Evaporation in Lake Travis

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Evaporation in Lake Travis
Wil Sarchet Surface Water Hydrology
2
Introduction
Lake Travis

• Northwest of Austin
• Formed in 1942 with the construction of the
  Mansfield Dam
• Average water volume of 1.13 million acre-feet
• Depths up to 190 feet deep
• A water source for Austin

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Objectives

• Examine the relationships between evaporation
  and precipitation, temperature, radiation, and
  time in Lake Travis
• Evaluate the accuracy of the available data
  sources for evaporation in Lake Travis

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Data Collection

• US Army Corps of Engineers
• Lake Evaporation
• Lake Lavon, Collin County, Texas

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Data Collection
TWDB

• TWDB
• Evaporation/Precipitation
• One degree quadrangles (111.3 km quadrangles)

• Monthly Gross Lake Evaporation Rates
• Computed by a GIS based program ThEvap
• Based off of TWDB and National Weather Service
  collection sites
• Pan coefficients reflect both spatial and
  seasonal variation

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Data Collection
NARR

• North American Regional Reanalysis
• Result of the National Centers for Environmental
  Prediction (NCEP) Eta Model
• 32 km scale
• Improved by the Regional Data Assimilation
  Systems (RDAS)
• Surface Evaporation Potential Evaporation Data

• Potential Evaporation
• Potential water vapor capacity of the air
• Amount of evaporation that would occur if a
  sufficient water source was available

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Results
5 year and Long Term
y -0.0000x 5.0411
TWDB
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Results
Diurnal Variation
Winter Potential evaporation is an average of 2.9
times greater than evaporation with a max of 3.9
times greater Summer Potential evaporation is an
average of 3.5 times greater than evaporation
with a max of 5.5 times greater Comparison The
maximum value of potential evaporation is 7.4
times greater in summer than in winter The
maximum value of evaporation is 3.3 times greater
in summer than in winter
NARR
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Results
Temperature and Radiation
Energy Balance Method Er 0.0353Rn
TWDB/NCDC/TSRDB
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Results
Precipitation
TWDB
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Results
Lake Travis Evaporation Comparison
Evaporation estimates are notoriously
uncertain (Ruiz-Barradas and Nigam 2005)
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Results
Lake Lavon Evaporation Comparison

• Army Corps/NARR Potential
• Avg. 0.885
• St. Dev. 0.127
• Army Corps/TWDB
• Avg. 1.148
• St. Dev. 0.222

NARR Potential Adjusted p value 0.172
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Results
Lake Travis Evaporation Comparison
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Conclusions

• Significant seasonal and diurnal variation in
  Lake Travis evaporation data
• Data supports the use of the Energy Balance
  Method as a valid way to predict evaporation
• There is an inconsistency amongst data sources
  for Lake Travis evaporation

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Questions