Publication Date:
2013-04-03
Description:
We seek to improve scientific understanding of urban storm event hydrologic response through analyses of high-resolution rainfall and discharge data for the Baltimore metropolitan region. High-resolution radar rainfall fields, developed at 1 km 2 spatial resolution and 15-minute time resolution, and high-resolution, one- to five-minute, discharge data provide the detail necessary to accurately characterize storm event hydrologic response in small urban basins. We examine flood-producing rainfall properties and storm event hydrologic response for nine drainage basins in the Baltimore region, each with drainage area of approximately 10 km 2 . The sample of watersheds includes seven urbanized basins, a forested reference basin, and a predominantly agricultural basin. Analyses are performed for the 50 largest flood events during a ten-year period in each of the nine basins. We find expected contrasts in flood peak distributions and storm event runoff production between the urban and non-urban watersheds, but we also find a spectrum of storm event hydrologic response among the urban watersheds. Moores Run and Dead Run are end-members of this urban spectrum, with Moores Run producing anomalously large flood peak magnitudes and Dead Run producing anomalously large storm event runoff ratios. Hydrologic response to the storm events for each basin is summarized through relationships between maximum basin-averaged rainfall rates and peak discharges. Analyses show that runoff production and timing of hydrologic response are linked to stormwater management infrastructure and play a central role in the spectrum of storm event response. Detention basins in these watersheds appear to operate as intended by original stormwater legislation to lower peak discharges but not necessarily lower runoff volumes. Antecedent moisture does not appear to significantly impact storm event hydrologic response in the urban or non-urban basins. Clustering of flood events is an important element of urban flood hydrology in the Baltimore region. The rainfall climatology of flood-producing storms varies from urban to non-urban watersheds with urban watershed flood frequency displaying a pronounced warm season maximum while the non-urban watershed flood frequency exhibits a more uniform intra-annual distribution. The diurnal cycle of flood occurrences exhibits a stronger evening maximum in urban watersheds than in non-urban watersheds, highlighting the central role of warm season thunderstorm systems for urban flooding in Baltimore.
Print ISSN:
0043-1397
Electronic ISSN:
1944-7973
Topics:
Architecture, Civil Engineering, Surveying
,
Geography
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