Back to D Session Agenda

Upper Little Patuxent Restoration – 10 Years of Lessons Learned

Jeremy Koser, PE
JMT
Hunt Valley, Maryland

Authors:  Jeremy Koser (JMT); Ryan Cole (MDOT SHA)

This presentation will cover observations of a Design-Build stream restoration project over a 10-year period from design through monitoring and beyond.  This includes a discussion of what went right and what went wrong and why based on best available data.  The site experienced 2 historic flooding events in 2016 and 2018.  Potential missed opportunities for additional ecological uplift based on existing resource preservation tradeoffs and current site condition observations will also be highlighted.

Background: The Upper Little Patuxent (ULP) River Stream Restoration was competed for the MDOT SHA to meet MS4 permit pollution reduction goals.  It is located in Howard County, MD, west of U.S. Route 29. The project included 3,700 linear feet of ULP and 600 linear feet of an unnamed tributary.  Design began in early 2013 and construction was completed in mid-2015.  Post-construction monitoring included five (5) distinct periods beginning in 2016 through 2020.

Presentation Outline, Project Goals & Objectives:
Goals:  “The work will consist of stream and floodplain improvements that will reduce erosion, excess sediments, nitrogen and phosphorus discharged to the Little Patuxent River.”  (RFP language)

Objectives: 

• Remove legacy sediment from channel overbanks

• Lower channel banks and create a more well-connected floodplain wetland surface

• Improve hyporheic exchange

• Improve aquatic habitat through bedform diversity, stable mixed-size substrates, woody bed, bank and floodplain materials/structures and diverse native vegetation planting plan  

Incentives: LOD Reduction  ESC QA Ratings

Constraints:

• $1,700,000 Maximum Price

• Parallel and crossing sanitary sewers (ACP)

• Adjacent existing wetlands, specimen trees, and forest

• Valley pinch points/slope encroachment

Design Approach: Priority 2 restoration, including channel realignment, bank height reduction, and creation of a lower inset floodplain surface to promote wetland creation/enhancement.
Instream Structures:  cross vanes, constructed riffles, toewood, channel, and floodplain log sills 

Monitoring Results: Includes a discussion of pre-construction boundary conditions and how the restoration responded to changes in boundary conditions due to the restoration interventions and other external corridor / watershed factors.

Lessons Learned / Missed Opportunities