GIS Tools for Watershed Delineation

Public Policy Perspectives

Teaching Public Policy in the Earth Sciences

April 21, 2006

Gary CoutuDepartment of Geography and Planning

West Chester University

Contents

• Watershed Perspectives in Policy

• Environmental Mandates

• GIS Data for Watershed Characterization

• Tools for Watershed Delineation and Analysis

• Examples for Classroom and Research

• Issues

Watershed Perspectives in Policy

•Watershed- EPA approach for

managing land and water quality

•TMDL: Total Maximum Daily

Load

•303d List of Impaired Waters

•EPA Support- Data, GIS tools

and Models

•Issue- National data sets versus

local information and data

Many Agencies support data and model development for environmental assessment, management and mitigation

Environmental Perspectives• TMDL (Total Maximum Daily Load): calculation of the maximum

amount of a pollutant that a waterbody can receive and still meet water quality standards. Established in the Clean Water Act, section 303.

Section 303(d) of the Clean Water Act

Under section 303(d) of the 1972 Clean Water Act, states, territories, and authorized tribes are required to develop lists of impaired waters. These impaired waters do not meet water quality standards that states, territories, and authorized tribes have set for them, even after point sources of pollution have installed the minimum required levels of pollution control technology. The law requires that these jurisdictions establish priority rankings for waters on the lists and develop TMDLs for these waters.

http://www.epa.gov/owow/tmdl/overviewfs.html

Total Maximum Daily Loads on the WebTMDLs and the 303d list are developed concurrently. EPA publishes information and local links on their web site.

Reporting and analysis: Based upon a large set of spatial data for watershed and stream locations. Most of this data developed by USGS

USGS Data:

Hydrologic UnitsNational Hydrography DatasetStream Gauges

GIS Data for Watershed Characterization

DEM: Digital Elevation Model.

Grid of elevation points (each cell

has an elevation value

HUs: Hydrologic Units. Nested

watershed units

NHD: National Hydrography

Dataset. Networked streams and

features for modeling (includes

human and natural waterways,

damns, ponds, etc.)

USGS Gauging Station Data

Hydrologic Unit Maps

• Regions (21 major geographic areas)• Sub-regions (222 subregions) • Accounting units (352 hydrologic units) • Cataloging units (2150 SubBasin)

Hydrologic Unit Code (HUC): Consists of two to eight digits. The 6 digit accounting units and the 8 digit cataloguing units are generally referred to as basin and sub-basin. Two new levels, watershed and subwatershed, are under development.

Watershed address system

Description Proper Name Address

Region Ohio River 05

Subregion Wabash/Patoka/White Riv 0512

Basin Wabash River 051201

Subhead Vermilion River 05120109

Watershed North Fork Vermilion 0512010909

Subwatershed   Lake Vermilion 051201090905

Represent watershed areas used for policy and environmental analysis/management

Nested Hydrologic UnitsAll Federal and State Agencies use this nested hierarchy

0204 (Delaware)020402

(Lower Delaware)02040205

(Brandywine-Christiana)

0204020535(Upper Reach

Brandywine Creek)

Sample Watershed for

this Presentation(560 Acres)

National Hydrography DatasestsGIS layers (ArcGIS Geodatabase) stored as a Microsoft Access Database

USGS Gauging Stations: Real-time Data

Tools for Watershed Delineation and Analysis

BASINS: Water Quality ModelBetter Assessment Science Integrating Point & Nonpoint Sources: Environmental analysis system integrating GIS, national watershed data, and environmental assessment and modeling tools.

Watershed Delineation Process• Foundation of watershed analysis in the

classroom

• Steps:– Fill Sinks– Flow direction– Flow Accumulation– Define Watershed– Analysis

Delineation Process: Fill Sinks

Filled SinksValue

High : 173.500000 Low : 47.400002

DEM: 10 Meter ResolutionValue

High : 173.500000 Low : 46.500000

Sink: Cells of the DEM that do not drain

Issue: Watershed commands won’t workTeaching: Students are exploring limitations of modeling

Sinks

Delineation Process: Flow Direction/Accumulation

Flow Direction: Assigns Direction of flow from cell to next lowest elevation (D-8 algorithm)Flow Accumulation: Total number of cells flowing into that cell (Can calculate streams and ridges)

0 1 3

0 2 4

0 0 6

32 64 128

16 X 1

8 4 2

Delineation Process: Use/Interpretation

Flow Accumulation: Generate Streams

Flow Direction: Identify Water Flow Slope

Delineation Process: Watershed

Pour point at Stream confluence

Watersheds represent the drainage area to a point (known as the “pour point”.) Delineation tools allow a user to define the watershed for a selected drainage.

Watershed Delineation: Use/Interpretation

DEM Contours Steep Slopes

Data sets can be clipped for local watershed areas for analysis

Stream Network ModelingStream networks from the National Hydrography Dataset can be included in watershed analysis. Stream, watershed and land use data are used to explore environmental impact.

Downstream Impact Commercial Site ImpactWatershed Parcels

Parcel Classification

Commercial

Public

Farm

Residential

Land use/Water Quality

Land use Acreage

0

50

100

150

200

250

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Hig

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Ind

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Land use

Ac

res

Type Acres

Open Water 1

Low Intensity Residential 157

High Intesity Residential 9

Commercial 14

Deciduous Forest 203

Evergreen Forest 4

Mixed Forest 76

Pasture Hay 89

Row Crops 4

Land use within a watershed can be isolated and quantified:

Land use

Commercial

Deciduous Forest

Evergreen Forest

High Intesity Residential

Low Intensity Residential

Mixed Forest

Open Water

Pasture_Hay

Row Crops

Watershed CharacterizationStudents perform this analysis and tasks as part of a watershed study. Could be combined with field work.

Example Issue: DEM Resolution and Stream Layer Accuracy

1. DEM Resolution (10 meter vs 30 meter)

2. DEM Generated Stream Accuracy

3. Stream confluence and DEM confluence mis-match

Stream

30m DEM

10m DEM

10m DEMStream

Confluence

Student Experience:

1. Resolution/Scale Issues2. Stream Map Generation3. Field Data Integration4. Context of Modeling

Web Sites• EPA Surf Your Watershed:

• http://www.epa.gov/surf/

• EPA TMDL:

• http://www.epa.gov/owow/tmdl/intro.html

• EPA BASINS:

• http://www.epa.gov/OST/BASINS/

• USGS DEM:

• http://www.usgsdigital.com/Elevation.htm

• USGS Stream Gauges:

• http://water.usgs.gov/nsip/

• National Hydrography Data:

• http://nhd.usgs.gov

Contact

Gary CoutuDepartment of Geography

and PlanningWest Chester University

West Chester, Pennsylvania

Email: gcoutu@wcupa.edu