Segment 1403--Lake Austin at Tom Miller Dam

Site Analysis- Dissolved Oxygen

Lake Austin-CRWN Site # 1403.0100, LCRA Site #1403.0100, River Segment 1403

These sites are located on the downstream end of segment 1403 above Tom Miller Dam. The volunteer (CRWN) site is located about 0.4 miles upstream from the professional (LCRA) site. The volunteer site is a level 1 site monitored by an employee of the LCRA, who is not a professional monitor. It is worthwhile to note that the CRWN data is consistent throughout the year for the entire monitoring period being considered.

A time span of approximately four and a half years was used for the analysis:

Descriptive Statistics

 The mean and median values are very close for both sets of data. There are about three times more data values for the CRWN site. The skewness values are very small and both sets of data have about the same range. Essentially, the two data sets are very similar. The descriptive statistics indicate normal distribution of the data.

Cumulative Frequency Distribution

Both cumulative frequency distribution graphs show good linearity in the data mid-section, indicating normal distribution of the data.

 Histograms

The histograms show a normal distribution also.

 t-test

The t-value of 1.395 indicates that statistically the data sets are the same.

 Error Statistics

The LCRA data has a much lower standard error than the CRWN data even though there are fewer measurements. The range for the volunteer data around the mean for n=90 is 0.69 or the mean DO with 95% confidence is 8.05 ± 0.35 mg/l. The range for the professional data around the mean for n=27 is 0.11 or the mean DO with 95% confidence is 8.53 ± 0.055 mg/l.

The graphs of the standard error of the mean for each data set:

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