1. INTRODUCTION
As GIS software matures in functionality, speed, and flexibility, issues of the use and
suitability of GIS the extraction of the hydro-geometric information. This study is about
the extraction of hydro-geometric data to manage water resources more effectively. GIS
technique is applied to extract spatial information from an experimental watershed, and
analysis is carried out to evaluate the results which will be used for management of water
resources.
Besides being applied for the extraction of hydro-geometric data such as physiographic
factor, soil, landuse and characteristics of watershed. GIS can be used to reduce the time
and manpower needed in the tedious manual task of collecting such data. ArcInfo was used
with DEM to extract and quantify the geometric characteristics and topographic
characteristics of streams. It is anticipated that the result of this study will be used
for the implementation of the database of a water information system and will contribute
to the management of water resources.
2. SCOPE AND MAJOR OBJECTIVES
An experimental area was selected as the Pyongchang River basin one of the headwaters of
South Han River, South Korea. 4 sheets of 1:50,000 topographic maps were scanned then
contours were vectorized to get a TIN. DEM was then formed to formulate the stream line.
The flow direction was determined using the fact that water flows toward the steepest
direction and the stream network and watershed boundary was induced from the determined
flow direction. Also various cell sizes was tested by comparing computed streamlines and
actual stream features on the topographic maps. Using the computed stream network, stream
order was found by Strahler method and various hydro-geometric information factors were
determined such as contributing drainage area(CDA), average basin slope(BS), main channel
length(MCL), basin perimeter(BP), total stream length(TSL), number of first streams with
contributing drainage area(FOS). The results were then compared with results obtained by
conventional graphic method and evaluated. It is hoped that the hydro-geometric
information of Pyongchang River basin extracted by the GIS method presented in this paper
will be useful in decision makings of the management and operation of water resources.
3. METHOD
The study area, Pyongchang River basin which is one of the representative basins of the
International Hydrological Program(IHP),is comprised mostly of mountainous areas and
starts from Mt. Kebang (1,577 meters) and is located at E 128 15 45 - E 128 31 30, N 37 24
34 - 37 43 55. The geometric characteristics parameters extracted by conventional graphic
method is as follows. The CDA is about 523.79 km2, MCL is 51.85 km, the TCL of tributary
and main water is 712.77 km and the BS by Hortons method is 0.333 radian. 4 sheets of
1:50,000 topographic maps published by the National Geographic Institute was scanned and
contour lines, spot height symbols and streams were vectorized. The input data used is as
in table 3.1. Themes selected are contour lines, spot height symbols, stream network and
administrative boundaries. Watershed was extracted with reference to administrative
boundaries and contour lines. Table 3.2 shows the layers of the digital maps used and Fig.
3.1 shows the components of the software used.
Table 3.1 Input data of Pyongchang River basin
+-------------+---------------------+---------------+--------------+
| type of map | sheet number | scale |administration|
+-------------+---------------------+---------------+--------------+
| | NJ52-10-10 | | |
| +---------------------+ | |
| | NJ52-10-11 | | national |
| topographic +---------------------+ 1 : 50,000 | geographic |
| map | NJ52-10-17 | | institute |
| +---------------------+ | |
| | NJ52-10-18 | | |
+-------------+---------------------+---------------+--------------+
Table 3.2 Digital basemap of Pyongchang River basin
+----------------+-------------+---------+-----------+---------------------+
| layer |data source | scale | data type | attribute data |
+----------------+-------------+---------+-----------+---------------------|
|contour line | | | line | elevation |
+----------------| | | | |
|spot height |topographic |1:50,000 | point | elevation |
+----------------+ map | | | |
|stream network | | | line | river name |
+----------------+ | | | |
|watershed | | | polygon | watershed name |
+----------------+ | | | |
|administration | | | polygon | administration name |
+----------------+-------------+---------+-----------+---------------------+
+-----------------------------------------------------------+
| AML Menu Interface |
+-----------------------------------------------------------+
+-----------------------------------------------------------+
| AML Program |
+-----------------------------------------------------------+
+-----------------------------------------------------------+
| ArcInfo |
+-----------------------------------------------------------+
$)C
!h!i
+-------------------- ArcInfo DATABASE ------------------+
| +--------+ +--------+ +--------+ |
| | +-----+ +-----+ | |
| +--------+ +--------+ +--------+ |
| Terrain DB Attribute DB Hydro-information |
+-----------------------------------------------------------+
!h!i
+-----------------------------------------------------------+
| Vectorizing |
| (AUTOCAD, IRASB, IGEOVEC) |
+-----------------------------------------------------------+
Fig.3.1 Components map of software
GIS can be effectively applied to spatial analysis tasks which requires repetitive manual
observations. The spatial analysis of watersheds leads to extraction of input data for
runoff model and information for watershed management.
In this study, watershed parameters such as average slope of watershed, topographic
analysis of watershed, 3 dimensional perspective display were extracted from DEM using
GRID analysis of ArcInfo. The extracted spatial information was quantified by using
various formula for hydrologic and topographic analysis. The result was compared with
values of conventional methods and evaluated for the applicability of GIS for this
purpose.
The area and perimeter values of conventional graphic method and GIS method is shown in
Table 3.3. The difference in area was quite small which was about 3.12 km2 and the main
channel length was about 0.53 km. The difference in the perimeter of the watershed is due
to the size of the cell which determines the DEM of the basin area. Also the fact that dry
rivers which are not shown on topographic maps but were taken into account in GIS
analysis, could contribute to the difference in the TSL of the river. This could lead to
the fact that the difference in type of river, MCL and TSL will increase with the increase
of map scale.
Table 3.3 Comparison of geometric factors of study area
between graphical method and GIS technique
+-----------------------+-------------------------------------+
| hydro-geometric | (1:50,000) |
| information +-------------------+-----------------+
| | conventional | GIS method |
| | graphic method | |
+-----------------------+-------------------+-----------------+
|Contributing Drainage | | |
| Area (km2) | 523.79 | 520.67 |
+-----------------------+-------------------+-----------------+
|Basin Perimeter(km) | 118.84 | 148.82 |
+-----------------------+-------------------+-----------------+
|Main Channel Length(km)| 51.85 | 52.38 |
+-----------------------+-------------------+-----------------+
|Total Stream Length | 712.77 | 1,549.74 |
| (km) | | |
+-----------------------+-------------------+-----------------+
|Stream order | 5 | 7 |
+-----------------------+-------------------+-----------------+
|average Basin Slope(°) | 19.079 | 20.375 |
+-----------------------+-------------------+-----------------+
| Basin Relief (km) | 1.220 | 1.190 |
+-----------------------+-------------------+-----------------+
|Main Channel Slope(°) | 3.140 | 3.410 |
+-----------------------+-------------------+-----------------+
| effective Basin | 14.74 | 14.95 |
| Width(km) | | |
+-----------------------+-------------------+-----------------+
| Slope Ratio | 0.165 | 0.167 |
+-----------------------+-------------------+-----------------+
| Shape Factor | 0.412 | 0.427 |
+-----------------------+-------------------+-----------------+
| Form Ratio | 0.068 | 0.068 |
+-----------------------+-------------------+-----------------+
| Main Channel Sinuosity| 1.448 | 1.495 |
| Ratio | | |
+-----------------------+-------------------+-----------------+
| Rotundity of Basin | 0.323 | 0.335 |
+-----------------------+-------------------+-----------------+
| Elongation Ratio | 1.761 | 1.729 |
+-----------------------+-------------------+-----------------+
| Drainage Frequency | 0.629 | 0.789 |
+-----------------------+-------------------+-----------------+
| number of First Order| 365 | 413 |
| Stream | | |
+-----------------------+-------------------+-----------------+
| Relate Relief | 0.010 | 0.008 |
+-----------------------+-------------------+-----------------+
| Stream Density | 1.350 | 2.959 |
+-----------------------+-------------------+-----------------+
| Constant of Channel | 0.741 | 0.338 |
| Maintenance | | |
+-----------------------+-------------------+-----------------+
| Ruggdeness Number | 1.647 | 3.521 |
+-----------------------+-------------------+-----------------+
| Compactness Ratio | 1.459 | 1.853 |
+-----------------------+-------------------+-----------------+
| Compactness | 0.685 | 0.545 |
+-----------------------+-------------------+-----------------+
| Main Channel Slope | 29.261 | 28.370 |
| Proportion | | |
+-----------------------+-------------------+-----------------+
4. CONCLUSION
The extraction of basic data needed for a comprehensive water resources management of
basins involves tedious manual tasks with topographic maps.
This study has addressed this problem by applying the various spatial analysis of GIS to
the database established for the Pyonchang River basin. Also the various topographic and
hydrologic information is extracted and quantified. As a result of applying GIS method for
the extraction and analysis of hydro-geometric information of large scale basin, the
following conclusions can be made.
As a result of implementation of DEM of Pyongchang River basin from 1:50,000 topographic
maps and comparing various parameters extracted by conventional graphic method and by GIS
method from DEM, the difference in area of river basin showed 3.12 km2 for the 1:50,000
scale which indicates acceptable reliability of the GIS method.
The stream channel do topographic maps and the GIS extracted streams showed some
differences and this can be evaluated by the review of the topographic maps which had been
used for the computation of hydro-geometric information.
To evaluate and analyse the difference showed between the GIS method and conventional
graphic method it is advised that detail topographic study of the area be carried out by
interpretation of aerial photos and remotely sensed space imageries. Further studies will
be carried out to form a database with the extracted hydro-geometric data for the
computation of runoff and a comprehensive management of water resources. It is also hoped
that there will be activities carried out for the development of a water resources
management specific GIS software.
5. ACKNOWLEDGEMENT
The support of Inha University Foundation, President Dr. Sung Wook Cho of Inha Technical
Junior College and President Dr. Ha Ryong Chung of Hanjin GIS Co. is gratefully
acknowledged.
6. REFERENCES
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CHANG HAHK HAHM et al., Water Quality Management Environmental Information Display and
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