hydrological modeling

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Hydrological Modeling. Overview. Introduction Watershed delineation Automatic delineation Flow length. Introduction. Watershed management. Definition of watershed. “The region draining into a river, river system, or body of water” American Heritage Dictionary - PowerPoint PPT Presentation


  • Hydrological Modeling

  • OverviewIntroductionWatershed delineationAutomatic delineationFlow length

  • Introduction

  • Watershed management

  • Definition of watershedThe region draining into a river, river system, or body of waterAmerican Heritage DictionaryThe upstream area of any given point on the landscapePhysically defined by drainage point and upstream areaAlso known as basin, sub-basin, catchment, and contributing area

  • Watershed delineation

  • How it worksWater always flows downhillFor any point on a grid representing a landscape, a drop of water can be traced downhill direction of flow is known for every DEM cellFor any point on a grid representing a landscape, a flow pathway can be traced back uphill flow accumulation is known for every DEM cellUphill back-tracing proceeds to a ridgeline or to the edge of the gridTermination of uphill back-tracing defines watershed boundary

  • Watershed delineationSteps (with ArcToolbox):Create a depressionless DEM Calculate flow direction Calculate flow accumulation Create watershed Pour points Delineate watersheds

  • 1. Creating a depressionless DEMDEM must eventually drain off edge of gridAreas of internal drainage will result in unprocessed areasFILL routine fills in sinks or cuts off peaks creating a new grid with no drainage errors

  • 2. Flow directionEvery cell flows into another cell or off the grid edgeFlow direction is calculated as the direction of steepest downward descentFlow direction is calculated for each cell, resulting in a new grid theme

  • 2. Flow directiondirection of flow is saved as a code number

  • 2. Flow directionnorth-flowing cellscoded as 64

  • 2. Flow directionFlow direction grid

  • 3. Flow accumulationEach cell has been coded for direction of flowCumulative flow is calculated from flow directionOutput grid is created where values are the number of upstream cellsLower accumulation values are ridge topsHigher accumulation values are valleys & stream channels

  • 3. Flow accumulation135

  • 3. Flow accumulation

  • single class legendshows high flow cells3. Flow accumulation

  • Fit depends on accuracy of the DEM and stream layers 3. Flow accumulation

  • 4. Watershed Pour pointsWatersheds are defined by outlets (pour points)Pour points should be placed in high-flow pathwaysBasins will be generated from pour point to ridgeline or to upstream sub-basinPour points should be numerically coded per sub-basinPour points must be converted to a grid layer

  • 4. Watershed Pour pointsCreate as many pour points as necessary

  • 5. Delineating watershedsPreliminary steps are completedFilled DEMFlow directionFlow accumulationPour points created & converted to gridRun tool to create watersheds

  • 5. Delineating watershedsWatersheds represent area upstream from Pour points and terminate at ridgelines, uphill sub-basin boundary, or edge of the grid

  • 5. Delineating watersheds

  • Automatic delineation

  • Automatic delineation

    Pour points automatically selected by intersection of highest-flow pathways and grid edge

  • Automatic delineation

  • Flow length

  • Flow lengthFlow distance for every cell to outlet

  • Flow lengthFlow distance for every cell to closest stream

  • Flow lengthEuclidean distance vs. flow distance

  • HomeworkRead: Hydrological Modeling & Watershed Delineation, Map Layouts

    Study for the exam

    Presentations:3/5 Luke, Jennifer, Josh3/7 Chris, Prati, Carolyn

    ****Important topic in modern landscape managementIn the past, landscapes have been managed by ownershipPlant & animal species do not obey ownership boundariesNeed for physically or biologically based land divisions



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