A Simple Drainage Enforcement Procedure for Estimating Catchment Area Using DEM Data David Nagel, John M. Buffington, and Charles Luce U.S. Forest Service, Rocky Mountain Research Station Boise Aquatic Sciences Lab Boise, ID October 20, 2011

Study Area 10,000 km of rivers and streams ~ 1,000 km used by salmon Middle Fork Salmon River

Our Purpose Estimate catchment area Discharge Grain size Salmon spawning habitat

Data 10 m NED DEM dataset NHD stream lines

Problem Flow accumulation lines from DEMs do not match vector stream lines NHD stream DEM flow line

Drainage Enforcement Objective Recondition the DEM so all cells drain toward the stream and downstream Non-enforcedEnforced

Foundation of Watershed Analysis 1)Fill 2)Flow direction 3)Flow accumulation FillDirectionAccumulation

Flow Accumulation Counting up the number of cells that contribute to a location on the stream = catchment area 1,000 12,000

Raster Accumulation to Vector Raster accumulation 12,000 cells Attribute corresponding vector

Mismatch Between Raster and Vector Without Enforcement EnforcedNon-enforced Can’t attribute vector if data are mismatched

Why the DEMs and Stream Lines Do Not Match in Flat Valleys

DEM Production Process 1) Aircraft2) Aerial photo3) Stereo plotter 4) Map production5) Scan and tag 6) LT4X LT4X, Infotec Development, Inc.

Original Contours and 10 m DEM Model Original 40’ contours 2 m contours derived from 10 m DEM LT4X Blue box = 100 m x 100 m 500 m

Original Contours and 10 m DEM Model With Streams Original 40’ contours 2 m contours derived from 10 m DEM LT4X

LT4X made the DEMs from the original contours There were no contours in flat valleys, so there wasn’t information for generating the DEM data Cartographers drew stream lines where they saw them, independent of the LT4X model

Why Not Use LiDAR? Site scale vs. landscape scale

Drainage Enforcement Algorithms 1)ANUDEM - ArcGIS 2)AGREE – Arc Hydro Tools 3)IDDEA – Forest Service

ANUDEM Implemented by ArcGIS (Topo to Raster) Not designed for reconditioning DEMs directly - requires contour lines or point input Not designed for reconditioning DEMs directly - requires contour lines or point input Contour file sets may become too large Contour file sets may become too large Avoids “trenching” Avoids “trenching” Hutchinson, M.F., A New Procedure for Gridding Elevation and Stream Line Data with Automatic Removal of Spurious Pits. Journal of Hydrology, 106:

AGREE Algorithm Implemented by Arc Hydro Tools Dewald, T., NHDPlus User Guide, U.S. EPA and USGS, April 29, 2008 Hellweger, F., AGREE — DEM surface reconditioning system. Center for Research in Water Resources

Drainage Enforcement with AGREE OriginalReconditioned Arcs must point downstream Arcs must point downstream Sharp drop may modify watershed boundaries Sharp drop may modify watershed boundaries Uses “trenching” Uses “trenching”

IDDEA Method Inverse Distance Drainage Enforcement Algorithm 1)Grid stream lines 2)Generate Euclidean distance from all stream lines 3)Drop stream by constant value (e.g. 200 m) and 4)Invert distance, multiply by constant: (1/d) * )Subtract result from original DEM Where c ij, 200, else e ij – ((1 / d ij ) * 1000) c ij is a stream channel cell at raster location ij e ij is the elevation at ij d ij is the Euclidean distance at ij

1) Grid Stream Lines Vector to raster conversion

2) Euclidean Distance from Streams

3) Inverse Euclidean Distance Force constant drop (200 m) at stream channel Force constant drop (200 m) at stream channel Enforcement decreases away from the channel Enforcement decreases away from the channel (1/d) * Value decreases (unitless)

DEM Minus Inverse Distance minus =

Profile Results Preserves relative topography and watershed boundaries

Run Flow Accumulation Enforced Non- enforced

Attributing Vectors EnforcedNon-enforced Higher probability of accurately attributing vectors with the correct contributing area

Results Comparison

Disadvantages of the IDDEA Method 1)“Trenches” the DEM 2)Meander bends smaller than cell size get cut off and reroute flow “Trenching”Cut-offs

Advantages of the IDDEA Method 1)Works relatively quickly at landscape scales 2)Preprocessing of raster or vector data is not required 3)Preserves relative topography and watershed boundaries

Thank you