Brianne Smith

Exploring storage and runoff generation processes for urban flooding through a physically based watershed model

A physically based model of the 14 km2 Dead Run watershed in Baltimore County, MD was created to test the impacts of detention basin storage and soil storage on the hydrologic response of a small urban watershed during flood events. The Dead Run model was created using the Gridded Surface Subsurface Hydrologic Analysis (GSSHA) algorithms and validated using U.S. Geological Survey stream gaging observations for the Dead Run watershed and 5 subbasins over the largest 21 warm season flood events during 2008–2012. Removal of the model detention basins resulted in a median peak discharge increase of 11% and a detention efficiency of 0.5, which was defined as the percent decrease in peak discharge divided by percent detention controlled area. Detention efficiencies generally decreased with increasing basin size. We tested the efficiency of detention basin networks by focusing on the “drainage network order,” akin to the stream order but including storm drains, streams, and culverts. The detention efficiency increased dramatically between first-order detention and second-order detention but was similar for second and third-order detention scenarios. Removal of the soil compacted layer, a common feature in urban soils, resulted in a 7% decrease in flood peak discharges. This decrease was statistically similar to the flood peak decrease caused by existing detention. Current soil storage within the Dead Run watershed decreased flood peak discharges by a median of 60%. Numerical experiment results suggested that detention basin storage and increased soil storage have the potential to substantially decrease flood peak discharges.

Hydrologic Analyses of the July 17-18, 1996, Flood in Chicago and the Role of Urbanization

On July 17–18, 1996, two mesoscale convective systems (MCSs) passed through northeastern Illinois, causing a record 440-mm total storm rainfall within a 24-h period at Aurora, Illinois, with values exceeding 200 mm throughout a broad area of the region. The storm caused flooding with a return period larger than 100 years at different USGS regional stream gauging locations. The Davenport, Iowa, Weather Surveillance Radar–1988 Doppler (WSR-88D) radar coverage allows high-quality characterization of the storm at fine spatial and temporal scales. Of particular interest is the inter- and intravariability in watershed response to the two pulses of intense rainfall. Spatial distribution of rainfall and the degree of urbanization of the individual basins are the dominant factors determining the magnitude of runoff response. These properties are highly dependent on the extent and history of urbanization. Examination of the annual maximum instantaneous peak discharge and the peaks-over-threshold (POT) time series at three stream gauging stations in Illinois (Blackberry Creek, DuPage River, and Sawmill Creek) over the past 50 years points to the large effect of urbanization on the flood peak distribution in the greater Chicago metropolitan area.

The Flashiest Watersheds in the Contiguous United States

AbstractThe authors identify the flashiest watersheds in the contiguous United States based on frequency of discharge peaks exceeding 1 m3 s−1 km−2. The entire digitized record of USGS instantaneous discharge data is used for all stream gauging stations with over 10 years of data. Using the 1 m3 s−1 km−2 threshold, the flashiest basins in the contiguous United States are located in urban areas along a swath of states from the south-central United States to the mid-Atlantic and in mountainous areas of the West Coast, especially the Pacific Northwest. The authors focus on small watersheds to identify the flashiest cities and states across the country and find Tulsa, Oklahoma; Baltimore, Maryland; and St. Louis, Missouri, to be the flashiest cities in the contiguous United States. Thunderstorms are major agents for peak-over-threshold flood events east of the Rocky Mountains, and tropical cyclones play a secondary role, especially in the Southeast. West Coast flood events are associated with winter storms. F...

Structure and evolution of flash flood producing storms in a small urban watershed

The objective of this study is to examine the structure and evolution of storms that produce flash floods in “small” urban watersheds. The study site is Harry’s Brook, a 1.1 km urban watershed in Princeton, New Jersey. A catalog of 15 storms is developed for Harry’s Brook based on paired observations of streamflow and rainfall. Lagrangian analyses of storm properties are based on storm tracking procedures utilizing 3-D radar reflectivity observations from the KDIX (Fort Dix, New Jersey) Weather Surveillance Radar, 1988 Doppler. Analyses focus on the storm elements that were responsible for the peak rainfall rates over the watershed. The 22 July 2006 storm, which produced the record flood peak in the catalog (a unit discharge of 26.8m s 1 km ) was characterized by thunderstorm cells that produced more than 50 cloud-to-ground lightning strikes and “collapsed” over Harry’s Brook. The 3 June 2006 storm, which produced the third largest flood peak (a unit discharge of 11.1m s 1 km), was a “low-echo centroid” storm with no lightning. We use cloud-to-ground flash rate, echo top height, maximum reflectivity, and height of maximum reflectivity as key variables for characterizing convective intensity. Storm motion is examined through a time series of storm speed and direction. The 22 July 2006 and 3 June 2006 storms provide end-members of storm properties, centering on “convective intensity,” which are associated with flash flooding in small urban watersheds. Extreme 1–15min rainfall rates are produced by warm season convective systems at both ends of the convective intensity spectrum.

Flash Flood–Producing Storm Properties in a Small Urban Watershed

AbstractThe structure and evolution of flash flood–producing storms over a small urban watershed in the mid-Atlantic United States with a prototypical flash flood response is examined. Lagrangian storm properties are investigated through analyses of the 32 storms that produced the largest peak discharges in Moores Run between January 2000 and May 2014. The Thunderstorm Identification, Tracking, Analysis, and Nowcasting (TITAN) algorithm is used to track storm characteristics over their life cycle with a focus on storm size, movement, intensity, and location. First, the 13 June 2003 and 1 June 2006 storms, which produced the two largest peak discharges for the study period, are analyzed. Heavy rainfall for the 13 June 2003 and 1 June 2006 storms were caused by a collapsing thunderstorm cell and a slow-moving, low-echo centroid storm. Analyses of the 32 storms show that collapsing storm cells play an important role in peak rainfall rate production and flash flooding. Storm motion is predominantly southwest-...

Lead in New York City Soils

Urban soil is a sink for anthropogenic lead (Pb) and the latter is a persistent threat to human health, especially to children and the gardening population. In the past decade, several organizations have tested soil samples for Pb in New York City. Here we summarize the available soil Pb data for New York City and create a spatial distribution map. The highest Pb levels were present in the oldest parts of the city, and mostly industrial and high traffic areas. There is overlap between high Pb areas with areas of high population density and high poverty rates. The analyses help delineate parts of the city that are most affected, possible sources of Pb, and where to prioritize resources for mitigation and remediation.