Department of Water Resources Home
EMP Banner
Small Scale Spatial Variability Study (SSSVS) and Generalized Random Tessellation Stratified (GRTS) -- Heather Fuller
Every three years, the State Water Resources Control Board's D-1641, Condition 11(e) requires a "Programmatic Review" of the interagency Bay-Delta Monitoring and Analysis Section (EMP) "to insure that the goals of the monitoring program are attained." In response to the 2001-2003 review, two benthic monitoring special studies were developed and conducted. The first was a Small Scale Spatial Variability Study (SSSVS) designed to measure species richness, abundance and variability in a 64 hectare neighborhood around each of 6 benthic monitoring sites (see Figure 1). The study was conducted once in April of 2005 and again in July of the same year. One sample was collected from each location in the sampling neighborhood and comparisons were made between all grabs within each area.
Small Scale Spatial Variability Study (SSSVS) around site D4-L Figure 1: Small Scale Spatial Variability Study (SSSVS) around site D4-L
The second study employs a Generalized Random Tessellation Stratified (GRTS) sampling design (see Figure 2). In response to the program review and from trends seen in SSSVS, it was concluded that the representativeness of benthic data in the part of the Estuary monitored by the EMP needed to be improved. As a result, the 5-year twice-yearly GRTS study is conducted. Each May and October, beginning in 2007 and ending in 2011, 175 sites from San Pablo Bay to Stockton and lower Cache Slough to Clifton Court Forebay are sampled. 50 of these sites are sampled each sampling event while the other 125 change yearly. The goal of both studies is to develop a more comprehensive and accurate method of monitoring and analyzing the Delta benthos.
Generalized Random Tessellation Stratified (GRTS) sampling design, 2008 Figure 2: Generalized Random Tessellation Stratified (GRTS) sampling design, 2008