Introduction to GIS and Water Resources

Phil GuertinSchool of Natural Resources and 

the Environementdguertin@cals.arizona.edu

Types of ApplicationsSurface Water – Watershed Management

• Current Watershed Conditions• Change in Watershed Conditions• Mapping of Hazards

– Erosion, Landslides, Floodplains, Pollutants

• Support Hydrologic Modeling• Watershed Assessment and Analysis• Watershed Planning

San Pedro River, AZ – AGWA Example

Kepner et al., EPA-NERL/ESD http://www.epa.gov/nerl1/land-sci/san-pedro.htm

Change in Land Cover Extent

1973 1997

Human Use Index (HUI = 100 * Total Area in Human Use / Total Area)

Area near Sierra Vista, AZFast-growing city

Courtesy Bill Kepner, US-EPA

Hydrologic Modeling

• Goal: Find stream discharge, Q, at a location for a given precipitation.

• GIS is used to summarize terrain and hydrologic characteristics of the watershed for input to a model.

• Many ways to calculate Q.– Statistical methods

• USGS regression equations (NFF, StreamStats)– “Physical” modeling (rainfall‐runoff models)

• HEC‐HMS, SWAT, AGWA

AGWAAutomated Geospatial Watershed Assessment:

GIS-based Hydrologic Modeling Tool for Watershed Assessment and Analysis

© Copyright Adriel Heisey

Watershed Discretization(model elements) +

LandCover

Soils

Rain (Observed or

Design Storm)

Results

Run model and import results

Intersect model elements with

Watershed Delineation using Digital Elevation

Model (DEM)

Sediment yield (t/ha)Sediment discharge (kg/s)

Water yield (mm)Channel Scour (mm)

Transmission loss (mm)Peak flow (m3/s or mm/hr)

Channel Disch. (m3/day)Sediment yield (kg)

Percolation (mm)Runoff (mm or m3)

ET (mm)Plane Infiltration (mm)

Precipitation (mm)Channel Infiltration (m3/km)

SWAT OutputsKINEROS Outputs

AGWA Conceptual Design: Inputs and Outputs

Output results that can be displayed in AGWA

Spatial and Temporal Scaling of Results

High urban growth1973-1997

Upper San PedroRiver Basin

#

#

ARIZONA

SONORA

Phoenix

Tucson

<<WY >>WY

Water yield change between 1973 and 1997

SWAT Results

Sierra Vista SubwatershedKINEROS Results

N

ForestOak WoodlandMesquite DesertscrubGrasslandUrban1997 Land Cover

Concentrated urbanization

Using SWAT and KINEROS for integrated watershed assessment Land cover change analysis and impact on hydrologic response

0 100 200 300 4000

4

8

12

Run

off (

mm

/hr)

Time (min)0 100 200 300 400

0

0.04

0.08

0.12

Time (min)

KINEROS model runs for rainfall events

5-year, 30-minute rainfall 100-year, 60-minute rainfall

1973

1973

1997 1997

Simulated Runoff From the Small Watershed Near Sierra Vista Output – Tools for Water Quality Planning

LowMediumHigh

Total Erosion for 5-year Event

TMDL PriorityLOWMEDIUM20 0 20 Miles

N

EW

S

4 0 4 8 Miles

3 0 3 6 Miles

Currently being used for watershed-based planning in AZ and to assess impacts of energy development in WY.

Characterizing the Watershed

complex topography land cover/use soilshigh spatial variabilitycomplex watershed response

Drainage System

Watershed (Basin, Catchment, Contributing area) Watershed Boundaries

(Drainage Divides)

Pour Points (Outlets)

GIS Tools for Describing Surface Water Movement

DEM

FLOW DIRECTION

SINK

FILL

FLOWLENGTH

FLOW ACCUMULATION

WATERSHED

SNAP POUR

DepressionlessDEMAre there any sinks?Are there any sinks?

No

Yes

STREAM LINE

STREAM ORDER

STREAM LINKApp

ly T

hres

hold

App

ly T

hres

hold

DEM Errors – Sinks and Spikes• Sinks: when sinks are (or are not) sinks – lakes, depressions, …– Global fill– Dealing with internal basins

– Selective fill• Depth• Area

SinkSinkFilled sinkFilled sink

Flow Direction

64 128

116

8 24

32

128 128

2

2 2

2

2

2

4

4

4

8

1 1 2

1

4

2

8

4

4

8

2

1

2

1

1

1

4

1

4

4

4

16

4

878

74

72

67

69

56

71

49

58

50

69

64

53

58

44

55

37

22

38

31

48

24

68

74

61

53

47

34

21

12

16

11

19

12

46

49

Elevation

Direction Coding

Flow Direction

GIS Background: Flow Direction

2 2 2 1 128

1 1 1 12864

3264128128128

128 64 64 32 80

Flow Direction Surface

100 100 100 100 94

100 97 96 95100

1001009998100

100 100 100 100 101

Original Surface

Flow Accumulation0

0

0

1

0

1

0

2

0

0

0

0

3

0

7

0

5

20

4

0

0

1

0

0

0

2

0

4

1

7

24

35

0

2

2

0

64 128

116

8 24

32

Direction Coding

GIS Background: Flow Accumulation

Flow Accumulation Surface

DEM Flow Direction Flow Accumulation

Creating Vector Streams

1 1

1 2 2

2 2 2 2

2 2

Value = No Data

NET_GRID

StreamToFeature

RasterToFeature

Stream Link

• Assign a unique value(s) to each stream segment.– Can be used as input to Watershed

Stream Ordering

Strahler Shreve

3

1

11 1

11

1

2 2

2 2

2

4

7

1

1

1

1 1

11

22

3

3

Watershed• Delineate the contributing area to a cell or group of cells.

• Input– Pour Point– Flow Accumulation– Flow Direction 

SnapPour• Snap the “pour point” of a watershed to the cell of highest flow accumulation within a neighborhood.– Prevents accidental creation of tiny watersheds on channel 

side slopes. Snap distanceSnap distance

Cell you clicked onCell you clicked on

The cell that will be selected(cell with highest flow accumulation)The cell that will be selected(cell with highest flow accumulation)

Flow Length• Calculate the length of the upstream or  downstream flow path from each cell.

Summarizing Watershed Characteristics(Zonal Statistics)

• A zone is all the areas/cells with the same value.

• Calculate a statistic within the zones for each cell in a raster. 

• Input zones can be feature or raster.• Output as a raster, summary table, or chart.

– Max flow length per watershed– Average slope per watershed– Average curve number per watershed

Zonal Overlay (cont.)

Slope

Watersheds

Mean Slope per Watershed

Where is this functionality?

• ArcInfo GRID Functions• ArcView 3.x Spatial Analyst

– Avenue requests– Sample extension

• ArcGIS Spatial Analyst 10.x– Tools in the Spatial Analyst Toolbox– Hydrology ToolKit 

GIS Hydrologic Modeling Tools

• Automated Geospatial Watershed Assessment– http://www.tucson.ars.ag.gov/agwa/

• ArcSWAT– http://swatmodel.tamu.edu/software/arcswat/

• ArcAPEX – http://apex.tamu.edu/ 

• HEC – GeoRAS; HEC – GeoHMS– http://www.hec.usace.army.mil/