Prof. Dr. D. Schröder
Page 1
GIS in Hydrology and Water ResourceManagement - ENWAT
Tutorial: ArcGIS Tools for Hydrology – Run Off Calculation
In this tutorial, a typical workflow for hydrological analysis using ArcGIS for surface water
will be introduced. Most of the used tools are part of the extension Spatial Analyst, which is
an extension for raster analysis. Thus most of our analysis will be based on raster maps. The
study area is the Rems watershed.
The main tasks of this tutorial are:
 Interpolation
 Runoff calculation
As input data the following raster and vector layers are available:
 Precipitation data of climate stations
 Soil vector map (infiltration classification)
 Corine Land Cover vector map
 DEM
All data is with respect to the Datum of the Hauptdreiecksnetz and uses Gauss-Krüger
projection (zone 3).
In the scenario it is assumed, that a heavy storm rain in summer has happened in the Rems
watershed. All the precipitation of the month August was available in one strong rain event in
only 24 hours.
Workflow:
Step 1: Interpolation of Precipitation data
Event theme
The text file climate_stations.tab contains precipitation data at some climate station in our
study area. The file includes the station name, its Gauss-Krüger coordinates, its height,
monthly precipitations, and summed annual precipitation.
The file can be added as a text file to our project (remark: in the text file the tab is used as
column separator. Other characters as separator are also supported, but from experience tab
causes less problems. Interpreting the file contents,
ArcGIS will use the regional settings of the
operating system. Different settings, e.g. for the
decimal point, may cause problems!)
After loading the file to the TOC, we can visualize
the locations of the climate stations, as the file
contains their coordinates:
table right mouse click in the TOC  Display XY
data…
Make sure that the x- and y-columns have been
properly selected and don’t forget to set the
coordinate system. A text file, where the
coordinates of point features are stored in columns
is called an Event theme in ArcGIS.
Prof. Dr. D. Schröder
Page 2
GIS in Hydrology and Water ResourceManagement - ENWAT
Interpolation
Now we can interpolate the data. Here we have two options:
 Using the interpolation tools of the Spatial Analyst. This makes sense, if you know
already what the best method for interpolation is or if you want to integrate the tool in
the Model Builder.
 Using the Geostastical Analyst. Here you have more option to explore the data first
and control and check the results. But the tool can’t be included in the Model Builder,
so have to explore the data manually.
We will use here the Geostastical Analyst. A first overview we will get with the Trend
Analysis. Remember that the x-axes is pointing East whereas the y–axes is pointing North.
We
will
try
now
som
e
inter
polat
ion
meth
ods.
Figure 1: IDW (with default parameters; RMS 6.306)
Figure 2: Local Polynomial (default parameters; RMS 6.272)
Prof. Dr. D. Schröder
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GIS in Hydrology and Water ResourceManagement - ENWAT
Figure 3: Ordinary Kriging (default parameters; RMS 6.351)
Figure 4: Completely regularized Splines ( default parameters: RMS 6.244)
Validation
For a real validation more data points should be used. Nevertheless, here the concept will be
shown. First we have to create two subsets with a randomly selection. As the tool works only
on shape file or geodatabases, we have first to export the event theme to a shape file.
- right mouse click the layer  Export
- Geostatistical Analyst  Create subsets
You can specify how many of the data points you want for training or testing.
The Training subset will be used for the interpolation, whereas the Test subset will be used to
check the results by comparing the predicted values with the measured ones.
Now we can repeat the interpolation steps. A new dialog step will be added showing the
results of the comparison as RMS. The calculation can be easily repeated for a different
Prof. Dr. D. Schröder
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GIS in Hydrology and Water ResourceManagement - ENWAT
method just by using the back button (RMS for different methods: IDW: 5.603; Local
polynomial: 6.172; Kriging: 5.752; completey regularized spline: 9.551)
For our data, IDW and Kriging show the best results. Here we will continue with the Kriging
results.
Step 2: Calculation of the runoff for each pixel
Here the curve number method will be used, which can be implemented easily in GIS. The
idea is that the filtration is a function of the soil type as well as of the land use. In the
literature there exist tables for assigning curve numbers, e.g. United States Department of
Agriculture (1986). Urban hydrology for small watersheds, , Technical Release 55 (TR-55).
Runoff Curve Numbers
Group A Soils: High infiltration (low runoff). Sand, loamy sand, or sandy loam. Infiltration
rate > 0.3 inch/hr when wet.
Group B Soils: Moderate infiltration (moderate runoff). Silt loam or loam. Infiltration rate
0.15 to 0.3 inch/hr when wet.
Group C Soils: Low infiltration (moderate to high runoff). Sandy clay loam. Infiltration
rate 0.05 to 0.15 inch/hr when wet.
Group D Soils: Very low infiltration (high runoff). Clay loam, silty clay loam, sandy clay,
silty clay, or clay. Infiltration rate 0 to 0.05 inch/hr when wet.
Table of Runoff Curve Numbers
Description of Land Use
Hydrologic Soil Group
A
B
C
D
98
98
98
98
Paved with curbs and storm sewers
98
98
98
98
Gravel
76
85
89
91
Dirt
72
82
87
89
Without conservation treatment (no terraces)
72
81
88
91
With conservation treatment (terraces, contours)
62
71
78
81
68
79
86
89
39
61
74
80
Meadow (grass, no grazing, mowed for hay)
30
58
71
78
Brush (good, >75% ground cover)
30
48
65
73
45
66
77
83
Fair (grazing but not burned; some brush)
36
60
73
79
Good (no grazing; brush covers ground)
30
55
70
77
Paved parking lots, roofs, driveways
Streets and Roads:
Cultivated (Agricultural Crop) Land*:
Pasture or Range Land:
Poor (<50% ground cover or heavily grazed)
Good (50-75% ground cover; not heavily grazed)
Woods and Forests:
Poor (small trees/brush destroyed by over-grazing
or burning)
Prof. Dr. D. Schröder
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GIS in Hydrology and Water ResourceManagement - ENWAT
Open Spaces (lawns, parks, golf courses, cemeteries, etc.):
Fair (grass covers 50-75% of area)
49
69
79
84
Good (grass covers >75% of area)
39
61
74
80
Commercial and Business Districts (85%
impervious)
89
92
94
95
Industrial Districts (72% impervious)
81
88
91
93
Residential Areas:
1/8 Acre lots, about 65% impervious
77
85
90
92
1/4 Acre lots, about 38% impervious
61
75
83
87
1/2 Acre lots, about 25% impervious
54
70
80
85
1 Acre lots, about 20% impervious
51
68
79
84
With the help of the curve numbers, the runoff can be calculated according to the following
equation:
Q = (P-Iα)2 / (p-I+s); I = 0.2 s; s = 1000/cn -10 where cn is the curve number
or
Q = (P-0.2 ( 1000 /cn-10))2 / ( P-0.2 ( 1000 /cn-10))
So we have to classify soil and land use, so that cn numbers can be assigned. The soil map has
already a classification of the infiltration according to the scheme of LGRB in five classes
with additional subclasses, and a sixth class for “highly changeable value”. The classes have
already been mapped to the soil class scheme for curve numbers according to:
Classes
Soil category
1
D
2-3 and 6
C
4
B
5
A
Intersecting the soil map and the land cover map the new map will contain all the needed
information. The only problem is that the classification systems are not compatible, so they
have to be mapped to each other. Unfortunately, it is not possible to use two fields for joining
in ArcGIS. Thus no lookup table can be used. So we have to use a more complex way by
adding a new field to the attribute table and to populate it according to the two values for land
cover code and soil category. Again we will use a more generalized scheme according to the
following table:
Land cover code
Hydrological soil type
A
B
C
D
100-199 (urban)
98
221,222,242 Agriculture without conservation
62
71
78
81
232, 321, 331 pastures
39
61
74
80
311, 312, 313, 324 forest
33
57
71
78
- Add a new column to of the intersection result attribute table.
- Use the field calculator to populate the column. To do in one step, use the following VBA
code by copy and paste in the advanced window (don’t forget to assign the variable output to
the new field!)
Prof. Dr. D. Schröder
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GIS in Hydrology and Water ResourceManagement - ENWAT
dim output as integer
if [soil_landuse.CODE2000]<200 then
output = 98
elseif [soil_landuse.CODE2000] =211 or [soil_landuse.CODE2000]=243 then
if [soil_landuse.category] ="A" then
output = 72
elseif [soil_landuse.category] ="B" then
output = 81
elseif [soil_landuse.category] ="C" then
output = 88
elseif [soil_landuse.category] ="D" then
output = 91
endif
elseif
[soil_landuse.CODE2000]
=221
or
[soil_landuse.CODE2000]=222
[soil_landuse.CODE2000] =242 then
if [soil_landuse.category] ="A" then
output = 62
elseif [soil_landuse.category] ="B" then
output = 71
elseif [soil_landuse.category] ="C" then
output = 78
elseif [soil_landuse.category] ="D" then
output = 81
endif
elseif
[soil_landuse.CODE2000]
=231
or
[soil_landuse.CODE2000]=331
[soil_landuse.CODE2000] =321 then
if [soil_landuse.category] ="A" then
output = 39
elseif [soil_landuse.category] ="B" then
output = 61
elseif [soil_landuse.category] ="C" then
output = 74
elseif [soil_landuse.category] ="D" then
output = 80
endif
elseif
[soil_landuse.CODE2000]
=311
or
[soil_landuse.CODE2000]=312
[soil_landuse.CODE2000] =313 or [soil_landuse.CODE2000] =324 then
if [soil_landuse.category] ="A" then
output = 33
elseif [soil_landuse.category] ="B" then
output = 57
elseif [soil_landuse.category] ="C" then
output = 71
elseif [soil_landuse.category] ="D" then
output = 78
endif
endif
or
or
or
Prof. Dr. D. Schröder
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GIS in Hydrology and Water ResourceManagement - ENWAT
Now we can rasterize the map using the new cn field as value for the raster map (Conversion
Tools to Raster  Polygon to Raster).
- Use Map Algebra to calculate the available runoff based on the formula
Q = (P-0.2 ( 1000 /cn-10))2 / ( P-0.2 ( 1000 /cn-10)) * A ; where A is the pixel size and P is
the interpolated precipitation from the first step.
Step 3: Calculation of the accumulated water for the Rems watershed
Based on a hydrological correct DEM we can calculate the accumulated water for runoff
using the Q values as weights in the accumulation. Here the steps:
- Fill the sinks to get a hydrological correct DEM
- calculate the flow direction map
- calculate the accumulation using the Q map is weight map (remark: the weight map should
have the same resolution as the original map. The resolution can be changed by resampling
the map (Data Management Tools  Raster  Resample. Use the resolution of the DEM to
resample the Q-map)).
(The runoff at Waiblingen is about 50 000 000 m3 in 24 hours. From the gage station at
Neustadt/Waiblingen
(http://www.hvz.baden-wuerttemberg.de/cgi/daten.pl?id=0030&m=W&t=M) we know that
the discharge of 100 year return flood is about 314m3/s i.e. 27 000 000 m3 per day. So may be
we have to improve our results by carefully checking all the assumptions and our input data as
well!)