Water Quality Data

       Table of  Contents

• Reservoir Water Temperature Animation

• Dissolved Oxygen Data in the Reservoirs

• Reservoir Dissolved Oxygen Animation

• Turbidity Data

• Reservoir Water Levels

Temperature Data in the Reservoirs

The Water Bureau has been collecting water samples from both reservoirs over a long period of time.  These samples have been taken over various depths in the reservoirs at a few monitoring locations. In the past few years samples have been taken from several additional locations within each reservoir.  These depth measurements have provided a first look at some of the water quality conditions in the reservoirs. Figure 3 was generated for various sample times using the water temperature data collected over the depth of the reservoir at one location in each reservoir throughout the year.  Maps indicating the locations of these sample sites are in Figure 1 and Figure 2.  For Reservoir #1, the temperature data was from monitoring station number 59-1 and for Reservoir #2, monitoring station number 60-1 was used.

The vertical temperature profiles in Figure 3 indicate Reservoir #1 experiences thermal stratification as the year progresses from early spring into summer.  This stratification can be explained by the withdrawal elevations used in the reservoir to supply water to the lower reservoir. Figure 3 shows during the same time period that the vertical temperature profile in Reservoir #2 remains relatively constant over depth indicating the reservoir is well mixed.  This can be attributed to the withdrawal from Reservoir #2 occurring over a large depth range.
 
 

Reservoir Water Temperature Animation

Using the reservoir temperature depth measurements made in both reservoirs, an animation of still images was made to illustrate the changing water temperatures in both reservoirs over the course of several years.
 
 

Dissolved Oxygen Data in the Reservoirs

Using data collected over the depth of the reservoir at one location in each reservoir, Figure 5 was generated for various sample times throughout the year.  Maps indicating the locations of these sample sites are in Figure 1 and Figure 2.  For Reservoir #1, the dissolved oxygen data was from monitoring station number 59-1 and for Reservoir #2 monitoring station number 60-1 was used.
Figure 5 indicates the dissolved oxygen concentration in Reservoir #1 is well-mixed in the early spring and as the season progresses the concentration of dissolved oxygen begins to drop (as reservoir temperatures rise).  Late in the summer and in early fall there is some dissolved oxygen stratification in the reservoir.  Reservoir #2 in Figure 5 shows a similar dissolved oxygen concentration decrease as the season progresses but remains relatively well-mixed throughout the season with the exception of a slight stratification in the late summer due to withdrawal over a wide range of depth.
 
 

Reservoir Dissolved Oxygen Animation

Similar to the water temperature animation, the same process was repeated using dissolved oxygen concentration data.

Turbidity Data
Reservoir Turbidity Animation

Similar to the animations for water temperature and dissolved oxygen, turbidity measurements were also made at various depths and used to generate color contour plots of the cross sections of the reservoirs, Figure 6. Unlike the other animations there was much less turbidity data available to use in this analysis approach.  Additionally there was no turbidity data available from tributaries feeding into the reservoirs for the dates when measurements were made in the reservoirs so this information could not be included.  Overall, the animation reveals that the turbidity in the reservoirs remains consistently low except for dates when there are major storm events such as on October 27th, 1994 when Headworks recorded 6.8 inches of rain and a few days later (10/31/94 - 11/1/94) the Headworks received over 5 inches of rainfall.  This resulted in the turbidity in the upper reservoir increasing from less than 1 NTU to around 5 to 7 NTU.

Reservoir Water Levels

Reservoir water levels were plotted for 1996 through 1999 for Reservoir #1 and #2. Reservoir #1 water levels were maintained relatively constant, at a seasonal full stage level, except for large drawdowns in the reservoir in the late summer period with the largest in the summer of 1998.  The water level in Reservoir #2 was also maintained relatively constant except for summer time drawdowns.  The drawdowns in Reservoir #1 are much larger than drawdowns in Reservoir #2.  For example, in the summer of 1996, Reservoir #1 was drawn down about 21 m in the course of 100 days while Reservoir #2 was only drawn down 6 m during the same time period.