A REVIEW ON WATERSHED DELINEATION USING GIS TOOLS MD. RASHEDUL ISLAM Dept. of Civil Engineering, 415 Engineering Building, University of Manitoba, Winnipeg, Canada, R3T 5V6. In earlier days, watershed delineation was mainly conducted by the method of hand delineation. Recently, this has been suppressed by the GIS techniques. GIS tools are being widely used for delineation of watershed divide and identifying stream network. It is a matter of question, how much it differs between hand delineation and GIS delineation. GIS delineation is mainly based DEM data and there are several methods to prepare DEM. In this study, differences have been observed between hand delineation and delineation from GIS using two types of DEM. One DEM has been prepared from traditional stereo images and another DEM has been prepared by Australian National University Model. The latter incorporates the knowledge of actual river network and a different algorithm for filling sinks. The watershed of Southern Manitoba Region of Canada has been used for this study. The ANU DEM for this region has been prepared by Dr. K. Snelgrove. It is found out that this DEM provides more accurate delineation. Using this delineated watershed, rainfall-runoff hydrograph has been simulated by HEC- HMS using SCS Curve Number method for the three small watersheds of the region. This simulated hydrograph is compared with the actual hydrograph. It is explored that, the actual and computed hydrograph is quite similar. These watersheds are controlled by the flood-detention reservoir. Using HEC-HMS model, the outflow hydrograph for the reservoir has been computed. The computed reservoir outflow and the observed outflow also match appreciably. Basin lag time has been calculated using two different methods and their outcome has been analyzed. It has been found that, hand delineation is cumbersome and laborious, but it is consistent with output from computer algorithm. INTRODUCTION The scope of this study is to delineate watershed by GIS tools and compare with hand delineation. Thereafter, rainfall runoff computation was carried out using HEC-HMS tools using the GIS delineated watersheds and compared with actual hydrographs. The study area is approximately surrounded by from Latitude 49 o 15 / to 49 o 30 / and longitude 98.00 o West to 98 o 30 / West. Fig. 1 shows 3D topography of the Manitoba province as well as the study area. The 3D view has been created using 3D Analyst extension. METHODOLOGY For hand delineation, drainage divides have been located by analyzing contour lines. From contour lines, attempt has been made to identify downslide direction, and an array has been plotted to note down the direction. A divide line has been drawn where arrows