First Flush - Water Quality Analysis Plan

Author

Dave Bosworth

Published

March 26, 2026

WQ Hypotheses

Turbidity will increase faster and higher during a first flush event compared to later storm events.
Salinity will decrease more dramatically during first flush compared with other storms.
Dissolved oxygen will decrease during first flush but recover afterwards.
Chlorophyll will decrease more during first flush and stays low during later storm events.

Data Exploration

Visual exploration of WQ time-series in relation to storm events at select stations

Stations:
- USGS Sacramento River at Freeport (11447650)
- DWR_CEMP San Joaquin River McCune Station near Vernalis (SJR)
- DWR_CEMP Sacramento River at Rio Vista Bridge (RVB)
- USGS San Joaquin River at Jersey Point (11337190)
- DWR_CEMP San Joaquin River at Prisoners Point (PPT)
- DWR-NCRO (WQES) Old River at Quimby Island near Bethel Island (B9520000)
- DWR-NCRO (WQES) Middle River near Holt (B9545800)
- DWR-NCRO (WQES) OBI at USGS Pile (B9525100)
- USGS Middle River at Middle River (11312676)
- USGS Old River near Byron (11313315)
- DWR-NCRO (WQES) Grant Line Canal near Clifton Court Forebay (B9529500)
- DWR-NCRO (WQES) Old River at Tracy Wildlife Association (B9537800)
1. Turbidity - most stations started around 2010
  1. Increases in relation to storm events.
  2. Is it typically highest after first event of the year? Maybe look at rate or difference (pre vs. during) instead of raw values.
  3. How does turbidity increase downstream of SR at Freeport? Similar patterns, raw values, lag in response.
  4. Sacramento River vs. San Joaquin River - how do they compare? How often are storms occurring system-wide vs. in just one watershed?
2. Salinity
3. Dissolved Oxygen
4. Chlorophyll
Other visuals besides time-series plots - boxplots?

Metrics

Turbidity
1. temporal rate of increase or raw difference (before vs. during storm)
2. time lags at downstream stations (days between first day of storm and turbidity maximum)
3. spatial extent of turbidity increase
4. gradient calculations between SR and SJR influenced stations
Salinity
Dissolved Oxygen
Chlorophyll

Statistical Analyses

Turbidity
Salinity
Dissolved Oxygen
Chlorophyll

--- title: "First Flush - Water Quality Analysis Plan" author: "Dave Bosworth" date: today date-format: long format: html: code-fold: true code-tools: true execute: message: false warning: false --- # WQ Hypotheses 1. Turbidity will increase faster and higher during a first flush event compared to later storm events. 2. Salinity will decrease more dramatically during first flush compared with other storms. 3. Dissolved oxygen will decrease during first flush but recover afterwards. 4. Chlorophyll will decrease more during first flush and stays low during later storm events. # Data Exploration 1. Visual exploration of WQ time-series in relation to storm events at select stations Stations: - USGS Sacramento River at Freeport (11447650) - DWR_CEMP San Joaquin River McCune Station near Vernalis (SJR) - DWR_CEMP Sacramento River at Rio Vista Bridge (RVB) - USGS San Joaquin River at Jersey Point (11337190) - DWR_CEMP San Joaquin River at Prisoners Point (PPT) - DWR-NCRO (WQES) Old River at Quimby Island near Bethel Island (B9520000) - DWR-NCRO (WQES) Middle River near Holt (B9545800) - DWR-NCRO (WQES) OBI at USGS Pile (B9525100) - USGS Middle River at Middle River (11312676) - USGS Old River near Byron (11313315) - DWR-NCRO (WQES) Grant Line Canal near Clifton Court Forebay (B9529500) - DWR-NCRO (WQES) Old River at Tracy Wildlife Association (B9537800) a. Turbidity - most stations started around 2010 i. Increases in relation to storm events. ii. Is it typically highest after first event of the year? Maybe look at rate or difference (pre vs. during) instead of raw values. iii. How does turbidity increase downstream of SR at Freeport? Similar patterns, raw values, lag in response. iv. Sacramento River vs. San Joaquin River - how do they compare? How often are storms occurring system-wide vs. in just one watershed? b. Salinity c. Dissolved Oxygen d. Chlorophyll 2. Other visuals besides time-series plots - boxplots? # Metrics 1. Turbidity a. temporal rate of increase or raw difference (before vs. during storm) b. time lags at downstream stations (days between first day of storm and turbidity maximum) c. spatial extent of turbidity increase d. gradient calculations between SR and SJR influenced stations 2. Salinity 3. Dissolved Oxygen 4. Chlorophyll # Statistical Analyses 1. Turbidity 2. Salinity 3. Dissolved Oxygen 4. Chlorophyll