Monday, September 14, 2009

Drenching rains help, but do not end drought

Drought Stage: Critical (yes, we're still in it!)
Barton Springs flow: 38 cfs (10-day average estimated at 23 cfs; declining quickly--see below)
Lovelady Depth to water: 197.2 ft (up nearly 0.4 ft)

While the rain temporarily boosted springflow (up 31 cfs) and Lovelady water levels (up 0.4 ft), more rain, and in the contributing watershed, is needed to end the (groundwater) drought. Rainfall totals of locally over 9 inches produced some good runoff and recharge to the Edwards Aquifer, but it was very short-lived. Not enough rain occurred in the contributing watershed of the aquifer, so many of the creeks only flowed temporarily. For example, Bear Creek only flowed for about 4 hours. It is significant to note that Onion Creek, the largest contributor of recharge to the aquifer, did not flow at all, despite some local significant rainfall in its watershed (a testament to how dry that watershed is).

Barton Springs and the Lovelady well have responded (both rising) to the recharge that did occur. However, the rise in springflow and water levels has already begun to recede. Without more rainfall to sustain the flow in the creeks springflow and water levels will reach pre-rain conditions in the next week or two.

Rainfall totals over since Thursday (9/10) through Sunday (9/13) were highly variable throughout the contributing watershed and recharge zone. Locally rainfall was 9.7 inches over that period causing local flooding and sinkholes to back up and fill with water. Unfortunately, these types of totals did not occur in the contributing zone of the aquifer which would produce lasting creekflow and therefore significant recharge over a longer period of time.

This photo by Brian Smith shows a manual rainfall gauge with about 7.5 inches of rain. The gauge is located about 1 mile northwest of Brodie Lane and FM 1626.

This rainfall total map over the last 7 days is from the LCRA's hydromet website. Note totals span less than 2 inches to greater than 7 in the contributing zone. To access rainfall data go to


It appears that most of the urbanized creeks (Slaughter and Williamson) had significant, albeit short-lived, flow. For example, Williamson and Slaughter creeks reached at peaks of 197 and 667 cfs on 9/12, respectively (at the eastern edge of the recharge zone). Other creeks that are not as developed (less impervious cover) did not has as much flow. Bear Creek peaked at 200 cfs on 9/12 at the eastern edge of the recharge zone. The flow in Bear Creek only lasted about 4 hours and then was back to zero! Onion Creek, the largest watershed and contributor of recharge, did not flow at all despite some locally significant rainfall.

This photo of Slaughter Creek (Elm Creek Waterhole) was taken at the peak flow of 667 cfs on 9/12. The flow is completely covering a concrete low-water crossing and Elm Waterhole on the right side of the photo that is about 12-15 feet deep.

This photo of Onion Creek was taken near Dripping Springs (off Creek Road) on 9/13. As you can see, the creek is not flowing and only has local ponds of water. The Blanco River near the town of Blanco is similarly dry.

Barton Springs responds very quickly (and notoriously flashy) due to rainfall and creekflow. This is due to the karstic nature of the rocks (e.g. caves and sinkholes) that allow rapid flow into, and through, the aquifer. Barton Springs responded very quickly to the rain that began on 9/11 and continuted through 9/12. It reached a peak of 48 cfs on 9/12 11:00 pm and has been receding ever since (see figure; data from USGS). Currently the springflow is at about 38 cfs and will continue to decline to the pre-rainfall levels very quickly. Sustained creekflow is needed to recharge the aquifer substantially.

It is also noteworthy that Jacob's Well (spring) only increased in flow of 0.5 cfs.

Lovelady Water Levels

Water levels in the Lovelady well rose about 0.4 ft (from 197.6 to 197.2) in response to the recharge that did occur. Unless more recharge occurs, water levels will likely level off over the next few days and then will begin to follow a steep declining trend similar to Barton Springs.

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