Advanced water quality
analysis with GIS
RESM 575
Spring 2010
Lecture 11
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
2
Part A.
Introduction to Watershed
Analysis with GIS
Overview




GIS significance
Important datasets
Concepts
Analysis Tools
4
Why watershed analysis with GIS?


Watershed analysis is a spatial issue
Used to analyze regional stressors
5
Regional stressors
1.
2.
3.
4.
5.
6.
7.
Stream
sedimentation
Habitat loss
Forest
fragmentation
Acid mine drainage
Acid rain
Flooding
Invasive and nonnative species
6
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
7
Watershed cataloging units
USGS Regions (2 digit)
USGS Sub-regions (4 digit)
USGS Sub-basins (8 digit)
USGS 8-Digit sub-basins in WV
8
Watersheds for WV
NRCS 10 and 12 watersheds in WV
(5th and 6th level)
n=342
n=745
9
Issues



More local watersheds needed
One to one relationship between land cover
runoff and receiving stream segment
Track runoff from land to stream
10
Example of scale differences
DNR Stocked streams
Tier 2.5 - Reproducing
trout streams
Impaired streams
Watershed boundaries
11
Solution

Delineate watershed boundaries using the
topography to guide us
12
Manual method
13
Subwatersheds
14
GIS and Water Resources

Geographic information systems (GIS) is a
valuable tool in water resources
management
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
15
GIS use in the hydro cycle
16
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
17
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
18
DEM sources for WV

30m (1972) found in the c:/gis-data06/grids/
directory as wv_elev


10m (1972) derived from 1:24,000 hypsography on
the WVU Tech center website


Mosaic statewide
By 24K quad – partial state coverage
3m (2003) derived from 2003 SAMB photos on the
WVU Tech Center website

By 24k quad
19
20
Helpful ArcGIS commands
To combine dems
If you have a *.dem file
21
3m to 30m DEM comparison
22
National 30m seamless DEMs
23
Other hydro products to note for WV

Segment level
watersheds

1:24K
hydrology
24
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!
25
Flow direction



Created from an elevation surface
Direction values are assigned
Flow direction grids are used in many
hydro GIS functions
32
64
16
8
128
1
4
2
Flow direction map
26
Flow direction



Created from an elevation surface
Direction values are assigned
Flow direction grids are used in the other flow functions
32
64
16
8
128
1
4
2
Flow direction map
27
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
28
29
Summary of spatial techniques and tools
available within a GIS
Elevation grid
Fill sinks
Any sinks?
Yes
Flow direction
No
Flow accumulation
Allows for additional landscape based analysis
Stream delineations
Watersheds
Stream order
Riparian areas
30
Delineate watersheds
Hydro toolbar
in ArcGIS 9
31
Delineate watersheds interactively
Interactive
delineation
for a point
32
Track flow from a point
33
Track flow from a point
34
Find intermittent stream paths
Mapped
streams
from the
1:24,000
topomap
35
Find intermittent stream paths
Mapped
streams
from the
1:24,000
topomap
36
Find intermittent stream paths
Intermittent,
debris slides,
accumulators,
path of easiest
descent exist
37
38
39
Find intermittent stream paths
40
5. Calculate drainage area
Flow accumulation grid = tells us the
number of cells of a certain area that
flow to a point
Drainage
area?
41
5. Calculate drainage area
Flow accumulation grid = tells us the
number of cells of a certain area that
flow to a point
42
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
43
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 by
1.
2.
3.
4.
5.
Elevation grids
Delineate watersheds
Track flow from a point
Find intermittent stream paths
Calculate drainage areas
44
For basic hydrological modeling

ArcGIS9 toolbar

Lab 12 Hydrological Analysis Basics
45
Part B.
Advanced Water Quality
Analysis with GIS
Overview

Terrain analysis




concave/convexity, moisture index
Finding potentially affected streams
Expected mean concentration modeling
WCMS (Watershed Characterization and
Modeling System) ArcGIS 9 extension
47


Rainfall - runoff
relationships
Runoff - above curve
Losses - below curve




interception
depression storage
evapotranspiration
infiltration
Time
Runoff
Rainfall

Runoff
Surface hydrology
Time
48
Runoff curve from gauge
Source: www.americanwhitewater.org
49
Watershed characteristics affecting
runoff

Watershed configuration






Topography
Geology


soils, infiltration and erosion characteristics
Surface culture



size
shape
orientation
stream network
agricultural practices
residential land use practices
Structures

hydrologic modification
50
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
51
Possible Land-Water Transform
Coefficients
Land-Water
Connection
Transform
Coefficient
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
52
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
53
Calculating a moisture index



Compute a flow accumulation grid
Compute a slope grid
Input into the raster calculator:
54
55
Curvature
56
Curvature


Areas of convex profile curvature = areas of
erosion
Areas of concave profile curvature = areas of
deposition
Concave surface
Convex surface
Positive profile
curvature
Slope increasing
Negative profile
curvature
Slope decreasing
Deposition
Erosion
57
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.
58
Curvature result
convex
concave
59
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
60
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
61
What we are
trying to show –
which streams
and where in the
streams runoff
enters
62
Water quality estimation

Mass balance approach
B
A
E = fn (A, B, C, D, E)
Or
C
E/flow = A/flow + B/flow +
C/flow + D/flow
D
E
63
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
64
EMC Export Coefficients
Factors likely to vary across watersheds:
• 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
65
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
66
EMC modeling approach
EMC grid
Annual
runoff grid
* Cumulative
runoff grid
/ Stream flow
grid
Annual
= runoff grid
Pollutant
=
output grid
67
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)
68
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
69
70
WCMS ArcGIS 9 extension
71
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.
72