A tropical feeder band from Hurricane Joaquin is streaming high levels of moisture is into South Carolina. Three day rainfall totals across South Carolina and North Carolina have been impressive. With locations near Charleston seeing 20 + inches of rain. Much of the rain in South Carolina has fallen within the past 24 hours.
This is leading to significant flooding across the state. Most NWS River Forecast location in South Carolina are experiencing or forecast to experience moderate (the red boxed locations shown below) to Major river levels (purple boxes shown below.)
An additional 5 to 10 inches of rain is expected in the low country of South Carolina through Monday morning before the rains will start to diminish.
An area that has been especially hard hit is Colombia, SC. Local reports are indicating significant flash flooding in several areas of the city including sections along the Gills Creek in the eastern part of the city. Rainfall amounts in the Gills Creek drainage basin has ranged between 14-16 inches of rain in the past 3 days (since Thursday, 10/1.) with 12 to 14 inches of rain falling in the past 24 hours.
Gills Creek at Columbia river gauge is not a river forecast location for the National Weather Service, which means they do not provide future river level information. But we do have the river level observations for Gills Creek provided by the USGS. The left graphic below shows the river observations in blue rising very quickly Saturday and into Saturday night. Then at 7 am on Sunday (10/4) the river gauge stops reporting. Give the latest reading was 7.65 feet above the previous flood of record of 9.43 ft. set on July 24, 1997, the river gauge was likely inundated with water and the electronics have been damaged or the river gauge was potentially washed away. Thus we will not know an actual crest for this location until the USGS is able to perform an in person survey evaluation. The right graphic below provides a perspective of how the river spreads as the levels rise near the river gauge location. The Aqua areas outlines the 1% flood risk (100 yr flood plain) area while the orange area is the 0.2% risk area (500 year flood plain). NOTE: 1% risk means there is a 1% chance every year that this area could be flooded.
Significant flooding has occurred along much of Gill Creek. WLTX has several videos of flash flooding in the Colombia area. One area in particular is Gills Creek at Decker Blvd which is to the north and upstream of the river gauge as noted in the left graphic below. In looking more closely at this location via the FEMA Flood Maps (right graphic below), Decker Road is actually in the Floodway or in the main river channel area (as show in the Right graphic below in the red circle) when the river rises to the 1% level. Unfortunately the road was built and the area developed in these risk areas. (This area was likely developed before we understood the actual flood risk.) Thus, the river responded as expected and the fast moving current area over topped the road. Unfortunately looking at the swift water rescues, they were not able to close the road prior quickly rising water inundating the roadway and people were caught in a serious situation. This is why you should never drive into a flooded roadway, even if the water seems slow moving or just ponded. You do not know how quickly the situation could change, how deep the water is or if the road has been washed out underneath.
With additional 2 – 5 inches of rain expected in the Colombia, South Carolina area local officials have declared a State of Emergency and requesting people stay at home and off the road.
Those with interests along creeks, river and in lower areas along the coast are urged to remain aware for changing water levels.
The team at WxIntegrations will continue to provide relevant information and resources to help you better understand and prepare by incorporating weather impacts into your planning and response.