Long-Term Bed Degradation in Maryland Streams (Phase IV): Western Shore of the Coastal Plain Province

Estimation of potential long-term down-cutting of the stream bed is necessary for evaluation and design of bridges for scour and culverts for fish passage. The purpose of this study was to improve predictions of this potential long-term bed degradation (LTBD) in Maryland streams through the measurement and analysis of stream bed and waterway structure survey data and bridge plans. LTBD was defined as the vertical change in the channel profile other than that caused by local or contraction scour. A total of 22 sites in Baltimore City and Harford, Baltimore, Anne Arundel, Prince George’s, Calvert, Charles, and St. Mary’s counties were selected for data collection. Drainage areas of these sites in the Western Shore of the Coastal Plain province ranged from 0.7−30.5 mi² . At each sampling site, the vertical drop at the outlet of the structure was measured with a pocket rod and a hand level. These rapid measurements were conducted where a step, a series of steps, a steep section, or a riprap-protected streambed was at the outlet of a culvert or a bridge with a paved or riprap-protected invert or downstream apron. Five of the six factors that may influence a site’s risk of LTBD were investigated. These include (1) the valley slope, (2) the effective floodplain width, (3) discharge, (4) downstream channel entrenchment, and (5) bed material characteristics. The possibility of developing regional relations between LTBD and percent impervious area was evaluated for the physiographic province, but the data were inconclusive. Three relations between LTBD and the risk factors were examined: LTBD and valley slope; LTBD and an index combining Factors 1-4; and LTBD and an index of bed mobility. Data indicated no trend in LTBD with either of the two indices. The relation based on valley slope was compared to a relation based on drainage area. The comparison revealed that valley slope was a better predictor of the susceptibility of a site to LTBD than drainage area. The relation between valley slope and LTBD was recommended to estimate LTBD for streams with slopes of less than 0.014 ft/ft. The relation should not be applied, however, to structures located in deep deposits of sediment created by backwater from dams or other structures or to structures located in streams with evidence of active channel degradation or recent downstream channelization. The development of rate relationships for LTBD was also considered, but the number of available structure plans was insufficient to develop a rate relation. The development of a rate relation should be explored further in future research on LTBD in Maryland.

• Record URL:
  • http://www.roads.maryland.gov/OPR_Research/MD-18-SP609B4H_LTBD_PhaseIV_Report.pdf
• 
• Corporate Authors:

  RK & K

  81 Mosher Street
  Baltimore, Maryland  United States  21217

  Maryland Department of Transportation

  State Highway Administration, Office of Policy and Research
  707 North Calvert Street
  Baltimore, MD  United States  21202
• Authors:
  • Parola Jr, Arthur C
  • Oberholtzer, Ward L
  • Altland, Drew
• Publication Date: 2018-7

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Appendices; Figures; Glossary; Maps; Photos; References; Tables;
• Pagination: 45p

Subject/Index Terms

• TRT Terms: Bridges; Culverts; Degradation (Hydrology); Drainage; Forecasting; Slopes; Streambeds; Streams; Structural analysis
• Geographic Terms: Maryland
• Subject Areas: Bridges and other structures; Highways; Hydraulics and Hydrology; Planning and Forecasting;

Filing Info

• Accession Number: 01675087
• Record Type: Publication
• Report/Paper Numbers: MD-18-SP609B4H
• Contract Numbers: SP609B4H
• Files: TRIS, ATRI, STATEDOT
• Created Date: Jul 18 2018 9:51AM