DEM for surface analysis
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DEM FOR SURFACE ANALYSIS OF THE CATCHMENT AREA
OF ARAKERE LAKE
Vishwanath B.C.*
Hanjagi D Ashok**
Research Scholar, Department of Geography, Bangalore University, Bangalore.
Associate Professor, Department of Geography, Bangalore University, Bangalore.
Abstract
Water is one of the most essential & scare natural resource in the terrestrial ecosystem of the
world. To meet the increasing demands of water, efficient management of surface and ground
water is needed. Bangalore lakes occupy about 4.8% of city’s geographical area covering both
urban & rural areas. With the increasing the industrialization & urbanization in the city fresh water
has been polluted. Out of which Arakere Lake also polluted because of the unchecked urban
water discharged by into it. Hence, the Arakere Lake has been selected for piece of research
work. Arakere Lake situated about 11 km south from center of the Bangalore city. Arakere lake
situated between 120 52’ to 120 53’ North latitude and 770 35’ to 770 36’ east longitude and at the
elevation of 900 meters above mean sea level. The research paper analyses the DEM of the
catchment area of the Arakere Lake for watershed management. Topomap & GPS points are
used as data and Arc GIS, Erdas & GPS are used for achieving of the set aim. In this way we
completely focus on the Arakere lake catchment area.
Key words: DEM, Surface Analysis, Catchment Area.
Introduction
A lake is a terrain feature, a body of liquid on the surface of the earth. It is a body of
fresh or salt water of considerable size that is surrounded by land. The earth is called “The
water planet because it has approximately 14.108 cubic Km of water of which 97.5% exists in
the seas and oceans 1.5% locked up in the Antarctic or Arctic ice caps, ground water.
Therefore, we can
freely access lake water only (0.007%). Hence lakes are the best
freshwater sources available on the earth’s surface “Lakes are valued as fresh water sources
not only for that and also for fishing, water transport, recreation and tourism.
Every one lives within a catchment area. Catchment area is a geographical region
where all the water that falls within it arrives to a common point, such as a lake. A catchment
area is an extent or an area of land where surface water from rain & melting snow or ice
converges to a single point. Other terms that are used to describe a catchment area are
drainage basin, catchment basin, drainage area, water basin, and watershed. Each catchment
area is separated topographically from adjacent basins by a geographical barrier such as a
ridge, hill or mountain. The limits of a catchment area are the heights of land. The amount of
water reaching the lake from its catchment area depends on the size of the area, the amount of
precipitation, & the loss through evaporation & through absorption by the earth or by the
vegetation. The health of the upland area of a watershed affects the quality & quantity of the
water downstream. We have to think of the watershed as a whole connected unit, with the
upland conditions affecting the quality of water, air etc. what happens upstream will influence
everyone who lives downstream. The catchment area is one of the primary considerations in the
planning of lakes for water supply purposes.
Surface represents phenomena that have values at every point across their extent. The
values at the infinite number of points across the surface are derived from a limited set of
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Vishwanath B.C., Hanjagi D Ashok
sample values. These may be based on direct measurement, such as height values for an
elevation surface, measured locations values are assigned to the surface by interpolation.
Surfaces can also be mathematically derived from other data, such as slope and aspect
surfaces derived from an elevation surface.
Objectives of the study
To demarcating the catchment area boundary of Arakere lake. To know the Stream
ordering. To know the Flow Direction.
Methodology
Topomap, GPS data, personal observation are used for demarcate the catchment area.
DEM, Topomap and personal observation are used for identify the streams in the catchment
area. To create DEM GPS data are used. To know the stream ordering Strahelr’s stream order
method is used. To know the flow direction DEM, Arc GIS, personal observation is used.
Techniques of research
Arc GIS used for mapping. GPS and ERDAS used for modeling.
Importance of the study
In the catchment area of Arakere Lake available land and water resources are not
utilized effectively to improve the livelihood & socioeconomic conditions of the inhabitants.
Rapid growth of Population, Human settlements, Industrialization & Public sewage sources are
the chief factors for the degradation of lakes. Now a days Arakere Lake catchment area sees
flooding immediately after rains. The flooding causes lot of suffering & damage. It is important in
all such area to build storm water drains & divert rain water through these drains. The storage
capacity of lakes should also be improved to hold as much water as possible. It is very
expensive and difficult to visit each point of the study area to collect data regarding surface like
height and flow direction. Hence the research work has been taken for Arakere lake watershed
management.
DEM
Digital elevation models are rapidly available data sets that represent the elevation of
the earths surface at discrete points in a regular, rectangular grid. DEM has a Z values at
regularly spaced intervals in x & y. Digital elevation models are data files that contain the
elevation of the terrain over a specified area, usually at a fixed grid interval over the Bare Earth.
The intervals between each of the grid points will always be referenced to some geographical
coordinate system.
The principal components of a drainage basin are its topographic form & the topologic
structure of its Drainage network. Knowledge of the drainage divides of the drainage network
can be used to provide better estimates of slopes & aspects. A raster DEM contains sufficient
information to determine general patterns of drainage & watersheds. A DEM is a raster
representation of a continuous surface, usually referencing the surface of the earth. The most
common digital data of the shape of the earth's surface is cell-based digital elevation models
(DEMs). This data is used as input to quantify the characteristics of the land surface. In this
research paper streams are generated and flow direction was identified with using DEM and Arc
Map GIS software.
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Study area
Arakere Lake situated about 11 km south from center of the Bangalore city. Arakere
lake situated between 120 52’ to 120 53’ North latitude and 770 35’ to 770 36’ east longitude and
at the elevation of 910 meters above mean sea level.
LOCATION MAP OF ARAKERRE LAKE
Figure 1. Study Area
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Vishwanath B.C., Hanjagi D Ashok
Figure 2. DEM for study area
Stream ordering
In the drainage basin analysis the first step is to determine the stream orders. In the
present study, the channel segment of the drainage basin has been ranked according to
Strahler’s stream ordering system. Stream ordering refers to the determination of the
hierarchical position of a stream within a drainage basin. A drainage basin consists of its several
branches having different positions in the basin area and they have their own morphometric
characteristics and therefore, it becomes necessary to locate the relative position of a segment
in the basin, so that the hierarchical organization of stream segments is visualized thus stream
order is defined as a measure of the position of a stream in the hierarchy of tributaries. The
smallest un branched stream segment was designated as the first order stream. The one
formed by the merging of two such first order segments was designated as the second order
stream & so on.
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Figure 2. Stream ordering
In this map Blue lines shows the Fist order streams, Red lines shows the Second order
streams, green lines.
Table 1. Stream order, stream number & stream length
Stream Order
NO of Streams
First Order Streams.
53
Second Order Streams.
17
Third Order Streams.
4
Fourth Order Streams.
1
Total Length of streams
8.8 KM
6.5 KM
2.1 KM
0.2 KM
The characteristic of the study area it exhibits is a 4th order drainage basin (Figure-2). In
this catchment area there are 53 first order streams, 17 second order streams, 4 third order
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Vishwanath B.C., Hanjagi D Ashok
streams and 1 fourth order stream are identified. In the selected watershed number of stream
will decrease when the stream order is increasing. Drainage patterns of stream network from
the basin have been observed as mainly dendritic type which indicates the homogeneity in
texture and lack of structural control.
Flow direction
Study of the flow direction also one of the important analysis to know the morphometric
status of the drainage basin. One of the keys to deriving hydrologic characteristics about a
surface is the ability to determine the direction of flow from every cell in the raster. This is done
with the Flow Direction function. This function takes a surface as input and outputs a raster
showing the direction of flow out of each cell. If the output drop raster option is chosen, an
output raster is created showing a ratio of the maximum change in elevation from each cell
along the direction of flow to the path length between centers of cells.
There are eight valid output directions relating to the eight adjacent cells into which flow
could travel. This approach is commonly referred to as an eight direction (D8) flow model and
follows an approach presented in Jensen and Domingue (1988). The direction of flow is
determined by finding the direction of maximum drop from each cell. This is calculated as
Maximum drop = change in z-value / distance
Figure 3. Flow Direction
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Findings & Conclusion
The drainage basin is being frequently selected as an ideal geomorphologic unit.
Watershed as a basic unit of surface analysis has gained importance because of its topographic
and hydrological unity. GIS techniques characterized by very high accuracy of mapping and
measurement prove to be a competent tool in surface analysis. Stream ordering, Flow direction
are the most use full measure for the surface analysis of drainage basin which certainly control
the runoff pattern, sediment yield and other hydrological parameters of the drainage basin.
Selecte ddriainage network has dendtrict drainage pattern hence the watershed has flow in all
direction.
The characteristic of the study area it exhibits is a 4th order drainage basin . Drainage
patterns of stream network from the basin have been observed as mainly dendritic type which
indicates the homogeneity in texture and lack of structural control.
Reference
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Badar Md. 2005, HydroGeomorphology, New India Publishing
Bolstad Paul, 2005, GIS Fundamentals, (2nd Edition), Edier Press.
Chorley & Kennedy, 1971Physical Geography A Systematic Approach, The Pitman Press
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Downs, 1988, The Geographic Eye: Seeing through GIS, Transaction in GIS.
Malik Imran M., 2011, Watershed Based Drainage Morphometric Analysis Of Lidder Catchment
In Kashmir Valley Using Geographical Information System, Recent Research in Science and
Technology.
Rao K Nageswara., 2010, Morphometric Analysis of Gostani River Basin in Andhra Pradesh
State, India Using Spatial Information Technology, International Journal of Geomatics And
Geosciences Volume 1, No 2.
Singh Savindra, 2006, Geomorphology, Prayag Pustak Bhavan.
Singh Savindra, 2007 Fundamental of Physical Geography, (Third Edition), Rawath
Publication,
Strahler & Arthur N. Strahler 1988, Modern Physical Geography, (Fourth Edition), Von
Hoffman Publication.
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