Recommendations for future characterization. Lester McKee San Francisco Estuary Institute. Mallard Island data supplied by David Schoellhamer USGS

Transcription

1 Sediment And Pollutant Transport From The Sacramento / San Joaquin Delta During Large Resuspension Events: Recommendations for future characterization. Lester McKee San Francisco Estuary Institute Mallard Island data supplied by David Schoellhamer USGS

2 Inset A Sacramento River Sacramento Inset A Inset B Stockton San Joaquin River California, U.S.A Inset B Los Angeles Location of Suisun Bay Chipps Island Sacramento R. the study area Mallard Island Sampling Location San Joaquin R.

3 Sediment concentrations in the Delta Suspended sediment concentrations (SSC): 1) Increase during flood. 2) Show first flush effects. 3) Vary with the daily tides. 4) Vary with spring-neap tide patterns. 5) Vary with the ebb-flood tide and these are even evident during flood flow. 6) Vary seasonally associated with wind-wave action in the summer months. 7) Vary throughout the cross-section of a channel.

4 Tide at Mallard Island for the 1997 water year Gauge height (ft) Month beginning October

5 Tide and sediment at Mallard Island during the first 14 days of 1997 Tide height (m) SSC (x1mg/l) Delta outflow (x1,,m3/s) Tide height (m) 3.5 SS(x1mg/L) 3. Dayflow (x1,m3/s) /1 1/2 1/3 1/4 1/5 1/6 1/7 1/8 1/9 1/1 1/11 1/12 1/13 1/14 1/15 Date

6 SSC during non-flood periods Suspended sediment (mg/l) /1 1/31 3/2 4/1 5/2 6/1 7/1 8/1 8/31 9/3 Date

7 Mallard Island SSC data Optical Back Scatter (OBS) data are currently collected 1m below the water surface every 15 minutes. Water samples are collected and analyzed for suspended sediment concentration (SSC). Concentration data is regressed against OBS data to give a continuous calculation of SSC in (mg/l). Data collection is funded (by CALFED) to continue at least until 24.

8 Methodology for calculating loads On days with recorded SSC data, data were averaged and combined with Delta outflow (the DWR modeled estimate) to derive a load for each day. On days without SSC data, load was estimated by one of four methods: 1) Linear interpolation. 2) Rising stage regression. 3) Falling stage regression. 4) Dry season regression.

9 Discharge of suspended sediment at Mallard Island Suspended sediment discharge (x1 t/d) Me a s ure d Predicted Year

10 Sediment loads entering the Bay from the Delta Author Smith (1963) Schultz (1965) USACE (1967) Krone (1979) Porterfield (198) Ogden Beeman (1992) This study Calculation period???? Average (M t/y) ±.6 (1.3±.3-3.±.7)

11 Testing for a trend R 2 = Ye a r Average suspended sediment load (1, t/d)

12 Another trend test R 2 = Ye a r SSC Flow-weighted Mean Concentration (mg/l)

13 Quantifying the trend Flow weighted mean concentration (mg/l) y = x R 2 = y =.7816x R 2 = Mean annual water discharge (Mm3/d)

14 Conclusions There is much known about the sediment dynamics and sediment loads entering the Bay from the Delta. The methodology used here for calculating loads is simple (C*V). Numerical filters can be applied to time series concentration data to remove tidal and other temporal effects and produce tidally averaged daily SSC data. However, error analysis provides confidence in the results shown here.

15 SSCcontaminant relationships (Schoellhamer 1996)

16 Contaminant loads based on SSC and Schoellhamer regressions Silver Chromium Copper Mercury Nickel Lead Zinc Previous estimate (t/y) Davis et al 2.5* ** This study (t/y) 1.14± ±88 24±55.9± ±72 85±2 439±11

17 Problems with the existing methodologies The regressions developed by Schoellhamer were for a different purpose The calibration space for the regression models do not cover the full range of sediment concentrations / OBS that occurs at Mallard Island The data used by Davis et al was uncharacteristic of the variability of the Delta (even the 1997 flood) Loads of sediment related pollutants of concern are likely to be underestimated and the precision is unreliable

18 Zn (ug/l) Ni (ug/l) Cu (ug/l) Ag (ng/l) y =.1369x R 2 = y =.463x SSC- R 2 = y =.125x R 2 R 2 =.749 = contaminant y =.184x relationships (this study) Pb (ng/l) Hg (ng/l) Cr (ug/l) Cu (ug/l) Ag (ng/l) 3 y =.1369x R 2 = y =.1552x R 2 = y =.1955x y =.463x R 2 = R 2 = y =.1552x R 2 = y =.184x R 2 = y =.148x R 2 =.7661 Ni (ug/l) Cr (ug/l) Hg (ng/l) 4 35 y =.1955x R 2 = y =.125x R 2 = y =.148x R 2 = Zn (ug/l) Pb (ng/l)

19 Recommended next steps 1) Continue to use Mallard Island data for estimates of Delta loads. 2) Work with DWR to improve our understanding of Dayflow errors. 3) Receive advice and review from appropriate experts and determine appropriate sampling design for loads monitoring and episodic toxicity at Mallard Island. 4) Collect water samples and analyze these for sediment related pollutants of concern and toxicity as in (3). 5) Develop regressions using the Mallard Island data. 6) Estimate time continuous (one day time step) pollutant concentration data for Mallard Island and combine these data with Delta outflow to determine pollutant loads entering the Bay from the Delta.