History

History

Hill Country Flood in September 1952

The following information about the September flood of 1952 highlights intrinsic characteristics of drought and flooding in the Hill Country. Large amounts of precipitation fall in a very short time. Most of this rainfall is shunted off the land before plants, animals or people can effectively use it. It is important to retain as much of this moisture high up in the landscape as possible to prevent damage from flooding and drought.

Drought

This particular flood happened during a time of extreme drought. According to the records of the Lower Colorado River Authority, Lake Travis’s all time low is 619.06 feet, recorded on September 6, 1952. The Llano River at Llano had virtually dried up in August, requiring the city of Llano to ship in water on train cars. The federal government had sponsored a program called “Operation Haylift” to ship hay from Iowa to Texas and there were very little crops being grown in Texas. Many Hill Country streams were at their all time record lows. Texas in the early 1950s was a very dry place in need of a reprieve.

Rainfall

In September the Hill Country received torrential rainfalls exceeding 20 inches in 48 hours. On September 9 gentle showers settled the dust with 1-3 inches of rain over various counties. Then the gentle showers turned into the heavy deluges that this area is known for, ranging from 3-8 inches across the Hill Country. On September 11 Blanco received 17.5 inches, Hye 20.7 inches, Llano 12.5 inches.

The Blanco River at Wimberley had only 11 cfs flowing on September 10 at 4 A.M. At 8:30 am on September 11 the river had rose to 30.10 feet and attained a peak flow of 95,000 cfs. In San Marcos, the floodwaters from the Blanco caused the San Marcos River to flow backward. The backflow of the San Marcos River over topped the highway 81 bridge. Once this extreme amount of runoff enters the river it is lost and cannot do its job to mitigate drought conditions. It may sound unrealistic, but much of this runoff could have been mitigated with just a few percentage increases in soil organic matter. For example raising the soil organic matter by 1% on one acre allows the soil to hold an extra 25,000 gallons of water. Raising it 1% on a 1000 acres yields 25,000,000 gallons of water storage in the soil, or around 75 acre feet of water volume stored in the soil via soil organic matter. We can also preserve our current water storage capacity in the soil by protecting the soil from erosion.

The Pedernales River received the most intense runoff of this event; 15 inches of rain fell in Fredericksburg, 26 inches down poured in Stonewall and Hye. The Pedernales at Johnson City had no flow on September 9^th and on September 11 achieved a new record flow rate of 441,000 cfs and a new peak height of 40.8 feet. The USGS noted that cypress trees 5 feet in diameter “were broken off like matchsticks” and pecans 2ft in diameter were uprooted and washed away. This is reminiscent of the 2015 Memorial Day flood on the Blanco River in Wimberley where the cathedral of cypresses was lost and the landscape changed dramatically. The flood scraped the river bottom down to bare rock. The bridge on Highway 281 over the Pedernales had lost large sections and beams. Lake Travis gained 701,000 acre-feet in a single day, nearly tripling its volume in 24 hours. The level of Lake Travis gained 57 feet and filled the lake for the first time in seven years. Lake Travis did a great job of harvesting this floodwater and at the same time has been able to provide water to people during times of drought. However, the risks involved with this amount of water storage far exceed the benefit and only treats the symptom of the floods. In order to mitigate to high financial cost of flooding and the further degradation of our riparian areas water should be encouraged to infiltrate into the soil with all appropriate means as high up in the landscape as possible. This helps dissipate the high energy of the water in riparian areas.

No Drought Relief

Despite the intense rainfall, drought conditions persisted in the Hill Country and all of Texas. There was little to no rain reported for the entire month of October. This highlights the cycle of drought and flood in central Texas. Water storage capacity in the soil can be improved with polycultural forestry, intensively managed grazing systems, appropriate earthworks or a combination of all. Harvesting water high in the landscape via infiltration turns the problem of intense rainfall and flash flooding into a profitable and sustainable solution. Extreme flood events like this should be stored to mitigate drought, storing it in the soil is the cheapest and most effective way to do so. Instead the flood of 1952 caused damage to the soil that further degraded out water storage capacity in the soil. One Farmer in the Hye area had as “Fine a field as to be found in Gillespie Country before the rain. Now the field is just gravel and clay since all the topsoil was washed away.” This farmer’s field like many, is now less drought resistant than before because of the loss of topsoil which is rich in organic matter that holds tons of soil moisture, 113 tons of water per acre for every 1% organic matter. Subsoil’s that are exposed to the elements also erode more quickly and allow less infiltration resulting in increased runoff which exacerbates flooding. Optimizing lands ability to harvest water requires 100% ground cover 100% of the time. Damaging floods will be ended by ending bare soil.

Pete Van Dyck

Sources

“Flash Floods in Texas” Jonathan Burnett 2008

“Chapter 1 The Climate” Regrarians eHandbook 2015

https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb1082147.pdf

Photo:http://www.theatlantic.com/national/archive/2015/05/wimberley-texas-flood/394307/