SSCAFCA shares study on Rio Rancho rain amounts in big July storm

RIO RANCHO — Remember that brief but strong two-hour storm July 3? Rio Rancho evidently got 3 inches of rain that day within a couple of hours, which was a big deal for the Southern Sandoval County Arroyo Flood Control Authority at its July 17 board meeting.

Hydrologist Dr. Gerhard Schoener gave a presentation on preliminary data from the Star Heights Rainfall monitoring project at the meeting.

“We spent a considerable amount of effort, developing a new model, all in the interest of our models that are so crucial for everything we do at SSCAFCA because they inform the building plot for planning and designing for the ultimately constructed flood-control projects. Models heavily inform the planning process to figure out where our deficiencies are and where infrastructure can be built,” Schoener said.

This project, he said, was perfect for comparing how flood mitigation is working compared to areas that haven’t been set up with flood control. SSCAFCA members asked if they could get that represented with data. Schoener said he thought that was a good idea.

As with any data, Schoener explained, it is difficult to get 100% accurate representations. “One thing we’ve been working on very hard is to try to get our models as accurate as possible,” he said.

He added that it is a balance of working in the field and working with theory.

Schoener said the method used to collect data for the July 3 storm had just been implemented this summer prior to the storm. The last sensor was put in last month. “It was lucky,” he said.

He and his team strategically placed rain collectors in the Star Heights area, which consisted of the area to the southwest starting at the intersection of Southern and Unser boulevards.

“That area has a network of channels and several flood control ponds that have been built. We decided to instrument this area, so we added eight more rain gauges and then we also added eight new locations where we monitored flow,” he said.

The goal was to collect high-resolution rainfall and runoff data in an urban environment, according to Schoener. However, he clarified that this study area was a mix of urban, residential and undeveloped regions of Rio Rancho.

He said Rio Rancho doesn’t produce as much high-density rainfall data because storms tend to be “very spotty” with low chances of the entire area getting any rainfall. “We get it and storms, but it’s really hard to predict where they’re going to occur,” he said.

Despite this, the storm July 3 hit the study section dead on and set records for rainfall amounts.

“The question is always, ‘What kind of event are we looking at?’ and that’s actually not an easy question to answer because real storms don’t follow statistics specifically, but if you look at the historical data for this area, you can plot rainfall intensity against duration,” Schoener said.

He showed the group graphs representing how many inches of rain per hour the study area had. The start of the storm had about 1 inch per hour, but as it progressed into the second hour, it got up to about 3 inches per hour.

Schoener said this storm fell between what a 10-year storm would be and a 100-year storm would be, which means as the intensity of rainfall increases, the less chance there is of it occurring in a year. This storm had a slimmer chance because the intensity was higher with nearly 3 inches in that couple of hours. This does not mean that the area won’t have another storm of that intensity for another 99 years but rather the chance of getting the storm is 1%, according to Schoener.

“Real storms don’t follow statistics,” he added.

He said in terms of the impact of the storm, it was a very rare event for the area.

“I’ve been here for 18 years, and we have had gauging stations out that have not measured that much for most of that time,” he said.

He compared the storm to a similar storm in 2017 that flooded people’s homes and trashed their yards, adding that the flood control minimized that damage this year. He told SSCAFCA board members and staff that he will have comparisons of that damage control to share with them in the near future.

He also brought up the flooding in Ruidoso recently, which he said may have had similar rain amounts to this storm.

For more information on SSCAFCA, visit sscafca.org.