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Geographical Information System (Dam and Watershed Analysis)

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Contour maps are converted to digital contour files and ... contour maps/toposheets ... The elevation of each point is increased and the resultant DEM is stored ... – PowerPoint PPT presentation

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Title: Geographical Information System (Dam and Watershed Analysis)


1
Geographical Information System (Dam
and Watershed Analysis)
  • Kumar Digvijay Singh
  • 02D05012

Under Guidance of Prof. Milind Sohoni
2
Outline
  • Watershed delineation
  • Sinks, flat areas, flow direction, delineation
    etc.
  • Dam Construction
  • Visualization and Calculation of Storage and
    Catchment
  • Parameters regarding dam and field usage
  • Demo. of tool

3
Introduction
  • What is GIS?
  • GRAM
  • GIS package developed by CSRE, IIT Bombay.
  • Software with modules of Map editing, Raster
    analysis, Terrain Modeling, Watershed
    delineation.
  • Objectives of project.

4
Watershed
  • Total area of water flowing towards an outlet
    point (Pour point).
  • Water flows in the direction of the terrain
    steepest downhill slope. Streamlines (blue
    arrows) are orthogonal to the contour lines.
  • Drainage line (red line) are found along the
    highest points of the terrain.

5
DEM
  • Digital Elevation Models (DEM) are grids of
    elevation.
  • Contour maps are converted to digital contour
    files and elevation values are interpolated from
    irregularly spaced points to regular grid points.
  • Watershed delineation can be based on DEMs rather
    than contour lines.

6
Digitizing the Map
  • Map models
  • Raster Model
  • Tin Model
  • Methods of digitizing
  • Digitizing through spot heights
  • Digitizing through contour maps/toposheets
  • Input map for our tool is in the form of raster
    grid, with each cell value being elevation above
    mean sea level.

7
Watershed Delineation
  • Removing sink
  • Sink or depression is a cell or a group of cell
    which is at a lower elevation than all its
    neighboring cells.
  • Convert sink to flat area by increasing the
    height of sink to minimum height of neighbor.
  • Remove flat areas
  • A cell is said to be part of a flat area, if all
    of its neighbors have the same elevation as
    itself, or a higher elevation.
  • Each cell identified as being part of a flat area
    is incremented by a small increment

8
Watershed Delineation
  • Flow Directions
  • The eight-direction pour point algorithm (D-8)
    assigns a flow direction code to each cell, based
    on the steepest downhill slope as defined by the
    DEM.
  • The flow direction code indicates the cell
    towards which the water flows.
  • Flow direction is calculated by comparing the
    distance weighted drop of neighboring cells.

Flow direction codes
9
Watershed Delineation
  • Flow Accumulation
  • Flow accumulation is a measure of the drainage
    area in units of grid cells.
  • The flow accumulation value of a cell is the sum
    of the flow accumulation values of the
    neighboring cells and the number of neighboring
    cells which flow into it.

32 64 64 128
16 8 16 1
16 1 1 1
8 4 4 2
0 0 0 0
0 1 0 0
2 0 1 2
0 0 0 0
Transforms to
10
Watershed Delineation
  • Apply Threshold
  • Threshold is given to find out all pixels
    having a flow accumulation value above a certain
    value. The value is supplied by the user and the
    flow of water in drainage is calculated on the
    basis of this threshold.
  • Pour Point.
  • Watershed delineation around the drainage.

11
Dam Construction/Visualization
  • End point is selected by the user and a line is
    drawn between these end points to give a view.
  • Various parameters given by user
  • Aspect Ratio
  • Width of top of dam
  • Height of dam( lt Maximum height)
  • Foundation depth
  • The elevation of each point is increased and the
    resultant DEM is stored as a raster image.

12
Storage Calculation
  • Find all those cells that will be covered by
    water after dam construction.
  • A 2-D array corresponding to the cells of DEM
    with each cell having a value from
    -1,0,1,2.
  • Value assigning scheme
  • -1 end cells of image.
  • 0 Cell that is not in storage area.
  • 1 cell currently processing
  • 2 cell in the storage area.

13
Storage Calculation
  • Initially assign all cells except border cells a
    value 0.
  • Start with a single cell in area and recursively
    go on visiting all those neighbor cells which are
    connected to this cell and are at height lesser
    than dam height.
  • Give all the visited neighbor a value 2 and color
    these neighbors, showing the storage.

14
Storage Visualization
Raster Map of Gudwan area Before Dam construction
Storage with Dam
15
Storage Visualization
  • Data Collection Limitation
  • Null Values for unknown points giving a low
    value outside the considered area.

16
Catchment Visualization
  • Catchment is defined as area through which inflow
    of water occurs into the dam.
  • The inflow will be towards a cell if neighboring
    cell have FD value as in figure

17
Catchment Visualization
  • Assign a 2-D array corresponding to the cells of
    DEM as values
  • -1 Border cells of image.
  • 0 The cell that is not in catchment area 1
    Currently processing cell
  • 2 cell in catchment area
  • 3 cell in storage area
  • 4 cell with dam constructed
  • All those cell whose inflow is towards any of
    storage cell ( excluding the dam cells) will
    contribute towards the catchment area.

18
Dam Calculations
  • Volume Calculation
  • Consider the cross section of dam as above figure

19
Dam Calculations
  • Volume Calculation
  • Cross section area is
  • W( H f ) B( H 2f )
  • Where
  • W width of top of dam
  • H Elevation of dam above mean sea level
    Elevation of cell before dam.
  • f foundation depth
  • B base of dam (H / AS)
  • AS Aspect ratio
  • H Maximum height of dam from the ground
  • Length of dam can be calculated by using end
    points and scale factor for dam.

20
Dam Calculations
  • Volume Calculation
  • The volume contribution of each cell for dam
  • Vc Length/ (number of cells)
  • Therefore volume is given as
  • V sum( W ( Hi f ) (H/AS)( Hi 2f) )Vc
  • Where
  • Hi height difference of each cell

21
Dam Calculations
  • Surface Area Calculation
  • The perimeter of cross-section is given as
  • PM W 2(slant height)
  • Where,
  • slant height is the length of inclined surface
    of dam.
  • SA sum( W 2( Slant height of each cell) )Vc
  • For both , the volume and the surface area the
    scale factor can be found from the header
    information of raster image.

22
Dam Calculations
  • Spill Height
  • Requirements
  • Flow rate at the bottom of dam
  • Velocity of water at bottom of dam
  • Dam inflow rate ( Maximum volume of incoming
    water at peak rainfall )
  • Number of spill ways
  • Taking the incoming water flow rate as
  • Vmax (n.h.d( v2 2.g.D)1/2)

23
DEMO
  • Some of the visual Images After dam construction

24
Error Possibilities
  • The exact contribution of each pixel cant be
    found which may lead to some errors.
  • Variation of Scale factor.
  • Number of cells with increased heights.
  • Error in volume and surface area calculation.

25
Field Work
  • During the course of this project we have
    analyzed the work of construction of check dam in
    the areas of Gudwanwadi and Belachiwadi of Karjat
    area.
  • The severe water storage problem of Karjat Taluka
    of Raigad district.
  • The detailed description for the dam construction
    can be found at
  • http//www.cse.iitb.ac.in/ctara

26
Conclusion
  • With the help of this visual tool a rough
    estimate of water storage and various parameters
    of dam can be found.
  • Future Scope
  • Automatic location of optimal dam site for a
    given map.

27
References
  • Ian Heywood, Sarah Cornelius, Steve Carver. An
    Introduction to Geographical Information System.
    Pearson Education Press, 2003.
  • P.Venkatachalam, B.Krishna Mohan, Amit Kotwal ,
    Vikas Mishra,V.Muthuramakrishnan
  • and Mayur Pandya. Automatic delineation of
    watersheds for hydrological application.
  • Robert J. Fowler and James J.Little. Automatic
    extraction of Irregular Network Digital terrain
    models, ACM 1979.
  • 4. Andy Mitchell. The ESRI Guide to GIS Analysis.
    Environmental System Research Institute,
    California 1999.

28
Questions or Comments??
29
Thank you
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