Advanced water quality analysis with GIS

RESM 575

Spring 2010

Lecture 11

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Today

Part A Introduction to watershed analysis with GIS

Part B Advanced water quality analysis Terrain analysis

Lab 11a and 11b Basic hydro analysis tools Advanced watershed analysis with WCMS

Part A.Introduction to Watershed

Analysis with GIS

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Overview

GIS significance Important datasets Concepts Analysis Tools

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Why watershed analysis with GIS?

Watershed analysis is a spatial issue Used to analyze regional stressors

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Regional stressors

1. Stream sedimentation

2. Habitat loss

3. Forest fragmentation

4. Acid mine drainage

5. Acid rain

6. Flooding

7. Invasive and non-native species

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Watershed based frameworks

Integrative approach Legislative roots in the 1972 Clean Water Act

Goal to clean up and protect US water bodies from point and nonpoint sources

Designated uses – evaluated as part of the Clean Water Act

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Watershed cataloging units

USGS Regions (2 digit) USGS Sub-regions (4 digit)

USGS Sub-basins (8 digit)

USGS 8-Digit sub-basins in WV

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Watersheds for WV

NRCS 10 and 12 watersheds in WV(5th and 6th level)

n=342n=745

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Issues

More local watersheds needed One to one relationship between land cover

runoff and receiving stream segment Track runoff from land to stream

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Example of scale differences

DNR Stocked streams

Tier 2.5 - Reproducing trout streams

Impaired streams

Watershed boundaries

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Solution

Delineate watershed boundaries using the topography to guide us

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Manual method

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Subwatersheds

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GIS and Water Resources

GIS in watershed management:

1. Elevation surface is key

2. Delineate watersheds

3. Track flow from a point

4. Find intermittent stream paths

5. Calculate drainage areas

Geographic information systems (GIS) is a valuable tool in water resources management

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GIS use in the hydro cycle

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Surface hydrology

Determine where the water came from and where it is going

Describe the behavior of water as it moves over the surface of the earth

Analysis starts with the creation of a hydrologically correct surface (no sinks or peaks interrupting drainage direction)

Include the entire drainage

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Elevation surface or grid The starting point for all hydrological modeling in GIS USGS Digital elevation model 30m or 10m elevation

cells, or 3m for WV Each cell or grid represents a value for the elevation

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DEM sources for WV

30m (1972) found in the c:/gis-data06/grids/ directory as wv_elev Mosaic statewide

10m (1972) derived from 1:24,000 hypsography on the WVU Tech center website By 24K quad – partial state coverage

3m (2003) derived from 2003 SAMB photos on the WVU Tech Center website By 24k quad

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Helpful ArcGIS commands

If you have a *.dem file

To combine dems

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3m to 30m DEM comparison

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National 30m seamless DEMs

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Other hydro products to note for WV

Segment level watersheds

1:24K hydrology

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Sinks

Depressions in the DEM where water gets trapped A sink prohibits calculating future flow direction grid

values. A sink occurs when all neighboring cells are higher

than the processing cell. Sometimes they are natural features!

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Flow direction Created from an elevation surface Direction values are assigned Flow direction grids are used in many

hydro GIS functions

Flow direction map

32 64 128

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248

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Flow direction Created from an elevation surface Direction values are assigned Flow direction grids are used in the other flow functions

Flow direction map

32 64 128

1

248

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Flow accumulation

The accumulated flow is based upon the number of cells flowing into each cell in the output grid. The current processing cell is not considered in this accumulation.

Output cells with a high flow accumulation are areas of concentrated flow and may be used to identify stream channels.

Output cells with a flow accumulation of zero are local topographic highs and may be used to identify ridges

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Summary of spatial techniques and tools available within a GIS

Elevation grid

Flow direction

Fill sinks

Allows for additional landscape based analysis

Flow accumulation

Any sinks? Yes

No

Watersheds

Stream delineations

Riparian areas

Stream order

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Delineate watersheds

Hydro toolbar in ArcGIS 9

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Delineate watersheds interactively

Interactive delineation for a point

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Track flow from a point

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Track flow from a point

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Find intermittent stream paths

Mapped streams from the 1:24,000 topomap

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Find intermittent stream paths

Mapped streams from the 1:24,000 topomap

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Find intermittent stream paths

Intermittent, debris slides, accumulators, path of easiest descent exist

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Find intermittent stream paths

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5. Calculate drainage area

Flow accumulation grid = tells us the number of cells of a certain area that flow to a point

Drainage area?

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5. Calculate drainage area

Flow accumulation grid = tells us the number of cells of a certain area that flow to a point

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Calculate drainage area

So, if there are 280,721 cells that flow to that location…

and each cell is 3m by 3m in size (9sq meters)

Then

The total drainage area is (280,721) * (9) = 2,526,489 sq meters

Or

2,526,489 sq meters * 0.00024718 = 624 acres

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Summary points

Watersheds are the key unit of analysis for examining water quality issues

Scale issues require us to delineate smaller watersheds for local issues

GIS can aid in watershed management by1. Elevation grids2. Delineate watersheds3. Track flow from a point4. Find intermittent stream paths5. Calculate drainage areas

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For basic hydrological modeling

ArcGIS9 toolbar

Lab 12 Hydrological Analysis Basics

Part B.Advanced Water Quality

Analysis with GIS

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Overview

Terrain analysis concave/convexity, moisture index

Finding potentially affected streams Expected mean concentration modeling WCMS (Watershed Characterization and

Modeling System) ArcGIS 9 extension

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Surface hydrology

Rainfall - runoff relationships

Runoff - above curve Losses - below curve

interception depression storage evapotranspiration infiltration

Ra

infa

ll

Time

Runoff

Ru

no

ff

Time

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Runoff curve from gauge

Source: www.americanwhitewater.org

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Watershed characteristics affecting runoff

Watershed configuration size shape orientation stream network

Topography Geology

soils, infiltration and erosion characteristics Surface culture

agricultural practices residential land use practices

Structures hydrologic modification

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Watershed Characteristics Affecting Runoff Watershed shape

For a given area, watershed width affects the overland flow pattern Effects can be seen in terms of the time of concentration of flow The larger the width the longer the time of concentration

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Possible Land-Water Transform Coefficients

Land-WaterConnection

TransformCoefficient

Water yield Runoff coefficient, C

Flood runoff SCS Curve Number, CN

Groundwater Recharge rate (mm/yr)

Water quality Expected Mean Concentration(mg/l)

Sediment yield Erosion rate (tons/ha-yr)

Water

Land

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Moisture index

Simply a function of two factors: How much water is flowing into the area How fast the water can flow out

Ln [(catchment area + 1) / (slope + 1)]

NOTE: this is a relative moisture index, so the resulting numbers do not have units Higher more positive numbers are wetter Lower more negative numbers are drier

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Calculating a moisture index

Compute a flow accumulation grid Compute a slope grid Input into the raster calculator:

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Curvature

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Curvature

Areas of convex profile curvature = areas of erosion

Areas of concave profile curvature = areas of deposition

Convex surface

Positive profile curvature

Slope increasing

Erosion

Concave surface

Negative profile curvature

Slope decreasing

Deposition

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ArcMap Curvature tool

Output profile curve raster dataset.

This is the curvature of the surface in the direction of slope.

This is the curvature of the surface perpendicular to the slope direction.

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Curvature result

convex

concave

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Identifying potentially affected streams Overland flow non point source pollution is the number one water

quality problem in WV (2006 303d List WVDEP) Almost 20% of the streams in WV are impaired and not meeting

designated uses Sources include mine drainage, leaking or overflowing sewage

systems, illegal homeowner discharges, runoff from agriculture and urban areas

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Identifying potentially affected streams Source of potential pollution can be mapped

as points (discharge seeps), lines (mining headwalls), or polygons (nonpoint source pollution)

The source is used as the weight grid in the flow accumulation function

A network streamgrid shows the stream and the location where the potential pollution would enter the stream

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What we are trying to show – which streams and where in the streams runoff enters

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Water quality estimation

Mass balance approach

AB

C

D

E

E = fn (A, B, C, D, E)

Or

E/flow = A/flow + B/flow + C/flow + D/flow

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Expected mean concentration modeling

• EMC input is a land cover grid

• Aggregated classes and coefficients from literature (see refs at end)

Total Nitrogen Total Phosphorous Total Suspended Solids

Urban 1.89 0.009 166

Open/Brush 2.19 0.13 70

Agriculture 3.41 0.24 201

Woodland 0.79 0.006 39

Barren 3.90 0.10 2200

Wetland 0.79 0.006 39

NOTE: per acre loadings are aggregated to 30m pixels for mg/L concentrations

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EMC Export CoefficientsEMC Export Coefficients

• year to year changes in precipitation

• soil type

• slope and slope morphology (convex, concave)

• geology

• cropping practices

• timing of fertilizer application relative to precipitation events

• density of impervious surface

Factors likely to vary across watersheds:

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EMC modeling approach

• Nutrient export coefficients are multiplied by the amount (area) of a given land cover type

• Incorporates the location of the cover class in the downstream routing of the pollutant

• Used as simulations to estimate the probability of increased nutrient loads from land cover composition

• A screening approach due to assumptions

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EMC modeling approach

EMC grid Annual runoff grid

Cumulative runoff grid

Stream flow grid

Pollutant output grid

*

/ =

=

Annual runoff grid

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Limitations with stream flow model

• lack of interception, evapotranspiraiton, baseflow from groundwater

• rate of areal distribution of rainfall

• monthly averages was crude

• Limited to natural systems (no dams or impoundments)

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Limitations with EMC approach

• year to year changes in precipitation

• soil type

• slope and slope morphology (convex, concave)

• geology

• cropping practices

• timing of fertilizer application relative to precipitation events

• density of impervious surface

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WCMS ArcGIS 9 extension

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Further reading

Jenson S. K. and J. O. Domingue. 1988. Extracting Topographic Structure from Digital Elevation Data for Geographic Information Systems Analysis, Photogrametric Engineering and Remote Sensing. Vol. 54, No. 11, November 1988, pp. 1593-1600.

Haith A. D and L.L Shoemaker. 1987 Generalized Watershed Loading Functions for Stream Flow Nutrients. Water Resources Bulletin, American Water Resources Association, Vol 23, No. 3. Pp 471 – 477.

Mark, D. M. 1988. ‘Network Models in Geomorphology’, Modeling in Geomorphological Systems. John Wiley.

Olivera, F., R. J. Chareneau and D. R. Maidment. 1996. CRWR Online Report 96-4: Spatially Distributed Modeling of Storm Runoff and Non-Point Source Pollution Using GIS.

Saunders, W. K. and D. R. Maidment (1996), A GIS Assessment of Nonpoint Pollution in the San Antonio-Nueces Coastal Basin, Center for Research in Water Resources Online Report 96-1, University of Texas, Austin, TX.

Saunders, W. K. (1999) Preparation of DEMS for use in Environmental Modeling Analysis, In: Conference Proceedings: 1999 ESRI User Conference, Environmental Systems Research Institute, Redlands, CA.

Shreve, R. L. 1966. Statistical Law of Stream Number, Journal of Geology. Vol. 74, pp. 17-37. Strahler, A. N. 1957. Quanitative Analysis of Watershed Geomorphology. Transactions of the American

Geophysical Union. Vol. 8, Number 6, pp. 913-920. Tarboton, D. G., R. L. Bras, I. Rodriquez-Iturbe. 1991. On the Extraction of Channel Networks from Digital

Elevation Data, Hydrological Processes. Vol. 5, pp. 81-100. Reed, S.M., and D.R. Maidment. 1995. CRWR Online Report 95-3: A GIS Procedure for Merging NEXRAD

Precipitation Data and Digital Elevation Models to Determine Rainfall-Runoff Modeling Parameters.