Very heavy rainfall of 12 to 14+ inches has fallen across parts of East Texas, Louisiana, Arkansas, and Mississippi over the past few days. While much attention has been across northern Louisiana where the heavier amounts of 20+ inches occurred, Southeastern Louisiana and Southern Mississippi also saw an axis of 10 to ~ 12 inches which has cause/is still causing major to record flooding.
Bogue Falaya River
One location of interest is the Bogue Falaya River. The river gauge at Boston Street in Covington, LA exceeded the previous record of 17.1 by nearly 3 feet Friday Night (3/11/16). The preliminary crest level is 20.07 ft. which occurred at 1 am CST or 7 Zulu time. The previous flood of recorded dated to January 21, 1993.
Jack Bushong and his son captured areal footage of the Bogue Falaya River on Saturday Morning (3/12/2016) near the river gauge after the river crested at 20.07 ft. They took the video around 9 am CST when the river was at ~ 17.47 feet. This was after the crest and ~ 2.5 feet lower than the new crest level.
The image below is looking to the northwest and shows the inundation on the west side of the river, just upstream US Bus 190 which is where the river gauge is located.
The full video is below or YouTube link
FEMA Flood Maps
Unfortunately, the FEMA flood map analysis for this area has not been updated since 1989. So these maps do not incorporate new topography data or LiDAR (Light Detection And Ranging) data sets that would improve the modeling and mapping of the river location.
The graphic below shows the latest floodplain mapping information with the location of the river gauge outlined as the yellow “X”. The areas shaded in the darker grey are referred to as the zone A regions which delineates the 1% annual flood risk (aka 100 yr flood), while the lighter grey regions referred to Zone B show the 0.2% annual flood risk (aka 500yr flood.)
The USGS has a poster with more information on a 100 year flood.
Areal footage such as what was captured by Jack will be invaluable to the USGS, NWS and local flood plain managers for understanding the inundation impacts of this flood and hopefully to reinforce the need to update the flood maps in this area.
In addition, the USGS is seeking funding to help support this river gauge as the Bogue Falaya River at Boston Street gauge website shows it is on the USGS River Gauge endangered list. This means that unless cooperative funding from other government agencies or local businesses is received, the river gauge may be discontinued.
It will take some time for this area to recover form the floods. While rainfall forecasts over the next few days are light, another system for mid to late in the week will bring rainfall amounts in the 1 – 2 inch range. So, this may cause secondary rises on rivers as the ground is saturated and will only be able to absorb limited additional rainfall.
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.