Flash Flood — Imperial, California

2023-09-01 · near Niland, Imperial, California

Event narrative

Widespread 1 to 2 inches of radar estimated rain fell in Niland and areas just east into the Chocolate Mountains. A large area of considerable runoff flowed through Niland and the surrounding area, as evident in reports and before and after Sentinel2 satellite images, with upwards of 6 inches to 1 foot of flowing water in some areas, per photos and videos. Major flash flooding impacts were experienced. The East Highline Canal east of Niland, was overcome with flood waters and silt, mainly north of of Flowing Wells Rd. The overflowing canal was first reported a little after 1600PDT and only exacerbated the flooding. Several roads became impassable, unsafe, and subsequently closed due to flood water. At least a few cars became stuck in flood water leading to swift water rescues by land and air. The exact number of rescues is unknown. In Niland, several photos and videos showed flooded streets and yards, with water coming up to homes and businesses. There were a few reports of water entering homes, but it is unknown how many homes were impacted. Also impacted in the area was agriculture, as several fields had flood water moving through them. It is unknown the extent of any damages to the agricultural fields or the exact number. Sentinel2 satellite images showed evidence of all the disturbed earth, deposited mud and silt, through Niland, the agricultural fields and surrounding areas. In a statement by Imperial Irrigation District, the impacts to East Highline Canal resulted in a delay of 133 water deliveries. Also the O Lateral canal, which branches from East Highline canal, suffered structural damage. The main highway through the area, Hwy-111, was flooded in several locations, which hampered relief efforts. The small town of Slab City, to the northeast of Niland, was cut off from the rest of the Imperial Valley due to the flooded roads. As a result of the significant impacts, the County of Imperial issued an emergency proclamation for additional and better resources. Red Cross assisted in relief and a couple shelters for evacuees were established. There were no injuries reported from this event and specifics on property and crop damage is unknown and thus grossly estimated.

Wider weather episode

A deep southerly fetch of rich moisture up from the Gulf of California led to scattered to widespread heavy rainfall in Imperial and eastern Riverside counties during the afternoon of the 1st. Moisture values were well above normal for the time of year with precipitable water values analyzed around 2.0-2.2 inches. A Flash Flood Watch was issued for much of the region. Favorable dynamic and orographic forcing helped lead to strong updrafts and training of storms over certain terrain areas. Radar estimated rain rates were up to around 2-3 inches per hour with locally higher rates over shorter periods. There was a RAWS station in eastern Imperial County that measured right around 3 inches in 1 hour. These high rain rates led to areas of high rainfall accumulation, with many areas seeing at least 1 inch of rain and isolated areas up to 3.5-4.5 inches, radar estimated. This resulted in numerous reports of considerable flash flooding around the region. The hardest hit was the town of Niland and immediate surrounding area. A few inches of rain fell east of Niland leading to a canal being overcome with water and silt. This exacerbated the flooding and several inches of water flowed through the town and surrounding areas. The major impacts led to an emergency proclamation by the County of Imperial. In addition to the road closures, there were several swift water rescues across Imperial and Riverside Counties, both by land and air. One of the air rescues was completed by the San Diego US Coast Guard. On top of all the flooding, the heavy mass loading and strong updrafts resulted in strong to severe downburst winds, which caused a couple semi truck rollovers, downed many power poles, and generated dense blowing dust.

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Source: NOAA Storm Events Database, event_id 1141473. Narrative written by the NWS forecast office that issued the report.