual inspection of playas on

transect across study area

• 30 Playas in corridor classified

as wet, wet soil only, or dry

• Attributes overlaid on Landsat

imagery for further review.

Location Map of all

Field-Verified Playas

CLASSIFY PLAYA WATER AREASField Verification—Wet Playas

Landsat-5 TM, Spectral

Band 5 (Wet Playa)Detail of Wet Playa

DETAIL AREA

CLASSIFY PLAYA WATER AREASField Verification—Wet/Dry Playas

Landsat-5 TM, Spectral

Band 5 (Wet/Dry Playa)Detail of Wet/Dry Playa

DETAIL AREA

CLASSIFY PLAYA WATER AREASField Verification--Dry Playas

Landsat-5 TM, Spectral

Band 5 (Dry Playa)Detail of Dry Playa

DETAIL AREA

CLASSIFY PLAYA WATER AREASCreate Final Footprints

• Contour using Spatial

Analyst:

--input raster = Band 5

--contour interval = 60

• Isolines ≠60 removed

and non-playa water

areas clipped

• Remaining feature lines

converted to polygons

using Data Management

Tools in ArcToolBoxWet Playa Footprints, October 15, 2010

PART 2

OBTAIN PLAYA SURFACE ELEVATION

AND

BASIN TOPOGRAPHY

PLAYA SURFACE ELEVATION AND

BASIN TOPOGRAPHYEvaluate Available Elevation Data

• Five data-sets evaluated: National Elevation Dataset

(NED), Shuttle Radar Topography Mission (SRTM),

Digital Elevation Models (DEM), and Global 30-Arc-

Second Elevation Dataset (GTOP030).

• Major considerations included: seamless coverage,

matching scale, current data, and easily accessible

� NED Data selected (http://seamless.usgs.gov)

• regularly updated composite of the latest DEM

• seamless

• 10-meter resolution – best available for study area

PLAYA SURFACE ELEVATION AND

BASIN TOPOGRAPHYNED (Floyd County, TX)

PLAYA SURFACE ELEVATION AND

BASIN TOPOGRAPHYObtain Playa Surface Elevations

• Project elevation data to UTM using ArcINFO Workstation

• Create Raster point file using ArcToolBox conversion tools

• Associate maximum surface elevation with individual

playa footprints using spatial join. However…

• Extremely long processing times (11 hours!) when using

the entire NED data set so an interim step was introduced

• Spatial query used to extract points inside or near playas,

then the spatial join was applied to the refined point data

set (spatial join processing time now <2 hours).

PLAYA SURFACE ELEVATION AND

BASIN TOPOGRAPHYCreate Final Elevation Data Set

SUMMARIZE ON PLAYA-ID

TO OBTAIN MIN/MAX

ELEVATION VALUES

PLAYA SURFACE ELEVATION AND

BASIN TOPOGRAPHYMin/Max Elevation Attributes now

Associated with Wet Playa Footprints

PART 3

ESTIMATE PLAYA WATER VOLUME

ESTIMATE PLAYA WATER VOLUME

Work Directly with Raster Data

Top Surface: Generated using Polygon to Raster based

on Max Grid Elevation value

Bottom Surface: Obtained directly from projected NED

raster (no additional processing involved)

Volume Method: Use Spatial Analyst CutFill

ESTIMATE PLAYA WATER VOLUME

Inspect Tabular Results

ESTIMATE PLAYA WATER VOLUME

Visually Inspect “0” Volume Area(s)

ESTIMATED WATER VOLUME, FLOYD COUNTY, TEXAS

(OCTOBER 15, 2010)Final Results

• Water identified in 741 of

the 1,721 mapped playas in

Floyd County

• Water area = 18,395 acres

(2.89% of Floyd County)

• Water volume = 97,216,952

cubic meters or 78,815 acre-

feet in Floyd County playas

on October 15, 2010.

WHAT’S NEXT?

Additional Method Validation

and Volume Estimates

Next Steps

Method Validation

• Playa surveys

• Area-volume and depth-

volume relationships

• Water level

observations

• Compare with remote

sensing

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Elevation, ft msl

Bivins Playa -Elevation - Area

Method Validation

• Accuracy of RS estimates limited by:

– Image pixel size, pixel classification, and contouring

– Local accuracy of NED surface

– Landscape changes over time since underlying

topographic data collected

• Field data accuracy limited by:

– GPS accuracy (~ ½ inch vertical for Trimble R6)

– Number and distribution of grid points

– Access limitations

• Single Floyd County

playa with field data for

10/15/2010

– RS volume estimate of

43,247 cubic meters

– Field volume estimate

of 51,218 cubic meters

based on 38 cm water

depth

– 16.9 relative percent

difference

Method Validation

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Floyd Crop Playa

Validation Data Set

• Scale up to area of

one Landsat image tile

• TWDB data

• No TWDB playas in

image area filled in

2011

• No data for 2010

• TTU/ARS data

• 16 playas monitored

in 2010

• Look at images from 9

June, 25 June, 12

August, and 15 October

2010

TTU/ARS Playa

TWDB Playa

QUESTIONS