Water Resources Research Act Program

Details for Project ID 2019MD126B

Investigating precipitation patterns in Maryland: Implications for infrastructure design and planning

Institute: Maryland
Year Established: 2019 Start Date: 2019-05-31 End Date: 2020-05-30
Total Federal Funds: $10,110 Total Non-Federal Funds: $24,090

Principal Investigators: Kaye L. Brubaker

Project Summary: Communities throughout Maryland face threats from coastal inundation and/or precipitation-driven flooding. While coastal flood risk and projections of sea level rise are moderately understood, there is a paucity of information on the changing patterns of extreme rainfall over land. Planners, engineers, and decision makers require an improved local understanding of evolving extreme rainfall when designing and investing in longlived stormwater management infrastructure to protect life and property. The design of stormwater facilities in Maryland follows the Maryland Stormwater Design Manual (MSDM) (MDE 2000, rev. 2009). Among other recommendations, the MSDM recommends annual exceedance probabilities (“return periodsâ€) to be applied in sizing stormwater storage and conveyance. MSDM provides corresponding precipitation depths, by county, and specifies the use of TR-55 or TR-20 (now WinTR-20) – or approved equivalent – to determine peak discharge. As stated by the U.S. Department of Agriculture, Natural Resources Conservation Service (USDA NRCS, 2015), the “[r]ainfall distributions used for design of engineering projects are different from actual storms.†Standard design storm distributions implemented in WinTR-20 are based on NOAA Atlas 14 rainfall frequency; they have a period of maximum intensity at or near the middle of the time period, with lower intensities at the beginning and end. Although their greatest concern is the total storm depth, practitioners are concerned that use of the standard design storm may not accurately predict system response to regional rainfall, especially as rainfall patterns change.