Clean Water Program

The sediment is not uniformly deposited along the length of the SLD. In general, sediment tends to build up near the check structures. To obtain an accurate determination of sediment deposition, it is necessary to take more frequent readings near these structures. Sediment thickness measurements will be taken at the locations that were used in Summers Engineering survey (March 1987). The distances from the structures and locations at which measurements were taken are documented, and the sites can reliably be resampled.

Several sampling techniques will be used to collect samples, including grab, time and depth integrated. The techniques used at each location are summarized on Table 4.3.1. Because of the remoteness of the region and the staffing limitations, an auto-sampler will be used to collect time-composite samples and samples that must be collected more than once per week.

Frequency of water quality sample collection is summarized in Table 4.3.1. The frequency of sample collection is based on data uses and the historic variability of the measurement. Comparison of hourly data collected over 48 hours (Thomas and Cooper, 1989), daily data (Westcot et al., 1992, Karkoski and Tucker, 1993), and historic data collected since 1985 of the CVRWQCB, indicate that weekly sampling adequately characterizes seasonal and temporal variations.

Water quality sampling locations are depicted in Figure 4.1 and are described in Table 4.3.1. Data will be collected at the SLD, Mud Slough (north), the San Joaquin River, Grasslands channels, and Salt Slough.

Summers Engineering, March 1987

Depth Measurement Locations

Checks 17-18, 14-15, 10-11, 1-2

Stage measurements can be converted to discharge values and current shifts in site flow rating curves can be used to correct estimated discharge using standard analytical techniques. These techniques can be found in any hydraulics textbook or the USGS Water Supply Paper 2175 (USGS, 1982).

The site description of the flow monitoring stations are listed in Table 4.2.1. Figure 4.1 shows the relative locations of the primary sites, including flow monitoring sites in north GWD and along the San Joaquin River. Many of the Monitoring Plan flow monitoring stations have been established for more than a decade and provide data that can be compared to the present flow conditions.

The monitoring plan relies on the use of the following techniques: flow monitoring, water quality monitoring, sediment quality monitoring, biotic tissue sampling, community analysis, toxicity testing, and bioaccumulation analysis. Subsections 4.2 through 4.6 describe in detail the methods by which each of these monitoring techniques is applied.