Regulated Tileline & Ditch flowshed delineation: a comparison study Regulated Tileline & Ditch flowshed delineation: a comparison study Larry Theller,

Regulated Tileline & Ditch Regulated Tileline & Ditch flowshed delineation: a flowshed delineation: a

comparison studycomparison study

Larry Theller, Larry Theller, Agricultural and Biological Engineering Dept., Purdue UniversityAgricultural and Biological Engineering Dept., Purdue University

Greg Lake, Greg Lake, Howard County Surveyor’s OfficeHoward County Surveyor’s Office

Goals: Goals:

Produce tile/ditch flowshed map for Produce tile/ditch flowshed map for regulated drainsregulated drains

Compare ease-of-use and utility between Compare ease-of-use and utility between traditional ArcINFO and new ArcHydro traditional ArcINFO and new ArcHydro methodologymethodology

Produce and deliver training aids to county Produce and deliver training aids to county staffstaff

ArcINFOArcINFO ESRI product.ESRI product. Traditional script-based watershed Traditional script-based watershed

delineation delineation process.process. User User interface isinterface isdifficult anddifficult andobscureobscure

ArcHydroArcHydro

Interface and data model for ArcGIS 9Interface and data model for ArcGIS 9 Interface portion is used in this projectInterface portion is used in this project Data model is not used in this project – yet.Data model is not used in this project – yet.

Interface is organized set of menus that Interface is organized set of menus that step user through each phase of process step user through each phase of process in sequence.in sequence.

ArcHydro Tools organizes the watershed tools into a sequential menu

Process:Process: Prepare water features (regulated and unregulated)Prepare water features (regulated and unregulated)

Create DEMCreate DEM

Prepare hydrologically correct DEM:Prepare hydrologically correct DEM: Water should flow through true path in DEMWater should flow through true path in DEM All water should drain from mapAll water should drain from map Prepared DEM must extend beyond area of interestPrepared DEM must extend beyond area of interest

Calculate flow direction and accumulation layersCalculate flow direction and accumulation layers

Calculate drainage lines over the DEMCalculate drainage lines over the DEM

Use drainage and flow direction to create “catchments”Use drainage and flow direction to create “catchments”

Subdivide “catchments” to match regulated portionsSubdivide “catchments” to match regulated portions

Existing water features, based Existing water features, based

on USGS layers, were not accurate enoughon USGS layers, were not accurate enough

Stream features not in bottom of valleyStream features not in bottom of valley

Preparation of water features includes Preparation of water features includes digitizing of tiles, ditches, unregulated digitizing of tiles, ditches, unregulated waters and “drainage points” where waters and “drainage points” where regulation changes.regulation changes.

Tiles and ditches were digitized by Tiles and ditches were digitized by georeferencing scanned maps over aerial georeferencing scanned maps over aerial photos, and reconciling differencesphotos, and reconciling differences

Creation of DEM used model Creation of DEM used model built for previous aerial photo built for previous aerial photo projectsprojects

Traditional method to create hydrologically Traditional method to create hydrologically accurate DEM is to “burn” a slot into the accurate DEM is to “burn” a slot into the DEM following the actual mapped flow of DEM following the actual mapped flow of waterwater

Major difference in two Major difference in two methods is this: ArcHydro methods is this: ArcHydro uses a “valley” not a “slot”uses a “valley” not a “slot”

Traditional ArcINFO methodTraditional ArcINFO method

ArcHydro default methodArcHydro default method

Catchments adjusted to legal drainsCatchments adjusted to legal drains

Problems:Problems:

Problems:Problems:

Places where the DEM does not truly Places where the DEM does not truly describe reality can require edits. describe reality can require edits.

4 Lane Highway4 Lane Highway

Model says Model says this water this water drains under drains under highwayhighway

High groundHigh ground

Problems:Problems:

May require an onsite visit to checkMay require an onsite visit to check

Problems:Problems:

Accuracy suffers if the mapped pathway Accuracy suffers if the mapped pathway of water is across the side of a hill rather of water is across the side of a hill rather than the bottom of the valleythan the bottom of the valley

Problems:Problems:

Check drainage path versus actual tilesCheck drainage path versus actual tiles

TrainingTraining

Excellent tutorial from UTExcellent tutorial from UT http://www.crwr.utexas.edu/gis/gishydro04/index.htmhttp://www.crwr.utexas.edu/gis/gishydro04/index.htm see see

“exercises”“exercises”

Flash Movie based training from PurdueFlash Movie based training from Purdue http://pasture.ecn.purdue.edu/~caagis/PurdueGIS/video/howard/indexhttp://pasture.ecn.purdue.edu/~caagis/PurdueGIS/video/howard/index

Book:Book: Arc Hydro: GIS for Water Water Arc Hydro: GIS for Water Water Resources Resources edited by Dr. Maidment. edited by Dr. Maidment.

ConclusionsConclusions

ArcHydro adds excellent user direction to ArcHydro adds excellent user direction to follow a complicated sequence.follow a complicated sequence.

Drainage patterns are represented in the Drainage patterns are represented in the DEM in a more realistic fashion.DEM in a more realistic fashion.

For the future, a network-based approach: For the future, a network-based approach: http://www.crwr.utexas.edu/gis/gishydro04/index.htmhttp://www.crwr.utexas.edu/gis/gishydro04/index.htm