C. R. NAIDU ET AL.293
constitutes nodes and lines. The node data refers to
Sluice OT and line refers to canal. The flow direction
and continuity errors were taken care while digitization
and later checked for continuity in the ArcGIS Network
Module.
The canal ID is created with a unique multi digit
number constitutes a combination of alphabets and
numbers. All canal reaches have only one upstream reach
but have more than one downstream reaches. Only the
upstream reach ID is kept for each sections in the devel-
oped data system. The hierarchic relationship can be re-
trieved through th e use of Upper id.
3.4. Creation of Contour Map, Digital Elevation
Model (DEM) and Aspect Map
Digital representations of the terrain often form one of
the main elements of the mapping process. Digital Ele-
vation Model (DEM) [15] represents continuous varia-
tion of topography over space that helps in assessing
landscape characteristics and has a wide application in
surface hydrology modeling. These characteristics help
to determine slope, flow directions, areas, boundaries
and outlets of drainage basins and ultimately in delineat-
ing the Block and Chak boundaries for this study. Using
GRASS GIS the DEM is generated.
Contours are digitized from the Block maps collected
from the Irrigation Department. These contours used as
an elevation data for creating the Digital Elevation Mod-
el. The DEM is used as an input for creating the Aspect
Map.
3.5. Delineation of Command Area, Block and
Chak Boundaries
The delineation is based on surface modeling techniques
available in many GIS and Remote Sensing [16] Tech-
niques. GRASS Software is used for doing the surface
modeling. One of the most soph isticated GIS capabilities
which are very useful in hydrographic modeling is the
digital representation of the topography of the catch-
ments. Surface modeling is a general term which is used
to describe the process of representing a physical or ar-
tificially created surface by means of a mathematical
expression. Terrain modeling is one particular category
of surface modeling which deals with the specific prob-
lems of representing the surface of the earth. The tech-
niques of terrain modeling are of widespread use and
have been app1ied widely in the physical and earth sci-
ences.
The DEM [16] provides 3D [16] input data for calcu-
lating flow direction across terrain, which is subse-
quently used for creation of stream networks. Delinea-
tion of surface Hydrology Features from DEM data has
become standardized on the eight-direction pour point
model in which each cell is connected to one of its eight
neighbor cells (four on the principal axes, four on the
diagonals) according to the direction of steepest descent.
Given an elevation grid, a grid of flow directions is con-
structed, and from this is derived a grid of flow accumu-
lation, counting the number of cells upstream of a given
cell. Streams are identified as lines of cells whose flow
accumulation exceeds a specified number of cells and
thus a specified upstream drainage area. Extracted stream
lines obtained with this give us general information
about the characteristic of terrain.
The Chaks and Block Boundaries under each canal are
delineated reference to canal network, DEM, Aspect and
drainage network extracted from surface modeling and
SOI Topo maps. The Chaks are mapped as per the type
of canal and its flow direction. If the canal is a ridge ca-
nal Chaks are identified on both sides of it and if it is a
contour canal Chaks are on one side only. Spread of a
Chak is between the canal and the drainage line.
4. Results and Reports
The canal network with line and nodes are represented in
Figure 3. The canal network is overlaid on DEM and the
the streams and valleys are extracted from the hydraulic
model. The canals and streams are combined together to
form block and chak boundaries are shown in Figure 4.
There are 13 canals mapped in network model and in-
cluding major canal and under each canal the sub-blocks
and chaks are identified with reference to DEM and
identified topographic features. Canal and corresponding
sub-block are coded with same identification code.
Chaks under each sub-block are prefixed with canal and
the corresponding sub-block id.
The gross comman d area under each block under each
canal and the lengths of the canals are given in Table 3.
The command area under WL2 Canal is shown in Figure
5 using spatial query.
The gross command area of each chak under an indi-
vidual block i.e. WR6 is shown in Table 4.
The delineated block boundaries are compared with
the existing block maps. The measurements of block
areas and canal lengths in GIS are matching with the
statistics given by the irrigation department. The GIS
database found very usefu l in identification of canals and
corresponding block and chak boundaries. Due to the
hierarchy and the unique identity of block and chak un-
der each canal the spatial queries and retrieval of data
and results are more conven ient for decision making and
planning of water releases for effective water manage-
ment [17].
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