Residence Times in Texas Bays: 1975 2000

1
Residence Times in Texas Bays 1975 - 2000

• Laura Chu
• UT Marine Science Institute
• CE 394K Surface Water
• April 26, 2005

2
Background

• Residence time
• Why Study Inflows?
• Climate change
• Water Balance in Texas
• Constant vs. flashy system

3
Residence Time

• Estimate of the rate at which a volume of water
  moves through a bay.
• Several methods to compute
• Tidal-Prism method
• Freshwater Fraction method

4
Tidal Prism Method

• Method based on changes in estuarine volume due
  to tides

INSUFFICENT DATA

• Officer (1976)

5
Fresh-Water Fraction Method

• Uses the salinity to calculate the residence time.

• Assumptions
• Hydrography
• Constant bay volume

6
Hypothesis

• Ho1 Variation in freshwater inflows does not
  change the turnover time for Texas Bays
• Ho2 El Niño has no effect in changing the rate
  of turnover in Texas Bays

7
Data

• Inflows
• Monthly for 6 bays estuaries
• TXWDB 1941-2000
• Salinity
• Monthly on a grid
• TXPWD 1975 present
• Volume of water
• CRWR G. Ward
• El Niño SOI index

• Estuaries Bays
• Sabine
• Trinity / Galveston
• Guadalupe / San Antonio
• Lavaca / Matagorda
• Mission - Aransas
• Nueces/Corpus Christi

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Methodology
Salinity
Bay Volumes
Water Balance
Residence Time Equations
SOI Index
Analyze data
Hydrography
GIS mapping
9
Residence Times and Latitude
10
North South Differences
11
SOI Index Values
12
Effects of El Niño on Residence Times
13
Some Conclusions

• Seasonal freshwater inflows drive changes in
  residence times in Texas
• Hypersaline conditions
• No overall long-term trend
• No significant El Niño effects

14
Future Work Questions

• Relating inflow modeling to species abundance and
  ecosystem health
• Effects of hydrography
• Visualizing data in GIS
• Implications for controlled flow regimes