Evaporation in Lake Travis Wil Sarchet Surface Water

Evaporation in Lake Travis Wil Sarchet Surface Water Hydrology

|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

|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 § Evaporation/Precipitation § One degree quadrangles (111. 3 km quadrangles) Monthly Gross Lake Evaporation Rates § Computed by a GIS based program Th. Evap § 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

|Results| 5 year and Long Term y = -0. 0000 x + 5. 0411 TWDB

|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

|Results| Temperature and Radiation Energy Balance Method Er = 0. 0353 Rn TWDB/NCDC/TSRDB

|Results| Precipitation TWDB

|Results| Lake Travis Evaporation Comparison “Evaporation estimates are notoriously uncertain” (Ruiz-Barradas and Nigam 2005)

|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

|Results| Lake Travis Evaporation Comparison

|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|