This is an aerial view of the Highline Canal at Delgado Avenue in Belen facing east. Photo from June 6, 2021
Elected officials across Valencia County are continuing to work together to create a plan that will create a flood authority and flood-control infrastructure in areas hard hit by summer downpours coming off the west mesa.
Last month, representatives from the Middle Rio Grande Conservancy District, the city of Belen, village of Los Lunas, village of Bosque Farms, city of Rio Communities and Valencia County, gathered to discuss next steps in forming a local flood authority, with taxing ability.
Mike Hamman, chief engineer and CEO of the MRGCD, said in the seven years he’s been with the district there have six separate flooding incidents due to upland flooding, where water comes off the west mesa and crashes into the High Line Canal, filling it with sediment, overtopping the canal and in some cases, breaching the canal wall.
“We try to be good neighbors and partners in serving our constituents, but we, as a district, do not have the authority, infrastructure or tax base to serve as a flood control authority,” Hamman said. “It is not part of our operational authority to address upland flooding events. Our primary response is the river levees that run through those areas.”
After flooding events, the problem is often framed as an “MRGCD infrastructure problem,” said Jason Casuga, the district’s chief operations officer and an engineer for the district. “What is the problem is fast-moving thunderstorms that drop a lot of precipitation fast.
Casuga presented rainfall data from four events from September 2017 to the most recent flooding July, which produced anywhere from 1.7 to more than three inches of rain in as little as 45 minutes as the storms moved west to east over the mesa and into the valley.
He added that which ever side of the fence someone is on in regards to climate change, the number of fast moving, high precipitation events has increased since 2016.
“What’s clear is these events are happening relatively regularly,” Casuga said. “I’ve been here since 2016 and there have been almost one a year.”
Hamman said many residents view the High Line Canal as a way to address flooding, but he said even if it were empty at the time of a storm event, the 60-foot wide irrigation canal would be easily overwhelmed.
“If we see a storm system coming, we evacuate (the water from the canal) as quickly as possible,” he said.
The High Line has historically run a maximum capacity of about 664 cubic feet per second, Casuga said, and one basin on the mesa could produce 1,500 cfs of runoff during a storm.
“And you could have three or four (basins). The High Line, like homes, highways and any property without the proper infrastructure to route that water, you’re just in the way. The storm is going to win.”
Valencia County Commissioner Joseph Bizzell asked what the district’s protocol was to determine when to shut off irrigation ditches during a storm.
Casuga said it was a tough call, with staff monitoring radar and forecasts. He said the ditch runs about 17 miles through Valencia County and it takes more than 24 hours for water to travel that distance.
“If we’re wrong and turn it off, you have 30 to 40 irrigators depending on scheduled (water) delivery,” he said. “Our primary mission is to deliver irrigation water. As soon as that storm event was over in July, while everyone was recovering from the flood, some of the first calls we got were, ‘When are you delivering water?’”
Casuga said the only way to really effect the amount of water in the canal where it runs through the city of Belen is to make the call to shut it off 24 hours before a storm hits.
“In July, we had effectively zero water in the High Line and the storm busted through the canal like it wasn’t there,” he said. “We turned it off a day and a half in advance.
“The easiest (storms) to plan for are the really big ones, but the surprise or small ones …
“We’ve all seen it. It’s forecast for 60 percent chance of rain and we get .03 of an inch. It’s 20 percent and we get nailed.”
Belen City Councilor Frank Ortega said when the city was flooded badly in 2017, state representatives pledged almost $2 million in funding for flood control, but since then nothing’s happened.
Hamman theorized there wasn’t the “political will” in 2017 to get a flood control authority started in valencia County.
“Now everyone is seeing these 100 year events happening every year. I’m getting the sense political will is building, constituents are demanding change,” he said.
He advised the local agencies do two things to prepare for forming a flood authority — create a flood master plan and do a rate study to determine the minimum amount of taxation needed to build and maintain flood control infrastructure.
The CEO added the district was willing to help fund the two studies, which he estimated would cost about $1.5 million. A flood control agency is created by the New Mexico Legislature and typically requires a plan as well as a defined area for taxation to support infrastructure.
“I think legislators would sign on for funding tomorrow but you need a master plan,” Hamman said. “You also need to spread the tax base out as far as you can.
“There might be areas that are not in the cross hairs now but the continued urbanizing of the valley corridor is going to do nothing but expand, especially with the second (Interstate 25) exit.”
Philip Sublett, the Valencia County Planning and Zoning commissioner for District 4, brought up the idea of making the High Line deeper — thus able to carry more water coming off the mesa — and creating a network of drainage ditches coming off the canal to move water out of it quicker.
Casuga said the idea of making the canal deeper had been studied but the problem was the slope of the structure, not the depth.
“If you look at (other flood control structures) they all flow downhill. The slope of the High Line never changes cause it follows the river,” he said. “It’s pitch is .0005. It was designed to match the river. The biggest thing that matters is the slope.”
If the majority of the watersheds on the west mesa are producing runoff at the rate of 500 cfs during a 100 year flood event, that would put 15,000 cfs of water into the High Line, Casuga said, well above the current 664 cfs capacity.
“It is going to be hard for the community to accept the idea of flood control until it accepts that the infrastructure doesn’t exist already,” he said.
Valencia County Manager Danny Monette said there were a lot more meetings in the future to form a flood control agency and to do the appropriate planning.
“Please keep coming. I know this is a dry topic, no pun intended, but this isn’t going to stop happening,” Monette said.