City taps online weather forecasting for library rainwater collection

On a recent rainy May morning, water whooshing down the roof of the Twin Oaks library in South Austin rushed through a gutter system before settling into a pair of 2,500-gallon cisterns.

It had rained just the day before, but the cisterns had already automatically emptied themselves of that precipitation — in seemingly magic anticipation of the current rain.

As part of an innovative experiment marrying ancient rainwater collection techniques with modern technology, the city of Austin is experimenting with a program that uses online weather forecasting to govern when the cisterns release water. The goal is to maximize water capture.

This month the $33,000 project won a state Rain Catcher Award, part of a rainwater harvesting competition sponsored by the Texas Water Development Board.

When the library was remodeled a half-dozen years ago, architects emphasized sustainability, using recycled bricks for the exterior and a state-of-the-art lighting system that automatically dims when there is sufficient daylight, as well as the rainwater collection system.

Austin, working in collaboration with the Water Environment Research Foundation and Geosyntec Consultants, chipped in $15,000 toward the initial costs of the rainwater project, which got off the ground in 2012. The other partners made up the difference through in-kind contributions. (Austin paid another $3,000 in maintenance in 2014.)

The real-time controller detects when the cisterns are less than half full and then automatically reduces the volume of water released to irrigate plants on the library site, in the Bouldin neighborhood. The controller also folds in weather forecasts and automatically drains the cisterns when the chance of a storm exceeds 60 percent, thus increasing the storage capacity for stormwater runoff.

In 2015, the system delivered 29,000 gallons of rainwater and air conditioner equipment condensate: 10,000 gallons were used for regularly scheduled irrigation (every two weeks), and 19,000 gallons were released ahead of forecasted rain events.

Governed by the weather forecast, the system is “one of the most sustainable features in our Twin Oaks library,” said Heidi Tse, who heads facilities services for the library system.