St. Peters, Missouri
Client: City of St. Peters
Stream bank erosion and the possibility of flood damage was threatening homes along a 4,000 linear foot long stream reach in St. Peters. This stream was eroding in the immediate vicinity of single and multiple-family residences as well as a retirement community.
For this highly-confined project area, Terra Technologies designed a biotechnical engineering solution utilizing natural stream bank stabilization techniques including gabion toe/wire turf reinforced back slope and gabion wall/cellular confinement retaining walls, pre-planted coir logs, and appropriate tree-shrub thinning. In many locations, scour will be minimized through the use of a traditional rock blanket replanted with native species of riparian grasses, wildflowers, shrubs, and trees.
Importantly, designed improvements focused on the dissipation of storm water energy from upstream engineered improvements. A simple and cost-efficient fluvial accumulation pool was designed to store a defined amount of water prior to release into the downstream project segment. Minor bank grading was required in conjunction with non-degradable turf reinforcement matrices designed to interface with native riparian plant species. Most existing trees were saved and overbank storm conveyance was contained with a defined short segment of flood wall along the project reach.
Engineered in-stream grade controls controlled headcutting. This approach also reduced street and residential structure flooding during large storm events while allowing the stream to continue to have an open channel to allow for the transportation and deposition in-stream sediment throughout the defined project reach.
Completion of the design for this project required hydraulic analysis of the 48-inch storm pipes and reinforced concrete box culvert under existing and future runoff conditions. Analysis began with the City’s HEC-RAS model, and added updated data from topographical survey, City-provided utility plans, and as-built plans of recent development.
This project involved approximately 1,400 cubic yards of gabion baskets, 47,000 native plants, and 920 feet of pre-vegetated coir logs. Construction of the stormwater improvements began in late 2006 and concluded in fall 2007.
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