Geology topics

Christopher W. Nealen

Publications and source records attributed to Christopher W. Nealen.

3 recordsLinked to original sources

USGS2021

Storms and floods of July 30, 2016, and May 27, 2018, in Ellicott City, Howard County, Maryland

Introduction On July 30, 2016, and May 27, 2018, the downtown area of Ellicott City, Maryland (fig. 1), was severely flooded by intense, short-duration rainfall that resulted in loss of life; significant damage to buildings, roads, infrastructure; and hundreds of vehicles washed away. Precipitation from the 2016 event totaled 6.60 inches in 3 hours (National Oceanic and Atmospheric Administration, 2016). Precipitation from the 2018 storm totaled 6.56 inches in 3 hours (National Oceanic and Atmospheric Administration, 2018). In the aftermath of both storms, personnel from the U.S. Geological Survey (USGS) performed indirect discharge measurements to determine peak flow on the three streams that drain through the downtown area of Ellicott City and empty into the Patapsco River. High-water marks were flagged on selected reaches of three streams, Hudson Branch (station 01589017), Tiber Branch (station 01589019), and New Cut Branch (station 01589021) (fig. 2). Peak flows were computed using flow-through-culvert techniques with road overflow for Hudson Branch and slope-area techniques for Tiber Branch and New Cut Branch. This fact sheet describes the basin characteristics, hydrologic characteristics, and flood history of the Ellicott City, Maryland, area. The storms and flood characteristics for July 30, 2016, and May 27, 2018, are described. Peak discharges computed from the indirect discharge measurements for Hudson Branch, Tiber Branch, and New Cut Branch are presented for the storms and floods of July 30, 2016, and May 27, 2018. To provide historical perspective on these floods in Ellicott City, results from the indirect discharge measurement computations were compared to peak flows from 75 USGS streamgages and 6 miscellaneous sites in Maryland and Delaware that resulted from intense storms in August and September 1971 (Carpenter, 1974). The findings indicate that although the Ellicott City storms and floods from July 30, 2016, and May 27, 2018, are considered very rare in terms of their probability of occurrence, other storms have occurred in the Maryland and Delaware regions in the past that have produced comparable runoff characteristics relative to drainage-area magnitude.

Maryland↗

USGS2021

Precipitation, peak streamflow, and inundation in the Bynum Run and Winters Run watersheds in Harford County, Maryland

The Harford County Department of Public Works and the U.S. Geological Survey have been working cooperatively to monitor continuous streamflow at several streamgages in Harford County, Maryland, including Bynum Run and Winters Run. A perceived recent uptick in the number of flooding events in the Bynum Run and Winters Run watersheds have led to questions about the relative frequency and magnitude of floods experienced by county residents. Precipitation, stage (water elevation), and peak flow analyses and trends were evaluated. Although there was no one contributor to point to for the perceived increase in flooding, it is most likely attributable to a combination of precipitation, stage, and peak flow. There have been numerous rainfall events with exceedingly long return intervals, but none were statistically out of the ordinary. The stages of the streams at higher flows are slightly higher (less than 0.5 feet) than historical stages, but likely are not great enough to cause a significant increase in flooding. The ratings (stage discharge relationship) for the streams have changed slightly. The latest ratings indicate erosion and deposition in the streambed over the years of observation, but again these alone do not result in more flooding. These factors taken together may point to an observational bias for incidental flooding. With the increase in land development, there may simply be more observations of flooding in the county.

Maryland↗

USGS2019

Hydrologic study at Farm Creek Marsh, Dorchester County, Maryland, from April 2015 to April 2016

In 2015, the U.S. Geological Survey began a 1-year hydrologic study to investigate the extent and cause of inundation at Farm Creek Marsh, in Dorchester County, Maryland. In combination with a tide and precipitation gage, a representative section of the marsh was instrumented with surface-water monitors and shallow groundwater piezometers to capture the spatial and temporal extent of inundation. In addition, water-quality data (major ions and nutrients) were collected to help discern the cause of inundation. Results indicate that during the year-long study, all sites were periodically inundated, ranging from a total of 108 days to the entire study period of 353 days. The depth of inundation was typically between 0 and 0.2 feet (ft) (above land surface), with the exception of large storm events. Less than 0.5 ft of elevation was the difference between a site being inundated during the entire study period of 353 days and a site being inundated for 36 consecutive days out of 108 total days of inundation during the study period. Water-quality data showed a large difference in pH between marsh surface water (6.1 to 6.9 standard pH units) and shallow groundwater (3.0 to 3.6 standard pH units), with differences also observed in concentrations of silica, iron, manganese, and potassium. Collectively, the combination of water-quality, hydrologic, and soils data indicate that inundation is caused by tide and storm events rather than groundwater discharge.

Maryland↗