The City of Portsmouth’s Olde Towne Historic District experiences localized flooding throughout the drainage area due to aging infrastructure and changing environmental conditions. In the lowest portion of the drainage area, rainfall events as small as 0.1-inches of rain in 24 hours in conjunction with high tides can flood streets with 1 foot of water at the curb. Predictions of sea level rise and climate change in the Tidewater region indicate that the issue of flooding will only become more of a problem in coming years if the City does not develop effective stormwater control measures.
In order to address localized flooding in the Olde Towne neighborhood, Jacobs is assisting the City in designing a stormwater pump station that will function as an integral part of the City’s flood protection program. The Olde Towne Pump Station project is governed by a number of key constraints, including:
- The pump station location is on City-owned property that is known to have contaminated soils and groundwater.
- The pump station design must be able to manage flows from a 0.5-inch rainfall event to a 6.6-inch rainfall event.
- The Phase 1 construction cost must be within a budget of $7 million.
The Olde Towne Pump Station design applies hydrologic modeling, pipeline hydraulics, and stormwater pump intake design while also being responsive to community issues. Construction is planned in two phases – Phase 1 will be the installation of the pump station, stormwater structures, and three pumps which will equip the pump station to manage flows from 90 percent of rainfall events in the drainage area. Phase 2 will be the installation of the three remaining pumps and a natural gas generator housed inside a structure. Phase 1 design is currently at the 90-percent level.
This presentation will highlight the unique challenges of designing a stormwater pump station for the unique design challenges of the site, wide range of flows, and budget, and the creative solutions that can make it possible. This versatile pump station design can be used as a model for other municipalities that need a similar solution to address flooding due to climate change and sea level rise.