Term Project Outline

CE 394K Surface Water Hydrology
University of Texas at Austin

Speed of Sound in Texas Reservoirs

by R. Warren Payne

In this term project I intend to:

Hydrographic surveys are conducted by the Texas Water Development Board (TWDB) in order to gain knowledge of the sediment distribution and sedimentation rate in Texas’ reservoirs.

One factor which influences the results of hydrographic surveys is the ability to accurately measure water depth. Water depth is determined through the use of depth sounding (echo sounding) equipment. The depth sounder measures the time required for an acoustic pulse to travel from the depth sounding transducer to the reservoir bottom, reflect off the bottom surface, and return to the transducer. The depth sounder used by the TWDB is calibrated with an operator input of the speed of sound in water. This single value of the speed of sound sets the frequency of a crystal oscillator within the depth sounder. By measuring the elapsed time and number of oscillator cycles between transmission and receipt of the acoustic pulse, a depth can be calculated. The value of the speed of sound is determined through the use of a velocity profiler which averages the measured speed of sound as a sensor probe is lowered through the water column prior to survey data collection.

The speed of sound in water is known to be a function of temperature, pressure and salinity. Because these parameters vary significantly with depth, the speed of sound is also a function of depth. Using data gathered from multiple sources, speed of sound profiles will be developed for reservoirs within the Brazos River basin. These profiles will in turn be used to assess the likely error in depth measurements made during the course of hydrographic surveys.

Data collected during a hydrographic survey is used to develop a spatial model of the reservoir’s bottom surface. These models are developed in the geographic information system ARC/INFO and are called triangulated irregular networks (TINs). The effects of depth measurement error on reservoir volume calculations performed with the TINs will be assessed.


Return to the Course Home Page