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Intense rainfall here in late July seemed to have broken a drought through which most of the Southwest had suffered in recent years. But with those monsoon downpours came flood damage here, some of it unusual. While most of the stormwater damage Friday July 23 hit properties below the escarpment, especially between Camino Arco Iris and West Meadowlark Lane, erosion of the ditchbank along the Corrales Interior Drain was largely unexpected. Rain and stormwater flooding threatened Casa San Ysidro Museu, leading to its closure August 3. “Thanks to the professiional work of the Albuquerque Museum collections management team, historical objects, furniture and other collection items were moved, and are safe and secure, while repairs are being made,” museum officials said. “We are assessing what steps need to come next before we are able to reopen to the public.”

Yet other flood-prone neighborhoods fared better than in previous heavy rains due to long-sought drainage improvements. Among those were areas below Intel’s east property line following major drainage upgrades along its paved Skyview Trail and within the Salce Basin watershed along Sagebrush Drive and nearby neighborhoods. “The hardest hit areas are from Mission Valley south to Meadowlark lane,” Corrales Public Works Director Mike Chavez told Corrales Comment. “When we get from two to three inches of rain in half an hour, the ground has no time to absorb the water and run-off will occur.” Chavez said that was the reason the Interior Drain ditch bank eroded in an unusual manner near its intersection with Rincon Road. Typically that doesn’t happen much in the valley bottomlands east of Corrales Road. “What a storm we had last Friday afternoon!” Mayor Jo Anne Roake posted on the Village website. “Many villagers noted the quick response by Public Works, Fire and Police Departments as they worked to remove mud and earth from the roads.”

Results of the intense downpour should motivate homeowners here to clear out and maintain stormwater ponding sites on their property, she advised. “It’s time for the citizens of the village to inspect the retention ponding on their properties, especially if you live west of Loma Larga on a sloped lot… but know that anywhere in the village is subject to flooding.” the Village warned on its website. “Because the Village of Corrales has no storm sewers, on-site stormwater reetention is the method we use to help reduce that flood risk.” No official data is available for the intensity of rains in Corrales over the weekend of July 23, but clearly the amount and duration of rains were exceptional. The storm also brought torrents of hail higher up in the sandhills. The late Ernest Alary kept meticulous records of precipitation on his farm at the north end of the valley, but Corrales Comment is not aware of anyone here currently collecting that data.

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Monsoon rains are expected to continue through this month and next; Corraleños may recall that some of the village’s most intense storms have come in August and September. (See Corrales Comment Vol.XXXII, No.15 September 21, 2013 “Raging Stormwater in Jones Channel Threatens.”) After the weekend rains July 23-25 and subsequent storms, about nine percent of New Mexico still was considered in “exceptional drought,” an improvement from 21 percent the week before and 53 percent as the summer began. Although Public Works Director Chavez’s suggestion that Corrales may have gotten two to three inches of rain in a half-hour span has not been corroborated, it would not be improbable.

Chuck Thomas, executive director of the Southern Sandoval County Arroyo Flood Control Authority (SSCAFCA), reported that an August 22, 2018 storm had “measured peak rainfall intensities in excess of .33 inches in five minutes, or close to four inches per hour.” That 2018 storm lasted a little less than three hours, although most of the rain fell in the first hour. (See Corrales Comment Vol. XXXVII No.11 August 11, 2018 “Monsoons Dump Tons of Silt.”) Cumulative rainfall measured in SSCAFCA’s gauges from July 1 to August 3, 2018 reached 3.73 inches in a station near Southern and Unser in Rio Rancho. Another gauge at Northern and Rainbow indicated 3.03 inches had fallen.

A SSCAFCA gauge at the north end of the Corrales Valley measured a cumulative 2.22 inches during that same period. Corrales homeowners experienced minor wash-outs along driveways and roadways in steeper terrain. As silt-laden stormwater drained from the areas west of Loma Larga, quantities of sediment were deposited at points such as Camino Arco Iris and Loma Larga as well as West Ella. A homeowner on Ashley Lane measured one and a quarter inches of rain in 2o minutes. A neighbor’s rain gauge showed two inches in 90 minutes which produced run-off that flowed into a home there.

In the past, concerns over intemse storms focused on water pouring through the Harvey Jones Channel in the Montoyas Arroyo which drains a good portion of Rio Rancho. Since the channel was built in the early 1990s, the biggest danger was at the Corrales Road bridge over the channel. Analysis by the U.S. Army Corps of Engineers demonstrated conclusively that the two box culverts under the bridge were too small to convey rushing stormwater pouring down from Rio Rancho. A series of corrective actions were finally taken in 2015-16 which seem to have resolved those risks. (See Corrales Comment Vol. XXXV No.8 June 11, 2016 “Corrales Arroyo Project  Hailed as Model for Southwest.”)

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