Transcript GIS and Remote Sensing in Water Resources Management

Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Application of GIS in
Watershed Analysis
Dr. A.K.M. Saiful Islam
Institute of Water and Flood Management (IWFM)
Bangladesh University of Engineering and Technology (BUET)
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Watershed analysis using ArcGIS
This training will be on:
1.
2.
3.
4.
5.
6.
7.
Digital Elevation Model (DEM)
Flow direction
Flow accumulation
Identify and removing sink
Stream Network
Stream Links
Watershed analysis
Input Data
DEM data of Bangladesh (Resolution 900m)
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
How to turn on Hydrologic Modeling
1. First turn on Spatial Analyst
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Hydrology Tools
Activate
ArcToolbox from
window menu
Expand
“Hydrology” from
“Spatial Analyst”
Tools
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
1.Digital Elevation Model
• Add digital elevation model of Bangladesh
• Click on + icon and select bgd900dem
DEM of Bangladesh
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
(Resolution 900m)
This DEM will be used
To calculate Flow direction
WFM 6202: Remote Sensing and GIS in Water Management © Dr. Akm Saiful Islam
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
2. Flow direction
Flow directions simplified: “Dump a bucket
of water on your surface and see which of
way it flows!”
Shows the direction water will flow out of
each cell of a filled elevation raster.
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Flow Direction for cell
1014
1011
1004
+1
1019
1015
1007
-4
1025
1021
1012
-10
Cell Elevation
+0.71 +4
+7.78
-4
+8
-7.07
-6
+4
-6
1.414
1
+8
+3
1
Distance weight
Elevation difference
32
64
16
8
+2.12
Distance weight Gradient
+11
Flow direction
128
1
4
2
Flow direction
Number
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Flow direction using ArcToolbox
• Click flow direction and select bgd900dem
as input surface raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Flow direction raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
3. Flow accumulation
 Flow accumulation simplified: “Accumulate flow for each
cell considering ALL uphill cells!”
 Used to estimate rainfall volume within a watershed and
delineates drainage.
 A flow accumulation raster tabulates for each cell the
number of cells that will flow to it.
 A flow accumulation raster records how many upstream
cells will contribute drainage to each cell ( the cell itself is
not counted).
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Flow Accumulation in cell
1014
1011
1004
996
1019
1015
1007
999
1025
1021
1012
1003
1033
1029
1020
1003
Flow direction
Cell Elevation
0
0
1
2
0
0
2
5
0
0
1
1
0
0
0
0
Flow accumulation
From
0
1
2
3
4
To
1
2
3
4
5
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Flow accumulation using Arc
Toolbox
• Click flow accumulation and select
flowdir_bgd91 as input surface raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Flow accumulation raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
4. Identify and removing sink
• Sink is surrounded by higher cell. It can
artificially terminate streams by trapping flow.
• It is caused by possible error in the elevation
data and need to be removed before attempting
hydrology analysis.
Sink
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Filling Sinks
• Filling sinks is an iterative process.
• Sink cell values are changed to equal neighboring
elevation cell values. Lowest value is used.
• Use Merge to put new sink values in the elevation
theme. Test again for more sinks.
Fill to lowest
Neighboring cell
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Identify sink using Arc Toolbox
• Click on Sink from hydrology
• Select flowdir_bgd91 as input flow
direction raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Sink raster
• A total of 4621 sinks found
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Fill Sink using Arc Toolbox
• Click on Fill from hydrology
• Select bgd900dem as input flow direction
raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Filled sink DEM
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Use filled sink DEM
Now create Flow direction raster aging
using this filled sink DEM.
Create Flow Accumulation raster using
this new Flow direction raster.
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Flow Direction raster
using filled sink DEM
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Flow Accumulation raster
using filled sink DEM
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
5. Stream network
• You can use the flow accumulation grid to identify
drainage courses by extracting those cells with the
highest accumulated flow values ( cell contains the most
water are stream channel).
• You can create a drainage network of any detail by
choosing the appropriate volume values (300 is used for
this data).
• Choice of threshold value can be arbitrary. It should be
corresponding to high resolution topographic maps of
filed maps.
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream Network using ArcToolbox
• Select Flow
accumulation
as input
conditional
raster
• Set 1 as
constant value
• Expression:
Value > 300
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream Network raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream network on Flow
accumulation raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
6. Stream Links
• After a stream network is derived from a
flow accumulation raster, each section of
the stream raster line is assigned a unique
value and is associated with a flow
direction.
37
36
35
Arbitrarily assign unique values to each link of the stream networks.
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream link using Arc Toolbox
• Select Stream network as input stream
raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream Link
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream Order
• Assign a numeric order to stream link. Use either
Shreve (true) or Strahler (false) ordering
methods.
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream order using Arc Toolbox
• Select streaml_con_1 as input stream
raster.
• Stream ordering method is STRAHLER
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream Order raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Steam as Shape object
• The stream link raster file can be
converted into line feature class.
• Streams can be represented as shape file.
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream to Feature using Arc
Toolbox
• Select Streaml_con_1 as input stream
raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Stream as Shape file
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
7. Watershed Analysis
• Watersheds delineate a drainage area.
• Drainage basin, water sheds, basin, catchments area,
and contributing area are synonymous terms referring to
an area of drainage that contributes water to a common
outlets (pour points).
Water
sheds
Pour
Point
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Water shed using Arc Toolbox
• Select stream link as input raster
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Watershed
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Change symbology of watershed
• Double click and change as Unique values
Concept Course on Spatial Analyst @ Dr. A.K.M. Saiful Islam
Unique Basins