- Owner: Keith Steele
- Sample Type: Area Master Sample
- Created: 5/3/2012
Details of The Dalles Reservoir Master Sample
Here is a 100-row excerpt of the The Dalles Reservoir Master Sample design file to aid in understanding what the data looks like. You may download the entire file (6.2 MB).
Design Documentation for The Dalles Reservoir Master Sample
USGS CRRL-Columbia River Research Laboratory
The area contained within the floodplain of The Dalles Reservoir on the mainstem Columbia River. This includes the river and floodplain area upstream of The Dalles Dam to the tailrace of The John Day Dam.
The sample frame was constructed by delineating the areal extent of the Dalles Reservoir floodplain using a 10 meter resolution Digital Elevation Model (DEM) from the USGS and the elevation of the upstream reservoir (John Day Dam) with ArcGIS. The DEM is reclassified using the elevation of the next upstream dam, thus selecting the area within the elevation range. The grid area of interest is then converted to a polygon shapefile. Using spsurvey 2.1 within the spsurvey package, R code was used to convert the polygon to a sample frame of points using a 30 x 30 m resolution. In other words, the total areal extent is divided by 900 in order to get the desired number of sample points for a 30 x 30 m point resolution. This uses a Generalized Random Tessellation Stratified (GRTS) survey design framework and equal probability of inclusion as stated below.
A GRTS survey design for an areal resource was used. The GRTS design includes reverse hierarchical ordering of the selected sites.
The areal extent was 66,038,588.91 m2. The sample size was selected to have a sample site approximately every 30 x 30 m. This assigns a weight approximately equal to 900 for each sample site, which is the equivalent of being equal across all sites. The number of sites included in the reservoir floodplain is 73,376.
Sites are listed in siteID order and must be used in that order. All sites that occur prior to the last site used 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 the reservoir and it required that 61 sites be evaluated in order to locate 50 reservoir sites able to be sampled, then the first 61 sites in siteID order would be used.
The sample frame covers an area 66,038,588.91 m2 in size and includes the floodplain of The Dalles Reservoir.