Rains Cause 1000 Year Flood

Observation: 6 inches of rain in 3 hours. The local government claimed that we suffered a "1000 year flood" during the day, night, and into the morning of July 30-August 1, 2016. The Old Historic District is within a narrow granite/solid rock valley (21043, 21042 main zip codes) with the Patapsco River at the bottom of the watershed. The main smaller tributaries that contributed the most water from up hill are called the Tiber and Hudson which drain large parts of the Ellicott City watershed west and north of the Patapsco River which empties directly into the Inner Harbor of Baltimore MD. The area has had historic floods before especially with hurricanes but this storm was massive in the amount of rain that flooded the valley from the top down NOT the bottom up! Source: NOAA's NWS Weather Radar

This radar loop, from around 5:30pm to around 9:00pm and centered on Ellicott City, shows the evolution of the rain across the Ellicott City/Baltimore area. Several convective cells formed ahead of a larger area of rain, which then was followed by persistent heavy rain, with very little lightning, in a west-to-east band for around 90 minutes between 6:45pm and 8:30pm, and especially heaviest between 7:45 and 8:00. The National Weather Service issued a flash flood warning, which included Ellicott City and Baltimore, at 7:18pm. The first report of flooding near Ellicott City was in the Chatham area west of downtown at 8:01pm. Based on video evidence and resident interviews, the most severe flooding occurred between 8:05pm and 9:00pm.

Total Rain — The MRMS (Multi-Radar/Multi-Sensor) precipitation estimates from the event show the swath of most persistent heavy rain that occurred from northern Montgomery County, Maryland to Baltimore City. The image below is filtered to show only amounts over two inches. Areas in yellow are over 2.5 inches; red is over 4 inches; and the pixels of white near Ellicott City are estimates of over 6 inches. Much of this rain fell in 90 minutes or less. Stream Response / Flooding

Certainly, rain of this severity will cause a sharp rise on streams, and this was reflected in numerous automated stream gauges monitored by the NWS. The largest river impacted in this event was the Patapsco River, which is the county border between Howard and Baltimore Counties for much of its reach. At Ellicott City, the Patapsco rose just over 13 feet in 100 minutes (7:20pm - 9:00pm), and rose over two feet in just five minutes (8:40pm-8:45pm). This sharp 2+ foot rise coincides with the time when the most significant reports of flooding began to be received by the National Weather Service.

Nichols - There were 2 fatalities and total destruction of several businesses and people's homes along the business district and the west end (Frederick Rd) residential side of EC.

NOAA Post-Storm Survey — The National Weather Service joined the Howard County Office of Emergency Management and Howard County Department of Public Works in conducting a survey of affected areas of Ellicott City, Maryland on August 1st, 2016. The survey revealed clear signs of flooding both from the Patapsco River and from flash flooding within Ellicott City. Signs of flooding, including damaged pavement, were observed as far up as the intersection of Rogers Avenue and Frederick Road, where Hudson Branch came out of its banks. From this location, eyewitnesses reported seeing water not only in the creek, but moving swiftly down Main Street beginning "just after dark". The intersection of Rogers Avenue and Frederick Road is about 140 feet higher in elevation than the lower part of Old Town Ellicott City. Erosion was noted on both the street side and the creek side of homes along Main Street in a portion of the 8500 block.

The next signs of damage were in the 8300 block of Main Street, with damage again observed both on the creek/river side and the street side of Main Street. The creek/river side is where the most vehicles were impacted, in "Lot D".

In the 8200 block, surveys and surveillance footage show water anywhere from 6 inches to two feet inside buildings on Main Street along with substantial damage to sidewalks and infrastructure outside the buildings.

The most significant damage observed was near 8100 Main Street, where the street curves slightly. Based on topographic maps, this general area is also approximately where the extent of the Patapsco flooding would have reached based on the observed peak of 128.05 feet. Although we cannot say for certain, it is possible that this area being the meeting point of the upstream and Patapsco floodwaters could have caused more significant damage in that immediate area. Video surveillance footage reviewed after the event clearly indicates that water from the Tiber River was flowing through buildings on the south side of Main Street in this area, toward the street.

Closer to the Patapsco, damage continued with water marks observed 6-8 feet high on and in most buildings. The force of the floodwaters swept away the iconic Ellicott City clock as well as the historical flood marker that was attached to the railroad bridge. Although the survey team did not visit the Baltimore County side of the river during the survey, there are multiple reports of at least minor flooding of Oella Avenue and Route 144 due to the Patapsco escaping its banks.

We extend our appreciation to Howard County for coordinating the survey and accompanying the NWS to the affected area.

Nichols - I walked the entire length of the west end of main street several times over the next few days and observed massive damage to infrastructure and peoples homes. EC is still recovering and will be for a while.