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TOPIC: Preparing Maps for Map-Based Surface Flow Simulation Model
(Han-River Basin in Korea)

TABLE OF CONTENTS

• Introduction
• Procedure

Map-Based Surface Flow Simulation Model, which is developed by CRWR, is designed to simulate surface flow runoff based on the precipitation or soil moisture contents defined on the subwatersheds of a river basin. To apply the model we need digital base maps for the application basin. One of the methods to get vector based digital map is using a DEM. Next Procedure presents the process to delineate watershed polygons and streamlines using USGS 30" DEM for the Han River in Korea. Arc/Info Grid and ArcView is used to do the work.

PROCEDURE

• Get 30" DEM from USGS

  We can get 30" DEM over the internet from USGS using anonymous ftp.

     > ftp 152.61.128.6
     > cd pub/data/30ASDCWDEM/ASIA
     > get asia_dem3.bil.gz
    

• Decompress the file and obtain the DEM

     > gunzip asia_dem3.bil.gz

  We get asia_dem3.bil

• DEM to GRID conversion

     > arc
     Arc :  grid
     Grid :  imagegrid asia_dem3.bil asia_dem3

  We can get the GRID file

• Display the whole area and Select a region for analysis

  We can get the Korean region from the original asian area.

     Grid :  mape asia_dem3
     Grid :  gridpaint asia_dem3
     Grid :  setwindow * (Select the Korean region using a user defined box)
     Grid :  kdem = asia_dem3(Create a new grid called kdem)
     Grid :  clear
     Grid :  mape kdem
     Grid :  gridpaint kdem value linear nowrap gray

  We get the GRID file of the Korean region, See Figure 1

• Projecting the Grid onto a Flat Map Surface

  We use utm projection to convert the grid points defined on a lat-long mesh to points defined on a cartesian mesh. The projection file is geoutm.prj

     Grid :  kpro = projection(kdem,geoutm.prj,#,500)

  Figure 2 is the kpro GRID

• Select the portion which is land, i.e., delete the sea area.

     Grid :  klan = select( kpro, "value > 10000" ) 

  Figure 3 is the klan file.

• Filling in the Pits

  In order that water can flow across the land, any spurious pits have to be filled in.

     Grid :  fill klan kfil SINK 100 #

• Make Flowdirection Grid

  The flowdirection function in grid assigns to each cell a number corresponding to which of the 8 neibouring cells lies on the path of the steepest descent.

     Grid :  kfdr = flowdirection (kfil) 

• Make Flow Accumulation Grid

  The flow accumulation grids counts all the cells upstream of a given cell

     Grid :  kfac = flowaccumulation(kfdr)

• Stream Network Delineation

  • Create a Grid of Streams

    A grid of the streams can be created from a flow accumulation grid. Delineation criteria is based on the minimum drainage area upstream necessary to define a stream

            Grid :  kstr = con(kfdr > 900,1)

  • Convert the Grid to the Coverage

            Grid :  strcov = gridline(kstr)

    Figure 4 is the stream coverage created against a backdrop of the original dem

  • Seperate the Zone of Cells

    Seperate each reach of the stream network into a diffrent zone of cells

            Grid :  klnk = streamlink(kstr,kfdr)

• Watershed Delineation

  • Find the Location of the Outlet

            Grid :  kacc = zonalmax(klnk,kfac)
            Grid :  kout = con(kacc==kfac,klnk)

  • Find the Watershed

            Grid :  kshd = watershed(kfdr,kout)
            

  • Convert the Watershed to the Coverage

            Grid :  wshcov = gridpoly(kshd)

    Figure 5 is the watershed coverage

• Select the Han River Basin

  An area to be analized can be selected using Arcedit
  Figure 6 is the Han River and Watershed

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