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Columbia Basin Master Sample

Columbia Basin Master Sample
ID: 1
  • Created: 2/25/2012
  • Updated:

Details of Columbia Basin Master Sample

Here is a 100-row excerpt of the Columbia Basin Master Sample design file to aid in understanding what the data looks like. You may download the entire file (81.8 MB).

Design Documentation for Columbia Basin Master Sample

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Phil Larsen

Anthony (Tony) R. Olsen
Western Ecology Division
200 S.W. 35th Street
Corvallis, OR 97333
Voice: 541-754-4790
Fax: 541-754-4716


All stream and river channels within USGS Hydro Region 17 and portions of Hydro Regions 16 and 18 that are within boundaries of Oregon and Idaho. This covers all of Idaho, Oregon and Washington as well as small sections of Montana, Wyoming, Utah, Nevada and California that are part of the Columbia River Watershed.

Sample frame was constructed in two parts: (1) NHD Plus (downloaded August, 2005) where all segments within NHD Plus are included and (2) NHD Plus (downloaded March 2010) where all segments are included. Strahler order and other NHD Plus attributes were added from the October 2008 release. This newest version had directional corrections to the original dataset in places, as well as adjustments to other NHDPlus features not used directly for sample frame design (see release notes for NHD Plus - Pacific Northwest).

A Generalized Random Tessellation Stratified (GRTS) survey design for a linear resource was used. The GRTS design includes reverse hierarchical ordering of the selected sites.


The master sample is stratified by Hydro Region 17, Hydro Region 16 & 18 within Oregon, and Hydro Region 16 within Idaho. Stratification was required when a decision was made to include the portions of Hydro Regions 16 and 18 that are within boundaries of Oregon and Idaho.


The sample size was selected to have a sample site approximately every 1 km. This results in a weight approximately equal to 1 for each sample site. The number of sites in Hydro Region 17 is 532,268, Oregon supplemental stratum (OR_S) is 11,793 and Idaho supplemental stratum (ID_S) is 6,985.


Sites are listed in siteID order within each stratum and must be used in that order within each stratum. All sites that occur prior to the last site used within a stratum must have been evaluated for use and then either sampled or reason documented why that site was not used. As an example, if 50 sites are to be sampled within a stratum and it required that 61 sites be evaluated in order to locate 50 stream sites able to be sampled, then the first 61 sites in siteID order would be used.


The Hydro Region 17 sample frame has 532,267.94 km of stream channel length. The Idaho supplemental sample frame stratum has 6,984.832 km of stream channel length. The Oregon supplemental sample frame stratum has 11,792.76 km of stream channel length. Note that in order to select all sites for a state, make sure to query for border river sites which are denoted by ST:ST in the State attribute field (i.e. sites on the Columbia River would are denoted as OR:WA). Sites on border rivers are treated the same way in the County field.




Diaz-Ramos, S., D. L. Stevens, Jr, and A. R. Olsen. 1996. EMAP Statistical Methods Manual. EPA/620/R-96/002, U.S. Environmental Protection Agency, Office of Research and Development, NHEERL-Western Ecology Division, Corvallis, Oregon.

Stevens, D.L., Jr. 1997. Variable density grid-based sampling designs for continuous spatial populations. Environmetrics, 8:167-95.

Stevens, D.L., Jr. and Olsen, A.R. 1999. Spatially restricted surveys over time for aquatic resources. Journal of Agricultural, Biological, and Environmental Statistics, 4:415-428

Stevens, D. L., Jr., and A. R. Olsen. 2003. Variance estimation for spatially balanced samples of environmental resources. Environmetrics 14:593-610.

Stevens, D. L., Jr., and A. R. Olsen. 2004. Spatially-balanced sampling of natural resources in the presence of frame imperfections. Journal of American Statistical Association:99:262-278.

Web Resources:

Aquatic Resource Monitoring:
NHD web page: http://nhd.usgs/gov
NHD Plus web page: (July 2006)