Upper Walnut Creek Austin's Blog

This blog has details about the monitoring site 290-Walnut Creek by the Metric Blvd. bridge (roughly half a mile SE of Parmer and MoPac; map).  To view the site monitoring results (numbers of dissolved oxygen, pH, temperature etc) go to http://crwn.lcra.org/. That page also has links to more information about the Colorado River Watch Network (CRWN) program. The FAQs link includes a lot of details.

The direct link for our specific site is crwn.lcra.org/events.aspx?qrySite=290.  Video of the stream is available at www.youtube.com/crwnwater.

We’ve been monitoring this site since October 2006 and have watched the effects of the changing seasons and, as of Sept. 2009 the (so far) 2-year drought. We’ve watched the grass turn brown and crunchy and the algae completely disappear from the creek. But amazingly, although the water level is very low, the stream has never completely dried up. And over time, as the rains returned during the winter of 2009-2010, the stream has risen slightly.

Update: as of April 2015: the drought continues and is now in its 8th year. We’ve had a few heavy rains, such as Tropical Storm Hermine in 2010, the Halloween 2013 flood and the October 2015 flood. Even with these occasional heavy rains, the drought continued through mid 2015. The Highland Lakes (including Lake Travis, a primary water source for Austin) are still only about 32% full at most…until the end of May 2015 deluge.  The June 2015 monitoring post has 2 photos of Lake Travis from shortly before and then after that historic rain – it’s hard to believe the difference.

Walnut Creek has clearly been in this stream bed for a very long time, and from the rock formations close to the Metric overpass, has been much higher in the past. Here are some photos

Explanations of some of the monitoring terms

pH

pH indicates the alkalinity or acidity of the water. 7.0  is neutral.  Aquatic life is sensitive to changes in pH.

Below 7.0 is acidic – battery acid is 0.3, orange juice is 4.3, milk is 6.9
Above 7.0 is alkaline – seawater is 8.0, ammonia is 11.4 and  bleach is 12.7.

Specific Conductance

Specific conductance measures the ability of the water to pass an electrical current. Many variables affect the conductivity:

• inorganic dissolved solids including as chloride, sulfate, sodium, calcium and others
• the materials of the stream bed if they dissolve and ionize – granite doesn’t dissolve into ionic compounds, limestone and clay soils do dissolve into ionic compounds (Wikipedia page on ionic compounds)
• pollutants, including from urban runoff, from streets and parking lots
• water temperature – warmer water has a higher conductivity
• extended low flow/dry conditions; they tend to concentrate dissolved solids in less water

The expected levels of specific conductance for most river watersheds are between 300-700 microsiemens per centimeter.

E. Coli

E. coli is a species of fecal coliform bacteria that is specific to fecal material from humans and warm blooded animals. The EPA established contact recreation water quality standard single-grab samples is 394 cfu’s (colony forming units).

This site usually has high e-coli counts. LCRA contacted City of Austin staff, who ran a camera up the box culvert storm drain and didn’t find anything suspicious (i.e. broken pipes), but that it is still the most likely explanation.  The City staff also pointed out that a large input of bacteria could be coming from the pigeons that roost under the bridge.

Temperature

Among many other things, temperature affects the maximum amount of dissolved oxygen that a stream can hold. The colder the temperature the higher the possible dissolved oxygen.

Transparency

Transparency,  an important indicator of the health of a stream, measures how far light can penetrate into a body of water. Sunlight provides the energy for photosynthesis and determines how deep algae and plants can grow.