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*Corresponding author: E-mail: rosedaffi@gmail.com, daffir@unijos.edu.ng;
Asian Journal of Environment & Ecology
4(4): 1-8, 2017; Article no.AJEE.35972
ISSN: 2456-690X
Delineation of River Watershed and Stream Network
Using ILWIS 3.7.1 Academic
R. E. Daffi
1*
and I. I. Ahuchaogu
2
1
Department of Civil Engineering, University of Jos, Jos, Nigeria.
2
Department of Agricultural Engineering, University of Uyo, Uyo, Nigeria.
Authors’ contributions
This work was carried out in collaboration between both authors. Author RED designed the study,
performed the GIS analysis and wrote the first draft of the manuscript. Author IIA managed the
literature searches. Both authors read and approved the final manuscript.
Article Information
DOI: 10.9734/AJEE/2017/35972
Editor(s):
(1)
Edward Ching-Ruey, Luo, National Chi-nan University, Taiwan.
Reviewers:
(1)
Angelo Paone, University of Naples "Federico II", Italy.
(2)
Nnamdi E. Ekeocha, University of Port Harcourt, Nigeria.
(3)
Daniel Jaleta Negasa, Ethiopia.
Complete Peer review History:
http://www.sciencedomain.org/review-history/21883
Received 5
th
August 2017
Accepted 14
th
October 2017
Published 13
th
November 2017
ABSTRACT
The delineation of watersheds can be carried out manually using topographic maps but these maps
are mostly outdated, scarce and incomplete for most parts of Nigeria and may be of different scales
for large watersheds that require several sheets of the map. Watershed boundaries need to be
delineated accurately because the areas and perimeters of watersheds are used in many
hydrological analyses. This study is aimed at delineating the River Dep watershed and stream
network using 90m SRTM Digital Elevation Model and Geographic Information Systems technique
and comparing the shape and pattern with the one previously delineated manually using
topographic maps and areal photographs. The 90 m SRTM Digital Elevation Model used for the
study was obtained from the Global Land Facility Cover site and processed in ERDAS Imagine 9.2
before exporting to ILWIS 3.7.1 ACADEMIC. The watershed area obtained from the GIS delineation
processes was 10640 km
2
while it was 9600 km
2
from the report of the one delineated by manual
methods in 1980. The same 1980 manually delineated watershed when scanned, imported,
georeferenced and digitised in ILWIS 3.7.1 gave a watershed area of 10244 km
2
. The differences in
the watershed area could be due to the effect of input data or errors from the estimation using
Original Research Article
Daffi and Ahuchaogu; AJEE, 4(4): 1-8, 2017; Article no.AJEE.35972
2
traditional delineation. The study showed similarity in shape and pattern for both the watersheds and
stream networks delineated using the two methods. The study shows the capability of the ILWIS
DEM hydro-processing tools used for watershed and stream network delineation using the 90m
SRTM Digital Elevation Model and it is recommended that the both can be used with a reasonable
level of accuracy.
Keywords: Watershed; stream network; GIS; remote sensing; DEM; topographic map.
1. INTRODUCTION
Watershed modelling is an ideal application for
GIS which allows the simulation of hydrologic
processes in a more wholistic manner, compared
to many other models [1,2]. A key component of
watershed modelling is the watershed area that
contributes flow to the point of interest [1]. Each
stream or river is bounded by a watershed divide
and is defined by the highest elevations
surrounding the stream. Watershed, catchment
and drainage basin are terms that are used
interchangeably to refer to, 'the topographic area
that collects and discharges surface streamflow
through one outlet' [3].
Watershed delineation is the process of
identifying the drainage area of any point on a
stream or river network. Topography is usually
the main input in determining a river watershed
therefore its delineation requires the use of
topographic maps which are sometimes not
easily available and outdated in most places [4],
including Nigeria. They are mostly of different
scales when more than one sheet of topographic
map is needed to cover the area of interest.
Though watersheds can be delineated manually
using topographic (contour) maps, it can
however prove to be a very tedious and difficult
task especially in flat terrains [5]. Digital
Elevation Models (DEM) and Geographic
Information System (GIS) softwares are tools
that can be used for modeling of stream
networks [6], delineation of watershed to obtain
parameters that are important for management of
water volume and quality, soil conservation, flood
control, wild life habitat and other hydrological
analyses. The accuracy of the result mostly
depends on quality and type of DEM and the
computer algorithms used. The paper by [7]
buttressed the fact that GIS with remote sensing
(RS) technologies have played an essential role
in supporting both data collection and analysis in
the development of watershed modelling
capabilities.
The use of Digital Terrain Model and GIS
techniques in delineating watersheds in flat and
arid terrains of western Iraq desert was also
demonstrated by [5]. Three GIS packages were
used (Arc Hydrotools, TNTmips and RiverTools)
within two DEMs: the 90m and 30m SRTM in
addition to ASTER 30m. The result showed that
automated watershed analysis of flat terrains
cannot be done without manual evaluation and
correction either by using several seeding points
or river burning technique.
The use of standard Digital Elevation Model for
watershed delineation in ArcGIS 9.1 was also
demonstrated by [8] for the Ayer Hiram forest
Reserve, Selangor. The DEM was obtained by
interpolating a contour map. The automated
watershed delineation was carried out, though
they pointed out that despite its potential
advantages, automated generation of watershed
boundaries has several practical challenges.
Errors could arise because topographical maps
rarely align perfectly, especially in moderate to
low-relief terrain resulting in error of different
interpretations of watershed flow pathways.
Since GIS is fast becoming a very viable
automated alternative for the delineation of
watershed boundaries with results that are
independent of human decisions [5], there is the
need to the check the accuracy and
effectiveness of this alternative because the
areas and perimeters of watersheds are used in
many hydrological analyses.
DEM resolutions for watershed delineation have
been tested as shown in the work done by [9].
The Shuttle Radar Topography Mission (SRTM)
DEM (90m), Advanced Space-Bone Thermal
Emission and Reflection Radiometer (ASTER)
DEM (30m), and Land Development Department
(LDD) DEM (5m) used for the delineation of
characteristics of 144km
2
watershed showed that
the watershed sizes and shapes obtained were
only slightly different.
The finer the DEM resolution the more the
processing time and data storage needs for
modelling with no significant difference in the end
results [9,10,11], therefore coarser DEM may be
Daffi and Ahuchaogu; AJEE, 4(4): 1-8, 2017; Article no.AJEE.35972
3
used as opposed to a finer resolution DEM for
watershed delineation depending on the
watershed size.
Since water flows in the direction of a terrain’s
steepest downhill slope and drainage divides
defined by highest points of the terrain,
watershed and stream network delineation in GIS
are mainly based on Digital Elevation Models
(DEMs). DEMs are grids of elevation that store
the same type of information as contour lines but
with a different data structure.
This study is aimed at delineating the River Dep
watershed boundary and stream network using
the 90m SRTM DEM as input data and ILWIS
3.7.1 ACADEMIC and comparing the size and
shape with the one previously delineated
manually using topographic maps and areal
photographs obtained from [12]. This is with a
view to assessing the suitability of the 90m DEM
for the fast and effective watershed and stream
network delineation in ILWIS 3.7.1.
1.1 Study Area
The Dep River Basin lies between latitudes
00’00”N to 9°20’00”N and longitudes 8°20’00”E
to 35’00”E as shown in Fig. 1. It is situated in
the South Eastern and South Western parts of
Plateau State and North Eastern part of
Nasarawa State in North Central Nigeria. The
catchment covers an area of over 10,000 km
2
.
The upper reaches are very steep at elevations
of up to 1300masl while the lower reach is
relatively flat at elevations of between 78 – 200
masl.
2. METHODOLOGY
Softwares: ILWIS 3.7.1 Academic - GIS analysis
software with spatial and attribute data.
Data Used: 90-metre Shuttle Radar Terrain
Mission Digital Elevation Model (SRTM DEM) of
the study area collected from the Global Land
facility Cover website.
The Digital Elevation Model (DEM) of the study
area, which is the main input data, is shown in
Fig. 2.
Daffi and Ahuchaogu; AJEE, 4(4): 1-8, 2017; Article no.AJEE.35972
4
2.1 Watershed Delineation in ILWIS 3.7.1
Most of the GIS softwares carry out watershed
delineations by considering the following basic
steps as extracted from the ILWIS 3.7.1 HELP
Menu [13]:
Fill Sinks Operation: This is used to clean up
the DEM to remove sinks, which are areas where
water flows into and not out because all
surrounding pixels are higher in elevation.
Flow Direction Operation: This operation
indicates the pixel, out of the eight neighboring
pixels, in a block of 3 by 3 pixels, towards which
water will flow naturally.
Flow Accumulation Operation: This operation
performs a cumulative count of the number of
pixels that naturally drain into outlets. It
represents the amount of water that would flow
into each cell assuming all the water became
runoff and there was no interception,
evapotranspiration or loss to groundwater. The
operation can be used to find the drainage
pattern of a terrain.
Drainage Network Extraction: This operation
extracts a basic drainage network.
Drainage Network Ordering: The operation
examines all drainage lines in the drainage
network map from the Drainage Network
Extraction Operation.
Catchment Extraction Operation: This
operation constructs catchments for each stream
found in the output map of the Drainage Network
Ordering Operation. The operation uses a Flow
direction map to determine the flow path of each
stream.
Catchment Merge Operation: The Catchment
merge operation merges adjacent catchments
found from the Catchment Extraction Operation.
Catchments can be merged in two ways:
By specifying a point map that contains
locations of the stream outlets within a
catchment
By simply specifying a Strahler or Shreve
ordering value
As output a new catchment raster map, polygon
map and attribute table are produced.
The DEM hydro-processing Raster Operations in
ILWIS 3.7.1 Academic were used to identify the
watershed by:
i. Identifying and filling sinks in the DEM
using the Fill Sinks operation.
Daffi and Ahuchaogu; AJEE, 4(4): 1-8, 2017; Article no.AJEE.35972
5
ii. Calculating and creating the flow direction
map with new filled DEM using the Flow
Direction operation.
iii. Calculating and creating flow accumulation
map using the Flow Accumulation
operation.
iv. Creating stream network map from the flow
accumulation grid using the Drainage
Network Extraction operation.
v. Creating stream order raster from the
stream network raster map using Drainage
Network Ordering operation. The method
of stream ordering used was STRAHLER.
vi. Calculating and creating catchment for
each of the streams found in the output
map of the Drainage Network Ordering
operation using the Catchment Extraction
operation.
vii. Merging adjacent catchments from the
catchment extraction operation based on
the Drainage Network Ordering using the
Catchment Merge operation. A stream
order of 5 was used for the processing.
The following processes were used to subset the
watershed of the Dep River Basin from the raster
map obtained from the Catchment Merge
operation:
i. The map from the previous operation was
polygonized to show all the catchments
created.
ii. The watershed of interest was manually
digitized using the create segment map
operation and also using a domain
identifier.
iii. The segment map was polygonized to
produce a polygon map of the delineated
watershed.
iv. A raster map was created from the polygon
map using the polygon to raster operation.
v. Map calculation was used to subset the
irregular shape of the watershed boundary
from the map obtained from the Drainage
Network Extraction operation.
2.2 Stream Network Delineation in ILWIS
3.7.1
The stream network for the Dep River Basin was
processed using the create segment map
operation where the stream network within the
subset watershed boundary was manually
digitized.
The GIS and manually delineated watersheds
and stream networks were overlaid in the
software and compared.
3. RESULTS AND DISCUSSION
The map produced from the Catchment Merge
operation is shown in Fig. 3. The digitized,
polygonized and rasterized Dep River catchment
boundary is shown in Fig. 4. From the attribute
table produced from this process, the total
catchment area for the Dep River watershed was
10640 km
2
. The delineated catchment was seen
to be pear-shaped at the top and narrowing down
at the bottom portion towards its confluence with
River Benue and similar to the watershed
manually delineated.
Daffi and Ahuchaogu; AJEE, 4(4): 1-8, 2017; Article no.AJEE.35972
6
The drainage network which was subset to
the shape of the catchment boundary is shown
in Fig. 5, this gives an indication of the
stream network within the River Dep Basin. The
digitized stream network and watershed
boundary for the Dep River watershed is shown
in Fig. 6.
The GIS delineated stream network and
watershed boundary for the Dep River Basin
follows the same pattern as the one delineated
manually by Comprehensive Engineering
Consultants in 1980 as given in its Final Report
submitted to Lower Benue River Basin
Development Authority, Nigeria. The two maps
are observed to be identical when compared as
shown in Fig. 7.
The total catchment area obtained for the
GIS delineated watershed was 10640km
2
while
it was 9600km
2
for the one delineated by
manual methods in 1980, as recorded in the
report. The same 1980 manually delineated
map when scanned, imported and digitised
in ILWIS 3.7.1 gave the total watershed area
as 10244km
2
. These differences could be as
a result of the effect of input data, which is
the 90m SRTM DEM for the GIS delineation,
or inability of some topographic details to
be captured in estimation using manual
delineation as a result of human limitation.
This shows there was an underestimation
of the catchment area by the manual
delineation.
Using the Strahler method for stream network
ordering for DEM hydro-processing, the stream
order of the river drainage network was
estimated to be 5 and a manual estimation of the
stream order using the delineated stream
network also showed that the stream order is 5.
This shows that GIS can effectively capture the
real watershed characteristics.
The results obtained from the GIS delineation of
the watershed boundary and stream network
compared favourably with the one delineated by
manual method using topographic map as seen
in Fig. 7. The 90m DEM used in delineation was
effective in producing results that would not be
much different had other finer spatial resolution
DEM been used as seen from the work of [9]
where 90m, 30m and 5m DEMs were used for
watershed delineation and the result showed that
there was no significant difference in watershed
sizes and shapes. Also, the results of the work
by [11] showed that although extremely high
resolution data are more readily available now,
the use of such data may not necessarily result
in better DEMs for hydrologic applications. This
suggests that the results obtained are
satisfactorily acceptable.
The differences in the values of the watershed
area obtained using the two methods do not
reduce the effectiveness of the GIS method as
an alternative to the manual method which could
still produce differences from two individuals
carrying out the same task.
Daffi and Ahuchaogu; AJEE, 4(4): 1-8, 2017; Article no.AJEE.35972
7
5. CONCLUSION AND RECOMMENDA-
TION
The results showed that the use of ILWIS DEM
hydro-processing tools with 90m SRTM DEM
produced watershed and stream network similar
in shape, size and pattern to the ones delineated
by manual method. The good agreement
between the results of GIS watershed delineation
and the hand delineation using a 90m resolution
DEM points to the promising future of the use of
remote sensing and GIS as useful data and tools
for hydrological processing and analyses. Thus
with proper ground truthing and other necessary
checks the GIS method can be used for
delineation of watersheds and stream networks
and estimation of other watershed
characteristics. This will help in overcoming the
problem of using topographic maps which are
mostly unavailable, outdated, scarce, incomplete
and of different scales for most parts of Nigeria.
The ILWIS 3.7.1 hydro-processing tools are
recommended for use for the delineation of
watersheds and stream networks with the 90m or
higher resolution DEMs. This is cost effective as
both ILWIS 3.7.1, an open source software, and
the 90m SRTM DEM can be obtained at no cost.
COMPETING INTERESTS
Authors have declared that no competing
interests exist.
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_________________________________________________________________________________
© 2017 Daffi and Ahuchaogu; This is an Open Access article distributed under the terms of the Creative Commons Attribution
License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any
medium, provided the original work is properly cited.
Peer-review history:
The peer review history for this paper can be accessed here:
http://sciencedomain.org/review-history/21883
ResearchGate has not been able to resolve any citations for this publication.
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Using GIS to Delineate Watersheds
  • E Poyer
Poyer E. Using GIS to Delineate Watersheds. [Online].
Integrating Remote Sensing at the Global, Regional and Local Scale. Pecora 15/Land Satellite Information IV Conference
  • G Savant
  • L Wang
  • D Truax
Savant G, Wang L, Truax D. Remote sensing and geospatial applications for watershed delineation. Integrating Remote Sensing at the Global, Regional and Local Scale. Pecora 15/Land Satellite Information IV Conference. Denver, Colorado 10-15 November 2002. American Society of Photogrammetry and Remote Sensing.
The effects of data reduction on LiDar-based Digital elevation models. Image and Signal Processing (CISP) 4 th International Congress
  • J Immelman
  • Lgc Scheepers
Immelman J, Scheepers LGC. The effects of data reduction on LiDar-based Digital elevation models. Image and Signal Processing (CISP) 4 th International Congress, 15 -17 October 2011. IEEE. DOI: 10.1109/CISP.2011.6100417