Utilizing Automated Tools in ArcGIS Accuracy Assessment of Methods for Quantifying the Upper Virgin River Watershed Basin Utilizing Automated Tools in ArcGIS November 2004

Data Background In 2001 intensive research began assessing the health of the Upper Virgin Watershed OBJECTIVES: Baseline assessment Create an archive of digital resources (GIS) Current health assessment (digital & field collected) Package data analysis in a GIS querying tool for water managers GISWR Project

GISWR Term Project Utilize ArcHydro Terrain Processing tools as a secondary method to compare against methods and results from the Upper Virgin River Watershed Analysis project – compare and contrast differences 1) Location 2) Terrain 3) Process

OBJECTIVES Accuracy assessment of methods: comparing streams, catchments, and DEM conditioning created using automated tools from ArcGIS, with those delineated from low elevation aerial flights. Dual site comparison: results from highly varied terrain and extreme vertical relief (DEM investigation) Quantitative & qualitative evaluation – prevention of cost prohibitive data investigation SUMMARIZE Summary of methods & analyze differences Suggest implications of those differences and what they mean to GIS data processing

Southwestern Utah, Washington County Geographic Location Southwestern Utah, Washington County

Process Steps Data Acquisition Site Selection (2) Connectivity Representative (digitally) Scale Terrain Processing (ArcHydro Tools) Results (site comparisons) Drainage Density Inclusions/Exclusions Scale, Processing Quantitative & Qualitative Evaluation Processing Cost Perspective Time Investment

2.) Site Profiles Question….How does terrain processing handle a flat watershed vs. a watershed with extreme vertical relief?

Site-1 Aerial Photos of red frames above Relatively flat terrain along river corridor, connective, representative, 10m cell size Elevation range: min = 736 m (3513 ft) max = 1800 m (9427 ft) mean = 1278 m (4191 ft) Stream/drop and buffer parameters set to 10/10/5 for AgreeDEM Expected results: 1% threshold rule should apply resulting streams should be comparable to aerial digitized streams catchments should be consistent, connective, and representative of the landform

Site-2 Terrain is not flat along river corridors, disjointed landforms Elevation range: min = 1071m (3513 ft) max = 2874m (9427 ft) mean = 1972 m (6469 ft) Stream/drop and buffer parameters set to 10/10/5 for AgreeDEM Expected results: 1% threshold will not apply, toggling stream threshold will be required resulting streams may not match aerial delineated and digitized streams difficult to define streams and catchments across natural barriers of extreme relief

AgreeDEMs shown with normalized color scale 3.) Terrain Processing AgreeDEMs shown with normalized color scale

Results from DEM Reconditioning using the Agree Method

3a)Terrain Processing – Result 1 Agree & Fill (ABS[[orgDEM/AgreeDEM]-1]) Agree Interpolated Elevation Pixels Burning & Fencing, Fill Sinks In blue & green, pixels that have changed from their original values % change km2 count Driving values for ArcHydro Terrain Processing Retest with natural barriers set to NODATA Prevention of computations (ABS[[orgDEM/FillDEM]-1]) Fill Sinks

3b)Terrain Processing – Result 2 Stream Definition & Catchments Stream definition occurring across vertical boundaries or natural barriers? Toggle stream threshold Catchments occurring across vertical boundaries or natural barriers? Compare against low elevation aerial photography Stream Definition Catchments

In Process…. 4.) Results Summary Data Acquisition Site Selection (2) Connectivity Representative Scale Terrain Processing Results (site comparisons) Drainage Density Inclusions/Exclusions Scale, Processing Aerial Comparison Quantitative & Qualitative Evaluation Comparative Processing Cost Perspective Time Investment In Process….

5.) Quantitative & Qualitative Evaluation In Process…. Toggling of Stream Thresholds, stream/drop ratio and buffering for best watershed representation