evaporation in lake travis

Evaporation in Lake TravisEvaporation in Lake Travis

Wil SarchetSurface Water Hydrology

|Introduction| 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

Lake Travis

|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

|Data Collection|

NCDC Temperature

Austin-Mueller Airport

TSRDB Solar Radiation

University of Texas Campus

US Army Corps of Engineers Lake Evaporation

Lake Lavon, Collin County, Texas

|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

|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

1999-2004 Lake Travis Surface Evaporation

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1954-2004 Lake Travis Surface Evaporation

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January-54 January-64 January-74 January-84 January-94 January-04

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Eva

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5 year and Long Term

y = -0.0000x + 5.0411

TWDB

|Results|Diurnal Variation

February 1, 2000

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Tim e

Mo

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Evaporation Potential Evaporation

August 1, 2000

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Evaporation Potential Evaporation

WinterPotential evaporation is an average of 2.9 times greater than evaporation with a max of 3.9 times greater

SummerPotential evaporation is an average of 3.5 times greater than evaporation with a max of 5.5 times greater

ComparisonThe 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

|Results|Temperature and Radiation

1999-2004 Lake Travis Average Temperature and Evaporation

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Temperature Evaporation

TWDB/NCDC/TSRDB

1999-2004 Lake Travis Average Radiation and Evaporation

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/m2)

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Radiation Evaporation

Energy Balance Method Er = 0.0353Rn

|Results|Precipitation

1999-2004 Lake Travis Surface Evaporation and Precipitation

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TWDB

|Results|Lake Travis Evaporation Comparison

Comparison of Evaporation Data

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TWDB NARR NARR Potential TSRDB Predicted

“Evaporation estimates are notoriously uncertain”(Ruiz-Barradas and Nigam 2005)

|Results|Lake Lavon Evaporation Comparison

Army Corps/NARR PotentialAvg. = 0.885St. Dev. = 0.127

Army Corps/TWDBAvg. = 1.148St. Dev. = 0.222

NARR Potential Adjustedp value = 0.172

Comparison of Evaporation Data for Lake Lavon

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TWDB NARR NARR Potential Arm y Corps

Comparison of Evaporation Data for Lake Lavon

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TWDB NARR NARR Potential Arm y Corps NARR Potential Adjus ted

|Results|Lake Travis Evaporation

Comparison

Comparison of Evaporation Data

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TWDB NARR NARR Potential TSRDB Predicted NARR Potential Predicted

Comparison of Evaporation Data

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TWDB NARR NARR Potential TSRDB Predicted NARR Potential Predicted

|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

|Questions|